c/EPA
United States
Environmental Protection
Agency
Health Effects Research ani)
Environmental Monitoring ar, i
Support Laboratories
Research Triangle Park NC 2~/ '11
EPA 600/9-79-032
June 1979
Research and Development
Proceedings of the
Symposium on the
Development and Usage
of Personal Monitors
for Exposure and Health
Effect Studies
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S.
Environmental Protection Agency, have been grouped into nine series.
These nine broad categories were established to facilitate further
development and application of environmental technology. Elimination
of traditional grouping was consciously planned to foster technology
transfer and a maximum interface in related fields. The nine series
are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports.
COVER: A physiologic monitoring device incorporated into a piece
of jewlery. The device contains a monitoring electrode that
transmits the ECG through electronic circuitry to activate a
liquid crystal display of the subject's electrophysiologic heart
pattern. The left-hand picture shows the device in an open
position; the center picture shows it with the electrodes in place
on the body; and the right-hand picture shows the device in a closed
position, the configuration in which it is usually worn. (Photos
courtesy of Mary Ann Scherr and Dr. George S. Malindzak, Jr.)
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EPA-600/9-79-032
June 1979
Proceedings of the
Symposium on the
Development and Usage
of Personal Monitors
for Exposure and Health
Effect Studies
Sponsored by
U.S. Environmental Protection Agency
January 22-24, 1979
Chapel Hill, North Carolina
Symposium Chairmen
David T. Mage, Ph.D.
Statistical and Technical Analysis Branch
Environmental Monitoring and Support Laboratory
Research Triangle Park, North Carolina
and
Lance Wallace, Ph.D.
Office of Monitoring and Technical Support
Office of Research and Development
Washington, D.C.
Coordination and Editing by
Kappa Systems, Inc.
Arlington, Virginia 22209
U.S. Environmental Protection Agency
Health Effects Research Laboratory
and Environmental Monitoring and Support Laboratory
Research Triangle Park, North Carolina 27711
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DISCLAIMER
This report has been reviewed by the Health Effects Research Laboratory, and
the environmental Monitoring and Support Laboratory, U.S. Environmental Pro-
teitlon Agency, and approved for publication* Approval does not signify that
the <<>nterita necessarily reflect the views and polities of the U.S. Environ-
mental Protection Agency, nor does mention of trade names or commerlral products
constitute: endorsement or recommendation for use.
ii
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Contents
Foreword
Opening Remarks
Ralph W. Stacy, Ph.D.
Role of the EPA Environmental Monitoring and
Support Laboratory in the Development of Personal
Exposure Monitors
Thomas R. Mauser, Ph.D.
Personal Air Quality Monitors; Uses in Studies
of Human Exposure
Lance Wallace, Ph.D.
The Need for Personal Air Pollution Exposure 19
Monitors and Applications in Energy Development
Leonard D. Hamilton, M.D., Ph.D.
Current NI08H Research on Passive Monitors 27
Mary Lynn Woeblcenberg
ill
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Electrochemical Methods for Development of 35
Personal Exposure Monitors
Joseph R. Stetter, Ph.D., Donald R. Rutt,
and Michael R. Graves
Portable Ozone and Oxidant Monitors for Random 47
Field Surveys
Gary P. Heitman and Richard L. Sederquist
Personal Sampler for Measurement of Ambient 57
Levels of N0_
Edward D. Palmes, Ph.D.
In-Vehicle Air Pollution Measurements: A User's 65
Perspective
Richard A. Ziskind, Ph.D.
Calibration of Personal Exposure Monitors for 77
Personal Exposure and Health Effect Studies
Charles L. Kimbell
A New Family of Miniaturized Self-Contained CO 83
Dosimeters and Direct Reading Detectors
Arnold H. Gruber, Arnold G. Goldstein,
Anthony B. LaConti, Ph.D., Harry G. Wheeler,
and John Martin
Design and Performance of a Reliable Personal 101
Monitoring System for Respirable Particulates
William A. Turner, John D. Spengler, Ph.D.,
Douglas W. Dockery, and Steven D. Colome
Personal Exposure to Respirable Particulates 111
and Sulfates: Measurement and Prediction
Douglas W. Dockery and John D. Spengler, Ph.D.
iv
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The Tandem Filter Package 131
Robert W. Shaw, Ph.D., and Robert K. Stevens
An Evaluation of Personal Sampling Pumps in 145
Sub-Zero Temperatures
Carl D. Parker and Joan C. Sharpe
Electrochemical Air Lead Analysis for Personal 161
Environmental Surveys
Francis J. Berlandi, Ph.D., Gerald R. Dulude,
Reginald M. Griffin, Ph.D., and Eric R. Zink,
Ph.D.
Studies of Semiconducting Metal Oxides in 173
Conjunction with Silicon for Solid State Gas
Sensors
Angel G. Jordan, Ph.D., David J. Leary, Ph.D.,
Gulu N. Advani, and James 0. Barnes, Ph.D.
Microcomputer Control and Information Processing 191
Technology for Semiconductor Gas Sensors
David T. Tuma, Ph.D., and Paul K. Clifford
Management Strategy in the Design and Use of 207
Personal Monitors for Environmental Studies
Ralph W. Stacy, Ph.D.
The Usage of Personal Monitors for Determination 217
of Dosage and Exposure in Health Effect Studies
David T. Mage, Ph.D.
Carboxyhemoglobin Determinations from Expired Air 229
Harold W. Tomlinson
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Intelligent Personal Physiologic Monitors in 237
Clinical Environmental Health Effects Research
(Part I)
Mathew L. Petrovick
Design of Personal Monitors for External and 259
Internal Physiologic Studies in Health Effects
(Part II)
Mathew L. Petrovick and Edward D. Haak, Jr., M.D.
Personal Cardiopulmonary Electrode Monitoring 281
Paul N. Kizakevich
A Respiration-Controlled Personal Monitor 297
Donald J. Sibbett, Ph.D., and Rudolph H.
Moyer, Ph.D.
Personal Monitor Cosmetology: An Aesthetic 309
Approach
George S. Malindzak, Jr., Ph.D., and Mary
Ann Scherr
'Shirtsleeve Workshop" 327
A New Personal Organic Vapor Monitor with In Situ 365
Sample Elution
Donald W. Gosselink, Ph.D., David L. Braun,
Haskell E. Mullins, and Sandra T. Rodriguez
A Combination Sorbent System for Broad Range 383
Organic Sampling in Air
Joseph J. Brooks, Ph.D., Diana S. West,
Donald J. David, and James D. Mulik
vi
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Adapting Commercial Voltammetric Sensors to 413
Personal Monitoring Applications
Manny Shaw, Ph.D.
Solid Sorbent for Acrolein and Formaldehyde in Air 425
Avram Gold, Ph.D., Thomas J. Smith, Ph.D.,
Christoph E. Dube, and John J. Cafarella
Passive Membrane-Limited Dosimeters Using 437
Specific Ion Electrode Analysis
Charles E. Amass
Personal Monitoring by Means of Gas Permeation 461
Philip W. West, Ph.D., and Kenneth D.
Reiszner, Ph.D.
Personal Air Pollution Monitors: New Developments 473
Robert W. Miller and Byron Denenberg
A New Sampling Tool for Monitoring Exposures to 479
Toxic Gases and Vapors
John C. Gillespie and Leah B. Daniel
Panel Discussion 493
vii
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Foreword
The many benefits of our modern, developing, Industrial society are
accompanied by certain hazards. Careful assessment of the relative risk of
existing and new man-made environmental hazards Is necessary for the estab-
lishment of sound regulatory policy. These regulations serve to enhance the
quality of our environment to promote the public health and welfare and the
productive capacity of our Nation's population.
The Health Effects Research Laboratory, Research Triangle Park, North
Carolina, conducts a coordinated environmental health research program In
toxicology, epidemiology, and clinical studies using human volunteer subjects.
These studies address problems In air pollution, nonlonlzlng radiation, envi-
ronmental carclnogenesls, and the toxicology of pesticides, as well as other
chemical pollutants. The Laboratory participates In the development and re-
vision of air quality criteria documents on pollutants for which national
ambient air quality standards exist or are proposed, provides the data for
registration of new pesticides or proposed suspension of those already In use,
conducts research on hazardous and toxic materials, and is primarily respon-
sible for providing the health basis for nonlonlzlng radiation standards.
Direct support to the regulatory function of the Agency is provided In the fora
of expert testimony and preparation of affidavits as well as expert advice to
the Administrator, to assure the adequacy of health care and surveillance of
persons having suffered imminent and substantial endaangerment of their health.
ix
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Measurement and monitoring research efforts are designed to anticipate
potential environmental problems, to support regulatory actions by developing
an in-depth understanding of the nature and processes that impact health and
the ecology, to provide innovative means of monitoring compliance with regula-
tions, and to evaluate the effectiveness of health and environmental protection
efforts through the monitoring of long-term trends. The Environmental Monitor-
ing and Support Laboratory, Research Triangle Park, is responsible for develop-
ment of: environmental monitoring technology and systems; Agency-wide quality
assurance programs for air pollution measurement systems; and technical support
to the Agency's operating functions, including the Office of Air, Noise, and
Radiation, the Office of Toxic Substances, and the Office of Enforcement.
This conference was conducted by the Environmental Monitoring and Support
Laboratory, Research Triangle Park, at the request of the Health Effects Re-
search Laboratory. Thirty-five papers were presented on advances in personal
monitor designs and applications. The Environmental Monitoring and Support
Laboratory will play a continuing role in their development through programs of
field testing, quality assurance, and determination of their equivalence to the
EPA-designated instruments for the pollutants to be monitored.
F.G. Hueter, Ph.D.
Director
Health Effects Research Laboratory
Thomas R. Hauser, Ph.D.
Director
Environmental Monitoring
and Support Laboratory
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Opening Remarks
Ralph W. Stacy, Ph.D.
Clinical Studies Division
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina
I trust that no one will dispute my contention that human research on
health effects of air pollutants, carried out on controlled and carefully
selected cohorts of human subjects under carefully controlled conditions,
is entirely necessary in the scheme of research required for the intelligent
determination of ambient air standards. This type of research is the primary
mission of the Clinical Studies Division of EPA. Our facilities, located
here in Chapel Hill, N.C., are among the most sophisticated in the world, and
we are currently carrying on a heavy research schedule.
However, none of us at the Clinical Studies Division labors under the
delusion that our research will supply all of the answers required for air
pollution control. Our highly controlled scientific studies, carried out on
selected subject groups with exposures artificially produced in an idealized
time pattern, supply the most accurate data available on the response of
humans to pollution exposure, but we can never hope to study more than a
small and narrowly defined sample of the population. These studies will
form a data base that is more accurate and more carefully defined than we
could obtain outside the laboratory, and they will probably function as a
comparison standard for other types of studies.
Ultimately, however, we must have information on: 1) the response of
all segments of the population to pollutant exposure, 2) the amounts and time
patterns of pollutant exposures which actually do or are likely to occur in
the general population, and 3) the correlation of the exposures that occur
with the effects that result. The exposure data and the health effects data
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must be obtained simultaneously on people who are of all ages, both sexes,
well and ill, of all ethnic groups, and in all existing life situations.
Only when we have such all-inclusive data can we make assuredly correct,
defensible judgments of regulatory requirements. In the final analysis, this
is an epidemiological problem, and it is an extremely important and difficult
one. I repeat—this problem is a very large one; we dare not treat it lightly.
Recent clinical researches on air pollution effects have made it abun-
dantly clear that humans vary enormously in their physiologic responses to
polluting agents. For example, we have shown clearly that in a group of 100
individuals, we can expect that between 15 and 30 of them will be quite sen-
sitive to photochemical oxidants (specifically, ozone). Some 20 to 30 of these
persons will not respond at all to the same exposure, and the remainder will
respond to some degree. This is actually a very important observation be-
cause it means that the usual scientific experiment—in which the means of a
number of individuals in a control group and an experimental group are com-
pared—is simply not applicable to a true understanding of pollutant effects.
We expect this variability to become a great deal more apparent when we ex-
pand our studies to include the very young, the old, the ill, and so on.
This means, of course, that we must re-examine our epidemiological and sta-
tistical techniques, and that we must be sure that they are adequate.
We have also shown clearly that pollutant health effects often are not
synchronized in time with pollutant exposure. An effect may be delayed, or,
with continued exposure, an effect may be appreciably reduced or even eli-
minated entirely. Thus, we need continuous measurements over extended time
periods, and this imposes additional methodological requirements.
In addition, we are now able to identify some health effects data which
are significant indicators of pollutant-produced health decrements; others
are now known to contribute little to the identification of hazards; and there
are some whose significance has not been tested. Thus, we have some homework
to do before we can head into the final design of measuring devices.
All of this simply means that the kind of information we really must have
is a total picture of pollutant exposure and health effects in the general
population, measured under normal living conditions. This leads us directly
to the conclusion that the measuring instrument must accompany the monitored
individual wherever he or she goes and in whatever he or she does. It is not
enough to measure one-time health status of members of the population and to
compare these effects with pollutant exposure patterns obtained at some fixed
measurement station years or blocks or miles away.
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It means that we at the Clinical Studies Division are completely con-
vinced of the importance of the development of personal monitors, especially
those in our own field of competence, and that we anticipate that our ex-
posure chambers may well turn out to be the ultimate proving grounds for the
personal monitors developed by our engineers and bioengineers, and for those
monitors developed by other parts of EPA and other Agencies.
We are under no illusions concerning the scope and difficulty of the
problems of development of personal monitoring equipment and the techniques
involved in their use. We know that taking on this additional task will put
further strain on our already critical staffing and space problems. Neverthe-
less, we intend to do our part and to do it to the very best of our ability.
We welcome this opportunity to play a role in what we feel is one of
the major developments in environmental control of this time period. We also
recognize the value of this symposium, and we appreciate the contribution it
can make to this important human effort. We pledge our support and colla-
boration to the development of personal monitors for pollutant exposures and
health effects measurement.
We look forward to taking part in this symposium, and we hope that all of
you enjoy the symposium and the Carolina setting in which we are meeting.
MAILING ADDRESS OF AUTHOR
Ralph W. Stacy, Ph.D.
Clinical Studies Division
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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Role of the EPA Environmental Monitoring
and Support Laboratory in the Development
of Personal Exposure Monitors
Thomas R. Mauser, Ph.D.
Environmental Monitoring and Support Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina
INTRODUCTION
Among other programs, the EPA Environmental Monitoring and Support
Laboratory (EMSL) at Research Triangle Park (RTP), N.C., has organizational
responsibility for evaluating and selecting air pollution monitoring instru-
ments for use in studies required by the Clean Air Act as amended in 1977.
In this capacity, EMSL recommends to the Administrator monitoring instruments
for EPA designation, analytical techniques, and instrument performance spec-
ifications, in addition to conducting the air monitoring equivalency program.
The EMSL/RTP also develops total monitoring systems and is responsible for
the development and operation of the air pollution monitoring quality assur-
ance program. Along with the EMSL/Las Vegas, the EMSL/RTP is currently
applying its expertise in these areas to study designs using personal air
monitors for human exposure assessment.
EXPOSURE MONITORING
The EMSL/RTP has responsibility within the EPA for the air pollution
monitoring studies performed jointly with the Health Effects Research Labo-
ratory/ RTP health studies on human subjects exposed to both ambient and cham-
ber-controlled concentrations of air contaminants. These air quality data
and health data are analyzed by EPA biostatisticlans to determine the degree
of association, if any, of the measured health effects with the air quality
data. Examples of two studies currently underway are measuring the effects
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of CO intrusion into vehicles and the effects of short-term exposures to high
levels of N02.
We recognize that the ambient exposure levels monitored at a single
fixed location may not be representative of the total exposure of residents
in the study areas. To obtain a better definition of the spatial variability
of pollution within the study community and the variations of exposure re-
ceived by the subjects, a combination of fixed monitoring stations, mobile
monitoring stations, and personal exposure monitors can be used to give a
better estimate. The personal monitors used in these studies are tested by
EMSL/RTP for interferences, accuracy, precision, temperature stability, etc.
The results of the personal exposure monitoring data collection can be analyzed
to test the hypothesis that the fixed-station data represent the average
community exposure concentrations within a specified concentration bound
and level of confidence. If the variations in exposure are significant,
the biostatisticians can relate the measured variability of exposure to the
health data by statistical techniques.
At the present time, the state-of-the-art personal exposure monitors
have been developed primarily for occupational exposures to high levels of
pollutants. We in EMSL see a need for increased development of personal
exposure monitors for the lower ambient levels to which the general public
is exposed.
In summary, I hope that this conference will Improve communication
between personal monitor users and personal monitor manufacturers and stimu-
late progress in their development as reliable instruments for human exposure
studies. We anticipate that personal monitors will be used with increasing
frequency as research monitoring tools for studies of health implications
of air pollution and for relationships of different monitoring strategies.
MAILING ADDRESS OF AUTHOR
Thomas R. Hauser, Ph.D.
Environmental Monitoring and Support Laboratory (MD-75)
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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Personal Air Quality Monitors: Uses in
Studies of Human Exposure
Lance Wallace, Ph.D.
Office of Monitoring and Technical Support
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C.
I would like to explain very briefly how this conference fits into EPA's
R&D Program. The Office of Research and Development (ORD), is one of the
six main offices of the EPA. The other offices are often called the program
offices, and are responsible for carrying out EPA's legislative mandate in
areas such as air, water, noise, radiation, pesticides, solid waste, and
toxic substances. These offices express their needs for research to ORD,
which is then expected to find a way to answer those needs. This conference
is one way we have chosen to address the need expressed in many different
ways recently, by groups both inside and outside EPA, for methods of measur-
ing human exposure directly.
In the last 2 years alone, four major groups have specifically requested
action on the development and use of personal air quality monitors to measure
day-to-day human exposure to air pollutants.
The National Academy of Sciences, in a 1977 report entitled Enviromental
Monitoring, said: "We recommend that EPA coordinate and support a program
to foster the development of small, quiet, sensitive, and accurate personal
air quality monitors for use in conjunction with other methods of measuring
human exposure to ambient air quality" (1). In 1977 the Second Task Force on
Research Needs in Environmental Health Sciences recommended that: "...research
is needed on the application of promising instrumental approaches to the develop-
ment of personal monitors which, through use of micro-electronic components and
small pollutant sensors, could be used to monitor individuals within popu-
lations of interest" (2).
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EPA's own task force, the Standing Air Monitoring Work Group, charged with
recommending an Agency-wide 5-year monitoring strategy, stated: "As a concluding
observation, SAMWG believes that EPA should take a more active research role In
determining the usefulness of personal air pollution samplers to measure the
exposure dose to representative individuals'* (3). And, a congressional commit-
tee in April of 1978 authorized a large increase in appropriations for studying
effects of criteria pollutants, stating that: "...the Agency needs to improve
the data base relating actual personal exposures to monitored ambient air pol-
lution levels in order to increase the reliability of epidemiological studies.
This should be done by development of personal dosimeters..." (4).
The last major conference on personal air quality monitors was held 3 1/2
years ago at Brookhaven National Laboratory. There, many possible technologies
were ranked according to their probability of payoff within a few years, and
a national R&D program of about $1.5 million a year for 5 years was recommended
(5).
Such a program has not materialized to date, but some activity is taking
place. For example, the Environmental Sciences Research Laboratory here in
Research Triangle Park, N.C., has a project to develop a portable monitor for
organics. This project will be further described later in this conference.
This same laboratory supported a feasibility study (6) for personal monitors
several years ago, and is now working on a monitor for respirable particles
and gases, which will be described in the paper by Dr. Robert Shaw and Mr.
Robert Stevens. A second ORD laboratory, the Health Effects Research Labora-
tory, has a briefcase-sized monitor for SO-, CO, and N0_ that it has developed
over the past 2 years and may use in epidemiology studies. A third ORD labora-
tory, the Environmental Monitoring and Support Laboratory in Research Triangle
Park, has used a commercially available CO dosimeter in a congressionally man-
dated study (7) of CO intrusion into sustained-use vehicles such as buses,
taxis, and police vehicles. This will be described further in the talk by
Dr. Richard Zisklnd. Also, a fourth ORD laboratory, the Environmental Moni-
toring and Support Laboratory in Las Vegas, is administering an interagency
agreement with the National Bureau of Standards (NBS) to develop one or more
personal monitors for a pollutant or pollutants yet unnamed. Dr. Jimmie
Hodgeson from NBS is here to give more information on NBS experiences with
personal monitors.* Thus, I believe we are seeing the first stages of an effort
that may lead to far more detailed knowledge of human exposure than we dreamed
of 5 years ago.
^Editor's Note: A copy of Dr. Hodgeson's symposium paper was not available
at the time of printing and thus does not appear in these Proceedings.
8
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For this effort to continue, however, even at a level far below the major
national commitment called for by the Brookhaven workshop, it is necessary to
keep its benefits clearly in mind. What are the benefits of a balanced program
of development, evaluation, and use of personal monitors? I can see the
following six major uses:
1) More detailed knowledge of individual, day-to-day exposure. Obtaining
this knowledge requires that a large sample of people within a community be
equipped with personal monitors and keep records of their activities. Together
with fixed-station measurements, traffic and commuting records, and other
personal activity models, the monitoring results will eventually allow esti-
mates to be made of the frequency distribution of exposures for the entire
community.
2) Identification of high-risk subpopulations and quantification of
their exposures. The exposures at the high end of the frequency distribution
are the controlling factors in determining the adequacy of our standards.
The more precise our knowledge of the exposures of the sensitive portion of
the population, the more precisely we can set our standards, avoiding both
unnecessary economic impact if the standard is too stringent, and inadequate
protection of human health if it is too weak.
3) Measurement of exposures during episodes. Although it is generally
accepted that certain infamous air pollution episodes have cost scores or even
thousands of lives (or at least they have hastened deaths that were imminent),
no actual measurements have been made of individual exposures during episodes.
To effectively measure exposures during episodes, which last only 3 or 4
days, it would be necessary to have a team of trained volunteers and the means
of supplying them with monitors within a day of the beginning of the episode.
4) Validation of diffusion models and activity pattern models. Use of
personal monitors in the field can provide data from hundreds of spatially
dispersed points, multiplying by many times the number of points available
from fixed-station locations. The same data can be used to validate the
models of personal behavior—including commuting, shopping, and recreational
travel—that will be necessary to develop as part of our total exposure models.
5) Calibration of fixed-station readings. A very valuable contribution
of personal monitor studies would be the establishment of a solid relation
between the fixed-station readings in a community to the exposures of at least
some population subgroups in that community. If this is possible, then it
would be conceivable that fixed-station readings in other communities would
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bear a similar relationship to exposure. This would allow estimates of ex-
posure to be made for more cities than those in which personal monitor studies
had been carried out, and would also open up the possibility of using his-
torical records of fixed-station measurements to estimate past exposures of
community groups. Since chronic respiratory diseases depend on exposures over
a number of years, this information would be valuable to the epidemiologist.
6) Development of dose-response curves. All five of the above purposes
can be achieved without any concurrent measures of effects; they are pure
exposure studies. Such studies presuppose that the effects at various concen-
trations—the dose-response curves—have been adequately established by clini-
cal or epidemiological studies, and have been documented in the criteria
documents or other publications. Of course, for many pollutants, this is not
the case. For those pollutants, full-scale epidemiological studies, utilizing
personal monitors for measuring dosages and lung-function tests or other med-
ical end points for measuring responses, are necessary.
At present, the studies just outlined have yet to be carried out. As
an illustration of the likely cost and time involved in carrying out such a
study, I borrowed some equipment—the CO dosimeter (9000 series) of Energetics
Science and the Dupont personal sampling pump—and measured my exposure while
commuting from Reston, Va., to Washington, D.C., by bus for a period of 4
weeks last summer. This period proved sufficiently long to characterize my
average exposure to within 10 percent. The instrument used is a small, light
electrochemical device that can fit into a pocket or hook onto a belt. The
Dupont pump is attached to the sensor by a flexible tube and can be inserted
in a nearby pocket. A somewhat larger readout device can be placed in one's
lap to allow minute-by-minute records to be kept, or it can be kept at the
office or at home to give a total exposure reading. I preferred to keep a
continuous record, which required leaving the dosimeter plugged in to the
readout device while casting periodic glances (about every 5 minutes) at the
edgemeter to document the changes that occurred in ambient concentrations.
Figure 1 shows a typical exposure record obtained using this technique. You
can see the high concentration in the bus as I boarded it, at a pick-up
point where the engine had been idling for about 5 minutes. The concentration
falls rapidly on the expressway (between 15 to 20 miles from D.C.), and then
begins to rise as stop-and-go traffic is encountered near the city. It falls
again while crossing the Potomac River, rises to a peak of about 30 to 35 ppm
in the center of the city, and falls to 5 ppm or so as I walk to work. The
smooth curve is the integrated exposure for the length of the trip, measured
in ppm-hours. The total exposure was 35 ppm-hrs, over a total travel time of
53 minutes, which results in an average concentration for the trip of 40 ppm*
10
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Instantaneous
CO concentration
(ppm)
(36) (80)
(Puff from
bus exhaust)
Bridge
across
Potomac
Integrated
CO exposure
(ppm-hrs)
30
20
10
7:50A.M.
8:10 8:20 8:30 8:40 8:50 9:00 9:10 9:20 9:30 A.M.
FIGURE 1. Exposure to carbon monoxide during commuting: sample trip.
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About 30 one-way trips were taken, and the range of exposures varied be-
tween 5 and 35 ppm-hrs, except for one trip. Figure 2 shows the concentrations
encountered on this trip. The instant I got on the bus, the dosimeter sent
the edgemeter needle right off the scale (max = 100 ppm). Thinking it might
be defective, I replaced it with another one from the kit, but this one
behaved equally startlingly. The bus was air-conditioned with all of the
windows closed, so 1 opened a window to test whether outside air would make
a difference. (At 90° F on a bus full of hot commuters, this is not an act
undertaken without careful deliberation.) Within a minute, the needle fell
to values between 25 and 75 ppm, oscillating swiftly in response to traffic
conditions. Closing the window resulted in a rapid buildup to values MOO ppm.
The total exposure for a 1-hour trip was 65 ppm-hrs, and would have been >100
ppm-hrs if I had left the window closed, as I would have done had I not been
measuring the CO concentrations. For a normal 8-hour working day, the driver
would have been exposed to between 800 and 1,000 ppm-hrs, which would be con-
siderably greater than the Occupational Safety and Health Administration
limit of 400 ppm-hrs.
This exact bus (the identical vehicle) had been ridden the day before
without displaying excessively high concentrations. Thus, an intriguing
possibility—possible high exposures to vehicle exhaust gases due to mainte-
nance problems—presents itself. This type of observation was in fact the
precipitating factor in leading Congress to mandate the CO intrusion study
described earlier that our laboratory in the Environmental Monitoring and Sup-
port Laboratory, Research Triangle Park, is carrying out.
Figure 3 compares the average concentrations measured inside the buses
with those measured at the Community Air Monitoring Program (CAMP) station in
the central city. The values encountered inside the vehicles were typically
two-to-four times those measured in the city. There was no correlation be-
tween the ambient and in-vehicle measurements.
One unusual finding here was that air-conditioned buses appeared to have
CO concentrations 60 percent above nonair-conditioned buses, the difference
being statistically significant. Since the buses were diesels with a separate
gasoline-powered jeep engine driving the air-conditioner, it seems possible
that the exhaust of the air-conditioner motor may have accounted for the higher
concentrations. At any rate, the value of the personal monitor in such studies-
first in quantifying exposure, second in detecting possible unsafe levels,
and third in suggesting hypotheses for the source of the in-vehicle pollution—
has perhaps been adequately demonstrated (8).
12
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Concentration
(ppm)
100
Instantaneous Concentration
Integrated Exposure
C- Windows Closed
0- Windows Open
Integrated
Exposure
(ppm-Hrs)
1100
80
60
40
20
12:30 P.M. 12:40i ,12:50' 1:00 1:10 1:201
1:30 1:40 P.M.
FIGURE 2. CO exposure during commuting: worst case (air-conditioned bus).
-------
CO CONCENTRATIONS IN VEHICLE COMPARED TO AMBIENT LEVELS IN CITY
Carbon Monoxide
Concentrations In Vehicle
Ambient CO Concentrations (ln City
During Commuting Hour*
I / / 1 i I I I 1 I i 1 1 I I I
7 8 9 1011 12 13 14 15 16 17 18 192021 2223 / 1345678910111213141516
July August
FIGURE 3. Commuter exposures to carbon monoxide: Washington, D.C., summer
1978.
FUTURE DIRECTIONS
My final topic deals with the future directions of research in this field.
Four major questions require answers:
1) What pollutants are of highest priority?
2) What technologies are most promising?
14
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3) What is the optimum balance among development, evaluation, and
utilization of personal monitors?
4) How should this research be funded?
To the first question, I can bring responses recently solicited from EPA
representatives of relevant program offices. The air program office has men-
tioned fine (inhalable) particulates as a high priority. We are in the midst
of preparing for a possible standard on Inhalable particulates, with a decision
to be made in the early 1980's. A monitor capable of being deployed in
fairly large numbers to establish dose-response curves and exposures to
sulfates, nitrates, trace metals, and other components of the total respir-
able particulate load, would be highly desirable. Both the air office and
the Office of Toxic Substances would also favor a monitor capable of collect-
ing organics for later analysis in the laboratory. The extent of nonworkplace
exposure to organics and to carcinogenic vapors is only hazily comprehended
as yet. Other air pollutants of high priority to EPA will be discussed at
the Tuesday evening workshop.
I will not attempt an answer to the second question: "What technolo-
gies are most promising?" It will be the major topic of our workshop session
Tuesday evening and of the summary panel discussion Wednesday afternoon to
which all are invited to attend.
The question as to what is the optimum balance between development and
evaluation of personal monitors and their utilization in exposure studies may
be partially attacked in the following manner: since the seven criteria
pollutants have already had their health effects quantified, relatively in-
expensive pure exposure studies—involving no concurrent health effects meas-
urements and utilizing the most reliable commercially available instruments—
should be of high priority. These studies will have the immediate benefit
of providing the first reliable estimates of the exposures of an entire com-
munity population to a given criteria pollutant. This far more detailed
knowledge of the population at risk could allow more efficient protective
measures to be taken. Of course, a necessary prerequisite to such pure ex-
posure studies would be the rigorous evaluation by EPA laboratories of the
commercial instruments.
On the other hand, the development of new instruments must look beyond
the criteria pollutants to the problems of the future—in particular, the
toxic organics and fine particulates. This is not to say that development
of instrumentation for S02, N02, ozone, and CO should not be supported; only
that limited resources will require hard choices to be made.
15
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This brings me to the final question—also called the bottom line—the
question of funding. I have for several years advanced the thesis that in
the absence of a mass market for personal monitors, the Federal government
must support their development. At the same time, I felt that it could be to
industry's advantage to fund development, since the more precise knowledge
of exposures would allow fine-tuning ambient standards, with a probable re-
duction of economic inefficiency associated with too-stringent standards.
A paper published by the National Academy of Sciences in 1977 called for an
industry/government coalition on a development program (9).
Now, as a representative of government, I would make the same appeal—
that we work together on developing and using the methods for determining more
exactly our day-to-day exposure to air pollutants. I am very much heartened
by the excellent response of the industry to this symposium, and I am certain
we have a stimulating 3 days ahead of us.
REFERENCES
1. National Academy of Sciences. Environmental Monitoring. Studies for the
U.S. Environmental Protection Agency, Vol. IV. Washington, D.C., May 1977.
2. U.S. Department of Health, Education, and Welfare. Human Health and
the Environment—Some Research Needs. Report of the 2nd Task Force on
Research Planning in Environmental Health Sciences. NIEHS, HEW Publi-
cation #77-1277. Washington, D.C., 1977.
3. Environmental Protection Agency. Air Monitoring Strategy for State
Implementation Plans. Office of Air Quality Planning and Standards,
Research Triangle Park, N.C. EPA 450/2-77-010. June 1977.
4. U.S. House of Representatives. Authorized Appropriations to the Office
of Research and Development, Environmental Protection Agency. 95th
Congress, 2nd Session. Report #95-985, p. 7. March 17, 1978.
5. Morgan, M.6., Morris, S. Individual Air Pollution Monitors: An Assess-
ment of National Research Needs. Report of a workshop held at Brookhaven
National Laboratory, July 8-10, 1975. BNL 50482. Energy Research and
Development Corporation. January 1976.
6. Harrison, 0. et al. Development Strategy for Pollutant Dosimetry.
EPA, Research Triangle Park, N.C., 1976.
7. Zisklnd, R. et al. Final Report: Carbon Monoxide Instrusion into the
Passenger Area of Sustained-Use Motor Vehicles. Report to Congress
by the Environmental Protection Agency. Washington, D.C., July 31, 1978.
16
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8. Wallace, L. Use of Personal Monitor to Measure Commuter Exposure to
Carbon Monoxide in Vehicle Passenger Compartments. Paper submitted to
1979 Annual Meeting of the Air Pollution Control Association. June 1979.
9. Wallace, L. Personal Monitors. In: Supplement to Vol. IV, Environ-
mental Monitoring. National Academy of Sciences. Washington, D.C., 1977.
MAILING ADDRESS OF AUTHOR
Lance Wallace, Ph.D.
Office of Monitoring and Technical Support
Office of Research and Development
RD-680
U.S. Environmental Protection Agency
401 M St., S.W.
Washington, D.C. 20460
Discussion
NADER: John Nader, EPA, Research Triangle Park. I would gather concern-
ing these personal monitors that they will be switched on and off as one en-
ters from, say, environmental exposure outdoors to any kind of exposure in-
doors. Is this correct?
WALLACE: In the particular case that I was talking about, the monitor
had enough range so that it was sensitive to both the concentrations that I
was meeting on the bus and in the office. So, I left it on in the office for
the first few days until I was determining that my exposure there was so low
that it added essentially nothing to my exposure in the community. After that,
I used the time to charge up the battery.
NADER: But the intent of personal monitors for environmental exposure
would be to separate the exposure outside from the exposure inside; is that
true?
WALLACE: I think it would be valuable to be able to make that separation.
On the other hand, there may be cases in which it is far cheaper to collect
something over the full 24-hour day, say, and send it off to the laboratory
to look at.
In that case, you would only get an integrated exposure, and you won't
be able to differentiate. But the cost benefit may make that worthwhile in
some cases.
NADER: Doesn't that raise a question on the validity of the data so far
17
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as CO is concerned? For example, you might get considerable CO exposure in-
doors under smoking conditions, and this would affect your data?
It would give you the true fact of exposure. But as to attributing
that exposure to outdoor levels, of course, that would be flexible.
WALLACE: Presumably one could get around that if, in the case you men-
tioned, we had a cheaper way of getting the total integrated exposure.
For statistical purposes, we could equip a large number of people with moni-
tors with the analysis done the cheaper way, and then equip a smaller statisti-
cal sample for continuous exposure such that we could differentiate the ex-
posures due to various components of the data.
MAGE: Dr. West?
WEST: Phil West of Louisiana State University. I think John has already
raised part of the question. Was there much smoking in the bus when you meas-
ured these levels that we are talking about so far?
WALLACE: In this case there was no smoking.
JOSEPHSON: Julian Josephson, Associate Editor, Environmental Science and
Technology Magazine (ES&T). Do you believe that the source of the CO was the
gasoline-powered air conditioning rather than the diesel engine of the bus,
or is this not really determined?
WALLACE: It is not determined. But I have talked to people at the De-
partment of Transportation, and they tell me that diesels do not put out much
CO and that gasoline engines do, and that their guess was that it was the
air conditioning. They also point out that these were older buses and that
most newer buses operate the air conditioner off the same power plant—the
diesel power plant. So, this particular problem may be seen less often in
newer buses.
JOSEPHSON: You are talking about the famous Reston commuter bus—right?
WALLACE: That is right. They have about 70 buses. They are all diesels,
circa 1955, and they have over 700,000 miles on them.
DOCKERY: Doug Dockery, Harvard School of Public Health.
What are the policy implications if we go out and do personal monitoring
and find that personal exposures are not related at all to what the outside
environment is actually telling us they are, and then we relate that back
to health effects? What is EPA going to do about setting standards and chang-
ing their policy?
WALLACE: That is a very serious policy question about the Indoor aspect
of exposures. Many people feel that it has fallen through the crack with
EPA doing outdoors, OSHA doing the workplace, and indoors and inside vehicles
being not quite covered by any group.
18
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The Need for Personal Air Pollution
Exposure Monitors and Applications in
Energy Development
Leonard D. Hamilton, M.D., Ph.D.
Biomedical and Environmental Assessment Division
Brookhaven National Laboratory
Upton, New York
There has been much research in the past few years devoted to air pollu-
tant transport and chemistry. These efforts provide a. much better basis for
relating ambient pollution levels to sources. Knowledge of the relation
between ambient air pollution levels and individual or population exposure,
however, is still very limited. People move around, spend most of their time
indoors, and are exposed to pollutants from smoking, faulty auto exhaust
systems, gas ranges, the workplace, and other sources. Even in air pollution
epidemiology, where medical surveillance may be extensive, exposures are too
often estimated from fixed monitoring stations serving neighborhoods or whole
communities.
In investigating health-damage functions for use in comparing the health
implications of various energy alternatives, our group concluded that the
weakest link in determining such damage from air pollution is the accuracy
of quantitative estimation of individual or population exposures to pollutants.
In 1975 we convened a workshop of health and instrumentation specialists
to consider the role of personal pollution exposure monitors in air pollution
health effects studies, and to assess research needs in this field.
Two early conclusions of the workshop were that "the importance of popu-
lation exposure estimates in air pollution epidemiology makes it imperative
that future epidemiological studies include exposure estimates more repre-
sentative of what people actually breathe," and that "the use of individual
air pollution monitors is a necessary factor in the design or performance of
definitive studies of the health effects of air pollution" (2,3).
19
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The Brookhaven workshop produced a first-order ranking, according to
promise of ultimate performance, of a number of the candidate instrumentation
technologies. These rankings, shown in Table 1, reflect a loose consensus
of the participants at the time of the workshop.
For each technology, the workshop developed a first-order estimate of
the research needs.
It seemed advisable to support development work on several of the more
promising technologies in parallel before concentrating on a smaller number
for further development.
Since the workshop, the Department of Energy has funded several projects
aimed at developing personal exposure monitors.
Recently, Brookhaven was asked to organize and chair a working group to
assess industrial hygiene needs for coal conversion and oil-shale industries,
with an eye to the possible expansion of an instrumentation program already
underway. A preliminary report of this working group has been issued (5).
This has given us an opportunity to review the rather considerable advances
in instrumentation made over the last 3 years.
Coal conversion plants will emit conventional combustion products (parti-
culates, SO., NO ) from the boilers needed to supply process heat to the
fc *V
conversion units. On an energy-produced basis, these pollutants are emitted
at much lower levels than from coal-electric power plants. Conversion pro-
cesses, however, involve the production of much more hazardous materials.
These include heterocyclic compounds and reduced sulfur compounds. Facili-
ties are designed to prevent the escape of these materials, but exposure of
workers (particularly maintenance workers) must be considered. Since full-
scale plants have not yet been built, the potential extent of public exposure-
cither routinely or in accident situations—cannot be well defined. Some
surveillance among the public, at least during the start-up and early opera-
tion of such plants, seems warranted. Gammage et al. have pointed out the
gap between the sophisticated analytic tools used in the laboratory to char-
acterize pollutants from synfuels operations and the crude techniques avail-
able for measuring polycyclic materials in the field (1).
Among the range of heterocyclic compounds, the question of what specifi-
cally to monitor is especially important for field monitoring of population
exposure. The need to develop one or more indices is important. Use of in-
dices was strongly recommended by an interagency-supported investigation on
health and safety guidelines for coal gasification (4).
20
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TABLE 1
Tentative Ranking Developed by Participants in the Brookhaven Workshop on Individual
Air Pollution Monitor* of Candidate Gas- and Particle-Sensing Instrumentation Techniques
(Performance criteria applied in the ranking were the development of a prototype device
of lunch box size or less with annual support of $200,000/year or less. The rankings are not
based on a full quantitative analysis and should be viewed only as a qualitative guideline.)
Probability of Payoff
Within <3 yr
Within 3 to 6 yr
Outstanding
Good
Fair to poor
GAS METHODS*
Sorption
Gel tape colorimetry
Electrochemical cells
Coulometric and amperometric devices
Fluorescence devices (SG^) I
Nondispersive spectroscopy (CO)
Chemiluminescence (Os, NO,)
PARTICLE METHODS6
Virtual impactor (M, 2D, C)
Filters (M, —.V.—.D.C)
Diffusion batteries with filters (C(D))
ft meter (Af)
GAS METHODS
Microwave devices (CO)
PARTICLE METHODS
Diffusion battery with
condensation nuclei counter (M, D)
GAS METHODS
Gas chromatography
Cryogenic sampling
Electronic solid state devices
Nondispersive spectroscopy
(gases other than CO)
Piezoelectric gas sensors
Microwave devices
(gases other than CO)
PARTICLE METHODS0
Piezoelectric mass balance (M)
Optical scattering (~JV, D)
Sorption methods
Colorimetry (tape based)
Electrochemical cells
Coulometric and amperometric devices
Fluorescence devices (SO2)
Nondispersive spectroscopy (CO)
Chemiluminescence (Os, NO*)
Virtual impactor (M, 2D,C)
Filters (M, -JVT, ~D, C)
Diffusion batteries with filters (C(£»))
Optical scattering (A', D)
ft meter (M)
Electronic solid state devices
Nondispersive spectroscopy
(gases other than CO)
Piezoelectric gas sensors'
Microwave devices (CO)
Gas chromatography
Virtual impactor (Mt >2D,C)
Diffusion battery with condensation
nuclei counter (JV, D)
Piezoelectric mass balance
(M, ~JV, ~fl)
Optical scattering (~N, D)
Cryogenic sampling
Bioluminescent methods
Optoacoustic methods
Microwave devices
(gases other than CO)
•When the classification depends on the gas of interest, this has been indicated in parentheses. Techniques which
were discussed but which me group did not feel qualified to evaluate included fluid-immersed solid state sensors and
gas-sensitive liquid crystals.
bAf indicates device appropriate for measurement of total suspended paniculate mass; JV, for measurement of total
number of particles; and D, for measurement of particle site distribution. ID indicates that sizing into two categories
such as >3 urn and <3 /im is possible. C indicates device appropriate for collecting samples of particles for chemical
analysis, and C(D), that chemical composition can be estimated for two or more separate ranges of particle size.
^Other candidate technologies considered but viewed as unsatisfactory or inappropriate for use in individual air pol-
lution monitors included liquid impingers, centrifugal separation, conventional impactors, thermal precipitation,
electrical mobility, and microwaves.
21
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A single index may not be appropriate for all situations. Gasification
and liquefaction have different characteristics, and even different exposure
situations from the same plant may be best evaluated with different indices,
due to variations in the mix of compounds in the pollutant stream. Identi-
fication of indicator compounds needs to consider both the chemical charac-
teristics of the mix of compounds and their biological activities. A problem,
especially difficult in personal samplers, is that PNA's are likely to be in
aerosol form or in vapor form subject to condensation in the sampling train.
From our perspective, other recommendations for future efforts include:
1) Personal air pollution exposure monitors are an essential step in
quantifying individual and population exposure for protection, epidemiology,
and regulation.
2) Passive samplers offer a cheap and convenient tool. They should be
exploited much more extensively in population studies. New substrates should
be developed to expand the diversity of measurable compounds.
3) Passive monitors are inadequate to fulfill the full promise and need
from personal exposure monitoring. Development and demonstration of active
devices which can sample and record short-time exposures are important.
4) Samplers must be field-tested under various conditions of inter-
ferences, temperature, pressure, humidity, etc.
5) Personal monitoring of particulate exposure is an area of great
need, but it does not seem ripe for exploitation. Areas where continued
support seem warranted are: a) improving efficiency of collection; b) improv-
ing extraction efficiency and separation techniques; c) chemical specification;
d) in situ separation of soluble and insoluble particulates.
CONCLUSIONS
Regulatory decisions on air pollution control—which involve direct and
indirect costs of billions of dollars—are being made without adequate know-
ledge of the health impacts of air pollution. The weakest link in the studies
of health effects is our knowledge of individual exposures. The importance
of population exposure estimates makes it imperative that future studies in-
clude exposure estimates more representative of what people actually breathe.
22
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Personal air pollution exposure monitors that are easily carried or
worn are essential for the design or performance of all definitive studies
of the health effects of air pollution. Such monitors also have prevention
and regulatory uses in public and occupational situations.
Given the enormous costs of air pollution control and regulation and the
considerable uncertainties in our present understanding of the health Impacts
of air pollution, a coordinated national program of support for the develop-
ment and use of personal air pollution exposure monitoring instruments should
be initiated without delay.
REFERENCES
1. Gammage, R.B., Vo-Dinh, T., Hawthorne, A.R., Thorngate, J.H., Parkinson,
W.W. A New Generation of Monitors for Polynuclear Aromatic Hydrocarbons
from Synthetic Fuel Production. In: Jones, P.W., Frudenthal, R.I.,
Carcinogenesis, Vol. Ill, Polynuclear Aromatic Hydrocarbons. New York,
Raven Press, 1978, pp. 155-173.
2. Morgan, M.G., Morris, S.C. Individual Air Pollution Monitors. An
Assessment of National Research Needs, BNL 50482. January 1976.
3. Morgan, M.G., Morris, S.C. Individual Air Pollution Monitors, 2. Examin-
ation of Some Non-Occupational Research and Regulatory Needs, BNL 50637.
January 1977.
4. U.S. Department of Health, Education, and Welfare and EPA. Recommended
Health and Safety Guidelines for Coal Gasification Pilot Plants, DHEW
NIOSH Pub. 78-120/EPA-600/7-78-007. January 1978.
5. White, 0. Working Group on Assessing Industrial Hygiene Monitoring
Needs for the Coal Conversion and Oil Shale Industries, BNL 24925.
August 1978.
MAILING ADDRESS OF AUTHOR
Leonard D. Hamilton, M.D., Ph.D.
Biomedical and Environmental Assessment Division
National Center for Analysis of Energy Systems
Brookhaven National Laboratory
Upton, New York 11973
23
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Discussion
JOSEPHSON: Josephson, ES&T Magazine. Do you foresee that the present
effort concerning the anti-inflation fight might have an adverse effect on
the development of this instrumentation and coordinating activity that you
advocate?
HAMILTON: No; I frankly don't think so, because from what my job is and
from the point of view of inflation, one is thinking In terms of controls,
as they apply to plants 10 or 15 years from now.
I am not quite sure what those capital requirements for those plants are—
whether the capital has to be on line for many years In advance or not.
But it seems to me that what we are talking about is a few millions of
dollars. It is so insignificant when I compare it to the gross national
product of the United States that I can say that it would have actually no
relationship whatsoever*
The only thing is this: If we did have a better understanding of what
the dose effect relations were, we would feel more confident as to whether
or not we were justified In spending these large sums on control. Let me
Just say this: we are going to spend these large sums on control anyway.
We are committed to this even In the present state of uncertainty. For ex-
ample, the health effects of something such as sulfate are uncertain. Al-
though we can't say with 95 percent certainty that sulfate is causing an in-
creased mortality, certainly we can say this with 60 percent certainty,
and under these circumstances, we have to go ahead with these expensive con-
trols. What I am saying is that from the point of view of public policy,
this tiny Investment In air pollution and personal monitors is kind of a
dreary thing for many people. I don't think they like to support the idea
of developing measuring Instruments. I think this is one of the reasons why
it possibly hasn't been supported.
ZISKIND: Richard Zlsklnd from Science Applications. You mentioned the
problem for the need to develop indices If one wants to deal with the events
called commercial processes. What are the limitations right now as you see
them in developing such Indices? Are there monitoring problems or Identifi-
cation of levels or substance identification that should be of concern?
HAMILTON: I frankly don't think there are any problems. A more likely
problem is apt to be in having to develop a good personal monitor. I am sure
we can raffle off a number of possible indices. I have already mentioned one
of them.
What we need la a monitor for a simple heterocycllc compound characteris-
24
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tic of what might come out of the process. I feel that the problem lies
In the development of the actual good personal Instrument rather than In the
choice of the Indices.
But again, that Is the sort of subject I feel one could develop In the
process of discussion.
CHASE: Paul Chase of Beckman Instruments. You mentioned the DOE Is
sponsoring the development of some Instruments. Is that only your shop, or
did I misunderstand what you said? How about a portable gas chromatograph?
HAMILTON: The pocket-sized gas chromatograph? I am not sure who Is
actually doing that* However, It Is almost at the commercial stage. But
I am not sure who that would be.
I think that Beckman would be very interested In commercializing It.
25
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Current NIOSH Research on Passive
Monitors
Mary Lynn Woebkenberg
Measurements Research Branch
Division of Physical Sciences and Engineering
National Institute for Occupational Safety and Health
Cincinnati, Ohio
I would like to take this opportunity to describe to you the work that
is currently being undertaken by the National Institute for Occupational
Safety and Health (NIOSH) and its contractors in the area of passive monitors.
We are studying not only points of current interest, but also future applica-
tions of passive personal monitors.
For lack of any other, I would like to offer the following definition
of passive personal monitors. (Please keep in mind that this definition is
dependent upon the interests and responsibilities of NIOSH in the area of
personal exposure monitoring.) A passive personal monitor is a device worn
on an individual for the purpose of measuring—without the use of an active
flow mover—personal exposure. The key aspects of the definition are three-
fold: 1) the device is worn on the individual—preferably within the breath-
ing zone; 2) the device uses no active flow mover, such as the typical pump
that is necessary with the various solid sorbent tubes; and 3) the device
measures personal exposure. These characteristics are the opposite of those
of an area monitor.
There are several advantages to passive monitors. This type of monitor—
interchangeably referred to as a badge—is small, lightweight, and easily worn
by any individual. This is an advantage over personal sampling pumps, which
can weigh up to 2 pounds each. The monitors are free of liquid content, which
makes them preferable to impingers and bubblers. The subsequent chemical
analysis of passive monitors is generally similar to existing methods. The
badges, however, are not without disadvantages. Whether the badge uses the
27
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principle of diffusion or permeation through a membrane, there is an extra
factor (not necessary with the use of sorbent tubes and pumps), which is
either the diffusion coefficient of the species through air, or the permea-
tion constant of the species through the membrane material used in the badge.
This constant must be known for each compound. In addition, there is evidence—
even with sorbent tubes—that high humidity alters the adsorption of various
solvents. In the case of sorbent tubes, desiccant tubes may sometimes be
used preceeding the sorbent tube. It is not yet apparent what can be done
to correct for high humidity effects in passive monitors.
The emphasis of NIOSH's current research with passive monitors centers
on the passive organic monitors. Most of the studies involve the Gasbadge,
marketed by Abcor Development Corporation, and the Organic Vapor Monitor,
marketed by the Minnesota Mining and Manufacturing Company. One study also
includes the MiniMonltor, marketed by the Reiszner Environmental and Analytical
Labs, Inc.
The Abcor Gasbadge is 8 cm long, 5.7 cm wide, and 2 cm deep. It weighs
approximately 40 g and consists of seven parts: the sliding cover; the front
plate of the badge, which has a 4.4 cm x 3 cm opening to allow diffusion of
gases; a protective screen; a draft shield; an open grid that defines the
diffusion geometry; the collection element; and the back plate of the badge.
One unique feature of the Gasbadge is that the newer-designed case allows for
placement of a second collection element which can be used to take a second
sample or can be used as a field blank. The Gasbadge is reusable by replacing
the collection element.
The 3M Organic Vapor Monitor is a circular badge that is 10.2 cm long
(including the clip), 4.4 cm wide at its widest point, and 1.2 cm deep. The
sampling opening is circular with a 3-cm diameter. This badge weighs 13.5 g.
During sampling, the unit consists of six pieces: the outer rim; the draft
shield, which is held in place by the outer rim; an open grid that defines
the diffusion geometry; the collection element; and the solid back piece
of the monitor. The sixth piece is the clip for attachment to the person.
The 3M monitor is the only passive monitor that we are currently using that
allows for in situ sample elution. The 3M badge is not reusable.
The MiniMonitor, which was developed by Philip West at Louisiana State
University, is also a circular badge. Its diameter is 5.0 cm, it is 0.625 cm
thick, and it weighs 35 g. There are two features unique to the MiniMonitor:
the badge works on 1) the principle of permeation of contaminant gases and
vapors through a membrane; and 2) adsorption of the pollutant(s) onto
28
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approximately 1.35 g of PCB activated charcoal. This is free-flowing, as
opposed to the collection elements of the two previously mentioned badges. The
MiniMonitor case is reusable by introducing a fresh supply of charcoal.
The most basic ongoing research with the passive monitors is an evalua-
tion of the passive monitors that is being conducted at the Utah Biomedical
Test Laboratories under contract to NIOSH. The purpose of this study is to
establish the reliability and the working characteristics of the Gasbadge, the
Organic Vapor Monitor, and the MiniMonitor. This effort consists of eight
tests that are designed to study various properties of the badges. All of the
tests are being conducted in a specially designed and constructed exposure
chamber with accurate control and monitoring of temperature, humidity, concen-
tration of the contaminant being used in the study, face velocity, and exposure
time. Even though independent checks are being constantly run on the concen-
tration—i.e., via GC, PID, or other calibrated instruments—in all of the
tests in this study, charcoal tubes are being used in side-by-side sampling
with the badges. The charcoal tube sampling is used as a reference because
the method represents the state-of-the-art in sampling for organic vapors and
is the best "primary standard" available.
In the first test with the badges and the tubes, we will consider the
precision of the measurement with the badges, and the comparability of the
badges with the charcoal tubes. Under conditions of constant temperature,
humidity, face velocity, and time, the badges and charcoal tubes will be
simultaneously exposed in 12 tests. The 12 tests are comprised of four con-
taminants at three concentration levels each. The contaminants to be used in
this study are vinyl chloride, acetone, toluene, and a mixture of n-hexane
and acetone.
The effects of storage on the sample accuracy will be studied. In this
test, one set of monitors and charcoal tubes will be exposed to methylene
chloride. A matching set of monitors and charcoal tubes will be exposed to
toluene. Monitors and tubes from each exposure will be divided into three
groups to be analyzed at three times—within 1 day of exposure, on the 7th
day following exposure, and on the 14th day following exposure.
Perhaps the most difficult test is that which will consider maximum and
minimum levels of quantitation and the capacity of the monitors. These tests
have been designed to determine over what concentration range and exposure
times the sampling and analytical methods for the monitors will provide a pre-
cision and accuracy of + 25 percent of the "true" value for 95 percent of the
samples.
29
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A fourth study will look at the effects of face velocity on the badges.
The face velocities will be varied from essentially stagnant conditions to
400 fpm. Orientation of the badges will also be studied, with the contami-
nant approaching from the front, side, and back of the badges in three sepa-
rate tests.
Effects of temperature from 0° to 40° C and humidity from 10 to 80 per-
cent relative humidity will be studied in two different series of tests.
Out-gasing or back-diffusion from the badges could be a serious short-
coming of the monitors. It is possible that back-diffusion could occur in a
situation where a worker would be exposed to a very high concentration of some
contaminant and then move to an area of no exposure. Back-diffusion could
occur, due to the concentration gradient, depending upon how tenaciously the
contaminant is adsorbed to the collection element. To study this phenomenon,
three tests have been designed that look at nonconstant concentration exposure
and continually varying concentrations.
The final test in this contract involves exposing the monitors to a com-
plex mixture, such as refined petroleum or coal tar products, and comparing
the badge results to the charcoal tubes.
The Division of Surveillance, Hazard Evaluation, and Field Studies of
N10SH is undertaking an effort to accumulate comparative field sampling data
between the Gasbadge, the Organic Vapor Monitor, and charcoal tubes. This
effort will result in a report later this year that contains 500 points of
comparison data between passive monitors and charcoal tubes—all from field
applications.
We are also engaged in research that involves possible future applica-
tions of passive organic monitors. Our Organic Methods Development Section
is attempting to develop a passive monitor for aldehydes. Their approach is
based on a derivative formation.
Another of the more complex problems with the passive monitors is the
question of saturation. How do we know when the collection elements have
reached their capacities for adsorption of contaminants? In the laboratory—
under controllable conditions—it is easy to determine the point of satura-
tion. But what happens in the field if the exposure of a worker is being
measured and the passive monitor saturates? To address this question, we are
undertaking an effort to look at two-stage passive monitors. In this study,
we determine the capacity of a collection element by plotting exposure time
30
-------
versus percent recovery. Saturation of the collection element is indicated
by the drop off in the curve from the theoretical 100 percent recovery, and
the capacity of the element can be calculated from this exposure time.
What we hope to be able to detect is the breakthrough of the contaminant
through the first collection element and to determine the validity of the
sample. When the first collection element is saturated, there will be a con-
centration gradient to the back of the badge in the direction of the second
collection element. There will probably also be a less dramatic gradient
between the first collection element and the ambient air. Because of these
developing gradients, we hope to be able to detect the contaminant on the
second element after the badge has been exposed up to its saturation point.
This will be a great aid in using the passive monitor in the field.
Another type of passive monitor is a personal atmospheric gas sampler
with a critical orifice which was developed through an interagency agreement
between NIOSH and the Naval Research Laboratory. This whole air sampler uses
the leak through a critical orifice to meter the air flow into an evacuated
container. The critical orifice admits air at a constant rate up to one-half
atmospheric pressure. An 8-hour sample can be taken. For analysis, the sam-
pler is connected to a gas chromatograph, through a gas sampling loop inter-
face. The pressure of the gas sample is measured using a manometer placed in
the gas sampling loop. The advantages of the whole air sampler—besides being
small, lightweight, portable, and requiring no personal pump—are that the
sample taken never undergoes a phase change, the sample is never handled,
and there are never breakthrough and desorption problems. One disadvantage
to the whole air sampler is that it does not provide an enrichment step, and,
therefore, sample analysis requires sensitive analytical instrumentation.
Substances with low-level standards may not be sampled in this fashion.
Passive monitors are currently available for NO , SO,,, Hg, and the organic
—* «W fc
solvents. The U.S. Army Environmental Hygiene Agency has been working on a
passive monitor for ammonia. Soon, independent companies will make available
passive monitors for NH,, S02, HC1, and NO , as well as marketing uniquely
designed passive monitors for organic solvent vapors.
NIOSH is planning to look further into passive monitor use by testing
different solid sorbents as the collection element and perhaps looking into
some electrochemical applications of passive monitors. As far as their
application to ambient personal monitoring goes, the present state-of-the-art
passive monitor has some major drawbacks: 1) the monitors generally lack
specificity (a drawback of some other sampling techniques as well); and
31
-------
2) the detection limits of the monitors—at the low end of the scale—may not
meet the needs of ambient sampling. While it Is true that collection on the
element is an enrichment step, it could take quite a long time to accumulate
a detectable sample from ambient air. With certain new products that are
coming out, and as the technology allows ue to develop more effective monitors,
passive monitoring will be useful in the ambient situation.
MAILING ADDRESS OF AUTHOR
Mary Lynn Woebkenberg
Measurements Systems Section
Measurements Research Branch
Division of Physical Sciences and Engineering
National Institute for Occupational Safety and Health
4676 Columbia Parkway
Cincinnati, Ohio 45226
Discussion
WALLACE: Lance Wallace, EPA. Is that cold air sampler going into com-
mercial development?
WOEBKENBERG: MDA markets It.
WEST: Phil West, Louisiana State University. I can make a comment,
which is not a question. One is that the permeation-type badge does handle
liquids. In fact, they use that on a chlorine badge that we have just de-
veloped. In that case, incidentally, it is specific for chlorine if the
ozone does not Interfere.
I might also mention that so far humidity has no effect on the badges
that we have developed based on permeation.
WOEBKENBERG: Some of the studies that we have run have shown a humidity
effect. The data have not been worked up yet, but we have seen a minor humid-
ity effect.
But that is true about the liquids. There are some passive monitors
that will be available. In fact, there are some that are already available
that do use liquids as the collection element. Some of them will be talked
about today. And some of them are not yet ready to be spoken of. But there
are some liquids also available.
32
-------
THOMAS: Charles Thomas. You mentioned that some of the monitors were
specific and some were not. If they aren't specific, how do you get around the
problem of determining what the lowest level of exposure should be if the col-
lection efficiencies vary from gas to gas?
WOEBKENBERG: Well, I said that the monitors are not specific. Gener-
ally, I mean in the case of the organic vapor monitors. The charcoal col-
lection elements will trap organic vapors, and in that case, they are not
specific.
In order to resolve the question of specificity, then you have to rely
on your analytical method to do that for you. However, in the case of some
of the passive monitors—as Dr. West mentioned, they have one for chlorine
and 3M has one for mercury—there are certain monitors that are specific.
But in the case of nonspecificity, they have to rely on the analytical method
to resolve that problem for you.
THOMAS: Isn't it a collection device and not a monitor?
WOEBKENBERG: That is true; yes.
33
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Electrochemical Methods for Development
of Personal Exposure Monitors
Joseph R. Stetter, Ph.D., Donald R. Rutt, and Michael R. Graves
Energetics Science Division
Becton Dickinson and Company
Elmsford, New York
INTRODUCTION
Recent social and legal requirements have given great impetus for the
development of personal exposure monitors for a variety of gaseous pollu-
tants. Since the exposure of a normally active individual is not accurately
represented by a fixed-site monitor, there is a need for personal monitors
in order to measure the actual human exposures.
The application of our electrochemical sensing method has resulted in a
variety of practical monitors for the measurements of CO in ambient air.
This established technique has been applied to personal dosimetry for CO in
the workplace environment. An evaluation of this device demonstrates that
the performance characteristics of the larger fixed-site instruments can be
achieved in a compact, lightweight personal exposure monitor.
This instrument approach to dosimetry overcomes many of the historical
disadvantages of integrated dosage measurement. The CO Dosimeter, Ecolyzer
9000 Series, enables accurate measurement of dosages over short-time intervals
and correlation of exposure and physical activity.
A PERSONAL MONITOR FOR CARBON MONOXIDE
The success of the electrochemical method for the measurement of carbon
monoxide in the workplace environment is well known. In the sensor, carbon
35
-------
monoxide is electro-oxidized to carbon dioxide at a potentiostatically con-
trolled platinum electrode in aqueous electrolyte and follows the reaction
CO + H20 •*• C02 + 2 H+ + 2 e~
The signal produced upon exposure of the sensor to an air mixture is propor-
tional to the partial pressure of carbon monoxide in the gas which is analyzed.
This current flows between the sensing and counter electrode, and the
reaction at the counter electrode is
02 + 4 H+ + 4 e~ •*• 2 H20
therefore yielding an overall cell reaction of
2 CO + 02 •*- 2 C02
This sensing method has been developed and adapted for personal monitor-
ing. In order to accomplish this task, it was required that the sensor be
miniaturized and designed for ruggedness. Further, accurate measurement of
the TWA while worn by the worker performing routine activities necessitated
that the instrument performance be insensitive to both orientation and
vibration.
The gas is Introduced into the sensor (shown schematically in Figure 1)
by means of a sampling pump. The sensor is a miniaturized three-electrode
electrochemical cell. The Teflon-bonded diffusion electrodes are in con-
tact with the aqueous electrolyte, which Itself is suspended in an immov-
able matrix. The matrix allows the sensor to be operated in any special
orientation.
The sensor is interfaced with an instrument system, which is described
schematically in Figure 2. The compact system design has a volume of approxi-
mately 300 cc and a weight of 0.43 kg (12 oz). The critical working elements
consist of pneumatics, sensor and electronics for power control, amplification,
and storage. During operation, an external pump draws a sample of ambient air
through the pneumatic system at a constant flow rate. The sensor continuously
monitors the concentration of carbon monoxide in the sampled air stream. This
concentration-related signal is amplified and converted into digital pulses
for storage in a digital circuit. The battery pack is capable of supplying
power in excess of 2 years of dosimeter operation. A flow-adjust valve allows
for fine control of the sample flow rate. The prefilter removes particulates
36
-------
EXHAUST FITTING
ZERO CONTROL
SIDE CONNECTOR
CIRCUIT BOARD
ASSEMBLY
FLOW ADJUST
VALVE
SPAN CONTROL
^—FILTER AND
fi ./ INTAKE FITTING
Af
BATTERY
PACK
MANIFOLD BLOCK
SENSOR
FIGURE 1. Dosimeter schematic.
SAMPLE
EXHAUST
NiCad
Batter}
Pack
1
I
READ-
OUT
—
READOUT
SAMPLE
INPUT
DOSIMETER
FIGURE 2. Instrument system schematic.
37
-------
and Interfering gases, giving a high degree of specificity to the analysis.
Zero and span controls allow for convenient calibration of the continuous CO
monitor section of the dosimeter.
A side connector is made so that it can be plugged into a readout device.
The dosimeter readout is a self-contained rechargeable instrument which is
used for dosimeter calibration and also for dosage measurement. The data col-
lected in the dosimeter is digitally transferred to the readout by depressing
the read button. This process does not clear the dosimeter, and the same dosi-
meter can be read any number of times within any given time period. Clearing
of the stored dosimetric data is accomplished by depressing the "clear" button
with simultaneous depression of the "read" button twice. This virtually elimi-
nates accidental clearing of the integrated CO reading stored in the dosimeter.
Typical response of the dosimeter to a variety of CO concentrations is
illustrated in Figure 3. For this particular instrument, 98 percent of signal
is obtained in less than 45 seconds. For 100 instruments studied, we have found
that 100 percent of signal is obtained between 20 and 60 seconds after initial
gas exposure. This means that calibration can be accomplished in approximately
1 minute and that the dosimeter will accurately record fluctuations in the
ambient concentration.
For this instrument, the magnitude of the response can be expressed by
the equation
ppm = 0.98x - 0.38
where ppm and x represent the instrument signal and actual CO concentration,
respectively. This excellent linearity of response allows the instrument to
be calibrated at a single point and still record dosage accumulations with
accuracy over a wide range of exposure concentrations.
One hundred instruments were studied by placing them in an environmental
chamber and introducing an 84 ppm CO/air mixture Into each dosimeter at
100 cc/min. The gas mixture was drawn continuously through the dosimeter,
and dosage readings were taken at hourly intervals over the course of a 6- to
8-hour exposure. During this exposure, the temperature was changed from
40° C to 22° C to 0° C. At each temperature the instrument span and zero
were recorded. Analysis of this data revealed the instrument performance
characteristics at three temperatures and over a long time exposure.
The data is summarized in Table 1 for 100 instruments. The system error
38
-------
90
80 - _
70 - -
60 - -
20-_
10-.
50 4-
PPM
40 -
30 J- /
•HB
A+
RECORDER SCALE
SIGNAL CO (PPM) (PPM FULL .SCALE).
A
B
C
D
E
F
200
23
375
50
85
93
400 _
PPM
0-1000
0-100
'.-1000
0-100
0-100
0-100
0 1 2
TIME (MIN.)
FIGURE 3. Dosimeter response versus time at various CO concentrations.
39
-------
TABLE 1
Ecolyzer Performance Summary
100 Dosimeters
SYSTEM ERROR1
Mean
Variance
Std. Dev.
22° C
+ 0.46
9.0
+ 3.0
40° C
+ 0.96
24.2
+ 4.9
0° C
+ 2.5
27.8
+ 5.3
2
Combined
+ 2.10
11.6
+ 3.41
Percent deviation from theoretical dosage
2
For 25 instruments, random selection
was calculated by comparing the actual dosage measured with the theoretical
dose exposure. To obtain a theoretical exposure, the instrument span at 22° C
was multiplied by the total time of exposure. Excellent stability is found
for these 1-hour exposures at each temperature. It is significant to note that
the mean deviations of the dose from theoretical values are within+^ 2.5 per-
cent, even when operated at a temperature 20° C different from the calibration
temperature. The standard deviation of this 100-unit sample indicates that
the accumulated dosages are within the design goal of + 15 percent error with
an extremely high reliability. Errors not included in this analysis, however,
are those due to the operation, such as calibration, and those due to equip-
ment failure, such as the sampling pump and calibration gas. However, it
should be possible to keep such fluctuations well within +^ 5 percent by using
appropriate precautions and following proper procedure.
Examination of the individual variations of instrument stability with
temperature is shown in Figure 4. The error bars are two standard deviation
units wide and demonstrate that the instrument's sensitivity to temperature
changes is small. Operation can occur outside the 0° to 40° C range and will
result in only slightly higher errors than those measured here. The sensor
can be operated at temperatures as low as -10° F before failure is observed.
In order to demonstrate the instrument analog/digital characteristics
under various concentration/temperature conditions, we performed the experi-
ment summarized in Table 2 and Figure 5. Here, five dosimeters were simul-
taneously exposed to: 1) 85 ppm CO at 24° C, 2) 50 ppm CO at 24° C, 3) a
temperature change to 40° C with 50 ppm CO exposure, 4) continued 50 ppm
40
-------
PPM
CO
92
88.
84.
80_
76t
72
•
68
64
60
56
•
52
48
44
40
36
32
•
28
24
20.
16,
12
8.
u
0
-4
-8
"< I 1 -f9-
- J.^
10 15
TEMP. °C
20
25
35 4(4.
FIGURE 4. Dosimeter zero and span versus temperature.
41
-------
4s
N>
TABLE 2
DATA
POINT
A
B
C
D
E
F
DOSIMETER NUMBER
1179
THEOR. ACT. Z
DOSE PPM DEV
PPM MRS. MRS
0
85 84 -1.2
142 140 -1.4
196 190 -3.2
246 236 -4.1
335 320 -4.5
1091
THEOR. ACT. Z
DOSE PPM DEV.
PPM HRS. HRS
o
86 85 -1.2
142 140 -1.4
197 190 -3.6
247 235 -4.9
336 318 -5.4
1206
THEOR. ACT. Z
DOSE PPM DEV.
PPM HRS HRS
o
87 88 -1.2
143 140 -2.1
197 189 -4.1
247 234 -5.3
338 315 -6.8
1291
THEOR. ACT. Z
DOSE PPM DEV.
PPM HRS. HRS
o
89 86 -3.3
144 137 -4.9
198 186 -6.1
248 231 -6.9
339 314 -7.4
1191
THEOR. ACT. Z
DOSE PPM DEV.
PPM HRS. HRS
o
90 90 0
145 144 -0.7
199 196 -1.5
249 245 -1.6
341 333 -2.5
-------
u>
FIGURE 5. Dosimeter analog output versus time.
-------
exposure, 5) 85 ppm CO at 40° C, and 6) zero ppm CO at 40° C. The recorder
trace shows the analog output for each instrument for a 1-minute duration
once each 5 minutes. In Table 2, a comparison of theoretical and experimental
dosages (digital outputs) is summarized; the dosimeters had a mean error of
-3.4 percent +2.1 percent. One observes that the instrument is capable of
following dosages accurately with a single calibration at the initiation of the
test and in the presence of 20° C temperature changes and concentration changes.
PERSONNEL MONITORING
Other personnel monitors that are based upon this electrochemical sensing
method are available for hydrazines (1,2), NO- (3), and H.S (4). These instru-
ments have not been miniaturized to the same degree as the previously described
carbon monoxide dosimeter; however, they are portable analyzers weighing 5 to
10 kg. Further, other devices are possible with existing technology for
gases such as NO and SO..
The future holds great promise for development of personal monitors of
miniature size using Energetics Science electrochemical gas sensing methods.
This technique offers the advantages of small size, light weight, low power,
stability over long sampling periods, ease of operation, sensitivity, and
ruggedness. Primary areas which will require development to provide electro-
chemical personal monitors are related to: 1) improved sensitivity and sta-
bility to widen the application range without reducing accuracy; 2) development
of auxiliary instrument systems related to pneumatics and electronics; and 3)
improved specificity for expanding the application to a wider range of con-
taminated environmental samples.
REFERENCES
1. Stetter, J.R., Blurton, K.F., Valentine, A.M., Tellefsen, K.A. The
Electrochemical Oxidation of Hydrazine and Methylhydrazine on Gold:
Application to Gas Monitoring. J Electrochem Soc 11:1804-1807, 1978.
2. Stetter, J.R., Tellefsen, K.A., Saunders, R.A., DeCorpo, J.J. Electro-
chemical Determination of Hydrazine, Methyl- and 1,1-dimethylhydrazine
in Air. Talanta (in press).
3. Ecolyzer Model 6632 Analyzer, Energetics Science Division, Becton
Dickinson and Company, 85 Executive Boulevard, Elmsford, N.Y. 10523.
4. Ecolyzer Model 6430 Analyzer, Energetics Science Division, Becton
Dickinson and Company, 85 Executive Boulevard, Elmsford, N.Y. 10523.
44
-------
MAILING ADDRESS OF PRIMARY AUTHOR
Joseph R. Stetter, Ph.D.
Energetics Science Division
Becton Dickinson and Company
85 Executive Boulevard
Elmsford, New York 10523
Discussion
ZISKIND: Richard Ziskind of Science Applications. I wonder if you are
concerned about electromagnetic interference with these devices, such as
radio transmission—something like that?
STETTER: Yes. The circuitry is susceptible, and there are a lot of
wires and things. We don't find high-frequency interference on most of our
monitors because they have metal cases.
On these particular small ones, they have light plastic cases. And we
found it necessary to coat the inside of the plastic case with a metallic
coating which is grounded. We had one of these successfully tested at the
Kennedy Space Center. And it shows indeed that the HF sensitivity is very
low.
SPENGLER: John Spengler, Harvard School of Public Health. A couple of
questions: one is about cell life, and two, have you ever actually field
tested this alongside of an ND1R CO monitor? Because 1 am concerned about
the highly fluctuating nature of real CO exposure.
STETTER: Early in the game, we compared the electrochemical technique
and NDIR for CO measurement. We found that by and large our response times
were much better because they have a lower purge rate for the larger cell.
You can purge this cell very rapidly so you get a very good response charac-
teristic. In terms of cell life, we warranted these kinds of cells for 6
months. And generally speaking, with proper care and normal ambient con-
ditions where the relative humidity is, you know, 40 to 80 percent, you should
get a lifetime in excess of a year.
SPENGLER: What is the cost of the cell and the unit?
STETTER: The instrumentation comes in a kit of five which gives you
the readout and five dosimeters for about $3,000, give or take a little bit.
WILLIAMS: Marsha Williams. Do I understand that it was tested with
flow rates, temperatures, and humidity checks like that at ambient levels
which are more typical in the environment that EPA would like to monitor?
45
-------
STETTER: There is a field test now; at least these devices have been
and are actually being used in the field.
WILLIAMS: I don't mean field testing. I am talking about your sensiti-
vity test to see how sensitive they are to flow rate.
STETTER: Right. In the laboratory, we of course did the flow rate study,
which was easily accomplished.
WILLIAMS: Have you done any studies at low level concentrations to see
whether or not there is a difference in effect?
STETTER: Yes. And there is no difference in effect because the re-
sponse is linear. It is a percent of span. In other words, if you have
50 ppm and you drop 1 ppm or 1 percent of span where you measure 100 ppm
at the same flow rate, you would get 98. That would be 2 percent of the
signal. It is a percent span change with flow rate—that is the character-
istic.
Now, we have done relative humidity at all three temperatures, at 0 to
100 percent. The only effect you get is dilution of your calibration gas.
It is the only effect you can see, and there is no signal to monitor at all.
HODGESON: Jlmmie Hodgeson, National Bureau of Standards. Can you give
us any more details—is there an active relation between your electrical
signal and electrical return in the amount of CO going through the sensor?
STETTER: Yes. There is a signal relationship. For example, if you
went to higher flow rates, you can get higher currents—put more CO through
it. So, in terms of more detail: yes, in effect.
SPENGLER: You didn't show any data on interferences. I know there are
several with the Ecolyzer such as NO. And it is the same principle, I assume?
STETTER: Well, there is not an interference due to NO with a proper
filter. The filter has scrubbers and adsorbents in it which take out NO,
N0_, S02, H2S, and other electrochemically reactive gases. So, you get a high
degree of specificity. Without the filter in place, you can get signals
from other electrochemical reactive gases.
SPENGLER: Would that be a concern with personal monitoring as opposed
to stationary monitoring?
STETTER: Yes.
-------
Portable Ozone and Oxidant Monitors for
Random Field Surveys
Gary P. Heitman and Richard L. Sederquist
Mast Development Company
Davenport, Iowa
INTRODUCTION
Small, portable electrochemical instruments capable of measuring ozone
(O^) at the parts-per-billion (ppb) level are widely used in industry as
safety monitors near ozone generators and ozone-producing processes, and in
quality control of ozone-producing appliances such as photocopy machines and
electronic air cleaners. Similar instruments, or measuring techniques, may
be suitable for use in ambient air monitoring at remote locations, complement-
ing the existing fixed-station network.
AVAILABLE INSTRUMENTATION
While the once-popular colorimetric potassium iodide (KI) analyzers
are no longer manufactured, amperometric KI instruments are currently avail-
able in several convenient configurations. Similar in design to the well-
known Mast Ozone Meter (Model 724-2), which was widely used for ambient air
pollution studies prior to 1975, Mast Series 724 Oxidant Monitors utilize
an electrochemical sensor with buffered 2 percent KI reagent. Details on the
detection technique have been given by Mast and Saunders (4). Recent instru-
ments, while retaining the original detection technique, offer several design
improvements, including a signal amplifier which allows multiple-range direct
readout, increased sensitivity at low Og levels, and zero/span adjustments.
Reagent is supplied from a single reservoir with enough capacity for up to
30 days continuous operation. Two models are appropriate for ambient level
47
-------
03 monitoring—Model 724-5, a.c. powered (see Figure 1), and Model 724-4,
battery powered (see Figure 2). The battery-powered model was designed
according to National Institute for Occupational Safety and Health (NIOSH)
guidelines for construction and performance standards for compliance moni-
toring in the industrial environment (6) and will operate 20+ hours on a
fully charged battery. Both instruments weigh less than 12 pounds and are
easily transported.
PERFORMANCE, OPERATIONAL STABILITY
Although relatively low in cost and simple to maintain and operate,
certain electrochemical monitors can exhibit exceptional performance.
A Mast amperometric KI oxidant monitor was evaluated against analyzers
using chemiluminescent and ultraviolet absorption measurement methods in a
field study at Los Angeles and St. Louis during 1970-1972 (3). Long-term
calibration stability and general operational characteristics were compared.
Results are shown in Tables 1 and 2.
More recently, a Model 724-5 monitor was evaluated by a project team at
Harvey Mudd College, Claremont, Calif., for potential use as a commercial
aviation 0_ monitor. The instrument was calibrated prior to shipment using
the 1 percent neutral buffered potassium iodide (NBKI) procedure. After 30
days of continuous use at the college, the instrument's calibration was
checked at the State of California Air Resources Board station at El Monte.
The Air Resources Board (ARB) uses a Dasibl UV absorption monitor and a
special three-meter ultraviolet instrument for comparison in calibration (11).
The Mast monitor, Serial Number 2370, agreed with the ARB standards within
six-tenths of 1 percent (0.6 percent) (11).
Parker (6) reported similar calibration stability in a study for NIOSH
and also determined that neither changes in relative humidity (0 to 100 per-
cent) or changes in ambient temperature (10° to 40° C) significantly affect
the measuring efficiency of the Mast monitor. Other operational character-
istics which make the Mast monitor suitable for field use are convenient size,
quiet operation, low maintenance, and long-term unattended operation.
PERFORMANCE, ACCURACY IN OB MONITORING
Obviously, there must be some disadvantages in the use of an ampero-
metric KI system. Photochemical oxidants have been traditionally defined
48
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FIGURE 1. Model 724-5 Oxidant Monitor, front door open. Oxidant measuring
ranges are 0-0.1 to 0-1 ppm.
FIGURE 2. Rear view of Model 724-4 Oxidant Monitor. High-capacity lead acid
battery powers monitor for 20+ hours.
49
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TABLE 1
Long-Term Calibration Summary for 0, and 0 Instruments
J X
a
Instrument
Bendix Env. Sci.
Bendix Process
RTI (Solid Phase)
Dasibi
Sectarian
Mast b
Technicon
Pollutant
°3
°3
°3
°3
°x
°x
°x
Number of
calibration
points
23
105
52
21
67
103
74
Minimum
detectable
concentration
(ppm)
0.0066
0.0003
0.0004
0.0011
0.0122
0.0003
0.0118
Average
zero drift
(ppm/day)
0.0001
-0.0000
-0.0000
-0.0001
-0.0001
0.0000
-0.0004
Average
span drift
(%/day)
0.072
-0.128
-0.074
-1.749
0.592
-0.129
-0.552
• Correlation
coefficients
0.882
0.998
0.992
0.967
0.963
0.993
0.947
a. Reference 3
b. Mast QX, Model 724-2
TABLE 2
General Operational Characteristics for 0_ and 0 Instruments
J A
Bendix Env. Sci. 03
Bendix Process 03
RTI (Solid Phase) 03
Dasibi 03
Mast O^
Technicon 0^
Beckman 0^
Number of
days tested
94
74
185
32
256
256
65
Ambient
monitoring
tire (%)
94.7
94.3
94.1
98.5
, 94.2
87.5
90.0
Calibration
time (%)
2.9
2.4
2.7
1.4
3.3
4.5
5.5
Downtime
2.4
3.3
3.2
0.1
2.5
8.0
4.5
a. Reference 3
b. Mast Ox, Model 724-2
50
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as substances which will oxidize a KI reagent, which responds to 03 with nearly
100 percent efficiency, and to a lesser extent, to peroxyacetal nitrate (PAN)
and hydrogen peroxide—all components of the photochemical oxidant mixture—
and also to nitrogen dioxide (NO.). Sulfur dioxide (S02) reacts negatively,
reducing an oxidant-caused signal. The most important disadvantage of the
amperometric KI system, therefore, is its nonspecificity. Sulfur dioxide is
a major interferent because it reduces iodine formed in the KI reaction from
contact with oxidant back to potassium iodide, producing a strong negative
interference. A SO filter (Model 725-30) is available for the Mast instru-
ment. Consisting of glass fiber paper impregnated with chromium trioxide and
sulfuric acid, as described by Saltzman (7), it has proven to be effective in
over 7 years of field use and experimental evaluation (5,7). A potential dis-
advantage in the use of this filter is its ability to oxidize nitric oxide (NO)
to N0_, causing additional interference in 0« determination. This may not
present a problem, however, since 0« and NO rarely coexist. Use of the filter
would be disadvantageous in only a few areas (such as Los Angeles), where
concentrations of NO are relatively high and those of S02 low (7).
The Mast monitor will also respond to approximately 12 percent of PAN
present in a sample and to 9 percent of hydrogen peroxide (2). Since these
compounds generally exist at low levels in ambient air, compared to ozone
levels (1), interference potential is usually insignificant.
Assuming S0_ is filtered or is not present, the major interferent to
contend with is N0>. The efficiency of the Mast monitor in measuring NO^
is approximately 6 percent. The efficiency drops at high ozone levels. For
instance, if an 0_ level of 0.25 ppm is being sampled concurrently with a
0.55-ppm level of N02, instrument response will be 0.28 ppm 0 (9), an error
of only 5 percent.
In actual field use, an electrochemical KI oxidant method can show
equivalent performance when compared with a chemiluminescent and UV photo-
metric 0. method. Wendt (10) reported that the California ARE compared, at
three separate stations, a total oxidant analyzer (colorimetric KI), an
ethylene chemiluminescent ozone monitor, and an ultraviolet photometric
ozone monitor. The experimental results showed the total oxidant, ultra-
violet photometric, and ethylene chemiluminescent monitoring methods to
be equivalent over a range of 0 to 500 ppb at the three sites. Other recent
comparisons also show, in general, small differences between KI oxidant data
and ozone data, especially when instruments are standardized with the same
calibration atmosphere and when appropriate corrections for major interferents
are considered (1).
51
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A MINIATURE SENSOR FOR PERSONAL EXPOSURE MONITORING
A miniature KI oxidant sensing device currently used in a Mast Brewer
ozonesonde may be adaptable for use as a personal 0, exposure monitor. Figure
3 shows the major components of a Mast bubbler/pump assembly, and the general
dimensions.
Packaging, including electronics, readout, and housing, would produce a
miniature monitor about the size of a cigar box weighing less than 1 pound.
(See Figure 4.)
Table 3 gives estimated performance specifications. Other parameters
have not been fully evaluated. (See Figures 5 and 6.)
The bubbler sensor is a small electrolytic cell which contains a few
milliliters of KI reagent. A miniature pump forces ambient air continuously
through the cell at a constant rate of 200 cc/min. The cathode is fine plati-
num gauze, and the anode is a silver wire. The arrangement of the cell is
such that the bubbling action also provides the maximum possible flow of the
solution through the cathode gauze. When a potential of 0.42 V is applied
across the cathode and anode, it balances a spontaneous emf associated with the
detector, and no current will flow unless free iodine is present. As the air
containing 0 bubbles through the electrolyte, free iodine (I ) is formed
X £,
which contacts the cathode screen, through diffusion and the sensor bubbling
TABLE 3
Estimated Performance Specifications of Mast Miniature Bubbler
PERFORMANCE PARAMETER UNITS OXIDANT
Range ppm 0-0.5
Noise ppm 0.005
Lower detectable limit ppm 0.009
Zero drift, 8 hour ppm 0.005
Span drift, 8 hour ppm 0.005
Rise time, 90 percent Minutes 5
Fall time, 90 percent Minutes 2.5
a
Tested on bromine permeation tube standard
52
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-5 cm
KOH+H20
PLATINUM
CATHODE
SILVER
ANODE
FIGURE 3
9 cm
1 —
--
_ — ~.
-
~ —
Zerc
__L.
00-9
1
-r I — IT
-
-
.
)
0^8
-
•*»M^B«
— - —
-
_
07
— .~
^— —
-
- •
- - -
~— 1 -
0 6
••^•^•M
'
o : 5
-
-
—
~
—
.". :.
—
04
—^
'.'.".
• - -
0 - 3
— '
/
!; 1
\
-•-
• • PP
-—
_ .",.
-
3 — 1
-
- -- -
0 C
= I
FIGURE 5
3~- 1
— :-
-
— _^.-
0 --2
— ^_
- - .
-
0--3
-
-
— —
0 1 4
,
- - -
-
0 5
—
06
0^1 7
-
-
0 8
Start
-
0
9
-—
- -
0 -10C
: ;-
—
-- ;
FIGURE 4
FIGURE 6
FIGURE 3. Miniature oxidant sensor.
FIGURE 4. Experimental bubbler-monitor weighs less than 16 oz.
FIGURE 5. Typical chart recording from oxidant bubbler. Bubbler is ranged
for O-.l ppm 0 full scale. Chart speed is 5 cm/hr.
FIGURE 6. Chart shows Mast bubbler output over a 6-hour period. Oxidant
source level is 0.084 ppm. Chart speed is 2 cm/hr.
53
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action, and is reconverted to iodide (21 ). At the anode the I. is re-
formed, but it is prevented from recirculating through the formation of
practically insoluble silver iodide (Agl). In principle, each ozone mole-
cule entering the sensor gives rise to a flow of two electrons in the
external circuit of the sensor.
FEASIBILITY OF USING OXIDANT BUBBLER AS DOSIMETER
The electrochemical processes of the Mast bubbler are such that an
insoluble layer of silver iodide is formed on the silver anode:
Ag + I -e -*- Agl
As the silver iodide (Agl) is relatively inert to the electrolyte, the
amount of iodide plated on the anode should be equivalent to the amount of
oxidant which has passed through the cell.
Due to the small concentration of oxidant being sampled (less than 1 ppm)
and to the relatively low flow rate of the pump (nominally 200 cc/mln), the
amount of iodide plated on the silver in light hours is too small to be
determined gravimetrically. However, Perone et al. (8) have reported using
cathode stripping voltammetry for the determination of iodide using silver
electrodes.
In the determination of iodide, the iodide is first electro-deposited
on the silver anode in a pre-electrolysis step. The actual analysis occurs
when the iodide is stripped from the electrode. In the bubbler, the chem-
istry is much the same as in the pre-electrolysis step. The amount of iodide
on the electrode can then be determined using a cathodic stripping method.
Due to the stability of the silver iodide, the stripping analysis may not
need to be done immediately, but may be done at a later time.
DISCUSSION
The EPA has suggested (1) that, ideally, 0_ should be measured at loca-
tions downwind from the source-intensive center-city area, if peak 0- concen-
trations are to be recorded. Increased rural surveillance has also been
suggested. Since concentrations of NO in an urban air mass decays rapidly
as the air moves away from the city (1), nonspecific KI oxidant monitors
may be suitable for this task. The cost-ratio for chemiluminescent Og or
54
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UV photometric 0^ methods versus the amperometrlc KI (Mast) method is nearly
five-to-one.
A miniature KI oxidant instrument, currently used for atmospheric 0^
research, may be useful as a personal exposure monitor, or, when used with
a tethered radiosonde, a tool for tropospheric mixing and transport studies.
Amperometric KI oxidant monitors and sensors are rugged, small, low in
cost, and exhibit excellent stability. These versatile instruments may prove
useful in supplementing data collected at fixed-monitoring stations.
REFERENCES
1. Air Quality Criteria for Ozone and Other Photochemical Oxidants.
U.S. Environmental Protection Agency. EPA-600/8-78-004. April 1978.
2. Bufalini, J.J. Gas Phase Titration of Atmospheric Ozone. Environ Sci
Technol 2:703-704, 1968.
3. Decker, C.E., Royal, T.M., Tommerdahl, J.B. Field Evaluation of New Air
Pollution Monitoring Systems, Final Report. Research Triangle Institute,
EPA Contract No. CPA 70-101. 1972.
4. Mast, G.M., Saunders, H.E. Research and Development of the Instrumenta-
tion of Ozone Sensing. ISA Trans 1:325-328, 1962.
5. Miller, D.F., Wilson, W.E., Jr., Kling, R.G. A Versatile Electrochemical
Monitor for Air-Quality Measurements. J Air Pollut Control Assoc
21:414-417, 1971.
6. Parker, C.D. Evaluation of Portable, Direct-Reading Ozone Meters.
Research Triangle Institute, NIOSH Contract No. HSM-99-73-1.
7. Saltzman, B.E., Wartburg, A.F., Jr. Absorption Tube for Removal of
Interfering Sulfur Dioxide in Analysis of Atmospheric Oxidant. Anal
Chem 37:770-782, 1965.
8. Shaln, I., Perone, S.P. Determination of Iodide Using Stripping Volt-
ammetry at the Silver Electrode. Anal Chem 33:325, 1961.
9. Tokiwa, Y., Twiss, S., deVera, E.R., Mueller, P.K. Atmospheric Ozone
Determination by Amperometry and Colorimetry. In: Determination of Air
Quality. New York, Plenum Press, 1972, pp. 109-130.
55
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10. Wendt, J.F., Torre, K.J. Ozone Measurements, Field Instrumentation and
Comparative Data. Unpublished paper presented at Conference on Air
Quality Meteorology and Atmospheric Ozone, ASTM Committee D-22. Boulder,
Colo., 1977.
11. Private communication from Steven C. Runo, Harvey Mudd College, Clare-
mont, Calif., June 26, 1978.
MAILING ADDRESS OF AUTHORS
Gary P. Heitman and Richard L. Sederquist
Mast Development Company
2212 E. 12th Street
Davenport, Iowa 52803
56
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Personal Sampler for Measurement of
Ambient Levels of NO2
Edward D. Palmes, Ph.D.
Institute of Environmental Medicine
New York University Medical Center
New York, New York
INTRODUCTION
The NO- sampler to be described is a "passive" device. The only driving
force for the collection of molecules of the contaminant gas is the random
motion of the molecules themselves. There are, therefore, no requirements
for pumps, flow regulators, or batteries. Because of this, the devices can
be made very lightweight, inexpensive, and maintenance-free. These charac-
teristics make them ideally suitable for the purpose for which they were de-
signed; i.e., the measurement of N02 in underground mines. Prototypes of this
kind of sampler were reported by Palmes and Gunnison (4) in 1972 and published
(5) in 1973. The subject device was published by Palmes et al. (6) in 1976,
a publication which describes the N02 sampler both from the practical and
theoretical standpoints (the reader is advised to consult this publication
for details of construction, operation, and application to the workplace
environment). An attempt will be made in this paper to describe the general
features of the device and the theoretical background, as well as to demon-
strate the applicability for monitoring NO. at the community and the indus-
trial levels.
DESCRIPTION OF SAMPLER
The sampler consists of a 3/8-inch I.D. acrylic tube, approximately
3 inches long. One end of the tube is permanently closed with a close-fitting
polyethylene cap, inside of which are three stainless steel screens coated
57
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with triethanolamine (TEA), which is an excellent absorbent for NCL, as
reported by Levaggi et al. (2) and by Blacker (1). During sampling, the
other end of the tube is open to the environment to be sampled. Since the
TEA maintains the N0_ concentration at the closed end of the tube at or very
near zero, a concentration gradient is set up between the open and closed ends
of the tube. This causes a net flow of NCL from the environment to the TEA,
where it is captured. For storage both before and after sampling, both ends
of the sampler are capped. The complete sampler weighs approximately one-
quarter ounce. The materials for the construction are inexpensive, and all
of the components except the polyethylene caps are cleaned and reused. It is
estimated that a technician could either prepare or analyze approximately
100 samplers in a working day.
THEORY
The quantity of NO- transferred by diffusion during an exposure can be
calculated using Pick's First Law of Diffusion. This law states that if there
is a concentration difference between the two ends of a diffusion barrier,
there will be a flux of the gas species for which the concentration difference
exists. This flux will increase linearly with the concentration gradient
and with the cross-sectional area of the diffusion path, and will decrease
linearly with the length of the diffusion path. The quantity of gas trans-
ferred by diffusion will also depend on the time of the diffusion flux. This
can be expressed in the equation
A
n = D — ct
%)2 U L CC
where QNO = quantity of NO- transferred during exposure (moles)
2
D = coefficient of diffusion of NO- in air (moles/cm )
2
A = cross-sectional area of tube (cm )
L = length of tube (cm)
3
c = concentration difference between open and closed end (moles/cm )
t ° time of exposure (sec).
Thus, it is seen that the sampler depends on three constants, D, A, and L,
and on two variables, c and t. Since for a particular tube the dimensions
are known and the coefficient of diffusion can be estimated from values in
the literature, when one measures the quantity of N02 trapped and knows the
time of exposure, he/she can calculate the time-weighted average concentration.
58
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SAMPLER PERFORMANCE
To determine the accuracy and precision of the samplers, it was necessary
to set up known environments of N02 and to expose the samplers for definite
times to these environments. Known concentrations were produced by diluting
the output of an N02 permeation tube maintained at a constant temperature.
The constants for the sampler described were:
DNo2-Air = 0'154 cm2/sec'
A - 0.71 cm2,
and L = 7.1 cm.
Substitution of these constants and conversion to more conventional
units gives the expression:
-9
QNQ = 2.3 (ppm N02 x hrs) x 10
Average N0~ concentration was calculated from QN_ and time of exposure.
The agreement with permeation tube values, and between individual sam-
plers receiving identical exposures, was excellent. The calculation of results
was greatly simplified because the N02 was apparently converted quantitatively
to nitrite in the final determination, which was essentially that of Levaggi
et al. (2) and Blacker (1). It was found more accurate and convenient, however,
to combine all of the reagents and to add a single volume of combined reagent
directly to the sampler. It was then transferred to a cuvette and read at
540 nm.
A number of trials were conducted in which samplers were mailed to coop-
erating laboratories, exposed by them, and returned to NYU for analysis. Re-
sults reported to the cooperating laboratory in ppm N02 x hrs and the NYU
value obtained by dividing by the time of exposure were compared with the
measured concentrations at the cooperating laboratory. All of the compari-
sons gave very good agreement, even one in which the samplers were mailed to
Johannesburg, South Africa, and returned to New York for analysis. The con-
centrations used in these comparisons varied from fractional parts of a
million up to several parts-per-million.
59
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USE OF SAMPLERS FOR INDOOR AMBIENT MONITORING
In the course of the earlier work, it had been demonstrated that the
samplers were quite stable both before and after sampling. This made possible
the mailing of samplers to distant points while still obtaining satisfactory
results. The standards for occupational exposure are, however, approximately
100 times higher than those for ambient air pollution by N02. It was con-
cluded that the sampler would be satisfactory for measuring lower levels,
however, if the time of exposure was increased from 1 working day to a full
week. Using a 1-week exposure, a study (7) was carried out on 10 dwellings
equipped with gas stoves and 9 with electric stoves. Since all of these
dwellings were in the metropolitan New York area, all of the homes were cen-
trally heated. It was found that the homes with gas stoves had very signi-
ficantly higher NO- concentrations than did those with electric stoves. This
was true both in the kitchen and nonkitchen areas. It should be pointed out
that the level found in the kitchen of the gas stove dwelling was 49 ppb,
which compares to the U.S. Primary Air Quality Standard of 50 ppb (annual
average). Electric stove kitchens in this study, however, showed an average
of about 8 ppb. A second study carried out in cooperation with a group in
London (3) showed very similar results in two kitchens with gas stoves and
two with electric stoves. A further study was carried out on homes in the
Gainesville, Fla., area and included homes with 1) no unvented gas appliances,
2) gas stoves, 3) gas space heaters, or 4) combinations of gas stoves and gas
space heaters. The results of this pilot study (to be published elsewhere)
would indicate that the unvented gas space heater can be a significant con-
tributor to indoor NO,, concentrations.
Finally, outdoor air has been monitored on a weekly basis for 2 years on
the 2nd and 14th floors of a building in Manhattan; these results are being
analyzed.
CONCLUSIONS
It is concluded that the N02 sampler can be a very effective tool for the
monitoring of this gas at ambient levels.
The device is light, inexpensive, maintenance-free, and can be satisfac-
torily exposed by untrained personnel.
A 1-week sampling period appears to be suitable for air pollution
measurements.
60
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The stability of the samplers, both before and after sampling, makes
feasible their distribution by mail and return to a central laboratory for
analysis. They therefore appear to be very practical for simultaneous mea-
surement in a number of areas of either indoor or outdoor N(>2 concentrations.
ACKNOWLEDGEMENTS
This work was supported by Grant No. G0133066 and No. G0177042 from the
U.S. Bureau of Mines, and is part of a center program supported by Grant No.
ES00260 from the National Institute of Environmental Health Sciences.
REFERENCES
1. Blacker, J.H. Triethanolamine for Collecting Nitrogen Dioxide in the
TLV Range. Am Ind Hyg Assoc J 34:390-395, 1973.
2. Levaggi, D.A., Siu, W., Feldstein, M. A New Method for Measuring
Average 24-hour Nitrogen Dioxide Concentrations in the Atmosphere.
J Air Pollut Control Assoc 23:30-33, 1973.
3. Melia, R.J.W., duV. Florey, C., Darby, S.C., Palmes, E.D., Goldstein,
B.D. Differences in NO, Levels in Kitchens with Gas or Electric Cookers
Atmos Env 12:1379-1381, 1978.
4. Palmes, E.D., Gunnison, A.F. Personal Monitoring Device for Gaseous
Contaminants. Presented at AIHA Annual Meeting, San Francisco, 1972.
5. Palmes, E.D., Gunnison, A.F. Personal Monitoring Device for Gaseous
Contaminants. Am Ind Hyg Assoc J 34:78-81, 1973.
6. Palmes, E.D., Gunnison, A.F., DiMattio, J., Tomczyk, C. Personal Sampler
for N02. Am Ind Hyg Assoc J 37:570-577, 1976.
7. Palmes, E.D., Tomczyk, C., DiMattio, J. Average N02 Concentrations in
Dwellings with Gas or Electric Stoves. Atmos Env 11:869-872, 1977.
MAILING ADDRESS OF AUTHOR
Edward D. Palmes, Ph.D.
Institute of Environmental Medicine
New York University Medical Center
550 First Avenue
New York, New York 10016
61
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Discussion
MAGE: Before I take any questions, I would just like to make a comment.
I think the diffusion coefficient is proportional to the square root of ab-
solute temperature. So, you would expect the 1 percent increase with a 10°
Fahrenheit rise. That would be about 2 percent change in temperature on
the absolute scale. So, that would be a 1 percent increase.
PALMES: Per 10 degrees?
MAGE: You said Fahrenheit, and you got 1 percent.
PALMES: Well, the thing is that as the temperature rises, the volume
also increases. That is_one power. So, it actually goes T % divided by
T , and so it goes by T A It is thus absolute temperature to the one half.
ZISKIND: Richard Ziskind, Science Applications. I had never seen it
addressed in health studies. Maybe you can tell me if any account was taken
of the NO- level in the interior of the homes when they classified this as
a high exposure/low exposure district. 1 wonder if that might be a real
confounding factor that wasn1t taken into account?
MAGE: I believe the classifications were according to the ambient levels
of N02. If there is anybody here who would like to correct me, please do so.
WHITE: Otto White, Brookhaven Laboratories. It appears from the equa-
tions that if you increase the area or decrease the length that you increase
the sensitivity. Is it that simple?
PALMES: It is that simple up to a point. If one gets down to a very
short tube, then it starts behaving as if it were not quite so short. We
have taken these down as low as 1 centimeter by using much smaller diameter
tubes than this. But we have actually changed just the length in a tube of
the constant diameter, and this has a direct linear effect.
If, however, you change both the diameter and the length, then we found
that so long as we stayed above about 1 centimeter in length, then transfer
could be predicted quantitatively.
GOLD: Avram Gold, Harvard School of Public Health. Have you ever con-
sidered the possibility of losses of the NO. onto the acrylic?
PALMES: We have certainly considered that, and we have tried the ef-
fect of storage on exposed samples and then analyzing them. We have done
this for at least a couple of months after exposure and have obtained the
same results.
62
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In other words, once sampled, we can then measure for a very consider-
able period after exposure and still get the same results.
GOLD: I think that that was what I was wondering—essentially whether
you have lost NO. into the wall during the sample that you would never get
back?
PALMES: You are talking about the acrylic, not the plastic. Well, we
get the theoretical transfer. Now, there might be a monolayer of NO,, laid
down onto the acrylic. I don't know.
Incidentally, we get exactly the same results with glass as we do with
acrylic.
GOLD: Glass can soak it up. I have had some experience with this.
PALMES: I want to finish my story on this one. The first time we took
these into a. mine, they said we couldn't take them below ground. They wouldn't
allow any glass down there. So, we stuck them on the wall. But after I got
down there and saw these big loaders running around when we had only silly
little lights on our heads—because otherwise they would never know we were
there, and there is no place to hide—I thought, boy, glass or plastic is the
last thing I would worry about.
DEBBRECHT: Fred Debbrecht, AID. Relative to the length versus diameter
again, do you have a gut feel for the ratio that they must be to still pre-
serve the diffusion effects?
PALMES: The A to L ratio is going to determine the sampling rate with
the given coefficient of diffusion. Our sampler would have the equivalent
sampling rate of approximately 50 ml per hour. The 3M sampler, which is again
based on an air gap, has a sampling rate, as I recall, of around 30 ml per
minute.
But in any event, it is almost a factor of 60 or so difference in this
area to length ratio, so that it looks like it can vary quite widely. Now,
If one is going to get involved with that, I think that the effect of turbu-
lence is going to become much, much greater—that is my gut feeling on it.
SPENGLER: John Spengler. I am really fascinated by your measurements.
Some of the measurements Inside gas-cooking homes are very similar to the ones
we have been making In our health study. But I encourage you to make out-
door measures simultaneously, because really the relative difference seems
to be important. And have you noted whether you have seen an effect with
venting In the kitchen? Because this apparently will change the value drasti-
cally in the gas-cooking homes that we have been measuring, as to whether
there was venting or not in these kitchens.
PALMES: We did not check whether or not the gas stoves were vented in
63
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those which we measured. What we find generally Is that people use the vent
only when they are frying Chinese food or something that smells or gets
a lot of splashing. In other words, It is not used to control the combustion
gas part of It. We have not done this, but It certainly would make a dif-
ference; there Is no question about that. Now, we have used this for out-
door measurements, but have been having difficulty finding good values with
which to compare ours. We have 2 years of measurements In New York.
TURNER: Bill Turner. Do you know If your method Is at all susceptible
to NO Interference?
PALMES: It is absolutely not susceptible to NO interference. We have
modified this, and the article is in press now. So, we can use it for NO
by converting the NO to N0« with the dichromate. But if you let it go
through the screen, bounce off the dichromate, and then try to bounce back,
it gets caught.
So, we can determine, then, both NO and N0~ simultaneously. Of course,
there are different coefficients of diffusion. But if you run one of these
samplers along with an analytical sample, then you can determine their dis-
tribution.
64
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In-Vehicle Air Pollution Measurements:
A User's Perspective
Richard A. Ziskind, Ph.D.
Science Applications, Inc.
Los Angeles, California
INTRODUCTION
Science Applications, Inc. (SAI) conducted measurements of gaseous
pollutants in heavy-duty diesel tractors; transit, school, and mini-buses;
taxlcabs; and police cars. In performing these research programs and in
planning future ones, we have concluded that in order to accomplish study
objectives, a good deal of thought must be given to the selection of instru-
mentation and that compromise is expected. This manuscript will review our
user experience in formulating and conducting in-vehicle air pollution meas-
urements as they relate to the development and usage of personal exposure
monitors.
The basic elements of two in-vehicle monitoring projects are summarized
below. General conclusions are made about the objectives and requirements
of such programs.
PROGRAM OVERVIEW—TOXIC GASES IN HEAVY-DUTY DIESEL TRUCK CABS
An experimental program was conducted for the U.S. Department of Trans-
portation (DOT) to measure cab concentrations of toxic gases. Driver com-
plaints, accident autopsy results, and very limited testing results motivated
the DOT to sponsor this scoping study. Program components were to:
• Survey the heavy-duty diesel truck population and measure cab
concentrations of toxic gases under a variety of conditions;
65
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• Interpret the results In terms of short- and long-range driver
health and performance effects.
PROGRAM OVERVIEW—CARBON MONOXIDE INTRUSION INTO THE PASSENGER AREA OF
SUSTAINED-USE MOTOR VEHICLES
This study, sponsored by the Environmental Protection Agency, was
specifically to look at the problem of carbon monoxide (CO) exposure in
sustained-use vehicles such as school buses, taxicabs, police cars, etc.
Here, the motivation for the study was similar in that incidents of drivers
or passengers being overcome by CO had been reported, and concentrations
in the 100-ppm range measured. The components of the study were to:
• Conduct a literature survey dealing with issues related to the
problem—i.e., concentrations measured, causal factors of source and path-
ways, measurement approaches (biological and air concentration), and the
concentration/effects relationship;
• Delineate factors affecting CO exposure, including vehicle design,
operation control conditions, utilization characteristics, maintenance,
and ambient control techniques;
• Conduct a limited sampling of vehicles in order to develop test proto-
col for a full-scale sampling program, observe the effects of postulated
controlling factors, identify a worst-case subpopulation, evaluate instrument
performance, and establish the range of CO concentrations within and among
vehicles.
OBJECTIVES AND REQUIREMENTS—IN-VEHICLE POLLUTION STUDIES
Such studies can easily be seen to have a number of objectives. Phrasing
these as questions, we may ask the following:
1) To which substances may a driver or a passenger be exposed?
2) How are these measured satisfactorily, including both biologically
by performance or by instrumentation?
3) What are the sources of this exposure? How does it get to the
driver or passenger?
4) What conditions control or affect exposure? Is vehicle self-
contamination important?
5) Is any segment of the population at risk? If so, who and to
what degree?
6) Are additional regulations needed? What form should they take?
66
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Other questions could be posed; however, all of the above directly
Impact on Instrumentation requirements. Specifically, In order to determine
which substances may be present in the vehicle interior (Question 1), we
could draw up the body of emissions measurements made up principally of exhaust
analyses and urban ambient monitoring. This does not directly consider fuel
evaporation and blowby. Nor does the emissions literature deal with differ-
ences in the source to interior transfer function among pollutant species.
Secondary pollutant formation and photochemical or other conversion reaction
rates are not well established between pollutant production and occupant expo-
sure for the same vehicle. It would appear to be necessary to initially con-
duct a screening of the principal Identified toxic emissions. This requires
a variety of portable instrumentation which is preferably direct reading.
Additionally, we must have a good deal of confidence that the error caused by
interference of other substances in a detector is minimal or well known.
This brings us to Question 2. If substances act synergistically, is
it more appropriate to measure performance indicators or physiological func-
tions such as respiratory parameters? Even for a single pollutant such as
CO, it is more direct to measure exposure effect or risk by blood carboxy-
hemoglobin (COHb) level through expired air or blood analysis sampling. How-
ever, in order to identify exposure levels for individual substances, and to
determine pathways and dependence upon postulated factors, specific air
sampling instrumentation is needed. In our initial effort to survey instru-
mentation for the continuous monitoring of CO, NO, NO-, and hydrocarbons,
161 instruments were evaluated for 22 different performance characteristics.
These 22 characteristics could be grouped into six general categories:
simplicity, portability, dependability, reproducibility, ease of calibration,
and stability.
Specifically, for our diesel tractor exposure study, we evaluated the
particular needs of this program, such as the ability to quickly and easily
perform a large number of idling and on-the-road measurements and the par-
ticular requirements of the diesel cab testing environment. We established
the following requirements that the measurement system had to meet:
1) The instrumentation system had to be integrated into a single, rela-
tively compact, and lightweight package with self-contained power supplies
sufficient for continuous operation for at least 10 hours.
2) A system had to be capable of measuring ambient and truck cab level
concentrations of carbon monoxide (CO), nitric oxide (NO), and nitrogen
dioxide (N02), with required accuracy (+ 2 percent).
67
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3) The system had to be capable of accurately and automatically record-
ing the CO, NO, and NO^ concentrations measured on a permanent record, so that
the operating technician would have sufficient time to note and record the
other important test variables and parameters (such as cab entry configurations,
traffic and road conditions, and temperature and elevation), to readily sample
ambient air, and to generally control the time-wise flow of the test program.
4) The instrumentation system and concentration levels recorded had
to be insensitive to the vibration levels encountered in the diesel truck
cabs, and they had to be relatively position- and orientation-independent
(i.e., not require a flat horizontal surface for accurate instrumentation
readings).
5) The system had to be capable of measuring any particular conditions
(e.g., temperature and atmospheric pressure) that would affect the concentra-
tion readings. Power supplies for all components for the instrumentation
system had to be quickly and easily rechargeable overnight by simple plug-in
to any available 120-VAC source (e.g., a motel room outlet).
6) The system had to include internal pumps for continuously drawing
the sample air through the measuring instruments, and to have a convenient
set of lines and manifolding to enable easy sampling of the air at any loca-
tion within the truck cabs (including sleeper cabs) and of the external
ambient air environment. All such sampling lines and manifolding had to be
constructed of materials that would not significantly alter the concentrations
of CO, NO, or N0« in the air passing through them. The system had to include
appropriate chemical scrubbers in the input to each instrument to remove
potentially interfering constituents.
7) The system had to include small portable subsidiary devices for the
measurement of external factors such as wind speed and direction, particularly
for idling testing.
8) All electrical cables and devices carrying the concentration data
signals from the three measurement instruments to the final recording point
had to be shielded from spurious electrical signals (truck-generated and
external) , and the instrumentation system had to be fully capable of operation
on either the self-contained power or external 120 VAC.
9) The instrumentation had to be able to respond quickly enough to
track transients in the cab due to temporary conditions such as cigarette
smoke, tunnel passage, road grades, etc.
10) The cab environment should not be contaminated by the instrumen-
tation exhaust.
The specialized measurement system designed and constructed to meet the
above requirement is shown in Figure 1 and is schematically illustrated in
block diagram form in Figure 2. Air to be sampled is pulled in (from a cab
68
-------
FIGURE 1. Continuous sampling instrumentation assembly.
100 80 60 I 40 20 0
FIGURE 2. Field measurement system and data output schematic.
69
-------
Interior location or the ambient external environment) through sampling lines
and manifolding of Teflon and 316 stainless steel construction. The instru-
ments are each direct reading, portable AC, or battery-operated gas analyzers
with self-contained pumps, batteries, and battery chargers. The sensors are
of the electrochemical voltametric type with linear output and direct reading
in parts-per—million by volume. The instrumentation was verified to be posi-
tion/orientation-independent and Insensitive to electrical signal output
vibration. The output signals were transmitted through shielded coaxial
cable to a special multiplexing switch in order to allow the three levels to
be recorded on one single-channel, lightweight, portable stripchart recorder.
The instruments could be automatically sequentially cycled over an adjustable
period or manually controlled.
We believe this type of approach is a suitable compromise when the study
focus is divided between gathering survey data on exposure levels in a number
of vehicles and attempting to establish source importance, mechanisms of in-
trusion, and parameters which affect interior concentrations.
In order to consider the previously posed fifth question—whether any
segment of the population is at risk, and, if so, to what degree—a distinctly
different testing approach should be considered. Specifically, as we formu-
lated a sampling program to assess the CO problem in sustained-use vehicles,
we developed a multisegmented monitoring approach. Initially, we surveyed
the large variety of instruments and devices available for the measurement
and detection of CO in air at ambient occupational levels. For the purpose
of this study, we restricted consideration of relatively nonportable labora-
tory instruments to serve only as standards or for comparison purposes.
Measurement approaches reviewed included portable CO instruments/detectors,
biological monitors, tracer gases, and exhaust analyzers. Although all these
measurement approaches are incorporated in the protocol, only the first cate-
gory, portable CO instruments/detectors, will be considered here.
Portable CO Measurement/Detection Devices. These devices are identified
by characteristics of size, weight, power requirement, and insensitivity
to position, movement, vibration, and vehicle acceleration/deceleration.
Suitable specifications for the class could be taken as less than 1 ft volume,
15 Ib weight, and requiring only external DC power (if any) or internal bat-
teries with minimum 8-hour life between charging. Instrument bulk temperature
range should span 40° to over 100° F, relative humidity up to 95 percent, and
in-vehicle pressure range from up to 7,000-ft elevation, equivalent to slight
overpressure due to ventilation blower. Accurate correction factor/charts
70
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should be available. Temperature correction/stability should separate sampled
air temperature (0° to 100° F) in addition to the bulk instrument range.
Suitable devices should ideally be free from significant interferences due to
other gas species and from intermittent interferences caused by specialized
conditions such as the electromagnetic wave environment due to CB radios, etc.,
operating in the near vicinity.
Classification of Portable CO Devices for Ambient-Occupational Use. Al-
though maximum values of characteristics such as sensitivity, accuracy, etc.,
are nearly always desirable and sought after, the practical and sufficient
level—from both test purposes and cost viewpoints—depends greatly on meas-
urement purpose and objectives, the ultimate use of the data and overall re-
sults, and, of course, the present state of technology. For example, the least
sensitivity and accuracy would be required of simple indication/detection
devices used in large population sampling, or of limited detection uses where
the device would be affixed to the vehicle interior to indicate the presence
of CO concentrations exceeding some limit value, such as 35 ppm. Such a de-
vice would require minimal sensitivity of approximately the limit value—for
example, 35 ppm—and an accuracy of perhaps +_ 25 percent.
In order to span the broad use/purpose and performance characteristic
spectrum of portable CO measurement/detection devices of potential in-vehicle
use, the devices have been categorized in four use/effectiveness classes.
The classes are: continuous analyzer, cumulative dosimeter, intermittent/
spot sampler, and limit detector. The basic use, measurement techniques,
and the approximate overall ranges in physical characteristics, performance
specifications, and costs for each of the four classes are listed in Table 1.
The continuous analyzer class includes relatively high-performance
portable instruments capable of continuous CO concentration measurements and
of providing output for continuous recording. Some are position/orientation
sensitive due to the particular design of the liquid electrolyte or use of
humidifying reservoirs in the internal sampling stream. This type will be
used in a selected subgroup of the sustained-use vehicles to conduct a detailed
investigation of particular vehicles to determine effects of various factors
(exhaust system condition, ventilation effects, leak paths, ambient levels,
the spatial concentration distribution in the vehicle, etc.). These instru-
ments should approach performance characteristics of stationary monitoring/
laboratory instruments, such as 1 or 2 ppm sensitivity and + 1 or 2 percent
accuracy.
71
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TABLE 1
Classification of Portable CO Measurement/Detection Devices
and Summary of Characteristic*
CLASS
Measurement Type
Measurement Princl-
pie
CONTINUOUS ANALYZER
Continuous
Electrochemical
Infrared
Catalytic Combustion
Gas Filter Correlation
CUMULATIVE DOSIMETER
Cumulative
Electrochemical
Stain Tube/Pump
Colorimetric Tube/Pump
Stain Tube
INTERMITTENT/SPOT
SAMPLER
Instantaneous
Blec trochemlcal
Stain Tube/Band Pump
Colorimetric Tube/
LIMIT DETECTOR
Limit Detection
Colorimetric
Indicator Badge
Ceramic Disc
Accuracy
Sensitivity
Range
Size
Weight
Position Sensitivity
Power
Cost Range
Typical Cost
+1 to + 5 percent
0.1 to 2 ppm
0-50 to 0-1,000 ppm
0.1 to 1 ft3
3 to 20 Ib
Some
Battery
$600 to $4,000
$600 Catalytic,
$1,200 Electrochemical,
Higher for Others
^15 to + 25 percent
1 to 100 ppm-hr
1-100 to 10-3,000 ppm
1/2 hr to 7 days
0-999 ppm-hr
Shirt Pocket
1 oz to 1 Ib
No
Battery/None
$1 to $600
$500 Electrochemical,
$250 Tube/Pump,
$1 Tube
(Plus reading device)
Hand Pump
+2 to + 25 percent
2 to 10 ppm
0-50 to 10-1,000 ppm
Pocket to 0.2 ft
1/2 to 2 Ib
Some
Battery/Human
$100/$1,000
$250-$!,000 Electro-
chemical
$90 Tube/Band Pump
+ 25 percent at beat
50 to 200 ppm
N/A
Pocket, Badge
1/2 to 2 oz
No
None
$1 to $5
$1
Portable CO measurement devices of the cumulative dosimeter class are
distinguished by providing a cumulative measure of CO exposure. These personal
air quality monitors are designed to be attached to an individual, without
Interfering significantly in normal activities, sampling air in the breathing
zone, and providing a cumulative CO dosage measurement over the sampling time.
Several different measurement principles have been employed, including:
• Electrochemical cell types with solid state electronics,
• Stain tubes with air throughput by pocket-size sampling pumps, and
• Nonaspirated stain tubes.
Sample times can range from one-half hour to days among the categories.
Position insensitivity is critical, as is the operating time between battery
recharges or replacements. This equipment class will provide an important
part of the program for several reasons. They measure actual CO exposure and
dosage for the individual during normal activities. They do not require con-
tinuous technician presence. They can provide nearly simultaneous data to
allow comparison across several groups.
Additionally, we will utilize nonaspirated stain tubes to measure inte-
grated exposure in a large number of vehicles. These inexpensive devices
72
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will be used as a screening tool to survey randomly selected vehicles in
various fleets and locations in order to investigate for hot spots and
establish sampling strata for more expensive and intensive subsequent testing.
Devices of the intermittent/spot sampler class provide the capability
of measuring the instantaneous CO concentration at the specified sample loca-
tion. They differ from the continuous analyzer class, which also includes
an instantaneous measurement capability, by the fact that they are typically
more portable, less expensive, and do not provide a continuous recording
capability.
The limit detector class includes devices which can be attached to
an individual or a fixed location. They provide a positive indication of
exposure to CO concentrations above some design levels. Some school buses
are currently equipped with such devices, which are checked periodically to
see if a particular CO level was exceeded.
In Summary. Devices in each of the four classes described above may
have an application in a measurement program. The selection of an appropriate
class of device or combination of classes will depend on the measurement pur-
pose and objectives, the ultimate use of the data in overall results, and, of
course, the study's size and funding.
Needs that we have identified in personal samplers, related to their
utilization for in-vehicle pollution studies, include a sensitive range,
nitrogen dioxide (N0«) personal cumulative dosimeter, and a respirable
fraction particulate personal sampler.
MAILING ADDRESS OF AUTHOR
Richard A. Ziskind, Ph.D.
Science Applications, Inc.
1801 Avenue of the Stars
Suite 1205
Los Angeles, California 90067
73
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Discussion
MEIER: Eugene Meier, EPA, Las Vegas. Why do you say that you need
very sensitive N0_ dosimeters, in this particular case from the health point
of view?
ZISKIND: In our diesel truck study, of the gases that we measured, we
found NO. levels to be the closest to the levels of known toxic effects.
MEIER: Was it exceeding these levels or just close to them?
ZISKIND: Well, it can exceed a criterion level momentarily. But in
general, it was highly time dependent and condition dependent. That is, we
could see that it would be very useful to have a personal sampler rather than
an electrochemical detector or instrument so that we could do more of a sur-
vey to really identify more explicitly the conditions of N02 emission leading
to these levels.
MAGE: David Mage, EPA. What standard was being violated? Was it an
occupational standard or an ambient standard?
ZISKIND: It was an occupational standard. If I am contrasting it with
the NIOSH proposed standard of one part-per-million and a half part-per-
million action level ceiling, then that was commonly found to be violated
where we considered the ambient and the vehicle contribution.
If we considered the public secondary or primary standards, that was
violated all the time.
MEIER
: So you are saying it was a relatively high concentration of NO-?
ZISKIND: We are talking about trucking operations that in this case
are located in urban areas. And specifically, we did the Southwest, and then
we are driving along on crowded freeways. We are getting a lot of NO..
MEIER: Then relate that back again to buses.
ZISKIND: We haven't made any NO. measurement on buses—only on diesel
trucks.
MEIER: So, it is primary occupational at this time in terms of truck
drivers?
ZISKIND: In terms of truck drivers, yes.
We are taking ambient levels, and we are taking in-vehlcle levels. We
74
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are trying to look at the difference. And we are also looking at the people
who are driving along right next to these trucks. And they are both the cause
of emissions, and, also, the people are getting some N0_ from the trucks.
WILLIAMS: Marsha Williams, EPA. I am curious about the CO results on
the diesel trucks because I would expect, just due to the emissions from the
diesel trucks, that you would see much higher interior N02 levels in trucks
than you would CO, relatively speaking, because of what they are putting out.
ZISKIND: That is right.
WILLIAMS: So, I am curious about what the CO results were. And the
other thing is: What kind of data capture did you have on the instrumen-
tation of your trucks? You lose a tremendous percentage of your data just
due to instrument problems with vibration and such.
ZISKIND: Well, we had the equipment shock mounted. And we were monitor-
ing continuously.
WILLIAMS: Do you know what kind of capture rate you had, then?
ZISKIND: We manifolded these things. So, we alternated one, two, and
three in the Instrumentation. We came back to each one. Not too much happens
between readings. We get a pretty good square wave. It is constant for 20
seconds. Sometimes you get fluctuations when something drives by.
What we were looking for was driving along and setting up a different
condition. The condition may be speed; it may be vents, heater, air condi-
tioning, or something like that. We were looking at what the effect is.
So, we looked for the equilibrium to be reached, and then it is reached.
And then we say go on to another condition. We got essentially 100 percent
capture, if I can be so bold as to make that statement. But we didn't have
any loss on that method.
You are right about the conclusion. Carbon monoxide in diesel trucks
did not appear to be as significant as in gasoline vehicles.
75
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Calibration of Personal Exposure Monitors
for Personal Exposure and Health Effect
Studies
Charles L. Kimbell
Houston Atlas, Inc.
Houston, Texas
BACKGROUND
Standard reference gas mixtures are required to calibrate personal ex-
posure monitors. This paper describes a device whereby a low parts-per-
million (ppm) mixture of carrier gas and pollutant can be generated in minutes
with + 1 percent accuracy.
In the past, compressed cylinder mixtures, permeation tubes (2), dynamic
flowmeter blending, or exponential dilution techniques were used. These
methods require long lead times of several weeks for preparation and careful
adjustments, and they cannot easily be converted for use over wide ranges
or to use with different gases. Permeation tubes require close temperature
control and are subject to inaccuracies which have not been adequately de-
scribed in the literature.
The data shown in Figure 1 illustrate errors associated with permeation
devices. Long-term stress on Teflon causes creep, resulting in a change in
permeation rate over a period of days. Temperature changes cause excessive
permeation rate change, except in controlled laboratory environments and with
good temperature controls.
STANDARD REFERENCE SAMPLE GENERATOR
This paper describes a Standard Reference Sample Generator (1) that is
ideally suited to preparing ppm samples of any trace gas in any carrier gas.
77
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DAYS 2 4 6 8 10 12 14
FIGURE 1. Plot of ppm generator by Model 601 and by permeation tube.
ROLLER BEARINGS
CARRIAGE RODS
SYRINGE CLAMP
FRONT-STOP
KNOB
THRUST PLATE
DRIVE SCREW
STEPPER-MOTOR and HOUSING
ADJUSTABLE
LEGS
FORWARD BUTTON
FIGURE 2. Precision syringe drive
POWER
ON/OFF
FAST/SLOW x SWITCH
BUTTON
REVERSE CALIBRATED
BUTTON POTENTIOMETER
PULSE INDICATOR
MANUAL STEP BUTTON
FIGURE 3. Laboratory Analyzer, Houston Atlas Model 825R.
78
-------
The equipment can be removed from storage, and, within minutes, a contin-
uously flowing gas mixture is available either for short-term use or for
continuous flow for an indefinite period. The only materials required are
reagent-grade pure trace gas and a carrier gas of a volume slightly greater
than the amount of sample required.
This convenient method of preparing any type of ppm mixture is well
adapted to calibration of personal exposure monitors and instruments, and
for generation and maintenance of known atmospheres in environmental cham-
bers. When an enclosure is purged, with a flowing trace gas mixture of four
times the enclosure volume, then the trace gas in the enclosure will be with-
in 2 percent of the original ppm mixture. The trace gas generator can con-
tinue purging the enclosure and will eliminate any deterioration of the en-
vironmental chamber contents by absorption or adsorption.
PRINCIPLE OF OPERATION
The Standard Reference Sample Generator is basic in its operation. A
volumetrically metered minute quantity of trace gas is mixed with a continu-
ously flowing fixed quantity of carrier gas.
Minute quantities of gas are very difficult to accurately produce with
the usual flow devices. The sample generator uses a microliter sampler to
incrementally inject a fixed volume of trace gas into the flowing carrier.
Accurate timing and rapid injection result in ppm mixtures that are accurate
to + 1 percent. Labyrinth mixing results in a uniformly blended sample.
An alternate to the microliter sampler method of injecting trace gas is to
use a precision-type syringe drive actuated by a synchronous stepping motor
(Figure 2).
VERIFICATION OF SAMPLE
To determine accuracy and long-term stability of the Reference Standard
Generator, a stable analyzer was required. A Model 825R Houston Atlas hydro-
gen sulfide (H2S) analyzer was used. (See Figure 3.) The unique first-de-
rivative principle of operation provides stable zero and span even at low
ppm. (See Figure 4.) Linearity of response and accuracy (Figure 5) allowed
accurate measurements. The data shown in Figure 1 above were obtained in this
manner.
79
-------
Tungsten Lamp
Primary
Focusing Lens
Mirror
Photocell Fine Focus
Balancing Lent
Reference Photocell
Measuring Photocell
Electronics
Indicator
-Sample Chamber
Reaction Window ' PATENTED PRINCIPLES OF OPERATION
FIGURE 4. Rate reading analyzer principle.
100
80
UJ
_)
§60
_i
_i
£«>
O
#
20
I i
Comparison of Photorateometric
Method and Manual Tit rat ion.
>
<^
<&
*•*/
^v
•jff»
. Manual umpl
reeding n ihi
5^
y
gave no
lavel
<^'
X"
/&
X
X
20
100
40 60 80
PPB H2S IN AIR
FIGURE 5. Comparison of Houston Atlas Model 825R H^S Analyzer and manual
titration analysis.
TEST: Model 601 PPM Reference Standard Generator
FIGURE 6. Sample generated by Houston Atlas, Inc., Model 601 Reference
Standard Sample Generator.
80
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RESULTS
Chart recordings verified the repeatability, accuracy, and long-term
stability of this method for generating trace gas mixtures. Figure 6 is a
chart recording of the sample generated by the Houston Atlas, Inc., Model
601 Reference Standard Sample Generator. The analyzer provided sample and
hold readings every 3 minutes. This recording shows a 5-hour run with a
1-hour shutdown period. Note that no overshoot occurs and that a stable
reading is obtained in minutes. This proves that long-term storage does not
interfere with ready availability for quick use.
This system easily lends itself to automatic verification and cali-
bration of continuous monitors. Several installations in the field have
proven dependability during more than a year of unattended operation.
This parts-per-million generator can also easily provide parts-per-
billion samples intermittently or continuously. The simplicity and ease of
operation allows handling by laboratory technicians. No delicate accessory
equipment, such as a microgram balance, is required. This enhances portabil-
ity and field worthiness.
Personal monitors can be calibrated and their accuracy verified by
feeding sample directly to the monitor or by placing it in a chamber whose
environment is maintained constant by continuous flow from the ppm generator.
This equipment removes the calibration and verification of equipment
from the realm of the research laboratory to that of a practical field tool
for day-to-day use by technicians in the field.
REFERENCES
1. Kimbell, C.L., Method of Testing an Analyzer to Determine the Accuracy
Thereof and a Volumetric Primary Standard Apparatus for Doing the Same,
U.S. Patent No. 4,114,419.
2. O'Keeffe, A.E., Gas Dispensing Device. U.S. Patent No. 3,412,935.
MAILING ADDRESS OF AUTHOR
Charles L. Kimbell
Houston Atlas, Inc.
9441 Baythorne Drive
Houston, Texas 77041
81
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A New Family of Miniaturized Self-Contained
CO Dosimeters and Direct Reading
Detectors
Arnold_H. Gruber, Arnold G. Goldstein, Anthony B. LaConti, Ph.D.,
Harry G_. Wheeler, and John Martin
Direct Energy Conversion Programs
General Electric Company
Wilmington, Massachusetts
INTRODUCTION
The Direct Energy Conversion Programs component of General Electric (GE)
Company has been engaged since 1958 in the development of solid polymer elec-
trolyte technology for use in water and brine electrolysis, oxygen concen-
trators, fuel cells, and toxic gas sensors. In 1962-1966, fuel cells were
produced for the Gemini spacecraft program. In 1964-1968, an improved ver-
sion of the Gemini fuel cell was used on the Biosatellite spacecraft program.
As GE fuel cell technology advanced, other applications of this technology
were developed.
In 1972, using this technology, General Electric introduced a small
commercial hydrogen generator for laboratory instrumentation and chromato-
graphic applications. This small (<1 cu ft), high purity hydrogen generator
produced laboratory hydrogen safely and on demand, eliminating the need for
hazardous hydrogen cylinders in the laboratory.
The feasibility of a miniaturized hydrated solid polymer electrolyte
sensor cell was demonstrated with hydrogen in 1965 (1). Polarographic and
potentiostatic techniques of maintaining the sensing electrode at a fixed
voltage versus a stable reference electrode were shown. This effort was
extended to the detection of carbon monoxide and other toxic gases, as re-
ported in 1971 (2). Prototype carbon monoxide (CO) instruments specifically
designed for mine use were developed under a Bureau of Mines contract (3,4).
83
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In a CO sensing instrument, a measurable electrical current is generated
through electrochemical reaction of the contaminant gas at the potential
controlled electrode. The sensor can be designed to selectively detect NO,
N°2' H2' H2S> S°2' ethan°l> an<* other gases, depending upon the biasing volt-
age placed on the cell, the sensing electrode composition, and the scrubber
system for removal of interfering gases.
The electrochemical cell is particularly adaptable to small, portable
personal dosimeters (5) and detectors, as the cell can be miniaturized and
can be used with solid state electronics, lightweight pumps, and rechargeable
battery systems. The major significance of the specific electrochemical
cell as a sensor is the reduction in size and weight of the instrument. Now
possible are pocket personal dosimeters and small, lightweight belt or strap-
carried detectors weighing 1 pound or less; the final unit size is limited
by the additional features of readout, alarms, etc., rather than sensor size.
Figure 1 shows a photograph of the new family of miniaturized portable
instruments developed by GE for the detection and monitoring of CO levels in
air. From left to right are the support console, personal dosimeter, hand-
held direct reading detector, and detector case with carrying straps.
CELL SYSTEM
The heart of any gas detection device is the sensor or transducer. These
instruments utilize a hydrated solid polymer electrolyte membrane cell (Figure
2) in an electrically biased fuel cell mode. The cell generates an electrical
signal proportional to the CO concentration of the sample gas in the cell,
and displays excellent stability over long operating periods. Circuit compen-
sation is provided to correct for shifts in sensor span signal due to tempera-
ture changes; no zero compensation is required.
The fuel cell utilized is packaged in a housing 1.51 in wide x 1.0 in
deep x 0.92 in high. The solid polymer electrolyte membrane, which is ap-
proximately 0.01 in thick, serves as both an electrolyte and separator.
Bonded to the membrane on one side are the gas sensing and reference elec-
trodes (the sensing electrode is directly exposed to the sample), and the
current collecting counter electrode on the other side. The second side
is also exposed to a renewable supply of distilled water from the reservoir,
since the membrane functions only when hydrated. Lexan® plastic support
members hold the membrane cell in position, while directing the gas flow over
84
-------
FIGURE 1. Carbon monoxide instrument family.
FIGURE 2. Detector and dosimeter cell.
85
-------
the sensing electrode and the water flow to the counter electrode. The
sensing electrode of the cell is held at a fixed predetermined anodic volt-
age using an efficient electronic control circuit.
As with conventional fuel cells, the relevant reactions are:
1) Sensor electrode
CO + HO •*• CO. + 2H~*~ + 2e
2) Counter and reference electrodes
2e + 1/2 02 + 2H+ •*- H20
Note: the counter electrode reaction is dependent upon the cell configuration
and design, and does not affect output signal.
The hydrated solid polymer is extremely efficient, durable, stable in
long-term response to CO, and has a low background (zero CO) current. Unlike
cells employing liquid acid or alkaline electrolyte, there is no need for
electrolyte normality control; the hydrated cell unit is stable to extreme
variations in humidity. No corrosive electrolytes are added to the cell;
the only routine maintenance needed for cell operation is the periodic fill-
Ing of the water reservoir with distilled water.
SYSTEM INSTRUMENTATION
A system schematic for the direct reading detector and personal dosimeter
is shown in Figure 3. In both units, the CO containing gas sample flows
through the dust filter and gas scrubber chamber, then through the pump, sen-
sor cell, and rotameter (flow indicator), and is subsequently vented. The
pump speed is set to 60 cc/min by a trim adjustment. Although the sensor
response is somewhat sensitive to sample flow rate (see the Operational Test
Results section), field experience has shown the flow system to be remarkably
stable, and trimming is required very infrequently.
The filter and gas scrubber serves to remove small particles of dust
from the flow system as well as removing interferant gases which might affect
the output of the cell assembly. Potassium permanganate on alumina is used
for gas scrubbing; the effectiveness of this scrubber for potential inter-
ferant gases is shown in Table 1. The scrubber material should be changed
86
-------
AIR SAMPLE
IN
FILTER
PUMP
1
1
1
1
1
I
Ni-Cd
BATTERY
PACK
•__ -_ _ _
1'
lll§:
CELL
ASSEMBLY
1
|
n, i
ELECTRONIC
CONTROL
CIRCUIT a
SWITCH
AIR VENT
(INSIDE CASE)
F LOW
INDICATOR
T
1 DDDD LCD DIGITAL READOUT
1
1 i 1 *
, REMOTE OUTPUT
-> I
I i ^J""V.A AUDIO AND LED ALARMS
J
[ ] ACCUMULATED CO
SAUDI C Alp PI DW
* DETECTOR ONLY
FIGURE 3. System schematic.
ELECTRICAL
TABLE 1
Effect or. Instrument CO Response by Potential Interferants
INTERFERANT*
GAS
H20 VAPOR
CH4
co2
NO
NO2
SO,
C2H2
HCHO
H2S
°2H4
GAS CONC.
IN AIR
50 to 100% RH
16 to 90%
3%
1%
50 PPM
10 PPM
25 PPM
100 PPM
100 PPM
5 PPM
10 PPM
100 PPM
EQUIVALENT CONC.
(PPM) OF CO
0
0
0
0
0
0
0
2
16
0
0
18
*KMn04 ON ALUMINA (PURAFIL) FILTER
87
-------
when the color changes from red-purple to brown. As can be seen from the
table, only ethylene and acetylene (of the listed gases) provide any signifi-
cant interference to CO with the use of the filter.
The power supplies for the instruments are rechargeable 5.2 V, 250 MA-hr
nickel-cadmium battery packs, which allow a minimum of 10 hours continuous
operation after an overnight battery charge. As previously noted, the current
resulting from the electrochemical oxidation of CO is directly proportional
to the concentration of CO in the gas stream. The ensuing output signal is
then amplified for visual readout (direct reading detector only) or visual/
audio alarms, and is simultaneously stored in an integrating coulometer for
later determination of time-weighted average exposure. The detector also
has an output jack for providing a signal to an external recorder (0 to 1
volt).
Operational specifications for both instruments are presented in Table 2.
SPECIFIC INSTRUMENT PARTICULARS
Both the direct reading, hand-held detector and the personal dosimeter
utilize many common primary components (i.e., pump, sensor cell, flow indi-
cator) and have similar features (i.e., 5.2 V nickel-cadmium battery pack,
filter system, alarm system, accumulated CO readout); however, each unit was
specifically designed to handle different tasks. A tabulation of instrument
particulars is presented in Table 3. Details of the design characteristics
of both instruments follow.
Direct Reading Detector
The miniaturized portable self-contained direct reading detector was
developed for use in a wide variety of applications, including: 1) to be
worn by Individuals for immediate personal assessment of carbon monoxide
in working areas such as mines, factories, motor vehicles, etc.; 2) to be
used as a portable continuous area monitor; 3) to be used as a personal do-
simeter for obtaining time-weighted average exposure to CO; 4) to be used in
conjunction with a recorder for obtaining a permanent, continuous record of
CO exposure. The detector (Figure 4) has many features, including a one-
half-inch LCD digital readout (0 to 1,000 ppm CO) which is readily visible
at the top of the case. The instrument is lightweight (1.1 Ib), small
(5.9 in high x 3.8 in wide x 2.3 in deep), and is totally self-contained with
88
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TABLE 2
Carbon Monoxide Instrument Specifications
CARBON MONOXIDE INSTRUMENT SPECIFICATIONS
ACCURACY ± 10% FOR RANGE 0-500 PPM CO UNDER
THE FOLLOWING CONDITIONS:
TEMPERATURE: 1-40°C
ORIENTATION WITHIN 45° OF VERTICAL
RELATIVE HUMIDITY: 0-100%
DAILY ZERO AND SPAN CALIBRATION
OXYGEN LEVELS ABOVE 16%
INTERFERENCE COMMONLY FOUND IN
AMBIENT AIR, NO. N02, H2S, S02,
NH3, C02. DUST, ETC.
INSTRUMENT RANGE
WARM-UP TIME
INITIAL ACTIVATION TIME
RESPONSE TIME (90%)
SPAN DRIFT
ZERO DRIFT
STORAGE TEMPERATURE
RANGE
OPERATING TIME WITHOUT
RECHARGE
TRANSDUCER LIFE
CONSUMABLES LIFE
SAFETY
0-1000 PPM
15 SECONDS (2 MINUTES - DOSIMETER)
14 HOURS TO FULL ACCURACY
< 2 MINUTES
± 10% (1 WEEK)
± 2 PPM (10 HOURS)
1 TO 50°C
10 HOURS (4 HOURS WITH ALARMS ON)
MINIMUM OF 6 MONTHS
MINIMUM OF 1 WEEK
DESIGNED TO MEET THE MECHANICAL
AND ELECTRICAL SAFETY REQUIRE-
MENTS OF APPROVAL AND TESTING,
MSHA SCHEDULE 2G
89
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TABLE 3
Instrument Particulars
1. DIMENSIONS
LENGTH
WIDTH
DEPTH
15ECS3CO
Hand Held Detector
5.9 in.
3.8 in.
2.3 in.
15ECS1CO
Dosimeter
5.3 in.
2.9 in.
1.4 in.
2. WEIGHT
3. BATTERY PACKS
4. USEFUL RANGE
5. LOWER DETECTABLE
LIMIT
6. DIRECT READING LCD
IN PPM
7. ACCURACY
DIRECT READING
INTEGRATING
COULOMETER
1.1 Ibs. 0.63 Ibs.
5.2 VDC. 250 MA-HR., RECHARGEABLE NI-CD
0-1000 PPM CO 0-1000 PPM CO
1 PPM CO
YES
1 PPM CO
NO
< * 10% OVER 0-500 PPM RANGE
110% OF 8 HRS. TIME WEIGHTED AVERAGE
8. ALARMS
9. SELF-CONTAINED
10. ADDITIONAL FEATURES
RED LIGHT
WARNING AND AUDIBLE
ALARM @ 200 PPM CO
AMBER LIGHT
WARNING®
100 PPM CO
RED LIGHT WARNING
AND AUDIBLE ALARM
@ 200 PPM CO
YES
YES
(NO ADDITIONAL PUMPS, FILTERS. BATTERIES, ETC. FOR
OPERATION)
SELF-TEST
REMOTE READOUT
OPTION
EARPLUG ATTACHMENT
LOW BATTERY SIGNAL
SELF-TEST
its own pump, filter system, and rechargeable battery pack. A leather carry-
ing case with shoulder strap or belt mount is available.
The carbon monoxide detector controls, adjustment points, and performance
observation windows are shown in Figure 5. The unit contains both visible
and audible alarms set normally for 200 ppm CO, and an earphone connection
90
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FIGURE 4. Detector and case.
SENSOR CELL
WATER FILL
PUMP SPEED
ADJUST
ZERO ADJUST
SPAN ADJUST
COULOMETER READOUT
AND INPUT TO REMOTE
RECORDER
BATTERY CHARGER
CONNECTION
FIGURE 5. CO detector controls and adjustment points
91
-------
for operation in noisy areas. Windows are available in the case for obser-
vation of pump speed on a rotameter, the color of the filter material, and
the distilled water level in the sensor cell. Distilled water fill and air
inlet sample ports are visible on the top of the case. Conveniently located
on the side of the case are the off-on pushbutton switch, the coulometer
readout and input to a remote recorder or readout (Q to 1 volt), the earphone
connection, and the battery charger connection. Also located on the side
of the case for convenient setting are the pump speed adjust, and zero and
span adjust screws. In addition to a direct LCD readout of CO in ppm, the
unit contains an integrating coulometer for time-weighted average data, which
can be read out on the Support Console. The unit also features a self-test
circuit which enables the alarms and amplifying system to be checked each time
the unit is turned on. In addition, approximately 1 hour prior to the need
for battery recharge, a low battery warning is provided by the appearance of
three decimal points, a semicolon, and an arrow on the LCD display. The
alarms are momentarily activated, and the instrument display automatically
turns off when the battery voltage falls below a predetermined level.
Calibration of the direct reading detector is carried out as shown in
Figure 6. A zero and span gas cylinder kit is optionally available from
General Electric Company. The regulator on the calibration kit is set for
150 cc/min. The pump on the unit will draw 60 cc/min of zero or span gas.
Adjustment of the direct readout is made by setting the zero and span pot
adjust screws.
Per s ona 1 Dosimeter
The personal dosimeter was designed for daily use by a worker in a haz-
ardous area. The dosimeter (Figure 7) is extremely compact—being pocket-
sized (4.75 in high x 2.75 in wide x 1.38 in deep) and light (0.6 Ib).
No external pumps are required; the unit is completely self-contained with
built-in pump, 5.2 V rechargeable nickel-cadmium battery pack, and alarms.
The small filter attaches to the unit air input and clips to the worker1s
collar so that the input taken is in the worker's breathing zone. The in-
strument has a coulometer for recording the worker's exposure to CO during
the working period.
The unit also features alarms for the safety of the worker which respond
as follows: 1) an amber LED will light if the instantaneous concentration
of CO exceeds 100 ppm, and 2) a red LED and buzzer will alarm if the instan-
taneous concentration of CO exceeds 200 ppm. The alarm levels are preset
92
-------
FIGURE 6. Calibration of direct
reading detector.
FIGURE 7. Carbon monoxide do-
simeter.
FIGURE 8. Carbon monoxide
dosimeter, rear view.
93
-------
but can be modified by factory adjustment. A self-test circuit is available
for the alarms, so that when the unit is turned on the alarms will illuminate/
buzz for approximately 15 seconds to advise that the alarms are functioning.
The dosimeter unit has all of its adjustment controls recessed in the
face of the unit and covered by a key-locked door. This feature is provided
to minimize the possibility of the worker tampering with the controls during
operation. Visible to the worker (on the rear of the unit, Figure 8) are
windows showing the level of distilled water in the cell, and a rotameter
showing the pump speed (and that the pump is working). A pump speed adjust
pot is also located on the rear of the case.
Controls and adjustment points for the personal dosimeter are shown in
Figure 9. Behind the keyed door of the dosimeter are the battery and pump
on/off switches, the zero and span adjust screws, and the cable connection
for readout of the coulometer at the support console and charging of the
battery. Both a gas sample inlet port and a distilled water fill port are
available on top of the dosimeter case.
Support Console
A support console (6 in wide x 6 in high x 6 in deep) is required in con-
junction with the personal dosimeter and can also be used with the direct
reading detector. The console digitally displays the total cumulative carbon
monoxide dosage during the prescribed operating period. The console also
provides a digital display of the instantaneous carbon monoxide level when
used in conjunction with the dosimeter. This latter display is used for
calibration of the dosimeter, as shown in Figure 10.
The support console also provides a battery charging capability for the
dosimeter. A single and six dosimeter charging support console (Figure 11)
is available. The multiple charge support console also has the capability
of testing the state of the battery charge, and it has a jack plug for use
with a external recorder.
Maintenance
A table of maintenance recommendations for the detector and dosimeter
units are presented in Table 4.
94
-------
FIGURE 9. CO dosimeter controls and adjustment points,
FIGURE 10. Dosimeter and support console.
95
-------
LINE CORD
DOSIMETER
CABLE
COULOMETER
SWITCH
BATTERY CHARGING
LAMP
LINE/CHARGE SWITCH
CO DOSAGE
COUNTER
CALIBRATE
METER
FIGURE 11. A single and six dosimeter charging support console.
TABLE 4
Function and Maintenance
CHARGE NI/CD CELLS FOR 14 HOURS AT A NOMINAL CURRENT = 30 mA.± 3 mA. (DAILY)
VERIFY WATER LEVEL IN CELL IS AT LEAST HALF FULL OF DISTILLED HgO - FILL AS RE-
QUIRED. (WEEKLY)
VERIFY FILTER MATERIAL IS PURPLE. REPLACE FILTER WHEN COLOR CHANGES TO
BROWN. (WEEKLY)
VERIFY SAMPLE AIR FLOW OF 2+0.2-ON FLOW INDICATOR SCALE. ADJUST PUMP SPEED AS
REQUIRED WITH HAND-HELD UNIT IN UPRIGHT POSITION. (WEEKLY)
VERIFY INSTRUMENT SPAN WITH CO IN AIR STANDARD. (WEEKLY)
CALIBRATE ACCUMULATED CO DOSAGE LEVEL USING 15ECS2CO CONSOLE OR EQUI-
VALENT. (MONTHLY)
EMPTY CELL WATER RESERVOIR AND REFILL WITH FRESH DISTILLED WATER. (MONTHLY)
96
-------
OPERATIONAL TEST RESULTS
Typical results of operational testing of the dosimeter and detector
units are presented in the next series of figures*
Response versus Concentration
The indicated response of the units to various concentrations of CO in
air (at 60 cc/rain pump rate, 24° C) are shown in Figure 12. The data follow
the linear response curve anticipated over the entire 0 to 1,000-ppm range
of concentration.
Response versus Time
The indicated response of a specific CO detector unit to CO gas concen-
trations at various time intervals is shown in Figure 13. In these tests,
three different CO concentrations (97 ppm, 460 ppm, and 1,040 ppm) were sep-
arately fed to the instrument for 200 sec (at 60 cc/min, 24° C). At the end
of 200 sec, CO-free air was fed to the instrument. The response time obtained
lies well within the specified response time.
Response versus Temperature
The indicated response of dosimeter and detector units to various con-
centrations of CO (21, 58, and 97 ppm) at different temperatures is shown in
Figure 14. In these tests, the sensing instrument was left at the specified
temperature a minimum of 60 minutes prior to obtaining the reading. The
results obtained are within specifications established for the instrumen-
tation.
Response versus Flow Rate
The indicated response of the detector to variations in sample flow rate
with 97 ppm CO calibration gas, after calibration at 60 cc/min and 24° C, is
shown in Figure 15. The results show some sensitivity of output response to
flow rate change. The pump is, however, extremely stable in operation and
will maintain the pump rate within + 2 percent in normal daily operation.
Variations encountered as a result of normal flow rate changes lie well with-
in the specifications established for instrumentation.
97
-------
1100
MO -
RESPONSE
(PPM CO IN AIR)
700 -
FEED FLOW - 60 CC/MIN
TEMPERATURE - 24*C
1000
600 -
0 100 300 600 700 900
CONCENTRATION OF CO IN AIR (PPM)
1100
FIGURE 12. Response versus concen-
tration for a General Electric port-
able CO detection instrument.
r
BOO
1040 PPM CO IN AIR
600
RESPONSE
(PPM CO IN AIR)
FEED FLOW 60 CC/MIN
TEMPERATURE-24'C
400
zoo -
CO-FREE AIR
460 PPM CO IN AIR
97 PPM CO IN AIR
CO-FREE AIR -
80 160 240 320
RESPONSE TIME (SECONDS)
FIGURE 13. Response versus time for
a General Electric portable CO detector
to CO in air feeds.
100
ao
60
RESPONSE
(PPM CO IN AIR)
40
20
1 T 1 1 1
"T* X SINGLE THERMISTOR USED FOR SPAN
~ .* f "X. COMPENSATION. IMBEDDED IN
' CALIBRATION HUMIDIFIER BOTTOM PLATE.
POINT
SENSING INSTRUMENT LEFT APPROXI-
MATELY 60 MINUTES AT A GIVEN
TEMPERATURE PRIOR TO TESTING A
READING.
ff^**"^ \~~*****+
CALIBRATION
POINT
FEED FLOW » M CC/MIN
— DOSIMETER
1 — - DETECTOR
CALIBRATION
POINT
1 1 1 1 1
110
90
70
RESPONSE
(PPM CO IN AIR)
50
0 10 20 30 40
TEMPERATURE CO „
30
FIGURE 14 . Response versus tempera-
ture (° C) for General Electric CO gas 10
detection instruments.
A
I I I I I I I ^
^^^^
"~ .^^^ ~
^^^
_ ^^^ —
^r
^r
~- ^^ — -
/
J
_ * —
/
-
/
— ' —
/
/
, INSTRUMENT CALIBRATED WITH
97 PPM CO AT 60 CC/MIN _
/ TEMPERATURE - 24°C
7
1 i i i i i i i
SAMPLE FLOW (CC/MIN)
FIGURE 15. Effect of flow on response
for a General Electric CO detection
instrument.
98
-------
CONCLUSION
A new family of miniaturized self-contained carbon monoxide dosimeters
and direct reading detectors have been described. The units are extremely
lightweight, versatile, self-contained, and meet the requirements for in-
trinsically safe operation. The cell needs no acid; only distilled water is
required. The units are an outstanding example of the combination of func-
tional design engineering and technical experience based on fuel cell tech-
nology.
REFERENCES
1. LaConti, A.B., Dantowitz, P., Kegan, R., Maget, H.J.R. Hydrogen Sensors,
Electrical Bias Approach. TIS Report #66 ASD3, General Electric Company.
1966.
2. LaConti, A.B., Maget, H.J.R. Electrochemical Detection of H,, CO and
Hydrocarbons in Inert and Oxygen Atmospheres. J Electrochem Soc 118:
506, 1971.
3. Schnakenberg, G.H., LaConti, A.B. Improved CO Detection Systems.
Proceedings, 17th International Conference, Bulgaria, 1977.
4. Dempsey, R.M., LaConti, A.B., Nolan, M.E., Schnakenberg, G., Chilton, E.,
Torkildsen, R. Gas Detection Instrumentation Using Electrically-Biased
Fuel Cell Sensor Technology. PB 254823, NTIS, Springfield, Va. 1978.
5. Jones, R.C., LaConti, A.B., Nuttall, L.J. Carbon Monoxide Monitor
Features Hydrated Solid Polymer Electrolyte Cell. Proceedings, American
Industrial Hygiene Conference, New Orleans, La,, May 1977-
MAILING ADDRESS OF PRIMARY AUTHOR
Arnold H. Gruber
Direct Energy Conversion Programs
General Electric Company
50 Fordham Road
Wilmington, Massachusetts 01887
99
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Discussion
ZISKIND: Richard Ziskind, Science Applications. How much field experi-
ence has been accumulated on this instrument?
GRUBER: The dosimeter has been in the field for well over a year.
The detector is being introduced at this point in time. The circuitry and
design of both the detector and the dosimeter are quite similar.
Before we introduced the product, we at GE did considerable testing of
the product, both in-house and with some field testing as well. Both units
have been tested for at least 2 years, the detector being tested for at least
1 year prior to its introduction.
ZISKIND: The other question I had was the question that was asked before
about electromagnetic interference.
GRUBER: As a matter of fact, the unit also has a plastic case. The
plastic case is metalized. One of our specifications is no electromagnetic
interference, and the units will meet that specification.
WILLIAMS: Marsha Williams. To what extent has the instrument been test-
ed at temperatures below zero Centigrade?
GRUBER: As with some of the other electrochemical cells used below zero,
we have a water cell. The water will freeze, and you can deteriorate your
cell at low temperatures. This is the same with all of the electrochemical
cells.
All of the electrochemical cells have specific temperatures to which
they can go down. Regarding a water cell, obviously you wouldn11 want to go
below zero degrees Centigrade. With some of the acid cells—they can go down
below zero Centigrade.
MEIER: Could you say something about cost?
GRUBER: Vic Socol, would you like to say a couple of words?
SOCOL: The dosimeter costs $595. There are various options on the sup-
port console, which cost from $695 to $825, and a direct reading indicator,
at $945.
McSTRAVICK: John McStravick, Energetics Science. Just for the record,
the current Energetics Science dosimeter sensor can go to -17° Centigrade.
100
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Design and Performance of a Reliable
Personal Monitoring System for Respirable
Particulates
William A. Turner, John D. Spengler, Ph.D., Douglas W. Dockery, and
Steven D. Colome
Department of Environmental Health Sciences
Harvard School of Public Health
Boston, Massachusetts
INTRODUCTION
Personal exposure to respirable particulates and sulfates is being meas-
ured as a part of a long-term prospective epidemiological study of the res-
piratory health effects of air pollution, the Harvard Six City Study (1).
The purpose of this monitoring program is to develop better estimators of
actual personal exposure from comparison of the direct measurements of
personal exposure with simultaneous measurements of the normally measured out-
door air, the air inside each participant's home, and records of the daily
activities of each participant. Results are reported elsewhere in these
Proceedings (2).
Respirable particulates and sulfates were selected for monitoring be-
cause they were considered to be important potential toxic agents. Further-
more, for practical considerations, reliable sampling equipment which modeled
the definition of "respirable particulates'' (3) was commercially available
and readily adaptable for use in the community.
The commercially available samplers have been designed to meet Federal
requirements for respirable dust exposures in mines (4). In this program,
MSA Model G and Bendix BDX-31 samplers were used. The sampler consists of
a 10-mm nylon cyclone presampler to remove the nonrespirable particles,
followed by a filter to collect the respirable fraction. Air is drawn through
the sampler by a battery-operated diaphragm pump which is equipped with
101
-------
a stroke counter and miniature rotameter. The pump is designed to operate
from the batteries for a normal 8-hour work shift. Flow is controlled by a
needle valve. Normal operation calls for overnight charging of the batteries.
At the beginning of the sample, the pump is turned on and allowed to run for
approximately 15 minutes to eliminate initial battery voltage surge before
setting the flow to 1.7 liters-per-minute (1pm). At the end of the sample,
the flow is checked and the total number of strokes recorded as an indication
of total sample volume.
In applying these samplers in the community, the first problem we en-
countered was unacceptable noise. The situation was somewhat improved by
placing the pump in a hard plastic box lined with sound-absorbing material.
The box was equipped with a shoulder strap, and the cyclone was mounted on
the outside of the box. Problems arose with sampling lines being crimped
within the box with this setup.
The second major problem was with the limited sampling time. A sampling
time of 24 hours was desired for comparison with regular State and Federal
air pollution sampling programs, and also to ensure sufficient collected
mass for analysis. Given a nominal battery life of 8 hours, a supplementary
power source was required. The battery chargers operate in two modes—16-
hour and 64—hour recharging. At the high rate, 16 hours, the chargers supply
enough power so that there is only a slight drain on the batteries. Thus,
the participants were instructed to place the monitor in some fixed location
whenever they were in a room for some extended period—for example, on their
desk while working in their offices. The charger was then plugged into 120
VAC outlet and then into the pump.
This procedure proved to be less than ideal. The pumps were still noisy.
The chargers were bulky and inconvenient to carry around. In the first sam-
pler program in Watertown, Mass., 37 people agreed to participate. Thirteen
did not last through the first sampling day. In the end only 18 highly moti-
vated people remained. In addition, we encountered several electrical prob-
lems. First, if the MSA chargers were plugged in while the pumps were op-
erating and the charger was on, they blew their internal fuse. Secondly,
the higher voltage supplied by the chargers quickly deteriorated the motor
brushes, and we had a very short motor life. The charger connected to the
pump was not secure so that the plug often slipped out without the partici-
pant's knowing it.
The final problem was variation in the flow rate. The actual flow was
102
-------
proportional to the voltage supplied to the motor. Since even with the
chargers attached, the pumps still drew power from the batteries, the flow
declined during the day as the battery voltage decayed. On the average,
the end flow was 80 percent of the nominal initial setting.
The commercial samplers were modified at several steps along the way,
but it was readily apparent that these samplers were not acceptable for our
program. As a result, the Harvard/EPRI sampler was developed.
The design criteria were:
1) Provide a constant flow rate of + 0.1 liter-per-minute (1pm) over
the range of 0.5 to 3.0 1pm;
2) Include the self-contained capability to be recharged overnight and/
or to run off line voltage;
3) Produce a noise level acceptable for home and office use;
4) Operate for 12 hours or more on batteries;
5) Portable, lightweight, rugged, yet simple to operate;
6) Provide a sample comparable to our fixed-location indoor/outdoor
monitoring system; i.e., system operating where no pulsation is present.
One hundred personal monitoring pumps have been built and have passed
initial testing. They are presently being field tested and will be put into
full use during a personal monitoring program during the spring of 1979.
SPECIFICATIONS
Size: 6 in x 6 in x 3 in
Weight: 4 Ib
Pump: "Brailsford" Brushless TD-3LL or TD-3L
Battery Pack: "Gould" 12 V-1.2 SC cells Ni-Cad
Flow Control: Variable Constant Voltage
Range of Operation: 0.5 to 3.0 1pm
Case Metal: Aluminum
Cyclonic Separator: 10-mm nylon with filter
Features:
• Self-contained battery charger
• No warm-up time required to reach stable flow
• 14 to 20 hours sample time on battery mode, indefinite from line voltage
• Minimum maintenance brushless pump (10,000 hours before service)
• Quiet operation.
103
-------
PRINCIPLE OF OPERATION
Air is drawn through the 10-mm nylon cyclone, a 1.0 y pore size Fluoro-
pore filter, and a pulsation damper by a constant displacement pump (Figure
1). The flow control through the system is controlled by varying the speed
of the pump instead of by conventional throttling methods. This allows for
precise flow control with minimum energy loss due to pumping losses induced
by throttling. The variable constant voltage power supply allows the pump
to be set at a given flow rate and will maintain the flow + .05 1pm under
normal sampling loads and 4^ .1 1pm under severe filter loading conditions.
The Harvard/EPRI sampler has a six-position switch as follows:
1) Battery Run
2) Line Run
3) Line Run and Charge Low
4) Charge Low (36 to 40 hours)
5) Charge High (12 to 14 hours)
6) Off.
These six positions allow the unit to serve as a portable personal
monitoring device or a stationary 24-hour sampling unit. The unit has a
detachable 8-foot, three-wire safety power cord and a detachable 48-inch
carrying strap. The respirable sampling cassette and cyclonic separator can
be detached and located apart from the main body of the sampler.
RESULTS OF FIELD TESTING
Flow Stability
Laboratory and field tests conducted between October and December of 1978
have shown the flow to be stable to +_ .05 1pm under normal filter loadings
for 12 to 24 hours, after an initial break-in period for each unit (72 hours).
This break-in period is required to seal the pump valves and to establish a
diaphragm set. On some units it has been necessary to install a restricting
orifice in line to allow the pump to obtain lower flow rates. This does not
affect the stability or designed sampling life times while operating from
batteries.
Effects of Pulsation on Cyclone Efficiency
The effects of air flow pulsation on the cyclone collection efficiency
in personal sampling devices have been investigated by numerous researchers
104
-------
MUFFLER
DAMPER
FILTER
CASSETTE
•CYCLONE
LINE VOLTAGE
VOLTAGE REGULATING BCARD
AND CHARGING CIRCUIT
BATTERY PACK
FIGURE 1, Schematic of flow system,
JS*-CYCLONE
•PNEUMOTACHOGRAPH
-AP TRANSDUCER
AMPLIFIER
=]—FILTER
to<
-DAMPER
-PUMP
SCOPE
FIGURE 2. Test apparatus.
105
-------
(5,6,7). To determine the flow characteristics of the Harvard/EPRI pump,
a Fleisch Pneumotachograph (#7316[000]) and a pressure transducer were coupled
to an amplifier and oscilloscope. Figure 2 is a schematic display of the
test apparatus. For comparison with other pumping systems, an index of
, .. ,D [MAX FLOW - MIN FLOW]. , . _ . ... .
pulsation (P = -»• MEAN FLOW ' a e fre
-------
-2.1
FIGURE 3A. H/E without damper.
5
Q_
FIGURE 3B. H/E with damper.
107
-------
In addition, the self-contained charging circuitry and lower noise level have
eliminated the nuisance characteristics that prevented broader participant
acceptance. The Harvard/EPRI pump has been designed to meet the particular
sampling requirements of assessing community personal exposures in an epi-
demiologic air pollution health study.
ACKNOWLEDGEMENTS
Steve LeMott, Harvard School of Public Health, Department of Physiology,
for aid and use of the pulsation measurement equipment.
Pat Quinlan, for pump assembly and circuit testing.
Electric Power Research Institute, Palo Alto, Calif., Contract No.
RP1001-1.
National Institute of Environmental Health Sciences, Grant No. ES01180.
REFERENCES
1. Air Pollutants and Health: An Epidemiologic Approach. Environ Sci
Technol 11:648-650, 1977.
2. Dockery, D.W., Spengler, J.D. Personal Exposure to Respirable Partic-
ulates and Sulfates: Measurement and Prediction. Proceedings of the
Symposium on the Development and Usage of Personal Monitors for Exposure
and Health Effect Studies, Chapel Hill, N.C., January 22-24, 1979. (EPA
symposium.)
3. Llppmann, M., Harris, W.B. Size-Selective Samplers for Estimating
"Respirable" Dust Concentration. Health Physics 8:155, 1962.
4. Federal Coal Mine Health and Safety Act of 1969.
5. Caplan, K.T., Doemeny, L.J., Sorenson, S.D. Performance Characteris-
tics of the 10 mm Cyclone Respirable Mass Sampler: Part I. Monodisperse
Studies. Am Ind Hyg Assn J 38:83-95, 1977.
6. Caplan, K.T., Doemeny, L.J., Sorenson, S.D. Performance Characteristics
of 10 mm Cyclone Respirable Mass Sampler: Part II. Coal Dust Studies.
Am Ind Hyg Assn J 38:162-173, 1977.
7. Blackman, M.W., Lippmann, M. Performance Characteristics of the Multi-
cyclone Aerosol Sampler. Am Ind Hyg Assn J 35:323-325, 1974.
108
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MAILING ADDRESS OF AUTHORS
William A. Turner, John D. Spengler, Ph.D.,
Douglas W. Dockery, and Steven D. Colome
Harvard School of Public Health
Department of Environmental Health Sciences
665 Huntlngton Avenue
Boston, Massachusetts 02115
Discussion
(NOTE: The discussion for this paper appears following the text of the next
paper, "Personal Exposure to Respirable Particulates and Sulfat^s: Measure-
ment and Prediction.")
109
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Personal Exposure to Respirable Particulates
and Sulfates: Measurement and Prediction
Douglas W. Dockery and John D. Spengler, Ph.D.
Department of Environmental Health Sciences
Harvard School of Public Health
Boston, Massachusetts
INTRODUCTION
Epidemlological studies of the health effects of air pollutants have in
the past frequently depended on ambient air quality measurements at a single
site within a community for correlation with observed health effects. Given
that Americans normally spend 95 percent of their time Indoors (1,2), such
measurements of outdoor air pollution levels may not represent the actual
air pollution exposure of the sample population.
Jackson and Newill (3) noted that "perhaps the weakest link in our at-
tempts to establish the exposure-response relationship is in obtaining an
accurate quantitative estimate of exposure." Morgan and Morris (4), in a
study of the needs for personal monitoring, concluded that "the importance
of population exposure measurements in air pollution epidemiology makes it
imperative that future epidemiological studies include exposure estimates
more representative of what people actually breathe."
A monitoring program to measure personal exposure to respirable parti-
culates and sulfates was undertaken as part of a long-term epidemiologic
study of the respiratory effects of air pollution (5). These observations
were compared to measurements of the ambient outdoor environment and of the
indoor environment in each participant's home. In a similar study, Binder
et al. (6) had 20 school children carry a suitcase sampler with them for 1
day. They concluded that outdoor measurements do not accurately reflect the
particulate exposure of individuals who live in the area of sampling.
Ill
-------
With observations of actual personal exposure to respirable particulates,
we hope to develop a method to characterize the personal air pollution expo-
sure of individuals in terms of their personal activities, characteristics
of their home and household, and ambient pollution level. Average exposure
can be estimated by a simple time-weighted model of the form
~C »** t c / *• t
L i Eici ' i Ci
where C is the average exposure, t is the time spent in activity i, and c.
is the air pollution concentration associated with that activity.
Ideally, the air pollution concentration associated with each activity
would be known, so that the exposure of any individual could be estimated
directly from his or her activities. It Is unrealistic to expect that we can
specify air pollution concentrations for every activity, but hopefully we
can make reasonable estimates for broad classes of activities. While not
specifying exposure exactly, these estimates should be significantly better
than the outdoor values alone.
The method used, therefore, was to measure the integrated exposure of
individuals with different activity patterns. Comparison with simultaneous
measurements outside and inside their homes allowed the most important factors
in determining exposure to be identified and quantified.
PROCEDURE
Volunteers were asked to carry a small, personal particulate monitor
with them for 24 hours as they went about their normal daily activities.
They were also asked to keep a diary of their activities that day. Similar
monitors were run concurrently at fixed sites in their home and at several
locations outside in the community. Samples were taken in Watertown, Mass.,
every 6th day for 2 months in the summer (July and August 1975) and 2 months
in the winter (mid-January to mid-March 1976). The study was repeated in
Steubenvllle, Ohio, in June 1976. In this case, 12-hour samples were taken
on Monday, Wednesday, and Friday each week.
Volunteer Selection
Volunteers were solicited at random from census lists. The study was
described to the potential participants in a letter followed by a phone call*
112
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Those interested in the study were visited and shown the equipment. Although
the intent was to draw a representative sample of the population, this did
not occur. In general, anyone doing physical work could not conveniently
carry the monitor. Most working people with manufacturing jobs were not al-
lowed to bring the monitors to work by their employers for fear that they would
uncover occupational health violations. Many potential participants found
the program too burdensome. The final set of volunteers provides a very
wide range of exposures and activities, but was not representative of the
sample population in the health study.
Whenever possible, we attempted to have both the husband and wife in a
family participate. A total of 37 people participated, 18 in Watertown and
19 in Steubenville. There were five smokers in the Watertown sample, and
one in the Steubenville sample. Twenty-one of the participants were women,
and 23 were employed away from home. All those working had white collar jobs
except for one self-employed plumber.
Pollutant Measurements
In order to characterize those particulates which are most likely to
have a significant respiratory health effect, we chose to measure only those
small enough to penetrate deep into the lungs. The AEC Los Alamos criteria
(7)—which specify that 50 percent of the 3.5-um particles penetrate deep
into the lungs, while particles larger than 10 ym will not—was used. This
also provides a convenient starting point for measuring individual exposure
to air pollution in the community in that sampling devices had been developed
for the industrial environment based upon these criteria.
The sampler consists of a Dorr-Oliver 10-tnm diameter hyd roc lone pre sam-
pler, followed by a 37-mm Fluoropore filter with a 1-ym pore size. Air is
drawn through the sampler by a Mine Safety Appliance Portable Pump—Model
G was used in Watertown, and a Bendix BOX Super Sampler in Steubenville.
A flow rate of 1.8 liters-per-minute has been shown by Seltzer, Bernaski, and
Lynch (8) to deposit particulates in the cyclone presampler in close approxi-
mation to the Los Alamos curve* This was the flow used in this sampling.
The American Industrial Hygiene Association (9) has recommended a flow of
1.7 llters-per-minute (1pm) for the 10-wm cyclone. Knight and Lichti (10)
have shown essentially no change in the mass collected on the filter between
1.3 and 2.65 1pm. It is felt, therefore, that this difference in flow rate
does not compromise the samples.
The pumps are battery-operated, with a nominal operating time of 8 hours.
113
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It was possible to operate the pumps for longer periods by connecting them
to their battery chargers with only a small drain on the batteries. Since
initial tests showed that the major obstacle for people participating in
the study was the noise of the pump, the pump was placed in a sound-insulated
box with a strap so that the monitor could be carried over the shoulder, as
shown in Figure 1.
Sampling Plan
In Watertown, samples were collected for 24-hour periods every 6th day
to coincide with Federal and State air quality sampling programs. In Steu-
benville, 12-hour samples were taken on Monday, Wednesday, and Friday, be-
ginning at 8 a.m. At that time, the volunteer turned on his personal monitor
and a similar one placed in the home in the room with the most activity (ex-
cluding the kitchen). At the same time, outside monitors were turned on by
automatic timers. Thus, we had three measurements for each sample—personal,
inside the home, and outside.
We assumed that the particulates were uniformly distributed over volumes
the size of a room. The actual placement of the monitor on the person was
therefore not critical, and breathing zone samples as required in industry
were not necessary. Volunteers were instructed to connect the pumps to the
chargers whenever they were in one area for an extended period. In this way,
we were able, in most cases, to run the samplers for up to 24 hours. (This
type of operation is not recommended by the manufacturer.) The volunteers
were also asked to keep a diary of their activities during the sampling period,
including how many cigarettes they were exposed to each hour.
Outdoor monitors were located throughout the community. The outdoor
monitoring was part of a continuing program to evaluate the indoor/outdoor
pollution relationships. The outdoor data were pooled to give the mean out-
door value for each day with observations. Hereafter, this pooled outdoor
mean will be referred to as the "outdoor concentration." This is the concen-
tration which would be obtained by an ambient air pollution monitoring site
using this sampling technique.
Sample Analysis
Filters were preweighed on a Cahn 4100 Electro-Balance in a humidity-
controlled room (RH <50 percent) and sealed in plastic sampling cassettes.
The volunteer was visited after each sampling day, the filters were changed,
and the operation of the pump was checked. Flows were checked periodically,
114
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FIGURE 1. Personal respirable particu-
late monitor showing sound deadening
box and normal carrying mode.
PERSONAL raMITORI'IO DATA SliEET
Filter
—
name
aauress
&>c AW«
occupation
Smoker £no)
—-~^—^—~ Ti^f
yes:
Sanolint:
Mode (circle one)
(^"Personal-' Fixed (describe location —
TTrtTT'SldlT. > etc.)
PAn<-
oax-ia.
1/2 pk/day
1 pk/day
1 1/2 pk/day
2 pk/day
Sar"nlinr
Start
Finish
Filter '.'
Exposure
ITRP
Period oo
— '• • J ••-. i-'. 8" - ° Vv\.
\- f \ . ^ f\f\ o "* ?^ ^-^ ^ - rvi-
t. Pre
Post
/ /• T UF/n3
2+ pk/day
Summary of Activities
In transit car
other (descr-.be)
Home outdoors
Indoors:
sleeping
kitchen area
living rn, den, etc.
other
Indoors (Hrs/Dav) Outdoors (Hrs/Dav)
s
Working
outdoors
Indoors
Shopping/Recreational outdoors
Indoors
Totals
Grand Total (better be
close to 2l»)
Summary of Exposure
Hear or In smoke
Time you were smoking or It of
cigarettes/day
."Jear or In dusty area
vacuuming
construction
road dust
other
Summary of Transportation
1. Label nap with sampling date and filter nunbers and name.
2. Locate home (H) and work (W). Trace transit route.
3. Trace and/or locate general travel (non-core-.ute).
O
0
0
C
FIGURE 2. Example of personal monitoring data sheet used
in 1976 winter sample.
-------
but not after each sampling day. The used filters were returned to the lab-
oratory and conditioned for 24 hours before reweighing. The filters were cut
in half, one half being stored for future analysis. The other half was ex-
tracted in 1,100 pi of water with 50 pi of ethanol as a wetting agent in
an ultrasonic bath. The soluble sulfate was then measured by a modified
turbidimetric technique (11).
The measured concentrations were then analyzed to compare the personal
exposures, the indoor, and the outdoor measurements. The activity patterns
from the diaries were used to evaluate the proposed linear time-weighted model
for exposure.
Activity Diary
Each participant was asked to keep a diary of his or her activities during
the sampling period. Each was asked to make special note of the number of
cigarettes smoked in his or her vicinity, or of any other source of pollution
of which he/she was aware. Figure 2 is an example of the activity diary
used in the first sampling period. The volunteer was asked how much time was
spent indoors and outdoors at home, work, and other locations, plus the time
spent in transit. There was space for the volunteer to make notes on the ac-
tivities hour by hour, but this was only to assist him or her in determining
the total time spent in each activity.
The diary entries were aggregated to give the total amount of time spent
indoors at home, at work, and in other places—e.g., shopping. The amount of
time outdoors was determined at home, at work, in transit, and all other
places. Table 1 shows the mean time spent by the Watertown participants in
each of these activities for the two seasons. As would be expected, the total
amount of time spent indoors was significantly higher in winter (95 percent)
than in summer (86 percent). Although the amount of time spent outdoors in
winter is about one-third that of summer, in both seasons an average of 1
hour was spent in transit; that is, traveling by auto, public transportation,
foot, or some other method.
These results are similar to other time-usage studies (1), which have
shown people in 44 U.S. cities to spend 94.5 percent of their time indoors—
70.9 percent in the home. These studies also found that an average of 1.25
hours per day were spent in transit.
116
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TABLE 1
Mean Dally Time Spent In Various Activities for
18 Participants In Watertown, Mass.
Summer
Location Mean (SD)* %
Indoors
Home 16.8 (6.5) 71.9
Work 2.6 (3.9) 11.1
Other 0.6 (1.8) 2.6
Total Indoors 20.0 (5.9) 85.6
Outdoors
Home 1.7 (4.7) 7.3
Work 0.1 (0.3) 0.2
Transit 1.0 (1.2) 4.1
Other 0.7 (1.8) 2.9
Total Outdoors 3.4 (4.9) 14.5
Total All 23.4 100
Winter
Mean (SD)* %
18.2 (6.4) 78.5
2.8 (4.7) 12.0
1.0 (2.1) 4.2
21.9 (4.3) 94.8
0.0 (0.3) 0.2
0.1 (0.9) 0.4
1.0 (1.2) 4.2
0.1 (0.5) 0.5
1.2 (1.5) 5.2
23.1 100
*SD « Standard Deviation
One volunteer in Watertown attempted to evaluate the relative impacts
of different modes of transportation. One day, he took his car to work.
The next sampling day, he bicycled. The third day, he canoed down the Charles
River. Unfortunately, any differences which might have existed were masked
by the high partlculate levels from his smoking.
117
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RESULTS
In Watertown, a total of 287 personal and 251 indoor samples were col-
lected. Over half the potential samples were missing because of equipment
problems, vacations of the participants, voided observations, and scheduling
problems. In Steubenville, 245 personal and 131 indoor samples were collected.
The data-retrieval rate there was higher because of the shorter sampling time
and closer supervision.
Sulfate Relationships
There are two questions to be answered from this data. First, is person-
al exposure related to the normally monitored outdoor air pollution levels?
Secondly, if not, what is the best estimator of personal exposure, and what
is the minimum information required for that estimate?
We will consider only comparisons of mean levels for each individual in
the study. Observations are included only when we have a complete set of
personal, indoor, and outdoor measurements of concentration for that individ-
ual and that day. While cutting down the number of available observations,
this ensures comparability. We will also require each individual to have at
least three complete sets of observations in order to be included.
Consider the respirable sulfates first. Although sulfate particulates
are generated by matches (12) and the open burners of gas stoves (13), the
contribution is small compared to the concentrations of sulfate in the outdoor
air in Watertown and Steubenville. We can then easily explore the relation-
ship between personal exposure and outdoor concentration. In Figure 3, mean
personal exposure levels are plotted against the mean matched outdoor concen-
tration for each individual. The points are clustered into two groups:
o
Watertown observations with the lower values (mean outdoor « 5.8 yg/m ),
o
versus Steubenville observations with higher values (mean outdoor - 17.6 yg/m )
The correlation coefficient (r) between the outdoor and personal means
is 0.81, but from visual inspection it is clear that the outdoor means are
not good estimators of personal exposure. There is considerable scatter,
especially in Steubenville, about the perfect prediction line, the diagonal
in Figure 3. The proportion of the variance of the mean personal exposures
o
explained by a linear regression on mean outdoor concentrations (r ) is 65
percent. But considering the mean outdoor values to be a direct estimate of
personal exposure, a more appropriate statistic is the standard error about
that estimate, which is 4.86 yg/m .
118
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02
25.0*
a
25.0*
20.0*
S 15.0*
5
*H _
S 10.0+
* • •
• t
20.0*
15.0*
10.0*
5.0*
? •* 2*
5.0* 2
23 2
2 »
0.0*
0.0 10.0
5.0
15.0
20.0
Outdoor Mun Suim.
-*o3
25.0
FIGURE 3. Relationship between
mean outdoor and mean personal sul-
2
fate levels (ug/m ).
0.0*
0.0
10.P 20.n
5.0 15.0 25.0
Exposure Model
FIGURE 4. Relationship between mea-
sured personal mean sulfate levels
m ) and predicted personal mean
sulfate levels from time-weighted
exposure model.
c6
100.*
c6
100.*
80.t
60.4
60.4
40.4
20.*
* 2 •
2 »
•2
•
•2 »
3 •
] -
1 .
5 40.*
» • • *
20.4
0.+
0.*
0. DO. 80.
20. 60. 100.
Outdoor Hun Ruipirabl* P«rtlcul«t«
FIGURE 5. Relationship between
personal mean and outdoor mean
respirable particulate levels
(yg/m3).
o.
10.
80.
*o10
20. 60. 100.
TlM-N*ight«d Expoiur* Model
FIGURE 6. Relationship between
measured personal mean respir-
able particulate levels (yg/m )
and predicted personal mean
respirable particulate levels
from time-weighted exposure
model.
119
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We can test these pairs for a significant difference between them with
a paired t-test. In this case, the mean difference among the 37 observations
is 3.06 yg/m . The t value is 4.87, which implies a significant difference
at the 0.1-percent level.
We can also test the variance about the estimator—that is, the out-
door means—versus the variance of the personal means. The ratio of these
gives an F of 0.625, which is significant.
Assuming that there are no significant sources of respirable sulfate
particles indoors, the personal exposure should be equal to the mean of the
concentration outside weighted by the time spent outside, and the concen-
tration inside weighted by the time spent indoors. Assume that the indoor
concentration for each individual is represented by the level measured inside
his/her home. Figure 4 compares the mean personal levels for each individual
with the mean time-weighted model estimates of exposure. Comparison with Fig-
o
gure 3 shows less scatter of the data about the diagonal. The r has increased
o
to 0.765, and the standard error of the estimate has decreased to 3.75 yg/m .
The paired t for this data was 2.61, which implies the difference was still
significant at the 5-percent level.
Considering the fact that such a large fraction of the time is spent
indoors, it is reasonable to ask how good the indoor value by itself is as
a predictor of personal exposure. Table 2 compares the correlation, paired
t, and standard error of the estimate using outdoor, the time-weighted model,
and indoor measurement as estimates of personal exposure. The time-weighted
model does not perform significantly better than the indoor measurements alone.
TABLE 2
Comparison of Outdoor Means, Time-Weighted Exposure Model, and
Indoor Means as Estimator of Personal Exposure for 37 Observations
r2
SEE
t
Outdoor
0.654
4.86
4.87
SULFATE
Time Model
0.675
3.75
2.61
Indoor
0.728
3.89
1.91
RESPIRABLE PARTICULATE
Outdoor
0.479
20.18
-0.85
Time Model
0.570
14.29
0.71
Indoor
0.514
15.40
-0.003
120
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Respirable Particulate Relationships
Whereas the mean personal sulfate exposures are determined by outdoor
sources, personal exposure to respirable partlculates Is determined by both
outdoor and Indoor sources. The Watertown personal monitoring program demon-
strated the importance of smoking, as one source, in determining personal
particulate exposures (12).
Comparison of the mean personal exposure with the mean simultaneous
outdoor measurements (in Figure 5) shows more scatter than with the sulfates
7
(Figure 2). In this case, r = 0.479, and the standard error of the estimate
is 20.18 yg/m . Again we see the clustering of the Watertown data at lower
O
levels (outdoor mean - 17.5 vg/m ), and the Steubenville data higher (outdoor
o
mean » 67.3 wg/m ). There Is a tendency for higher personal values compared
to outdoor values in Watertown, where smokers were included in the samples.
In Steubenville, where smokers were not Included, the outdoor mean values
are more representative of actual personal exposure.
The paired t of -0.851 indicated no significant difference, but this
apparently results from the large variance.
Personal exposure was estimated by a time-weighted combination of indoor
and outdoor concentrations plus a time-weighted parameterization of smoking
exposure indoors away from home. Smoking within the home is intrinsically
included by the concentrations measured indoors. Smoking outside the home
was estimated from the number of smokers each participant reported he was ex-
posed to away from home. Regression analysis indicated that the impact of
3
each smoker added 20 yg/m to the average exposure. The resultant model was,
therefore,
"C + [t. . c. . + tt.c+t. . (c, .
1 home indoors out out other indoors
+ "smok ' 2° rt'l ' 'tot
where *C is estimated exposure to particulates, t, is the time spent at
home, c. . is the concentration measured indoors at home, t . is the
indoors out
time spent outdoors, c is the concentration measured outdoors, t . is
the time spent indoors away from home, N v is the number of smokers the
participant was exposed to away from home, and t is the total sample
length.
121
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Figure 6 compares mean personal exposures with mean values estimated
2
by this method. The r has increased slightly to 0.570, and the standard
3
error of the estimate has decreased, to 14.3 yg/m . The paired t test still
shows no significant difference. Personal values were regressed against
just the indoor values to assess the improvement in prediction of the time-
weighted model. Table 2 compares the statistics for all three methods.
While using indoor values significantly improves prediction of personal values
over Just the outdoor values, the addition of a smoking variable gives a much
better estimate. It is clear also that a best fit to the data in Figure 6
would give a non-zero intercept, indicating that there are other contributing
sources and exposure factors that have not been included.
CONCLUSIONS
Although personal exposure to respirable particulates and sulfates is
determined in part by outdoor levels, indoor concentrations are, because of
the large fraction of time spent indoors, a much better estimator of exposure.
In the case of respirable particulates, passive exposure to smokers contributes
significantly to personal exposure. In addition, other activities still to
be determined are adding to the particulate exposures. Further studies are
planned in the relatively clean ambient environment of Topeka, Kansas, this
spring in order to define these contributions.
ACKNOWLEDGEMENTS
This work has been supported by NIEHS Grant No. ESDI180. The study was
possible only through the understanding and cooperation of our volunteers in
Watertown and Steubenville.
REFERENCES
1. The Use of Time: Daily Activities of Urban and Suburban Populations
in Twelve Countries. (Szalai, A., ed.). Paris, Mouton, 1972, p. 114.
2. Chapin, F.S. Human Activity Patterns in the City. New York, Wiley-
Interscience, 1974.
3. Jackson, D.L., Newill, V.A. The Strengths and Weaknesses of Population
Studies in Assessing Environmental Health Effects. In: Proceedings
CEC-EPA-WHO International Symposium on Environment and Health, Paris, 1974
122
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4. Morgan, M.G., Morris, S.C. Needed: A National R&D Effort to Develop
Individual Air Pollution Monitor Instrumentation. J Air Pollut Control
Assoc 27:670-672, 1977.
5. Air Pollutants and Health: An Epldemiological Approach. Environ Sci
Technol 11:648-650, 1977.
6. Binder, R.E., Mitchell, C.A., Hogein, H.R., Bouhuys, A. Importance of
the Indoor Environment in Air Pollution Exposure. Arch Environ Health
31:277-281, 1976.
7. Lippman, M., Harris, W.B. Size Selective Samplers for Estimating "Res-
pirable" Dust. Health Physics 8:155, 1962.
8. Seltzer, D.F., Bernaski, W.J., Lynch, J.R. Evolution of Size-Selective
Presamplers, II. Efficiency of the 10-mm Nylon Cyclone. Amer Ind Hyg
Assoc J 32:441-446, 1971.
9. AIHA Aerosol Technology Committee: Guide for Respirable Mass Sampling.
Amer Ind Hyg Assoc J 31:133, 1970.
10. Knight, G., Lichti, E.K. Comparison of Cyclone and Horizontal Elutri-
ator Size Selectors. Presented Annual Meeting, Amer Ind Hyg Assoc,
Denver, 1969.
11. Tabatabai, M.A. A Rapid Method for Determination of Sulfate in Water
Samples. Environ Letters 7:237, 1974.
12. Dockery, D.W., Spengler, J.D. Personal Exposure to Respirable Partlcu-
lates and Sulfates Versus Ambient Measurements. Paper #77-44.6, Air
Poll Contr Assn Meeting, Toronto, 1977.
13. Hollowell, C.D., Budnitz, R.J., Traynor, G.W. Combustion Generated In-
door Air Pollution. Presented, 4th Intl Clean Air Congr, Tokyo, May
16-20, 1977.
MAILING ADDRESS OF AUTHORS
Douglas W. Dockery and John D. Spengler, Ph.D.
Harvard School of Public Health
Department of Environmental Health Sciences
665 Huntington Avenue
Boston, Massachusetts 02115
123
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Discussion
(NOTE: The following discussion took place after the presentation of
the papers "Design and Performance of a Reliable Personal Monitoring System
for Resplrable Participates" and "Personal Exposure to Respirable Particulates
and Sulfates: Measurement and Prediction.")
McCURDY: My name is Tom McCurdy. I work for the Pollutant Strategies
Branch, EPA, and my comments and question are for Mr. Dockery.
Our office is doing some time averaging in high pollution exposure
monitoring. We are into human activity. 1 also have a couple of comments.
One, Chapin is not a sociologist. He is an urban planner here at the Univer-
sity of North Carolina. He is a physical planner. 1 think he would reject
being called a sociologist.
Number two, there is a Dr. Robinson of Cleveland State University who
has some very good time activity data. Another comment is that for modeling,
we need hourly human activity data, not daily data like you aggregated.
That may be true only for pollutants with a 1-hour averaging time. Have you
published any of your summary of the activity data anywhere?
DOCKERY: We have presented papers at meetings in the past couple of years.
It hasn't been directly published.
On the averaging time, we are doing measurements on the health effects
every 3 years. And even if you get down to 24-hour average exposure, it is
much finer detail than we needed in determining what our health effects are
going to be, although it depends on whether the argument is the long-term
average health exposure or the peak levels that are really causing the
health damage.
We are trying to keep information down to the hourly level, but at least
in terms of exposure, or exposure models, we are using 24-hour average values.
McCURDY: I realize that. But for our purposes, we would really like to
have some hourly data. So, if you are running it, try to keep in mind the
most desired aggregated time we could get for a lot of people probably is
on the order of 1 hour.
One further question: I don1t understand what you are saying about your
regression line and your coefficient of determination.
You were putting up data that had less of an R-square value, but you
were saying that you had less data in that sample. It seems to me your data
124
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were contradictory with what you were saying.
(
DOCKERY: When you use this correlation, you are looking at an arbitrary
fit to any particular line that you can fit through there. The only differ-
ence in the one that you have compared this back to, the one-to-one reversing
line, is that we are comparing his actual measurements versus some predictor,
just to see how well that works.
In reality, what we are looking at is F testing, Student's t-testing,
things on that order. But I didn't want to get that deep into the statistics
today. I was just using the R-square as an indicator, trying to get an in-
dicator that everybody was familiar with.
The only point I really want to make is that when we have gone to more
complicated models beyond just looking at the indoor measurements, we have
seen significant Improvement in the statistics.
MEIER: Gene Meier, EPA. The first question I have for you is on the
type of instrumentation used. Your indoor personal measurements were taken
with your instrument. The outdoor numbers were obtained with what type of
instrument?
DOCKERY: It is the same cyclone. And the only difference is we used a
critical orifice to control flow instead of voltage control.
MEIER: The other question I had was, have you done any comparisons to
ensure that you are getting the same data with the two different types of
instrumentations so that that is not affecting your correlation?
TURNER: You are talking about Indoor-outdoor monitoring done with both
of the main orifices.
The personal exposure data were done with the commercially available moni-
toring unit I described.
MEIER: So, indoor-outdoor measurements were taken with the same in-
strument?
TURNER: Yes.
DOCKERY: I may have to qualify that a little bit, but we will talk about
that later.
MEIER: The other question I have is in terms of your correlation of
indoor-outdoor data. You have got a selected population group depending on
your volunteers. The homes that you are looking at may not be the average
home. So, even if you did find a correlation, that correlation may not hold
for the population as a whole.
DOCKERY: Well, I think the jump you are making is that we can relate
personal monitoring to the Indoor pollution. OK; I am not saying what the
relationship is between the indoor and outdoor pollution at this point. But
125
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with our more extensive indoor-outdoor network, then we can make that ad-
ditional step.
MEIER: The thing that we are looking at is trying to make the corre-
lation of the outdoor measurement to the indoor measurement—that is where
we would like to go eventually.
According to your data, we cannot do that because they don't correlate
well. And my question is this: whether or not in the population subgroup
that you selected, you selected a very narrow group of people or homes that
are either well-insulated because of their economic capability, with air
conditioning, etc., the house is well-sealed, compared to what you would ex-
pect in the average population subgroup?
DOCKERY: I think that you have a legitimate point there—that we don't
have a completely unbiased sample of what the population is. You know,^in
our indoor-outdoor monitoring, we tried to select homes based somewhat on
household characteristics and on variables that we are looking to better
define from this study.
As Jack Spengler said, we have gone through 2 years of this. And what
we are doing now is shutting down that monitoring, going through an analysis
phase, and trying to determine what the variables are that we have good handles
on, and what things we don't know about. Next year we will begin a new phase
of indoor-outdoor monitoring to pick up some of the other variables in the
household mix.
RICKEY: John Hickey, Research Triangle Institute. You mentioned that
whenever any of your volunteers went to work, the company industrial hygien-
ists threw them out. For whatever their motives, this may have been a bless-
ing in disguise, because the occupational limit for respirable dust is 5,000
micrograms. That may have completely masked any of your other respirable
dust data, plus the fact that the occupational exposure would be a site-specific
type of dust and not comparable to what they would be getting the rest of the
time.
DOCKERY: That is very true. It is just a little unsatisfying to us
because we have to characterize everyone in our population. We are not
selecting a population because they are working or nonworking people, and
especially in Steubenville, Ohio, we have a lot of steel workers, for example.
We actually did get some measurements in the steel mills, but I didn't report
on those.
PETERS: Edward Peters. I still don't quite understand your outdoor meas-
urements. Did each of your individuals have a personal meter and was it
directly associated with an outdoor meter?
DOCKERY: Each person has a personal meter, and each has one inside his
or her home. In addition, we had our indoor-outdoor network of monitors
running at the same time in the community.
So, we had five homes in each of these communities where we were taking
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our measurements at the same time. These were independent, in general, of
the taking of the personal measurements.
It gave us a spatial distribution across the community, and that is what
we were trying to define—whether there were big spatial distributions, so
that if a person moved from one area of the community to another, he was
getting a different outdoor exposure.
WHITE: Otto White, Brookhaven Laboratories. My question is, what is
the personal exposure to the individual obtained from the personal dosimeter
as opposed to a personal sample? By going to a weight-height measurement,
a lot of the activities performed in the home are done at that particular
height—the preparation of food, the dispensing of dry detergents.
DOCKERY: We have done some studies on this, looking at the distribution
of particulates throughout the home, looking at the vertical distribution
within the home. We really haven't seen any significant differences in any
of the homes.
I am sure these differences exist on a short-term basis. But when you
integrate that exposure over a long period of time—you know, when somebody
is cooking in the kitchen, you are going to get a high peak—but when you
average that out over 24 hours, the differences don't show up anymore.
WHITE: There is quite a bit of industrial data, obtained by putting dupli-
cate samples on a worker, that show a considerable gradient exists.
DOCKERY: Clearly, it is a different case in the industrial environment.
I mean, we are talking about levels that were two or three orders of magnitude
lower than what you see in the industrial environment, and you know, there is
rapid turnover there—air changes on the order of 1 to 2 air changes of the
whole building air per hour. There is very rapid mixing within the home.
WHITE: I would probably agree with that if that sample were taken in
the respirable zone—in the breathing zone.
DOCKERY: This system measures the respirable fraction of less than
3.5 microns, and you know, they have residence times on the order of days
because their settling velocities are very small and they are very rapidly
mixed.
I think the key to understanding the distribution is that there are
multiple sources in the home—smoking, vacuuming, and everything else that
can generate particulates outside the kitchen area. The monitoring we have
done to look at that specific question on distribution of particulates in
the home shows that it Is well mixed.
Now, we are facing contradictory evidence if you look at N0?> which
Ed Palmes points out is twice as high in the kitchen area as it Is in any
other living area of the house. So, you have that conflicting evidence ver-
sus what we see in the fine particulates, which is well mixed; no significant
differences between rooms in the house.
127
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We also looked in the vertical, too, and we can't see any differences
in the vertical.
I am not really that bothered by the difference between gases and the
particulates, because when we look at the outside air pollution data, we see
well-mixed particulates where you will see large gradients in the gaseous
pollutants in the vertical, especially in the vertical distribution.
SHAW: Bob Shaw from EPA. Isn't is possible that if you took into account
the lag between the time in which the outside levels reach a certain point
and the time it takes for it to leak into the hpuse, that your correlation
might be improved? Because you could have an excellent correlation, but it
may be displaced by some amount of time.
DOCKERY: Clearly, there is a buffering capacity in the home. We might
see the peaks following each other. In fact, other studies have shown about
a 2-hour lag in the particulates penetrating into the home.
SHAW: That would take care of it?
DOCKERY: Yes, but if that thing is happening—if we are getting a sharp
peak—potentially that is getting smoothed out. Lag is something we really
can't define with our sampling methods. We would have to go to the continuous
monitors.
LIN: Chin-I Lin, Lawrence Berkeley Laboratory. I would like to know
more about the measurements associated with the study, since one of your
slides showed indoor-outdoor pollution correlated better in wintertime than
in summertime. I would have expected it to have been the other way around.
Do you have any comment on that?
DOCKERY: I have looked at these data by season, and they showed much
better correlation in summer than winter. These indoor-outdoor data that we
presented are, you know, gross means. I don't think they are a good repre-
sentation of what the real situation is.
When you look at individuals, however, the correlation is much, much
higher in the summer than in the winter.
LIN: Do you make ventilation rate measurements in these study homes?
DOCKERY: We don't have a good indicator of ventilation. That is also
in the planning stage; we are trying to include it in our next series of meas-
urements. That is a real key.
WALLACE: Lance Wallace, EPA. Have you looked at the levels in traffic
as compared to indoors or outdoors? At least, I have noticed in my CO data,
for example, that I have got more CO in the 2 hours I commuted than in the
other 22 hours per day.
DOCKERY: Let me comment on that. I philosophically don't believe it
is important, because when you look at the amount of time you are spending
128
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In traffic, we are showing, and other studies have shown, that an hour per day
does not have a really significant impact, unless you are going to have 8
times or 20 times as much exposure in traffic.
We have got some data that show considerably higher particulate levels
in traffic. But I don't think they are large enough to really be of signifi-
cant impact.
I think that the key right now is the ventilation rate, as Dr. Lin men-
tioned—trying to determine that and relate that back to the data. We can
get information on the sources within the home, but if we don't know the ven-
tilation rate of the home, then we aren't able to parameterize that out.
SPENGLER: I feel like you do. This is where we have our difference.
We have done a lot of condensation nuclei counts in traffic. The highest
counts I ever see are associated with roadways and in automobiles* The order
is a magnitude higher. 1 think that is one exposure category with associated
exposure patterns that we have to define more carefully.
WALLACE: One might expect that the dust in traffic, particularly the
lead, and the gases have to be more toxic than the pollution in the home.
129
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The Tandem Filter Package
Robert W. Shaw, Ph.D., and Robert K. Stevens
Inorganic Pollutant Analysis Branch
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina
INTRODUCTION
The use of chemically treated filters to absorb gases of interest from
an air stream passing through the filter is not new. A computer-assisted
search of the literature has turned up about 20 research papers in which rec-
ipes for filter treatment are reported—the oldest of which was published in
1954. References are given here only to those papers appearing in the pub-
lished literature (1-14).
Almost all of this reported work is concerned with SO- and/or BLS. The
recipes for SO. collection include carbonates or bicarbonates (seven papers),
hydroxides (six papers), and zinc acetate, ferrous sulfate, tetrachloromer—
curate, and hydrogen peroxide (one paper each). The recipes for H~S collec-
tion include lead acetate (four papers), silver metal membrane (one paper),
and silver nitrate (three papers). Only a few of these papers report the
use of a prefliter for aerosol particles.
In addition to the work cited above, atmospheric analysis using chemi-
cally treated filters is reported by the British Factory Inspectorate for 26
dangerous gases, fumes, and dust in a particularly interesting series of book-
lets (22). These methods are intended to detect levels higher than the thres-
hold limit values.
The initial motives of the EPA's Inorganic Pollutant Analysis Branch
(IAPB) in developing the tandem filter package were: 1) to provide a means of
131
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separating and collecting various particulate and gaseous components of the
atmosphere; 2) to provide separation of the various chemical species of sulfur
in gaseous compounds (e.g., S02, HjS, etc.); 3) to permit the sample collec-
tion analysis to be carried out as simply and cheaply as possible with a
minimum of operator intervention but with sufficient sensitivity to allow
measurements at low (e.g., rural) levels; and, 4) to collect these components
in a manner suitable for elemental analysis using our X-ray fluorescence
(XRF) spectrometer.
The tandem filter package (TFP) consists of a series of filters in tandem,
each of which collects a different component from the air stream passing through
it. Aerosol particles are collected on porous, nonreactive filters through
which gases will pass (ideally) without effect. Gases are collected on filters
which are individually treated with reagents which will absorb and fix the
gas of interest. The following sections describe the TFP which we have devel-
oped. It separates and collects coarse and fine aerosol particles, SO. and
H.S. Analysis for elements present in the collected aerosols is carried out
by X-ray fluorescence. Analysis for sulfur is by X-ray fluorescence or by
wet chemical extraction of the collection filters; and analysis of the ex-
tract is by the Thorin-Brosset colorimetric procedure, by ion chromatography,
or by flash pyrolysis into a flame photometric detector. Development and
evaluation of the system for other atmospheric gases (e.g., NEL, nitrogen
oxides) are continuing.
AEROSOL COLLECTION
The choice of filters for collection of aerosol particles is based on
results by workers in the IPAB and their collaborators (15), and others (16).
Briefly, one uses a front filter of large-diameter pores which collects larger
particles, and a second filter of smaller-diameter pores to collect small
particles. We currently use a Nuclepore filter with 8- or 12-ym diameter
pores, and either a Nuclepore filter with 0.4-ym diameter pores or a Fluore-
pore (Teflon) filter with 1-ym diameter pores.
The collection efficiency of Nuclepore filters of large-pore diameter
has been studied in great detail by Parker (17), and that for small-pore
diameter filters by Liu and Kuhlmy (16). Their results show that collection
efficiency depends on many factors: velocity of the air stream through the
filter, particle density, filter porosity, filter flow resistance, etc.
Roughly speaking, however, the large-pore diameter filter collects particles
larger than 3-ym diameter, and the small filter collects particles at least
132
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down to 0.03-wn diameter with nearly 100 percent efficiency. The minimum
in the well-known bimodal mass distribution for typical atmospheric aerosols
occurs for particles having diameters around 3 ym; and the deposition of
particles during breathing occurs such that, very roughly speaking, particles
larger than 3 ym do not reach the lower areas of the human respiratory system.
Recent work by John et al. has shown that the tandem filters separate
solid and liquid particles with significantly different efficiencies (23).
These results, and our own experience (26), indicate that tandem filters give
only an approximate separation of fine and coarse particles.
CAPACITY OF THE PUMPING SYSTEM
In choosing a pumping system for the TFP, one is faced with the usual
compromise between the desire for the highest possible sensitivity and the
requirements that the system be relatively portable, compact, inexpensive,
etc. The specific requirements placed on the pumping system for rate of flow
through the filter depend on: 1) the atmospheric abundances of the elements
of interest, 2) the time permitted for sampling, and 3) the sensitivity
of subsequent analysis.
To illustrate how the above conditions dictate our choice of pumping
systems, let us say that we desire to be able to detect the gases SO. and H-S
at the 1 ppb (V/V) level and that the sampling time should be no longer than
8 hours. Our X-ray fluorescence analysis system has a sensitivity to S such
that about 1 yg can be detected quantitatively (to 10 percent). At 25° C
3
and 1 atmos, the concentration of S in H_S or SO- at 1 ppb is 1.3 yg/m .
Hence, to accumulate 1 yg of S on a filter of 100 percent efficiency, we must
pass about 3/4 m through it, and, to achieve this in 8 hours, the pump must
have a rate of about 1.6 1/min.
A pump, which will have the necessary capacity determined by considera-
tions as outlined above, must be able to sustain the pressure drop which
occurs across the filters at the desired rate of flow. Liu and Kuhlmey (16)
have measured coarse and fine particle collection efficiencies as a function
of pressure drop for various commercially available filters. The pressure
drop across the 1 ym Fluorepore filters used in this work for both fine
particle and gas collection is 10 Torr at a face velocity of 13 cm/sec. For
2
an exposed filter area of 8 cm , this face velocity corresponds to a flow
rate of about 6 1/min. For lower flow rates the pressure drop is corre-
spondingly lower, but Liu and Kuhlmey do not present any data for pressure
133
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.rops less than 10 Torr. We conclude that for a filter pack consisting of 3
1 wn Fluorepore filters, the pump must be capable of sustaining a pressure
drop of 30 Torr if the flow rate is to be 6 1/min. For lower flow rates the
pumping capacity is lower, and, hence, the requirements on the pumping system
are rather modest.
The pressure drop results quoted above are due to the resistance of the
filters to flow. As particles are collected on the aerosol filters, this
"loading" will increase filter resistance and, for very heavy loadings,
affect the sampling rate. For Teflon filters, the Impedance doubles at a
o
loading somewhat less than 100 ug/cm (18). Recent analyses of air samples
3
in major U.S. cities gave total suspended participates in the 20 to 60 yg/m
range (19). We conclude that filter loading is unlikely to cause excessive
demands on the pumping system for the TFP.
Size and weight limitations for a personal dosimeter create a severe
limitation on suitable pumps. A survey of personal sampling pumps by Parker
et al. (24) shows that none of a range of commercially available personal
sampling pumps can support the TFP given the demands outlined above. We
have used the Brallsford pump with the TFP in the field with good results,
and a compact and portable personal monitor using this pump has been developed
by Turner et al. (24).
GAS SAMPLING—SULFUR COMPOUNDS
The treated filter development for separation and collection of SO.
and H_S is based largely on the work by Huygen (13,14), who found that the
rate of uptake of these gases in the filter media was increased with increased
humidity. Huygen explained this behavior by attributing the rate of uptake
to diffusion into the liquid phase created by condensed moisture on the filter.
We add triethanolamine (TEA) to our collection solutions to provide a hygro-
scopic material which will keep the filter surface wet.
Sulfur is a relatively light element, and its X-rays are, correspondingly,
of relatively low energy. Consequently, if the sulfur is collected in the bulk
of the filter rather than on the surface, severe attenuation of the emitted
X-ray intensity will occur during X-ray fluorescence analysis. In order to
collect the sulfur gases on the surface of the filter, the collection solution
is applied to the filter surface in an aerosol spray. The filter medium used
is Teflon (Fluorepore), and, in order to prevent the aqueous solution from
accumulating on the hydrophobic Teflon surface in large drops, sufficient
134
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isopropanol is added to the solution to permit the solution to wet the filter
surface*
The absorbing and fixing agents for SO- and H-S are NaOH and
respectively. The absorption of SO- into basic solutions is well known.
In a basic environment, the sulfurous acid equilibrium is strongly shifted
to the ionized state, and the escape of SO- is hindered. Eventually, the
bisulfite or sulfite ion presumably undergoes further oxidation, possibly by
atmospheric oxygen, to SO,, and is fixed in the filter solution. The reaction
of H_S with metals and metal salts in the presence of water is also well
known. The reaction causes the formation of unsoluble, often colored sulfides,
which serves to fix the sulfur. Other workers have used Ag or Pb for this
purpose; however, these elements have X-ray transitions which can interfere
with detection of the S X-ray and, hence, are not suitable for X-ray emission
analysis on our instrument. We have chosen a salt of Cu which is tarnished
by hydrogen sulfide and which has no interfering X-ray transitions. The H-S
collection solution does not collect (CH-)-S.
The solution recipes for the SO- and H-S collection filters are:
2M NaOH(aq) 0.1 M Cu(N03>2 (aq)* TEA Isopropanol
S02 55% — 27% 18%
H2S — 45% 18% 37%
*The H2S solution is acidified to 0.01M with HN03
These recipes have not been systematically optimized, and adjustments
in relative amounts of their components may improve their collection proper-
ties. Work is continuing on the evaluation of the chemically treated filters
under varying conditions; e.g., gas concentration and humidity.
CHEMICAL ANALYSIS OF FILTERS
Analysis for sulfur as SO. can be carried out using ion exchange chro-
matography, or the Brosset-Thorin method (25). Filters are extracted by
placing them in a polypropylene bottle along with 10 to 20 ml of 5 x 10 N
perchloric acid. The bottle is put in a sonic bath for 20 minutes.
135
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Spectrophotometric-Thorin
The spectrophotometric-Thorin method was first presented by Persson
(21) and later modified by Brosset et al. (22). With two exceptions, this
method is identical to that proposed by Brosset et al.; instead of using
Dioxane or acetone as a solvent, isopropanol is used, and sulfanazo is used
to obtain a reference intensity level. Before analysis with the spectrophoto-
meter, the extracted solutions are put through an ion exchange column using
Dowex 50W-X8 50-to-lOO-mesh ion exchange resin. The columns are 15 cm long.
The spectrophotometer used is an Hitachi Model 101. Calibration is accom-
plished using a primary solution of 0.1N H-SO^ (Fisher) and diluting to cover
the range 10 N to 10 N in five steps. Five readings are taken at each
concentration, and the data are fit to a linear function by the method of
least squares. The calibration is done once for each set of samples or at
least once each day. Quality control solutions are run for each calibration
curve. Analysis of data shows the minimum detectable level for this method
to be 5 neq/ml. Concentrations can be determined to within +_ 5 percent.
Ion Exchange Chromatography
The second method used to determine sulfate is ion exchange chromatog-
raphy. The chromatograph used is a Dionex Model 14. If the sample has been
extracted using an acid, it is spiked with a base ( .003M NaHCO. + 0.02 M Na.CO-)
before running on the chromatograph. Calibration is accomplished by mixing
sodium salts (Fisher) with a buffer. Retention times and peak areas are ob-
tained from these standards, and a calibration curve is drawn. Analysis of
sulfate data shows the minimum detectable level to be 10 neq/ml. Concen-
trations can be determined to within +^ 10 percent.
Several SO- collection filters have been analyzed using the above proce-
dure. Table 1 shows the results for sulfur determination for three SO- collec-
tion filters by X-ray fluorescence analysis (XRF) and subsequently by extrac-
tion of the filter and ion exchange chromatography (1C).
TABLE 1
Comparison of XRF and 1C for Sulfur Analysis
Filters
715407
715408
715411
XRF
3.1
3.9
2.9
Sulfur (ug)
1C
3.2
3.7
2.8
136
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Chemical analysis of S on the H_S filters can be carried out using ion
= fc at
exchange chromatography, but the S must be converted to SO,. We are currently
investigating conversion procedures—in an initial experiment, we used a
solution of H-O- for extraction and conversion, and observed a peak corre-
sponding to SO? of about the expected size on the chromatograph. A major
interference occurs, however, because NO- from the H_S collection solution
elutes from the column just before the appearance of SO,, and the tail from
— H =
the NO, peak interferes with the quantitative determinations of SO, • This
interference could be avoided by using a different acid and copper salt (e.g.,
Cu acetate and acetic acid) in the collection solution.
Flash Pyrolysis with Flame Photometric Detector
A third wet chemical analysis for S is by sudden (flash) pyrolysis of
the extraction solution on a heated metal strip, and detection of S in a flame
photometric detector. Initial experiments using the extraction solutions
from H2S filters indicated the feasibility of this technique, but it has not
been developed further.
Summary of Chemical Analysis of Filters
Sensitivities of these various analyses for S are shown in the following
table, which assumes extraction of the filters into 10 ml of solution. The
following amounts can be determined to jh 20 percent or better:
Brosset-Thorin 800 ng
ion chromatography 16 ng
pyrolysis-FPD 320 ng
THE TFP HOLDER
We have designed a filter holder that is based on two principal criteria:
1) maximum simplicity and 2) minimum expense. An exploded view of the TFP
is shown in Figure 1. The filter frames are aligned by the four bolts which
hold the assembly together. The functions of the "0" rings as shown in Fig-
ure 1 are to hold the filter in the frame and to provide a pressure seal to
the next filter in line or to the holder assembly. It is sufficient to turn
the screws down finger tight to provide an adequate seal. In Figure 2 we show
a schematic drawing of a tandem filter package mounted on a pump assembly.
In this arrangement, the flow rate is controlled by a critical (limiting)
orifice. Although these orifices provide flow control in a very simple way,
137
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FILTER ALIGNMENT
AIR STREAM
\ VfllM
FILTER
FRAME
THE FILTER IN THE FILTER FRAME
FIGURE 1. Tandem Filter Pack, exploded view.
1 - 1 - LV
X
PANEL
MOUNTED •*.
ROTOMETER
s / / / / / *
EXHAUST
RAIN SCREEN
d
FILTER HOLDER
"O" RING
*r^ CRITICAL
ORIFICE
PUMP
///////////////s/////////
, PUMP
ENCLOSURE
FIGURE 2. Tandem Filter Pack and pumping system.
138
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they have the disadvantage of requiring applied vacua of 300 and 550 Torr
for 1.0 liter/minute (1/mln) and 14 1/mln orifices, respectively. A simple
alternative to the critical orifice is a calibrated rotameter (flow meter)
with a limiting needle valve. Our experiments indicate that the filter
frame-filter "0" ring assemblies will not tolerate flow rates greater than
2 1/min (filter face velocity of 250 cm/min). At higher flow rates, the
filters pull away from the frames. This can be avoided by using an adhesive
to seal the filters to the frames. We are now investigating the use of Teflon
filters bonded to the frames.
REFERENCES
1. Sensenbaugh, J.D., Hemeon, W.C.L. A Low-Cost Sampler for Measurement
of Low Concentration of Hydrogen Sulfide. Air Repair 4(1):1-4, 1954.
2. Lorenzen, J.A., Environmental Monitoring Device for X-Ray Determination
of Atmospheric Chlorine, Reactive Sulfur, and Sulfur Dioxide. Adv in
X-Ray Anal 18:568-578, 1975.
3. Okita, T., Lodge, J.P., Jr., Axelrod, H.D. Filter Method for the Meas-
urement of Atmospheric Hydrogen Sulfide. Environ Sci Technol 5(6):
532-534, 1971.
4. Natusch, D.F.S., Konis, H.B., Axelrod, H.D., Teck, R.J., Lodge, J.P., Jr.
Sensitive Method for Measurement of Atmospheric Hydrogen Sulfide. Anal
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Dioxide at Background Concentrations. Anal Chem 47(14):2460-2462, 1975.
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Dioxide on Membrane Filters. Anal Chim Acta 28:341-348, 1963.
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and Particulate Sulphurs in the Atmosphere by X-Ray Fluorescence Spec-
trometry. J Japan Soc Air Pollution 9(2):190, 1974.
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10. Liyv, R., Ott, R., Luyga, P., Pikkov, V. Cumulative Measurement of Sul-
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Filters. Anal Chim Acta 30:556-564, 1964.
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11:617-621, 1977.
16. Liu, B.Y.H., Kuhlmey, G.A. In: X-Ray Fluorescence Analysis of Environ-
mental Samples (Dzubay, T., ed.). Ann Arbor, Mich., Ann Arbor Science
Publishers, Inc., 1977, pp. 107-119.
17. Parker, R.D. A Fundamental Study of Particle Deposition onto Large
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N.C., 1975.
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19. Stevens, R.K., Dzubay, T.G., Russwurm, G., Rickel, D. Sampling and
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September 7-14, 1977.
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of a Reliable Personal Monitoring System for Respirable Particles*
Proceedings of the Symposium on the Development and Usage of Personal
Monitors for Exposure and Health Effect Studies, Chapel Hill, N.C.,
January 22-24, 1979. (EPA symposium.)
25. This work was developed in the laboratories of Northrop Services, Inc.,
by Russwurm, 6., Kistler, C., Stikeleather, J.
26. McClenny, W.A., Shaw, R.W., Baumgardner, R.E., Paur, R.J., Coleman, A.,
Braman, R.S., Ammons, J.M. Evaluation of Techniques for Measuring Bio-
genie Airborne Sulfur Compounds. EPA-600/2-79-004, January, 1979.
27. Parker, C.D., Lee, M.B., Sharpe, J.C. An Evaluation of Personal Sampling
Pumps in Sub-Zero Temperatures. NIOSH Report 78-117.
MAILING ADDRESS OF AUTHORS
Robert W. Shaw, Ph.D., and Robert K. Stevens
Inorganic Pollutant Analysis Branch
Environmental Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
Discussion
TRAYNOR: Gregory Traynor, Lawrence Berkeley Laboratory. You said that
not having a fine cut point may be a disadvantage in the tandem filter.
Wouldn* t it be an advantage since your nose and lungs don't have a fine cut
point?
SHAW: Well, you could take that point of view. And in fact there was
a big discussion recently at EPA having to do with the question of what sort
of samplers should be used in order to determine inspired-respired particu-
lates in the atmosphere.
I guess that my understanding of the discussion is that because people's
lung capacities are so different, and because it makes a difference whether
you are mouth-breathing or nose-breathing, and your level of ventilation,
that the inspiration curves are quite different between individuals. It
may be better to settle on some precise separation scheme rather than trying
to limit the human lung.
TRAYNOR: There is something that we do know. We know that the human
lung is not precise.
141
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SHAW: Yes. Well, I can't say any more than I did. There Is no average
human lung, so to speak. If there were, then you would want to repeat the
behavior—no doubt about it. But since different lungs act so differently,
the decision has been made to separate the particles according to their two
modes. There is more information on that.
GUDAP: Bill Gudap, Research Triangle Institute. Bob, do the essen-
tially damp or wet filters cause any problems?
SHAW: No, because the layer is very thin. So, they go right through
the X-ray spectrometer with no trouble. Actually, water doesn't adsorb X-rays
very strongly. And so that thin layer doesn't cause any trouble.
BROOKS: Joe Brooks, Monsanto Research Corporation. I have a question
concerning the pumps. Do you know what kind of pressure drops these pumps
will tolerate?
SHAW: Yes. The Brailsford can support 50 mm of Hg, pressure drop at
about 4 liters a minute. We use it to pump across some sampling devices which
have a much bigger pressure drop than this. This device has a very small
pressure drop. I don't know what it is, but it is much less than 50.
WHITE: Otto White, Brookhaven Laboratories. I am not sure that I under-
stand the comment about the comparison between the radiation exposure where
you wouldn't see the data for several days. I think my colleagues might
be at odds with me if I didn't comment, but there are pocket dosimeter devices
which can alarm. I think In this particular area—at least in the industrial
area—that you have similar type instrumentation where you want some type of
alarming device—such as the CO monitor talked about in a paper presented
earlier.
And you may have an accumulative device. So, I am not sure that I un-
derstand your meaning.
SHAW: Yes; I remember from the old days that when I would walk out of
the room where the scattering chamber was, I would occasionally wonder how
much exposure I had gotten while I was In there. We didn't have the kind
of dosimeters that you are talking about.
I was just trying to make a point that this particular system requires
that it be sent back to the lab for analysis.
One could develop chemically treated filters that would respond color-
imetrically so that you could compare right on the spot with a prepared scale.
But the system that we have now doesn't do that.
WHITE: I think both types of systems are appropriate. And whether or
not you want that type of immediate response depends upon the need for a gross
estimate.
ZISKIND: Richard Ziskind, Science Applications. You are going to get
142
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sulfate dioxide converted to sulfate. You are also going to get sulfate from
the air. You can't discriminate between those, can you, with the dosimeter?
SHAW: If you remember, the first couple of filters took out the par-
ticles and let the gases go through. And the next filters down the line
took out the gases according to their chemistry. So, that is how you get
the separation.
143
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An Evaluation of Personal Sampling Pumps
in Sub-Zero Temperatures
Carl D. Parker and Joan C. Sharpe
Research Triangle Institute
Research Triangle Park, North Carolina
INTRODUCTION
The development of the large oil reserves along the northern slope of
Alaska's Brooks Range and nearby Prudhoe Bay typifies the industrialization
currently taking place in cold environs. These developments—precipitated
by America's growing dependency on foreign oil, with its inherent threat of
crippling embargoes—are taking place in a severe environment which tests the
endurance of both men and machines. The growth of industrialization in these
and other cold regions has generated a growing need for air sampling instru-
mentation and methodology suitable for industrial hygiene investigations in
sub-zero temperatures. With a view toward these needs, the authors have in-
vestigated the suitability of currently available personal sampling pumps
for use in cold environs; i.e., to temperatures as low as -50° C. This paper
is a brief presentation of the results of these investigations. A detailed
description of these investigations is available in the Project Final Report
(1).
The pumps evaluated were tested at temperatures between 25° and -50° C.
While many environmental factors or stresses act in synergism with tempera-
ture, most are of significance only at high temperatures and were not incor-
porated into this experimental program. An environmental factor which does
have an important synergistic relationship with temperature at low tempera-
tures is humidity. Absolute humidity is low in cold environs; thus, air
sampled during these tests was obtained from a dry air manifold.
145
-------
The personal sampling pumps evaluated can be categorized into two differ-
ent groups. One group is the Coal Mine Dust Personal Sampling Units (CMDPSU),
for which a certification program has been defined (2). In order to be cer-
tified, the CMDPSU pumps must be capable of operating from their internal
battery packs at a nominal flow of 2 liters-per-minute against a resistance
of 4 inches of water for not less than 8 hours, presumably at room tempera-
ture. (There are other requirements.) This performance requirement was
used as a test condition for the evaluation tests described herein.
The second class of pumps is used with a variety of sample collection
devices under a variety of conditions. This suggests—and it is true—that
these pumps, in the aggregate, provide industrial hygienists a wide range of
sampling capability. A given pump, in contrast, may only function over a
narrow region of the aggregate range. Thus, it is impractical to define a
single set of test conditions which will be meaningful in terms of the capa-
bility of all of these pumps. The practice adopted for these evaluations
was to test each pump under a set of conditions which was somewhat representa-
tive of each pump's capabilities as stated by the manufacturer. Consequently,
the data reported herein are not intended to be used to compare one pump
against another. Instead, these data are intended only to demonstrate how
each pump's operation is affected by a low-temperature environment.
THE ALASKAN ENVIRONMENT
Since it was the rapid industrialization of the Alaskan oil fields that
largely precipitated these studies, it is of interest to briefly characterize
the Alaskan environment. North and central Alaska are divided into two cli-
matic divisions by a 600-nile stretch of low but rugged mountains known as
the Brooks Range. This expanse of mountains forms a natural partition be-
tween the Interior Basin to the south and the Arctic area to the north. The
Alaskan oil fields are located along the harsh, sub-zero environs of the
north slope of the Brooks Range; this is an area of primary concern.
The north slope of the Brooks Range is located in one of four extremely
cold winter regions. (The others are Greenland, northeast Siberia, and the
Antarctic.) In this region, the average temperature in January is -24° C,
and in July is 8° C. The temperature in some areas is below -40° C at least
10 percent of the time in the coldest month. The diurnal cycles are very
weak, and very low temperatures can persist for several days. At Pt. Barrow
in the Arctic area, for example, temperatures below -34° C have persisted
146
-------
for as long as 12 days, and temperatures below -40° C have persisted for 2
days. Temperatures of approximately 24° C have been observed at Pt. Barrow
in midsummer, but the average midsummer temperature at Pt. Barrow is only
2° C.
While extremely low temperatures largely characterize the Alaskan environ-
ment, there are other features which may also affect the responses of personal
sampling pumps. The absolute humidity, for example, is very low in extremely
cold environs. (The relative humidity is usually very high.) The average
precipitation is low, but it is usually in the form of solid precipitates.
TEST PROTOCOL
Most of the low-temperature tests described were conducted in a test
chamber which was cooled with liquid nitrogen. Figure 1 is a schematic of
the basic test facility. A pump under test sampled air metered from a dry
air manifold. The sample air passed-through a heat exchanger inside the test
chamber so that it was also cooled to the test temperature. The pressure
drop across the pump was measured with a water manometer located outside the
test chamber. The sample air was exhausted inside the chamber at the test
temperature. As illustrated, provisions were made in each pump to substitute
a power supply for the pump's batteries when the batteries became a perform-
ance-limiting factor. The volumetric change in the air mass between the roto-
meter (at room temperature) and the pump (at test temperature) is accounted
for in the data presented herein. Corrections for pressure variations were
small and are neglected.
TEST RESULTS
In the following paragraphs, some typical test results are presented
for the pumps that performed best. The reader^is cautioned that there is
some variance between pumps of a given model and some day-to-day variance
for a single pump. These data are presented as being somewhat typical al-
though they are from a single unit of each pump. As many as five units of each
pump were tested.
Mine Safety Appliances Company (MSA), Model G
The Model G is a certified CMDPSU pump and was tested with CMDPSU re-
quirements in mind. Figure 2 is a data plot that illustrates the flow rate
147
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PRESSURE
REGULATING
VALVE
HEAT
EXCHANGER
BATTERY / PUMP
LEADS
CONTROLLED - TEMPERATURE
CHAMBER
FIGURE 1. Schematic of the basic test facility.
stability of the Model G over an 8-hour period. The pump "load" or pressure
drop was approximately a constant and was 4 inches of water. During these
tests, the flow rate was sometimes adjusted to a maximum, and a power supply
was sometimes substituted for the pump's battery pack. These events are clear-
ly marked in Figure 2 and in other data plots which follow.
The data in Figure 2 show a marked flow rate dependency on temperature.
They show a significant pumping capability at -11° C and even at -22° C with-
out any adjustments. All were marginal at -30° C, and none were even margin-
ally satisfactory at temperatures below -30° C.
In Figure 3, flow rate is shown as a function of pressure differential
across the pump with temperature as a parameter for a different Model G.
These data were acquired after the pump equilibrated, nonoperating, at the
test temperature for 1.5 hours.
148
-------
•+t*C A -If »C
0-8*0 X-80»C
o-IO»C
M*A HOOCL 0
NOTES:
( I) ADJUST FLOW TO MAXIMUM
(«) SWITCH FROM • ATT CRY TO POWER SUPPLY
o .i«c
FIGURE 2. Flow rate stability, corrected for temperature, Model G.
MSA, Model G
2.0
2
i
Ul
ac
o
1-5
0»C
0*C CORRECTED
» 24* C
X[>X^K
xx'V
°x/v?
( In. of H20 )
FIGURE 3. Flow rate versus pressure differential, Model G.
149
-------
Mine Safety Appliances Company (MSA), Model S
The characteristics of the MSA Model S did not differ significantly
from the Model G, and, consequently, no Model S data are presented. Both the
Model G and Model S performed well as compared to other CMDPSU pumps tested.
Research Appliance Company (RAC), Model 2392PS
The Model 2392PS personal sampling pump is configured for use as a 2 1/min
pump; i.e., it has a rotometer calibrated between 1.6 and 2.0 1/min with a
resolution of about 0.1 1/min. Consequently, it was tested similarly to the
CMDPSU units. The RAC unit also has a similar series arrangement of rotometer,
control valve, damper, and pump as the CMDPSU units.
Figure 4 is a plot of the Model 2392PS measured flow rate, corrected for
the temperature, as a function of both time and temperature. As illustrated,
the room temperature performance was excellent. At 0° C, the flow rate was
significantly reduced but was stable over the 8-hour period. At -10° C, its
performance was marginal, and both a flow rate adjustment and a power supply
substitution were made in an attempt to maintain a satisfactory flow rate.
At low temperatures, flow rate adjustments have little effect on the Model
2392PS, and the power supply substitution was also of marginal value. At -20° C,
a flow rate adjustment at 1.5 hours had no effect at all. The pump continued
to operate from its battery pack at about 1.4 1/min (measured at room tempera-
ture) for about 5.5 hours. At -30° C, the flow rate was adjusted to a maximum,
and a power supply was substituted for the battery pack after 1.5 hours; thus,
a flow of about 1.2 1/min measured at room temperature was maintained.
The flow adjustment on the RAC unit is best described as a pinch or clamp
mechanism that clamps and restricts the sample flow tubing. At low tempera-
tures the tubing tends to remain '"set," and releasing the clamp mechanism
does not provide positive control over the flow.
Figure 5 is a plot of the flow rate of the RAC unit as a function of
the differential pressure across the pump with temperature as a parameter.
The pump was initially adjusted for a flow of 2 1/min at 4 inches of water
at 21° C. As with the Model G, it was equilibrated, nonoperatlng, at each
test temperature for about 1.5 hours.
The data in Figure 5 includes 21°, 0°, -10°, and -20° C curves. Curves
corresponding to both the measured flow rates (measured at room temperature)
and curves corrected to correspond to the test temperatures are included.
150
-------
Z.Z
NOTES:
(I) ADJUST FU)W TO MAXIMUM
(2) SWITCH FROM BATTERY TO POWEfl SUPPLY
o o—o——-o o 0* C
»«^ f 121
4 8
TIME (HOURS)
Flow rate stability, corrected for temperature, RAC Model 2392PS,
o o°C
o 0° C Corrected
C Corrected
-2O»C
20" C Corr«ct«d
0
FIGURE 5.
6
AP (In. H20)
Flow rate pressure differential, RAC Model 2392PS,
12
151
-------
Mine Safety Appliances Company (MSA). Model C-200
The MSA Model C-200 personal sampling pump is designed for a flow range
of 25 to 200 ml/min through a flow resistance of up to 2.5 inches of H20.
It is nominally adjusted by the manufacturer for a flow rate of 200 ml/min
at 1.5 inches of H.O, and most tests were conducted at this setting. The
pump incorporates a counter which indicates the number of pump strokes—thus,
the volume of air pumped.
Without altering the flow rate adjustment as received from the manufactur-
er, the Model C-2001s were operated for 8 hours against a flow restriction of
1.5 inches of lUO at several test temperatures. The results of these tests
for a typical pump are plotted in Figure 6. These curves show generally
excellent performances at room temperature at -2° C. At -10° C, the perform-
ance is marginal. In other units, the 10° C performance was unsatisfactory.
In no units were the performances acceptable at temperatures lower than -10° C.
A significant factor in the C-200's failure to perform satisfactorily
at low temperatures is that a mercury (Hg) reference cell is used in the pump's
electronics. Two voltages are available from the Hg cell, and these were ob-
served to decrease significantly with a decrease in temperature to limit low-
temperature performances.
The flow rate versus pressure-drop characteristics of the Model C-200
are shown in Figure 7 for room temperature and 0° C. The flow rates com-
puted from the counter are also included. The constant flow rates indicated
by the counters show the pump speed to be constant and indicate that a very
stable constant flow rate can be anticipated for a given temperature and
pressure differential. The measured flow rates at 25° and 0° C are observed
to vary reasonably linearly with pressure differential.
DuPont Model P-125
The DuPont Model P-125 sampling pump incorporates an electronic flow
controller that senses the air flow and controls the speed of the pump motor
to achieve a constant flow. Other distinctive features include a battery
charge status indicator, and a flow monitoring indicator that trips and latches
if the flow is interrupted or cannot be maintained near the calibrated value
for a period of time. The P-125 is specified as adjustable to flow rates
of 25 to 125 ml/min with a pressure drop of up to 25 inches of H^O. Signifi-
cantly, the P-125 is specified for an operating temperature range of -7° to
49° C.
152
-------
225r
100.
-32 °C
0 X I
4 5
TIME (HOURS)
FIGURE 6. Flow rate stability, corrected for temperature, Model C-200.
1
ui
I
250
200
150
100
'*—•«?
• +-25° C
Computed from Pump Counter
AP (In. of H20)
FIGURE 7. Flow rate versus differential pressure, Model C-200,
0" C
Corrected
_l_
7
153
-------
The flow rate stability of the P-125's was measured at 100 ml/min and
10 inches of H20; i.e., somewhat near the middle of the specified capability.
Data from a typical unit are shown in Figure 8. As with the other pumps, flow
rate measurements were made at room temperature and corrected for the differ-
ence between room and test temperatures. The performances at room temperature
are notably stable. They are also generally good at a nominal 0° and -22° C.
At -22° C, the temperature-corrected flow rates tended to be high by about 15
to 25 percent, but they were stable over an 8-hour period.
It is notable that three of the five P-125's maintained a useful flow
rate at -30° C for an 8-hour period, and that useful flow rates could be main-
tained at -30° and -40° C by substituting a power supply for the battery pack.
Thus, it is evident that the battery pack is a principal performance-limiting
factor in the DuPont P-125 at -30° C and -40° C. Therefore, useful sampling
at these temperatures may be possible with a larger battery pack.
The flow rates of a P-125 as a function of pressure differential, with
temperature included as a parameter, are shown in Figure 9. In the aggregate,
these data show remarkably linear characteristics between +25° and -20° C.
These results are further evidence of the P-125's generally excellent perform-
ance at temperatures as low as -20° C.
Accuhaler Model 808
The configuration of the Model 808 differs significantly from the other
pumps evaluated. It utilizes a limiting orifice that attaches integrally
to the pump to control the flow rate. The pump motor drives a pin-cam mechanism
that, in turn, initiates the following cycle of events. An exhaust valve to a
pump cavity opens, and a diaphragm (i.e., a piston with a flexible diaphragm
seal) is driven into the pump cavity, causing it to exhaust. At maximum
compression—i.e., minimum cavity volume—the exhaust valve closes, and the
piston/diaphragm drive mechanism springs back to a null position, opening the
motor circuit. The piston/diaphragm mechanism, driven by a spring, returns
to an extended, maximum-volume position as air bleeds into the cavity through
the limiting orifice. At the extended, maximum-volume position, the motor
is re-energized to repeat the cycle. Each cycle pumps a volume of air equal
to the displacement of the piston-diaphragm assembly, and the cycle rate is
largely controlled by the limiting orifice. Several sets of orifices are
available, and the orifice is readily changed with a wrench or nutdriver.
The flow rate stability of the Model 808's was measured using the test
154
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(I) SWITCH FROM BATTERY TO POWER SUPPLY
DUPONT P-129
120
-100
62
*^
$60
40
-22»C
-X -30 °C
.0 -2 *C
-•+Z5°C
•-40eC
4 5
TIME (HOURS)
FIGURE 8. Flow rate stability, corrected for temperature, Model P-125.
DUPONT P-125
200 -
-A——A-
-20° C
-20° C Corrected
I
\
50 -
A •"" "^^ ™*A ^^^^^ *£*™ " *"*JJ,****™^ o •«•
0 0 13 ft T
i i
024
A^*"^^» * M
0°C Corrected ~ ~"^~S
•"" ' •*"~~»"~~" »— —• •• •" ••• I.,.. ^ ..•-^-^».
*25° C
1 ( i 1 » i
68 10 12 14 16
AC (In. of H/»
FIGURE 9. Flow rate versus differential pressure, Model P-125,
155
-------
apparatus illustrated in Figure 10. (The sample flow through the Model 808
pulsates and cannot be measured with a rotometer.) The restricting valve was
set independently to drop 1.5 inches of H_0 at a flow rate of 100 ml/min.
Sample air was drawn through the restricting valve from the dry air manifold.
When flow measurements were made, the sample was temporarily drawn from the
soap bubble meter.
The limiting orifice that attaches to the pump is the only flow control
option available to the user. For a given orifice, the stability of the pump
is likely to be enhanced if the pressure drop across the orifice is larger than
the drop across the sample collection medium (i.e., the pressure regulatory
valve in Figure 10.)
The flow rate stability data for a typical Model 808 with a 100 ml/min
orifice is shown in Figure 11. (The flow rates were measured at room tempera-
ture, but the values plotted are corrected to the respective test temperature.)
At 25° C, the flow rates are reasonably uniform and tend to be within about
5 to 10 percent of 100 ml/min. The pumps did not operate for an 8-hour period
at 100 ml/min. It is clear that a lower flow rate would tend to extend the
operating period significantly. The pump operates on a periodic basis—a
quasi "duty cycle"—in that the battery circuit is closed and the motor cycles
the cam. During the "off" period, there is no load on the batteries.
BATTERY CONSIDERATIONS
All of the pumps evaluated were powered by secondary (i.e., rechargeable)
sealed, sintered plate nickel cadmium (Ni-Cd) batteries. These batteries
have very low internal resistance and can deliver high currents with little
loss of voltage. A very significant feature is that when delivering moderate
currents, they will perform satisfactorily at very low temperatures. These
cells can supply useful but reduced energy at temperatures as low as -40° C (3).
The capacity of a Ni-Cd battery depends largely upon the manner of battery
operation. Cells are usually characterized at 25° C and at a stated discharge
rate; e.g., C/5 or C/10, where C is the rated ampere-hour capacity. The actual
capacity is a function of the discharge rate and tends to decrease signifi-
cantly with an increase in the discharge rate. A cell characterized at a C/5
(5 hour) rate will yield about 80 percent of rated capacity at a C/l (1 hour)
rate, and about 108 percent of rated capacity at the C/10 rate. The cell
capacity is also influenced by temperature. At 0° C, for example, a Ni-Cd
cell will deliver approximately 90 percent of its room temperature capacity (3).
156
-------
ROOM
SAMPLING
MANIFOLD
\
TEST CHAMBER
DRY COMPRSSEO
AIR
PRESSURE
REGULATING
VALVE
SOAP BUBBLE
FLOW METER
PUMP
FIGURE 10. Test apparatus for the Accuhaler Model 808.
I20r
(I) SWrrCH FROM BATTERY TO POWER SUPPLY
MDA ACCUHALER 808
40,
3 4
TIME (HOURS)
FIGURE 11. Flow rate stability, corrected for temperature, Model 808.
157
-------
There is very little data available that is descriptive of the reliability,
i.e., cycle-life, of Ni-Cd cells at low temperatures. Data that are available
show a seriously reduced cycle-life at -18° and -34° C; however, these results
are attributable to the establishment of unsatisfactory operational conditions
rather than any failure to the cell itself (3). The reader should be mindful
that many factors other than temperature influence the cycle-life and perform-
ance of Ni-Cd batteries. These include use factors such as routine depth
of discharge, recharge practices, and discharge rates.
The results of these evaluations suggest that the Ni-Cd batteries used
in personal sampling pumps yield good performances. While they are inadequate
for the desired performances at low temperature, the problem is due largely
to pump characteristics. Indeed, battery capacity is reduced at low tempera-
ture; however, the pumps demand more current. Thus, the batteries must dis-
charge at the higher rate, which further reduced their capacities.
The battery pack should be used with care regardless of temperature.
Recharging should be carried out with the charger supplied by the manufacturer
according to instructions and at room temperature. In lieu of this option,
the batteries should be charged at a constant C/10 rate for about 15 hours,
or at a C/20 rate for much longer periods. (C is the ampere-hour rating of
the battery.) The battery should not be recharged unless a significant portion
of its capacity has been dissipated; e.g., C/3 ampere-hours.
SUMMARY AND RECOMMENDATIONS
All of the personal sampling pumps evaluated are sensitive to temperature
changes between 25° C and -50° C. There is considerable variance in the sensi-
tivity of the different models evaluated, and some variance within a single
model. All of the pumps evaluated are useful sampling instruments at 0° C,
and none are functional at -50° C. Between these extremes, the different models
are affected differently by temperature. From among these pumps, the industrial
hygienist can select a pump suitable for most any application to a low tempera-
ture of -20° C. At lower temperatures, however, the options are severely
limited. For the pumps evaluated, reasonable low-temperature limits are tabu-
lated as follows:
158
-------
PUMP LOW TEMPERATURE LIMIT (° C)
MSA Model G -20
MSA Model S -20
RAC Model 2392PS 0
MSA Model C-200 0
DuPont Model P-125 -30
MDA Model 808 -20
It should be emphasized once again that a comparison of the pumps evaluated
was not an objective of this effort. The pumps are rated or specified dif-
ferently by their manufacturers, and, consequently, comparison is somewhat un-
fair. Moreover, they were tested differently. This is especially true of
the pumps which were not tested as CMDPSU units. However, there is an obvious
quality of construction and room-temperature performance about some of these
pumps which should be acknowledged. The MSA Models G and S, the MSA Model C-200,
and the DuPont P-125 perform well at room temperature and give an impression
of quality construction. The Model 808 has a different operating mechanism
which could have some advantages. It should, for example, be relatively in-
sensitive to battery status until the pump fails to operate at all. The Model
2392PS is similar in many respects to the Models G and S. It is lighter, has
a smaller battery pack, and performs well for 8 hours at room temperature.
One objective of the evaluation effort was to evolve a set of recommended
standards for personal sampling pumps for use in cold environs. We concluded,
however, that the personal sampling pumps evaluated were not designed for use
in sub-zero environments. Instead, they were designed and optimized for use
in temperatures near 25° C. We conclude further that, in response to the
solicitation for pumps for this evaluation, standard models were submitted
without significant changes to optimize these units for low temperatures
because of insufficient time and incentive. Consequently, standards based
upon the results of these evaluations will tend to be premature and somewhat
pessimistic. Standards recommended in the Final Report should be considered
as preliminary, subsequent to further investigations and developments (1).
ACKNOWLEDGEMENTS
This study would not have been possible without the cooperative support
of the manufacturers of the pumps evaluated. These manufacturers made pumps
available for testing at no cost or risk to the authors.
This study was sponsored by the National Institute for Occupational
Safety and Health through Contract No. 210-76-0124.
159
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REFERENCES
1. Parker, C.D., Lee, M.B., Sharpe, J.C. An Evaluation of Personal Sampling
Pumps. Final Report, NIOSH Contract No. 210-76-0124, DREW Publication
No. (NIOSH) 78-117, September 1977.
2. Code of Federal Regulations, Title 30, Part 74.
3. Bauer, P. Batteries for Space Power Systems. (NASA SP-172) TRW for
NASA, Redondo Beach, Calif., 1968.
MAILING ADDRESS OF AUTHORS
Carl D. Parker and Joan C. Sharpe
Research Triangle Institute
P.O. Box 12194
Research Triangle Park, North Carolina 27709
Discussion
TURNER: Bill Turner from Harvard. Were you able to make any pulsation
measurements in any of your tests?
PARKER: No, we did not. One of the pumps that we looked at was very
unique in that it had a critical orifice that controlled the flow. The
pump exhausted the cavity of the diaphragm. The electrical system became
inoperative at that point. It came to a stand position, and then a spring
turned the diaphragm to its stand position, opening the cavity and drawing
the sample through a critical orifice.
This pump had a very unusual pumping mechanism. It would take the sample,
pull it through the orifice, and then recycle the diaphragm. But all these
were tested at relatively stable constant flow rates.
160
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Electrochemical Air Lead Analysis for
Personal Environmental Surveys
Francis J. Berlandi, Ph.D., Gerald R. Dulude, Reginald M. Griffin, Ph.D.,
and Eric R. Zink, Ph.D.
ESA Laboratories, Inc.
Bedford, Massachusetts
INTRODUCTION
Exposure to lead via airborne particulates has become a cause of in-
creased concern in the United States. The U.S. Government, via the Environ-
mental Protection Agency, has recently proposed an ambient air lead standard
of 1.5 jig/m (1). The justification for the enactment of this standard has
been the increased lead exposure from both mobile and stationary lead sources
by the general populace. This has been documented by the monitoring of blood
lead levels in both children and adults in high- and low-exposure zones. The
recommended method of measurement for determining air lead exposure is the
collection of the air particulate material on a filter medium, as in the
normal TSP methodology. The lead is then extracted from the filter into
a solution and measured by a chemical technique.
Since 1968, the use of anodic stripping voltammetry (ASV) to measure
blood lead levels in both children and adults has become quite widespread.
Over 20 percent of the medical and clinical screening facilities in the
United States use anodic stripping voltammetry as their major technique for
blood lead analysis (2). This paper describes the use of a rapid electro-
chemical technique for the measurement of air lead using ASV.
The method (3) is summarized as follows. The air filter to be measured
is placed in a test tube or another suitable container. The filter is soaked
for 10 minutes in a Metexchange® reagent. The lead particulate is eluted
and/or dissolved from the filter matrix with mechanical agitation. The sample
161
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reagent mixture containing both the solution and the filter is placed directly
on the electrode assembly on the ESA Model 3010A Analyzer. The analysis se-
quence is initiated, and, approximately 90 to 150 seconds later, a quantita-
tive measure of the amount of lead on the filter is available to the operator
as a digital display. A permanent record is also available in the form of
a recorder tracing.
The basic advantages of the technique include: a practical lower limit
of measurability for lead in the 1 to 10 nanogram range; accuracy and preci-
sion which compares favorably to a standard reference technique; and a conven-
ience of analysis which is both rapid and simple.
A GENERAL DESCRIPTION OF THE ASV TECHNIQUE
Anodic stripping voltammetry is an electrochemical technique involving
two steps. The first step is the plating or reducing of metal ions into a
mercury electrode by holding the electrode potential at a more negative value
than is necessary to cause the reduction of those metal ions of interest*
The potential of the electrode is then rapidly and linearly varied in a posi-
tive or anodic direction. When the potential of the test electrode reaches
the formal potential of a metal ion/metal couple, that particular metal will
reoxidlze back into solution, and a current will flow in the measuring circuits
external to the electrochemical cell. Because each metal has a unique formal
potential, a number of different metals can usually be analyzed simultaneously.
Figure 1 is a simplified picture of the two-step process called ASV.
In the first step, the metals are being reduced by holding the electrode at
a controlled potential. If the metal ions were present in relatively high
concentrations, it would be possible to quantitatively measure them during
the reduction step by integrating the area under the current-time curve dis-
played in the top half of Figure 1. When dealing with parts-per-billion
(ppb) metal ion concentrations, the contribution from reduction of all re-
ducible metal ions present to the current-time integral is small (as repre-
sented by the cross-hatched area of the plot).
The major fraction of the current-time integral will be due to reduction
of impurities (such as hydrogen ion) present in excess of the metal ions. If,
at the end of the plating step, the potential of the electrode is varied in
a positive direction, the current signal obtained will be almost entirely due
to reoxidation of each reduced metal present in the electrode. This step is
depicted in the lower half of Figure 1.
162
-------
M"
M"
i M
V
M"
M"
M"
PLATING STEP
Controlled Potential Electr.
M'
M'
M'
M'
M'
*&/
1
time
,
M'
M'
M'
M'
M'
STF
Anodic
0
1
DIPPING STEP
Stripping Voltammetry
(ASV)
M"
M"
M"
\
.•• r
M"
M"
VI"
FIGURE 1. Plating step and stripping
step.
time
Bi
-175 -340 -530
FIGURE 2. ASV scan.
matrix: 4F LiCI, 0.5F NaAc
phh 4.5
plate pot'I-. -1100mv
plate t ime: 30 minutes
sweep rate •. 60 mv sec
metal concentrations 20 ppb
Stripping Peak Potentials
vs. the Ag /AgCI reference
163
-------
When the test electrode is composed of a thin film of mercury deposited
on an inert substrate, such as the waxed graphite electrode, the result of
the anodic stripping step will be a very sharp and well-resolved current
peak for each metal deposited (into the thin film of mercury) during the
plating step. A typical ASV scan is shown in Figure 2.
Peak potentials serve to identify the mercury-soluble metals in the
sample. The height of each peak is proportional to the amount of metal ion
reduced into the mercury and is, therefore, proportional to the amount of
metal present in the sample. Figure 3 illustrates the kind of calibration
curve linearity that is regularly obtained with the composite mercury graphite
electrode (CMGE).
ASV AS A REFERENCE METHOD
Most analytical techniques (4) for air lead analyses require that the lead
particulate be extracted, dissolved, or totally digested from the air filter
matrix. The validity of the rapid, ASV analytical methodology is established
by comparing the measured lead values from this -new- methodology to a second
set of values obtained by using an EPA-recommended, acid extraction method
on the same or duplicate samples. The EPA methodology is fully described in
the Proposed Ambient Air Standard for Lead and is compatible with a final lead
determination by atomic absorption on anodic stripping voltammetry. At this
point, we define the ASV wet digestion as denoting an ASV analysis performed
on conventionally digested samples, whereas ASV extraction will denote the
rapid and relatively newer ASV techniques using samples treated with Metex-
change® reagent.
Since most of the comparison data developed in this study compare the ASV
extraction technique to the ASV wet digestion methodology (5), Table 1 summa-
rizes the ASV wet digestion performance on standard NIOSH lead air filter
sets from 1974 to 1977. The data demonstrate an excellent agreement of ASV
wet digestion data with results obtained from a variety of other methods such
as AAS and dithizone. Three years of comparison studies on ESA laboratory
performance on both air filter and blood lead proficiency standards provide
additional data as to the inherent validity of the ASV wet digestion method.
The ASV wet digestion methodology is also compared for agreement with AA
results obtained on duplicate samples of extract from hi-vol filters. The
summary of results is shown in Table 2. Based on the results shown in both
164
-------
1600
1400
1200 —
1000
800
400
600 —
200 —
0
200 400 600 800 1000
nanograms jnetal
FIGURE 3. Typical ASV calibration curves.
165
-------
TABLE 1
NIOSH "PAT" Summary for Air Lead
Number of value pairs = 64
Intercept = .00087
Slope = 1.01140
Correlation coefficient » .9914
If = .10057 "PAT" result average
Y = .10086 ESA reported average
TABLE 2
Hi-Vol Filter Results ASV Wet Digestion versus AAS
Number of value pairs = 20
Intercept = .235
Slope « .969
Correlation coefficient = .998
X" - 12.65 ASV wet digestion
Y = 12.50 AAS
Tables 1 and 2, the use of the ASV wet digestion methodology as a reference
method in the development of the ASV extraction screening approach is techni-
cally sound. In addition, it can be shown that the ASV extraction results
can be compared to either AAS or ASV wet digestion-generated data to establish
the validity and accuracy of the methodology.
AIR FILTER ANALYSIS
The previous section has established the technical basis for the use of
ASV wet digestion in lead analysis for those not familiar with the electro-
chemical methodology.
This section summarizes the data obtained in the direct comparison of
the ASV extraction air filter technique to both EPA filter standards and ac-
tual field samples.
Recovery of lead on air filters with this direct ASV extraction method
was checked using EPA standard air filters against the atomic absorption tech-
nique. Results are shown in Table 3.
166
-------
TABLE 3
EPA Filter Strip Comparison
EPA STANDARD FILTER ASV EXTRACTION AA
ug Pb/filter ug Pb/fllter ug Pb/filter
0 0 0.1
115 108 110
300 284 270
400 409 365
675 695 595
TABLE 4
Industrial Environment Filter Study
Number of pairs «= 12
Slope - .984
Intercept » .96
Correlation coefficient » .999
IT « 73.17 ASV wet digestion
Y • 72.95 ASV extraction
TABLE 5
Oxide Dissolution Study
TIME
1 mln
3 min
6 min
10 min
15 min
PbO
89%
91%
96%
92%
99%
Pb02
75%
98%
97%
97%
103%
Pb3°4
64%
84%
96%
99%
97%
Also, air filter pairs were checked from an industrial collection site
against total digestion procedures. Duplicate air particulate samples were
collected from each of several work environments. In each case, the dupli-
cate pairs were collected simultaneously with equal collection efficiencies.
One filter was analyzed using the direct ASV technique, and one was analyzed
using a total digestion ASV technique. Results are shown in Table 4.
Dissolution studies on the more common oxides of lead that could occur on
the air filter matrix were evaluated. Measured amounts of PbO, Pb02, and Pb30,
were placed in Metexchange* reagent. The amount of lead dissolved versus
time was measured at various time levels. Since the particulate size used in
167
-------
TABLE 6
Volumetric Air Lead Calculations
TIME
5 min
30 min
60 min
8 hr
3
0.1 yg/m
Filter
.001
.006
.012
.096
Air Concentration (yg Pb/m )
3 33
1 yg/m 10 yg/m 50 yg/m
Filter Filter Filter
.01
.06
.12
.96
.1
.6
1.2
9.6
.5
3.0
6.0
48.0
100 yg/m
Filter
1.0
6.0
12.0
96.0
the study was greater than 50 microns, the results are a conservative estimate
of the rate of dissolution for typical lead species found on a filter substrate.
Table 5 summarizes this data. Dissolution was complete in 6 to 10 minutes.
Discussion and Results
The advantage of both the ASV wet digestion and ASV extraction to air
pollution measurements is their ability to accurately measure lead down to a
level of 1 to 10 nanograms. The implications of this statement can be seen in
the namagraph of Table 6. Using a sample time of 5 minutes at an air flow of
2 liters/minute will provide the user with 10 nanograms of collected lead on
the filter if the air lead level is 1 yg/m .
The utility of the ASV extraction, rapid lead screening technique is best
demonstrated in a limited field study conducted using OSHA-type portable air
samplers. The study was conducted on December 8 and December 9, 1977. The
purpose was to derive data on the relative lead exposure to a typical suburban
commuter during a typical work day. A series of samples were collected during
the work-day period. The chronology is summarized as follows:
SAMPLE 1: Air sampling in suburban industrial facility in Bedford, Mass.,
adjacent to no known air lead sources except limited vehicular traffic.
SAMPLE 2: Air sampling during drive from Bedford to Winchester, Mass.,
during the evening commuter traffic.
SAMPLE 3: Air sampling .during drive from Winchester to downtown Boston
after major commuter rush hour.
SAMPLE 4: Air sampling at a professional society meeting held in a
second-floor conference room of an office building in downtown Boston.
168
-------
SAMPLE 5: Air sampling during drive from Boston to Winchester, Mass.,
in the midevening traffic.
SAMPLE 6: Air sampling during drive from Winchester to Bedford, Mass.,
on the following morning during commuter traffic.
The exposure study results are presented in Table 7 and demonstrate
the flexibility of the analysis to respond to a variety of sampling times.
The data also indicate the consistent air lead levels accompanying the driving
segments of the day.
The results demonstrate that the lead exposure on this day during transit
in a vehicle is much higher than the lead exposure measured in the suburban
industrial facility or in the downtown Boston office building. Plans are under-
way to extend the effort to monitoring pedestrian and nondriving exposure to
lead while in residence at various types of roadway conditions. Due to the
inherent simplicity of the method, the onsite evaluation of lead exposure is
possible using an ASV analyzer and an appropriate power source, although the
data presented here represents laboratory analysis.
A second series of samples was obtained on February 28, 1978, and analyzed
using a wet digestion methodology. The sample summary is as follows:
SAMPLE A: Air sampling during drive to Waltham, Mass., from Bedford on
Route 128.
SAMPLE B: Air sampling during meeting in office building one-half mile
from Route 128.
SAMPLE C: Air sampling during drive to Bedford from Waltham on Route 128.
TABLE 7
December Monitoring Study
SAMPLE TIME
1 1013
2 1710
3 1755
4 1835
5 2100
6 0810
DURATION
127 min
30 min
40 min
145 min
23 min
25 min
LEAD EXPOSURE
3
.04 yg/m
o
4.90 yg/m
3
4.40 yg/m
.69 yg/m3
4.46 yg/m3
4.06 yg/m3
169
-------
SAMPLE D: Air sampling In office building in Bedford.
SAMPLE E: Air sampling during drive from Bedford to Winchester, Mass.
SAMPLE F: Air sampling during drive from Winchester to Cambridge, Mass.
SAMPLES G & H: Air sampling in two meeting rooms at MIT.
SAMPLE I: Air sampling during drive from Cambridge to Winchester.
SAMPLE J: Air sampling during morning commute, Winchester to Burlington
to Bedford.
The exposure results are presented in Table 8 and show a similar pattern
to the December exposure data.
This second set of data is consistent with the December exposures ob-
tained using the rapid screen methodology. In both sets, the use of short-
term samples to document the exposure during specific event periods provides
the experimenter with a more accurate reconstruction of exposure events.
In conclusion, the sensitivity and convenience of the ASV rapid screen
methodology offer extreme flexibility in the design and implementation of an
ambient, air lead, field study program.
TABLE 8
February Monitoring Study
SAMPLE
A
B
C
D
E
F
G
H
I
J
TIME
1114
1125
1210
1230
1625
1715
1745
1910
2200
0800
DURATION
17 min
39 min
12 min
57 min
24 min
20 min
79 min
157 min
30 min
27 min
EXPOSURE
3.2 ug/m3
.9 ug/m3
9.2 ug/m3
3
•5 ug/m
4.7 ug/m
2.1 ug/m3
3
•7 ug/m
o
.4 ug/m
3.8 ug/m3
1.7 ug/m3
SITE
driving
in bldg.
driving
in bldg.
driving
driving
in bldg.
in bldg.
driving
driving
170
-------
REFERENCES
1. Proposed National Ambient Air Quality Standard for Lead. Federal Register
42, #240, p. 63076. December 14, 1977.
2. Blood Lead Proficiency Testing Summary. HEW-CDC Report. December 1977.
3. Direct Determination of Lead in Air Filters by Anodic Stripping Voltam-
metry. ESA Methodology, TMA-17.
4. NIOSH Manual of Analytical Methods, Volume I. P & CAM 173. April 1977.
5. Procedure for Analysis of Aerosol Pb and Cd Particulates by ASV. ESA
Methodology, M-30.
MAILING ADDRESS OF PRIMARY AUTHOR
Francis J. Berlandi, Ph.D.
ESA Laboratories, Inc.
43 Wiggins Avenue
Bedford, Massachusetts 01730
Discussion
SCHEIDE: Gene Scheide, Environmetrics. In the automobile, did you use
leaded or unleaded gasoline?
BERLANDI: I used leaded gas; we haven't gone to an unleaded car yet.
I have a Volvo that is kept tuned up pretty well.
SCHEIDE: It would be interesting to compare to see how much emission
you are getting from other vehicles on the road.
BERLANDI: Right. As I said, these are representative of a variety of
driving conditions. I suspect that either I am entraining the dust, or it
is coming from my car. I don't know. But certainly it is something that
has to be investigated.
As I said, this is done on our own. We would certainly like to pursue
this and do the study the way it should be done for documentation of this
type of exposure.
CLIFFORD: Paul Clifford, Carnegie-Mellon University. If you are using
a filter of 0.8 microns for a size cut, how much of the lead is smaller than
that? How much of it are you missing?
171
-------
BERLANDI: That is one thing that you have to remember about a 0.8 micron
filter. It doesn't mean that particles less than 0.8 get through. The filter
is sort of like a sponge. To my best knowledge, from the tests that I have
run on particle entrapment, I think you are getting down to maybe 0.02, 0.01
microns.
People have tried bubbler techniques behind filters in order to capture
the particle lead or any of the tetraethyllead. And from what they have been
able to determine, 97 to 99 percent of the lead is captured on the filter in
these cases.
CLIFFORD: So most of the combustion product of the tetraethylleads
are actually very large?
BERLANDI: Yes. They can end up on the filter strip particles. Maybe
someone else here would want to talk about vehicle exhausts. I am not an
expert on it. But I know that those who have looked for the gaseous lead
compounds, using the filter, have not seen significant transport to the in-
teriors through the filter.
172
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Studies of Semiconducting Metal Oxides in
Conjunction with Silicon for Solid State Gas
Sensors
Angel G. Jordan, Ph.D., David J. Leary, Ph.D., Gulu N. Advani, and
James 0. Barnes, Ph.D.
Carnegie-Mellon University
Pittsburgh, Pennsylvania
INTRODUCTION
This paper reports work at Carnegie-Mellon University dealing with semi-
conducting metal oxides, such as SnOj and ZnO, that hold promise as base ma-
terials for gas sensors. The research alms at the understanding of the role
played by dopants properly selected to enhance the sensitivity of the materials;
at the understanding of the mechanisms of electron exchange between bulk and
surface when the gases to be detected are sorbed onto the surface; at the under-
standing of the transport of charge carriers; and at the understanding of the
mechanisms involved in the preparation of the materials and devices, and the
characterization of such materials and devices. The research purports to study
the feasibility of materials* deposition and/or growth on conventional semi-
conductors, such as silicon. The work is being carried out by an interdisci-
plinary team from the Departments of Electrical Engineering, Metallurgy and
Materials Science, and Chemical Engineering.
An integral part of this research program is work aiming at the under-
standing of the most prominent commercially available devices, and the incor-
poration of these devices and the devices emerging from our own research in a
portable air pollution/combustible gas monitor. This part of the research is
presented in a separate paper by D.T. Tuma and P.K. Clifford in these Pro-
ceedings.
This paper starts with a section on SnO. as a material for gas sensors.
173
-------
Details of sample preparation by Radio Frequency Sputtering techniques are
given, and analytical characterization of the Sn02 thin films is described.
The electrical characterization of the films, with a variation of the oxygen
pressure within the sputtering ambient, is presented. A scheme is proposed
which incorporates a stable SnO- film and silicon bipolar transistors in an
integrated structure.
This paper proceeds with a section on ZnO as a material for gas sensors.
It focuses on polycrystalline thin films and the strong dependence of film
resistivity and gas sensitivity on grain size. The role of certain dopants in
controlling the stability of the films and the gas sensitivity to certain
gases is reported. Response times, reproducibility, and long-term stability
of films investigated appear to be adequate.
The last section of the paper deals with H_ and H_S detectors utilizing
MOS structures. These devices are Pd-SiO.-Si Schottky barrier diodes and
MOS capacitors. Both appear to be very sensitive to H_ and H_S.
A scheme is presented for incorporating Zeolite sieves on metal oxide
devices for separating gases before detection by the sensor. This technique
is also amenable for incorporation in Pd-SiO^-Si devices.
Sn02 AS A MATERIAL FOR GAS SENSORS
Sample P r e pa ration
Thin films of tin dioxide are prepared by Radio Frequency Sputtering.
The apparatus consists of a Randex 2400-J Sputtering system equipped with an
He closed-cycle cryopump with variable power splitting facilities for the
sputtering process. The target material is a sintered disc of SnO. prepared
by pressing high-purity SnO_ material obtained from Alfa Ventron Corporation.
A base pressure of 3.5 x 10 Torr is routinely obtained. The sputtering
is performed by plasma composed of high purity (five 9's) argon and oxygen
mixtures in dynamic equilibrium within the system. A water-cooled substrate
table with tungsten-halogen lamps provides a deposition temperature range
from about 120° to 450° C. The RF power supply is coupled to the anode (sub-
strate)-cathode (target) assembly through a tunable impedance matching network.
Typical RF powers for a deposition are in the range of 500 to 700 watts.
Similar techniques are used for ZnO depositions.
174
-------
Analytical Characterization of SnO Thin Films
Sn and 0_ combine to form several compounds, some of which are SnO, SnO_,
and Sn^Og. The tetragonal structure of SnO- has a lattice structure given
by a - b « 4.738 X, and a c/a ratio of 0.675.
Films are analyzed for their morphology, structure, and composition.
The Scanning Electron Microscope (SEM) and the Transmission Electron Microscope
(TEM) complement each other in supplying information of grain size. In gen-
eral, it is found that, for depositions carried out in an ambient of Oy^r
at a pressure of 25 mTorr, the grain size is typically of the order of a few
hundred angstroms.
Structural information is obtained from TEM and X-ray diffraction studies.
The information from these data suggests that the films are polycrystalline
in nature, with no particular orientation with respect to the plane of the
substrate.
Elemental analysis of the films is carried out with the Auger Elemental
Spectroscopy techniques (AES). The results are to be interpreted with caution
because of the difficulties with the measurement system; however, preliminary
results show that the Sn-to-0 ratio for stoichiometric SnO. is about 1.60.
Figures 1 and 2 summarize the results of analytical characterizations
on a Sn02 thin film.
Electrical Characterization of Sn02 Films
Figure 3 shows a plot of the room temperature measurement on as-sputtered
films of Sn02 with a variation of the oxygen pressure within the sputtering
ambient. As can be seen, the films for 0 percent and 100 percent 02 pressures
(corresponding to 100 percent Ar and 0 percent Ar, respectively) possess high
conductivities. The curve goes through a maximum in resistance, presumably
at that point where the stoichiometric composition of SnOj is reached. More
studies are underway to clarify this aspect.
Gas Sensitivity Response of SnOg Films
Several samples of SnO« have been studied for their response to oxygen
and hydrogen. Studies with 0- reveal information regarding chemisorption
phenomena. The tests are carried out in a clean vacuum system that can be
175
-------
26.609
Sputttrvd Film
33.88
51.8
FIGURE 1. Typical X-ray diffraction pattern for a thin film of SnO-. The
figures correspond to the Bragg angles (26) as specified In the ASTM cards.
The spread in the peaks is probably due to a strain in the lattice.
MotVldl
Sn/O
peak
ratio
SnO,
1.60
SnO 2.00
Conlftrllt 1.72
NESA gtau 1.80
100
300
500
700
900
FIGURE 2. Typical Auger spectrum of SnO_. The relative ratio of Sn-to-0
peak height remains substantially constant, although their absolute values
differ from one region to another depending on the morphology. The table shows
the relative ratios for various Sn/O combinations.
176
-------
Sputtering Ambient
oxygen / argon
25mTorrt600WRFps«
10 -
CC
*bb
L~40/lA
Gas Modulated
Resistor
I" 1
'CC
rce
BIPOLAR
TRANSISTOR
ISOLATION
OXIDE
HEATER/OXIDE
50
75
HEATER
SILICON
FIGURE 3 (left). Variations of resistance of sputtered SnO_ films as a function of the oxygen percentage
in the sputtering ambient. FIGURE 4 (top right). The proposed integrated gas sensor. The Sn02 serves
as a gas-modulated base resistor that alters the quiescent level, and hence the output voltage. FIGURE 5
(bottom right). Bipolar transistor structure incorporating an isolation region for thermal shielding.
The right-hand portion of the figure has a heater and the gas-sensitive oxide film. Figure used in compu-
ter study of heat analysis to evaluate the temperature distribution on the chip.
-------
pumped down to 1 x 10 Torr. The sample is heated in this pressure range for
an hour, after which 0. is introduced into the system. Very precise amounts
of the gas can be introduced by means of a special injection port. Readings
of the resistance as a function of time, when plotted on semi-log paper, illus-
trate a linear dependence, which is typical of an Elovic plot. This, in turn,
suggests a surface reaction. The sample is allowed to come to equilibrium
in this environment, after which controlled amounts of H. are introduced in
the system. A plot of the fractional change in resistance versus the prepa-
ration conditions of the sample shows Increasing sensitivity for samples pre-
pared in decreasing amounts of 0. in the sputtering ambient.
However, stability studies show exactly the opposite effect. Thus, the
most stable films are those prepared in 100 percent 02. The opposing nature
of these two results suggests that there is an optimum sputtering environment,
which probably agrees with the optimum doping levels appropriate to the grain
size of these films.
Devices
The results of the previous section indicate that some sacrifice can be
made on the sensitivity of the films in order to considerably enhance the film
stability. An increase in the sensitivity may, however, be made by coupling
the film to an amplifying device such as a bipolar transistor. Figure 4 shows
such a device, where it may be seen that the SnO_ layer serves as a variable
base bias to the transistor Ql. Figure 5 illustrates a prototype of such a
device which is currently being developed in our laboratory. The need for
integrating such a device calls for some isolation between the heater and the
transistor. Such an isolation has been attempted with some success. A com-
puter simulation of the heat transfer in such a device has also been carried
out, suggesting the feasibility of the idea. We should be reporting on these
aspects in short term.
ZnO AS A MATERIAL FOR GAS SENSORS
Polycrystalline Film Studies
Electrical properties of ZnO surfaces are very sensitive to ambient con-
ditions, and high-purity, single crystal specimens are valuable for studying
such processes. Gas-solid interactions by chemisorption processes involve
charge transfer of electrons to or from surface layers. Figure 6 illustrates
a specific example of oxygen chemisorption on n-type ZnO. Oxygen acts as an
178
-------
Dlitrtbutkxi
of oqrflM
occtptor
wrfoci
•wrfoc*
FIGURE 6 (left). Surface band bending in polycrystalline ZnO has a spatial
extent of the order of a Debye length, L_. FIGURE 7 (right). Conduction
process in polycrystalline ZnO where adsorbed oxygen plays a role at the
intergranular contact.
acceptor, introducing surface acceptor states that deplete electrons from the
solid. The energy band bending depicted in this figure extends over a distance
of the order of a Debye length, L_, into the solid.
Conductivity measurements on single crystal specimens, however, will not
reflect any surface sensitivity if L is small compared to the sample thickness.
In polycrystalline films, the surface charge transfer process is still at
play, and, with small crystallite sizes, the surface layers dominate the
measured conductance. Figure 7 is an illustration of possible processes in
polycrystalline films where individual grains are connected to form a conduc-
ting medium.
For the first situation, we show adsorption of oxygen at free surfaces.
This establishes a depletion region accompanied by a large reduction in free
charge. The depletion region can extend through the intergranular contact,
as shown, pinching off the conduction path between grains. In the bottom
figure, oxygen is adsorbed along grain contacts as well, resulting in a poten-
tial barrier to carrier flow between adjacent grains which is modulated by the
amount of oxygen on the surface. The expression for the measured resistance
of such films is
179
-------
R = g/
meas ° n --qv ,,
effM eff
where n is the effective carrier concentration in the individual grain, q
is the electronic charge, u .. is the effective mobility in the intergranular
region, and g is a geometrical parameter.
Studies by previous workers on films with this geometry have dealt with
the situation by considering a highly conductive grain to be separated from
its neighbors by a high-resistance phase which effectively determines the
measured resistance. Such an oversimplification does not deal with the elec-
tronic processes directly, and cannot give more than qualitative information
if applied to gas sensitivity.
A more fundamental approach recently applied to this situation has pro-
vided a semiquantitative description of electronic processes and a guide for
materials processing to optimize gas sensitivity of polyerystalline metal-
oxide semiconductors.
A chemisorption charge transfer model would be expected to depend critical-
ly on grain size and the corresponding number of free carriers taking part in
conduction and surface reactions. For the case of small crystallites, the
volume concentration of surface acceptors can be comparable to or even greater
than the volume density of free carriers inside. Such a case requires simul-
taneous solution of Poisson's equation and the charge neutrality equation
for each grain. We apply this approach to determine the crystallite surface
potential, and, then, the effective carrier concentration as a function of
the density of ionized surface acceptor states for a particular set of mate-
rials parameters (e.g., grain size and geometry, doping concentrations, donor
and acceptor energy levels distributed in the bandgap, capture cross section
for surface acceptor states, etc.) (1).
For the case of ZnO, the effective carrier concentration versus grain
size is plotted in Figure 8 for a given surface acceptor density, N . The
D 8
results of the computer solution suggest the existence of a sharp transition
in the effective carrier concentration between a highly conductive grain with a
large radius and a nearly fully depleted grain of small radius. The transition
occurs for small changes in grain size and, for a given doping level, is a
function of temperature and concentration of surface acceptor states. The
result suggests that material parameters might be adjusted such that small
ambient induced changes in surface acceptor density could give rise to large
changes in n . and the measured resistance of the film sensitivity. The
180
-------
10"
10'
T 10"
§
10'
ZnO
Comprfw ShniMkin
SS
10"
10
10'
10
Zm
T «600K
10'
Grain Sla R (nml
O' 10*
Groin Dionwler (run)
FIGURE 8 (left). Computer solution of effective carrier concentration in a single crystallite plotted
versus crystallite radius. FIGURE 9 (center). Computer solution of effective carrier concentration
plotted versus surface acceptor density on a single crystallite of ZnO. FIGURE 10 (right). Measured
film resistivity of as-sputtered undoped ZnO versus diameter. After heating in air, all films have
4
resistivity greater than 10 ohm-cm. Solid line is computer fit.
00
-------
effect of a distribution in grain size about a mean and a distribution in
energy of surface acceptor levels and bulk donor levels is shown to smear
out this sharp transition.
The situation is illustrated in Figure 9, where n -- (from the computer
solution) is plotted versus N . The surface acceptor concentration (for ZnO
material parameters) is listed in the figure. For the particular material
parameters used, an optimum sensitivity of n __ to N is determined for a
> f * S8
discrete grain size of 35 nm and doping level N * 1 x 10 cm
Experimental Confirmation of the Transition Region
In the effort to confirm the existence of a transition region in RF sput-
tered ZnO, and to justify the application of the model to gas sensitivity of
these films, resistivity measurements were taken. Grain size of sputtered
films was determined by TEM and SEM techniques. Grain size could be controlled
by varying the film thickness or substrate temperature during deposition.
The details of deposition and characterization of RF sputtered ZnO appear
elsewhere (1) .
Figure 10 shows data obtained for several films exhibiting the depend-
ence of resistivity of as-spurtered ZnO on grain size. The data are fitted
loosely to a computer-generated curve (solid line), where the fit was obtained
for N = 3.125 x 1016 cm"3, E - .05 eV, N = 2.2 x 1012 cm"3, and E - 0.8
u OSS A
eV. The Hall mobility could be measured in several of the lower resistivity
2
samples. Its value was less than 1 cm /V-sec. Yeh (2) reports that the
mobility in such films is independent of temperature and oxygen partial pres-
sure, whereas n f, changes with these parameters. We therefore infer that the
measured resistivities reflect changes in n ff. This suggests that the data
of Figure 10 provide a semiquantitative confirmation of the dependence of the
effective carrier concentration on grain size in polycrystalline ZnO.
Gas Sensitivity Testing of Sputtered ZnO Films
Gas testing has been carried out with the specific goals of 1) evaluating
the feasibility of this technology for personal monitors; 2) establishing op-
timal film doping and/or grain size; 3) determining sensitivity as a function
of temperature for various gases; and 4) exploring the use of additives such
as palladium or platinum which are known to enhance sensitivity to particular
gases. The response to hydrogen, carbon monoxide, and changes in the nitrogen/
oxygen ratio, are measured.
182
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Hydrogen testing is carried out by passing a mixture of forming gas
(5 percent 1^ 95 percent NZ) and synthesized air over the sample. Concen-
trations in the range 0 ppm to 9,000 ppm are employed. Carbon monoxide test-
ing at present is conducted under static conditions, using concentrations
in the 100-ppm range. The nitrogen/oxygen ratio is varied from 100 percent
N_ to 100 percent 0^. In all cases, the film temperature is monitored with
a chromel-alumel thermocouple. Film resistance is measured using an AC volt-
age and current; the AC technique is necessary because of the high thermo-
electric power of ZnO, which results in sizable DC thermoelectric voltages.
The resistance measurement is performed with an AC digital voltmeter.
However, a DC voltage proportional to the sample resistance is also derived
and recorded with a pen recorder.
Figure 11 shows the hydrogen response of two Ga-doped ZnO films which
were both sputtered onto substrates heated to 480° C. Both films are seen to
quite closely follow a dependence on the square root of hydrogen concentration,
i.e.,
f - A [H//2
o
where G is the conductance in air and A is a constant. Therefore, calibration
o
of a particular sensor is reduced to specification of the constant A for that
device. Comparing the two curves of Figure 11, it is seen that Device B has
a somewhat greater sensitivity. This device is similar to A, except that a
500 X film of palladium was sputtered onto the ZnO film in the last step of
fabrication. In Device B, palladium is probably acting to catalyze the dis-
sociation of hydrogen—a necessary step in the reaction of hydrogen with the
sensor surface. Based on the scatter in the data, a detection limit of 10
ppm H2 is indicated for Device B.
The response of a sensor to hydrogen is indicative of the response of
the device to a number of gases containing hydrogen; i.e., CH^, HgS, and NH.-.
In these cases, the parent molecule undergoes dissociation, neutral hydrogen
is produced, and the latter reacts with the sensor surface. Of particular
practical interest are detectors for CH^ and H2S. In the latter case, a palla-
dium device similar to Device B is particularly attractive, since palladium
is known to catalyze the dissociation of HjS (see below). However, ZnO devices
must be protected against direct exposure to sulphur compounds, which poison
this material by forming surface ZnS layers. Two solutions to this problem are
183
-------
100
[*"*• Concpif rof ion J
T
KHlllwet
to * \
III pp» CO
FIGURE 11
FIGURE 12
4.0
o
19
2.0
Temperature Dependence
of Hydrogen Response of
Device A.
I
J_
I
280 300 320 340 360
Temperature (*C>
FIGURE 13
FIGURE 11. Hydrogen response at 330° C.
FIGURE 12. CO response of Device A at
330° C. FIGURE 13. Temperature de-
pendence of the hydrogen response of
Device A. FIGURE 14. Reverse leak-
age current density of a Pd MOS diode
and flat band voltage of a Pd MOS
Capacitor plotted against hydrogen con-
centration.
10*
.10*
r
10'
. In otr T.JOO-K
800
400
300
K> NO WOO
Hg CorvCMMflo. too) b dr
FIGURE 14
184
-------
being evaluated. One Involves the use of a Zeolite molecular sieve (see
below) over the film. The Zeolite is chosen to allow passage of hydrogen
but not sulphur. Palladium is added to the outer layers of the Zeolite through
sputtering or other means such that the dissociation of H-S is promoted.
Since this device will also respond to hydrogen, it must be paired with a
device not sensitive to H2S, but instead to hydrogen. The latter could be a
Zeolite-covered film without palladium added to the Zeolite. The other solu-
tion being investigated involves cladding the ZnO film with palladium, which
is relatively unaffected by sulphur compounds and which is transparent to
hydrogen. In this case, the palladium acts to screen out sulphur.
Figure 12 is an example of the response of Device A to 111 ppm CO.
Device B showed negligible response to CO, presumably because the overlaying
Pd film prevented the CO molecules from reaching the ZnO film. Palladium or
platinum additives, therefore, are useful for detectors designed to respond
to small concentrations of methane or other gaseous hydrocarbons in the pres-
ence of large concentrations of CO.
In addition to the selectivity afforded by catalytic additives, the tem-
perature-sensitivity relationship may be a means of enhancing selectivity.
Figure 13 shows the temperature dependence of the hydrogen response of Device
A. The temperature dependence is believed to be a unique characteristic of
a particular gas. In the case of hydrogen compounds such as CH, or KLS, the
temperature dependence will reflect dissociation of the parent molecule, as
well as reaction of the film to hydrogen, and, therefore, should be unique for
a particular gas. Use of temperature as a means of selectivity will require
processing information from an array of sensors operating at different tempera-
tures. This approach is favored over scanning a single sensor through a tem-
perature range because of response time considerations.
The response time, reproducibility, and long-term stability of films
investigated thus far have been adequate for most monitoring applications.
The response time for exposure to a gas is on the order of seconds; this meas-
urement may reflect the response of the gas testing system itself and is there-
fore an upper limit of the film characteristic. Recovery following removal of
the gas appears to be somewhat slower, with the present sensors requiring sev-
eral minutes. Stability has been investigated over periods of 1 week, and the
conductance in air of a given film appears stable within a 10-percent range
for a film cycled over a range of temperature and exposed to a number of gases.
Long-term stability is, of course, critical to the successful operation of
gas sensors.
185
-------
AND HS SENSITIVE MOS STRUCTURES
Schottky Barrier Diodes and MOS Capacitors
Thin metal films which dissociatively dissolve H-, such as Pd and Pt,
have been incorporated in integrated diodes and capacitors on passivated
silicon substrates (3,4). Changes in work function at the metal-SiC^ inter-
face induced by ionized HZ and gases such as H2S and NH3 can give rise to large
changes in the reverse leakage current of a Schottky barrier diode or changes
in the flat band voltage of MOS capacitors. H. sensivitity is shown in Figure
14 with the structures operated at room temperature. The figure illustrates
diode sensitivity in terms of changes in reverse leakage current and changes
in capacitor flat band voltage versus hydrogen concentration. One to 10 ppm
H_ in air are detected, with the upper limit on sensitivity being near 1 per-
cent H..
MOS capacitors can be operated at elevated temperatures, which Improves
response times while the sensitivity to H_ is preserved. Both structures
are sensitive to BUS, but operation at room temperature results in a short-
term deterioration in response due to sulfur poisoning of the metal surface.
However, the sensitivity is entirely reversible at elevated temperatures above
160° C in air. Diode structures cannot be used at elevated temperatures,
whereas MOS capacitors essentially retain their characteristics in this tem-
perature range. As an alternative to measurements of changes in flat band
voltage with H- or H_S, the actual change in capacitance can be measured at
a given gate voltage. Figure 15 Illustrates the result of such a measurement.
The figure shows a change in differential capacitance versus H.S concentration
at elevated temperature in air. One to 10 ppm H.S can be determined. Device
sensitivity can be improved by minimizing the SiO. dielectric thickness.
Device Selectivity
The aspect of selectivity has been approached from several angles. Fig-
ure 16 constitutes a specific illustration where the addition of a catalyst
as an impurity shifted the ZnO temperature distribution for the response of
the film in the case of CO. In general, the sensitivity of a metal-oxide is
temperature dependent, and conceivably an array of devices operating at dif-
ferent temperatures with the associated signal processing could be used to
discriminate several gas constituents. Alternatively, preprocessing of the
gas ambient by filtering of the gas components—analogous to preprocessing
186
-------
60
20-
C (fftl
J"
>„ • «0ni»
V -IJ Volll
I-
WO W* K>' rf
MjS CONOOmunON (pom) hi ok
FIGURE 15
1*0 Vf Se
C03ppl
ZnO/KPd
225 300
FIGURE 16
10'
10*
8
I io*
K
10*
Ziollt* 3A
RF SpuHt'frt ZnO -
with 3A
(polion)
10
I..,
10
* .0*
10
wf 10* 10*
Conctntrotlon ppm
FIGURE 17
Zeolll. 3A
TGS*8I3 (SnOj
H.S
10 100
Conecnlration ppm
FIGURE 18
FIGURE 15. Differential capacitance in a Pd MOS capacitor plotted versus
concentration for a negative gate bias of -1.5 volts. FIGURE 16. Percent
change in resistance of ZnO film exposed to CO in air plotted versus temperature.
The presence of Pd in the film acts to shift the temperature dependence of the
response to lower temperatures. The sensitivity is improved. FIGURE 17. 3 X
pore size Zeolite incorporated on ZnO sensor effectively screens HjS separating
the response to H? and CO from H^S. FIGURE 18. 3 X pore size Zeolite on SnO.
is also used to separate H. from H2S.
187
-------
of communication waveforms before detection—can provide selectivity, as well.
We have been working to incorporate Zeolite molecular sieves with commercially
available devices and with our own integrated versions. Figure 17 demonstrates
the results of the use of a 3 angstrom pore size Zeolite deposited on ZnO as
a filter for CO. H.S, which is a poison to ZnO, is screened out because its
molecular size is too large to pass through the Zeolite. Responses to H_S
without the Zeolite are shown. With the filter, H-S is effectively screened
from the sensor. The currently employed deposition process for the Zeolite
is not fully compatible with standard planar processing techniques and, before
this technology can be fully Implemented, thin film deposition of molecular
sieve material must be developed.
Figure 18 illustrates the utility of 3A Zeolite for separation of H_ and
ELS. The results shown here are for a commercially available SnO.-based de-
tector. Two Identical detectors, with one incorporating the Zeolite, can
effectively discriminate the response to HLS from that to H2- This is also
of interest for the diode and capacitor structures referred to earlier.
CONCLUSIONS
Radio Frequency Sputtering is a powerful, versatile technique for the
preparation of thin films of SnO- and ZnO to be used as sensors for certain
gases.
In conjunction with Sn02, the fractional change in resistance versus
the preparation conditions shows increasing sensitivity for samples prepared
in decreasing amounts of 0_ within the sputtering system. However, the most
stable films are those prepared in 100 percent 0«. Thus, there appears to be
an optimum sputtering environment for both a reasonably stable, and yet an
adequately sensitive, film.
Reasonably stable films of SnO_ (albeit not very sensitive) may be in-
corporated with bipolar transistors in an integrated structure, with the gas-
sensitive portions being operated at elevated temperatures while the bipolar
transistor remains at near room temperature.
In polycrystalline films of ZnO (and also SnO.), the grain size depends
on deposition temperatures. There appears to exist an optimum grain size for
which the sensitivity of the film is significantly enhanced.
Ga doped ZnO films are stable, and with the addition of Pd can be used
L88
-------
for the detection of EZ and hydrogen bearing gases (CH,, H2S, NHj) with good
sensitivities. In the case of H.S, the ZnO must be protected agaitx'st direct
exposure to sulfur compounds which poison the material.
In addition to the selectivity afforded by catalytic additives, Ga
doped ZnO devices can be designed to operate at elevated temperatures, so
as to have an enhanced sensitivity to gases.
Schottky barrier diodes and MOS capacitors, both incorporating Pd-SiOj-Si
layers, can be utilized as very sensitive H. and hydrogen-bearing gases such
as H~S and NH«. In the diodes, their reverse current sets a limit to the
maximum temperature of operation. The capacitors, however, can operate at
sufficiently high temperatures (of the order of 160° C) so that the molecule
of the detected gas may be dissociated.
Zeolites molecular sieves may be incorporated in the devices above to
afford selectivity—by acting as filters against certain gases while passing
some others which would dissociate on the surface and modulate the electrical
properties of the sensor.
ACKNOWLEDGEMENT
This research was supported in part by the Department of Energy under
Contract No. EE-77-S-02-4346. Support of certain portions of the work by
Mine Safety Appliances Co. Is also acknowledged.
REFERENCES
1. Leary, D.J., Barnes, J.O., Jordan, A.G. Characterization of RF Sputtered
ZnO Films (to be published).
2. Yeh, K.W., Muller, R.S., Washburn, J. Characterization of RF Sputtered
ZnO Piezoelectric Films using TEM. 33rd EMfJA Meeting, Washington, D.C.,
1975.
3. Lundstrom, I., Shivaraman, M.S., Svensson, C. A Hydrogen Sensitive
Pd-Gate MOS Transistor. Journal of Applied Physics, 46:3876, 1975.
4. Lundstrom, I., DiStefano, T. Influence of. Hydrogen on Pt-SiOj-Si Struc-
tures. Solid State Communications 19:871-875, 1976.
189
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MAILING ADDRESS OF PRIMARY AUTHOR
Angel G. Jordan, Ph.D.
Carnegie-Mo lion University
Pittsburgh, Pennsylvania 15213
Discussion
MAGE: I wo>uld like to ask that the questions about this paper be held
until after the next paper, because it will be on the same topic from the
same department.
(NOTE: The discussion for this paper appears following the text of
the next paper, "Microcomputer Control and Information Processing Technology
for Semiconductor G.as Sensors.")
190
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Microcomputer Control and Information
Processing Technology for Semiconductor
Gas Sensors
David T. Tuma, Ph.D., and Paul K. Clifford
Carnegie-Mellon University
Pittsburgh, Pennsylvania
INTRODUCTION
A primary goal of our research is the eventual development of a portable
pollution monitor. The ideal monitor would be small, lightweight, safe,
rugged, inexpensive, and capable of continuous operation throughout the work-
day. As a gas-detection system, it would need to respond reliably to com-
bustible and polluting gases over a dynamic range of several orders of magni-
tude, with a time resolution of a few minutes and reasonable sensitivities
determined by flammable and toxic limits.
A gas-detection technology that seems suited to the eventual fulfillment
of these goals is that of semiconductor detectors. However, to date, semi-
conductor detectors have been characterized by low reproducibility, drift,
and very poor gas selectivity. These limitations cannot be overcome until
much more is known about the nature of the detection mechanism in the semi-
conductor material. Some of these limitations, however, appear to be in-
herently tied to the nature of the materials used in such a way that it is
unlikely that they will be completely overcome by materials research in the
near future. Although we will see the rapid evolution of a wide variety of
semiconductor sensors in the near future, they will remain broad-spectrum
devices. Aside from this lack of selectivity, it is likely that semiconductor
sensors will continue to exhibit highly nonlinear responses which are not
amenable to present "direct reading" instrument design.
If the computational power which is now becoming available at low cost in
191
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microcomputers can be used to compensate for the Imperfections of present
sol.id-state detectors, then the development of a portable gas-detection In-
strument may be possible. "Smart" instrument design through the use of
microprocessors may obviate the need for a simple linear response and provide
a means to enhance selectivity of existing or future detectors. This is
made possible only by the significant decrease in both size and cost of com-
puter systems over the past few years.
At Carnegie-Mellon University, we have been empirically investigating
the basic response mechanisms of semiconductor detectors. That is, we deter-
mine the dependence of the semiconductor material properties on temperature,
gas concentrations, fouling, past history, etc. The purpose of this investi-
gation is twofold. First, we seek to provide insight into the characteristics
which would be desirable in future detectors, thereby aiding in the develop-
ment of higher-performance detectors. Secondly, we are determining which
properties of the sensors are able to be exploited, by using innovative signal-
processing techniques, to overcome their seemingly Inherent limitations. A
synergistic cooperation between semiconductor and microcomputer, broad-spectrum
sensors and computational selectivity enhancement, may be necessary to make
the genesis of a truly personal, portable gas-detection system feasible.
Instrumentation Design
The design of personal detection systems to date has concentrated on
direct reading sensors with a simple linear response. They are most suitable
to portable technology. Unfortunately, direct reading sensors are not avail-
able for the plethora of environmental contaminants which need to be monitored;
the gap between specific sensors and monitoring needs is widening. For this
reason, instrumentation design will need to adapt its methods to sensors of
low gas specificity and nonlinear responses. Fortunately, this is possible
with the advent of miniaturized computers. A microcomputer-based detection
system would have the following attributes which may become indispensable in
a portable personal gas monitor.
Display. An Instrument for hazard detection would need to provide a
warning signal when a dangerous level of a particular pollutant is present*
A microcomputer could provide a hazard signal when either an instantaneous
dosage or cumulative exposure exceeds a preset level. The threshold levels
could be easily programed and may even be allowed to depend on other gas con-
centrations. In addition to warning alarms, a microprocessor-based instrument
could be easily interrogated by the wearer to provide a display on demand of
instantaneous, average, and cumulative exposures to one of several gases*
192
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Memory. Increasingly, the focus of personal pollution monitoring Is
shifting from hazard detection to trace gas monitoring. For this, automated
data analysis and data recording is needed to permit the handling of the
large amounts of data generated during routine monitoring. We need an in-
strument not only capable of direct gas analysis and small enough to be carried
by a worker, but it must also maintain a memory of gas exposure throughout
the day. This memory can then be transferred to a permanent record in a
centralized monitoring system. Such a personal monitor necessitates the
use of microprocessor technology with its attendant semiconductor memory.
Present processor technology enables us to visualize an instrument small
enough to be carried which would provide a hazard signal if one of four or
five gases exceeded safe levels, and which could maintain a memory of the day's
profile of gas concentrations. At the end of the day, that memory could be
dumped into a larger computer facility, providing permanent and detailed re-
cords of personnel exposures.
Control. A microprocessor* s capability for real time control extends
from the mundane to the esoteric. At one level, the microprocessor may be
used to reduce power consumption by intermittently operating the sensors.
Sensors may be sampled automatically, with power-conserving dead space between
samples. More Interestingly, the interactive control of semiconductor sensors
may extract much more information from the sensor than could be had statically.
Feedback to and control of the electrical bias point or device temperature,
based on computed results, may be needed to optimally exploit the semiconduc-
tor's detection properties.
Signal Processing. Information from a bank of sensors—each sensor of
which in itself is unselective but exhibits differing relative gas sensitivities-
can produce a system of nonlinear equations. These may be solved numerically
by a computer. Microcomputers having the computational ability and memory for
a task such as this (i.e., nonlinear regression of sensor information to pro-
duce gas concentrations), are now available in sizes and costs amenable to the
needs of personal dosimetry. Current trends in processor technology Indicate
that their signal processing abilities might well continue to grow; increasingly
complex algorithms may be implemented in real time.
SELECTIVITY ENHANCEMENT
Differential Sensitivities
Sufficient information must be provided to the microprocessor so that
193
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It is able to deconvolve the gas concentrations of interest. This may be done
either by using several detectors with different relative sensitivities to
the gases, or by using one sensor whose sensitivities to the gases may be
changed in time by computer manipulation of a controlling parameter. The
following methods may be used to gain differential sensitivities from otherwise
broad-spectrum sensors.
Detector Construction. Gas detection by semiconductor sensors is a com-
plex process involving absorption and desorption of gases on the semiconductor
surface, surface chemical reactions, diffusion of gases along grain boundaries,
and interaction of adsorbed species with the electronic structure of the ma-
terial. Layer thickness, grain size, heat treatment, dopant concentrations,
and any physical or chemical modification of the catalytic activity of the
surface may be used to change gas sensitivities. Although it may be difficult
to attain—for example, absolute selectivity by a change in dopant concen-
tration—at least the relative sensitivities to several gases may be suffi-
ciently changed to allow use of the device.
Filtering Techniques. Various filters may be used in conjunction with
wide-spectrum, metal oxide semiconductor detectors to render very different
relative gas sensitivities. In particular, we have had success with Zeolite
molecular sieves. This technology may be merged with silicon integration
techniques to yield single chip sensors composed of a dozen or so differently
filtered, metal oxide semiconductor devices. Such ultra-miniaturization may
soon produce a very powerful, general-purpose personal gas monitor.
Manipulation of Bias Conditions. Some semiconductor gas detectors (e.g.,
Pd-SiO_-Si Schottky diodes) have electrical bias conditions which may be made
subject to microcomputer control. Depending on the physical and chemical
properties of the particular gas species being adsorbed, a change in bias
of the semiconductor device may change its gas sensitivity. Hence, a change
of electrical bias by the microprocessor yields different relative gas sen-
sitivities. Simplicity of control, rapidity of response, and ease of inter-
facing, make electrical bias change a desirable form of control. Unfortunately,
there are few sensors which behave reproducibly and whose relative gas sensi-
tivities have yet been reliably measured.
A semiconductor gas sensor* s thermal bias—its temperature—is subject to
easy manipulation. Because the mechanisms of chemlsorption, gas diffusion,
chemical reactions, and gas-bulk electronic interaction are all strongly
temperature-dependent, a metal oxide semiconductor's sensitivity to a gas is
a very strong function of temperature. A single sensor, if operated sequenti-
194
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ally at several temperatures, will exhibit different relative gas sensitivities.
Each gas will have its own "eigenfunction" of sensitivity relative to tempera-
ture. By changing the temperature of a device, a processor may gain enough
independent sensitivities for the determination of several gas concentrations.
Development of the Detection Algorithm
After a bank of sensors exhibiting different relative sensitivities to
gases has been assembled by any of the above techniques, signal processing
can be used to deconvolve the individual gas concentrations from the collec-
tive response of the sensors. To construct the deconvolution algorithm, a
knowledge of the exact nature of the response of all the detectors to all the
gases is needed. Quantitative expressions of detector response can be deter-
mined empirically, guided by theoretical knowledge of the reaction mechanisms
and a suitable experimental data base. It is Important to note, however, that
a full understanding of a device's nature is not necessary for using that device.
A phenomenological knowledge of its behavior, derived empirically, is suffi-
cient. The microprocessor has the benefit of a collection of responses either
gained from a bank of sensors or a single sensor whose operating conditions
are changed sequentially in time (or any combination thereof):
Sl ' fl «V G2' - V
Sm - f (G , G , ... G )
m m 1 / n
where S. is the response in voltage or current;
f, is the predetermined functional dependence of response on gas
concentration; and
G, ...G are the concentrations of ambient gases.
I n
If m >^ n — that Is, if there are enough detector responses with different
relative gas sensitivities — then the gas concentrations, G. , G2, ... G , can
be determined. Of course, the f's will not in general be linear functions,
and the above system of equations will not be explicitly solvable analytically.
Numerical techniques, however, can be developed and used to solve such a
system. The efficiency of those techniques will depend on the specific
nature of the nonlinear functions. If m > n, then, as well as gas concentra-
tions, the solution can include a figure of merit or confidence interval for
each determined gas concentration. This is very desirable, since a personal
195
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pollution monitor will often be exposed to gases which it was not designed to
measure. Even though these extraneous gases will interfere with the gas meas-
urements, the confidence interval produced with each gas concentration will
signal its validity or error.
A technique of selectivity enhancement is presently being developed for
use with commercially available gas sensors. We are in the process of deter-
mining the functional dependence of device response on gases in the ambient.
TAGUCHI GAS SENSOR
Our research effort has concentrated on the testing of a variety of in-
house gas sensors as well as commercially available sensors. The Taguchi Gas
Sensor (TGS), which is manufactured by Figaro Manufacturing Company of Japan,
typifies the state-of-the-art in gas detection. Our purpose in studying it
is twofold. Its behavior is characteristic of many other metal oxide semi-
conductor detectors, so that knowledge of its parameters may guide research
and development of new detectors. Being commercially available, it is manu-
factured reproducibly; we can test large numbers of them inexpensively. The
other purpose of the study is the identification of parameters of the Taguchi
Sensor which may be conducive to microcomputer selectivity enhancement. It
may be that an already-existing detector which is used in only smoke detection
may be suitable for use in gas identification.
The TGS is constructed of a highly porous, n-type, tin oxide semiconduc-
tor whose conductivity is greatly affected by the gases present at its surface.
The surface reactions which determine the sensor's detection properties are
strongly temperature-dependent. To control the sensor temperature, a heating
coil is imbedded within the sensor. A power of 600 mw dissipated in this coil
is capable of heating the TGS to about 400° C. Heating in order to achieve
reasonable sensitivities to gases is a method likely to be used by most
detectors we plan to test.
When heated, the Taguchi Gas Sensor is responsive to a wide variety of
gases. Because of the complexity, nonlinearity, and nonspecificity of the
Taguchi Gas Sensor's response to gas concentration, these devices are used
only for smoke detection or explosive level indication; they are not used for
low-concentration detection or gas identification.
Measurement Apparatus
A dual microcomputer data acquisition and analysis system developed by
196
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the authors is used for all measurements. It consists of three parts: a
clean gas system, a dedicated microcomputer data acquisition system, and a
data analysis microcomputer.
Gas System. The gas system consists of several exponential dilution
bottles in which the semiconductor sensors are mounted. Gas concentrations
in these bottles can be maintained accurately down to a few parts-per-million.
It is possible with these systems to produce slowly changing concentrations
of gases so that the data acquisition system can take data unattended over
long time periods. There are several dilution bottles so that some may be
dedicated to an automatic data collection system while others can be used for
rapid manual testing of detectors.
Data Acquisition. A real-time data acquisition computer system measures
and records the resistances of a bank of sensors mounted in the clean gas
system. The data can be output in readable form to the teletype or, under
program control, be transferred to the data analysis computer. The forte of
this microprocessor-based data acquisition system is that it can log huge
amounts of important data in an automatic, reproducible manner over long
periods of time, thereby freeing the experimenter from this costly task.
Data Analysis System. The heart of the data analysis system is a SOL-20
(Processor Technology Corp.) 8080 microprocessor-based computer system. This
system has a keyboard and video display for human interface. A floppy disc
mass storage system gives the computer sufficient memory capability to run
an Interactive high-level language. The functions of the data analysis
system are the following:
1) To control the microprocessor*based data acquisition system. Control
parameters are passed to the data acquisition system, telling it when to take
data and how to change the sensor heater voltage. The accumulated data is
passed to the main computer, where it can be processed.
2) The raw data can be stored on a floppy disc, from which it can be
retrieved at will.
3) An interactive high-level language (BASIC) can be used to program
the data analysis functions. The data analysis will consist predominantly of
curve-fitting techniques. Trial functions will be fit to the raw data, and
the goodness of fit will be tested.
4) Outputs—such as best fits of curves, functional parameters, or inr-
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portant intermediate results—can be delivered to either a teletype or video
display.
Experiments. Data acquisition and analysis experiments are of two broad
classes: investigation of the steady state response of the detectors to am-
bient gas concentrations; and determination of the dynamic response of the
sensors to a step change in gas concentration or temperature. Most experiments
are done automatically by the computer system so that they may be reliably
repeated at a later time or for other conditions.
Results
Steady State Response. When TGS sensors operating at 5-V heater voltage
are placed in pure N_, their resistances drop from "air" values of approxi-
mately 10 to 20 K« to very low values (.5 to 2 K«). In addition, the sensors'
resistances are observed to drift over a large range (of up to a factor of 2)
over time periods of hours to days in a constant environment. If 0_ is added,
the resistances increase—nearly following a power-law relationship—until in
pure 0_ they are the greatest observed (500 Kfl to flm). Figure 1 shows this
power-law response for several sensors. Resistances of individual sensors
start at vastly different values, but all show similar power-law slopes.
If one starts with a high 0_ concentration (for instance, pure 02 or air)
and adds either H», CH,, wet CO, or HjO, very similar curves are produced
(as shown in Figure 2). The resistance versus concentration is again de-
scribed by essentially a power law, but now the resistance decreases. The
remarkable feature of these curves is that their slope is the negative of the
slope of increasing resistance in 0_ concentrations.
An equation which fits these curves very well is found to have the
following form
R = (KQ + K[C])~6
for H2, CH^, CO, H20; and for 02, replace - 8 by + 8.
Where R = resistance of sensor
K = a detector dependent constant
o
which describes the finite
resistance at zero gas
concentration
198
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R
B
S
I
S
T
A
N
C
E
(Kfl)
1000. .
100.
10-
10
OXYGEN CONCENTRATION (ppm)
FIGURE 1. TGS resistance versus oxygen concentration in ni-
trogen. The response approaches a power law for high con-
centrations. R/'KfO-J where 8 is the power-law exponent.
R
E
S
I
S
T
A
N
C
E
(Kft)
1000- •
100
10-
wet CO
10*
10
10
10
GAS CONCENTRATION (ppm)
FIGURE 2. TGS resistance versus reducing gas concentrations
in an air ambient. For high concentrations, the response
•* A
is power law: RrK.fC.] . Differing gas sensitivities,
K's, are evident in the separation of the curves.
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K - a constant which Is specific
to a sensor and the type of gas
[C] « concentration of gas (ppm)
3 « power-law slope.
In the above equation, the B is very similar from sensor to sensor or gas
to gas, but it changes sign for concentrations of 0.. The gas sensitivity
coefficient, K, for a particular gas is in general independent of the con-
centrations of other gases. However, there are important exceptions* In parti-
cular, the sensitivity to carbon monoxide is dependent on the concentration
of water vapor. Its K is the product of a temperature-dependent term and the
water partial pressure. For all other gases measured, the K's are all inde-
pendent of gas concentrations. In general, the gas sensitivity coefficients
change from sensor to sensor, gas to gas, and temperature to temperature.
It is this temperature variation that will need to be exploited if these sensors
are to be used to selectively identify a gas. Imbedded in the K term are
the drift effects.
For a single sensor operating at constant temperature, there is a day-to-
day variation in resistance, even in a very "clean" atmosphere. If the depend-
ence of sensor resistance on CH, concentration in air is measured on different
such days, a family of curves is obtained, each with a different starting
point but with other essential features much the same. If these curves are
optimally fit to
R = (KQ + K[C])~B
g is found to be constant to + 25 percent and K constant to + 10 percent.
Almost all variation is found in the K term. We feel this variation is due
o
to slow chemical reactions, the products of which foul the surface.
Based on preliminary results, we feel that the dependence of a sensor
resistance on the simultaneous presence of concentrations of several reducing
gases can be expressed by
R = (KQ +Z Kf [C^)"8
where [C ] is the concentration of the i reducing gas, and K. is a strongly
th
temperature-dependent gas sensitivity coefficient for the i gas.
This expression suggests that if there is enough temperature variation
200
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among the sensitivity coefficients K , then it may be possible to produce
gas specificity by varying the temperature. Long stabilization times and
hysteresis effects greatly complicate data collection when the temperature is
varied. If, however, at different temperatures the resistance versus concen-
tration characteristic is measured, and then the corresponding relationship
between resistance and temperature at constant concentrations is obtained,
then a graph similar to that shown in Figure 3 would be obtained. Here, we
can see that temperature dramatically affects the zero-concentration resistance
as well as the sensitivity to the gas. If such curves for different gases
show different sensitivity functions versus temperature, then, conceptually
at least, we have a means of improving the specificity of the sensors to
various gases.
The dependences of the sensitivity coefficients on temperatures have not
as yet been well determined for any gas other than methane. Preliminary data
suggest, however, that they are characteristically different functions, as
shown in Figure 4. Experimental effort is continuing to characterize these
functions further.
Transient Response. When the temperature of a Taguchi Gas Sensor is
abruptly changed, its resistance exhibits a very complex transient response,
as shown in Figure 5. There is a sudden peak (or dip, depending on the direc-
tion of temperature change) and a slow relaxation towards the initial value.
This is followed by a very slow drift in resistance extending from 10 minutes
to 3 hours* The sudden peak and its relaxation can be understood in relation
to the chemisorption processes occurring at the surface of the material. Other
metal oxide semiconductors show very similar behaviors. The very slow change
occurs as the material reaches a new equilibrium with the oxygen ambient.
This interpretation is confirmed by studies using Auger Elemental Analysis,
which show changes in the oxygen content and stochiometry of the tin oxide
material with changes in temperature. Measurement of the transient response
for many step changes of temperature in the 400° to 800° K range, and subse-
quent analysis of the time constants observed, are yielding valuable insight
into the evolution of chemisorptive models for device behavior.
TGS Selectivity Enhancement
The general response of a Taguchi Gas Sensor to the reducing gases H-,
CH, , and CO is:
R - (K + KHJ + K[CH4] + K3[CO])"8
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to
O
FIGURE 3
1000 -
R
E
S
I
S
T
A
N
C
E
(KB)
Methane
Concentration
0 ppm
100 •
10
100 ppo
400
600
TEMPERATURE (*K)
800
R
E
S
I
S
T
A 300
N
C
E ZOO
500 -H
400 "
(KB)
100
FIGURE 4
•*•
•*-
400*K
600*K
TEMPERATURE
800' K
FIGURE 5
10
-I 1—
100 1000
TIME (sec)
10000
FIGURE 3. Detector resistance versus temperature in various concentrations of methane in air. The detec-
tor's sensitivity steadily increases with increasing temperature. FIGURE 4. Variation of gas sensitivity
coefficients with temperature (not to scale). The sensitivity to each gas is a characteristic function
of temperature. FIGURE 5. Transient response of the TGS to a step change of temperature. The initial
peak and relaxation reflects a change in chemlsorptive equilibrium at the semiconductor surface. The
subsequent slow drift, due to chemical and stochiometric change, may persist for several hours.
-------
Because the K's are strongly temperature-dependent, the response may be
measured at several temperatures and the system of equations solved numerically
for the gas concentrations. A complication arises with the gas CO. Sensitiv-
ity to it depends on water concentration; an Independent measurement of water
vapor pressure may be necessary. It is possible that in an atmospheric ambient
of normal relative humidity, the error introduced by ignoring the dependence
on water vapor will be negligible. Measurement of the gas sensitivity coef-
ficients will reveal whether this is the case.
Another important complication is the long stabilization time introduced
by an abrupt change in temperature. This prevents the measurement of response
by sequentially changing the temperature. We are rapidly gaining knowledge
of the causes of long stabilization times and expect to be able to computation-
ally extrapolate stable values from initial transients. This wilj. enable the
manipulation of temperature in real time, producing detection times suitable
for personal dosimetry. An alternative would be to use several sensors, each
of which operates at a different temperature. Because the temperature of each
is constant, the detector's behavior is stable. The only disadvantage to
using several sensors is the power consumption needed to maintain the high
temperatures of the devices—about one-half watt each.
Of course, filters may be cascaded around several Taguchi Gas Sensors,
expanding the above response equation into a system of independent equations.
The filters need not select perfectly for and against specific gases; they
need only produce sufficiently different, effective sensitivity coefficients
for a computer solution to be possible. A disadvantage of this solution is
the bulkiness of the sensors and filters and the resulting power consumption.
On the development front, we expect the integration of several sensors and
filters on one chip, obviating many of these difficulties.
CONCLUSION
Materials research will continue to alter the catalytic activity of semi-
conductor surfaces so that solid state gas detectors will become more selec-
tive. But, at the same time, pollution research monitoring needs are evolving
from the measurement of hazardous levels of a few simple gases to the deter-
mination of less than a part per million of many highly complex organic vapors.
To keep up with these needs, we will not only need more sensitive and selective
sensors, but also increased intelligence in the measurement instrument.
The newly developed microprocessor technology can meet this need.
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Microcomputers of sufficient capability and small enough size for personal
dosimetry are now being marketed as hand-held data-entry terminals for inven-
tory control and costing (due to their massive memory and market considerations)
at about $900. This cost could easily drop, for a mass-produced instrument,
to the $30 range. Fully programable scientific calculators are now available
for under $30. The projected downward cost of microprocessors and their
peripherals should make the microprocessor-based system increasingly attractive
for personal monitor applications.
We have shown that, at constant temperature in an oxygen-rich ambient,
the TGS resistance, R, varies with reducing gas concentration [C] as R K[C] ,
where K is a sensitivity coefficient peculiar to the reducing gas and the op-
erating temperature, and is a power-law exponent. It seems possible that
the dependence of the sensitivity constants K for various gases on detector
temperature can be utilized to enhance the TGS selectivity in gas detection.
The major complication to this scheme would be the long stabilization times
involved when temperature is changed. Nevertheless, a synergistic combination
of semiconductor sensors and microcomputer-based signal processing is expected
to help overcome the most significant limitation of present sensors—their
lack of selectivity.
ACKNOWLEDGEMENT
The authors acknowledge the support of Dr. A.G. Jordan. This research
was supported in part by the Department of Energy under Contract No. EE-77-
S-02-4346.
MAILING ADDRESS OF AUTHORS
David T. Tuma, Ph.D., and Paul K. Clifford
Carnegie—Mellon University
Pittsburgh, Pennsylvania 15213
Discussion
(NOTE: The following discussion took place after the presentation of
the papers "Studies of Semiconducting Metal Oxides in Conjunction with Silicon
for Solid State Gas Sensors" and "Microcomputer Control and Information Pro-
204
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ceasing Technology for Semiconductor Gas Sensors.")
SHAW: Bob Shaw from EPA. I would expect that water vapor would be
tenaciously absorbed on these surfaces—much more strongly absorbed than the
molecules that are of interest. And since there can be several percent of
water vapor in a typical atmospheric sample, the water vapor could very likely
be taking up most of the sites on the surface. Would you have to dry the
samples?
CLIFFORD: Most of the metal oxides1 detectors were achieving the detec-
tion efficiency at very high temperatures. At very high temperatures, there
is not much of anything really adsorbed sitting on the material at one time,
so that the surface coverage is much less than a monolayer for water and all
of the other gases of interest.
Now, we may have trouble with a lot of water sitting on the material
condensed, as well as maybe some other gases at the lower temperatures. So
far we have been operating at high temperatures, and it is not a problem.
There is a sensitivity to water just as there is a sensitivity to other
reducing gases.
SHAW: I guess I missed hearing about the mechanism of operation. It
seems to me that if water vapor is more strongly adsorbed than many of these
other gases—and yet if it is the modulation of the adsorbed oxygen that
gives you the change in resistivity—I just don11 see how raising the tempera-
ture will correct this?
JORDAN: Of course. We operated at temperatures on the order of 200°,
300°, 400" Centigrade.
SHAW: But then all these other gases will be desorbed way below those
temperatures?
CLIFFORD: They are desorbed at specific temperatures. The surface of
the material is very heterogeneous. There are adsorption activation energies
that cover a wide spectrum of energy, so that in any given temperature range
a great many gases are adsorbed in different ways and at different activation
energies.
SHAW: What I should have asked, I suppose, is have you seen that relative
humidity does not affect the behavior of your detector surfaces?
JORDAN: Of some temperatures, more; of some temperatures, less. Three
hundred or 400° Centigrade temperature is the range for the device with which
I am working. The effect is not deleterious.
CLIFFORD: Also, water vapor is actually detected by the sensor.
JORDAN: It is another component of the mixture which you have to reckon
with.
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BURTON: Bob Burton, EPA. What is the probability of getting your sen-
sitivity down by a factor of 10?
JORDAN: The ppb*s rather than ppm*s?
BURTON: Yes.
JORDAN: It is fair to say that at the moment our lead oxide, tin oxide
for leading devices, was in ppm's. I think you can go to lower. 1 think it
would be coupled under there.
SCHEIDE: Gene Scheide. One of your original advantages was to use a
single broad purpose sensor to sense many gases. But in the end, are you
saying that you have to use one sensor for each gas operating under a differ-
ent condition?
CLIFFORD: We won't need one sensor for each gas. What we need are a
couple of independent sources of information. That can be three or four sen-
sors or one sensor operated at three or four temperatures.
SCHEIDE: You need a different sensor operating on a parameter for each
gas?
CLIFFORD: For each gas; that is right.
SCHEIDE: Do the number of variables have any relation as to the equal
number of gases being analyzed?
CLIFFORD: Yes; we need at least that many degrees of freedom or more
for independent methods. The advantage of deconvolving this information
through the computer is also that when we have more sources of information, we
determine, as well as the gas concentration, the degree of validity of that
concentration—an error down the line for every gas measured.
JORDAN: But remember this is not going to be coupled. But they are
beginning to be coupled already to the silicon chip.
CLIFFORD: So, we can see one sensor that eventually has mounted on it
12 different filtering arrangements or 12 different sensors. But by being
swept in temperature, it gives us essentially 100 temperatures now.
SCHEIDE: But another one of the problems was temperature stability—
correct?
CLIFFORD: Yes. Right now there arc metallurgical problems with that.
Also, we don't really know a lot about the temperature reactions. It may be
that once we know a little bit more about them, that just by looking at the
initial transient when the temperature is changed, we can predict what the
stable value would be an hour later.
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Management Strategy in the Design and
Use of Personal Monitors for Environmental
Studies
Ralph W. Stacy, Ph.D.
Clinical Studies Division
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina
It is not difficult to develop justification and enthusiasm for the
development and application of personal monitors for advanced epidemiological
studies on environmental pollution problems. Indeed, by this time most of
the participants at this symposium are probably at a fever pitch in their
realization of the Importance of the whole thing. In a situation like this,
it would be all too easy for us to go screaming off in all directions, wasting
an enormous amount of time and effort and requiring us to come back later and
do the careful preprogram planning that we should do at this time. This is
a plea for careful attention to such planning at the management level.
To begin with, what we are proposing to do is to develop a system for
measuring and recording a variety of parameters (exposure and health effects)
that are not easy to measure accurately, even under carefully controlled lab-
oratory conditions. We proposed to design these measuring and recording devices
into a single package, small enough to accompany an individual human through-
out his or her entire day's activities, cheap enough so that we can afford to
place thousands of these in the field, yet powerful enough so that we can be
thoroughly confident that the measurements made with the system are of such
quality and validity that they can be defended against the most vigorous attack.
One of the most important factors in this development is that when these
personal monitoring devices are placed in the field, they must be of one single
design for any one complete study. It may be that we will eventually end up
with several devices from which we can choose one to be used in a particular
study; a little later on, I will espouse the value of the development of a
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modular system that can be adapted to a particular study* In any case, we
cannot depend on haphazardly dissociated competitive development for this
particular task.
To be sure, the individual devices or components will surely be developed
by various agencies—governmental, university, and private industry. But in
the long run, these Individual components must be assembled into a personal
monitor within a single, well-defined program unit. An agreed-upon set of
Quality Assurance criteria must be met, and there must be a carefully designed
and implemented performance testing program. Therefore, the planning phase
of the entire development program is at least as important as the actual devel-
opment. This planning is the responsibility of management, and management
must be made aware of this responsibility at the outset of the program.
I suspect that almost all of us here are aware that the program we are
discussing is no small effort. Indeed, when one carefully considers the re-
quirements of the ultimate development and compares these with the state-of-
the-art in the several fields of instrumentation involved, the whole affair
becomes a little frightening. My thesis is that we must somehow manage to
impart this appreciation of the magnitude of the task facing us and the diffi-
culties involved to the management components of every agency to be involved.
Only with the intelligent and enthusiastic participation of management can
the program be mounted at all.
All of us who work daily with the generation and measurement of air pollu-
tants and air pollutant mixtures are constantly aware that accurate measure-
ment of those pollutants is a continuing problem, even in the fixed-laboratory
situation. The amount of time and effort spent in checking, calibrating, and
adjusting the measurement instruments is large. Now we are proposing to de-
velop a system which will measure and record those values without constant
attendance over a considerable period of time, and which will be small enough
and portable enough so that it can accompany the individual human subject as
he or she moves around in his or her normal daily routine.
The state-of-the-art in pollutant measuring devices can only be described
as being in the early developmental phase. To be sure, there are a number of
devices in existence which give promise of being useful for personal monitor
development. When these devices are finally evaluated for use under the con-
ditions I have described, some of them will in fact prove to be useful, and
others will not. I am virtually certain that some measurement components
will have to be developed almost from scratch.
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We remember, of course, that the personal monitor is intended for the
continuous measurement of not only the air pollutant levels, but also those
health effect parameters that are indicative of deleterious effects of the
pollutants. And if we are completely honest about it, we have to admit that
we may face more difficulty in this phase of the development than in the
pollutant-measurement phase. The physiological parameters that are easy to
measure—the EGG, body temperature, respiratory movements, and so on—are
unfortunately not useful as indicators of health effects decrements produced
by ambient levels of air pollutants.
In fact, the physiological variables which are indicative of pollutant
effects are very difficult to measure with the accuracy required, even in the
laboratory environment. Let us examine just a few of these to support this
statement.
It is well established that the most detectable physiological changes
associated with exposure to most pollutants are changes in lung mechanics,
and that most significant among these is the resistance of the airways.
This effect of pollutants on airway resistance is especially important in
people who are already suffering from pulmonary disease—asthmatics, people
with emphysema, people with black lung disease, byssinosis, silicosis, and
so on. Unfortunately, the measurement of airway resistance is a relatively
difficult process, especially under the conditions under which the personal
monitors are expected to be used.
There are two ways of approaching the airway resistance problem. One
of these is direct measurement, and the other is derived measurement from
the analysis of air flows in special respiratory maneuvers. For field epi-
demiological studies, the direct measurement of airway resistance is hopeless
at the present state-of-the-art. There are only two commonly accepted methods
for this; one is the use of a body plethysmograph, which by no stretch of the
imagination could be made into a personal monitoring device. The other re-
quires the measurement of the intraesophageal (representing intrathoracic)
pressure, and this involves the subject having an intraesophageal balloon
in place. It is inconceivable that general population subjects could be in-
duced to have such a balloon introduced and left in for the required length
of time. Therefore, unless someone comes up with an entirely new technique
for direct measurement of airway resistance, we can forget that approach.
I will not say we are completely dead in this area. It is barely possible
that the relatively noninvasive but not thoroughly proven forced oscillation
technique might be developed to the point that it could become useful in per-
sonal monitoring. In its present condition, this would not be true.
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The indirect measurement gives more promise for personal monitor use.
This indirect measurement is actually a measurement of the maximum rate at
which the subject can expel air from the lungs. This maximum flow rate can
be measured with a device called a pneumotachometer, which can conceivably
be developed into an instrument that could be clipped or pinned to the sub-
ject and used only at intervals. My conception of the ultimate form of this
pneumotachometer is shown in Figure 1. Its output is electrical, and thus
is amenable to recording and/or analysis in portable monitoring equipment.
The use of this pneumotachometer unfortunately requires that the sub-
ject perform a very special kind of respiratory maneuver. He or she must
expel the air from the lungs at a maximal rate. In the laboratory, he is
coached into putting all his effort into the air expulsion, and even with such
coaching, the maneuver is not always successful. For field use, the subject
would have to be carefully trained to perform the maneuver in the right way,
and would somehow have to be programed so that he would make a maximal effort
at every measurement time. There would be no attendant coaching him or ob-
serving his performance. If he does not perform quite to the maximum, the
indicated maximum air flow is reduced, and this sort of reduction is exactly
what we would be looking for if a pollutant effect were experienced. There-
fore, it is going to be very difficult to tell whether an apparent decrement
in air-flow capability is due to a pollutant effect or to a failure on the
part of the subject to exert maximal effort. It is obvious that even in this
relatively simple sort of measurement, its adaptation to personal monitoring
is highly questionable.
What else can be measured that might give some indication of deleterious
effects of air pollution? Not much. We have reason to believe that some
pollutants have effects on the body's immune systems, but these cannot be
measured in the personal monitoring situation. Some of them may (and probably
some do) have carcinogenic effects, but these cannot be measured in personal
monitoring. It is possible that air pollutants may affect cardiac performance
in those individuals (cardiac patients) who do not have a reserve on which
they can call in pollution-stress situations. Therefore, the EGG probably
should be measured and/or recorded. Unfortunately, EGG interpretation is not
amenable for use in the personal monitoring situation; it still depends almost
entirely on the use of pattern recognition by trained humans. There are, of
course, computer programs that can be adapted to this analysis, and I am sure
that these could be developed to make EGG analysis more feasible for personal
monitoring purposes.
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floorer cuf*
PNEt/MOTACUOMETER (M/T DESIGN)
FIGURE 1. Diagram and sketch of one way to design a transducer for use in
a personal monitoring system. Currently used pneumotachometers have the
pneumotach tube and screen, the differential pressure manometer, and the basic
circuitry as separate components, and are very large and cumbersome.
There are some fairly interesting developments occurring in electrical
impedance plethysmography which could be of value in personal monitoring.
This field, and the techniques associated with it, would have to be explored
thoroughly. I am sure this would provide a way for continuous recording of
general respiratory movements, so that we could monitor coughing frequency,
etc. In general, electrical impedance-measured parameters are at best only
semiquantitative.
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The measurement of body temperature is well within the state-of-the-
art, but is of doubtful utility in personal monitoring for air pollution
health effects. It might help us to detect those individuals who have an
infection, and there is always an outside chance that ambient levels of some
as yet unknown pollutant may have a body temperature effect. I doubt that
it would cost us much money or effort to include this measurement capability.
One other possibility is the development of some measure of mental
alertness, responsivity, etc. Certainly some attention should be paid to
this, for behavioral effects always lurk in the background as possible pol-
lutant deleterious effects.
Thus, there are not many meaningful measurements that can be made in
the personal monitoring situation on the human himself. We who are working
all the time in the field are constantly on the lookout for significant meas-
urables, and we may be required to make a concerted effort in this direction.
Again, laboratory management components should be aware of the importance of
this kind of development and be prepared to support it with funds, space, and
personnel.
As we all know, technology has come a long way in the production of
integrated circuitry, both analog and digital, and in the development of
microcomputers, digital memory, and both analog and digital recording. My
next thesis probably needs little defense: the state-of-the-art is such
that with reasonable effort and fund expenditure, all components of personal
monitoring systems that follow the transducer can be developed in relatively
short order. Therefore, a major portion of the development effort will have
to be toward the development of transducers and the procedures for their
application.
My own conception of the personal monitor is of one utilizing full
modularity. With chip design and production as it now exists, it should
be possible to design and produce a series of integrated circuits, including
amplifiers, signal modifiers, A-D converters, telemetering circuits, counting
circuits, smoothing and differentiating circuits, and so on down the line.
These would be designed to be incorporated into a packaging unit having pins
on the bottom and sockets on the top, 30 that they could be stacked to pro-
duce any combination of circuits desired. One row of such connections would
carry through the entire stack, providing power from the bottom or base unit
to all the circuits in the assembly; another row would effectively serve as
a signal bus, carrying analog or digital signals as required. All package
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modules would be identical and could be assembled in any combination desired.
I visualize these as being approximately 1 inch X 2 inches X 1/4 inch.
Power modules would necessarily be larger than the circuit modules.
Thus, I have generally considered these as being the bottom units. The power
modules could be snapped together horizontally, so that several different
monitors could be incorporated into a single package. This general scheme
is visualized in Figure 2.
I have also considered that there will probably need to be two types of
terminal (top) units. One of these would be capable of recording or storing
in digital form the data derived throughout the period of monitoring. This
will become more and more in the realm of possibility as promising new de-
velopments in storage memory come to fruition, and when it becomes possible
to store millions of bits of information in a couple of cubic inches of space.
This type of storage would be limited to relatively small data productions,
for even if it is decided to accept 8-bit digital data, the number of data
words that can be stored has a quite finite limit. This concept is illus-
trated in Figure 3.
The other possibility (and I suspect this will emerge as the most im-
portant possibility) is the telemetering of Information from the unit worn
on the person to a receiver/computer/recorder combination housed separately
in a briefcase-type of enclosure that could be set anywhere within a few
hundred feet of the monitored individual. This unit would only need to be
moved if the individual himself moved beyond the range of the telemetering
device. This unit could also be the source of an alarm signal which would
alert the individual to the fact that it was time to perform a required
respiratory maneuver, etc. This unit might also include a voice tape record-
er on which the subject could note any special activities he engaged in—
again, by telemetering to the recording unit.
Thus, those of us in clinical research do have a major interest in
personal monitoring, and we have some ideas for the design of such moni-
tors which we think may be of value. At this time, we are pursuing these
ideas at a low level, and we hope to increase our effort in the near future.
Ultimately, it is likely that the greatest contribution the Clinical
Studies Division of EPA can make to the personal monitoring development pro-
gram may be in the Quality Assurance procedures which will be required before
the monitors can be accepted for field use. Not only will it be necessary
213
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tlUf CMHKTIOHS
FtMALf CONNECTIONS
MODULAK. CONCEPT
PEK5OML M0ni7O&S_
FIGURE 2. Conception of a modular system for design of personal monitors.
Each monitor assembly would serve for monitoring one parameter. Multiple
parameter monitors would consist of several of these fastened together side-
by-side.
/
x urrriA MODULE
ALTEHHAT1VII DATA TELtHTITBED
TOiBltrCAM SUffOBTUNrr
cntmu.ccwunnini)
MTAtrOMOI
IN MTA COLUCT VAN
AL-BKHATIVEi OATASTOBtD IM MOMfTOOfAC
ANALVZCO LOCALLY BY UlCftOCOMniTIM
ALTtRKATIVECCMEnALSCHEMO fOfl PtMQMAt MOMITOHINO
FIGURE 3, Two possible ways of handling the problem of data storage and/or
recording in the personal monitoring situation. In Alternative 1, the sub-
ject would "wear" the transmitting monitor, but recording would be carried
out in a larger, heavier but still portable briefcase-size package. In Al-
ternative 2, which depends on not-yet-available digital storage capacity,
the data are stored in the monitor itself.
214
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to show that the individual monitors can measure air pollutants or health
effects parameters with acceptable accuracy and dependability, but it will
also be necessary to show that the monitors can be worn by the subject all
day long without causing him or her undue discomfort or without restricting
his/her movements. The monitors must be tested with all components (environ-
mental and health) operating in a situation where actual changes in pollutant
levels are occurring. This kind of testing—the final step in certification
of quality assurance—can only be carried out in exposure chambers of the type
that we have.
In the final analysis, only the clinical scientist can make the most
important judgment of all—whether observed alterations in the monitored
health variables can be considered to be indicators of decrements in human
health. That is what the whole program is about. The Clinical Studies
Division of EPA wants and expects to play a significant role in the personal
monitor development program, as well as in the ultimate program of use of
the monitors.
The personal monitor development program will surely involve the efforts
of many individuals from many different fields. If any major effort were
ever multidisciplinary, this one is. Management components of the agencies
involved, whether they are government laboratories, university laboratories,
private research organizations, or industrial groups, must be aware of the
total requirements of the program, and must be made to recognize that a new
and unique type of effort is required in this program. There must be a de-
gree of organization of the effort which has not been put together up to this
time, and this will require new management techniques.
Without complete management involvement and collaboration in this de-
velopmental effort, the tasks will be much more difficult. On short notice,
there must occur some major reprograming of funding and staff assignments.
I believe that each of us must carry this message to our management, and
those of us in management must launch a major search for ways and means of
accomplishing the important job needed for the development of personal en-
vironmental and health monitoring systems.
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MAILING ADDRESS OF AUTHOR
Ralph W. Stacy, Ph.D.
Clinical Studies Division
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
216
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The Usage of Personal Monitors for
Determination of Dosage and Exposure in
Health Effect Studies
David T. Mage, Ph.D.
Statistical and Technical Analysis Branch
Environmental Monitoring and Support Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina
INTRODUCTION
The health effects of a pollutant are a function of the amount of the
material absorbed by the human protoplasm through exchange processes in the
lungs, the digestive system, the skin, and other organs. For the gaseous
pollutants such as carbon monoxide (CO) and ozone (0-), the health effects
are primarily produced from exchange processes in the lungs, although eye
irritation may be caused by absorption directly into the eye. For ozone,
eye Irritation and lachrymation may be dependent on the exposure to concen-
tration of 0_ at the eyeball surface. However, for lung irritation and
respiratory effects, the health effect may be dependent upon dosage of mate-
rial absorbed into the protoplasm at the gas exchange Interface. In design
of epidemiological studies to test hypotheses of health effects produced by
pollution, it is important for us to consider both dosage and exposure as
variables upon which the health effect is dependent.
The following sections describe the technical considerations for studies
to assess exposure and dosage and the application of personal monitors in
these studies.
EXPOSURE ASSESSMENT AND RELATION TO HEALTH
A health effect of oxidants such as ozone and peroxyacetylnitrate (PAN)
217
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is eye irritation. We may hypothesize that the severity of the effect during
the study period is a function of the number of oxidant molecules which are
absorbed into the eye fluids per unit time. The rate of mass transfer from
the ambient air into the eye fluid may be modeled as a function of the am-
bient concentration and the physical properties of the fluids such as solu-
bilities, diffusion coefficients, etc. Because these physical properties
are relatively constant for exposed individuals, the only necessary variable
to be measured is the ambient concentration. The chemical properties of
the eye fluids will vary between individuals and cause different responses
to a constant exposure. In this case, the dosage to the eye is directly
dependent upon the ambient concentration, and a correlation can be made be-
tween the measured health effects and the exposure.
During an epidemiological study, a person is exposed to air pollution
in many different ways. For simplicity, four exposure categories may be
defined as follows:
1) Ambient (outside buildings)
2) Residential (indoors at home)
3) Occupational (at work, indoors, or out-of-doors)
4) Miscellaneous (in a vehicle, at a theater, etc.).
The average exposure X_, in the period T, can be represented by Equation 1.
= |/T Xdt [1]
where X represents the concentration to which the person is exposed in each
of the four categories described above during the study period T.
Assuming a control is available for the experiment by a measured re-
sponse to low-level exposures, X^aO, the excess health effect can be defined
AHE=f(XE)-f(0). The excess health effect AHE can be plotted versus X£ and
a correlation developed. Figure 1 shows the expected results from an experi-
ment in which the underlying relationship is linear. The data points will
scatter about the regression line, and the correlation coefficient will be
close to 1. These results are obtainable if the exposures of all the experi-
mental subjects are computed by Equation 1. In practice, however, this may
not be possible. Several epidemiological studies have compared the excess
health effects observed in the study populations, A HE, with the average am-
bient or outside air concentration of the pollutant, X.. If we were able
to measure Xg for all study subjects, the distribution of the integrated
exposures would have a finite variance, and X. may or may not be close to
the average exposure concentration of the n subjects in the health study
218
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EXCESS
HEALTH
EFFECT
HOC)
0
hypothetical relation
of health to exposure
EXPOSURE TO POLLUTION X
FIGURE 1. Linear relation of excess health effect to pollution exposure.
p(X)
NUMBER OF|
SUBJECTS
WITH
EXPOSURE X
mean
arbitrary
distribution
of personal
exposures
EXPOSURE X
FIGURE 2. Hypothetical frequency distribution of population exposure to
pollution.
219
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defined as 5^ where X£ = S XE /n. A distributional relationship may be as
n n j=l j
shown in Figure 2. The data from an ambient exposure experiment can lead to
a valid conclusion when AHE is functionally related with JL if Xf JL . This
n
is demonstrated by the following analysis. We can define the probability
of a health effect for the ith individual exposed to air pollution as the
integral over all possible exposures of the probability of receiving an expo-
sure, X^, times the probability that a health effect will occur at exposure X_,
This relation can be expressed as:
p(H)1 = /"p(X) H(X) dX [2]
where: p(X) is the probability of exposure Xp,
H(X) is the probability of a health effect given exposure X_,
is the total probability of health effect in the individual i.
Let us assume H(X)=k X_., where k. is a complex function of other vari-
ables such as age, sex, race, smoking habits, physiological state, and past
exposures to pollution of the ith individual. Substitution into Equation 2
gives:
OD _ — —
p(H)i - / k1XEp(XE)dXE [3]
If the health study examines n individuals, we may estimate the total number
of individuals m who exhibit a health effect as:
i-n
m = £ p(H) [4]
11 oo _ _ _
and m = IS k^pCX^dXg. [5]
Since k. is a function independent of
and m =
where k is the average value of k. in the population n
i7'
220
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If the average ambient air concentration, X., is approximately equal
to the mean value Xg , (X^Xg ), then the experiment can lead to a valid
n n
relationship between health effects and measured exposures. In the case where
* Xj, the relationship will either underestimate or overestimate the
n
effect of the pollutant on human health unless there is a known consistent
relation between X. and X- .
n
EXPERIMENTAL DESIGN
The design of an experiment to relate population exposure to health
effects requires knowledge of both the average value of k (k) and the average
value of XgCX., ). The value of k can be determined from clinical evaluations
n
and knowledge of the age-health relations of the population. The value of
Xg requires measurement of the distribution of Xg. One method for estimating
n
the mean exposure of the community is to use the technique of random sampling
(1). An outline of a study design contains the following elements:
1) Estimation of the variance of the exposure distribution. A pilot
study of selected Individuals may give estimates of the minimum and maximum
2
exposures as well as the variance (o ) of the distribution.
2) Detailed Study Design. Based upon the estimate of the variance, a
detailed sampling design can be made to achieve an estimate of the true mean
exposure with any combination of accuracy and confidence level desired. The
constraints of time, cost, logistics, etc., are all considered, and the
number of individuals to be sampled is chosen. The result is a study de-
signed to measure the mean population exposure within AX ppm at a y percent
level of confidence. In general, the measured mean of a set of n random
samples, in the limit as n becomes very large (»), is a member of a normally
distributed population with mean Xg and variance o /n. For small n, the
n
Student's t-distribution is required to set the levels of confidence. For
example, if we estimate the variance of the distribution of exposures as 16
ppm and we take 36 random samples, the mean of the 36 samples will be with-
1.35 ppm of the true mean, 95 percent of the time.
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3) Conduct the experiment. Sample the exposures of n individuals chosen
in accord with the study design.
DOSAGE ASSESSMENT AND RELATION TO HEALTH
The dosage, D, is the mass of pollutant that the subject accumulates
during the study period T. For this discussion we will assume that inhalation
is the only significant pathway for the material to enter the body during the
period of the study. The dosage can be computed by Equation 8.
4
D = Z/ T(X -X )v#v)dt [8]
i=l 1 eq
3
Where: X is the exposure in the ith category, |»g/m
i
C
ec
body fluids
X is the concentration of pollutant in equilibrium with the
v is the ventilation rate, m /min
<^(v) is the fraction of the theoretical mass transfer which is ob-
tained, 0«£(v)X. (2). The health effect may also be depen-
dent on the dose received per unit body weight, M. For the purpose of this
analysis, we will assume that <£(v)=1.0, X =0, and that AHE is dependent
on dosage D, although in practice one should compare the results of the ex-
periment by correlating AHE with both D and D/M.
As in the case of linearly related exposure health effects, it can also
be shown that if excess health effects are linearly related to D, then meas-
urement of D produces valid results when correlated with AHE.
In the past, several epidemiological studies have been performed as
exposure experiments when the excess health effect observed was dependent
on dosage. In these cases, the health effects were correlated with exposure
instead of dosage, and, as a result, the true relation may have been hidden.
To demonstrate the difference between X. and D, let us imagine a group
of outdoor tennis players (A) being observed by sedentary spectators (B)
with a constant k for all (A) and (B). During the match, the (A) group has
222
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a ventilation rate of 30 liters/minute, and the (B) group has a ventilation
rate of 10 liters/minute. Both (A) and (B) have identical exposure in terms
of Xj, but (A) has three times the dosage of (B). On this day, if we study
the health of these type (A) and (B) people, during a period AT, we might
get results as shown in Figures 3A and 3B.
The plot of p(H) versus X^ shows variable health effects with a constant
exposure, but the plot of p(H) versus 5 shows increasing health effects with
an increase of dosage. Experiments have shown this type of relationship,
where increasing exercise levels at constant concentration leads to increasing
health effects of the subjects. The difference between X. and D can be
significant. Respiration and ventilation are at a minimum during sleep,
which usually occurs at night. During the day, when active, the respiration
and ventilation rates are higher. This relation is directly analogous to the
diurnal variation of ambient pollution, which is usually minimum at night
and maximum during the day. Consequently, there is a positive correlation
between v and X and in general D/v T>X_, where v is the average ventilation
rate. If AHE is analyzed with X. instead of iL , the difference in results
will be even greater. n
In order to estimate the dosage D, it is necessary to monitor the sub-
ject's activity and exposure to pollution. A table which could allow the
computation of D for an individual may look something like Table 1.
By estimating the ventilation rate, v, and pollutant exposure, X , at
each location, the integral of Equation 8 can be solved for D over the per-
iod of the study. A random sample of people can be studied, and as their
exposures and activities are determined, the distribution p(D) can be esti-
mated. As described previously for exposure, the necessary sample size for
the dosage experiment is a function of the expected variation of X. and v
throughout the study community, the desired accuracy, and the designed con-
fidence level. By taking a random sample of location of exposure and activity
pairs, we can determine the mean dosage of the subjects, which is an estimate
of the distribution mean.
The treatment of health data as being correlated with X. instead of D
may have contributed to the number of studies which produced nonstatistically
significant results. The treatment of AHE as a function of X. instead of D
may also have contributed to the difficulty in reproducing results of epi-
demiological studies.
223
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EXCESS
HEALTH
EFFECT
Difference between relations
of dose and exposure to health
EXPOSURE X
0
DOSAGE D
FIGURE 3A. Relation of excess health FIGURE 3B. Relation of excess health
effect to pollution exposure. effect to pollution dosage.
TABLE 1
Hypothetical Table of Activity and Location
TIME
LOCATION OF EXPOSURE
ACTIVITY
0000-0700
0700-0800
0800-0900
0900-1700
1700-1800
1800-1900
1900-2100
2100-2200
2200-2400
Home—indoors
Home—indoors
In car to work
At office—indoors
In car to home
Home-outdoors
Home—indoors
Jogging—outdoors
Home—indoors
Sleeping
Light activity
Sedentary
Sedentary
Sedentary
Light activity
Sedentary
Very active
Sleeping
224
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SUMMARY
The design of epidemiological experiments needs to consider whether
exposure or dosage of pollution is the independent variable. When dosage
is the governing variable, the correlation between exposure and ventilation
rate should be accounted for. Personal monitors can be used effectively to
define the exposure distribution by a random sampling procedure, and venti-
lation can be estimated by knowledge of activity patterns.
REFERENCES
1. Mage, D.T., Ott, U.R. Random Sampling as an Inexpensive Means of Meas-
uring Annual Average Air Pollution Concentrations in Urban Areas.
Paper #75-143, 68th APCA, Boston, Mass., June 1975.
2. Ott, W.R., Mage, D.T. Interpreting Urban Carbon Monoxide Concentrations
by Means of a Computerized Blood COHb Model. J Air Pollut Control Assoc
28:911-916, 1978.
MAILING ADDRESS OF AUTHOR
David T. Mage, Ph.D.
Statistical and Technical Analysis Branch
Environmental Monitoring and Support Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
Discussion
BRAUN: David Braun, 3M Company. I enjoyed your paper very much. I
would like you to comment, if you would, on the lung capture efficiency,
because not all of the pollutant that we ventilate is captured by the lungs.
MAGE: That is correct. It is a variable for some pollutants. As a
matter of fact, if your blood has higher COHb than the COHb which would be
an equilibrium with the ambient CO, you won't take any CO in; you will exhale
CO.
And the efficiency of captures of particles, for instance, is a function
of the ventilation rate. 1 have oversimplified here purposely in that I
assume my efficiency capture unit is constant. It is a variable that would
have'to be built in.
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ZISKIND: Richard Ziskind, Science Applications. Do you think there
might be any circumstances with something like sulfur dioxide or another
pollutant that the body may respond to by developing brochoconstriction or
something like that, so that you need to take that type of thing into account
in the deposition of these pollutants?
MAGE: I am not a physiologist or a medical doctor, but I believe that
those things are considered in all the analyses of the health effects which
are produced.
Is there anybody here from health effects who would like to comment on
that question?
STACY: Would you repeat the question?
ZISKIND: Dr. Mage is describing how you can measure ventilation for at
least respiration rate and utilize that to help you come up with dose.
And I was wondering that when you do get into an acute exposure, an episode
of some sort, whether there are adequate indices or just that particular case
where bronchoconstriction can occur or something like that that may alter
deposition even of gases?
STACY: I think the answer to that is in the kind of information that
does not exist. The biomathematics of the whole situation, the whole dosage
situation, is very poorly understood. We don't know how much is caught up
in the termination of noses, etc.
We know that in animals breathing ozone, part of it doesn't get down
into the lungs.
With participate matter, it depends entirely on the size of the par-
ticulate and the amount of ventilation. We just don't know how to model It
yet.
ZISKIND: If you don't know how to model deposition, you can't go to
the modeling of the effect of deposition.
STACY: The biomathematics of that situation is extremely crude at this
time.
SCHEIDE: Gene Scheide, Environmetries. You also have synergistic ef-
fects.
WHITE: Otto White, Brookhaven Laboratories. Two comments: one is that
comparison in your model for exposure with the radiation data and to see
whether or not you can predict a thousand dollars per person as being pro-
jected as the risk value in the radiation Industry; the second comment deals
with the linear dose response—I guess through all your relationships that
there is no threshold effect. Could you comment on that?
MAGE: I haven't looked at the radiational calculations that you pointed
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out, but I would be pleased to if we can get together later.
As far as a zero threshold, this is just my assumption. There are people
who see hockey sticks, that is, no effect below a certain value. It is quite
controversial whether there is such a thing as a threshold.
When you consider that you have a control group which can have positive
and negative deviations about their average response, and you compare it to
people with low exposures, sometimes it is very, very hard to differentiate
between no effect or no statistically significant effect.
Many times we have to have very large populations in order to get the
power of the test to discern it. I have just chosen the simplest model.
STACY: Dave, 1 would like to hear you defend the statement you made a
little earlier—that because most people are awake in the daytime, it would
be better to have high pollution at night and low pollution in the daytime.
MAGE: OK, 1 will defend it to you as a member of the population who
is concerned about the total number of people in the country who are exposed.
STACY: This is the question I am really asking: Should we be concerned
about the average individual and his average exposure? Or should we be con-
cerned about the worst case exposure?
MAGE: Let me give you a very clear definite answer: yes and no. Yes;
we should as human beings. No; not if we are starting to look at economic
evaluations, cost, and benefit. I mean, if there is only one person in the
whole United States exposed to a particular level and it produces a health
effect, it might be cheaper to give him or her $50,000 to move across town
rather than spend a billion dollars to clean up the stack.
These are decisions that somebody other than myself will have to make.
But these are also considerations that we have to look into.
DOCKERY: Doug Dockery, Harvard. You are concerned about the positive
correlation between inhalation and air pollution levels in that you would
breathe harder during high exposure.
I can't quantify this, but looking at our indoor-outdoor data and our
personal monitoring data, in my experience people are involuntarily respond-
ing to the bad air pollution levels by doing things to clean up their homes.
And what we are seeing on the whole when we look across all our cities
where we supposedly have a large difference in the air pollution levels—when
we look at the indoor levels and what their exposure is—we see very, very
small differences between this, because there has been this response of
people not wanting to dust as often. So, they are closing up their houses
and making other changes in their lifestyle to ameliorate their air pollution
exposure.
And I think the actual case is just the opposite of what you are con-
cerned about.
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MAGE: The positive correlation I referred to arises because people are
awake during the day and breathe at a faster rate. When pollution is higher
during daylight hours, there is a positive correlation.
CHAPMAN: Robert Chapman, EPA. Dave, I was concerned where the previous
discussion got left off by leaving in people's minds the impression that in
certain types of epidemiological studies, it wouldn't be very useful to have
an ongoing indication of what people's respiratory rate was.
I think it would be useful—very useful—in certain types of epidemio-
logical studies for this reason: no matter whether one gets a clear indication
of absolute dose from multiplying exposure times respiratory rate, one still
can, 1 think, get some decent indication of relative dose between or among
the people in the study on the grounds that the same type of pollution—and I
realize what I am about to say is challengeable—within limits can be expected
to affect all study participants in more or less the same way.
I know that there are a lot of holes in that statement. Still in all,
I think that the uniformity of response would be enough so that if you do
concentration measurements over the course of these people's exposure time,
as well as their respiratory rate over the same time, you would get a con-
siderably better indication of relative dose than we are able to get right
now.
MAGE: Yes; I agree.
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Carboxyhemoglobin Determinations from
Expired Air
Harold W. Tomlinson
ladec, Inc.
Albany, New York
Carbon monoxide is the most widely distributed and the most commonly
occurring air pollutant. Total emissions of carbon monoxide to the atmos-
phere exceed those of all other pollutants combined (1). Carbon monoxide
combines with hemoglobin to form carboxyhemoglobin (COHb). A new Instrument
called the Carboximeter was designed to measure this.
Hemoglobin has an affinity for carbon monoxide over oxygen of greater
than 200 to 1; thus, it displaces oxygen, resulting in an interference with
the oxygen transport system of the body. It also moves the oxygen dissoci-
ation curve to the left, binding the remaining oxygen more tightly. The pre-
dictability of carbon monoxide absorption and elimination in man makes the
test for COHb a method of estimating ambient carbon monoxide levels to which
a subject has been exposed. DHEW Secretary Califano's Office on Smoking and
Health has started emphasizing the adverse health effects of carbon monoxide
from tobacco smoke, which was highlighted in the recent Surgeon General* s
report. COHb and smoking are dose related, and the Office on Smoking and
Health now uses a Carboximeter to demonstrate this immediate biological ef-
fect of smoking.
The heart appears to be the most vulnerable target organ for elevated
COHb. Medical research has provided a new role for low-level COHb in heart
disease.
Some of these adverse health effects have been measured at only slightly
elevated COHb levels (2). For Instance, levels of about 2 1/2 percent have
229
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been shown to aggravate angina and depress the forcefulness of contraction.
Levels of about 3 percent have been shown to aggravate intermittent claudi-
cation. Electrocardiograms have been altered in normal subjects at about
8 1/2 percent COHb. Thus, with this kind of medical evidence available, the
measurement of COHb has become increasingly important. Most of the well-
known symptoms of carbon monoxide poisoning such as headache, nausea, etc.,
do not occur below the 15 to 20 percent COHb level. Thus, we are usually
unaware of elevated levels in these lower ranges, and a diagnostic test is
necessary to make that determination.
Traditionally, the test for COHb has been difficult to make. It re-
quires drawing blood and performing blood gas analysis on equipment that re-
quires expert calibration and highly trained personnel to operate it. It is
usually in a location remote from the patient, resulting in delays from
sample to results. It may not always be convenient to take a blood sample,
and the sample must be properly prepared and transported. All in all, these
traditional tests are not suitable for field use or for applications where
portability or on-the-spot results would be necessary. Thus, the rarity of
obtaining COHb measurements, even when they might be useful. An alternate
method of obtaining rapid COHb levels is clearly needed. The well-known
Haldane equation expresses the relationship between alveolar CO and COHb.
This relationship was used by Dr. Sjostrand (3) to determine COHb from al-
veolar CO.
In 1958, Dr. Jones (4) demonstrated that CO tension in the alveoli will
approximate the CO tension in the pulmonary capillaries using a 20-second
breath holding technique. In this technique, the air in the lungs is ex-
pired, then a deep breath is held for 20 seconds. It is necessary to expire
all the air from the lungs and collect the last portion of air from the al-
veoli. The alveolar CO is then measured. Using this technique, Jones demon-
strated an almost linear relationship between alveolar CO and COHb. Several
other studies using the Jones 20-second breath holding technique have cor-
roborated this relationship. Two curves derived from such studies are shown
in Figure 1 and compared to the curve of Dr. Jones. One is from Dr. Peterson
(5) and the other from Dr. Stewart (6). These are best-fit curves from mul-
tiple data points. Dr. Peterson derived the formula shown, and it is this
formula which we have selected to use for conversion of alveolar CO to percent
COHb. With this alveolar CO-COHb relationship well established, it was nec-
essary to develop an instrument that would measure alveolar CO accurately
and reliably, not only under lab or clinical conditions, but in field situ-
ations where portability is important.
230
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JONES, R.H.«al
PETERSON.J.E.
ff *COHb ' V 108.08 + 7.6 COA -11.89
10
30
PERCENT COHb
FIGURE 1. The relationship between alveolar CO and COHb after 20-second
breath holding.
Theoretically, any instrument that can measure CO in air could be used
to measure COHb by the expired-air technique. However, there are many po-
tential areas for error if an ambient CO monitor is used. The Ecolyzer,
with its accuracy, ease of calibration, and portability, has become one of
the most popular instruments for measuring CO In ambient air. Indeed, it
has been used to measure expired air CO for conversion to percent COHb.
The sensor has excellent linearity accuracy and repeatability, and a
minimum detectable sensitivity of .5 ppm. Thus, it has the ability to re-
liably read low concentrations and to measure normal COHb levels. For ex-
ample, 1 percent COHb—the approximate average normal for nonsmokers—repre-
sents only about 7 ppm of CO in expired air. This is a result of red cell
destruction and breathing naturally produced CO in ambient air.
Recognizing the need for a new instrument to measure COHb by the expired-
air technique, we joined with Energetics Science to design this new instru-
ment with the advantages of the sensor but without the disadvantages of the
ambient air monitor for this procedure. We designed out several areas of
231
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potential error possible when using ambient air monitors for making the
COHb test.
Figure 2 is a flow diagram of the system. The sample chamber is de-
signed to collect the last 20 cc's of air blown into it. This is important
because the accurate conversion of alveolar CO to percent COHb requires a
good alveolar air sample. Using bags for the collection of expired air
samples risks dilution of alveolar air and exposing the sample to ambient
CO. Our system eliminates the use of bags. The breathing technique for
blowing the sample into the sample collection system is also simplified. How-
ever, nonalveolar breath samples taken without the breath holding technique
are usually about 10 to 15 percent lower—close enough to make the Instrument
useful in obtaining immediate confirmation of CO exposure in uncooperative
subjects.
Our readout is directly in percent COHb. We eliminate the need to con-
vert the readings of ppm of CO to percent COHb, thus reducing the potential
for error. When using the ambient air monitor, we found it quite common for
a reading of, say, 20 ppm of CO to be recorded as 20 percent COHb.
We have added an automatic scale change on our dual scale. One scale
is zero to 10 percent COHb, and the other is zero to 33 percent. When the
reading goes over 10 percent, the needle will automatically move to the larg-
er scale, and a light will indicate that that scale should be read. When
the instrument is reset, it automatically goes back to the smaller scale.
This of course reduces the risk of reading the wrong scale. A sample-and-
hold circuit allows for proper reading and recording results. The peak CO
in the sample is measured and the meter indicates percent COHb, holding the
reading until the instrument is reset.
We isolate the alveolar air sample by use of a zero filter on the out-
board end of the sample chamber. Thus, when we pump the sample from the
sample chamber to the sensor, all ambient CO is removed, and the only CO to
reach the sensor comes from the lungs.
We have moved the high voltage outside the case with a UL-approved
battery charger, but we have retained the portability with rechargeable
batteries. The instrument can be used in its portable mode for up to 8
hours.
There are other design considerations that I will mention briefly.
232
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SAMPLE INPUT
I
INTERFERENCE
FILTER
INPUT VALVE
OPEN
SENSOR
PUMP
INTERFERENCE
FILTER
f OVERFLOW EXHAUST
SAMPLE
CHAMBER
SAMPLING MODE
INTERFERENCE
FILTER
INPUT VALVE I |
CLOSED
SENSOR
PUMP
INTERFERENCE
FILTER
f^tf+W*1 ••••••••••Mi
EXHAUST
SAMPLE pi i TCD
CHAMBER FILTER
ANALYZING MODE
FIGURE 2. Flow diagram of the system.
233
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We have angled the meter to make it easy to read and have added a carrying
compartment in the cover. We have gone to a simple pushbutton operation,
and we have even added a 20-second timer on the face of the panel so that
the 20-second breath holding technique can be performed without a clock or
watch. We calibrate with 20 ppm of CO, which converts to 4.3 percent on
our top scale. The instrument weighs only 10 pounds, and it is still pos-
sible to use the bag-sampling technique if the instrument and the subject
cannot be brought together.
Some of the uses for which the Carboximeter is being used include:
measuring shift workers before and after work to determine GO exposure on
the job, measuring the rate of heme catabolism, counseling smokers, and
correcting for COHb error from total saturated blood. It is important to
remember that even a small dose of CO can be detected if it is combined with
hemoglobin. Carbon monoxide in the ambient air never hurt anyone. When
attached to hemoglobin, it becomes very dangerous. The Carboximeter can
be carried to any location to determine not how much CO is in the ambient
air around the subject, but how much CO was actually inhaled by the subject
and combined with his or her hemoglobin.
In summary, this Carboximeter development project has resulted in an
instrument that is lightweight and portable, is accurate even at low COHb
levels, and will readout directly in percent COHb with a simple 30-second
breath test.
REFERENCES
1. Department of Health, Education, and Welfare. Air Quality Criteria for
Carbon Monoxide. March 1970, 2-1.
2. Goldsmith, Jr., Aronow, W.S. Carbon Monoxide and Coronary Heart Disease:
A Review. Environ Res 10:236-248, 1975.
3. Sjostrand, T. A Method for the Determination of Carboxyhemoglobin
Concentrations by Analysis of Alveolar Air. Acta Physiol Scand 16:
201-297, 1948.
4. Jones, R.H. et al. The Relationship between Alveolar and Blood Carbon
Monoxide Concentrations During Breathholding: Simple Estimate of COHb
Saturation. J Lab Clin Med 51:553-564, 1958.
5. Peterson, J.E. Postexposure Relationship of Carbon Monoxide In Blood
and Expired Air. Arch Environ Health, 21(9), 1970.
234
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6. Stewart, R.D. et al. Rapid Estimation of Carboxyhemoglobin Level in
Fire Fighters. JAMA 235(4), 1976.
MAILING ADDRESS OF AUTHOR
Harold W. Tomlinson
ladec, Inc.
1A Lincoln Avenue
Albany, New York 12205
Discussion
MAGE: Is there any restriction in the amount of expired breath that is
necessary? I am interested in school children; how small a child can use
this device and this technique?
TOMLINSON: One of the reasons we made the sample chamber so small is
for that very reason—so that we would not require a large sample. Almost
anyone who is capable of breathing into the instrument, regardless of the
size of his lungs, can get a big enough sample, a 20 cc sample, out of it.
As a matter of fact, this is being used in schools right now for smoking
education. And the kids love it. They have no problem using it. They blow
into it, and we are getting excellent results in that kind of application.
ZISKIND: Richard Ziskind, Science Applications. A couple of questions:
first, could you tell us anything about the school children levels of CO
you are defining compared to an adult level?
TOMLINSON: We have found that generally speaking, the carboxyhemoglobin
levels are—with the kids who smoke—above what we would find in adults.
I don't have all the data with me, but that is the overall look of it.
What is amazing is that the smoking age keeps going down. We get kids
smoking in the fourth, fifth, and sixth grades.
ZISKIND: Another question: I have seen one study that indicates a varia-
tion in regression coefficient between alveoli CO level and carboxyhemoglobin
which suggests that before doing any survey—especially if you are going to
look at many people and contrast, say, two groups such as control and ex-
posure—that they would recommend direct blood analysis be made at least on
some proportion of that population that they are going to look at.
Would you think that is not necessary?
235
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TOMLINSON: Well, we have done quite a number of tests on fairly large
groups of people. We have done bloods on the original development of this
with very good correlations.
As a matter of fact, Dr. Anderson at the University of Louisville has
two of these instruments. He reported to me last April that he was getting
a .96 correlation of bloods done on the new IL-282. The old 182 was not very
reliable for COHb, but the 282 is pretty good.
ZISKIND: What is the price?
TOMLINSON: $3,500.
SPEN6LER: I have done a lot of carboxyhemoglobin tests as you described
with an Ecolyzer and found that 1 had a lot of problems with someone who had
recently used an alcohol mouthwash. If any volatile stuff was ingested pre-
vious to the test, an instrument would give a positive reading for a long
period of time—sort of poison the action for a while.
Have you eliminated that problem?
TOMLINSON: The interference filter in the mouthpiece assembly is pri-
marily for alcohol. It will absorb a lot of it. There is a simple test to
determine when the filter begins to pass alcohol, but that is in calibration
gas through it.
But you are right; it will do that. If a guy has a "two martini lunch,"
even the mouthpiece filter will not take it out if it is used after the in-
gestion.
That is a problem. Particularly in exhibitions, in trade shows, people
come around after lunch and say, "I want to blow into your machine." And
it is very difficult to explain their responses.
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Intelligent Personal Physiologic Monitors in
Clinical Environmental Health Effects
Research (Part I)
Mathew L. Petrovick
Physiology Branch, Clinical Studies Division
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina
INTRODUCTION
The lack of a definitive data base in urban environmental health ef-
fects research (2,9,12,13,18) today is based to a large extent on systems
and devices representing extensions of hospital-oriented biomedical instru-
mentation* These devices are frequently designed as vital sign detectors
for patients with well-developed physiologic symptoms; i.e., known cardiac
history, emphysema, post-surgical recovery, and the acutely ill. Devices
of this type serve in life-saving roles and need not have the sensitivity
to detect subtle physiologic changes. Detection of subtle physiologic
changes in a normal, healthy, urban population requires considerable clinical
judgment as a means of screening out false positives. As such, conventional
biomedical instrumentation may not be adequate for assessment of subtle
changes in normal, mobile, healthy adults exposed to environmental pollutants.
Conventional biomedical Instrumentation systems may be useful in clinical
health effects research as baseline reference measuring devices. However,
the subject must be brought to the clinic, thus limiting the population
under study. The problem in urban personal monitoring requires incorporating
the biomedical and pollutant instrumentation on-board the attire of the test
subject as a means of data collection (12). The bulk, size, weight, power,
and lack of subtle detection sensitivity, and the lack of portability of con-
ventional hospital-like instruments, are incompatible with clinical epidemio-
logic research. Ideally, health effects protocols designed to search out
dose-response relationships must be extended from the clinical research lab-
237
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oratory to the field through implementation of properly designed "personal
monitors." The rationale of present-day clinical protocols does not lend it-
self to personal monitoring, in view of the high degree of test-subject
mobility and normal function in daily activities.
The above limitations have precluded the design and implementation of
clinically useful systems and, in effect, have limited the urban health ef-
fects data base. In order to circumvent the above limitations, a quantum
jump in the scientific design of biomedical instrumentation, transducers, and
pollutant dosimeters is imperative. Successful clinical epidemiologic re-
search, therefore, must be based on highly individualized noninvasive tech-
niques, interactive software systems, transducers, and highly sophisticated
systems managers in the form of microcomputers, all on-board the mobile ur-
ban test subject as exemplified in Healthe-Belt (12).
It is, therefore, the objective of this paper to establish a series
of basic and fundamental guidelines toward the design of environmentally
useful personal monitors, as opposed to classic hospital-like devices used
in clinical research. In view of the limitations of previous technology
(9,13), this design initiative is set forth herein through illustration of
several design examples requiring a significant change in operational and
clinical philosophy. Several new and original concepts are introduced which
take advantage of the modern measurement technology, very large scale inte-
gration (VLSI), and microcomputers (14,15,17), today and in the near future.
DESIGN STRATEGY FOR INTELLIGENT PERSONAL PHYSIOLOGIC MONITORS (IPPM)
Dose-response measurements on a normal individual performing daily ac-
tivities or work tasks within his/her environment must be based on two major
elements in order to represent credible and scientific health effects data.
These elements are the simultaneous measurement and documentation of pollut-
ant dose level and concomitant physiologic response. This philosophy must
be recognized as fundamental to any health effects research (9,12,13).
Further, this concept is the cornerstone of any management strategy in the
design of any personal monitor system In support of scientifically credible
legislation. Since design of pollutant dosimeters is an extensive subject
beyond the scope of this paper (18), only the physiologic data acquisition
system designs will be addressed herein.
Clinical epidemiologic requirements for personal monitors are broad and
238
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extensive. In order to introduce and establish the roots of a new design
philosophy (4,11,12), a series of design priorities are identified to illus-
trate the need, criteria, and methodology in attaining a quantum jump (11)
in system design required for EPA to fulfill its part in any Public Health
Initiative through intelligent personal physiologic monitors. Design of
personal monitors must include the following priorities:
• Test subject comfort and wearability;
• Design of clinical data base;
• Design of new physiologic parameters;
• Design of new multimode transducers;
• Design of new algorithms to replace conventional electronic circuits;
• Design of clinical field logistics and the means to clinically vali-
date and characterize system performance with clinical and air pollutant
standards.
USER DESIGN CRITERIA FOR INTELLIGENT PERSONAL PHYSIOLOGIC MONITORS
The EPA/Health Effects Research Laboratory response to the Office of
Health Effects mandates imposes the need for significant scientific flexi-
bility in collection of desired data base knowledge in support of preventive
environmental medicine and proposed legislation. This requirement, coupled
with the advancements of medicine and technology, creates the need for the
ever-changing variety of multlvariable protocols which have become a fact
of life in health effects research. Conversely, no organization can afford to
re-tool its scientific resources each time a new research issue or pollutant
episode develops. This is particularly critical in assessing environmental
episodes and concomitant health effects data. Clinical research in the past
has advocated the design of new systems and devices to suit specific protocols
wherein the design cycle time is Incompatible with pollutant episodes and the
need to characterize related health decrements. Frequently, when such systems
transfer from the development stage to the clinical-use stage, they are often
obsolete or the protocols have been changed to answer new research questions.
Therefore, utilizing conventional hospital biomedical instrumentation in this
type of research climate would render these systems almost useless. In order
to illustrate the type of design flexibility envisioned by the clinical in-
vestigator, the following criteria depict a few guidelines necessary for a
quantum jump in design of IPPM systems.
User Design Criteria
1) Design a legislatively defensible data base as a first-line scien-
239
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tiflc priority before any system designs are attempted.
2) Design means for software flexibility in protocol changes so as to
support the data base product.
3) Provide protocol flexibility through adaptive software designs and
elimination of hardware wherever possible.
4) Incorporate modularized prescription design for ease of protocol
adaptability.
5) Provide means of protocol replication by others through very large
scale integrated circuit memories erasable programmable read only memories
(EPROMS).
6) Design anatomically comfortable transducers which provide a natural
interface to male and female test-subject anatomy.
7) Design multimode transducers to acquire more than one parameter
from a given anatomic site and reduce subject encumbrance.
8) Design "intelligent transducers" which are capable of sensing phys-
iologic data and converting these data into meaningful clinical measurements
prior to reporting on call to a higher-level system.
9) Incorporate multimode statistical data base at the system level to
avoid extensive redesign of data base at the end of a given study.
10) Design standardized modular systems and sensors which are Inter-
changeable and adaptable to several protocols and/or research questions.
11) Maintain fixed hardware while software provides the key flexibility
and is varied to suit new research questions.
12) Ensure that system size, weight, power, and interfacing are com-
patible with normal human activities and acquisition of scientific data.
13) Ensure cost effectiveness through anticipatory design in support of
high-volume disposal IPPM systems.
14) Replace conventional (TTL) circuit logic with microcomputerized
algorithms performing circuit logic functions wherever possible.
240
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15) Design all systems in direct anticipation of changing needs and
minimize technological obsolescence when protocols or programs are changed.
INTELLIGENT PHYSIOLOGIC PERSONAL MONITOR (IPPM) MK-I
Intelligent personal physiologic monitors represent a significant depar-
ture from conventional clinical instrumentation in that IPPM devices (11,12)
are designed to respond to noninvasive environmental health effects needs
and not life-saving functions. The key design factors identified above are
reflected and illustrated in the design approach described here.
The design approach to IPPM systems and devices must be based on multi-
level modular designs geared to the ever-changing and accelerated technology
of today and to that of the next 5 years. It is not uncommon today to initi-
ate a given systems design effort only to find protocols were changed or be-
came obsolete 18 months later when the device was completed. It is, therefore,
imperative that the design structure advocated must be constantly and contin-
uously adaptable to changing needs throughout the design and development
cycle. The most effective approach to adaptive design is through flexible
microcomputer software. Previous technology (9,10,13) has not been respon-
sive to this design philosophy and has resulted in a multitude of surplus
instruments or hardware designs for each protocol or each new research ques-
tion. Conversely, hardware logic has its place in many endeavors. However,
the bulk, size, power, and weight of sensors and instrumentation would pose
considerable constraints on human anatomy by conventional design methodology.
Clinical criteria, changing protocols, new research questions, cost effective-
ness, and the need for mass clinical epidemiologic screening of the population
demand a "revolutionary change" in overall design approach of physiologic data
acquisition systems (PDAS) for any clinical research. The major attributes
of any PDAS system design (12) responsive to the above criteria and, specifi-
cally, to health effects personal monitors, are "clinical flexibility,"
"test subject comfort and acceptance," and "cost effectiveness." The design
of these attributes begins with interfacing the human anatomy to the phys-
iologic transducer (8).
ANATOMY-TO-TRANSDUCER INTERFACE
Considering today's technology, particularly very large scale integra-
tion of the next 3 to 5 years (14,15), the most promising approach in design
241
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of personal monitors is clinically interactive software which emulates hard-
ware logic functions in concert with human judgment. By imparting inter-
active human judgments or clinical rationale to the processing of health
effects data, we impose a level of human intelligence as an inherent function
of the system design. Hence, the name "intelligent personal physiologic
monitors."
The efficacy of any PDAS system is based on the type of analog signals
available which represent the range of human variance to be analyzed and
documented in a given data base design.
IPPM devices are unique in that five major constraints are imposed on
the designer and the clinical researcher. These are:
• All transducers and measurements must be noninvasive and painless.
• The need for subject freedom, comfort, and ease of wearability
without loss of scientific data is imperative to the success of IPPM.
• Significant limitations exist in the interfacing of noninvasive
transducers to both male and female anatomy in search of valid physiologic
parameters.
• Size versus function is a matter of technological trade-offs as
contrasted against a definitive data base design.
• Cost effectiveness must permit mass production in order to reach
statistically significant populations in support of any EPA Public Health
Initiative.
The significant constraints of human anatomy demand and impose the ac-
quisition of multimode physiologic transducers from the minimal number of
anatomic placements; i.e., multimode transducers (11) should provide two
or more parameters from a common transducer. Hence, time-shared transducers
represent a realistic approach in multiparameter sensing, which may jointly
aid in characterizing physiologic decrements resulting from air pollutants.
However, multimode transducers Impose a dilemma of excessive amounts of data,
that are frequently beyond human comprehension, being produced. The signifi-
cant need herein for an IPPM is the ability to screen multimode parameter
variance based on previous human judgment and clinical criteria to the extent
of reducing transducer outputs to an interim-processed level. This endeavor
may be feasible through specifically designed "intelligent physiologic trans-
ducers" (IPT) (4,11). IPT devices serve to screen out irrelevant data and
only utilize responses which have met a level of interactive Judgment through
the rationale of clinical software protocols. The criteria and clinical
rationale would be a function of the microcomputer algorithms within the
242
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transducers themselves. Hence, in higher-level PDAS memory systems, such an
IPPM would not be saturated with useless data, thus clogging the support
of an effective and defensible data base—as is the case in some clinical
laboratory PDAS systems in existence today.
The Concept of Transphysioware
The design of IPT devices advocated here is based on transducing (8)
a given physiologic signal from the human anatomy into its analog form.
However, the need is to convert the analog signal into some meaningful clini-
cal measurement which requires a form of clinical judgment; i.e., transduce
a physiologic function signal into a meaningful clinical measurement. Im-
parting the latter judgment to a transduced signal can be accomplished, within
limits, through an appropriate algorithm. This process is defined here as
"transphysioware" (11). This function is advocated at the transducer level
by incorporation of a microcomputer within the transducer itself. Ideally,
limited screening of data would occur at the transducer level, thus simpli-
fying the process function of the IPPM whose priorities and memory capacity
is spread over several other physiologic and air pollutant dosimeter para-
meters.
Advocating a specific philosophy in any endeavor is best illustrated by
realistic examples which address the principles, problems, and efficacy of
design integrity. The key design factors identified above are reflected and
illustrated in the following example designs.
DESIGN EXAMPLE
Multlmode Respiratory Intelligent Personal Physiologic Monitor
Preliminary pulmonary function studies within EPA suggest that exercise
respiratory tidal volume and heart rate provide a means of characterizing
pulmonary reactivity to pollutants to the extent that subtle changes in over-
all lung function are detectable. Clinical studies currently underway in the
EPA CLEANS facilities have served to develop the clinical rationale in res-
piratory tidal volume measurement. However, these protocols are precluded
from use at an IPPM level. The design issue is: how to extend a respiratory
tidal volume protocol to a personal monitor level. A preliminary design of
such a system at an IPPM level is illustrated in the subsequent design.
243
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A dedicated single chip 2K memory microcomputer (Intel 8748/8749) and
supportive preprocessing are employed in a preliminary IPPM design as follows:
1) A pneumotachograph for measurement of respiratory flow is incorpo-
rated into a construction worker's helmet.
2) The transducer is normally recessed in a frontal storage area and
is pulled out with the index finger by the subject on software auditory
beeper command.
3) The subject places the pneumotachograph in his mouth (for a pre-
determined period) and continues performing his duties.
4) The microcomputerized IPPM is preprogramed to present the subject
with a previously validated protocol based on a sequence command after the
pneumotachograph is placed in the subject's mouth.
Figure 1 illustrates a timing chart of multimode parameters desired in
a typical exercise tidal volume protocol wherein only one transducer is used
for pulmonary measurements. (With multimode parameters, one anatomic place-
ment is used.) The clinical interactive rationale provided in the software
algorithm provides four parameters; i.e., respiratory rate, volume, flow, and
tidal volume, or a total of four parameters from one transducer placement.
The algorithm converts respiratory flow to volume by mathematical integration
of the flow signal. Each flow breath rate and volume signal is stored in
RAM memory and displayed in an accumulative form over a 1-minute period,
resulting in a measure of tidal volume (see Figure 1). On a separate channel,
heart rate trend is recorded and constantly compared to the prescribed clini-
cal safety level within the algorithm for a given subject's age and maximum
heart rate. Hence, the 8748 microcomputer algorithm performs an interim
level of processing, thus providing the IPPM with trend information permitting
clinically meaningful judgment in detection of subtle changes; i.e., a trans-
ducer has sensed the physiologic signal, and a microcomputer algorithm has
converted one signal into four meaningful clinical parameters (transphysioware)
as health effects indicators. If preset trend levels exceed prescribed levels
of heart rate, a flag and alarm to "halt" the test subject from further ef-
fort are initiated, and the IPPM accesses the respiratory IPT for relevant
data in support of a dose-response data base.
Figure 2 illustrates a preliminary record of the actual 8748 microcom-
puter controlled analog signals and digital measurements. Figure 3 illus-
244
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,
ALPHA NUMERIC DATA
SUBJECTCODE
PULMONARY TIDAL VOLUME PROCESSOR.
%/AI I'rTATiriM AKIAI r\f* CIOMAI C
VALIDATION ANALOG SIGNALb
TIDAL VOLUME
RESPIRATORY RATE-
RESPIRAIQRYFLOW-
HEART RATE-
RESPIRATORY
TIDAL VOLUME
RESPIRATORY
VOLUME
RESPIRATORY
FLOW
HEART
RATE
INCREASED TIDAL-
VOLUME
*-WORKERS' EXERCISE-*'
STRESS PERIOD J
DECREASED ,'
TIDAL VOLUME i
• DECREASED VOLUME
' INCREASED RATE
INCREASED FLOW RATE
(*—ALARM PERIOD—*j
MAXIMUM HEART
RATE THRESHOLD
FIGURE 1. Ideal pulmonary function parameters from one transducer, 8748
microcomputer algorithm process. Heart rate, separate transducer.
i M -I I I f 41 I i !- i ' ! ' : :
-SPEED 1 mm/sec -^-
t i
(RESPIRATORY*
III HIM i! II '
PNEUMOTACH
TIDAL VOLUME
FIGURE 2. Actual human pulmonary record. Top, respiratory rate (digital).
Middle, respiratory flow. Bottom, respiratory tidal volume. See calibration
curve, Figure 3.
245
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7.5 T
CO
K
UJ
I
UJ
5.0-
L 2.5
0-L
£
111
i
.. I
S
§
0 20 40 60 80 100 120 140 160 180 200
ASR-33 DECIMAL TELETYPE OUTPUT
FIGURE 3. Respiratory pneumotach calibration based on Fisher-Porter Flow
Meter Model 10A1027A. System calibration includes A/D Converter and 8748
microcomputer.
8748
MICROCOMPUTER
VOLTS
ADC
2.3
2.8
2.3
2.9
3.1
2.7
2.6
TTY
DECIMAL
140
157
141
160
163
158
156
RESP.
RATE
7
7
7
7
7
7
7
TIDAL
VOL/L/M
5.8
6.1
5.1
6.8
6.9
6.6
6.3
FIGURE 4. Graphically derived 8748 microcomputer output for 1 minute of
tidal volume at rest.
246
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trates the calibration of the pulmonary tidal volume IPPM system used to pro-
duce the record of Figure 2. Figure 4 illustrates the microcomputer output
parameters computed during a 1-minute sample. Figure 5 illustrates a possible
configuration of a pulmonary IPPM built into a construction worker's head-
gear. Figure 6 illustrates design details of the exercise pulmonary tidal
volume processor contained in a construction worker's helmet.
DESIGN EXAMPLE
Multlmode Cardiopulmonary IPPM
Static cardiovascular measurement assessment of young normal test sub-
jects exposed to air pollutants may be difficult in terms of detecting subtle
change responses. Conversely, as in exercise pulmonary function, potential
for cardiac dose-response processing may be feasible through the appropriate
selection of the parameters and trend analysis.
Several cardiac parameter measurements (1,3) may be required in order
to accumulate a sufficient battery of data to establish correlation of subtle
trends or a dose-response index following pollutant episodes. As an example,
a current EPA system development study involving acquisition of cardiac
(treadmill exercise) systolic time intervals (STI) (a measure of myocardial
contractility) has demonstrated that STI measurements may be highly applicable
for field IPPM systems. The clinical validation of cardiac impedance meas-
urements has been well documented in the literature by Kubicek, Klzakevich
(5,6,7), and others. Definitions are beyond the scope of this paper and are
contained in the referenced literature (5,6,7,16,19). The multiplicity of
cardiac parameters available from impedance cardiography currently in de-
velopment at EPA/CSD clearly indicates the potential for use in IPPM systems.
(See Table 1.) Figure 7 illustrates a male electrode configuration for im-
pedance cardiography wherein STI provides an index of aortic impedance blood
flow velocity and aortic left ventricular ejection time (LVET) (5,6,7).
From these two basic cardiac measurements, it is possible through clinical
rationale to develop several parameters which give further insight to vari-
ations in normal cardiac performance. Figure 8 illustrates a real time
microcomputer display of heart rate during a "Bruce" exercise protocol. The
display incorporates a medical-legal safety monitor for heart rate (see 85
percent max) and a heart-rate trend throughout the protocol period.
An Intel 8010 single board microcomputer functions as a system controller
247
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(INTELLIGENT)
EXERCISE PULMONARY TIDAL VOLUME PROCESSOR
(CONSTRUCTION WORKER)
FRONTAL
COMPARTMENT
PNEUMOTACH COLLAPSES
AND FOLDS INTO
FRONTAL COMPARTMENT
PNEUMOTACH ^*
PNEUMOTACH PULLED OUT AND
INTERFACED WITH SUBJECT
DATA COLLECTION POSITION
NOTES:
• TEST SUBJECT PERFORMS HIS NATURAL ON-THE-JOB
WORK WITHOUT ENCUMBERANCE.
• THREE AUDIO BEEPS ALERT THE SUBJECT TO PULL OUT
PNEUMOTACH (1) SENSOR AND PLACE IN HIS MOUTH
UNTIL TWO AUDIO BEEPS ARE HEARD IN WHICH HE STOPS
AND RESTORES THE DEVICE IN THE HELMET.
• MICROCOMPUTER AND SIGNAL PROCESSING CIRCUITRY
CONTAINED WTTHIN STORAGE SPACE OF CONSTRUCTION
HELMET.
• ALL ALGORITHMS FOR PHYSIOLOGIC SIGNAL QUANTTTA-
TION ARE CONTAINED IN EPROMS RESIDENT IN EACH
SUBJECTS SYSTEM; I.e.. ALL CLINICAL PROTOCOLS IDEN-
TICAL IN EACH SYSTEM.
• ALL PROTOCOLS PREVIOUSLY VALIDATED IN CLEANS
PROTOCOL DEVELOPMENT PRIOR TO EPIDEMIOLOGY FIELD
USE.
FIGURE 5. Proposed tidal volume IPPM configured into construction worker's
helmet. Note details.
EXERCISE PULMONARY TIDAL VOLUME PROCESSOR
MARK I PROTOCOL
I 8748
MICROCOMPUTER
MEMORY & SIGNAL
PROCESSORS
EPROM MEMORY
WITH ALL EXERCISE
PROTOCOL STORED HERE
MODIFIED STANDARD
PLASTIC CONSTRUCTION
HELMET
NONUSE STORAGE
PNEUMOTACH
PNEUMOTACH
PULL-OUT RING
CHANGES IN CLINICAL PROTOCOLS
REQUIRE SIMPLE CHANGE OF
"EPROM" ADDRESS LOCATIONS
IN COMMANDING MICROCOMPUTER
FUNCTIONS
ALL CIRCUITRY IS BASED
ON VERY LARGE SCALE
INTEGRATED CIRCUITS
(VLSI) TECHNOLOGY.
ALL CIRCUITRY FUNCTIONS ARE
PERFORMED BY SOFTWARE
RATHER THAN HARDWARE
LOGIC WHEREVER POSSIBLE.
• MODULARIZED SOFTWARE
VLSI CIRCUITS
NOTE:
1. ONLY ONE TRANSDUCER REQUIRED TO OBTAIN THREE
RESPIRATORY VARIABLES; I.e.. PNEUOMOTACH FLOW «S
CONVERTED TO VOLUME AND TIDAL VOLUME MEASURE-
MENTS THROUGH MICROCOMPUTER ALGORITHMS.
2. HEART RATE REQUIRES ITS DEDICATED TRANSDUCER
WHILE MICROCOMPUTER ALGORITHM PROCESSES HEART
RATE AND SETS MAXIMUM HEART RATE THRESHOLDS
FOR INDIVIDUAL'S AGE; I.e., CLINICAL LEGAL SAFETY. IF
HEART RATE EXCEEDS PRESCRIBED RANGE, AN ALARM IN
THE FORM OF AN AUDITORY BUZZER GOES OFF IN
HELMET.
INPUT/OUTPUT AND
INTERFACE CIRCUITRY
FOR POST EXERCISE
INTERROGATION BY
HIGHER LEVEL
PROCESSOR
FIGURE 6. Design details and features of construction helmet.
248
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INFRARED LIQUID CRYSTAL AND
CHARGED COUPLED MATRIX
CAROTID ARTERY THERMAL
BLOOD FLOW SENSOR
PAIRED ALUMINUM ELECTRODE ALSO
SERVES AS SYSTOLIC TIME INTERVAL
DETECTOR
ECG ELECTRODES
STI ELECTRODES ALSO
SERVE AS RESPIRATORY
RATE TRANSDUCERS
INTELLIGENT MICROCOMPUTER
ALGORITHMS REDUCE DATA ON
BOARD THE SUBJECT AND STORE
IN NITRATE METAL OXIDE (NMOS)
32k MEMORIES FOR LATER RETRIEVAL
AND INTERROGATION BY CLINICAL
EPIDEMIOLOGIST
INTELLIGENT PHYSIOLOGIC
PERSONAL MONITOR
NOTE:
1. (4) ELECTRODE (3M) ALUMINUM TAPE
AND ECG PROVIDES STI
PHYSIOLOGIC VARIABLES.
2. MICROCOMPUTER ALGORITHMS TIME
SHARE TRANSDUCERS IN A SEQUENTIAL
SAMPLING THROUGHOUT ANTICIPATED
FIELD EPIDEMIOLOGIC PROTOCOLS; I.e..
REST, DAILY ACTIVITY, AND EXERCISE
PERIODS.
3. TRANSDUCERS SERVE IN MULTIMODE
FUNCTIONS PROVIDING MORE THAN
ONE PHYSIOLOGIC PARAMETER FOR
SINGLE ANATOMIC PLACEMENT.
4. ALL MEASUREMENTS ARE NONINVASIVE.
FIGURE 7.
ject.
Typical STI cardiac Impedance electrode configuration, male sub-
wherein the "R" wave of the electrocardiogram (ECG) triggers an algorithm
to perform ensemble averaging of the aortic impedance signal. Figure 9
illustrates a typical output supported by multiple parameters depicting an
index of myocardial contractibility through computation of systolic time-
interval measurement during treadmill exercise conditions. Figure 9 illus-
trates an ensemble-averaged aortic impedance signal recorded under conditions
of walking, jogging, and deep knee bends—conditions thus highly applicable
to mobile urban subjects. A microcomputer algorithm eliminates the classic
artifact, resulting in a clean, clinically useful waveform.
Figure 10 illustrates a trend plot of selected variables which have po-
tential for detection of subtle changes induced by air pollutant exposure.
Figures 8 through 10 illustrate the measurement of STI's on a male sub-
ject. However, the efficacy of a scientific statistical data base must
249
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TABLE 1
Impedance Cardiographic Parameters
PARAMETER DEFINITION
LVET Left ventricular ejection time
PEP Pre-ejection period
Ratio PEP/LVET, myocardial contractility
Heart rate Heart rate trend
Cardiac impedance 1st derivative aortic flow velocity
EMS Electromechanical systolic
R-R mask Expected R-R interval trend
R-R mean Actual data used
Av rate R-R rate
Av ctr No. cardiac cycles used
Efficiency Ratio—average over total cardiac cycles
Q-wave Component ECG waveform
T-slope Time to peak Z slope
TZ max Time to peak Z
DZA Time to diastolic peak
TZ rise Time to PEP to DZ max
TZ fall Time from max to DZX
include the measurement of identical parameters in the female population.
The transducer-to-anatomy interface on female subjects poses a unique set
of design problems, as indicated in the user design criteria. Further prob-
lems are reducing user resistance and enhanced wearabllity. Figures 11 and
12 illustrate an STI electrode configuration for a female subject wherein
comfort and natural anatomy-to-transducers interface is accomplished with
a brassiere and a choker necklace. To the left in Figure 12 is a male shirt
collar with STI electrodes built in. Figures 13 and 14 illustrate the in-
corporation of IPPM devices within shoewear for both male and female popu-
lations, as a means of Including these systems in a natural way without sacri-
fice of scientific data. (Note that both male and female measurements must
be identical in support of valid statistics.) In both users, comfort and
interface play a major role in valid physiologic data acquisition. In both
the shirt collar and choker necklace, an infrared bolometer transducer is
incorporated to monitor thermal blood flow rate; i.e., multimode transducers
or an illustration of transphysioware.
Finally, in the design of IPPM systems, every possible avenue of incor-
porating systems into clothing, headwear, shoes, belts, and jewelry must be
considered in light of the need of portable, humanly compatible IPPM systems
design.
250
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FIGURE 8
I HEART RATE
Kt/L-UK. EXERCISE DATA TO DISK
MVANCE TO NEXT STAGE
lEWIIHATE TREAOHILL EXERCISED
I 38 M 98 121 151 IN
FIGURE 9
TYPE CONTROL/I; TO COHTIHUEI
188 158 288 258 388 358 488 458 588
RUN HO RRNflSK RRHEAN AURftTE WCTR CYCLES EFFCY SHEEP
1 775 772 77 64 66 % 1*
(HMWE PEP TSLOPE TZHAX EHS DZA TZRISE TZFALL LICT
28 98 117 135 368 4
FIGURE 10
SELECT STI TREND DISPLAY
STI <»>, STIXEHS <1>, EXIT
-------
PARAMETERS
PEP
LVET
RATIO
ECG
AZDT
AZUP
ECG
ELECTRODES
ELECTRODE WIRES
STI ELECTRODES
ELECTRODE
CONNECTOR TO
MICROPROCESSOR
PDAS
ECG "P" WAVE
ELECTRODE
ARRYTHMIA
DETECTION
PERSONAL MONITOR IMPEDANCE CARDIOGRAM
FIGURE 11. Cardiac Impedance transducer-to-anatomy interface. Statistical
data base requires identical measurements on male and female subjects.
INFRARED THERMAL
BLOOD FLOW TRANSDUCER
CAROTID ARTERY AND
HEART RATE
SYSTOLIC TIME INTERVAL
IMPEDANCE CARDIOGRAM
ELECTRODES
SYSTOLIC TIME INTERVAL
IMPEDANCE CARDIOGRAM
ELECTRODES
INFRARED THERMAL
BLOOD FLOW TRANSDUCER
CAROTID ARTERY AND
HEART RATE
MALE
SHIRT COLLAR
TRANSDUCER
FEMALE
CHOKER JEWELRY
TRANSDUCER
NOTE: A NATURAL, COMFORTABLE
TRANSDUCER IS IMPERATIVE.
MULT1MODE ANATOMIC PHYSIOLOGIC TRANSDUCERS
FOR PERSONAL MONITORS
FIGURE 12. Cardiac impedance transducer incorporated into normal dress wear;
i.e., reduction of user resistance.
252
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TO TRANSDUCERS AND
OTHER SYSTEMS
FIBER OPTIC DATA
CABLE REPLACES NYLON
STOCKING SEAMS
(IPPM)
SYSTEM-TO-ANATOMY
INTERFACE DESIGN
SECLUDED ACCESS PORT
VLSI CIRCUITRY
COMPLETE IPPM (PDAS)
NOTES:
FEMALE WEDGIES
1. SHOCK PROOF PERSONAL MONITOR VLSI CIRCUITRY.
2. COMFORTABLE. EASE OF USE. AND ACCEPTANCE BY
SUBJECT.
3. DOES NOT INTERFERE WITH DAILY TASKS WHILE
COLLECTING DATA.
4. FIBER OPTIC CABLES REPLACE STOCKING SEAMS AS
DATA LINKS TO OTHER SYSTEMS.
FIGURE 13. IPPM devices must be incorporated within natural human attire.
(IPPM)
SYSTEM-TO-ANATOMY
INTERFACE DESIGN
EACH 4K MEMORIES.
COMPLETE VLSI IPPM (PDAS)
SINGLE CHIP
MICROCOMPUTER
NOTES:
MALE WORK BOOT
1. HEAVY BOOT. HAS IPPM MODULE AS
OUTBOARD SYSTEM.
2. IPPM IN LEFT BOOT, POWER PACK IN RIGHT
BOOT. USES FIBER OPTIC DATA AND POWER
LINKS BETWEEN BOOTS THROUGH CLOTHING
SEAMS
3. IPPM MODULE RETURNED BY MAIL FOR
MAINTENANCE. FIELD REPLACEMENTS AT
MODULAR LEVa.
FIGURE 14. IPPM system for construction worker.
253
-------
With software modification of existing STI systems and retaining the
common STI electrode configuration, it is possible to record respiratory
rate. Additionally, adding an infrared transducer or liquid crystal to the
neck electrode may provide an index of carotid blood flow through I-R thermal
radiation of blood which has a spectral emissivity at 9.3 microns. Hence,
infra-red blood flow index, ECG, STI, and respiratory rate measurements are
all feasible from the common placement of the STI electrodes. A further
enhancement of respiratory volume measurements is possible with impedance
pneumography, if calibrated against the pneumotachograph as illustrated in
the construction worker's tidal volume system. Combining STI and tidal vol-
ume measurements could be accomplished on a single individual through dedi-
cated IPT systems operating in a multimicroprocessor mode. The data array
made possible by this combination is listed below. This is a more specific
example of multlmode transphysloware.
Cardiopulmonary Parameters
Respiratory rate
Respiratory volume
Respiratory flow
Respiratory tidal volume
Heart rate
ECG
I-R blood flow rate
All STI and impedance measurements.
It should be noted again that the STI Intel 8010 microcomputer is serving
as an intelligence converter reducing the abundance of cardiac data into a
meaningful clinical measurement. Additionally, multimode parameters are dis-
played in the form of trend data (Figure 10) as an index of subtle response.
The stand-alone capabilities of the microcomputer (4,11,15,17) permit direct
support to a clinical data base without extensive statistical support of
large ADP systems such as the UNIVAC. This example illustrates the cost
effectiveness of "intelligent microcomputerized blomedical Instruments"
(IMBI). With 64K single chip microcomputers being introduced in 1979 (15),
the complete STI system software and ensemble averaging illustrated above
could be packaged (less graphics display) within the subject's belt, shoes,
or hat. With the abundance of high-density memory, nitrate metal oxide field
effects (NMOST), long-term memory storage (1 to 10 years) is also feasible.
NMOST memories could be interrogated in post-data collection analysis to
review graphics and trends for the generation of an urban data base. Ex-
tension of this design philosophy is the basis of IPPM, IPT, multimode trans-
254
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ducers, and multlmicrocomputer systems. Furthermore, this design philosophy
is expandable to include future designs adaptable to changing protocols
(through changing software, not hardware) within internal and external IPPM
devices presently beyond the state-of-the-art as of this writing. Addition-
ally, the design concepts presented here could well be the forerunners of
future internal and external IPPM and IPT 3 to 5 years hence.
CLINICAL VALIDATION OF EPIDEMIOLOGIC PROTOCOLS IN PERSONAL MONITOR DESIGN
Any new approach such as IPPM noninvasive physiologic measurement always
contains a question as to the efficacy of the parameter under analysis. The
clinical validation of IPPM systems advocated here are based on the use of
the EPA Clinical Environmental Laboratory (CEL) as an "IPPM test center" for
the evaluation and validation of all personal monitors. The efficacy of all
IPPM and dosimeter designs would be dynamically exercised under physiologic
and pollutant performance conditions prior to use in any epidemiologic urban
health effects program (13). As such, the CEL provides a unique controlled
clinical setting sufficient for semi-invasive and external physiologic data
acquisition system investigations.
Once preliminary IPPM systems become available, pilot studies in both
air pollutant and physiologic data acquisition may be conducted and evaluated
against known clinical and air chemistry standards. Use of the CEL as a
''national standards resource" for design, development, and evaluation of
IPPM would provide a common data base for the design of such systems. Further,
the CEL facilities would provide a basis for validating clinical and pollu-
tant dosimetry protocols advocated in IPPM systems prior to field epidemio-
logic studies. Hence, the urban health effects data base would be acquired
on a realistic basis. This validation approach is the only method that will
ensure a scientifically defensible data base in support of legislation or any
public health initiative.
It is advocated here that all IPPM systems would be designed and de-
veloped in this context, wherein the clinical and environmental standards
of the CEL would serve as the EPA national standard resource for those inter-
ested in certification of such systems and devices.
CONCLUSION
The advocacy of new personal monitor designs has been presented through
255
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implementation of microcomputer technology and interactive protocols. In-
corporating clinical rationale and Judgment within software algorithms at
the clinical level has been demonstrated through design examples. Extend-
ing this technique to the personal monitor level in population studies re-
mains to be implemented. However, with the acceleration of high-level VLSI
technology, microcomputers, and submicron systems in the immediate future,
the attainment of a clinical environmental preventive medicine data base
as an urban early-warning system is a realistic possibility. Conversely,
if epidemiologic research retains present methodologies, the results may
continue at present levels of knowledge.
A major thrust in the design and development of IPPM and IPX devices is
imperative if useful epidemiologic health effects data is desired. Develop-
ments of this type must be designed to maximize clinical flexibility in terms
of changing environmental needs, assessment of new pollutant episodes, and
adaptability to new research protocols. A significant barrier presently
exists in terms of adequately designed physiologic/anatomic transducers which
are compatible with male and female subjects. Subject comfort and ease of
use are paramount if physiologic data are to be collected in their natural
state. The concepts proposed here advocate a new design approach in physio-
logic transducers and systems which must be Incorporated within clothing,
shoewear, headwear, underwear, jewelry, and cosmetics. Additionally, trans-
ducers must function at an intelligent level through microcomputer software
as a means of reducing size, weight, and power while improving comfort and
clinical utility.
Finally, it is envisioned that any design initiated today must be flex-
ible enough to be adaptive and useful to new protocols 2 to 3 years later,
when priorities will most certainly change. It is, therefore, the responsi-
bility of systems designers and program managers to invest in appropriate
research and development efforts in the implementation of IPPM systems in
response to an effective public health initiative. Part II of this paper
addresses future needs through anticipatory research.
REFERENCES
1. Computers in Cardiology, IEEE Computer Society #75CH1018-1C. The
Netherlands, October 1975.
2. Costle, D.M. Health and the Environment. EPA Journal, July-August
1978:2-3.
256
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3. Harrison, D.C. et al. Cardiovascular Imaging and Image Processing.
The Society of Photo Optical Instrumentation Engineers, Vol. VXXII,
1975.
4. Hyman, W.A., Lively, W.M. Workshop Report: Microprocessor Impact in
Health Care. Proceedings of the 12th Hawaii International Conference
on Systems Sciences, pp. 272-275, January 1979.
5. Kizakevich, P. Personal Cardiopulmonary Electrode Monitoring. Proceed-
ings of the Symposium on the Development and Usage of Personal Monitors
for Exposure and Health Effects Studies, January 22-24, 1979. (EPA
Symposium.)
6. Kizakevich, P., Gallon, F., McDermott, J., Aranda, J. Continuous Non-
invasive Cardiac Monitoring of Cardiac Function: Its Applications in
Exercise Stress. British Heart Journal, 1978 (in press).
7. Kubicek, W.G. Development and Evaluation of an Impedance Cardlographic
System to Measure Cardiac Output and Other Cardiac Parameters. NASA
Contract #NAS-9-4500. June 30, 1969.
8. Lion, K.S. Instrumentation in Scientific Research. McGraw Hill Book
Company, Inc., 1959, pp. 74-84.
9. Love, G.J., Shy, C.M., Calafiore, D.C., Benson, F.B., Finklea, J.F.
The Strategy for Determining the Effects of Environmental Pollution on
Human Health. Environ Letters 3(1):13-20, 1972.
10. Medical Electronics Fifth International Conference, Liege, Belgium, 1964.
11. Petrovlck, M.L. Patient Owned Systems and Devices In Health Care.
Presented at the Texas A&M Conference on the "Impact of Microprocessors
in Health Care," September 18-19, 1978. (In preparation.)
12. Petrovick, M.L., Malindzak, G.S., Jr., Strong, A.T. The Role of Personal
Monitors in Environmental Health Effects Research. Proceedings of the
IEEE 1974 National Aerospace and Electronics Conference, NAECON 74,
pp. 152-159.
13. Shy, C.M., Finklea, J.F. Air Pollutant Effects on Community Health.
Environ Sci Technol 7:204-208, 1973.
14. Soucek, B. Microprocessors and Microcomputers. New York, Wiley -
Interscience Publication, John Wiley and Sons, 1976.
15. Strader, N.R. The Microprocessor Transducer Function. Proceedings
of the 12th Hawaii International Conference on Systems Science, pp.
256-265, January 1979.
257
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16. Steigbigel, J. et al. Quantitative Evaluation of First Derivative
Impedance Cardiogram. Circulation 42(11):67, 1975.
17. User's Guide, M6800 Exerciser. Motorola, Inc., 1975.
18. Wallace, L. Personal Air Quality Monitors: Past Uses and Present
Prospects. American Chemical Society 4th Joint Conference on Sensing
of Environmental Pollutants, pp. 390-394, 1978.
19. Welham, J.C. et al. First Derivative of Transthoracic Electrical Im-
pedance as an Index of Changes in Myocardial Contractility in the Anes-
thetized Dog. Intensive Care Med 4:43-50, 1978.
MAILING ADDRESS OF AUTHOR
Mathew L. Petrovick
Health Effects Research Laboratory
Clinical Studies Division
Physiology Branch
U.S. Environmental Protection Agency
Chapel Hill, North Carolina 27514
Discussion
CHAPMAN: Robert Chapman, EPA. Matt, I got a little confused. In the
middle of your talk, you showed a system on a male in which he had three
EGG leads on, and he had a couple of straps around his chest, and he also
had some straps around his neck. And then two slides later you showed a
picture of a shirt collar with some things In it. Would this now be part
of the same system, or are we sort of jumping ahead to an even smaller sys-
tem?
PETROVICK: No. This system requires two sets of electrodes—a pair
on the neck and a pair at the thoracic cage. The slide with the shirt collar
only indicated how that electrode could be packaged so it would be functional
and aesthetically pleasing. The other electrodes would be contained under
the shirt. So, there are four electrodes, and you seclude them in clothing
and such.
258
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Design of Personal Monitors for External
and Internal Physiologic Studies in Health
Effects (Part II)
Mathew L. Petrovick and Edward D. Haak, Jr., M.D.
Clinical Studies Division
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina
INTRODUCTION
Scientific assessment of urban health decrements resulting from air pol-
lutant exposures has eluded clinical Investigators to the extent that a de-
finitive urban health effects data base remains a high priority in support
of EPA legislation. More Importantly, a definitive urban clinical data base
would provide a means for establishing early-warning guidelines in preventive
environmental medicine as a public health initiative. However, the need
for an early-warning data base has not been uniformly recognized in terms
of epldemiologic research, due to the obvious lack of properly designed
transducers, clinical instrumentation, and logistic resources.
The key significance of an urban early-warning data base is predicated
on the ability to characterize dose-response relationships at a highly in-
dividualized level through personal monitoring. Systems which are capable
of accurately documenting both physiologic and air pollutant variables simul-
taneously are essentially nonexistent. It is, therefore, incumbent upon
clinical and environmental scientists to systematically assess the urban
epidemiologlc needs toward the design, development, and Implementation of
personal monitors capable of simultaneous physiologic and air pollutant data
acquisition.
Such a system, Healthe-Belt, was advocated by Petrovick et al. in 1974
(7). It was the opinion of several peer groups (in 1974) that technology
could not support a personalized pollutant and physiologic data acquisition
259
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system design. It is still common to hear various researchers suggest the
improbability of detecting dose-response variance in normal mobile adults
resulting from pollutant exposures. Unfortunately, such assessments of per-
sonal monitors are speculative and not based on credible scientific investi-
gation. Conversely, the latter rationale is reasonable and consistent with
antiquated clinical technology. Today, new technology (10,12,13) further
confirms the Healthe-Belt concept in that through appropriate research and
development, such a goal is entirely feasible. Specifically, the explosive
advances (10) in microcircuitry, submicron components, very large scale in-
tegration (VLSI), microprocessors, and microcomputers can be implemented
and configured for simultaneous pollutant doslmetry and physiologic data
acquisition systems. In view of the accelerated pace of VLSI technology and
the need for constantly changing health effects protocols, it is imperative
to design personal monitors (PM) with maximum flexibility toward adaptation
to changing clinical needs.
Part I of this two-part report sets forth design guidelines and criteria
for personal monitors using today's technology. This report is Intended to
set forth an entirely new philosophy 3 to 5 years beyond that advocated in
Part I, as a means of personal monitor design that is adaptable to and anti-
cipates changing clinical, epidemiologic needs. Accordingly, a research
rationale must be developed such that any R&D of PM attempted must anticipate
clinical needs and advances of modern technology in order to effectively respond
to the urban epidemiologic needs.
The following fundamentals are therefore proffered, somewhat specifically
in the area of clinical physiology and high-level technology as supportive
resources to a public health initiative capable of characterizing urban
health effects resulting from air pollutants. As such, these fundamentals
may be used as basic research guidelines in the design and development of
internal and external intelligent personal physiologic monitors (IPPM) in
search of new knowledge.
FUNDAMENTAL BASIC RESEARCH RATIONALE
It is imperative to:
1) Increase new knowledge and understanding of external and Internal
physiology in order to avoid present-day limitations in parameters, transducers,
techniques, and technology.
2) Conduct exploratory studies In the search of new physiologic para-
meters specific to assessment of urban health effects.
260
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3) Conduct exploratory research in wearable external and Internal
IPPM devices.
4) Conduct exploratory studies in the design and development of new
transducers, systems, and devices to permit assessment of internal and ex-
ternal physiology as a basis for increasing.new knowledge from which to
draw upon in the development of new parameters.
5) Apply the knowledge of existing and future technology—such as very
large scale integration, microcircuitry, microcomputer techniques, software
engineering, intelligent transducers, and interactive clinical Judgment—as
a means of developing new methodologies specific to urban epidemlologlc
assessment of health effects research.
6) Support an in-depth, comprehensive budget structure that is respon-
sive to cost effectiveness and long-term research support for the design
and development of new tools for this endeavor.
Implementation of the above rationale has considerable potential for the
evolution of several new physiologic parameters, transducers, and techniques
as basic research spinoffs. This potential can be realized in terms of
productive research that is "made to happen" by departure from traditional
technology and clinical techniques.
PHILOSOPHY OF INTERNAL AND EXTERNAL PHYSIOLOGIC MONITORS
The test subject transducer criteria (Part I) impose a significant
problem in the physical packaging of IPPM systems design. Use of multimode
transducers will require the basic analog sensors, electrodes, etc., followed
by a level of intelligent signal processing, artifact screening, rejection,
and simplification of data in response to call from higher-order multiprocessor
systems. Incorporation of these features can only be accomplished through a
revolutionary change in technology, such as implementation of micro- and sub-
micron-component technology in IPPM design.
In the search for new physiologic parameters and techniques to supplement
conventional physiologic data acquisition systems (PDAS) measurements, a new
design Initiative is Imperative to overcome the extreme limitations of con-
ventional noninvaslve clinical research. The development of new techniques
must permit feasibility studies for design and development of new systems.
261
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Feasibility prototypes must be investigated, constructed, and clinically vali-
dated before use in epidemiologic studies.
Noninvasive physiologic parameters have predominantly been associated
with some form of interfacing transducers to the external anatomy (8,12).
Few, if any, options exist for internal physiologic measurement, or it seems
that way in the sense of classic design rationale. However, properly designed
systems at the Internal level may serve as prototypes for future external
physiologic data acquisition systems. The latter is the basis of internal
exploratory research via IPPM PDAS designs described in this paper.
Physical size and available real estate (on-board the subject) for
transducers cannot in all cases be based on discrete component (TTL) logic,
in view of bulk, power, and physical encumbrances to the subject. However,
it is feasible to perform many discrete circuit functions, such as signal
processing, with software rather than hardware logic; I.e., a first-derivative
amplifier function can be accomplished with an algorithm corresponding to a
low-pass (hardware) filter function. Logic process control functions can well
be performed with software logic, thus eliminating the need for TTL circuit
logic devices without loss of basic function. Essentially, transducers de-
signed to incorporate software as a process function become uniquely compatible
in microcomputer-controlled personal monitors. It is immediately recognized
that software rather than hardware logic will require considerable memory
in each IPPM. However, with VLSI technology today, 64K microcomputer memory
modules (10) in a 40 pin dip package can easily accommodate transducer functions,
as well as most interactive protocols and emulated circuit logic. Herein is
the key significance of microcomputer technology. Transducers incorporating
microprocessors integral to their function may serve as IPPM system peripherals
in a multiprocessor mode (8,10). Each transducer could communicate through
an I/O port as a direct memory-addressable DMA peripheral. This approach
would free the bus master to operate on higher-level priority functions, while
system interrupts from peripherals would be initiated only when relevant sub-
tle changes occur. Incorporation of microcomputers, microprocessors, and
peripheral devices into transducers and IPPM systems cannot be accomplished
effectively unless a quantum jump (8,9,10) in component size and high-density
packaging is attained within industry. Furthermore, test subject space is
needed for air dosimetry sensors and devices on the same test subject to
ensure simultaneous PDAS and air pollutant assessment. The VLSI techniques
definitely are a move in the proper direction. However, the design of IPPM
external and internal systems advocates a combination of VLSI and submicron
component technology based on standardized modularized subsystems.
262
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To illustrate the design principles and problems advocated in IPPM
systems, several design examples are proffered as initial design concepts.
Design of IPPM systems requires a high degree of anticipation of clinical
need (8) prior to the principal investigator's own recognition of a given
need. As such, maximum software flexibility to changing protocols with mini-
mal hardware changes is a significant requirement in the design of IPPM de-
vices. The design philosophy expounded in this paper is based on today's
needs with tomorrow's technology. This approach ensures design flexibility,
cost effectiveness, and elimination of technological obsolescence at the com-
pletion of a given design.
It is Immediately recognized that several hardware and software devices
advocated here are not currently available. Therefore, these designs are
considered to be design goals and examples that should be attained in response
to urban epidemiologic needs. It is further recognized that availability
of such devices are possible, and that these designs can be made to happen
if a realistic public health initiative is advocated and supported. Designs
initiated at the present time will require a lead time of 18 months to 3
years, based on the acceleration of VLSI technology today. Hence, it behooves
program managers and designers to plan urban epidemiologic health programs
with these factors well in mind. The need for micro- and submicron technology
(8,10) in intelligent physiologic monitors is of significance in that urban
health effects personal monitoring cannot be successfully accomplished without
this resource.
ILLUSTRATIVE DESIGN
VLSI and Submicron Technology
With the packing density of VLSI, and with submicron technology increas-
ing and the physical size decreasing, standardized subsystems such as 8-16
bit microprocessors, I/O devices, static RAM, ROM, tri-state buffers 8, 16,
32, 64K memories, and system controllers could be manufactured as precanned,
modularized system wafers. Additionally, selection of individualized micro-
computers at the 4 to 16 bit level could be designed quickly and simply if
precanned hardware and software were available in modular wafer form. (See
Figure 1.) Modularized subsystems would be used as if they were discrete
(TTL) components, and IPPM designing would be accomplished at systems level
by utilizing prevalidated systems and software protocols. This design capa-
bility would provide significant clinical flexibility in adapting any system
modules to individualized IPPM systems.
263
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1. PHVSICIANS PRESCRIPTION DEFINES THE PROTOCOL
AND PARAMETERS OF MEASUREMENT!
2. SOFTWARE ENGINEERING ANALYZE* REQUIREMENTS,
DRAM ON STANDARDIZED ALGORITHMS FOR BIO-
MEDICAL MEASUREMENTS.
3. SYSTEMS ENGINEERING FILLS PRESCRIPTION THROUGH
ASSEMBLY TO MEET PHYSICIANS NEEDS.
4. 0-A BIOLOGICAL SAFETY CHECKS PERFORMED.
S. DELIVER TO CLINIC.
6. PHYSICIAN ADMINISTERS TO PATIENT.
7. UPON RETRIVAL, DATA INTERROGATION PROCESS
FEEDS RESULTS INTO DATA RESPONSE BANK.
I. PHYSICIAN REVIEWS RESULTS, ADMINISTERS
FURTHER HEALTH CARE MANAGEMENT OF
PATIENT. RELEASE FROM HOSPITAL
NOTE:
1. INDUSTRY STANDARDIZED WAFER
SUBSYSTEMS - PRESCRIPTION COMPONENTS.
2. PRESCRIPTION DESIGN BY PHYSICIAN AT A
BLOCK DIAGRAM LEVEL. COMPONENTS USED
AS IN DISCRETE COMPONENT CIRCUIT DESIGN.
FIGURE 1. Modular wafer subsystem components used as discrete systems rather
than the classic TTL logic approach.
ELEMENT ASSEMBLY
ASSEMBLED CATERPILLAR
PROCESSOR PACKAGING
END VIEW
LSI 8K RAM
WAFER
INTERROGATION
BUS
I/O BUS
FIBEROPTIC DATA BUS
CYLINDRICAL
CONFIGURATION
NOTES:
1. ALL I/O DATA BUS CONTROL
BASED ON TIME SHARED
FIBEROPTIC BUS STRUCTURE.
2. SINGLE WAFER ELEMENTS
SNAP TOGETHER MAGNETICALLY.
PERMITS STACKING AND SYSTEM
ASSEMBLY BY SEGMENTS TO MATCH
PHYSICAL CONFIGURATION DESIRED.
POWER *.1 VOC
MAGNETIC INTERLOCKING
PELLETS
MNOS-UKE IK STATIC
RAM WAFER
LSI CHIP
INTERFACE CONNECTORS
GROUND BUS
3. ALL WAFERS ARE MEMBERS OF
A STANDARDIZED STRUCTURE
PERMITTING BLOCK DIAGRAM DESIGN.
4. ALL MAJOR ELEMENT SYSTEM WAFERS
TO BE USED AS IF THEY WERE DISCRETE
COMPONENTS, U, RESISTORS/CAPICITORS.
ADAPTIVE CATERPILLAR
PROCESSOR PACKAGING
FIGURE 2. System wafer modules high density packaging for internal/external
physiologic exploration.
264
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Ideally, microprocessors used with IPPM should take the form of stand-
ardized devices (8,9,10) with specific capabilities in a physical configu-
ration, thus ensuring maximum flexibility to individually designed systems.
Additionally, the mechanical and electronic packaging should be in a form
which enhances all power, I/O data bus, control bus, and Interface connections
(Figure 2). The physical shape of modules used in any system should be easily
adaptable to individual subject configurations, thus enhancing ease of as-
sembly by semitechnical personnel.
Figure 2 illustrates an example of two adaptive wafer designs that snap
together in serial fashion. This packaging scheme would permit various shapes,
curvatures, or caterpillar-like segmented designs as an example. Ideally,
several wafer modules could be assembled to suit a particular study protocol
for urban health effects screening. Both pollutant dosimeters and PDAS systems
could be designed by this process so as to ensure miniaturized systems com-
patible with personal mobility.
Finally, the physical hardware should be designed at a modular level
such as a wafer configuration. Each module would serve as a subsystem such
as MCPU, I/O, RAM, ROM, and interface devices. This would permit the physi-
cian to prescribe a system design at a block diagram level, thus avoiding
unnecessary design detail. The physician would select his/her design based
on a diagnostic data base matrix (8) (see Figure 3), and the protocol he/she
feels is most beneficial in a specific urban epidemiological study. Design-
ing an IPPM with pretested, modularized systems would eliminate the use of
time-consuming discrete components, connections, and hardware debugging, while
ensuring standardization of selected protocols.
Clinically, the physician's physical examination and diagnosis of the
subject is at a physiologic-systems level, including, for example, judgments
on the EEC, blood pressure, blood chemistries, etc. Why not, then, tailor
the IPPM to follow a similar analytic rationale in collecting physiologic
data and provide for a total systems approach to health effects research.
Hence, upon completion of preliminary studies, the physician could write a
prescription to design an external IPPM to suit a specific protocol for a
selected population group and related pollutant (which is a form of pre-
scription engineering). The protocol would ensure exact measurements to be
made by previously proven algorithms which, in the final analysis, provides
the physician with data useful in the final data base. Semitechnical person-
nel would construct the IPPM in accordance with the prescription, and they
would return it to the physician to administer to the population group.
265
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PHYSICIAN'S DIAGNOSTIC DATABASE MATRIX
OB
4C
7F
-
34
-m
BM
2L
i— —
ADAPTIVE DESIGN
INTELLIGENT PERSONAL
PHYSIOLOGIC MONITOR
> MANUFACTURER'S STANDAROIZED IVISI)
CW ARMY BUS STRUCTURE AND
ASSEMBLY CODE
STANDAROIZED MICROPROCESSOR
PREPROCESSOR AND ALGORITHM
PROTOCOLS
FIGURE 3. This matrix is used to rationalize an IPPM design configuration
in a short period of time by utilizing proven protocols and systems. This
approach is much more responsive in assessment of pollutant episodes•
Traimrertiia thoracis
fntfrnal thnratie ttmth \
Left jihrenir
nerrr
Pulmonary pleura
Coatal pleura
Sum pathetic trunk
Thoracic duet
Atugot tein
Vaout nervet
FIGURE 4. Transverse section of the thorax showing anatomic relationship of
the esophagus to heart and lungs.
266
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In the search and exploration for new physiologic parameters and trans-
ducers, semi-invasive (internal) studies hold potential for the development
of new measurements and techniques for use in IPPM external systems through
new knowledge and techniques. However, suitable transducers and subsystems
do not presently exist on the shelf to permit such investigations, and,
therefore, must be specifically designed. The design of IPPM systems thus
advocates individualized systems which permit the charting and charac-
terization of limited internal physiologic function. Hence, a whole new phi-
losophy in the acquisition of external and internal physiologic data must
precede the design of IPPM's.
INTERNAL IPPM PDAS
Clinical gastrointestinology (1) has in the last two decades developed
a wide variety of techniques for swallowable instrumentation devices in the
form of EGG electrodes, temperature sensors, pressure transducers, telemetry
systems, and balloon-mounted devices, each representing discrete components.
To this date, there has been little effort toward the design of coordinated
internal multiparameter systems. Gastroenterology techniques, however, have
previously demonstrated that a number of physiologic parameters can be meas-
ured internally from the esophagus through and to the GI tract. Figure 4
Illustrates an anatomic transverse section of the thorax relative to the
heart, lungs, and the esophagus or survey site for semi-invasive IPPM for use
in clinical exploration. Table 1 illustrates an example of parameters detec-
table internally by the designs proposed herein.
The semi-invasive parameters available for clinical study and evaluation
in the design of IPPM systems provide a significant potential for a cardio-
pulmonary data base. Initially, the study of these parameters must be per-
formed under careful clinical management, such as in the "Clinical Environ-
mental Laboratory" or CEL (Strong 1978) (11). The major impasse, however,
is the lack of properly designed IPPM systems for internal data acquisition.
Utilizing the principles of the PDBM and VLSI technology, a brief illus-
tration of internal IPPM systems design is presented as follows.
EXPLORATORY INTERNAL PHYSIOLOGIC DATA ACQUISITION SYSTEM
Utilizing the IPPM wafer systems modules developed from the PDBM, a
500-mg envelope (Figure 5) is instrumented with two inflatable elastomer
267
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TABLE 1
Physiologic Parameters Detectable from Internal Esophageal PDAS
Respiratory rate
Respiratory volume
Respiratory tidal volume
Cough rate and intensity
Heart rate stress—medical-legal safety
EGG "P" wave arrhythmia detection
Heart sounds—cardiac valves
Temperature
pH
Echocardiogram
New parameters
docking rings, as a means of fixing and stabilizing the IPPM within the esoph-
agus at the level of the cardiac orifice (Figure 6). Each docking ring
contains a pair of transducers—one pair for pulmonary and one pair for car-
diac measurements. Measurement of respiratory volume, rate, and tidal volume
p
are all feasible from the piezoelectric (6) transducers ( Z ) located within
the inflatable docking rings located in the esophagus. Clinically, a flex-
ible tube (track) similar to an esophageal balloon leader is inserted through
the nasal-pharyngeal cavity until it is visible orally at the posterior pharyn-
geal wall of the mouth. The IPPM is contained within a 500-milligram envelope
and is attached through the mouth to the flexible track and then passed down
the track or to the monitoring site of interest. Once located anatomically,
the physician inflates the elastomer docking rings with the syringe, thus
placing the pulmonary and EGG transducers against the inner walls of the
esophagus at the level of the cardiac orifice or posterior of the heart.
p
Functionally, the piezoelectric transducers ( Z ) are used in a multlmode
transphysioware, wherein one transducer performs the initial anatomic in-
terface, and a software algorithm performs multiparameter acquisition of
cardiac parameters.
The piezoelectric (6) transducer lends itself to a wide variety of phys-
iologic measurements, such as low- and high—frequency pressure, and acoustic
sensing. It is well known that shunting a specifically cut piezoelectric
sensor with external resistance or capacitance can dramatically change the
268
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INFLATABLE ELASTOMER
ESOPHAOEAL DOCKING
RINGS
CLEAR AIR SPACE MINI-
MIZES AIRWAY RESIS-
TANCE WITHIN ESOPHA-
GUS
CM DEPTH MARKERS
m« ENVELOPE
PHONOCARDIOORAPHIC SENSOR (CVS)
INTERNAL EXPLORATORY SYSTEM
FOR PHYSIOLOGIC DATA ACQUISITION
INFLATABLE ELASTOMERS ARE MOLDED TO
PREDETERMINED SHAPE AND TAKE ON A
SET CONFIGURATION UPON INFLATION
• ECO ELEC-
TRODE
SENSOR WIRES FROM OUTER
PERIPHERV TO INTERNAL PREPROCESSOR
RECESSED STORAGE AREA
FOR DEFLATED DOCKING
REMOTE DEFLATE RINGS
. AND PINCH-OFF SYS-
TEM LAUNCH CONTROL
MANUAL SYRINGE
INFLATE UPON INITIAL
INSTALLATION
NOTES
1. ANATOMIC LOCATION AT CARDIAC ORIFICE TO
DETECT ECG AND HEART SOUNDS, !.«.. ~P" WAVE
DETECTION ARRYTHMIA PROCESSING. MVO-
CARDIAL INFARCT.
2. UPON COLLECTION OF CARDIAC DATA. THE SYS-
TEM IS REMOTELY LAUNCHED BY THE INVESTI-
GATOR BY DEFLATING THE CAPSULE AND THE
BREAKAWAY PNEUMATIC TUBE.
3. UPON SYSTEM LAUNCH. THE CAPSULE TRAVERSES
ITS ROUTE THROUGH THE G.I. TRACT COLLECT-
ING VARIOUS PHYSIOLOGIC DATA.
4. VALIDATION STUDIES TO BE CONDUCTED
IN LABORATORY ANIMALS.
FIGURE 5. This device is supportive to basic physiology in the search for
new parameters and transducers.
characteristics of the Zk element. Changes in "Q," the equivalent circuit
t p
merit, and the frequency response can cause the Z sensor to readily respond
to and detect DC to high-frequency information.
As a considered design approach, one could attain multimode functions
through remote tuning of a piezoelectric transducer with a software algorithm.
p
In this design, the objective is to remotely change the Zfc characteristics
within the swallowable microcomputer, upon software command, to sense the
following parameters:
• Gastric motllity
• Gastric pH
• Cough rate and intensity
• Respiratory rate
• Heart sounds
• ECG "P" wave-arrhythmias
• Heart rate.
269
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INTERNAL EXPLORATORY
PHYSIOLOGIC DATA ACQUISITION SYSTEM
POSTERIOR
PHARYNOEAL
WALL
VOCAL FOLDS
INFLATE SYRINGE
CONTROL
DEFLATE PINCH-OFF
LAUNCH CONTROL
MICROCOMPUTER SUBJECT-
OWNED SYSTEM PDAS
MPOSmON
CAPSULE INFLATED TO HOLD
POSITION WITHIN ESOPHAGUS
<. CARDIAC
•s ORIFICE
ENTRANCE TO -
STOMACH
NOTE:
1. SYSTEM INSTALLATION SIMILAR TO SWALLOWING
ESOPHAGEAL BALLOON.
2. CAPSULE IS ATTACHED TO THE LEADER LINE TRACK
AFTER PASSAGE THROUGH NASAL PHARYNGEAL WALL.
3. PHYSICAL ATTACHMENT THROUGH ORAL CAVITY AT
POSTERIOR PHARYNGEAL WALL AREA.
4 APPROPRIATE ANESTHETIC IS USED TO DESENSITIZE
GAG REFLEX - A NORMAL PROCEDURE.
& AFTER THE SYSTEM IS INFLATED AND INSTALLED.
THE LEADER LINE TRACK. SYRINGE. AND PHYSICIAN'S
LAUNCH CONTROL IS REMOVED.
6. THE LAUNCH CONTROL REMOVAL PINCHES THE
PNEUMATIC LINE SO AS TO PROVIDE A SLOW LEAK
ALLOWING SPECIFIC TIME BEFORE LAUNCHING
INTO THE STOMACH.
FIGURE 6. Internal PDAS is an investigative tool in support of external IPPM.
Z is interfaced to a specifically addressed input
A controlling algorithm applies a limited
Conceptually, the
port of the microcomputer device
voltage to a tri-state buffer-like and ladder network device.
By this process,
n
the Z is remotely tuned through a common MOST/FET-like voltage-controlled
resistor which changes the "Q" of the Z. for the measurement of a specific
P
physiologic parameter. This design advocates the use of one Z sensor which
270
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acts as a peripheral device containing a specific input port address. Access
of this input port to the control bus is through a form of trl-state buffer.
Each of the above parameters may be detected by a change of shunting impedance
p
to the Z , thus altering the low/high frequency-response to detect the above
parameters. This process is repeated in sequence to perform the above meas-
urements from internal firmware. Each sequence algorithm, of course, identi-
fies in memory the sensor mode, parameter, data, and subject ownership while
in use. Figure 7 illustrates how the same IPPM microcomputer can through
P
prevalidated (EPROM)-like algorithms, remotely tune or change Z character-
istics for use in pulmonary rate and volume measurements.
By this process, it may be feasible to detect two or more physiologic
measurements from a single transducer (multlmode). The related algorithm, of
course, would preprocess these signals into meaningful clinical measurements—
i.e., transphysioware. Another option is to retrieve data from long-term
memory (1 to 10 years), such as Is possible with the new metal-nitrate-oxide
slllcone transistor (MNOST) semiconductor memories within a given IPPM. Data
interrogation of the IPPM by high-level computer would permit a form of data
base development in the off-line mode through interactive graphic analysis,
as illustrated in Part I.
In another mode, the platinum electrodes on the 500-milligram PDAS,
(Figure 5) can detect heart rate and "P" wave arrhythmia through associated
clinical rationale in the form of a prevalidated algorithm designed for this
purpose. A further mode time shares the platinum electrodes for measurement
of esophageal pH or gastric pH if the IPPM is inserted beyond the cardiac
orifice and into the root of the stomach. If the IPPM is located at the
cardiac orifice, respiratory rate, cough rate, and cough intensity are also
possible to detect. The acoustic cough signal would be converted through
software (RMS signal processing) to a DC voltage and compared with the dia-
phragmatic pressure recoil during a cough. If both signals occurred simul-
taneously, a software logic algorithm would verify the cough rate, intensity,
and duration (as opposed to artifact). This would be of particular value in
exercise pulmonary ozone exposure studies, in which frequently there is a
coughing response after 4 hours of ozone at .6 ppm.
MYOCARDIAL CONTRACTILITY OF CARDIAC PUMP FUNCTION
Taking full advantage of semi-invasive internal IPPM, it is feasible to
perform "cardiac Impedance systolic time interval" (2,3,4,5) measurements
271
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MOST-LIKE VOLTAGE
CONTROllEO VCR fET
\t
INPUT
: PORT HS :
OIFA
-a.,:
*rT
OUTPUT
PORT
OIFF
REMOTE MUITIMODE
PIEZIOELECTRIC ELEMENT
EQUIVALENT FET RESISTANCE
CHANGE FREQUENCY RESPONSE
OF VCR-FET
REMOTE CONTROL WORD
SELECTS VCR VOLTAGE
REMOTE TUNING CONTROL
WORD FOR MUITIMODE
PZT
NOTE COMMON PZT TRANSDUCER
t. VCR RANGES
«. .1 • II Hi GASTRIC MOTIIITY
1. .1-10 Hi RESPIRATORY RATE
C. IN 500 Hj HEART SOUNDS
SWALLOWABLE MICROCOMPUTER WITH
REMOTE MULTI-MODE PHYSIOLOGIC
TRANSDUCER
FIGURE 7. When space constraints exist, and multiple parameters are desired,
this concept can be very effective.
INTERACTIVE INTELLIGENT
PERSONAL PHYSIOLOGIC AND
POLLUTANT MONITOR
2" x 3- x %
ADAPTIVE CATERPILLAR
SYSTEM MODULES
MCPU. I/O 8K MEMORY. SYSTEM
CONTROLLER, EPROM. MULTI-BUS
DMA. PRE-CANNED MESSAGE
ALGORITHMS
MICROCOMPUTER
BUS MASTER
IPPM SYSTEM
INPUT/OUTPUT
DATA AND POWER LINES
RUN UNDER SUBJECT'S
ARM TO SHOE OR
BELT PDAS/PEP SYSTEMS
MICROCOMPUTER CONTROLLED
1024 x 1024
MATRIX
LIQUID CRYSTAL
PICTORIAL DISPLAY
MICROCOMPUTER
8-BIT DATA WORD
DISPLAY
AUDITORY
ATTENTIONAL
BEEPER
SUBJECT RESPONSE
CONTROL SWITCHES
FIBER-OPTIC
SYSTEM IMBIUCAL
CONNECTOR TO
PDAS AND PEP
EXPANDABLE
WRISTBAND
NOTE: THIS ILLUSTRATION DEPICTS
THE INTEGRATION OF IPPM
SYSTEMS IN PART I AND PART II
FIGURE 8. IPPM display provides means of implementing systematic field pro-
tocols in the absence of supervisory clinical personnel* Pretraining of
subjects is required.
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as an index of myocardial contractility. Impedance STI measurements permit
an array of cardiac performance measurements similar to those reported in
Part I. However, if an internal IPPM system for this purpose is desired,
the system design would require a specific configuration as follows: a
conventional esophageal balloon is instrumented to include two foil electrodes
around its inner surface, while two additional electrodes are placed around
the subject's neck at the carotid artery level. The neck electrodes are
excited with a 100-KHz carrier signal, while the esophageal balloon electrodes
are positioned near the cardiac orifice or the level of the aortic root of
the heart.
As each cardiac cycle occurs, the electrical impedance carrier signal
is modulated by the aortic flow velocity (first derivitive impedance) at the
aortic root level, and an analog impedance signal is detected. Each cardiac
cycle is preprocessed by ensemble averaging and stored in memory. If immedi-
ate STI data is sought, signals are passed out through the nasal pharyngeal
cavity by fiber optic data lines to an external microcomputer. This process
would permit real time exercise analysis of STI, as illustrated in Part I.
If it is desired to collect and store periodic internal STI data for later
interrogation and analysis in an off-line fashion, this may be accomplished
by storing data in RAM within the IPPM and analyzing them later. The resulting
cardiac Impedance signals would then be stored in RAM for subsequent analysis
after exploratory surveys have been completed. This technique would provide
a means of cross-validating the external IPPM/STI device prior to field
epidemlologic use.
APPLICATION OF INTERNAL IPPM TO EXTERNAL PHYSIOLOGIC MONITORING
Upon the successful development of the modularized wafer systems (Figures
1 and 2), the packaged systems used for internal exploratory research may
also be applied to external personal monitoring.
A critical need in field epidemlologic health effects is the use of the
physician's assistant or clinical technician to ensure that field protocol
techniques are properly adhered to. Conversely, it is totally impractical
to provide clinical technicians with each IPPM during data collection. How-
ever, with implementation of microminiaturized visual display screens in the
form of a wrist-mounted device (WMD), a form of visual and auditory communi-
cation with the trained subject is feasible (as described below).
273
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IPPM WRIST-MOUNTED DISPLAY
The use of liquid crystal pictorial displays (LCPD) have been utilized
in recent military aircraft radar systems for target identification and de-
struction as part of the "Smart Bomb" weapons systems (14). LCPD modules
are available as 1-inch-square 100 x 100 visual matrix devices which, through
character generator techniques, appear as a postage stamp-sized TV set.
Each matrix contains 1,024 x 1,024 digital encoded pictorial elements, which
can be electronically stacked to form a 2 x 3-inch visual display (as illus-
trated in Figure 8). With precanned protocols built into on-board EPROM
devices in an IPPM, such a design could be used as a communicative prompting
device (STI, Part I) to have the subject follow specific protocol routines
without the assistance of a medical technician.
Operationally, the LCPD would have three basic modes of operation, as
follows:
• Systems management process controller
• Auditory attentional command and response functions
• Visual prompting and interactive instructions.
SYSTEMS MANAGEMENT PROCESS CONTROLLER (SMPC) MODE
A single microcomputer located in the wrist-mounted device will function
as a systems management processor which will control all messages to and from
the subject via the LCPD. The SMPC will function as a bus master in a multi-
microprocessor environment. One microcomputer will function as a physiologic
data acquisition system (PDAS) located in the subject's right shoe (heel)
or belt (Part I). A second microcomputer is a pollutant exposure processor
(PEP) located in the left shoe (heel) or belt (Part I). Each communicates
on-call to the bus master in the wrist-mounted device. The PDAS and PEP
systems will function as a multimode bus master/slave system. The bus master
will periodically "poll" the PDAS and PEP throughout protocol test periods,
thus accessing the two slave systems for relevant subtle response data.
The PDAS and PEP systems will be dedicated as IPPM systems and will
contain precanned protocols relative to the detection, processing, and low-
level diagnosis and/or interpretation of events. If no subtle effects within
the PDAS or PEP systems occur, these systems would report to the bus master
only on-call in a routine ''polling'1 mode. However, if a subtle change occurs
in either IPPM, either one or both PDAS' or PEP's could interrupt the bus
master for "relevancy analysis" by the bus master. In such an event, the
274
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bus master will weight out the significance of the physiologic or pollutant
effect, and sound an attentional tone to the subject to look at the LCPD
for further instructions.
AUDITORY ATTENTIONAL COMMAND FUNCTION (AACF) MODE
Based on a low-level analysis of the PDAS or PEP, the bus master will
sound an auditory tone (three beeps) to get the subject's attention. The
test subject then responds, acknowledging his/her attention by depressing the
"yes" button on the wrist-mounted device.
VISUAL PROMPTING AND INTERACTIVE INSTRUCTIONS (VPII) MODE
Upon test subject attentional response indicating "yes," the bus master
is told that the test subject's attention is available for interactive mes-
sages in that the subject is viewing the LCPD and awaiting information.
The VPII and LCPD are designed to display precanned messages stored in
an on-board EPROM device. An array of interactive prompting messages are
called by the bus master and displayed to the subject, depending on the cir-
cumstances. In the event of performing specific protocol functions based
on previous training in the EPA "CLEANS" facility (i.e., pulmonary function
exercise by a construction worker, as in Part I), the subject can be in-
structed via the LCPD messages and paced throughout a short protocol. As an
example:
1) An auditory tone beeps three times and gets the subject's attention.
2) The subject responds by depressing the "yes" button on the WMD.
3) The subject reads the message on the LCPD.
4) The prompting message will instruct the subject to:
a) Place pneumo in mouth;
b) Continue rest breathing until 1-minute tone;
c) Increase exercise until 5-minute tone, then stop.
5) If during the pulmonary exercise protocol the subject's heart rate
or other parameter exceeds the maximum level, the PDAS system alarms and in-
terrupts the bus master. The bus master automatically sends three auditory
275
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tone beeps to get the subject's attention. The subject responds with the
"yes" button, the bus master replies with the message "STOP"—"STOP," "GO TO
REST-STATE." After a period of 1 minute, the bus master polls the PDAS and
PEP again. If the subject's heart rate is in excess of prescribed limits,
the bus master sends three beeps, and the subject responds with a "yes."
The bus master sends the message, "LEAVE WORK AREA"~"SEE PHYSICIAN IMMEDIATELY.'
6) If only the PEP alarms without a physiologic response, the bus master
sends three beeps, the subject responds with "yes," and the message display
indicates "Pollutant Alarm" and continues to flash. A second message is dis-
played, "LEAVE AREA IMMEDIATELY," and also flashes.
With the combination of protocol-prompting of a trained subject, and low-
level diagnosis of PDAS or PEP as an "interactive intelligent personal monitor,"
IPPM can serve as a low-level adjunct human supervisor in support of and lack
of a medical technician of the test subject. Other algorithms and protocols
may also access the test subject's own known judgment through prompting mes-
sages. This approach permits a joint man-machine interactive rationale as an
"intelligent personal monitor" (Part I).
A wide variety of protocols, alarm messages, displays, etc., are feas-
ible through this approach. The functional features of an IPM design of this
type are within the state-of-the-art today. However, the submicron technol-
ogy of microcomputers, with the size and packaging density advocated here,
will require considerable research and development. Conversely, devices
such as the LCPD currently exist in military fire control systems. The
design issue requires access and design integration of a LCPD with an IPM
system.
CONCLUSION
The design examples and guidelines for external and Internal IPPM systems
have been presented through implementation of VLSI, submicron components,
and microcomputer technology. Through this process, the concept of the
"physician's data base matrix" has been presented as a means of developing
the principles of "prescription engineering" in IPPM devices. Prescription
engineering provides a key mechanism in the selection of prevalidated pro-
tocols and design of adaptive IPPM systems in response to changing research
needs, clinical feasibility, cost effectiveness, and the development of an
urban clinical data base. The prescription engineering approach to clinical
276
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epidemiologic research provides the means of replacing discrete circuit logic
with interactive intelligent software logic as a means of reducing physical
size, weight, and power. This approach enhances subject acceptance through
microminiaturization and elimination of technological obsolescence due to
changing health effects mandates.
Prescription engineering by the physician and his or her support team
illustrates the principles and problems involved in the Interfacing of human
anatomy to a physiologic data acquisition system. The anatomic-to-transducer
interface is the greatest Impasse in IPPM system design, along with concomitant
development of new health effects parameters. Further, the importance of
common clinical protocols for male and female populations Imposes severe
but not insurmountable design obstacles. Resolving such design obstacles is
illustrated by design examples in Parts I and II through Implementation of
the concept of multlmode transducers. Multimode transducers provide the means
of minimal physical transducer placement and maximizing the number of clini-
cally useful parameters. The cardiopulmonary transducers and algorithms
proposed here speak to this design philosophy without encumbering the test
subject or sacrificing clinical data. This approach also provides the means
of using standardized VLSI subsystems and microcomputers, which in quantities
needed in clinical epidemiologic research could be more cost effective than
any other approach currently available.
Finally, it is fully recognized by the authors that the level of the
VLSI technology required in the proposed designs is not currently available.
The design concepts presented here have been utilized as building blocks in
establishing design principles for the implementation of external/internal
IPPM systems in the near future, 3 to 5 years from today. Systems of the
type advocated here will not be in the making in the foreseeable future,
unless clinical and environmental scientists are enlightened by the potential
of new microcomputer technology and apply modern methods to the solution of
health care and environmental epidemiologic problems. Conversely, we must
recognize that microcomputers are not "cure all" devices and that their
implementation must be based on a balanced engineering approach. If we fail
to adopt the design principles similar to those defined in Parts I and II,
the lack of a realistic, simultaneous air dosimetry and physiologic data
acquisition system will continue to stagnate environmental science. A new
strategy for the design of personal physiologic monitors is required as a
means of implementing a public health initiative. The philosophy of internal
semi-invasive data acquisition systems is introduced as a means of conducting
exploratory physiologic research in support of this strategy. Through this
approach, it is anticipated that a new prospective will spawn new knowledge,
277
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parameters, and techniques that may be extrapolated to external intelligent
personal physiologic monitors.
It is abundantly clear that through technology of today and in the next
5 years, simultaneous pollutant and physiologic personal monitors shall be
implemented through the design philosophies and principles presented in Parts
1 and II. The issue is not how, but when, will clinical and environmental
researchers put forth the necessary research and development effort to bring
IPPM systems into being. Again, it is fully recognized that several concepts
and devices advocated here do not presently exist; they must be made to
happen, as was done in exploration of the moon. For this reason, appropriate
design goals presented here must be established. The internal/external ap-
proach to IPPM systems represents the ultimate design. Critics will scoff and
allude to such innovations as being products of technological intoxication.
However, we need only look back at the progress of personal monitor design
in the last 5 years to realize that personal pollutant and physiologic monitors
were advocated in 1974 Healthe-Belt, but still do not exist today; hence, a
loss of 5 years that could have better served the public.
A significant problem in epidemiologic urban health effects data ac-
quisition is lack of supervisory clinical technicians to administer the pro-
tocol as in the EPA "CLEANS" facility. The liquid crystal pictorial display
device is not a complete solution to the problem. However, such a system
could serve as an interim solution to the field logistics of urban epidemiology.
These proposed concepts and design philosophies will in all probability
meet with similar pessimism, as in the past, without the benefit of scientific
research. In considering the explosive technology of today and the next 5
years, the design cycle time for an external IPPM is 18 to 24 months• This
period of time must be followed by appropriate clinical validation studies
for an additional year. Once such a system is clinically accepted for field
epidemiologic use, a minimum of a 2-year field study would be required.
Hence, the design-to-data-base cycle time would not be unusual at 5 years.
The key question is: can an urban public health initiative afford to wait
another 5 years (a total of 10 years) before appropriate R&D support is im-
plemented to provide a supportive legislative health effects data base?
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Systolic Time Interval Analysis. Proceedings of Digital Equipment
Computer Users Society, pp. 795-798, May 1976.
3. Kizakevich, P., Gollan, P., McDermott, J., Aranda, J. Continuous Non-
invasive Cardiac Monitoring of Cardiac Function: Its Application in
Exercise Stress Testing. British Heart J, December 1978 (in press).
4. Kizakevich, P. Personal Cardiopulmonary Electrode Monitoring. Pro-
ceedings of the Symposium on the Development and Usage of Personal
Monitors for Exposure and Health Effects Studies, Chapel Hill,
N.C., January 22-24, 1979. (EPA symposium.)
5. Kubicek, W.G. et al. Development and Evaluation of Impedance Cardio-
graphlc Systems to Measure Cardiac Output and Other Cardiac Parameters.
NASA Contract #NAS-9-45. July 1967.
6. Mason, W.P., Thurston, R.N. Use of Piezoresistive Materials in the
Measurement of Displacement, Force, and Torque. J Acoustical Soc of
America 29, 1957.
7. Petrovick, M.L. et al. The Role of Personal Monitors in Environmental
Health Effects Research. Proceedings of the IEEE National Aerospace and
Electronics Conference, NAECON 74, pp. 152-159.
8. Petrovick, M.L. Patient Owned Systems and Devices in Health Care.
Presented at Texas A&M Conference on "The Impact of Microcomputers
in Health Care," September 18-19, 1978. (In preparation.)
9. Soricek, B. Microprocessors and Microcomputers. New York, Wiley—
Interscience publication, John Wiley and Sons, 1976.
10. Stroder, N.R. The Microprocessor Transducer Function. Proceedings of
the 12th Hawaii International Conference on Systems Science, pp. 256-
265, 1979.
11. Strong, A.T. Description of the CLEANS Human Exposure System, EPA R&D
Report #600/1-78-064. November 1978.
12. Van DeWater, J.M. et al. Monitoring the Chest with Impedance. Chest
64:597-603, 1973.
13. Wallace, L. Personal Air Quality Monitors: Past Uses and Present
Prospects. American Chemical Society 4th Joint Conference on Sensing
of Environmental Pollutants, pp. 390-394, 1978.
14. Winner, R.N. A Study of the Application of Reflective Displays to
Synthetic Array Radar. Hughes Aircraft Company, Technical Report AFAL-
TR-73-155. August 14, 1973.
279
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MAILING ADDRESS OF AUTHORS
Mathew L. Petrovick and Edward D. Haak, Jr., M.D.
Health Effects Research Laboratory
Clinical Studies Division
U.S. Environmental Protection Agency
Chapel Hill, North Carolina 27514
280
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Personal Cardiopulmonary Electrode
Monitoring
Paul N. Kizakevich
Research Triangle Institute
Research Triangle Park, North Carolina
Environmental health effect studies are usually designed to correlate
controlled pollutant dose with health effect decrement. In the experimental
laboratory, accurate dose measurements are compared to standard cardiopul-
monary parameters. Typical physiological measurements Include respiratory
rate, respiratory volume, alveolar-arterial oxygen gradient, heart rate, and
electrocardiogram stress response (30). While such experiments provide use-
ful and reproducible information, they could be supplanted with studies in-
volving subjects performing their normal daily routine by employing personal
exposure and physiological data monitors.
The initial target organ for airborne pollutants is the lung, and, con-
sequently, respiratory function measurements are commonly examined. Adverse
pulmonary function may affect oxygen transport with resulting changes in
cardiac performance, especially under Increased workloads. As heart and
lung disease are prominent in our society, a significant subpopulation is
sensitized and susceptible to adverse cardiopulmonary effects. Although
pollutants which permeate the pulmonary membrane may be transported to all
organ and tissue systems, it is unlikely that such health effects could be
studied with personal monitors.
Cardiopulmonary measurements are, therefore, the most promising choice
for personal monitor health effect studies; however, the selection of suit-
able nonlnvaslve cardiopulmonary measurement techniques is limited. The
necessary physiological data must be acquired with ease, comfort, and accuracy
281
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in order to gain favor with both the investigator and subject volunteer.
Using only surface electrodes, the electrocardiogram (EGG) is routinely
used for monitoring changes in heart rate, rhythm, and muscle physiology.
A second electrode technique, thoracic electrical impedance (TEI) measure-
ment, is an experimental method which detects changes in cardiac muscle per-
formance and pulmonary physiology. Together, the EGG and TEI provide a
comprehensive assessment of cardiopulmonary function and physiology which
appears well suited for personal monitoring and environmental health effects
research.
ELECTROCARDIOGRAM
The physiology and measurement of the ECG are well known and routine in
modern clinical practice (7,12). Contraction and excitation of cardiac mus-
cle are accompanied by tissue currents which give rise to millivolt potential
differences at the body surface. The normal ECG presents a rhythmic waveform
pattern which is fairly reproducible among different subjects with the same
electrode placement. Changes in the waveform may occur with drug therapy,
exercise, cardiac ischemia, and other physiological inputs.
Although the ECG electrode placement may vary, three-lead differential
amplifier input is generally used to provide high common-mode noise rejection.
The V5 precordical lead measures the ECG close to the heart, yields a large
amplitude with minimal motion artifacts, and is often used in exercise studies
(Figure 1). The primary electrode is placed on the mldclavicular line over
the fifth intercostal space, the reference electrode above the sternum and
the indifferent electrode on the lower right thorax.
In the apparently healthy individual, the ECG is primarily used for heart
rate measurement. Since systemic oxygen delivery is determined by cardiac
output (stroke volume * heart rate), the heart rate is a factor In determin-
ing the cardiac response to a given workload. Maximal stroke volume is
roughly attained at 40 percent of the individual maximal oxygen uptake (1,
14), and the remaining work response. Is accommodated by increasing heart rate
alone.
THORACIC ELECTRICAL IMPEDANCE
While the ECG has been studied for nearly a century, TEI measurement is
282
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FIGURE 1. Typical configuration for the TEI current source (solid), TEI
pickup (dotted), and EGG (dotted) surface electrode Interface.
TEI
AZ
TIE
FIGURE 2. Composite sketch of TEI waveform components: mean Impedance (Z ),
low frequency respiratory waves (DZ), and high frequency cardiac waves (ICG).
283
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a relatively recent development. First measured in 1932 (2), continued re-
search of the cardiopulmonary impedance effects (27,33) led to NASA instru-
mentation and clinical studies support (28). The fundamental properties are
well reviewed (11); however, the number of recent clinical publications
lends itself to further presentation.
A variety of electrode configurations have been reported, and each tends
to enhance a specific TEI physiological component. For cardiac and mean
thoracic impedance measurement, the four annular electrode system is most
popular (Figure 1). A very high frequency carrier signal (4 ma at 100 KHz)
is applied to the outer electrodes and passes through the thoracic volume.
At the designated frequency, the applied carrier current is completely safe
(11). The carrier signal, modulated by intraelectrode volume conduction
change, is monitored by the inner electrodes and demodulated to obtain three
physiological components (Figure 2). These are the mean or base impedance
(Z ), the low frequency impedance (AZ), and the high frequency Impedance (ICG)
waveforms.
The DC component (Z ) or mean thoracic impedance is a measure of intra-
thoracic fluid volume. In animals subjected to acute Intravenous hypervol-
umia and transient saline injections, a fall in Z accompanied Increases in
intrathoracic fluid volume (6,17,31). The noninvasive impedance measurement
generally preceded invasive central venous pressure measurement by as much
as 45 minutes (6,37). Investigators evaluating Z changes in human clinical
studies have confirmed that mean thoracic Impedance accurately follows the
clinical course of pulmonary congestion, edema, and intrathoracic volume
overload and forced diuresis (20,38,44,45).
Changes in Z can occur rapidly for both healthy and unhealthy individ-
uals, as was demonstrated by a 14-minute treadmill exercise test (5). An
increase in circulating blood volume and cardiac stroke volume presented a
3 percent Z decrease during the healthy subjects' exercise. The unhealthy
subjects, suffering from ischemic heart disease, had a reduced stroke volume
reserve and therefore could not accommodate the increased blood volume. Con-
sequently, they had progressive Intrathoracic fluid retention, as indicated
by a progressive Z decrease to a 15 percent total reduction.
Considering the magnitude of these Z changes and that patients suffering
pulmonary edema may have a 25 percent Z reduction, it is encouraging that
the normal Z may be predicted to 4.5 percent of the actual value by modeling
the thoracic geometry (21). Since a decrease in cardiac performance was de-
284
-------
tectable under exercise stress, changes in Z under transient environmental
stress might be detected. Furthermore, by computing an expected Z value,
thoracic fluid accumulation due to chronic exposure may be demonstrated with-
out requiring a 10-year study.
The low frequency TEI waves (AZ) due to respiration have been extensively
studied (11). The thorax consists of tissues, fluid, and air. Since air
is an insulator, the volume of air respired (AV) is related to the change
in impedance (AZ). While the ratio (AZ/AV) differs with individual vari-
ance in size, thoracic circumference, and subcutaneous fat (18), Improved
electrodes and individual splrometer or pneumotach calibration allow subse-
quent continuous resplred-volume measurement.
With calibration, AZ may be used for monitoring respiratory rate, as
is commonly employed for neonatal apnea detection. Regional lung pathology
is detectable by comparing AZ when each lung is monitored separately. The
subject thereby serves as his own control, and, again, calibration is not
required (8).
The high frequency TEI waves, synchronous with the cardiac cycle, are
the electrical impedance cardiogram (ICG) and the ICG first derivative (DZ/
DT) (Figure 3). Over 25 papers and abstracts have been published during
1976-1978 concerning the genesis and application of these waves.
Considerable evidence indicates that the cardiac impedance pulse re-
flects left and right ventricle ejection into the aorta and pulmonary artery
(3,19,35); however, the actual ventricular volume change contributes less
than 10 percent of the total Impedance change (35). The aortic contribution
was predominant in one study (19) and less than 30 percent in another (35).
Experiments in a calf with a totally Implanted cardiac prosthesis presented
an aortic contribution of 60 percent and a pulmonic contribution of 40 per-
cent (3). Clearly, the origin of the high frequency component is complex and
unresolved.
A close relation between DZ/DT and aortic blood flow has been observed
(28) and verified (43,46). Both the amplitude and time-to-peak derivative
of left ventricular pressure (DP/DT) have correlated with their counterpart
in DZ/DT (40,41,46). However, in one study, the relation of DZ/DT amplitude
to afterload (aortic dlastolic pressure) depended upon the experimental in-
tervention (32), which indicates that DZ/DT may be a reliable index of myo-
cardlal contractility under controlled conditions (41,42,46).
285
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ECG
ICG
DZDT
HS
FIGURE 3. Illustration of temporal relationship among the electrocardiogram
(ECG), impedance cardiogram (ICG), ICG first derivative (DZ/DT), and heart
sounds (HS).
ECG, DZ/DT,
. CYCLE
*" BUH-hK
NtVWU
ADC
^.
O£
CONTROL "
^ ADAPTIVE
^^ " TRIGGER
^
CYCLE
SELECTOR
,
\
MINHR,
HR
ANALYSIS
i
^
MAXHR
A
HR
^-
ENSEMBLE
AVERAGER
1QRS,
HR, :
WAVEFORM
ANALYSIS
i
HR
i
1 HR
1 BUFFER
DATABASE
MANAGER
DZ/DT
^0
SYSTOLIC TIME INTERVAL PROCESSOR
LABORATORY SYSTEM
FIGURE 4. Functional data flow for laboratory systolic time interval pro-
cessor.
286
-------
Impedance cardlography has long been a promising method for continuous
measurement of stroke volume (27,33). Early studies had resulted In Imped-
ance-calculated volumes of higher value than obtained by comparative methods
(11). Recent Improvements In the Impedance model and Its application have
reduced the differences to within experimental error (9,16,19,26,28,47).
Thus, by combining the EGG and TE1, heart rate, stroke volume, and cardiac
output are measurable.
The sequence of cardiac mechanical events, collectively called systolic
time Intervals (STI), correspond to DZ/DT waveform features (29). An auto-
mated system for STI measurement using DZ/DT and the heart sounds was first
developed In 1974 (22). The excellent correlation of DZ/DT STI features to
aortic and carotid STI features Is now well established (4,10,15,39). DZ/DT
STI measurements have proved reliable In exercise (13,24,36) and postural
(42) stress testing as indices of myocardial stress response.
SIGNAL PROCESSING
The necessity for EGG and TEI automated signal processing arises from
the complex nature In which the clinical information is contained. Certain
waveform features must be identified, interfeature amplitude and time meas-
urements made, and relevant clinical indices computed. As noninvasive
methods, both signals are subject to physiological artifacts, transductlon
artifacts, and uncertainty resulting from their indirect and remote trans-
ductlon of the physiological source. The TEI is sensitive to a variety of
physiological effects which must be isolated prior to measurement. These
challenges and their solution have been addressed by analog filter prepro-
cessing, cardiac component ensemble averaging, and waveform feature extrac-
tion algorithms (23,24).
The acquisition and analysis of the EGG, Z , and DZ/DT signals have been
the author's principal interest in this field. Recently, a laboratory-based
system for cardiac monitoring during treadmill exercise using these signals
was developed under EPA Contract No. 68-02-2772 (25). As an example of the
signal processing methods, the ensuing discussion will be limited to the
current system design rather than to project-specific processing requirements
for a personal monitor.
The EPA Systolic Time Interval Processor (STIP) uses analog signal
conditioning prior to digital signal processing and analysis. The EGG is
287
-------
ECG
ICG
FIGURE 3. Illustration of temporal relationship among the electrocardiogram
(ECG), impedance cardiogram (ICG), ICG first derivative (DZ/DT), and heart
sounds (HS).
ECG, DZ/DT,
x CYCLE
* BUhl-tH
NbWKV
ADC _
*.
'CLE
CONTROL
WAVE
„ ADAPTIVE
. " TRIGGER
^
CYCLE
SELECTOR
j
\
MINHR,
HR
ANALYSIS
i
MAXHR
A
HR
ENSEMBLE
AVERAGER
1QRS,
HR, ;
WAVEFORM
ANALYSIS
\
1
HR
BUFFER
r
DATABASE
MANAGER
DZ/DT
^0
SYSTOLIC TIME INTERVAL PROCESSOR
LABORATORY SYSTEM
FIGURE 4. Functional data flow for laboratory systolic time interval pro-
cessor.
286
-------
Impedance cardiography has long been a promising method for continuous
measurement of stroke volume (27,33). Early studies had resulted in imped-
ance-calculated volumes of higher value than obtained by comparative methods
(11). Recent improvements in the impedance model and its application have
reduced the differences to within experimental error (9,16,19,26,28,47).
Thus, by combining the EGG and TEI, heart rate, stroke volume, and cardiac
output are measurable.
The sequence of cardiac mechanical events, collectively called systolic
time intervals (STI), correspond to DZ/DT waveform features (29). An auto-
mated system for STI measurement using DZ/DT and the heart sounds was first
developed in 197A (22). The excellent correlation of DZ/DT STI features to
aortic and carotid STI features is now well established (4,10,15,39). DZ/DT
STI measurements have proved reliable in exercise (13,24,36) and postural
(42) stress testing as indices of myocardial stress response.
SIGNAL PROCESSING
The necessity for EGG and TEI automated signal processing arises from
the complex nature in which the clinical information is contained. Certain
waveform features must be identified, interfeature amplitude and time meas-
urements made, and relevant clinical indices computed. As nonlnvaslve
methods, both signals are subject to physiological artifacts, transduction
artifacts, and uncertainty resulting from their indirect and remote trans-
duction of the physiological source. The TEI is sensitive to a variety of
physiological effects which must be isolated prior to measurement. These
challenges and their solution have been addressed by analog filter prepro-
cessing, cardiac component ensemble averaging, and waveform feature extrac-
tion algorithms (23,24).
The acquisition and analysis of the ECG, ZQ, and DZ/DT signals have been
the author's principal interest in this field. Recently, a laboratory-based
system for cardiac monitoring during treadmill exercise using these signals
was developed under EPA Contract No. 68-02-2772 (25). As an example of the
signal processing methods, the ensuing discussion will be limited to the
current system design rather than to project-specific processing requirements
for a personal monitor.
The EPA Systolic Time Interval Processor (STIP) uses analog signal
conditioning prior to digital signal processing and analysis. The ECG is
287
-------
passed through an analog bandpass filter (0.05 to 50.0 Hz) to remove elec-
trode potential baseline shifts and to reduce 60 Hz and high frequency muscle
noise. The filtered ECG is passed through a QRS event matching filter (7.2 to
23.4 Hz) to produce the RWAVE event detection signal. The TEI signals (ZQ,
AZ, DZ/DT) are bandwidth filtered within the commercial impedance instrument
and only require amplitude and baseline adjustment.
The ECG, DZ/DT, and RWAVE are sampled at a 400-Hz rate and held in a
sample buffer (Figure 4). Each new cardiac cycle is detected by an adaptive
trigger algorithm that adjusts the trigger level to the running average
RWAVE height. Continuous RWAVE detection is thus assured without manual
intervention. With each new cycle, Z is sampled and stored with DZ/DT and
the ECG QRS complex in a cycle buffer. At the same time, the instantaneous
cardiac cycle duration is used to compute and queue the instantaneous heart
rate.
When a cardiac function measurement is requested, the remaining processes
are activated. In order to further isolate the TEI cardiac component and
to improve both the QRS and DZ/DT signal-to-noise ratios, an ensemble of the
acquired cycle buffers is averaged. Since the systolic DZ/DT waveform is
dependent upon the instantaneous cardiac cycle duration—a natural heart rate
variance—premature ventricular contraction or other anomalous ventricular
event would invalidate the ensemble average. By selectively averaging cycles
of similar duration, these problems are reduced.
To do this, the heart rate buffer is analyzed for the mean expected
heart rate (HR), and a 12.5 percent acceptance range (MINHR, MAXHR) is deter-
mined. Each successive cycle is compared to these criteria prior to Inclusion
in the ensemble summation process. The resultant averaged ECG and DZ/DT
waveforms are then smoothed and displayed (Figure 5).
The major clinical endpoints for the EPA system are the cardiac systolic
time intervals which are relative timing measures between waveform features.
Each waveform feature (0, ..., 4) is identified in several stages: 1) the
average heart rate is used to estimate the feature waveform segment; 2) the
segment waveshape pattern is classified; and 3) the feature is identified
using an algorithm based on the pattern classification. A list of quality
control parameters and selected clinical indices is then displayed. Finally,
the investigation may accept, reject, or flag the cycle for further analysis.
The data base management design has a comprehensive data structure suited
288
-------
roe cmmi/t TO
I I I f I T I I I I I
• 3lllli5l2*2»3»35l4ll«5l3»
I. MM* RMEM MIMTE «UCTI CYOB EFFCY. 90
3 tf2 Ctt tt M II IN 07
M PEP TOOK TZMX BK 03 TZINE T2NLL L«T
29 HI 139 197 IB 441 47 179 IB
FIGURE 5. Laboratory system graphic display of averaged QRS and DZ/DT waveforms,
waveform feature cursors, and resultant data list.
(KATE*
HSECO
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129
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IN.
"^ ^A
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91-1 98 -J
SELECT STI TREND DISPLAY
STI , STILUS <\>, EXIT
-------
for experimental laboratory analysis. Over a 12-minute acquisition period,
1,570 cardiac cycles may be saved on double-density floppy disc with heart
rates ranging from 40 to 175 beats/minute. Along with each sampled waveform
is a data vector containing instantaneous cycle duration, relative time,
exercise stage, experimental protocol, pollutant, and other individual cycle
data. By keying on a specific data vector element, the raw data are easily
recalled for automatic waveform analysis.
The waveform analysis output data are held in a memory array and stored
on floppy disc. Editing, transfer, and listing of the disc data are executed
via the memory array. For qualitative review of the treadmill exercise re-
sponse, a graphics procedure recalls select cardiac indices and displays
their response trend (Figure 6). Grouped statistical analysis and distributed
processing data transfer are further capabilities which could be implemented.
PERSONAL CARDIOPULMONARY MONITOR
The EPA STIP laboratory system described in the last section will receive
clinical and environmental health effect evaluations during the current year.
While a reduction in size and function may be a useful initial approach for
a personal monitor design, an expanded outlook for research and development
may present a better formulation.
The body-electrode Interface, electrode placement configuration, and
ECG and TEI signal transduction comprise the electrode interface system
(Figure 7). Each of these topics must be reviewed in the biomedical engi-
neering literature and alternative technologies studied for optimum trans-
duction of the desired cardiopulmonary signal components. Since no signifi-
cant change in TEI electrode technique has emerged in the last 10 years,
it is likely that improved electrodes and impedance detection electronics
could be developed using today's technology. The current STIP system would
be used as a basis for controlled clinical and subsequent environmental health
effect studies in the evaluation of electrode interface system developments.
The commercially available instrument for TEI measurement occupies a
volume of 1 cubic foot. This instrument must be redesigned as a functional
electronic component within the overall system concept. In this way, the
electrode interface and control, ECG and TEI transduction, TEI component
isolation, analog preprocessing, and digital signal processing could be in-
tegrated as a single hybrid microcircuit module. The output data would
290
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ELECTRODE
INTERFACE
SYSTEM
ECG, Zg
DZ/DT
SIGNAL
PROCESSING
SYSTEM
SIGNAL ACQUISITION & PREPROCESSING
WAVEFORM
ANALYSIS
SYSTEM
CLINICAL
DATA
DATABASE
& I/O
CONTROL
t-
SIGNAL ANALYSIS & SYSTEM CONTROL
FIGURE 7. Functional diagram of proposed personal cardlopulmonary monitor.
represent analog and digital preproceseed waveform complexes ready for pattern
recognition and feature analysis.
Specific physiological waveform processing, data base input/output, and
overall system characteristics in communicating with other monitoring devices
are general systems engineering problems which require study and formal
specification. Current techniques for automated waveform analysis would be
reviewed, and—based upon the intended application—appropriate software
would be designed. The data base and system functions would be governed
by the monitoring application, yet would be designed in a standard format.
Implementation of the signal analysis and system control module would rely
on standard microcomputer components. As a result, reduction of these system
functions from the laboratory system would be straightforward.
The clinical validation is a necessary aspect of any biomedical system
development. At the very least, the instrument must operate as specified
and record valid physiological measurements. Using controlled environmental
response studies and Inpatlent clinical observations, the cardiopulmonary
electrode monitoring concept would be tested. Based on known and expected
response patterns, experimental studies would be designed, performed, and
evaluated within the environmental laboratory setting. In this manner, the
291
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sensitivity, reproducibility, and accuracy of the personal cardiopulmonary
electrode monitor would be validated.
SUMMARY
The need for simultaneous personal monitoring of physiological response
and pollutant exposure was addressed, and a method for the required physio-
logical data acquisition was presented. An overview of the physiology,
transduction, signal processing, and significance of the electrocardiogram
and thoracic electrical impedance were discussed, along with research and de-
velopment requirements for a personal cardiopulmonary monitor. The further
investigation of these topics and the development of the suggested monitor
would provide new insight into environmental health effects and most likely
transfer its application to noninvasive monitoring of critically ill patients.
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System. Aerosp Med 37:1208, 1966.
28. Kubicek, W.G., Patterson, R.P., Witsoe, D.A., From, A.H.L. Impedance
Cardiography as a Noninvasive Method of Measuring Cardiac Output and
Other Cardiac Parameters of the Cardiovascular System. NASA, Houston,
Texas, 1969.
29. Labadidi, Z., Ehmke, D.A., Durin, R.E., Leaverton, P.E., Lauer, R.M.
The First Derivative Thoracic Impedance Cardiogram. Circulation 41:
651, 1970.
30. Linn, W.S., Hackney, J.D. Health Effects of Air Pollution. J Cardio-
vascular & Pulmonary Technol 7(2):50-55, 1979.
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Impedance: Quantitative Evaluation of a Non-invasive Measure of Thoracic
Fluid Volume. Am Heart J 85(l):83-93, 1973.
32. Moore, A.G., Baker, L.E., Rubal, B.J., Poder, T.C. The Relationship
Between the Maximum Rate of Change of the Thoracic Impedance Waveform
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33. Nyboer, J. Electrical Impedance Plethysmography. Springfield, 111.,
Charles C. Thomas, 1959.
294
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34. Patterson, R.P. The Use of Signal Averaging of the Electrical Imped-
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the Effect of Controlled Volume Change on the Thoracic Electrical Im-
pedance. Med & Biol Eng & Comput 16:531-536, 1978.
36. Poder, T.C., Gutgesell, H.P., Baker, I.E. Application of Impedance Car-
diography to Cardiovascular Stress Testing in Children. Fed Proc 37:
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37. Pomerantz, M., Baumgartner, R., Lauridson, J., Eiseman, B. Thoracic
Electrical Impedance for the Early Detection of Pulmonary Edema. Surgery
66:260, 1969.
38. Ramos, M.U., LaBree, J.W., Remole, W., Kubicek, W.G. Transthoracic Elec-
tric Impedance. Minn Medicine 58:671-676, 1975.
39. Rasmussen, J.P., Sorensen, B., Kann, T. Evaluation of Impedance Car-
diography as a Noninvasive Means of Measuring Systolic Time Intervals
and Cardiac Output. Acta Anaesth Scand 19:210-218, 1975.
40. Rubal, B.J., Poder, T.C., Baker, L.E. Correlations Between t-max DP/DT
and t-max DZ/DT. Federation Proceedings 37:776, 1978.
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Clinical and Experimental Use of Thoracic Impedance Plethysmography in
Quantifying Myocardial Contractility. Surgery 67:907, 1970.
42. Smith, J.J., Porth, C.J., Reinke, J.A., Ebert, T.J., Tristani, F.E.
Impedance-Derived Cardiac Indices in Coronary Heart Disease. Physiolo-
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Evaluation of the First Derivative of the Impedance Cardiogram. Cir-
culation 42(111):65, 1970.
44. Tempel, G., Jelen, S., Hundelshausen, B.V. Transthoracic Electrical
Impedance in Anaesthesia and Intensive Care. Resuscitation 6:97-105,
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45. Van De Water, J.M., Mount, B.E., Barela, J.R., Schuster, R., Leacock, F.S.
Monitoring the Chest with Impedance. Chest 64:597-603, 1973.
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295
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47. Yamakoshi, K., Ito, H., Yamada, A., Miura, S., Tomino, T. Physiological
and Fluid-Dynamic Investigations of the Transthoracic Impedance Plethys-
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14(4):365-372, 1976.
MAILING ADDRESS OF AUTHOR
Paul N. Kizakevich
Research Triangle Institute
P.O. Box 12194
Research Triangle Park, North Carolina 27709
Discussion
PETROVICK: Matt Petrovick, EPA. Paul, could you give the group an
idea about the practicality of the impedance cardiograph measurements in
a roving mobile subject? For example, let's take this scenario: when you
get up in the morning, you hop in your car or you walk to work, you get on
a bus, you sit down, you go to lunch, and you do all your daily activities,
and we would like to record periodically the measurements of systolic time
intervals through this process.
How practical do you think this technique is with regard to the severe
environment of the artifact from the electrodes? Would you please address
that?
KIZAKEVICH: As I have already demonstrated, we have been able repeatedly
to monitor patients doing treadmill exercises. In fact, from the work in
Miami, we have a paper published in the Heart Journal, December 1978, demon-
strating the expected response of systolic time intervals in treadmill ex-
ercise through a stage four program. And that is about as severe as you are
going to get. You know, that is equivalent to jogging—much faster than jog-
ging down the street. I think there is no problem.
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A Respiration-Controlled Personal Monitor
Donald J. Sibbett, Ph.D., and Rudolph H. Moyer, Ph.D.
Geomet, Inc.
Pomona, California
Although a considerable variety of instrumentation such as impingere,
cascade impactors, battery-powered air samplers, diffusion collectors, and
gas-stain detector tubes is available for applications relating to personal
monitoring in industrial and ambient environments, few of the results obtained
by such devices are easily relatable to the exposure or dosage of individuals
to noxious airborne components. Continuous, electrically powered, and diffu-
sion-controlled collectors fail to measure the varied physiological sampling
rates imposed in response to diverse demands for oxygen during a range of
activities* Thus, exposure to pollutants during periods of high activity
which result in deep and rapid inspiration are weighed equally, in a statis-
tical sense, with periods of shallow breathing, by collection devices uti-
lizing uniform sampling rates. For accurate correlation of exposure with
health phenomena, it is highly desirable that air sampling for analytical
chemical determinations be proportional to the ventilation rate of Individuals
under study.
The Geomet Personal Sampler provides a method for sampling air in pro-
portion with the respiration of the wearer. The method is characterized
by its use of a carefully designed air pump which is supported next to the
diaphragm. The pump is activated by the expansion and contraction of the
thoracic cavity during respiration and draws air through a collector which
may be varied in accordance with monitoring requirements.
The Geomet respiration-controlled personal monitor consists of five com-
ponents: 1) the pump, 2) a harness or vest, 3) a sample volume accumulator,
297
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4) a separated digital readout, and 5) a pollutant collector. With the digital
readout excepted, the total assembly weighs slightly over 1 pound in its current
configuration. The pump and harness weigh 293 g; the battery and accumulator,
207 g; and a typical gas sampler assembly weighs 30 g. A particulate sampling
head such as the Bendix Sampling Assembly, Part No. 3900-90, weighs 128 g.
Figure 1 shows the pump, harness, and signal accumulator which are worn
during sampling. The pump shown in the center of the picture is made from
black ABS plastic. This version, which normally pumps in the 150 to 250
ml/minute range, is 15.5 cm in height, 13 cm wide, and 3.7 cm thick when
expanded. Compressed, it is less than 2 cm thick.
The pump housing is connected to a lightweight Velcro harness by three
easily connected and adjusted plastic buckles. The harness is passed around
the wearer's abdomen and connects to the side ears on the outer pump panel.
Over—the-shoulder straps, connected to the circumferential band in the rear,
support the inner pump panel at its top. The harness may be adjusted for
abdominal measurements up to whatever dimensions are necessary. By use of
Velcro tabs, the excess strap is fastened back on itself. Dimensional ad-
justment of the harness is made at the buckles; the Velcro fastenings are
only used to avoid dangling ends.
The pump performance in terms of air displacement is monitored by use of
an electronic accumulator which is shown at the right side of Figure 1.
This cigarette package-sized instrument contains a 9-volt battery and elec-
tronic circuitry to monitor the motion of a linear potentiometer located with-
in the pump housing. The signal from the pot is transmitted through a shield-
ed lead which fastens to one end of the accumulator through a miniature
clamped hexagon connector. The accumulator measures and stores potentiometer
motion in both directions. The absolute magnitude of this signal is estab-
lished by screwdriver adjustment of a trim-pot through the package wall.
After calibration and adjustment, the accumulator may read out in any desired
volume units. As normally calibrated, the readout unit operates in milli-
liters.
A closer look at the pump is shown in Figure 2. The cross section en-
titled B on the right shows the extended position of the pump. The pump Is
returned to this position by the spring, which is shown schematically at the
bottom of the figure. All working components are contained within the molded
housing and are protected by it from accidental damage.
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FIGURE 1. The Geomet Personal Monitor. Pump, harness, accumulator, and a
typical harness.
) 1 Molded Housing
Diaphragm
8
Exhaust
Valve \
Spring—LI
to Accumulator
FIGURE 2. The Geomet Personal Monitor pump,
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Abdominal wall motion moves the base section of the housing to Impart
a pumping motion. On expiration, the spring drives the two housing sections
apart and two flapper valves control the air intake. On expiration, the
silicone rubber diaphragm is extended, drawing air through a sampling tube
Into the pump body through a tubing connector visible at the lower center
of the diagram. On compression of the diaphragm or expansion of the thoracic
cavity, the inlet valve closes and the exhaust valve—located between the rub-
ber diaphragm and the pump cover—opens. Repeated flexing of the diaphragm
produces pumping action. The signal-generating linear potentiometer is lo-
cated on the left side of the housing. The signal is passed to the accumu-
lator by a cable extending from the housing on the right-hand side.
This device, in the described size, pumps in the range from 150 to 250
ml-per-minute during most activities. Changed sampling rates may be achieved
by modification of the housing size.
To use the system, the harness is placed over the head, the vee-shaped
section is connected to the top coupling, and the circumferential belt is
connected to the sides of the pump. Appropriate tension is achieved by pull-
ing the side belting until the pump diaphragm is just slightly compressed dur-
ing normal exhalation. Harness tension should be barely noticeable. Excessive
tightening of the harness will result in poor performance of the pump* With
such incorrect adjustment, the pump will bottom (or close) during inhalation.
The harness may be held down by clips to a belt, if appropriate.
The procedure to determine the volume of air sampled during any interval
is carried out by use of a digital readout unit. This device, measuring
13 x 11 x 16.5 cm, is utilized at the start and termination of any operation.
At all other times, it is disconnected from the sampling device. Figure 3
shows the readout unit. Each switch has two operating positions; the mode
switch on the left permits direct recovery of the signal stored in the ac-
cumulator or gives a continuous monitoring of that storage. The up position
gives the stored value at the time that the center switch is depressed. In
the other position, the mode switch gives continuous readout, which is basi-
cally useful for demonstrations or short-calibration measurements. In the
depressed position, the clear switch zeros the storage system when the center
switch is activated. Elevated (the normal experimental position), the stored
signal is displayed on the digital meter. This procedure does not destroy
the storage.
The digital readout displays in six digits, which in current usage is
sufficient to sample 1 cubic meter less 1 ml. It is connected to a 115-V
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FIGURE 3. Digital readout, connected to electronic accumulator.
FIGURE 4. Personal monitor
in use.
"S
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60-Hz source by means of the power line from the back of the case. The
five-prong miniature hexagonal connector without the clamp is connected to
the matching terminal on the accumulator for use in measuring operations.
The readout device can be modified for operation on battery power.
At the start of any sampling operation—after the pump, harness, and
accumulator are adjusted on a wearer—the accumulator is connected to the
readout unit. With the clear switch in the depressed position and the mode
switch elevated, the middle switch is activated. This zeros the accumulator
and constitutes the beginning of the sampling interval. The accumulator is
then disconnected from the readout. The accumulator commences operating as
soon as the zeroing process is completed. However, the clear switch position
should be changed immediately to avoid loss of future data when another
challenge is made.
The personal sampler assembly may be used for collection of a wide
variety of airborne components. Figure 4 shows a typical example of the
full assembly set up to collect a gaseous component on a coated tube col-
lector. The collector in this case consists of a 20-cm ceramic tube which
is located under the collar clip. It is protected by a tygon sheath. Air
drawn from the neighborhood of the wearer's head passes through the tube.
The desired pollutant is collected on the inner surface of the tube by an
appropriate coating. For example, sulfur dioxide may be collected on a coat-
ing of sodium carbonate, and nitrogen dioxide on triethanolamine.
At the end of the collection interval, the coated collector tube is
placed in a screw-capped test tube and transmitted to a laboratory for anal-
ysis. Table 1 shows a selection of components which have been sampled by
the personal monitor technique.
Mercury is quantitatively removed by a short silver wire absorber packed
randomly in a 5-cm section. It is desorbed from the silver in an induction
furnace and passes directly into a UV photometer for quantitation. This
technique is also used to calibrate the sampling volume of the collector/
accumulator components. For this purpose, a constant concentration mercury
source was set up which gave 5 nanograms-per-liter of mercury vapor. The
silver plug collector was used to sample this stream by operation of the
personal monitor pump. The accumulator pot was adjusted until the digital
readout was 1 ml-per-digit.
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TABLE 1
Applications of Personal Monitor
GASEOUS COMPONENT ABSORBENT ANALYTICAL METHOD
Mercury Silver UV Photometry
Hydrogen Chloride Sodium Carbonate Luminol Chemilumines-
cence (LC)
Nitric Acid Sodium Chloride LC
Sulfur Dioxide Sodium Carbonate LC or Flame Photo-
metric Detection
The second example utilizes collection of hydrogen chloride on a sodium
carbonate coating placed on a small-bore collector tube which is part of the
gas inlet line to the pump. The acidic gas diffuses to the wall during
passage through the collector and is retained with high efficiency (>95 per-
cent)* The collector tubes are returned to the laboratory for analysis•
We have utilized a procedure which involves rinsing the carbonate/chloride
coating off the tube with a solution of potassium iodate in sulfurlc acid.
The evolved gas may be quantitated by use of the Geomet lumlnol chemilumines-
cence instrument. For hydrogen chloride, collection of about 50 nanograms
is required.
Similar techniques are available for the collection and analysis of
nitric acid and sulfur dioxide. Nitric acid is collected on a sodium chlo-
ride coating. In the laboratory, the analysis uses a sulfuric acid rinse
and the luminol chemlluminescence method for quantitation. Sulfur dioxide
is collected on sodium carbonate and may be analyzed by a similar luminol
chemiluminescence technique or by flame ionization photometry. Nitrogen
dioxide may be collected on a triethanolamine coating, diazotized, and read
out spectrophotometrically. These methods require collection of 10 to 40
nanograms of the pollutant.
Other applications of the collection technique may involve small col-
umns of absorbent in place of the coated diffusion collector tube. Table
2 shows a number of potential applications. For example, a variety of organic
compounds may be collected on styrene-dlvinylbenzene copolymer spheres such
as Chromasorb 102 or Tenax-GC. Thermal desorption Into a gas chromatograph
or a gas chromatograph/mass spectrometer combination provides analysis.
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TABLE 2
Applications of Personal Monitor
GASEOUS COMPONENT ABSORBENT ANALYTICAL METHOD
Selected Organic Compounds Styrene-Divinylbenzene Gas Chromatography
(GC) or GC/Mass
Spectrometry (MS)
Vinyl Chloride Charcoal GC
Pesticides Supported Ethylene GC/MS
Glycol
Polyurethane Foam
Carbon Dioxide Hydrazine-Crystal Spectrophotometry
Violet
Likewise, vinyl chloride may be collected on charcoal and desorbed into
a gas chromatograph for analysis. Pesticides may be collected on a variety
of materials and analyzed similarly. A novel procedure for carbon dioxide
utilizes a tube coated with hydrazine-crystal violet followed by a specto-
photometric determination of the remaining colored species.
In general, procedures can be devised which are specific and adequately
sensitive for most industrial gaseous species. However, care must be exer-
cised to match the sample collector, sample volume, air concentration, and the
sensitivity of the analytical laboratory technique.
Although this version of a personal monitor may be used without corre-
lation with the respiration rate of the wearer, a number of applications are
of interest in which dosage or exposure data may be obtained.
Table 3 shows a test which compares the volume sampled by the pump with
splrometer measurements of the wearer's respiration. In these tests a plas-
tic bag was filled with an air sample and pumped out by the personal monitor
pump, which was activated in position on a wearer. The exhaled volume was
measured by a simple spirometer. As the data show, in this test about 4.3
percent of the exhaled volume was sampled by the pump.
A second test was run on the same subject after the harness was removed,
replaced, and readjusted. Table 4 shows the data from the second test. In
this series, about 4.8 percent of the respired volume was sampled.
The difference in the fraction sampled in the two tests was 10.8 percent.
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TABLE 3
Respiration Correlation
TEST NO. 1
Sampled
Volume (1)
1.590
1.388
1.316
1.601
1.412
Spirometer
Volume (1)
38.3
30.3
30.1
37.0
34.3
Fraction
Sampled
0.0415
0.0458
0.0437
0.0433
0.0412
Mean 0.0431
C.V. 4.3 percent
TABLE 4
Respiration Correlation
TEST NO. 2
Sampled
Volume (1)
1.584
1.479
1.362
1.672
1.391
Spirometer
Volume (1)
31.0
32.1
27.8
33.5
30.7
Mean
C.V.
Fraction
Sampled
0.0511
0.0460
0.0490
0.0499
0.0453
0.0483
5.2 percent
This may be considered to be a tentative estimate of the reproducibility of
the sampling technique on a single wearer. Obviously, considerably more
data is needed on various individuals in a variety of activities before the
limits of the correlation are established.
Patent applications on this device are pending.
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MAILING ADDRESS OF AUTHORS
Donald J. Sibbett, Ph.D., and Rudolph H. Moyer, Ph.D.
Geomet, Inc.
2814-A Metropolitan Place
Pomona, California 91767
Discussion
PETROVICK: Matt Petrovick, EPA. I had a question regarding your com-
ments on the placement of the device over the abdominal wall. I wonder if
you have had a problem in subjects who might be abdominal breathers In one
case, and in the other case, thoracic breathers; and how you covered both
of those kinds of breathers?
SIBBETT: Actually, our anticipation is that the correlation might be
established for each individual. A short calibration with a spirometer or
something of that type would be necessary at the beginning In order to have
the dosage correlation at the end. In short, I don't know how good a gen-
eralized statement is on that point.
STETTER: Joe Stetter, Energetics Sciences. In terms of the way your
pump operates, does it pump when the subject is inhaling or exhaling, or at
the same time? And if so, would you give us an idea of what the flow rate
through the sampling tube would look like as a function over time?
SIBBETT: In general, each stroke is worth about 30 milliliters in each
direction if it is a full stroke. In normal respiration—meaning with the
subject at rest—about 40 percent of the time is actually involved in move-
ment of the pump.
Roughly 60 percent of the time the pump is inoperative.
BEADLES: Bob Beadles, Research Triangle Institute. You have an inter-
esting portable, self-powered device. Do you have any idea of what the elec-
trical equivalent power might be with it? You can use it in a variety of ways.
But in a very simplistic way you can drive a super miniature electrical
generator with it. What is the equivalent power?
SIBBETT: I don't know. We have used these accumulator modules with the
9-volt batteries since last September. The 9-volt charge does quite well for
the data storage.
MAGE: Dave Mage. Bob, you were asking if there were an electrical
conductor moving in a magnetic field could you power your microprocessors?
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BEADLES: Absolutely. That Is the question.
SIBBETT: Almost anything Is possible with microelectronics.
WOEBKENBERG: Mary Lynn Woebkenberg, NIOSH. I was wondering if you had
tried the pump with the commercially available sorbent tubes and charcoal
tubes?
SIBBETT: If you are talking about the kinds of things that adsorb
gases, I did try them. The pressure drop is too great.
WOEBKENBERG: What about the smaller charcoal tubes, where the drop
isn* t quite as large?
SIBBETT: Actually, in principle, of course, here you would like to
limit the pressure drop as much as possible through the adsorbent. We have
done a fair amount of work for NASA on dosage measurements in the field.
We find that—in regard to dosage measures on chemically coated tubes—that
a simple coating, say 5 percent sodium carbonate in the case of an acidic
component, lasts almost indefinitely. We have never really faced a case of
the concentrations to be collected being high enough to exceed the capacity
of the tube.
DOCKERY: Doug Dockery, Harvard. Did you say who is supporting this
research and what the purpose of it is?
SIBBETT: Up to this point, nobody has really supported It. The purpose
of it is quite clear: to develop a unique individual monitoring or sampling
procedure which may be of use in pollution studies of the type that we have
talked about earlier today.
The company I work for is involved in a fair amount of computer modeling
studies of exposures. This is just sort of a natural attachment to some of
the other things that they do.
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Personal Monitor Cosmetology:
An Aesthetic Approach
George S. Malindzak, Jr., Ph.D.
Northeastern Ohio Universities College of Medicine
Rootstown, Ohio
and
Mary Ann Scherr
Kent State University, Kent Ohio; and
Parsons School of Design, New York, New York
Currently, environmental and human health effects data are collected and
evaluated by techniques involving fixed-monitoring stations. The advantages
of and requirements for personal monitoring devices are being considered to
enhance the current devices to perform the environmental and health effects
surveillance function of air quality evaluation programs. An ideal personal
monitor system should: 1) record both physiologic and environmental para-
meters simultaneously; 2) be reasonably priced, personalized, lightweight,
portable, and suitable for use by human subjects; and 3) contain a solid state
memory with short-term data storage and data transfer capability. Few such
functional personal monitors exist in the desired configuration, although the
technology for development and fabrication is well known. The role of per-
sonal monitors in environmental and health effects research has been reported
earlier (1). The purpose of this paper is to 1) place in perspective the
physiologic and health consequences of environmental pollution in terms of
the pollutant sources, 2) develop guidelines as to how the physiologic moni-
toring process might take place; and 3) present and display prototypes of
"personalized" personal monitors, particularly for the female segment of the
population to be studied.
POLLUTANT SOURCES
There are several types of pollutants which have been shown to affect
the environment as well as the health of animals and humans. These include
atmospheric gases, aerosols, participate matter, pesticides, toxic substances,
3'09
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odors, noise, and radiation. Gaseous pollutants such as carbon monoxide (CO),
sulfur dioxide (S02), nitrogen dioxide (N02), nitric oxide (NO), peroxyacetyl
nitrate (PAN), and hydrocarbons (HC) are products of automobile exhausts,
power plants, and industrial exhaust gases due to the combustion of fossil
fuels such as coal and oil. The pollutant gases are generated as the by-
products of combustion and incomplete combustion, such as the generation of
S0_ from oxidation reaction of sulfur in fossil fuels. Complete combustion
of the fuels would produce carbon dioxide and water, which are not considered
to be pollutants. Carbon monoxide and hydrocarbons are products of incomplete
combustion. Nitric oxide is produced when the nitrogen is oxidized by the
high temperatures of combustion. The internal combustion engine of the auto-
mobile is the principal source of atmospheric NO and N0« pollution.
The ultraviolet energy of sunlight induces the oxidation processes to
form the photochemical oxidants. The photo-oxidation converts NO into N0_, 0-
into 0-, sulfur dioxide (SO^) into sulfur trioxide (SO*), and generates the
unstable PAN compounds due to the irradiation of nitrites in air or oxygen (2),
The formation of pollutants within the environment is the product of a
complex atmospheric chemical process. The atmospheric level of each pollu-
tant is dependent on atmospheric conditions, number and quality of combustion
sources, and the surrounding topography. The conversion of photochemical
oxidants is directly related to the amount of available sunlight and tempera-
ture of the polluted air mass. The available light is not only dependent on
cloud cover, but the amount of photochemical aerosols in a given polluted air
mass, which are themselves by-products of the interactions of the photochemi-
cal oxidants. The dilution of air pollutants is affected by winds, tempera-
ture inversions (which prevent pollutant dissipation into the atmosphere), and
elevation or air density. Other types of airborne pollutants include aerosol
sprays (hair, paint, and agricultural pesticides), industrial solvents, and
fine particulate matter (coal dust).
Noise sources have been shown to be harmful above 80 decibels A-weighted
sound level (dBA), and those annoying to the major segment of the population
are considered by the Environmental Protection Agency as pollution (3). En-
vironmental noises are produced by a wide variety of sources; for example,
automobiles, construction equipment, transport trucks, commercial aircraft,
and steel mills. Noise sources may be fixed, moving, transient, or temporary,
and may range in sound level from an average of below 35 dBA found in the
suburban home, to over 110 dBA measured in and around mineral mine operations.
Two hundred feet from a jet at takeoff, the sound level is 120 dBA (4,5,6).
Many industrial and transportation noises are above the 90 dBA maximum 8-hour
310
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Occupation, Safety, and Health Act (OSHA) exposure level. The reduction of
excessive noise levels at the source, and providing adequate hearing protection
to the exposed population, is clearly of interest to the health sciences as
well as to the regulatory agencies.
Human exposure to electromagnetic radiation is extensive when the expo-
sure from industrial, medical, and scientific devices is combined with the
exposure to home equipment, radio, FM, TV stations, military and civilian
communications equipment, navigational aids, and radar. The sources that
produce ionizing radiation are X-ray and radioisotope equipment, nuclear
power plants, atomic blasts and weapons testing, and solar radiation. Although
the physical characteristics of electromagnetic and ionizing radiation are well
understood, their Impact as environmental pollutants is less clear.
HUMAN HEALTH EFFECTS OF ENVIRONMENTAL POLLUTANTS
Environmental pollutants can affect the health of individuals in a
variety of ways, ranging in severity from physiologic changes of uncertain
consequence to pathologic changes leading to disability and, sometimes,
death. The more severe effects, such as chronic long-term illness and
death, are manifest in a relatively small portion of the population over a
long period of time, and they are difficult to quantify because other
complex factors difficult to quantitate are usually associated with death.
At the other end of the spectrum, slight physiologic and pathologic changes
may not be detectable with the degree of certainty desired because of the
unique ability of the human body to respond to and recover from most types of
environmental insults. Adverse health effects may result from short-term or
long-term pollutant exposure. Many factors contribute to differences in the
distribution of diseases associated with air pollution exposure, such as
age, sex, race, occupation, cigarette smoking habits, geographical location,
etc. The health effects discussion that follows is based on appropriate
statistical adjustments for these factors in assessing their environmental
health effect impact.
The vast majority of environmental pollutants are airborne and gain ac-
cess to the body via the respiratory tract (i.e., the lungs). Depending on
the particle size of the pollutant, its chemical composition and activity,
the effect of the pollutant may be restricted to the respiratory tract, or
it may be absorbed via the blood stream and exert its effect indirectly on
another target organ. A few pollutants have a direct effect on body tissue
and organs, such as, for example, radiation and environmental contaminants
311
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that irritate the external layers of the eyes. Other pollutants appear to
affect the brain and central nervous system and to indirectly produce changes
in behavior, control, and coordination of human activity. There are a wide
variety of human health effect responses that are yet to be identified, be-
cause they have not been examined thoroughly and systematically.
Basically, when foreign matter is introduced into the human airways, the
natural respiratory response is to expel it through the action of hairlike
cells sweeping the material out, washing the surfaces with mucus which is
constantly being secreted, or by coughing the material into the mouth for ex-
pulsion or elimination. Environmental pollutants act to increase the secretory
activity of the mucous cells (or inflame them), and inhibit the action of the
special hairlike "scrubbing" cells, thus producing an increase in frequency,
duration, and intensity of the compensatory cough mechanism. Irritation of
the mucous cells causes them to swell and partially occlude the airway, making
breathing more difficult (i.e., Increasing airway resistance). Decreasing the
activity of the "scrubber" cells produces a stasis of mucus material which
constitutes an excellent culture medium for the growth of bacteria and infec-
tious agents within the lungs and airways.
The site of irritation may be in the upper airways, small (lower) airways,
or within the lung tissue itself. If the inflammation reaches the gas ex-
change tissue (alveoli), normal exchange of needed 0. and unloading of C0« is
impaired. The greater the area of inflammation, the greater will be the re-
sulting decrease in lung function, or impairment of gas exchange. Chronic
inflammation increases tissue susceptibility to infection with pathogens.
N0_, for example, has been shown to be related to an increase in incidence of
respiratory infection in humans (6).
Basically, any irritation which produces an enlargement and inflammation
of mucous cells within the airways and increases secretions will decrease the
potential air volume which can be taken in and expelled and will affect normal
respiratory function. Focal irritation of large airway channels may produce
a substantial reduction in the lumen at that point. Air moving through this
constricted area can produce turbulence which in turn can be heard through the
chest wall as "wheezes" and "rhonchi." The greater the luminal constriction,
the more intense the turbulence and subsequent sound produced for a given
respiratory effort.
Environmental pollutants like N02, 0-, and SO,, produce changes in respi-
ratory airway membranes which in turn alter pulmonary function (6,7). S02,
for example, is highly soluble in water (forming ^2S03 mlst^ and is usually
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absorbed quickly in the proximal parts of the respiratory systems; hence,
principal effects are seen in the upper respiratory tract. NCL and 03, on
the other hand, are not as soluble in water and in the upper respiratory tract.
Their effect is seen in the smaller airways and in the lung tissue itself.
Epidetniologic studies have shown a greater incidence of respiratory infections
and a decrease in pulmonary function in people living in an environment high
in N02, 0^, and S02, compared with those living in a relatively pollutant-free
environment (6). 0« is also a powerful chemical oxidant and recently has been
shown to produce a radiomimetic (radiation-like) effect on peripheral blood
cells. Ozone has been shown to produce an increase in chromosomal breakage of
peripheral leucocytes—about 10 times that of nonexposed subjects.
Carbon monoxide traverses the alveolar membrane and combines with the
hemoglobin in the blood to form carboxyhemoglobin. As a consequence, hemoglo-
bin—the iron component of blood, normally used to carry oxygen to the tissues—
is rendered less effective. The net result is that the end organ or tissue,
dependent on the oxygen carried by the hemoglobin, is less efficient at perform-
ing its principal function. Recent studies have shown that the heart must work
harder in order to do the same amount of work following exposure to carbon
monoxide than before carbon monoxide exposure. In healthy young people, these
changes go almost undetected, due to the intrinsic ability of the heart to
compensate for the slight compromise in oxygen-carrying capacity. In subjects
with pre-existing coronary vascular disease, the changes produced in cardiac
function are more obvious and detrimental to the individual's health (8,9).
Radiation has been shown to produce a direct effect on cellular function
because of its ability to penetrate surface and deep structures. Excessive
ambient noise levels have been shown to produce an effect on human performance,
presumably due to interference in the reception sensory nervous signals by the
brain from multiple pathways (i.e., auditory, optic, tactile, etc.) during the
performance period.
The major adverse health effects observed thus far have been associated
with the respiratory system, mainly because of the respirable nature of air-
borne environmental contaminants and, to a limited extent, because of the
cardiovascular system and central nervous system. It is unclear (and indeed
unknown) to what extent and in what manner environmental contaminants affect
other organ systems, such as the kidney, the reproductive system, and skeletal
muscles. Eventually, each possible health effect should be explored in a
short-term and long-term exposure schedule in order to obtain the most complete
information regarding the relationship between environmental pollutants and
adverse human health effects.
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PERSONAL MONITORS
Currently, environmental and health effects data are collected and evalu-
ated through a combination of techniques, including data from fixed environ-
mental monitoring stations. Increasing public concern and national priorities
have dictated the need to expand the current data collection base to include
more detailed surveillance of a wider range of pollutants and a more comprehen-
sive evaluation of individualized health effects. In this context, the develop-
ment of personal monitors which measure physiologic and pollutant events
simultaneously are being proposed. Comprehensive personal monitor capability
will permit accurate monitoring of pollutant data and the concomitant physio-
logical response within the immediate vicinity and physical location of the
subject at all times.
Personal monitors are envisioned to serve as a means of providing a
more meaningful scientific relationship between the physiologic and environ-
mental pollutant exposure in human subjects. More specifically, a need appears
to exist for an individualized "early warning health effects surveillance
system" designed to sense and process physiologic responses and environmental
pollutant data simultaneously. Ideally, a complete physiologic monitor system
would include invasive and noninvasive clinical evaluation techniques. Prac-
tically, however, only noninvasive techniques are being considered.
An ideal personal monitor should be able to process and correlate simul-
taneous physiologic and environmental pollutant measurements at a scientific
laboratory level of accuracy coupled with short voice comments from the sub-
ject. It is imperative that multilevel feedback capability be available to
document the subject's assessment of discomfort relative to environmental
conditions, such as symptom reports, location, and general environmental con-
ditions. Such feedback capability has been shown to be invaluable in the
assessment of data collection and analysis programs in the past.
Physiologic Monitoring
With the many physiologic variables to monitor, it is unreasonable to
consider burdening the subject with an excessive number of transducers and
associated equipment which may be cumbersome and physically unattractive.
The transducer-to-anatomy interface and the transducer-to-pollutant interface
must be considered in any final personal monitor design. Ideally, transducers
could be optimally placed on male and female subjects to provide for the
measurement of multiple physiologic parameters. For instance, a piezoelectric
transducer designed to respond to acoustical energy might also measure
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simultaneously pressure transients, voice, ambient noise, heart sounds, heart
rate, and cough. The Incorporation of appropriate electrodes within the
piezoelectric transducer housing can provide the measurement of the electro-
physiologic activity of the heart (electrocardiogram). From specific signal
conditioning and filtering techniques of the complex acoustic (pressure) and
electrophysiologlc signals, a variety of additional relationships may be derived
which are not otherwise available from a single transducer. This design pro-
vides the basis of an "integrated transducer" which would have the capa-
bility of recording more than one phenomenon from a single transducer at a
single anatomic site.
1) Respiration-Pulmonary. Pollutants may cause irritation of the mucous
cells which line the respiratory tract, resulting in the reflex production of
a cough. Increased mucosal irritation, in turn, may cause narrowing of airways,
resulting in respiratory wheezing produced from airway turbulence. Cough events
may be detected and quantltated from the placement of a piezoelectric trans-
ducer over the lower abdominal wall to register cough diaphragmatic pressure.
Additional respiratory parameters, such as the ventilation rate (breaths per
minute) and indirect respiratory volume, may be detected by changes in thorac-
ic geometry by electrical Impedance or pneumographlc techniques.
Transducer-to-anatomy interface differences that exist in males and
females may be circumvented by installing the appropriate transducer within
the structure of conventional garment wear. For example, in female subjects,
the transducer for heart sounds may be placed in the base elastic strap of the
bra over the anatomic apex of the heart; for wheeze registration, the trans-
ducer may be placed within the rear bra strap area of the shoulder blades;
coughs may be recorded from a transducer placed within the abdominal wall
panel of panty hose.
It is well known that some people are "chest breathers," while others
are "abdominal breathers." In either case, the respiration rate transducer
might be a small pneumatic tube connected to a semiconductor transducer. For
"chest breathers," the transducer might be Incorporated in the base elastic
strap of the bra (for female subjects); for "abdominal breathers," the trans-
ducer might be incorporated in the abdominal panel of panty hose.
2) Cardiovascular-Heart. The personal monitor system should provide
the capability for sensing and characterizing the electrophysiologic and
hemodynamic events of the vascular system and heart. Typically, electro-
physiologic information is obtained through the electrocardiogram (EGG), and
hemodynamic information is usually obtained from the arterial blood pressure
(BP).
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The ECG measurements may be made with as few as a single pair of bipolar
surface electrodes, or with as many as 12 electrode combinations, depending on
the thoroughness of the electrocardiographic examination. The ECG waveform is
characterized by the P-QRS and T features which correspond to specific electro-
physiological events throughout the cardiac cycle. From this electrical infor-
mation, basic heart rhythm (heart rate), and the position of the S-T segment of
the waveform with respect to the isoelectric baseline, are important determi-
nants. Often, abnormal rhythms (arrhythmias) and shifts in the S-T segment of
the waveform occur under a variety of conditions, particularly when oxygen
(carried by the blood) is unavailable to the contracting heart. Recent studies
(8,9) have shown that exposure of subjects to 100 ppm (parts-per-million)
carbon monoxide (which decreases effective oxygen delivery to heart tissue)
produces a detectable shift in the S-T segment of the ECG during exercise in
normal healthy subjects.
Quantitation of the cardiac rhythm and the degree of S-T segment devia-
tion from the baseline may be accomplished with a special-purpose S-T segment
microprocessor integrated within the personal monitor system. Specific features
such as S-T segment duration, S-T segment amplitude (positive and negative),
and rate of change (first derivative) of the S-T segment are most important
and significant in assessing specific adverse cardiac health effects in response
to pollutant exposure*
The measurement of blood pressure may be accomplished by affixing a
piezoelectric transducer to the radial artery of the arm in such a way as to
detect maximum (systolic)/mlnimum (diastolic) arterial pressures, pulse
pressure (systolic minus diastolic), and heart rate.
Valuable cardiac performance information may be derived from the directly
measured cardiovascular parameters. For example, heart rate from the ECG
through a conventional cardiotachometer, and systolic time intervals (ST1)
from the combination of the phonocardiogram, the electrocardiogram, and blood
pressure. STI's provide information relative to the rate and duration at
which the heart is contracting and relaxing. The triple product combination
(heart rate, mean blood pressure, and ejection time of the heart) serves as an
index of the amount of oxygen the heart is consuming during the process of
contraction.
3) Central Nervous System. The central nervous system activity (electro-
encephalogram, EEC) is one of the most difficult signals to interpret in that
responses are often subtle and difficult to quantitate. Detection of behavioral
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patterns associated with changes in the EEC or the electro-oculographic poten-
tials (EOG) may be accomplished, but not without carefully planned and executed
experimental programs.
Central auditory responses are related to the temporal lobe of the brain;
recording of the EEC over the temporal area of the skull may provide an index
of auditory time discrimination judgments by a given subject. Recent studies
suggest that auditory time discrimination shows a decrement after exposure to
100 ppm of carbon monoxide for 4 hours.
The human eye is (as is the lung) directly exposed to environmental con-
taminants. Eye irritation can produce increased frequency of eye blinking,
fatigue of ocular musculature, and pain sensation. Eye blinking activity
may be monitored with silver chloride electrodes placed laterally and slightly
posteriorly to the eyes. Appropriate signal conditioning of the EOG signal
could provide a reliable electrical representation of an eye blink, blink
rate, and duration. Additional conditioning of this electric signal (such as
the first derivative) may provide information of ocular fatigue relative
to normal and abnormal environmental pollutant exposures.
4) Other. Tracking the location of the subject with a personal monitor
within a given geographic area will provide an additional means of referencing
and characterizing pollutants in a given area at any time of day, in contrast
to a fixed-station operation. Tracking may be accomplished as a function of
verbal or coded location reports into the system memory from the subject. The
monitoring of radiation, for example, might be coupled with location and
radiation film badge exposure levels through a similar process.
Data Acquisition System
The data acquisition system (DAS) design for personal monitors may be
implemented in a variety of ways, any one of which appears to require state-
of-the-art techniques. Physiologic transducers and air pollutant transducer
signals are different in nature; hence, a properly designed DAS must take these
differences into consideration. Most physiologic responses are dynamic,
rapidly changing, and almost periodic functions of time. Air pollutant levels
are usually static or change slowly In time. Therefore, the dynamic frequency
response of each transducer is an important consideration.
All transducers are subject to various forms of artifact (physiologic,
60 Hertz, movement artifacts, pollutants, interference from other contaminants,
etc.). The judicious rejection of these artifacts is an important factor for
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reliable DAS design. To ensure maximum DAS stability and reliability, it is
important to select a physiologic event as a time reference with which to
sense and reject any artifact from the system signals. For example, in
detecting a cough, a microphone or another appropriate acoustic transducer
may be employed. Coughing is an acoustical signal produced during the expira-
tory phase of the respiratory cycle. Any acoustical signal sensed by the cough
transducer during inspiration (such as talking, ambient noise, etc.) must be
rejected. However, during expiration, the expiratory gate would open for any
possible cough data that might occur.
All data collected on board the personal monitor might be stored in
digital form in solid state memories for subsequent playback, processing, and
display. The system should have the capability of recording data for 24-hour
periods, after which the data could be read out into a long-term storage device
for inspection and analysis. The solid state memory readout could be accom-
plished by a variety of ways; i.e., dataphone interface to local or regional
fixed stations.
A complete system design must consider playback, display, and processing
functions, which in turn are determined by the nature in which the data are
recorded. The system design should consider options to perform a wide variety
of information processing procedures, such as signal averaging, digital filter-
ing, tread analysis, and interactive graphics. Ideally, provisions to process
the personal monitor information should include on-line and off-line capabili-
ties. This capability is currently available with low-cost, high-efficiency
microprocessors.
PERSONALIZED PERSONAL MONITORS
Personal monitors are envisioned to provide more reliable physiologic
and environmental information on human pollutant exposures beyond the range
and capability of community health surveillance stations. Specifically, a
need appears to exist for individualized surveillance systems to sense and
process physiologic and environmental pollutant data simultaneously. Devices
have been developed to satisfactorily detect environmental contaminants and
their physiologic consequences. Fabricating these detection devices to
ensure user cooperation has not been a simple task. Compliance and user
resistance problems are particularly sensitive when dealing with the female
segment of the population to be studied.
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An attempt was made approximately 9 years ago to incorporate the (then)
state-of-the-art technology related to turning simple physiological and en-
vironmental monitors into devices that were portable, lightweight, and
reasonably priced. Pilot feasibility studies were conducted to evaluate the
effectiveness and practicality of personalized personal monitors, particularly
those which female subjects would be required to carry or wear. The remainder
of this presentation will deal with the results of the feasibility studies, in
which specific pollutant and physiologic monitoring devices were incorporated
with specific pieces of jewelry which are not only scientifically functional,
but also attractive.
1) Oxygen Pendant (Figures 1 and 2). A photo cell mounted in the pend-
ant senses the continuous samples of ambient air. When the level of environ-
mental contamination exceeds a preset threshold, an audio device is triggered
electronically which alerts the subject to the presence of pollution. The
pendant also contains a mask and a 10-minute supply of oxygen. This device
may be especially useful to subjects with a pre-existing respiratory disability
such as asthma. In these cases, the oxygen canister might also contain a
bronchodilator to relieve the distress and discomfort associated with an
asthma attack.
2) Heart/Pulse Sensor Bracelet (Figures 3 and 4). A piezoelectric
transducer relays the peripheral arterial (radial) pulse to circuitry which
activates a light emitting diode display device. Heart rates above the preset
threshold for an individual enables an oscillator to emit an audible frequency,
the output of which is connected to an earphone speaker to produce a warning
sound which alerts the subject to check his/her activity level, take appro-
priate medication, or seek professional assistance.
3) Body/Air Sensor Belt (Figures 5 and 6). This belt is made of stain-
less steel and liquid crystals designed to monitor toxic gases, ultraviolet
radiation, and air and body temperature. Increasing doses of X-ray radiation
progressively lower the color play range of cholesteric-phase liquid crystal
materials. The effect is enhanced when an effective amount of an iodine-
containing compound is used in the liquid crystal material. Novel iodine-
containing compounds in the appropriate proportions give direct indications
of the dose of X-ray radiation that has been received.
A layer of water-soluble plastic material is first deposited on a limb
or torso to serve as a barrier layer. A cholesteric layer is placed over the
barrier layer. A chromatic display of temperature of the limb or torso will
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FIGURE 1. Oxygen pendant (normal
closed position).
FIGURE 2. Oxygen pendant (open
position with mask and canister
exposed.
FIGURE 3. Heart/pulse bracelet in
place on hand.
320
FIGURE 4. Heart/pulse bracelet
with electronics and compartments
exposed.
-------
ro
FIGURE 5. Body/air sensor belt.
FIGURE
6. Body/air sensor belt and arm bracelet.
-------
be visible to the naked eye, including minute variations. Vasoconstriction
in the extremities in response to smoking and the vasospastic effects of
peripheral vascular disease may be clearly observed.
4) Liquid Crystal Heart Beat Display (EGG) (Figures 7, 8. and 9).
A monitoring electrode is attached to the body to transmit the EGG through
electronic circuitry to activate a liquid crystal display of the subject's
electrophysiologic heart pattern. Abnormalities in either the rhythm (or
rate) or the waveform will be manifest in an aberrant chromatic pattern.
5) Tracheotomy Necklace (Figure 10). An adorned standard medical device
fits into an opening, which is surgically performed on the trachea, to permit
ventilation. The tracheotomy device is available in sterling silver and
silicone plastic through conventional medical supply sources. The tracheotomy
necklace is constructed of gold, silver, gemstones, chain, and other materials
which may change the clinical appearance of the equipment, permitting it to
be viewed as a necklace rather than as a prosthetic device.
Each of these devices was designed utilizing the technology of approximately
5 years ago. Each device is large and obvious to attract attention. Each
device was (and can be) designed to suit the individual's taste and physiog-
nomy. Since the time of the original design and feasibility studies, further
developments in this area have nearly ceased due to the lack of appropriate
interest and support. However, the needed facilities and interest to continue
with these developments still exist. Current technology and fabrication tech-
niques could substantially reduce the size as well as the weight and cost of
each of these devices.
The Northeastern Ohio Universities College of Medicine is part of a
consortium of three universities—Kent State University, the University of
Akron, and Youngstown State University. The College of Medicine serves as the
base from which the basic medical science studies are conducted. Kent State
University has a Liquid Crystal Institute at which further and continued
studies with the liquid crystals may continue. The University of Akron has
an excellent School of Engineering, within which exists a competent Electrical
Engineering Department capable of developing and implementing any micro-
circuitry and microprocessor-based system required for further development in
this area.
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FIGURE 7. Liquid crystal heart beat
display necklace.
FIGURE 8. Liquid crystal heart beat
display necklace (electronics open
and exposed).
FIGURE 9. Liquid crystal heart beat
display necklace (electrode placement
and electronics exposed).
FIGURE 10. Tracheotomy necklace.
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ACKNOWLEDGEMENTS
This work was supported in part by the Northeastern Ohio Universities
College of Medicine Intramural and Biomedical Research Development Funds and
by the American Heart Association. Body monitor and jewelry prototypes and
research efforts have been predominantly funded by the personal resources of
Mary Ann Scherr, who is also a consultant designer for jewelry and a metal-
smith in New York City.
REFERENCES
1. Petrovick, M.L., Malindzak, G.S., Jr., Strong, A.A., Burton, R.M. The
Role of Personal Monitors in Environmental and Health Effects. Proceed-
ings, National Aerospace Electronics Conference (NAECON), pp. 152-159,
May 1974.
2. U.S. Department of Health, Education, and Welfare. Air Quality Criteria
for Photochemical Oxidants. National Air Pollution Control Administration
Publication No. AP-63. Washington, D.C., U.S. Government Printing Office.
March 1970.
3. United States Clean Air Act (42 U.S.C. 1857 et seg.) includes the Clean
Air Act of 1963 (PL 88-206) and Amendments made by the Motor Vehicle
Air Pollution Control Act - PL 89-272, October 20, 1965, the Clean Air
Act Amendments of 1966 - PL 89-675 (October 15, 1966), the Air Quality
Act of 1967 - PL 90-148 (November 21, 1967), and the Clean Air Amendments
of 1970 - PL 91-604 (December 31, 1970).
4. Botsford, J.H., Cudworth, A.L. Fifth Institute on Noise Control Engineer-
ing. Institute on Noise Control Engineering, Bethlehem, Pa., August 1972.
5. Peterson, A.P.G., Gross, E.E. Handbook of Noise Measurements, Sixth
Edition. West Concord, Mass., General Radio Company, 1967.
6. Shy, C.M., Finklea, J.F. Air Pollution Affects Community Health.
Environ Sci Technol 7(3):204-208, 1973.
7. Cohen, C.A., Hudson, A.R., Clausen, J.L., Knelson, J.H. Respiratory
Symptoms, Spirometry and Oxidant Air Pollution in Nonsmoking Adults.
American Review of Respiratory Disease 105(2), 1972.
8. Anderson, E.W., Andelman, R.V., Strauch, J.M., Fortuin, N.J., Knelson,
J.H. Effects of Low-Level Carbon Monoxide Exposure Onset and Duration
of Angina Pectoris. Annals of Internal Medicine 79:46-50, 1973.
9. Haak, E.D., Jr. CO and Cardiac Performance. In: Clinical Implications
of Air Pollution Research (Finkel, A.J., Duel, W.C., eds.). Publishing
Science Group, Inc., 1976, pp. 113-117.
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MAILING ADDRESSES OF AUTHORS
George S. Mallndzak, Jr., Ph.D.
Department of Physiology
Northeastern Ohio Universities
College of Medicine
Rootstown, Ohio 44272
Mary Ann Scherr
School of Art
Kent State University
Kent, Ohio 44240
Discussion
PETROVICK: Matt Petrovick, EPA. Dr. Malindzak and Ms. Scherr, I would
really like to commend you for a very unusual and very well designed approach
to looking at physiologic measurements in the female. The female happens
to be one of the most Ignored subjects in terms of science and in terms of
data acquisition.
I believe your design approach is going to have a significant impact
in placing our health effects data base into balance, which presently I don't
think it is.
WALLACE: Who supported this development?
SCHERR: This work? I do.
MALINDZAK: Totally and completely.
SCHERR: I am an Associate Professor of Art at Kent State University.
My interest in this subject started with seeing a woman who was very disturbed-
cosmetically disturbed—with the hole in her throat, and who wore many scarves
to mask herself. And I managed to see in my mind in one brief moment this
piece of equipment, and I asked her if she would like me to design something
that would be a little bit more interesting. And I did. And that set the
stage for another whole wave of research.
I think that maybe I am more or less a scientist, although I could never
compete in this area. I am a reactor. And in reacting to this lady, along
with the television programs of space technology and watching the space pro-
gram, I decided at this time to get involved in programs where maybe we
could monitor ourselves. And that was my own reaction to it.
I started then in all of these areas, trying to find devices that would
monitor anything. So, this is why is all started.
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"Shirtsleeve Workshop"
An informal session designed to arrive at a consensus on present abilities of
commercially available instrumentation and promising avenues for future research
DR. DAVID MAGE: This evening we would like to discuss informally some
of the aspects of personal monitoring that we have gone over more formally
during the meeting.
We have heard several papers about personal monitors for exposure
and for physiological variables. Some of us have been trying to act as a
kind of marriage broker to see if we could merge the two to fit into the same
package—we really see that as a necessity. We would like to have some dis-
cussion as to the needs that the different Government agencies have in this
area. We will have people from NIOSH, EPA, and other agencies speak on what
they perceive as being the needs for their agencies.
We would like to make it apparent to the people in industry as to where
their markets might be, and we want to stimulate competition to produce the
devices that we need to do our job.
The bottom line, I guess, is that, as Congressman George Brown said
in his keynote address, we have to show that our approaches to air quality
standards are reasonable, let alone correct. In order to do that, we have
to be able to demonstrate that people are being exposed and people are having
health effects from that exposure. It is one thing to put someone in an
environmental chamber and give him 0.4 ppm ozone while walking on a treadmill
and then document that he has had some kind of physiological response. But
then somebody can ask us, "Well, how many people on treadmills in Los Angeles
are breathing 0.4 ppm ozone," and, you know, we can't say 1, 10, 100, or 1,000,
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It becomes very difficult to quantify. As soon as it becomes difficult to
quantify, then it can also become very difficult to establish that we are
being reasonable. Can we state beyond the shadow of a doubt that there are
100, or 1,000, or 10,000 people who are having health effects?
If industries talk about their cost of pollution control, they talk in
units of billions of dollars. Can we justify this cost on the grounds that
there is a benefit to the public in terms of billions of dollars?
What I would like to do now is turn this portion of the meeting over to
Dr. Lance Wallace for some informal remarks. Some of the things we would like
to do is discuss with you some of the needs that we perceive for developments
of personal monitors. We would like people to let us know some of the prob-
lems that they perceive; for example, that perhaps we haven1t been funding
you when you have been submitting proposals to develop those monitors that
we would like to have.
I would like to get the discussion out informally so that we can have
some good interchanges among us.
DR. LANCE WALLACE: I feel that my horizons have been opened up quite
a bit by this meeting. I came here thinking of personal monitors basically
as being chemical and physical sensors, and by the end of 2 days, I have
realized that there are physiological measurements that can be made. There
are the cosmetological aspects. There are the microcomputer aspects. It
appears that we are on the verge of something considerably larger than I had
envisioned.
So, with that as a bit of an apologia, I will mention that what I have
done for the past 2 weeks before coming here was to ask the different offices
within EPA what chemical and physical measurement devices they felt were nec-
essary and what pollutants they felt were Important to develop personal
air quality monitors for. As I mentioned in my talk, the Office of Research
and Development acts as a service organization to some of the other program
offices within EPA. They express their needs for research, and we try to
accommodate them.
I spoke to several of the offices that are the most involved with this
topic, including the Office of Air, Noise, and Radiation, which includes
the Office of Air Quality Planning and Standards and the Office of Mobile
Sources. These offices have somewhat different areas of responsibility, and
different needs for personal monitors. I have obtained from the people in
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those offices lists of the pollutants for which they see a high priority
for developing personal monitors*
I have also spoken to the Office of Toxic Substances and received the
same sort of list from them, and to the other offices within the Office of
Research and Development and have received their nominations for high priority
pollutants.
But as a sort of straw man, it might be desirable for us to look at the
lists that we have come up with and using those lists to investigate the
possibilities for using monitors that are already available, that are al-
ready out there and can do ambient level measurements, to determine areas in
which further research is needed.
I would like to pass out these lists, and I will read them over with you.
Within the Air Office, the Office of Air Quality Planning and Standards'
staff members were mostly concerned with the criteria pollutants. The pol-
lutants that they found to be most important were carbon monoxide and nitrogen
dioxide. They desired that field studies be done as soon as possible for
these two pollutants if there were any personal monitors available that were
capable of making ambient level measurements.
From what I have heard in the past 2 days, it seems very possible that
we do have personal monitors that are capable of being used in field studies—
the ESI monitor and the GE monitor, both for CO. Dr. Palmes' NO, device also
seems possible.
Perhaps before 1 go any further, I could ask if there are comments about
just these two pollutants as to other devices that appear as possibilities
for immediate use in field studies? Are there any comments on the Energetics
Science's Ecolyzer 9000 series and the GE device that we have?
DR. MANNY SHAW: I am Manny Shaw of InterScan. We aren' t ready right
now to give you a dosimeter. We are tooling up on a different type of dosimeter
that will be of interest. And when I say different "type," I don't mean
necessarily a ppm-hour dosimeter. I mean a dosimeter which will alarm at the
TLV. 1 would say that within 6 months to a year we will be able to field
test the InterScan TLV alarm dosimeter.
DR. DONALD SIBBETT: Donald Sibbett, Geomet. I feel that with a short
validation program, our personal monitor could be used with NO,,. It is
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a resplrable pump driven by the abdomen. It can be used, I think, rather
readily with N02«
DR. JOHN BACHMAN: One thing that would be of use as far as we are con-
cerned is if some studies could be done on these two pollutants—CO and N0_—
at the same time. We want these data for two reasons: one is to help us set
better air quality standards for these pollutants, and the second is to do
a better job of assessing total exposure.
One of the reasons those two pollutants had high priority among the
people in our office was that the concentrations of these pollutants tend
to vary greatly over an urban area relative to certain other pollutants
because of the nature of the emissions and the formation.
NO- happens to be a secondary pollutant, as everyone knows. CO is a
primary pollutant. But they vary with the automobile. It would be of inter-
est to us to do both of these studies at the same time.
DR. FRANCIS BERLANDI: Francis Berlandi from ESA. Looking at the phi-
losophy of the development of the pollutants of interest, I notice that all
the pollutants are associated with air quality standards. And noticeably,
there is one pollutant here for which there is an air quality standard, and
yet there is no interest in seeing that a personnel monitor is available for
it.
In particular, I mean lead. In the future we are talking about arsenic
and cadmium. I was curious as to whether people didn't feel that there was
a monitor capable of making these measurements and that is why it is omitted,
or if nobody is really interested in the variety of sources that are available
to the person in his or her daily environment where he can actually uptake
lead?
BACHMAN: I think we feel that saying fine particulates is our shorthand
for saying anything you can measure on fine particulate filters. But in the
specific case of lead, right now we feel that the best personal monitor is
blood lead. There are other indicators. Because of the total body burden,
we have to measure the various pathways.
We felt first of all that a system that was capable of measuring for
fine particulates ought to be able to do lead. Second, right now we have some
fair indication of total body burden from the human body.
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Concerning the other pollutants, by the way, as Lance will go on to
talk about, vapor phase organlcs and some of the fine particulates cover a
whole host of things which are not related to air quality standards, but are
related to possible hazardous air pollutant standards.
BERLANDI: The reason I bring up the point about lead is that yes, I
understand that the body burden is a good indicator of lead exposure. But it
hardly provides sufficient data for the state to implement plans to control
the lead. We really don't know where individuals are picking it up in their
daily lives, whether it be in the home, whether the kids are getting it on
the streets or empty lots, or whether they are breathing it in, as opposed
to secondary entrained dust.
There could be some very costly strategies implemented whl«.h could back-
fire in the long run. This is why I mentioned the fact that I think the
technology is available, and maybe that formally it should be put down here.
BACHMAN: Again, from the program office point of view, talking to the
people who set the lead air quality standard, they didn1 t feel it would be
particularly useful in that application at this point.
DR. EUGENE MEIER: Gene Meier, EPA, Las Vegas. Another point is that
when our request went out, we were referring to immediate programs. "If
we had a monitor available, which one would you want to use now?" And some
priority had to come back. These are the first-thought priorities. These
are where we actually have programs now and where we feel we need monitors.
Your point is well taken. If we had the programs going on or the people
available, we would probably be working in those areas. But right now, the
other compounds listed are those which have first priority.
MR. PAUL KIZAKEVICH: Paul Kizakevich from Research Triangle Institute.
Admittedly I don't have much of a background regarding the physical monitoring
parameters and how they are measured. But in the sense of the physiological
measurements that we have talked about, it is expected that the changes we
would like to look at would either be transitory or perhaps accumulated over,
say, an 8-hour period, over a workday.
My question is; Are there any physical parameters that can be projected
to be measured and assessed so they can be compared to such dynamic studies
as a physiological response? The accumulation of 24 hours of the pollutant
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is not going to give very much information in relation to a person's change
in respiration rate or something else during his time at work.
WALLACE: At least for the CO, it did not depend on a 24-hour average—
we had a continuous readout. The N0_ is another matter.
KIZAKEVICH: Is that the only parameter that can currently be measured in
that sense?
WALLACE: In a continuous way?
KIZAKEVICH: In a relatively continuous or dynamic fashion.
11AGE: Well, I think that of all of the criteria pollutants, ozone
needs to be monitored continuously. Our air quality standard may be changed
in the future to another averaging time, but it would still have to be
monitored continuously.
KIZAKEVICH: You are not talking about the same thing, now. If you put
a monitor on an individual over an 8-hour workday and you expect to indicate
a health effect perhaps by the severe pollutants in the working environment,
are there any physical measurements to compare the physiological measurements
with at all, other than to say that the guy went to work for 8 hours, and as
a result during that work of 8 hours he just changes his physiology?
WALLACE: You mean rather than CO?
KIZAKEVICH: Anything. I don't care what it is.
DR. EUGENE SCHEIDE: Gene Scheide, Environmetics. Can you include phys-
iological measurements with pollutant measurements on the same scheme? Or
are you comparing apples and oranges? But is he saying should we also be
monitoring other physiological responses as well as physical parameters—is
that correct?
KIZAKEVICH: Well, gathering pollutants over a 24-hour period is certain-
ly not the same as measuring the distribution across the population, because
it depends on whether the person moves. I am interested in knowing which
parameters can be measured without resorting to gas samples over a 24-hour
period. That would provide no information on health effects whatsoever other
than ambient levels.
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MEIER: It really depends on the objective. In most cases, the objectives
are to profile the pollutant of interest, because we already have established
that there is a health effect. Now we are trying to find out what its con-
centration is in various locations in the environment so that we can determine
whether our standards are proper and our stations are located in the proper
locations*
In addition to that, information provided by personal monitors can give
us a better idea of where to locate a limited number of stations in our sam-
pling network. If management comes in and says, "You want 10 stations.
We are only going to give you 2," where do we best put those 2 monitors
that we have to get the most effective data to rate the health effects?
MR. MATHEW PETROVICK: Matt Petrovick, EPA. That is a rathpr interesting
comment you made. I wonder if you might enlighten me on which specific known
health effects you are alluding to?
MEIER: In terras of what? The standards?
PETROVICK: In terms of the standards and/or any pollutant?
WALLACE: Well, we have six or seven criteria pollutants now. The
criteria documents point out the levels at which health effects have been
noted for those pollutants.
PETROVICK: That is my question. Which health effects and which associ-
ated pollutants?
WALLACE: One for each of these six—the six criteria pollutants. It is
a different health effect in each case.
PETROVICK: Is it a lung function effect, or what?
BACHMAN: It runs from asthmatic attack, bronchitis, general heart and
lung disease, excess mortality, eye irritations. There are all sorts of ef-
fects listed, and each pollutant has its own—CO has its own special effects.
Each one has a number of effects, and these are documented. This is prob-
ably not the proper place to go into documentation of any specific health
effects for each of the pollutants.
But I think that the statement made about our personal monitor needs
was put well, at least for CO and N02. What we were asking was, having estab-
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lished standards already, an initial reason to do this monitoring is to do
a better job of assessing the exposure. And that will affect in turn the
standards that are processed.
Meanwhile, a second reason is to use these things later in health effect
studies. And therefore, you might want to measure the physiological para-
meters. But when we were asked what we wanted right away, we didn't speak
to that issue.
WALLACE: That is not to say that the other effects are known at certain
standards. We have a standard. We have documents that were written back in
1970. With the knowledge that was current then, there was a standard set.
So, for those six, one can do pure exposure studies and determine the
frequency distribution of exposures for a given population and find out what
percent are, say, exposed to levels above what those criteria documents found
to be important. That is one aspect.
The other aspect is for those pollutants for which you do not have stand-
ards. One is obviously not going to be able to stop at pure exposure studies.
And then, your question about the concurrent measurement of physiological
parameters becomes more important.
PETROVICK: One last comment. 1 have a very strong feeling that of the
effects that have been identified with the associated pollutants, most of
those relationships probably have not been measured in a dynamic sense,
such as Mr. Kizakevich was alluding to.
The issue is how the effect was determined and relative to what pollutant,
and was it a dynamic measurement or was it a static one? I have a strong
feeling that the effect is probably defined on the basis of an interview with
a group of panelists or subjects or through medical forms, rather than from a
dynamic active measurement right off a person in the mobile environmental
condition.
MEIER: That is true. But you don* t go out and kill someone to find out
what the LD 50 is. You go collect the data that you have available and make
your best judgment based on those data. Then you go out with your personal
monitor to find out if indeed people are being exposed to those concentrations.
And if so, then you go back for further studies, as you might want to do in
your case, and look at the physiological factors as well as the concentrations.
Then once you get a strong correlation, you are justified in using the other
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type of monitor. But right now, the only physical fact that you know is the
concentration level associated with a health effect.
WALLACE: Maybe I could suggest this: we do have a physiological con-
tingent of sorts here. If they could get together and make some specific
recommendations as to the pollutants for which physiological measurements
would be best suited to be taken concurrently with the measurements of the
concentration involved, that that could be an input to our workshop tonight,
and could be reported on tomorrow in a panel discussion by the chairman or
some representative of the group who has expertise in taking physiological
measurements.
Is that a possibility?
BACHMAN: Lance, wouldn't it be more productive rather than saying for
which pollutants, to first of all define the purpose of what we are doing?
I presume it would be to learn more about health effects, not just to catalog
exposure. And that means you are doing an epidemiological study of some sort,
unless you are talking about clinical studies, which is another breed of
cattle altogether.
In that situation, I think we have some people here who also know what
kinds of general, almost nonspecific, kinds of respiratory symptoms and other
symptoms people experience from air pollution. Also, let's talk about what
kinds of techniques and physiological measurements would be useful on a con-
tinuous and on a personal basis in that regard.
In a general sense, we are getting guidance on what is the state-of-
the-art in conducting epidemiological studies with respect to physiological
measurements on a personal basis; something that is a little more general
rather just related to CO or any other single pollutant.
WALLACE: Let me go on to discuss the entire list.
Another section of OAQPS mentioned two noncriteria pollutants as being
high priority—vapor phase organics and fine particulates.
But in the case of the fine particulates, the OAQPS added the reservation
that this would be important only if the health effects groups felt that con-
current epidemiological studies could be conducted. I did speak to the
representatives of the health effects group, and they thought that a personal
monitor for fine particulates would be important and useful.
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For the fine particulates, as you know, we have had some discussion as
to the proper size cutoff for fine particulates. For reasons that I do not
fully understand myself, there are cutoffs that have been chosen at 2.5 and
15 microns.
BACHMAN: The reason for that is because we are going to revise all of
the air quality standards by 1980, including the particulate standard. And
in doing that, all of us knew that we should look at particle size instead
of just garbage particles again—perhaps including chemical composition.
In looking at the array of definitions of respirable particles and fine
particles, we found so many different definitions that we felt that another
hard look at it was in order, and in protecting the public health of even
the most sensitive segments of the population—given that that is our mandate—
we asked our health effects group to take a look at what really is a respi-
rable particle.
They put together a team, which came back with its findings. For ex-
ample, if we want to protect even the mouth-breathing asthmatic, we should
look at particles less than 15 micrometers.
The 2.5 micron cutoff comes from the apparently natural distribution of
particles in the atmosphere, where certain particles that are formed from gases
or condensates fall into a range less than 2.5 microns in diameter, but
those particles that are kicked off the ground or are mechanically generated
are greater than 2.5 micrometers. That is one basis for the 2.5.
A second basis, which is a little more tenuous, is that is seems to be
an area where most subjects tested fall into a similar pattern.
This is an important definition as far as we are concerned. EPA is set-
ting up a network of some 300 stationary samplers for inhalable particulates.
It is a strong movement on our part toward measuring the impact of respi-
rable particles on ambient air quality.
So, for people who are making these instruments and are interested in
future epidemiological studies, we are looking at these numbers.
The second factor is, as I mentioned before, the chemical composition.
We feel that it is important in doing these kinds of studies to look at the
chemical composition, as well, in terms of epidemiological studies. So, what-
ever system is chosen should be amenable to some of the kinds of techniques
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that are becoming routine, such as X-ray fluorescence to do elemental analysis,
sulfates, or other important components of pollutants.
WALLACE: It does appear, just on my understanding from the first 2 days
of this symposium—and I know we have our organics contingent coming in to-
morrow—that in these two cases of the vapor phase organics and the fine
participates, we do not presently have a working personal monitor capable
of doing ambient level measurements.
MAGE: What averaging time are you talking about? Twenty-four hours?
Daily?
WALLACE: I think I would even be happy with a week averaging time if
that were necessary.
BACHMAN: There are two different needs. Doing epidemiological studies,
it depends on the nature of the study that you are talking about, a 1-hour
averaging time if you are looking for acute effects or a longer term. But
with the organics, we are talking in reality about carcinogens right now.
That is what we care about, at parts-per-billion and maybe even lower con-
centrations. We have a list of hot numbers right now which we are looking at.
So, there are some specific compounds that we are interested in in terms
of only semiquantitative analysis to start with, long-term kind of exposures
and the lifetime exposures. We need to know what is out there in terms of the
kinds of compounds.
We would accept something that is sensitive to low concentrations of a
number of compounds, 10 or 12 or 20, maybe. It would be useful in just get-
ting the gross idea of exposure.
Now, there are some techniques that are being used now in terms of stat-
ionary sites, but the idea of doing it with personal exposure would be some-
thing, of course. And later, as we become more sophisticated in what we are
doing, we would be more interested in maybe very quantitative or more quanti-
tative methods for specific compounds and specific studies.
SCHEIDE: There are some techniques available. There is charcoal tube
sampling. There are passive badges. These are concentrator devices, and they
can be worn very easily.
BACHMAN: I am not sure that they are good for ambient concentrations,
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however. Certainly they haven't been adequate in ambient samples. Charcoal
has been a big problem.
We are not sure that the technology that is useful in the occupational
setting immediately translates to the ambient area. The ambient area is a
lower order of magnitude in terms of concentration.
SCHEIDE: You are talking about longer sampling times, too.
BACHMAN: That is true.
DR. JOSEPH BREEN: Joe Breen, Office of Toxic Substances. At the lower
concentrations, you are getting quantitative recovery samples. But I believe
that people are looking at other absorbents that are being used.
DR. JOSEPH BROOKS: Joe Brooks, Monsanto Corporation. I will be report-
ing tomorrow on the work that we are doing with a combination sorbent collec-
tion system. We will be working and looking at 20 carcinogens in a study
next year. We are on step right now for validating this sampling system aga-
inst the 20 carcinogens.
I would say that in certain cases the technology is probably available
now. When you say vapor phase organics, you are talking about such a broad
range of compounds, and it is going to be a long while before that whole thing
is sorted out.
MS. MARY LYNN WOEBKENBERG: Mary Lynn Woebkenberg, NIOSH. We are cur-
rently involved in an evaluation program of several sampling techniques.
Since you mentioned carcinogens, we are looking at polynuclear aromatics.
We are looking at a mine sampling train which is for particulates and the
vapor phase of any PNA's that come through. They are looking at Tenax. We
have gotten back one set of samples which will give us approximately 400
data points, which will compare several aspects of the sampling trains.
We are looking at the possibility of using the glass fiber filters and
silver membrane filters. We are looking at the need for using the silver mem-
brane filters to see if the Tenax trap behind it will effectively trap all
of the vapor phase PNA.
We are looking at various slides in the 37-millimeter cassette 13. We
are looking at the 10 cc cyclone. We are also doing a particle size distri-
bution study.
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Most of the study that we are doing is taking place in foundry operations,
because we know that there does exist a reasonable concentration of polynu-
clear aromatics after the mold-pouring process and also after shake-out.
So, it is not of the ambient situation, but we are currently doing an
evaluation. With the rapid-scanning fluorescence detection that we have avail-
able to us, we will be able to look at 18 of the PNA's in relatively short
order*
MR. OTTO WHITE: Otto White, Brookhaven Laboratories. Perhaps later on
during the course of the evening, I will get a chance to give you some high-
lights on a project that Brookhaven has been involved in; that is, assessing
the industrial hygiene monitoring for the coal conversion oil shale industry.
The question of PNA's came up there, and the approach that the committee has
recommended in the process of getting the final report in is the use of so-
called indicators or proxy compounds—pretty much like SO. has been used as
an indicator of air pollutants in that the total number of carcinogenic PNA's
that are available are so large that you have to settle on looking at 10 or
20 compounds as indicators of the environment's conditions.
MR. DOUGLAS DOCKERY: Doug Dockery, Harvard. I am a little confused.
I am trying to understand what personal monitor data have to do with standard
setting. I can understand, and I am a little provincial about this, in that
we are doing active epidemiological research. I can see where there is a
direct need for personal monitoring in terms of health effects research. But
in terms of defining how many monitors we need or where they need to be placed,
I don't see the utility of that. The only use I see for these devices is in
determining health effects.
I would like to know what the motivation is for trying to get these data.
WALLACE: As I mentioned in my paper, of my six uses for the personal
monitors, five did not require the health effects measurements. That is,
those five uses were simply to gather exposure data for those pollutants,
six or seven in number, for which the health effects have already been deter-
mined.
The standard setting is affected very strongly by the frequency distri-
bution of exposures, because the standard setting is based on the sensitive
portion of the population. If indeed one finds that the sensitive portion
of the population is a rather small group that could perhaps be protected by
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other means, then a serious and strong change might be called for in the
standard setting process.
UK. ROBERT CHAPMAN: What other means, Lance, do you have in mind?
WALLACE: Well, for example, there was a paper study by Morgan and Morris
that took seven subgroups of the population and estimated their exposures to
SO.., as I recall. Only one of those seven subgroups was found to be anywhere
near the level set by the standard. That one subgroup was construction workers
who lived in the center of the city and worked outdoors in the daytime. I
haven't investigated this, but it does seem possible that respirators or some
other sort of individualized protection for them might be a possible alternate
reaction to the present approach of setting single, uniform, nationwide stand-
ards. However, there could be other possible approaches to the standard-
setting process—it could be regional or it could be more closely identified
with that portion of the population that may be at risk but for which we have
very little data now.
UK. CHIN-I LIN: We are here to talk about personal sensors, and yet we
are talking about a very wide spectrum. I wonder if EPA has released some sort
of tentative priority list.
WALLACE: I guess one of the problems is we have too many lists. We
have a series of lists put out by different offices. And with new informa-
tion coming in all the time from testing and so on, there is a standard
saying around EPA about the "pollutant of the month."
DR. PHILIP WEST: Phil West, Louisiana State University. I admit that
I am among those who are confused. Among other things, we see distributed
here a list of toxins that are of prime interest. Carbon monoxide appears
all the way down through the list. We have heard about carbon monoxide in
so many ways. What percent of the population, however, intermittently, al-
most every day in their lives, are inhaling 300 to 400 parts-per-million of
carbon monoxide from the moment they wake up until they go to sleep at night?
Why are we worried about the range of 10 to at the most 40 parts-per-million?
Why do we say we must have catalytic converters on automobiles, because we
can destroy carbon monoxide, when even in tunnels the levels nowhere approach
the concentrations that are present in each and every puff of a cigarette?
It seems to me that the priorities are a bit distorted here. We are over-
looking things that are much more important, it would seem to me, than some-
thing like carbon monoxide.
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BACHMAN: The real problem is, you know, whatever people care to do to
themselves—quick or slow suicide—in terms of voluntary risks from day-to-day,
the general population should be protected from involuntary risks imposed upon
them from others and from themselves in their automobiles.
Smoking—I always admit that it is a very real risk that smokers get.
While it may not kill them on the spot, it certainly kills a number of them.
To say that many people are exposed to high levels does not say that
the lower levels in the ambient area don11 cause a real risk and pose a ser-
ious threat to the rest of the population.
That is why, indeed, we care about much lower concentrations. Of course,
you could use the same argument about people in their occupations, I suppose,
who receive much higher concentrations.
Some of the people who don* t smoke can also be quite sensitive with re-
spect to carbon monoxide or perhaps other pollutants at lower concentrations.
And perhaps if they smoked, they would drop off much faster.
So, the basic premise is philosophy—the will of the people expressed
in the Clean Air Act. We can't have people imposing involuntary risks on the
general public just because a large percentage of the population—some 30 to
50 percent—is imposing on itself a much, much greater risk.
WALLACE: Perhaps I could continue going down the list of personal monitor
priorities expressed by EPA offices.
The mobile sources portion of the air program has a somewhat different
interest than the rest of the air program. Of course, they are most interested
right now in the diesel question. The automobile manufacturers need a decision
some time around the end of 1979 and the early part of 1980 as to health ef-
fects of diesel particulates. So, a personal monitor for diesel participates
is one of the high priorities for the mobile sources group.
They have also mentioned nitrogen dioxide, transportation-related pollu-
tants, including lead, and again, the ever-present organics.
Within ORD we have several laboratories that have cited their priorities.
The Environmental Sciences and Research Laboratory, which is responsible for
development of instrumentation for air pollution measurements, feels rather
strongly that the sort of work that we do on personal monitors should build on
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the work that has already been done; that pretty much limits them to the cri-
teria pollutants. Among the criteria pollutants, they have chosen ozone, with
CO as a close second, as their top priorities.
The next list is a list of pollutants selected by our Health Effects
Research Laboratory here in Research Triangle Park. However, the list is
dated March 1978, and EPA being such a volatile agency, I would be glad to
hear anything newer that our HERL representative, Dr. Chapman, has to give
us. The old list that we have here is basically the criteria pollutants in
a particular order.
CHAPMAN: I am Robert Chapman from EPA. I might say just to start off
that I am an epidemiologist concerned at the present time mostly with studies
of air pollution in communities as opposed to occupational studies of pollution
exposure.
1 have been asking myself and some colleagues back at work throughout the
conference what is perhaps a more fundamental question than questions that we
have all been dealing with up until now (that is from the standpoint of
epidemiologists interested in community health effects and air pollution
exposure): Where can personal monitors be appropriately used and where can1t
they be used? I wonder if we could grapple with this question a while?
When I think of health effects of air pollution and other types of
pollution, I am inclined to divide them into effects of long-term exposure and
effects of short-term exposure. 1 am having a very difficult time seeing how,
from the standpoint of epidemiologists, personal monitors are going to be
particularly helpful in our studies of long-term exposure effects.
1 would be delighted to be talked out of the way I am thinking right
now. But up until now, 1 have not seen any way in which we would be able to
put them to any particularly useful application in such studies, which leaves
me with the notion that 1 think they would probably be most useful—and I
am sure that I am not saying anything terribly new—in studies of relatively
short-term exposure.
This leads me to a couple of questions, one of which is: From a phys-
iologic standpoint, what kind of averaging time would be most relevant for
us to have a personal monitor that would be of any substantial use to us?
It seems to me that the type of monitor that we would be most interested
in would be one able to characterize, at the most coarse level, 24-hour aver-
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age exposures; and considerably finer gradation within that would be useful
to us, largely because we really don't have a good handle, as I think some
of you think we do, on short-term health effects of the pollutants.
We do have some fairly confident estimates of the types of health effects
that are being promoted by pollution exposure, but very, very few available
data can be characterized as being solid.
So, the finer the gradation of exposure that we can get a picture of
within the day, the better we are going to like it. I would say first that
we should have certainly 24-hour average exposures available to us for what-
ever pollutants we use personal monitors for. I would also say, in my mind
and I think in some of my colleagues' minds, that the second most desirable
type of exposure averaging time would probably be the daily maximum hourly
average within a day. The third most desirable—which is practically equal
in my mind to the second—would be some index of the maximum instantaneous
concentrations of the pollution in question for each day.
I don* t think that exposure times over a period longer than a day without
data for shorter exposures are going to be terribly useful to us, to be per-
fectly honest with you, because of the types of effects or the types of bio-
medical variables that I can see us measuring in those studies* I don't think
it is terribly plausible to think that that kind of variable would be affected
by pollution exposures a week ago as opposed to today or yesterday.
I don't really see much point in a big effort being made toward develop-
ing monitors whose finest capability is a week-long exposure.
WALLACE: Can I ask about the lead exposure time, which is a month?
CHAPMAN: I would have to admit, Lance, that I am not very good on that.
There are a lot of people who can tell you more than I can. I should probably
preface what I am saying: I think that what I know best is criteria pollu-
tants—criteria pollutants as they would have been defined up to a year ago.
Yes; you are quite right. I am trying to generalize here. There would
certainly be some exceptions. I think, however, that the exceptions as far
as I know aren't going to really have me change my mind too much, even though
individual ones—other individual ones—might well be thought of.
1 have been wondering whether I am right, for example, for a lot of the
organic substances. And I must say I am wondering, again from the point of
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view of a community kind of epidemiologist as opposed to an occupational one,
what kind of short-term effects can we hope to see in response to exposure
to some of the organics?
I must say I really don* t know the answer. 1 have come up with the
question that is rather large in my mind: How helpful to us are the various
organic types of personal monitors going to be? I won't say very helpful,
and 1 won't say not very helpful, but I will certainly say that the answer is
highly uncertain in my mind. 1 will have to also say that 1 can't really come
up with a specific application in an epidemiologic study of personal monitors
for organics.
I must say that the kind of monitors that I can best get a handle on
the use of, a) because 1 know this kind of pollution best, and b) because I
think there may be something to it, too, is the criteria pollutants, again
excluding lead.
WALLACE: You raised two questions in my mind, one of which is, among
the criteria pollutants, do you have a ranking or do you have studies that
are ongoing now that could be improved or enhanced by the addition of personal
monitors to those studies?
CHAPMAN: Well, I think there are studies ongoing now for really all
of the criteria pollutants, excluding lead, that would be enhanced by appro-
priate personal monitors. And 1 must say that I want to stress the word
"appropriate."
1 am very impressed by a lot of the technology I have seen in the last
2 days, but I have to voice some skepticism as to whether this technology
has really received the full gamut of laboratory and field testing that would
make us confident of using it.
1 say this largely because of assurances that we have gotten over the
years of the big instruments—the instruments that are put in ambient situ-
ations that are not worn by people. Even these instruments, to my way of
thinking, are not entirely debugged as yet.
1 think it would be an unrealistic request of any maker of a personal
monitor to ask within 2 or even 3 years of the conception of the instrument
to have it entirely ready for field use.
1 think, on the other hand, that it would not be fair to us epidemiolo-
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gists to plunge into the field use of such instruments until they were fully
verified both in the lab and in the field.
WALLACE: That is a perfectly reasonable request to make. Laboratories
within ORD would have the responsibility for evaluating these instruments
in the field. I am referring to the environmental monitoring units at our
laboratories, either here or at Las Vegas.
CHAPMAN: That is really what I am coming down to, if I could just
say another sentence or two. I really can't determine rank within the cri-
teria pollutants, and therefore would be inclined to go along with what I
think you said about the ESRL, and that is that 1 think we would feel the
most confident using first the monitor that presently is closest to develop-
ment. I think we could come up with an interesting and relevant application
for it, as long as we were convinced that it was really going to work.
That is more important in my mind than a specific pollutant which is
chosen to be measured.
DR. JOHN McSTRAVICK: John McStravlck, Energetics Science. You bring
up a very interesting point that is something we haven* t discussed here in
the past 2 days—that is, performance specifications. What are you looking
for?
OK. You make a very general statement which I accept. But what kind
of accuracy do you need? What kind of configuration do you need? These are
the things that we have to get sent back to us as well. I am hoping that this
will come out here tonight at the workshop.
CHAPMAN: I think that that is unrealistic. I think this is the kind
of thing that we would have to sit down together to discuss for several hours
for each substance, really.
WALLACE: John, correct me if I am wrong, but it does seem to me that
I remember you or someone at ESI stating that one of the reasons that you de-
veloped the 9000 series was because of Anthony Cortese1s studies in Boston
in which he used the Ecolyzer and stated that he needed something that was
more easily portable.
McSTRAVICK: Absolutely.
WALLACE: That seems to me to be an extremely important point, which is
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that industry will develop the sorts of things for which they are given some
indication that there is a need for. And it is, I think, a challenge to EPA
to come up with the specifications that we need.
For example, do we need tremendous accuracy in personal monitors for
some of the uses we are talking about? 1 am of the opinion that we do not.
We do need sensitivity. We need to go down to ambient levels.
But the sheer number of data points that we can get may make it possible
to compensate, by means of a large N, for the fact that they are not as accu-
rate as the large fixed-station monitors.
MEIER: Could I read off something that Joe Behar and I put together
last night? We did just what you asked. Don* t hold me to what I will read
to you as representing all of EPA. This is simply what we at Las Vegas
called desirable characteristics. It is quite a long list, but we worked it
out among ourselves and thought that we might present it here, which we have
not done so, so far.
Let me read some of the things to you, and they kind of answer your
questions, I think:
1) Lightweight—light enough to be worn easily by the general public;
less than 1 pound, including power supply, is desirable*
2) Durable—able to withstand treatment received by personal equipment
such as a wrist watch.
3) Dependable power supply—in our terms, a power supply must be able to
provide constant power over a minimum of 24 hours.
4) Easily changed.
5) Tamper proof.
6) No exposed controls that could be easily adjusted by the wearer.
7) Accurate—an accuracy of plus or minus 20 percent at 2 sigma is desired.
8) Sensitive—should be able to detect the parameter of Interest at
one tenth of the most stringent air quality standard.
9) Sensitive to range of concentration expected in air.
10) Easily calibrated.
11) Separate readout—hourly and dally Integrated readings are desired.
12) Reliable—less than 1 failure for 10 units.
13) Free of common Interferences—total interferences less than 10 percent
of total signal.
14) Traceable to a standard method If possible.
15) Inexpensive—less than $500 per instrument is desired.
16) Stability—capable of operating for a minimum of 24 hours without
changing components.
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Note that that was just a quick list that we put together.
DOCKERY: I would like to state a different viewpoint from what you were
saying about the instruments. We are kind of working at the edge of the
science here in trying to measure health effects for new pollutants that are
coming along, and things that we have little knowledge about. The instrumen-
tation we are having to use in doing this is really not field tested, hard
and fast instrumentation, but Instruments that are basically laboratory in-
struments that we are trying to apply in the field.
We have a lot of failures in going out and trying to use these. I think
if you are looking for a market where you are going to go out and sell a lot
of these monitors, it doesn't exist. There are going to be a couple of
e p id end o log leal studies, and then we are going to go on to something else.
I don't think the market exists.
McSTRAVICK: In the Industrial workplace, it does exist.
DOCKERY: In the industrial workplace, it does, but not in the ambient
environment.
McSTRAVICK: Well, I can address myself to both of them.
MR. DAVID BRAUN: Dave Braun, 3M Company. I am an engineer. I really
don't understand or know that much about epldemlological work. But going
back to your original idea of short-term and accessible effects that you can
look at, it seems to me that with systemic toxins, don't you really want to
have a data base for which the time interval is not so important, even if it
is a month? Doesn' t that fall into the realm of the kind of work you do?
CHAPMAN: Are you talking about things, exposure to which—such as vir-
tually any metal—would be manifestly bad for you?
BRAUN: No, but let's say carcinogens or anything where the long-term
effect is important. When you were saying that you really don't see the
reason for extended period sampling, 1 think I would submit that that is one
place where—or am I understanding your work incorrectly?
CHAPMAN: No, I don't think so. Let me try and give you some feeling
of why I think it is a limited application.
One problem is that we are absolutely proscribed from doing prospective
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studies in cancer, I think, given both the necessary sample sizes and re-
sources—financial resources—that would be required, even in the best of
all possible worlds. Given, at least for us Government researchers, the exi-
gencies involved in launching sustained studies, I think it is unrealistic
for a prospective seller of personal monitors, say for carcinogenesis, to
launch a heavy research and development program in expectation that scien-
tists in EPA are going to be able to monitor a truly big prospective study—
that would be a mistake.
1 think it is too bad, but 1 think it is true. I wish we could do it.
But up to now, we are just playing. We have not been able to because of
shifting tides that are out of our control.
Another thing that gives me trouble is that I am not really addressing
the physiologic part of the question right now. A more scientific than phys-
iologic reservation in my mind is the difficulty of using monitors now to
try and determine what exposures have been in the past. Because we are not
able to do prospective studies, we are more or less stuck doing retrospective
ones; that is, finding pockets, let's say, of high cancer Incidence, and then
trying to determine in a retrospective fashion what the people have been ex-
posed to.
Now, monitors might be useful to give us an indication of substances in
the town now that we didn't really expect were there, or that we thought maybe
were there but we didn't know about. But beyond that fact, in a retrospective
study—a fact that it seems to me could be turned up with a stationary monitor—
a very limited number of stationary monitors may be rotated throughout the
town. 1 really don't know what personal monitors could add. Do you see what
I mean?
BRAUN: Yes.
BACHMAN: Let me add something to that, though, because we made a request
to put vapor phase organics on the list.
1 agree with your comments with respect to epidemiologic studies. We
didn't put it on there because we saw a use in epidemiology.
What we see is a use in exposure monitoring, and stationary monitoring
is good and useful for this purpose; emissions monitoring is good and neces-
sary, and modeling is going to be used.
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In the standard setting with carcinogens, however, it is going to be im-
portant to us to have some studies of total body burdens and various exposure
•regimes to validate our models and to develop better exposure models than we
have now.
And we wish to measure what is in the air now so that we can regulate
the emissions that are coming out now to prevent future problems—not wait
to see the dead bodies 20 years from now.
So, the idea is to get these monitors used in standard settings. So,
we do see a use for these instruments, but certainly not in epidemiology.
CHAPMAN: So, you are talking about studies in which there are no specific
biomedical measurements?
BACHMAN: That is exactly right. We are assuming a risk of cancer.
We can do some extrapolations and get some ideas just from the exposure.
This is the use that we see for it.
WEST: First, I swear that I had no input whatsoever to what Gene said
a few minutes ago about certain specifications that would be desirable for
personal monitoring. He was obviously talking about passive units. And so,
three of us in the room right now bless him because he summarized what we
would summarize in our talks tomorrow.
I would like to comment on the incremental measurements of hazardous
materials. Personally, I have been involved in this work for some 27 years.
We started on S02 and worked on the acute toxins. These were obvious and
spectacular, and people were worried about them. Apparently, we are still
worried about them.
I sometimes think that this is in error, because regarding a few toxins,
if they don't kill you, don11 worry about them. If they do kill you, of
course, someone else is going to worry about them.
You have the acute toxins and the cumulative toxins. And there is another
group that seems to be overlooked, at least in most classifications—that would
be additive toxins. In the case of additive toxins, it doesn't matter very
much about how much you get in any one increment. But everything points to
an end point at which you have a certain liability that you must pay off.
Concerning radiologic exposures, the same thing applies. You can* t
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backtrack after you have had it. You smoke cigarettes. Now, loosened up by
martinis a good many years ago, someone who was very knowledgeable in the
industry confessed to me that he knew that a person could smoke one pack of
cigarettes a day for 40 years, and there was, say, a 20 percent chance of
dying of lung cancer. Or two packs of cigarettes a day for 30 years would give
you exactly the same chance. You could have four packs a day for 10 years.
You come to the same thing. So, it was strictly additive.
So, if that is the case, then 1 should think that we would be interested,
not in breaking this down to a daily exposure or even a weekly exposure, if
we just had the time range averaged for a month for some things. Suppose we
say vinyl chloride or benzene.
Now, 1 don't think that this is necessarily significant as long as it
is sublethal. It could be; we don't know. But it could be the additive
effect—that is, the total insult from all of these supplemental increments
that add up over 5 years or 10 years, or if you don't have very much of it,
it may take 30 or 40 years. But somewhere along the line, there is going
to be some sort of an accounting.
Now, if that is the case—then some type of monitor that is simple or
eloquent in its simplicity—truly 1 think a passive type monitor is perfectly
acceptable, and the accuracies certainly are good. 1 might add—and 1 will
point this out tomorrow—that we have monitors that will give us a time-
weighted average for a 30-day exposure.
I might mention also that we have personal monitors that are passive for
tetraethyl and tetraethyl lead that we could easily apply in the ambient
atmosphere and have 1 month exposures and get the time-weighted average for
that.
So, these are possibilities that I think should be explored. Now, un-
fortunately, funding agencies have been very parsimonius. We developed a
vinyl chloride monitor for $43,000, and we begged and cried to get that.
So, with a little money, I think there is a lot that can be done. But
I do think that extended periods are justified in some things.
CHAPMAN: I think that is right. I think it is right for compounds of
low concentrations. I might say that I would be delighted to eat the words
that I spoke at the outset of my remarks, especially if what we are constantly
doing in community health research and air pollutants is associating short-
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term—say dally or shorter—pollutant exposure with physiologic changes of
uncertain significance.
People will cough, for example. Some people may wheeze. Other people
may develop eye irritation. We have no real sense that a great many of these
symptoms that appear to be reversible are more or less innocuous. We have
no sense of the degree to which these are harbingers (after repeated exposures)
of some overt disease developing over the long term.
If, with respect to a lot of the compounds, in particular the organics,
certain short-term symptomatic or biochemical or hematologic responses could
be elicited and tied to the development of some real illness condition down
the road, I would be more than happy to take back in a minute what I said
before.
One thing that gives me a good deal of trouble, though, is the overuse
of scientific energy, or technology development to the exclusion, let's say,
of determining what the real meaning of some of these shorter-term responses
may be, be they after a month or after a day.
WEST: But not eliminate either one.
CHAPMAN: That is right. Bear in mind the necessity of the concurrent
effort.
DR. LARRY LOCKER: Larry Locker, Solid State Sensors. I just want to
make the comment that the people who are interested in personal monitoring
and selling equipment would like very much to see Government agencies in-
crease the criteria pollutants by hundreds, by thousands. And the instru-
ments that you need—the analytical instruments you need—to get the infor-
mation that you require, are, I think, quite different from what the prospective
market needs.
They want something that is low in cost, light in weight, and which they
don't have to change every day. They want something that can be used over
a long term. It is only a question of reliability of statistics, the way
I see it. For you to get statistics on health effects, you need a different
type of instrumentation than would be ideal for someone who wants to monitor
in an occupational situation.
CHAPMAN: We certainly want some common features without extreme unob-
trusiveness. We just really can't use them in our studies to any particularly
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good degree. That is every bit as important as the accuracy of the instru-
ment.
Maybe 1 shouldn't say this since by doing so I am pointing out the
limitations in our field. But I am inclined to agree with you, Lance, that
extreme accuracy isn't all that important. My first reaction is that the
precision of instruments, reproducibility of response from one instrument
to another, may be more important for us than very delicate accuracy.
DR. EDWARD McMADDEN: Ed McMadden, Gastek. As a manufacturer, 1 guess
I can say in all honesty that we are quite pleased with the possibility of
EPA1s getting into this kind of instrumentation.
But we seem to be talking a great deal about organics. I don't believe
there would be a challenge if I were to say that within the criteria that
were set down, which Include hourly accumulation, that there is nothing
presently in the wind other than 24 badges which are changed on the hour
at the stroke of the clock which are going to do that job for organics.
Rather than spending a lot of time chasing off on that tangent, it ap-
pears that within the criteria pollutants—although the instrumentation avail-
able right now does not meet all your specifications—in CO, it is quite close.
Out of our total of 16 entries for pollutants to be measured, CO constitutes
a quartet of those. The same basic type of technique can be used to measure
another group of the nitrogen oxides, sulfur dioxide, and so forth.
So, that takes care of a total of half the entries. Can we now eliminate
some of the things that probably are at best well beyond the horizon at the
present time ami concentrate particularly on CO because we could have something
reasonable with the technology that is available now?
I am not sure that your $500 criteria will be met. But be that as it may,
what numbers are we talking about? Are we talking about dozens? Are we
talking about hundreds or thousands?
This will be helpful to us if we can get specific and right down to the
point where we are close today as manufacturers.
WALLACE: Two comments in response to that. One is that that is a fair
question about the numbers. I can probably give you some response to that.
The other is that we really have two areas involved here. First, we have
studies that we could do almost immediately with existing (properly evaluated)
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instruments. Secondly, we look into the future and decide what we need to
develop for the next few years or the next dozen years or so. And there,
we do have to look beyond what is available now.
BACHMAN: I am afraid there is a misconception here. There are several
kinds of needs. Chad was talking about epidemiological needs. When he says
an hour, that is one thing, and it is useful in that short-term system.
You are asking for organic monitoring, and 1 think OTS and the others on the
list—by the way, there are four CO entries and four organic entries—any-
way, the other people are also asking for organic measurements. They are
talking about the same kinds of problems we are: carcinogens and these long-
term effects. What you are talking about is apropos, and maybe we are not
so far over the horizon. That is important to us. But I think it is a real
need you will have. A number of people are obviously interested in it. So,
I don't want to turn off anybody.
McMADDEN: 1 am not trying to down play organics. What I am saying is
that we have in one area an approach that is reasonably close to your desires,
What I am saying is that if this group cannot come up with some sort of meet-
ing of minds where we are close, I think it will be less productive to get
driven off on other things which really are much further away.
Granted, that for the long term, it is useful. But for manufacturers,
that would be another thing.
MAGE: I would like to ask Otto White if he wouldn't mind briefing us
on what was discussed at Brookhaven. 1 think maybe some of the very same
questions have been handled there, and perhaps it would be beneficial for us
to get this input from their point of view.
WHITE: Brookhaven was asked by the Department of Energy to assess the
industrial hygiene monitoring needs of coal conversion in the oil shale in-
dustry.
The way we attacked that was to formulate what we interpreted to be an
authoritative group, consisting of names within the field of industrial
hygiene. The committee met three times. The final meeting concluded with
a symposium similar to this, in which the theme of the first day was to
identify the industrial hygiene monitoring problems for the emerging possible
field industries. On the second day, the theme was to address the state of
the technology for performing these monitoring needs.
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We identified at that time a number of monitoring needs for the occu-
pational environment. They include things like the evaluation of health
effects, monitoring performance of engineering controls, monitoring trends
within those controls, developing designed requirements for doing the controls,
documentation of exposure levels, testing for compliance purposes, measuring
process losses, selection of suitable respiratory detector devices, identi-
fication of contamination sources, and assessing emergency conditions*
When we started attacking the problem, one of the things that turned out
to be extremely important were the polysaccharide hydrocarbons. If you look
at the process characterization—the effluent characterization studies—you
find some thousand compounds for which toxicological studies indicate that
some neoplastic or carcinogenic properties are associated.
We also associated the industries with their use of some very common
materials, a number of which appear on your list.
So, the first thing the working crew did was to categorize the hazardous
potentials of some of these materials. We developed four categories: the
first was materials immediately hazardous to life and health. The second
category was high risk but not immediately hazardous. The third was a moder-
ate risk, but not highly hazardous. Fourth was short-term, nonroutine, high
hazard conditions.
We had to ask ourselves some questions. The questions that required
answering were: What compounds were present in each hazard category class?
Is the monitoring technology currently available for that particular pollutant?
Is the current technology compatible with future needs? If not, is technology
being developed to meet that projected need, and when is the technology needed?
In the high hazard category we listed six compounds, hydrogen sulfide,
carbon monoxide, the oxides of nitrogen, oxygen deficiency, and coal and
shale dust, as well as hydrogen.
We said these materials were present in such concentrations within these
processes that acute irreversible effects could result from exposure. The
working group believed that the technology was available to provide equipment
which could be used as personal and area monitors for continuous and direct
reading and long capabilities for hydrogen sulfide, carbon monoxide, oxygen,
and hydrogen, of course.
However, the technology was lacking for monitoring exposure levels of
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coal dust and nitrogen oxides in a format that would give the personal capa-
bility. We also did not believe that these six substances were unique for the
coal conversion oil shale industry. So, this particular group recognized
no special priority from this standpoint for these particular forms of in-
strumentation.
The second category that we looked at was the high risk but not immedi-
ately hazardous category. We classified within this category materials which
cause irreversible effects but were not present in sufficient quantities to
produce acute toxicologlcal effects. The carcinogenic, mutagenic, and tera-
togenic organics are included in this group, as well as some of the trace
metals, dust, and fibers.
I don11 think it would be fair to you to read through the draft of the
report, but I will point out some of the specific research suggestions that
the committee will be recommending to the Department of Energy.
In terms of personal monitors for gases, the working group encouraged
that there be additional evaluation of current instrumentation under various
conditions of Interference, temperature, pressure, humidity, etc., to ascer-
tain the appropriateness for future needs.
It is likely that passive monitors will remain a primary monitoring tool.
Improvements needed include the development of a new substrate to expand the
diversity of measurable compounds and to allow higher flow rates.
We believe that this area is likely to provide high payoff in a few years.
We also recognized the need to increase personal monitoring pump flow
rates.
And that has been identified as one requirement for obtaining sufficient
samples to facilitate bioassay samples.
Both benzene-soluble fraction and benzo(alpha)pyrene have been recognized
as potential indicators in the coal conversion industries. There appear to
be some drawbacks in use of these particular tools as monitors in that you
need a little more material to run your sample than is currently available,
say, for dust samples.
So, we recognized that you need to have personal-type pumps, similar to
the MSA Model G. The committee looked at second generation instrumentation.
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The working group encouraged the development of new sampling instruments which
will facilitate automatic analysis and data recording to permit the handling
of large amounts of data. And the working group therefore encouraged the
development of the personal gas chromatograph. The Stanford research group
has a pocket-sized gas chromatograph which can monitor some 10 compounds and
give you a time-weighted average or the cumulative concentration or dose at
the end.
We would encourage this type of instrumentation, which presently has
been funded by NIOSH, but DOE should look at this for the polysaccharide hydro-
carbons which may require another type of detector and maybe some different
substrates in terms of the column.
Additionally, we felt that real time data reporting is necessary only
for the Class A compounds; that is, the carbon monoxide, hydrogen sulfide,
and those immediately hazardous compounds. We felt that in other cases, the
most attractive approach is a personal sampler, which either can report re-
sults of real time analysis over the course of a day or collect a sample over
the course of a day, and at the end of the day the sample is inserted into a
device which either analyzes or records the exposure automatically.
We also found that there is a need for looking at nitrogen compounds.
There are no good sampling techniques for ammonia and hydrogen cyanides, as
well as nitrogen, which are of particular interest in the oil shale industry.
In the area of aerosols, our comment here is that this is an area where
there are many needs, but that it is one that does not appear to be right for
exploration. For example, there is a need to do in situ chemical characteri-
zations, with no avenues for research in this area being evident, and a size
cutoff at 15 microns and 2 microns, consistent with the recent EPA finding
should be made. Current technology is adequate for this, and development of
more sophisticated devices is not recommended at this time.
We believe that in terms of particle or aerosol monitoring, we need to:
improve the efficiency of collection; improve the extraction efficiency for
the separation techniques, chemical specification, and in situ separation of
soluble and insoluble particulates; and to review the state-of-the-art used
for personal particulate samples to determine their needs in the future
research.
In the area of metals, we identified possibly five metals of concern.
They include arsenic, cadmium, chromium, and nickel. Lead was not included
in our particular list.
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However, we are concerned that the toxlclty of metals varies with their
biological availability. A classic example is chromium, and also chemical
compounds. Our current technology does not provide insights on these factors,
and research is needed to provide this additional information.
One area of exposure in terms of these new industries is the contamination
of surfaces—that neither are there safe permissible levels for skin contami-
nation, nor are there good techniques for evaluating skin contamination. We
recognized a need in that area.
One area where the committee wanted to provide some insight was in ana-
lytical development. We thought that we should encourage the refinement of
analytical tools and techniques for materials which are identified by those
characterization studies—that is, process streams and air pollutant characteri-
zations. But we did not believe that it would be appropriate at that time
to dilute the available funds to develop a few high technology devices. There
are a number of papers on the Auger spectrometer. We thought that that wasn* t
the particular analytical device that would receive funding in other areas.
Basically, that summarizes the committee's concern. We felt that person-
al monitoring had its place. We were concerned that these industries were
going to be approximately 1 square mile in terms of area. The use of area
monitors probably should be evaluated. But certainly for operations similar
to all refinery-type operations, personnel monitoring is probably going to
be one of the major tools.
It is interesting to find that some of the compounds that we are concerned
with are compounds that EPA is concerned with in the environment.
MAGE: Thank you, Otto. In your view, as a representative of the com-
mittee, did it also envision personal health monitoring and personal exposure
monitoring simultaneously?
WHITE: The area of personal health monitoring was not really addressed
by the committee. The committee was concerned about a time some 20 years
from now, having a Mancuso-type concern in terms of this particular industry.
And so, the need to get a handle on all the parameters that are available
la paramount. We did not address the physiological monitoring question; no.
MAGE: I would just like to say that we are thinking of epldemiological
studies of a thousand subjects and a thousand personal monitors, and that is
not the only use of the personal monitor.
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Everybody knows that there are economic considerations involved in setting
air quality standards and regulations* We have just witnessed the Automobile
Manufacturers Association's ability to get a relaxation of our standards on
vehicle emissions set back year after year. These are economic considerations.
One of the economic considerations that we have to take into account
is the number of people who are exposed to particular pollution levels.
We are setting standards which are required to be met by the States through
implementation plans. The States have to reduce emissions in order to bring
air pollution down below the standards.
It is going to be very important for us to prove that not only are those
measurements representative of communities, but indeed that there are a
significant number of people who are exposed. Also, we will have to answer
the question: "Are the effects of in-home and nonambient environments more
pertinent for us to worry about than the 1 or 2 hours of ambient exposure
that we might have outdoors?
So, there are many reasons why we should look at personal monitors other
than for the purpose of conducting epidemiological studies.
I look forward to the day that the personal physiological monitors are
inexpensive, handy, and reliable, so that we could put one out with each per-
sonal exposure monitor.
But I think until that day comes, 1 still see a use for personal exposure
monitors simply for characterization of exposure, if for nothing else.
WALLACE: All it requires is a redefinition of the word ambient, or rather,
going back to what it originally meant, which was surroundings—the air that
surrounds you in the vehicle and the home is ambient air.
DR. VIC SOCOL: I think we have a basic question here. I think we have
the manufacturer represented and the scientific community represented. Who
is going to lead the way? Is the manufacturer going to establish what he
can build, the criteria that he can build it to, and tell the scientific
community, "This is what we can do"? Or is EPA or the scientific community
going to tell the manufacturer what is wanted both qualitatively and quanti-
tively?
It is the question of the cart leading the horse or the horse leading the
cart.
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WALLACE: I think it is exactly that question.
SOCOL: That is what I hope will come out of this whole meeting.
WALLACE: Yes. We have one manufacturer asking to tell him what our
plans are. I think that it is the sort of challenge that we ought to try to
meet. In response, you can tell us whether we are off target, and perhaps
we can come together.
SOCOL: I think a manufacturer can do whatever the scientific community
requires him to do, although not necessarily at the cost that you have stated.
It is a question of numbers. It is a question of cost. It is a question
of what you really need.
DR. GEORGE MALINDZAK: George Malindzak from Ohio. I represent another
level of confusion, in that I presume that the majority of the group is talk-
ing about personal exposure monitors. I represent those individuals who are
concerned with the physiologic monitors.
My confusion is associated with the realistic need for collecting personal
exposure information in the absence of the physiologic consequences. Where
does that get you? I don't understand the purpose of putting all this effort
in collecting exposure information if you don't understand what the human
response is going to be.
WALLACE: There are two possible answers: one is that it is expensive
to collect extra information on health effects along with exposure; and the
second is that if you already have established health effects for given levels
of the criteria pollutants, then the exposure measurements satisfy certain
other needs and thus should be extended.
For some noncriteria pollutants, such as carcinogens, there may be some
purpose in collecting exposure information without concurrent physiological
responses, since they have already been shown to be carcinogenic in some
clinical or toxicological way.
I am not trying to say we should not collect physiological evidence.
I am in fact in favor of that. There are questions of funds that have to be
considered also.
MALINDZAK: Technologically, it is probably simpler to collect physio-
logical information than exposure information.
359
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WALLACE: There is also a factor of ignorance of the possibilities of
collecting physiological information on the part of the people who are in the
air pollution field, in many cases. I certainly speak for myself about not
knowing what is possible and what is not possible in that area.
I would really be anxious for the insights of the physiological contingent
to be brought forward.
DR. THOMAS FEAGANS: Tom Feagans, EPA. I would like to support Lance and
Dave in their thought that this second kind of information on personal exposure
would be very valuable to us in OAQPS. Whatever your level of knowledge
about health effects of a given pollutant, it helps us to estimate what the
consequence of various possible standards we might set would be, no matter
what the exposure levels would be.
MAGE: Even though 1 believe that the Clean Air Act says that the Ad-
ministrator of EPA is supposed to set the standard irrespective of economics,
I might say that economics do play a role. It is a significant question.
Now, in order to evaluate the economic effect, which of course is in
units of millions of dollars, we have to know what level of exposure the
general public receives, and we have to know, if we set a standard, how many
people we are protecting.
Thus, even though we may not be measuring the health effect directly in
an epidemiologic study, it doesn't preclude the need to measure the exposure.
On the other hand, we have to recognize that our standards are living
standards. They are not dead and fixed in concrete. The Clean Air Act re-
quires us—mandates us—to review our standards every 5 years at a minimum,
and the Administrator can change a standard at any time that he feels there
is new evidence to justify it.
There is a long-range payoff for control of air pollution or relaxation
of standards if you can justify it, so that it does justify expenditures of
millions of dollars in order to save billions. But it is hard to get those
millions.
I think that it will be very beneficial that we are doing the development
work on the personal physiological monitors, because 1 don't think that the
last epidemiological study has been done yet.
360
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CHAPMAN: I certainly hope not.
SCHEIDE: I have one comment. We have to keep in mind why we monitor.
The reason we monitor is to identify problems. Whether the action level is
set low or high is another question that Government organizations have to deal
with. No matter where it is set, we still need to monitor to identify pro-
blems. That is what we have to keep in mind.
MALINDZAK: But a problem represents the differential between what you
expect and what you find. If you never look at the physiologic information,
you are never going to change that standard with respect to physiologic con-
sequences. If you are going to devote all your effort to exposure monitors,
you are never going to change the physiologic consequence which you learn to
establish the standard to begin with.
My point is that there is a maldistribution of effort; that all the ef-
fort seems to be going into the exposure monitor. If you want to characterize
the population exposure, you don't need personal monitors. You very well
should have fixed stations.
But the object is to characterize the physiologic response to this ex-
posure, not just to collect exposure information.
FEAGANS: I agree with one point you made, but disagree with another.
I agree with the point that personal monitors can certainly play a role in
epidemiological studies to help us learn more about what patterns of exposure
cause what effects.
But I don't agree with the second point about a stationary monitoring
network being sufficient to tell us all we need to know about those patterns
to make the estimates that I mentioned the last time I spoke.
MALINDZAK: I said if you want to characterize the exposure of population,
you don't need personal monitors. The purpose was to characterize the popu-
lation exposure, not to know all about the exposure of that population.
FEAGANS: But I think the personal monitors give you a finer grade of
characterization that is very helpful to us in making the estimates we need
to make.
MALINDZAK: There is no question about that. I don't argue with that
at all.
361
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McKINNON: Not only a finer grade. I think it is necessary to char-
acterize the exposure initially. I think several people in the room will
agree that the air monitoring that is done in fixed sites certainly doesn't
account for a lot of population factors that determine exposures, even in
groups with large numbers of people.
MALINDZAK: I would like to make the record clear. 1 support personal
monitors, but for different reasons. I support your personal physiologic
monitors to run concurrently with exposure monitors so that the response to
these exposures can be characterized in a realistic and scientific manner, so
that we can respond to them in an intelligent way.
Right now we don* t collect the physiologic information concurrently with
exposure.
MAGE: Another reason for the use of physiological monitors is that we
must, as an agency, keep progressing the state-of-the-art. We are running
Clinical studies in parallel with epidemiological studies. We are doing new
and different things. We are discovering new things all the time.
A colleague of mine told me that there are some 8,000 medical journals
published throughout the world on all aspects of medicine. It is very possible
and very probable, that somebody is submitting for publication right now,
in some place in the world, something which will define a heretofore unobserved
physiological effect.
Suddenly we are going to have thrust upon us a request to replicate that
study or a need to go out and monitor. If these personal physiological moni-
tors aren't being developed parallel with all our thrusts in epidemiology,
in clinical studies, and personal exposure, we might find ourselves again with
our pants down, 3 years behind, simply because we didn't have the foresight to
recognize that although there might not be some kind of acute symptom that
we can see from the outside, perhaps some of the devices that George and Matt
developed could see from the inside, and had we spent the money, we might
have had those devices.
So, we need people who are looking ahead in the same way that we need
people who are looking today, to keep our feet on the ground. We need these
people who know the state-of-the-art of the developing technology, who see
the abilities of micro circuits and also know the physiology, and who can say,
"This is a possibility." Then, it will be here when we need it.
362
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Although it might be impractical at the moment to put a thousand of these
new devices out with a thousand subjects in a particular health study, we
can* t simply say we don't need it.
I think we need both long-terra and short-term research.
I have now heard about eight or nine Government agencies who are working
in this area and not all of them are talking to each other. We have EPA,
NIOSH, the Departments of the Interior, Commerce, and Energy; all kinds of
agencies. There should be some kind of coordinated plan. Perhaps Congressman
Brown's idea, of a bill which would establish a monitoring program, would
provide a mechanism for long-range research as well as short-range development.
Even though there is no immediate payoff from development c2 personal
physiological monitors in epidemiological studies scheduled for this year,
I think we should make certain people in the Government agencies recognize
that it is something that we definitely need in the future.
I can't imagine our not needing it in the future, as our ability to see
Inside the human body progresses.
SOCOL: I would like to change some of the things that I was going to
say based on what Dave Mage said.
When you go into personal monitoring and physiological monitoring, the
effect is going to be different on me—who weighs 130 pounds—than on a man
who weighs 180 to 200 pounds. It is going to be different on a child and
different on an adult. It is going to be different by age. It is going to
be different by sex.
I feel that personal monitoring is going to become more effective than
fixed-station monitoring, where you don't know what effect you are getting on
what particular individual. I think that you can achieve more physiological
information by the personal method than by the fixed method.
I am borrowing from what Dave has said to respond to your remarks.
WALLACE: OK, thank you very much.
363
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A New Personal Organic Vapor Monitor
with In Situ Sample Elution
Donald W. Gosselink, Ph.D., David L. Braun, Haskell E. Mullins, and
Sandra T. Rodriguez
Occupational Health and Safety Products Division
3M Company
St. Paul, Minnesota
INTRODUCTION
In considering a new approach to monitoring personal exposures to organic
vapors, the steps in an overall monitoring program can be Individually ad-
dressed:
1) Development of monitoring plan
2) Purchase of supplies
3) Preparation of equipment
4) Sampling of personal exposures (includes recording data during sampling)
5) Preparation of sample for analysis
6) Analysis and TWA calculation
7) Report communication and follow-through.
In examining and improving current methods for carrying out each of the
above operations, we have evolved a monitoring system which simplifies the
work while maintaining desirable objectives and monitoring requirements.
The monitoring system which evolved is the 3M Brand Organic Vapor Monitor No.
3500 (see Figure 1).
We can now consider the way in which this monitor interacts in each of
the above seven areas.
Step one, monitoring planning, is simplified because the 3500 system
allows the hygienist to work through trained aides in remote locations. It
also helps increase the number of samples taken in the case where the hygienist
365
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FIGURE 1. 3M Brand No. 3500 Organic Vapor Monitor.
FIGURE 2. Use instructions for the 3M Brand No. 3500 Organic Vapor Monitor.
(The numbers in the illustration refer to the steps outlined in the text.)
366
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is present for the monitoring, thereby lowering hygienist cost-per-sample.
Purchase of supplies, step two, is reduced, since only a single product is
needed. Step three is virtually eliminated, because the 3500 monitor needs
no preparation or calibration by the user.
In the conduct of step four, or the actual exposure sampling, the monitor
is readily accepted by employees wearing it. Monitors are individually identi-
fied, and the exposure time is recorded directly on the monitor. The package
can be used to record comments and other data. A cap terminates sampling and
hermetically seals the sample.
Sorbent transfers and other analytical preparations normally comprising
step five are eliminated because the capped monitor is already a discrete
sample ready for elution. Step six, the actual analysis, is aided by in situ
elution of the contaminants from the sorbent. Manual or automatic gas chro-
matographic analysis is also facilitated by the monitor design.
Efforts in preparation of reports, step seven, are reduced by having all
the needed information concerning the sampling on the monitor package for
calculation and reporting. In the next section, the objective is to techni-
cally describe the 3500 system.
PRODUCT DESCRIPTION
A pictoral representation of the monitoring and analysis method using
the 3M Brand No. 3500 Organic Vapor Monitor is shown in Figure 2. Referring
to the numbered steps as illustrated:
1) The monitor is removed from the package. Exposure start time is re-
corded on the back of the monitor.
2) The monitor is attached near the breathing zone of the worker. After
exposure, the exposure end time is recorded on the back of the monitor.
3) The white face of the monitor is removed.
4) The elutriation cap is snapped on, and the ports are sealed.
5) The sampling information is recorded on a package, and the monitor
is inserted. The package is sealed with the tubular closure.
6) The eluent is added through the center port, and the port is imme-
diately resealed.
7) After 1/2 hour (with occasional gentle agitation), the eluent is
decanted into the sampler vial, or an aliquot is removed from the center port
for manual injection.
8) The gas chromatographic sample analysis is carried out by conventional
means.
367
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The time-weighted exposure level is then calculated using the following
equations:
3
mg/m = Corrected weight on monitor (nanograms)
3
Sampling rate (cm /min) x sampling time (mln)
ppm - mg_ 22.4/mole T° K 760 mm Hg
m3 X m.w.g/mole x 273" K x Pmm Hg
The corrected weight on the monitor is obtained from the sample analysis after
corrections are made for blank samples and desorption efficiency. The sam-
pling rate for each contaminant is determined and published by 3M Company, as
discussed in the next section.
PRINCIPLES OF OPERATION
Diffusion Equation
The relationship between environmental contaminant concentration and the
weight of material collected by the monitor is given by Equation 1:
M = lAjt [1]
LI
where M = total mass of contaminant collect (nanograms)
2
D = molecular diffusion coefficient (cm /sec)
2
A = diffusion path area (cm )
L = diffusion path length (cm)
3 3
C = environmental contaminant concentration (mg/m - ng/cm )
t = sampling time (sec).
Equation 1 assumes that the contaminant concentration at the face of the
monitor closely approximates the environmental concentration, that the monitor
wall effects are negligible, and that the collection efficiency of the sorbent
element is unity.
In normal use, environmental concentration (C) is to be determined,
mass collected (M) is determined via gas chromatography, and the monitoring
time (t) is measured. Therefore, a value for the D^- term is needed to solve
L
the equation. Substitution of the appropriate units for D, A, and L reduces
to cm /sec units, which defines the sampling rate for the contaminant and shows
368
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the correspondence between diffusion-controlled monitors and conventional
pump methods. The diffusion-controlled monitors do, in effect, sample the
contaminants in air at a useful, calculable rate. The driving force for
sampling is the concentration gradient between the collection face and the
sorbent layer in the monitor.
Monitor Calibration
Parameters Calibrated. Monitor calibration data are provided by 3M
Company for many organic vapors of industrial hygiene importance. The items
which are provided are:
• Sampling rate (D=- from equation)
Li
• Recovery coefficient
• Exposure limit
• Environmental effects
• Sample storage recommendations
• Concise equations for calculation of results.
Calibration Apparatus. Monitor calibration requires that accurately
known exposures be made. Typical equipment for generating known, time-
weighted, average contaminant concentrations is shown in Figure 3.
The compressed air from the gas cylinder is passed through a charcoal
bed to remove any organic material which may be present. The air flow is
integrated by a calibrated flow meter. The organic liquid to be studied is
placed in the bottom of the diffusion column, which is divided as shown by
a porous membrane. The organic vapor diffuses into the dilution air stream
at a calculable rate, and a wide range of contaminant concentrations are
attainable by varying diffusion column diameter and length, dilution air
flow rate, or diffusion column temperature. The monitor exposure section
is a metal conduit with a series of ports into which monitors fit snugly.
The design permits easy exposure replication to give good estimates of monitor
precision. A simple insert makes adaptation to charcoal tubes possible for
comparison studies. The air stream finally enters a large collection chamber
where the relative humidity is monitored and the contaminant concentration
verified with a calibrated hydrocarbon analyzer. The monitors exposed in
series each removes a small fraction of the contaminant (usually less than
0.5 percent), but the amount removed is calculable, and corrections are easily
made. The dilution air stream can be humidified by several means between
the flow meter and diffusion column.
369
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FIGURE 3 (left). Monitor calibration ap-
paratus .
FIGURE 4 (right). Ethyl acetate
exposure limit.
1000 2000 MOO
EXPOSURE (PPH-HOUftS)
«000 5000
3M BRAND ORGANIC
VAPOR MONITOR
PRODUCT NO. 3500
Oualineallon Dili tot
Btnunt
Monitor Sampling Rata »0 cmVmfti
RKOvtry CoaHlclant Q.»*a.M _
Upptr Expotura Until1 >1MOppm-Houn
COMPOUND PBOMHTIM
• DATA
Motoeular Walght n.11 _
Vapor Prawura (JO*C) J7.B»niH»Jte
PubOthad OKItnlon ContUnt' fl.08» eaf/tue
Otiatty •
T.WJk. (TLV)
CALCULATION MOMMIM
1. Ocltnnim ma* at uMlylt In mteroflmni.
2. DittrmlM npowra Urn* In mlnutw.
3. Calculate conctnlrallon from:
mfl = 30.X (mlerogrmu) = 30.1
"Si1" (noevtry eMlfletenl) (mbiuSt) InOnuttt)
or»
ppm « MXjmlerearamt) = t.UO (naemgnmi
(raeewHy eotHleltnt) (mbnttet) (mbuto)
tfljpm
t. Tht Uppar Eipoturt Limit at MM R.H. It
t PuWterwd dlMutlon eonaldiU an provUad (or ganaral
Inttml only. -Monitor Sampllnfl Mf OJU lor taeh
compound It dttarmlnad by 3M Company.
9. ppm OMtd on M'C. 760 mm Ho.
'HEl
OUl
T = Charcoal Tube
OVM = 3M Organic Vapor Monitor
FIGURE 6 (above). Sampling sequence
gasoline exposure.
FIGURE 5 (above). 3M Brand Or-
ganic Vapor Monitor represen-
tative qualification sheet.
370
-------
When a substantial amount of liquid Is Introduced Into the diffusion
column, the system Is capable of equilibrating to generate stable, known con-
centration environments for long periods of time. More typically, a known
quantity of organic liquid Is added into the diffusion column and allowed to
evaporate to depletion as indicated by the hydrocarbon analyzer. Using this
method, an accurate time-weighted average contaminant concentration can be
determined by only two measurements; a gravimetric weight determination of
organic liquid (mg) and a calibrated flow meter reading (m ). As the organic
liquid evaporates, the concentration varies with time, but the time-weighted
average concentration is known at the end of the experiment. Both diffusion-
controlled monitors and pump methods are capable of integrating variable con-
centration, so this factor is of no consequence.
Calibration Techniques;
1) Sampling rate
The sampling rate of the 3M Organic Vapor Monitor is determined experimentally
by generating known concentrations of each contaminant, exposing and analyz-
ing the monitors, and solving Equation 1 for the D=- term. The published
L
sampling rate is generally based on three separate determinations in the
0.25-2 TLV, 8-hour exposure range. This experimental determination is con-
sidered necessary since desired diffusion coefficients (1,2) are not always
available, and their accuracy is not usually known.
2) Recovery coefficient
The recovery coefficient is determined by vapor-state spiking of monitors.
This is accomplished by removing the white barrier film of the monitor, plac-
ing a filter paper on the diffusion spacer plate, snapping on the elutriation
cap, and injecting a known quantity of the organic material onto the filter
paper through the center port. The monitor is aged 16 to 24 hours before
elution to allow total transfer of the organic material from the filter
paper to the sorbent. The published number represents the mean + 2 standard
deviations from the tests conducted by 3M. It is, however, recommended that
recovery coefficients be at least verified by the user, since techniques
and presence of multiple contaminants can affect recovery coefficients.
3) Exposure limit
The capacity of the monitor for each individual compound is based on molecular
structure, vapor pressure, environmental conditions, etc. The exposure limit
is specified in lieu of a need for a "back-up" section. This is done by
3M by plotting the weight of the contaminant collected by the monitor versus
exposure. (See Figure 4.)
371
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The exposure limit is specified as the weight of contaminant collected
when significant deviation from linear adsorption is noted. For strongly
adsorbed materials, this limit is usually of the order of 15 mg.
4) Environmental effect
The ultimate vapor capacity of the monitor is sometimes affected by relative
humidity. The exposure limit test described above is repeated at 80 + percent
relative humidity, and deviations due to relative humidity are noted.
5) Sample storage
Monitor samples which have received duplicate exposures are stored and ana-
lyzed after 1,7, and 14 days. If deviations are noted, refrigerated storage
is recommended.
Overall information and recommendations are published on qualification
sheets. Figure 5 shows a representative qualification sheet for benzene.
PRODUCT USE DATA
Benzene Monitoring
Using equipment as pictured in Figure 3, known benzene vapor concen-
trations were generated in air and monitored using the published benzene
3
sampling rate (33.0 cm /min). The analytical procedures outlined in the
"Product Description" section were followed. Table I is a summary of results
comparing the 3M Organic Vapor Monitor to the known generated benzene concen-
trations. Tabulated values for the 3M monitor represent the mean of four
separate determinations + 2 standard deviations. The values fall well with-
in the accuracy requirements contained in the OSHA standard.
Complex Mixture Analysis
It is recognized that in real field-monitoring situations, combinations
of organic vapor contaminants are typical, and that any feasible monitoring
system must be capable of complex mixture analysis.
Gasoline was used to test the capability of the 3M Organic Vapor Monitor
to sample complex hydrocarbon mixtures. It was reasoned that the high boiling
components of gasoline would not be present during a typical exposure. To
simulate a more likely field situation, a fraction of gasoline was distilled
372
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TABLE 1
Benzene Monitoring Test
3M ORGANIC VAPOR MONITOR
VS. TEST CONCENTRATIONS
Test
Concentration
(ppm)
7.80
4.13
2.27
1.32
0.99
3M Monitor
No. 3500
Measurement
(ppm ± 20)
7.75 ± 0.43
4.12 ± 0.23
2.22 ± 0.06
1.23 ±0.04
0.91 ± 0.06
TABLE 2
Results of Gasoline Exposure Test
Component!
ol
Gasoline
Pentane
Heptane
Octane
Benzene
Toluene
Xylenet
Test
Concentration
(PPM)
5.602
0373
0.294
0.928
1.768
1.153
3M No. 3500
Concentration
(PPM ±20)
5.832 1.408
0370 t .045
0.307 i .047
0.892 t .160
1.710 t .119
1.230 ±.086
Charcoal Tube
Concentration
(PPM i 2o)
5.053 t 300
0.578 i .082
0.329 t .056
0.873 i .180
1.S52 t .220
1.034 i .160
TABLE 3
Integration of Variable Concentration
UBuUOtnt
(«•"»
„. JL__-
All.
„. ill
1UH0.1MO
ConnnlrlUon
imi.io)
U7;M
ItHt '<
isu.ni
CMroMlTliM
ConctnliMlox
(Pni!lol
M*;>l
IHT ; i>r
Mm* in
373
-------
from a bulk sample. The fraction used was the first 80 percent of distillate
collected. The remaining 20 percent was discarded. A syringe was used to
inject 1.24529 grams of the light fraction through a septum capped port into a
receiving vial. An air flow rate of 9.1924 liters-per-minute was allowed to
pass over the open vial until all the gasoline had evaporated into the air
stream. At the conclusion of the test, the total air volume was determined by
the change in readings of a Model 175-S Rockwell flow meter. A total of 11.581
cubic meters of air had passed during the 21 hours required for the gasoline
distillate to evaporate. A flame ionization detector was used to verify the
test end-point. Charcoal tubes were used to collect samples for comparison and
correlation of test data. The tubes and 3M monitors were randomly selected but
placed in a set pattern on a sampling channel. Two charcoal tubes were placed
side-by-side in the first sampling port, followed by four 3M monitors in ports
two through five. Port six contained two more charcoal tubes, again placed
side-by-side (see Figure 6).
The charcoal tubes were positioned vertically to prevent channeling, and
the 3M monitors were positioned so that the air stream would be flowing parallel
to the face of the monitor at approximately 100 fpm air velocity. One and one-
half milliliters of spectroquality carbon disulfide were used to desorb the
collected gasoline vapors. The samples were allowed to set for 30 minutes with
occasional agitation, and were then transferred to a vial. Withdrawal of a 2
microliter aliquot from the sampling vial, and injection into a Hewlett Packard
5840A gas chromatograph, was accomplished by using a Hewlett Packard automatic
sampler (Model 7671A). The analytical column was a 7 .5 ft x 1/8 in S.S. tube
packed with 15 percent Carbowax 20M on 80/100 mesh Chromosorb W. A temperature
program was used, starting at 70° C for 5 minutes and increasing to 125° C at
the rate of 4° C per minute. A hold of 8 minutes was used on the final temper-
ature. Helium (30 cc/minute) was used as the carrier gas.
Quantification of pentane, heptane, octane, benzene, toluene, and xylenes
was accomplished by preparing four calibration standards for each component.
Each standard was individually prepared by injecting a known volume of each
component into a known volume of carbon disulfide. The four data points were
used to establish a best fit line from the linear regression method. The
weight of each component was determined by comparing the peak area of the sample
to the calibration line. This weight was corrected for desorption efficiency,
and the time-weighted exposure level was calculated in milligrams-per—cubic-
meter and converted to ppm. Figure 7 shows a replication of the chroraato-
graphic analysis made of the parent, 3M monitor, and charcoal tube samples.
374
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mmNTOMOUNt
FRACTION
(LUtMTflKW
MIMOMTtM
CMMCOALTUM
FIGURE 7. Chromatographic anal-
ysis gasoline exposure.
Inlet
-*
1
POROUS METAL
,- —..BAFFLES — —
1
o O
o O
o O
v^
-» /"N
o O
o O
o O
/ \
\
1
i
I
Outlet •
AIR VELOCITY
MONITORING PORTS
MONITOR EXPOSURE
HOLES
FIGURE 8. Monitor exposure
chamber air velocity study.
o
w
« «i
i • •
o
I .
§ -10 ,
§ -11
i
• *
i
r
•
'
I
1
100 110
AIR VELOCITY (FT/MM)
FIGURE 9. Air velocity depen-
dence (parallel-to-face) .
375
-------
The chromatographs are identical except for peak amplitude, which illus-
trates that both monitoring techniques sample each vapor as if it were pre-
sent Individually.
The desorption efficiencies for components of gasoline were determined
in the presence of one another. The recovery tests were done on both the
charcoal tubes and the 3M monitors. A known amount of each component was
injected onto 100 mg sections of the charcoal tubes or onto a piece of Whatman
filter paper 2.5 cm in diameter in the 3M monitor, as described earlier.
The analytical results of the charcoal tubes and 3M monitors agree very
well with each other, and with the actual test concentration (Table 2).
In all cases, the 3M monitors gave lower standard deviations and better
agreement with the challenge environment. The concentration of the selected
components in gasoline was determined by injecting known volumes of the
light gasoline fraction into known volumes of carbon disulfide and analyzing
in the same manner as the monitor samples.
Integration of Concentration Spikes
To verify the ability of the No. 3500 Organic Vapor Monitor to integrate
high peak concentrations, several test exposures of 1, 3-butadiene were made
using an exposure system as described in Figure 3, except that an injection
septum was placed in series between the flow meter and exposure channel.
In each case, charcoal tubes were used to collect samples for comparison and
correlation of test data. During sampling, a randomly selected charcoal tube
was positioned vertically and upstream of a 3M Organic Vapor Monitor. The
3M monitor was positioned in such a way that the air flow was parallel to the
3
face of the monitor. The charcoal tubes had a sampling rate of 52 cm -per-
3
minute. The sampling rate of the 3M monitor is 41.3 cm -per-mlnute for the
collection of 1, 3-butadiene.
Three different concentration levels were used to challenge the tubes
and 3M monitors, and each level was replicated three times. The first con-
centration used was a single spike generated by injecting 5 ml of butadiene
vapor into the air stream at a flow rate of 9.774 liters-per-minute, thus
giving a TWA of 528 parts-per-million as determined by the total air volume
(flow meter) and the weight of 1, 3-butadiene injected. The next concentration
(1,585 ppm) was generated by three injections of 5 ml each. The last test
concentration (3,170 ppm) was produced by three injections of 10 ml each.
The spike generations were monitored by a total hydrocarbon analyzer equipped
376
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with a flame ionlzatlon detector. The signal output from the detector was
connected to a millivolt recorder to give a chromatogram of each injection.
The sampling probe for the total hydrocarbon analyzer was placed downstream
from the charcoal tubes and 3M monitors such that no interferences would be
caused during the sampling. It was noticed from the recorder chart that each
spike was generated in approximately 6 seconds. This means that the actual
peak concentration was in the range of half a percent (5,000 ppm) for 5-ml
injections, and 1 percent (10,000 ppm) for 10-ml injections. The results
are shown in Table 3.
Clearly, both the 3M monitors and the charcoal tubes with pumps effectively
integrated the abrupt concentration changes to give a good estimate of the
time-weighted average concentration.
Air Velocity Effects
Diffusion-controlled environmental monitors require a slight air move-
ment across or impinging upon the face of the monitor. Use of Equation 1
assumes that the contaminant concentration at the face of the monitor is rep-
resentative of the overall environment. In stagnant air, the contaminant
is removed from the atmosphere by the monitor. This results in a depleted
zone at the face of the monitor and an underestimation of the true contaminant
concentration. Previous work (3) studied air velocities above 50 fpm.
Experiments were conducted to determine the air velocity requirements for
the 3M No. 3500 Organic Vapor Monitor. The exposure apparatus shown in Figure
3 was employed, but the monitor exposure channel was designed as shown in
Figure 8.
The air velocity in the exposure channel was controlled by adjusting air
flow rate.
Air velocity was calculated from the flow rate and the exposure channel
cross-sectional area. Uniformity of air velocity was also measured using
an anemometer probe in the ports indicated. Several exposures to known
benzene concentrations were made, and the sampling rate was determined. A
total of six monitors was exposed at each air velocity level. Elution and
analysis were done following standard procedures outlined previously. Figure
9 is a plot of the results.
The plot shows a significant drop in benzene sampling rate below 10 ft/rain
377
-------
face velocity. The + 2 standard deviation error bars indicate considerable
variability at low air velocity. This reflects the difficulty in achieving
reproducible, uniform, low velocity in the exposure channel. The mean values
do, however, conform well to the published sampling rate for benzene at the
higher velocities, and the results are believed to be valid. It should be
noted that this experiment tested only parallel-to-face air velocity effects,
which is the worst case situation.
As a result of these data, it is believed that the air velocity require-
ments of the 3M Organic Vapor Monitor are minimal and of no concern for per-
sonal monitoring. When used as an area sampler, however, placement of the
monitor should be considered so that stagnant air areas are avoided. This
situation could potentially exist against walls, in corners, etc.
Temperature and Pressure Effects
Both temperature and pressure affect the diffusion rate of gaseous con-
taminants in air. This could, in principle, lead to substantial monitoring
errors using diffusion-controlled monitors. However, the net effects of tem-
perature and pressure are offset to some degree- by corresponding changes in
contaminant concentration (4). In the case of atmospheric pressure, the
change in diffusion rate and concentration offsets each other exactly, and no
correction is required. The effect of temperature on diffusion coefficient
and concentration is given by Equations 2 and 3.
D - ttT"/*; [2]
«
C -
Therefore,
Weight collected -
The net temperature effect can be compensated, if desired, by increasing
the experimentally determined concentration in mg/m units by 1.08 percent
for every 10° F above 70° F (and reducing by 1.08 percent for every 10° F
below 70° F).
REFERENCES
1. Gilliland, E.R. Diffusion Coefficients in Gaseous Systems. Ind and
Eng Chemistry, June 1934.
378
-------
2. Nelson, G.O. Controlled Test Atmospheres. Ann Arbor Sci Publ, 1971.
3. MeGammon, C.S., Woodfin, J.W. An Evaluation of a Passive Monitor for
Mercury Vapor. Am Ind Hyg Assoc J 38:378, 1977.
4. Palmes, E.D. Personal Sampler for Nitrogen Dixoide. Pres Am Ind Hyg
Conf, Minneapolis, Minn., June 1975.
MAILING ADDRESS OF PRIMARY AUTHOR
Donald Gosselink, Ph.D.
Occupational Health and Safety Products Division
3M Company
St. Paul, Minnesota 55101
Discussion
PETROVICK: Matt Petrovick, EPA. I think you have a very nice little
exposure meter. The size particularly appeals to me from the standpoint
of human mobility. 1 think it is something that is easy and nice to wear,
and light.
It is the kind of thing that makes room for physiologic data acquisition
systems which may be bulky. And, together, I think they fit nicely. That's
one of the prime advantages that I think you have.
The other thought that occurs to me is this: Has there been any plan-
ning or any designing in an attempt to try and convert some of the measured
exposure levels to an electrical signal—for example, such that you may be
able to look at the integrated accumulative effects of these pollutants?
In other words, the transfer function from the electro-organic chemistry
level to some measurable signal that might be able to be placed into a micro-
computer or memory, so that if the level is exceeded, an alarm can be issued
so that the person who is exposed might be made aware of it? Is there any-
thing like that on the horizon?
BRAUN: I am an engineer at 3M. Sometimes I can understand what our
people in Central Research are doing, and I wouldn't be a bit surprised if
they are, but my own work has been mostly in the sampling and the diffusional
aspects. It could be done. I think you conveyed some very Interesting
thoughts.
PETROVICK: I have a very strong feeling that that's the way to go if
you want to alarm a person. It is no use to send the device to the lab, and,
you know, 4 days later find out he was endangered.
379
-------
BRAUN: That's a good point.
LOCKER: Larry Locker of Solid State Sensors. I think that's an ele-
gant way, but you look at the compounds like mercury, benzene, trichloroethyl-
ene—I think the long-term effects of low levels are what are of concern.
I think that the idea here is that you can monitor those for an extremely
low cost. And usually 4 days is not so bad to know that someone was exposed
to 10 or 20 parts-per—million of benzene* He's not going to die on the spot.
BRAUN: I would like to just comment, too, that we are really building
a record of safe operations, and that's a good thing to be doing; it really
is.
PETROVICK: But to respond to your comment: What about the person work-
ing in a factory who has been there 10 years, and he has an accumulative re-
sidual of this chemical, whatever it might be, and one of these days, he
crosses his tolerance threshold, and it is that day he might sicken or drop dead?
LOCKER: That's why he should have periodic monitoring, according to the
N10SH regulations.
PETROVICK: That's right. But, wouldn't it be nice for him to have some
early warning capability, in terms of something he can hear, saying some-
thing like: "Hey, get the heck out of the room"? That's the kind of ration-
ale I had in mind.
JENSEN: Janice Jensen, with the EPA in Washington. What kind of in-
terferences are there with a benzene monitor?
BRAUN: Well, you see—the analysis is by GC or GC mass spectrometry
or whatever method you utilize; because the monitor, up to the limits we are
talking about, would just collect most organics. We haven't worked with all
of them, but, you see, the answer is that the interferences, if there are
any, are resolved by the analytical instrument.
DEBBRECHT: Fred Debbrecht, AID. I didn't quite understand the calibra-
tion system that you used. Are you counting on that benzene evaporating
uniformly?
BRAUN: No, we don't care. When you inject the benzene through the
septum, you are going to get a rise and then a gradual drop off. The area
under the curve that the monitor integrates is milligrams-per-meter cubed.
And we don't care if the curve is level or not.
DEBBRECHT: Is the system reasonably similar to charcoal tubes? I assume
you have got some adsorbent there?
BRAUN: Yes.
DEBBRECHT: Certainly the efficiencies that charcoal tubes work at are
subject to the concentration of material and amount adsorbed, as opposed to an
integrated effect. They are not 100 percent efficient in capturing the pol-
lutant.
380
-------
BRAUN: As a matter of fact, the concentration profile is quite flat up
until you enter the device—we know about where it is within 10 percent,
so that we can Just operate reasonably. The main concept there is that it
is a simple, repeatable way to give a known time-weighted average; that's all
I am really saying*
HODGESON: The main question about the calibration system is are you
collecting all organic data with your exposure?
BRAUN: No; not at all.
HODGESON: How do you know how much; what's the efficiency?
BRAUN: Well, it is moving past the device, and that's just like the
configuration we use in the environment. In fact, about 1 percent is all we
collect.
HODGESON: One other question. You didn* t say much about the actual
construction of the device. Is it diffusing through a membrane?
BRAUN: Yes, and then through a static layer of air.
GOLD: I was curious to know whether you looked at the effect of water
vapor and temperature?
BRAUN: Yes; part of that qualification procedure is that we analyze
results at both high and low humidities. Usually the effect of water vapor
is to decrease the range of utility of the monitor by a little bit. Yes, we
do that.
GOLD: How about temperature?
BRAUN: Over the temperature range of normal human existence, this ef-
fect is negligible—at least for the compounds we are working on.
BREEN: I am not sure if I understood—do you have any data on parts-
per—billion exposures?
BRAUN: No. The data I showed were at the 450 parts-per-billion level
corresponding to occupational exposures.
WHITE: Are you limited in terms of the sensitivity of the GC mass
spectrometry?
BRAUN: That's correct.
WHITE: If you improved the sampling efficiency, as we were discussing
with Ed Palmes, you might be able then to go to the ambient exposure levels.
BRAUN: Yes, and then you can make it bigger, like a big sunflower.
BREEN: Well, isn't it part of the problem at the lower levels that you
may get quantitative desorption?
381
-------
BRAUN: We are not sure whether that occurs. That's why we would like
to look into it; absolutely. I would like to work with any interested
people at this conference to develop this device for use with daily ambient
exposures.
382
-------
A Combination Sorbent System for Broad
Range Organic Sampling in Air
Joseph J. Brooks, Ph.D., Diana S. West, and Donald J. David
Monsanto Research Corporation
Dayton, Ohio
arid
James D. Mulik
Organic Pollutant Analysis Branch
Environmental Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina
INTRODUCTION
The use of solid sorbent materials as sampling media is rapidly becoming
the method of choice for the collection and preconcentration of organic
pollutants in air. Unfortunately, no single sorbent material is available
that is universally applicable to the broad range of organic compounds that
may be present in environmental and workplace samples. For this reason, ad-
ditional sorbent materials are needed to supplement the sorbent character-
istics of the more commonly used materials (e.g., Tenax-GC and activated char—
coals) in applications requiring broad range sampling efficiency.
In light of this need, a program has been initiated to evaluate the
sorbent characteristics of some commercially available sorbent materials
with the aim of finding a suitable combination of sorbents that is capable
of efficiently collecting compounds representing a broad range of volatilities
and polarities. The ultimate objective of this EPA-sponsored program (Con-
tract No. 68-02-2774) is to develop a portable, sorbent-based collection
system that is capable of sampling a wide variety of carcinogenic vapors in
ambient atmospheres.
This paper describes the evaluation and selection of the sorbent materials
and suggests a technique for estimating the applicability of sorbent materials
for sampling a particular compound based on certain compound properties.
The anticipated performance characteristics of the selected combination sorbent
383
-------
system are also discussed.
DISCUSSION
Selection of Candidate Sorbents
Before initiating studies to evaluate and select sorbent materials, a
comprehensive review was conducted of available literature on the use of solid
sorbent materials for sampling organic vapors. Information was collected on
specific sampling applications for over 110 compounds using more than 30
different sorbent materials. This survey indicated three major classes of
sorbent materials: 1) porous polymers (e.g., Tenax-GC, Porapaks, Chromosorbs,
XADs); 2) carbonaceous materials (e.g., activated carbons and charcoals,
graphitized carbon black, Ambersorbs); and 3) others (e.g., molecular sieves,
silica gel, liquid-coated solid supports).
Generally, the porous polymers were found to have the most desirable
properties for air sampling, including low background and low reactivity,
as well as high capacities for many compounds. Unfortunately, the porous
polymers were found to have little capacity for the more volatile compounds.
On the other hand, the carbonaceous materials were noted to have much better
capacities for volatile compounds, but are plagued with reactivity problems
and problems associated with hydrophilicity. The other sorbent materials
generally had intermediate capacities and various associated sampling problems,
and they have not been widely utilized in air sampling applications. Specific
candidates were selected from these three groups of sorbent materials.
The goal of this selection was to choose a collection of commercially
available materials that, when used in an appropriate combination, showed
promise for quantitatively trapping compounds varying widely in volatilities
and polarities. To do this, it was necessary to compare the trapping capa-
bilities (capacities) of a sorbent for various compounds with parameters that
are indicative of volatility and polarity.
Consistent trends in sorbent capacities were seen when related to com-
pound volatilities, as indicated by either vapor pressure or boiling point,
with boiling point being the more convenient parameter. Unfortunately, find-
ing a single polarity parameter that resulted in consistent sorbent capacity
trends was not as easy.
384
-------
After considerable effort, an empirically derived relative polarity
ranking of compound functionalities was arrived at based on a weighted com-
bination of polarity parameters, including dipole moment, solubility parameter,
hydrogen bonding index, and polarity index. The order of polarity obtained
by this scheme was hydrocarbons < halogenated compounds < aldehydes w ethers «
esters « ketones < nitro compounds < nitriles « strong acids < amines <
alcohols « phosphates < water. This functionality ranking was used in plots
of boiling point versus relative polarity for a variety of compounds, and
consistent trends were observed for most of the available sorbent capacity
data when superimposed on these plots.
On the basis of these plots and related capacity information, Tenax-GC,
Forapak N, Forapak R, Ambersorb XE-340, and SKC activated charcoal were se-
lected for further evaluation.
These five sorbents represent three porous polymers and two carbonaceous
materials that have a variety of individual properties and the potential,
in some combinations, to effectively sample compounds of a wide range of
polarities and volatilities. Tenax-GC was selected for the collection of
moderately high to high boiling compounds, since it has a high temperature
limit. Tenax also has a slight preference for nonhydrogen-bonding compounds.
For moderately boiling compounds, the literature showed Porapak R to have the
greatest capacity, although retention time data indicated that Porapak N
(for which there were no capacity data) might actually have greater capacity.
These two Porapaks also show a preference for polar compounds. For highly
volatile compounds, a conventional activated charcoal (SKC coconut) was chosen
for evaluation, since activated carbons have traditionally been used in such
sampling applications. However, a new sorbent material, Ambersorb XE-340
(Rohm and Haas) was also included since it showed promising capacities for
highly volatile compounds (e.g., 81 1/g for butane [3]) without some of the
undesirable characteristics of charcoals (e.g., hydrophilicity).
Selection of Test Compounds
In order to evaluate the selected sorbent materials for their sampling
capabilities, it was necessary to establish a matrix of test compounds that
sufficiently describe the ranges of volatilities and polarities that could
reasonably be anticipated. Entries were sought for a matrix described by
low, medium, and high polarity in one dimension and low, medium, and high
volatility in the other. The ranges were established on the basis of relative
boiling points for volatility and compound functionality, as previously
385
-------
TABLE 1
Test Compound Matrix
Polarity
Hydrocarbons and
halogenated
compounds
Halogenated compounds,
aldehydes, ethers,
ketones and esters
Nitro compounds, nitriles,
amines, and strong acids,
alcohols and phosphates
Volatility
Low
n-Hexadecane [1]
T/HJ
Phenanthrene [10]
M6dium NaphSile^e [13]
„. . n-Butane [7]
Benzene [16]
Medium
Hexachloro-l,3-butadiene [2]
4-Bronvodiphenylether [11]
bis-(2-Chloroethyl) ether [5]
1 , 2 , 4-Tr ichlorobenzene [14]
Propylene oxide [8]
Benzyl chloride [17]
High
Succinonitrile [3]
-------
RETENTION TIME
(RT)
INJECTION FIRST ELUTION TIME
I(FET)
FIGURE 1. Elutlon analysis method for sorbent capacity determinations.
detector (FID). Sample sizes were within the Henry's Law region such that
retention times were not affected by variations. The data obtained included
the retention time (RT), which was considered to be the amount of time from
injection to peak maximum, and the first elution time (FET), which was the
TABLE 2
Retention Times and Capacities for
Selected Test Compounds on Porapak R
Ttmpora-
tur« (*C) n-Butan*
RT "
50*Vq "
222 PR-
'"v, '
RT •
182 50*Vg "
PR -
RT •
150 50%Vg "
PR -
RT •
100 M*Vg *
PR •
0.17 min
8.22 x 10*
0.04 Bin
1.94 x 10*
0.26 min
12.6 x 10*
0.10 min
4.84 x 10*
0.50 min
24.2 x 10*
0.30 Bin
14.9 x 10*
2.11 Bin
102 x 10*
1.6 Bin
t/g
t/g
t/g
t/g
t/g
t/g
»/«
Propylene oxide
RT -
50%Vg "
PET •
FBTVg "
RT -
50%V,-
PR -
FBTVg *
RT •
5Wv, •
PR •
RT •
PR -
77.4 x 10» t/g FRy •
0.20 min
9.68 x 10* t/g
0.05 min
2.42 X 10* t/g
0.33 min
16.0 x 10* t/g
0.15 min
7.26 x 10* t/g
0.68 min
32.9 x 10* t/g
0.40 min
19.4 x 10* t/g
3.49 Bin
169 x 10* t/g
2.9 min
140 x 10* t/g
Compound
Acrylonitril*
RT -
50%Vg '
FET "
mvgm
RT -
50%v, '
PR •
""vg"
RT •
M%Vg "
PR •
mvg"
RT «
50%V, "
PR •
mvg "
0.24 min
11.6 x 10*
0.12 min
5.81 x 10*
0.46 min
22.3 x 10*
0.35 min
16.9 x 10*
1.00 min
48.4 x 10*
0.8 min
38.7 x 10*
6.35 min
307 x 10*
5.4 min
261 x 10*
».'g
t/g
t/g
t/g
t/g
t/g
t/g
t/g
iio-Octan*
RT «
50»Vg '
PET •
^Vg"
RT "
0.85 min
41.1 x 10*
0.40 min
19.4 x 10*
2.67 min
t/g
t/g
50% - 129 x 10* 1/g
PET •
mvgm
RT •
2.0 min
96.8 x 10*
10.33 min
t/g
50«y > 500 X 10* t/g
PR »
8.45 Bin
PR • 409 X 10* t/g
RT •
*o«v9 •
PR «
""vg"
150 Bin
7,260 x 10*
125 Bin
6,050 x 10*
t/g
t/g
Bu»«n*
RT - 0.47 min
SOly - 22.7 x 10* t/g
PR - 0.25 min
PR • 12.1 x 10* t/g
RT » 1.12 min
50^ • 54.2 x 10* t/g
PR • 0.80 min
FBTy - 38.7 x 10* t/g
RT - 3.23 Bin
50*y • 156 x 10* t/g
PR - 2.60 Bin
PRy - 126 X 10* l/g
RT - 28.6 Bin
50^ - 1,380 x 10* t/g
PR • 23.5 min
mv - 1,140 x 10* t/g
387
-------
00
00
-4.0
•3.0
-2.0
-LO
ao
LO
2.0
3.0
4.0
5.0
6.0
7.0
10
n-SUIANE
PROPYUEHE OXIDE
ACRVLONITRILE
BENZENE'
ISO-OaANE
4.0
3.0
l/Trtciilfl1
2.0
LO
FIGURE 2. Plot of log 50%v
versus 1/T for selected test
compounds on Porapak R.
-4.0
-3.0
-to
-LO
ao
_ LO
S*
3.0
4.0
5.0
10
?.o
LO
n-BUTANE
. PROPYLENE OXIDE /
^
AamailTRIlE-^
BENZENE
ISO-OCTANE
4.0
3.0
2.0
FIGURE 3. Plot of log FETy
versus 1/T for selected test
compounds on Porapak R*
LO
•2.0
-LO
ao
LO
2.0
' 3.0
4.0
5.0
6.0
7.0
10
9.0
lao
BENZYL CHLORIDE
BIS-<2-aURO£THYl)
ETHER
4.0
10
2.0
FIGURE 4. Plot of log
V
versus 1/T for selected test
compounds on Porapak N.
LO
-------
TABLE 3
Volumetric Capacities for Selected
Test Compounds on Porapak R at 20° C
COMPOUND NAME FET (1/g)
Vg
n-Butane 4.93
Propylene oxide 12.4
Acrylonitrile 16.8
iso-Octane 3,550
Benzene 175
time from injection to peak initiation. These points are indicated in Figure
1. By multiplying the retention times and first elution times by the flow
rate, and dividing by the amount of sorbent within the chromatographlc column,
the 50 percent (50% ) and FET (FET_ ) volumetric capacities, respectively,
were obtained. Sample injections were then made at a variety of column
temperatures to obtain similar data.
An example of the experimental information obtained with Porapak R is
given in Table 2. These data were used to obtain an Arrhenius plot (log Vg
versus 1/T). Figures 2 and 3 are examples of these plots for the 50% and
FET values, respectively, for Porapak R. The FET.. values were then ex-
trapolated to 20° C to obtain the approximate ambient volumetric capacities,
FET.. ,2o° c*t of this sorbent for the test compounds. Table 3 gives this
information for Porapak R.
The volumetric capacities, for as many of the test matrix and low molec-
ular weight aliphatic compounds as possible, were determined for the other
sorbent materials in a similar manner from the plots shown in Figures 4, 5, 6,
and 7. They are compiled in Table 4.
The volumetric capacities (1/g) determined in these evaluations estimate
the volume of air that can be sampled per gram of sorbent materials before
sample breakthrough (i.e., exceeding capacity). This was determined to be
the most applicable measure of capacity for our studies since we wish to
sample quantitatively (i.e., no breakthrough).
Methods (2) are available for determining saturation (or weight) ca-
pacities, but for this project it was felt that sampling techniques, such as
389
-------
so
o
low Poumirv
A MEDIUM POLARITY
O HIGH POLARITY
aw j.o
im°m i vf
-4.0
-3.0
-2.0
-LO
ao
g* 2.0
§
3.0
4.0
5.0
6.0
7.0
LO
METHANE •
ETHANE-
PROPANE
/
BUTANE
PENTANC
t
HEXANE'
4.0
3.0
l/Tt°KI 1103
2.0
-4.0
-XO
•2.0
-LO
0.0
LO
t
f"
4.0
S.O
6.0
7.0
LO
METHANE'
ETHANE
PROPANE'
BUTANE
PENTANC
LO
4.0
3.0
urfcuio*
2.0
LO
FIGURE 5. Plot of log FETy
versus 1/T for all test compounds
on Tenax-GC. Numbers correspond
to bracketed numbers in Table 1.
FIGURE 6. Plot of log FETy
versus 1/T for standard gases on
Ambersorb XE-340.
FIGURE 7. Plot of log FETy
versus 1/T for standard gases
on SKC charcoal.
-------
TABLE 4
Compilation of Capacity and Solubility Parameter Data
Tenax-GC
Key
A
B
C
D(7)
B
8
9
P
16
4
6
3
18
17
13
5
12
15
10
1
14
11
2
Nane
Methane
Ethane
Propane
n-Butane
n-Pentane
Propylene oxide
Acrylonitrile
n-Hexane
Benzene '
1 BO- Octane
Bthylene glycol
Succinonitrile
Phenol
Benzyl chloride
Naphthalene
Bis- (2-chloroethyl)
ether*
o-Hitroaniline
m-Nitroanisole
Phenanthrene
n-Hexadecane
1,2, 4-Sr iohloro-
benzene*
4-Bromodiphenyl
ether"
Hexachloro-1 , 3-
butadiene"
(lit)
89
180
282
395
505
534
557
629
719
788
906
-
1176
-
1269
1402
-
-
1747
1811
-
-
—
(calc)
.
-
282
401
519
-
573
638
719
834
-
1073
1253
1410
1402
1657
1684
-
1766
2014
2616
*
2783
MH
16.04
30.07
44.09
58.12
72.15
58.08
53.06
86.17
78.11
114.22
62.07
80.09
94.11
126.58
128.16
143.02
138.12
153.13
178.22
226.43
181.46
249.11
267.6
FETVg(20°C)
U/g)
_
-
-
0.16
.-
3.14
9.35
.
82
0.532
120
1.04 x 10"
5460
1.02 x 10"
3260
1.06 x 10"
2.9 x 10"
1.14 -x 10"
1.9 x 10«
1.3 x 10°
1.57 x 10"
2.4 x 10«
1.15 x 10"
log
FETv«,
_
-
-
-0.800
-
0.497
0.971
-
1.914
-0.274
2.070
4.015
3.737
4.007
3.513
4.025
4.460
4.058
6.282
5.113
4.195
6.377
4.059
Porapak
FETVg(20"c)
U/g)
.
-
-
4.93
-
12.4
16.8
'
175
3550.
-
_
_
-
-
-
-
-
-
-
-
-
—
R
log
PETV
_
-
-
0.693
-
1.092
1.225
-
2.244
3.550
-
_
-
-
-
-
-
-
-
-
-
-
~
Porapak N
FBT IOQ
U/S) FETVg
.
-
-
3.9 0.591
-
17.6 1.246
69 1.839
-
239 2.378
2900 3.462
-
_
3 x I01ab 12.477b
6.6 x 10s 5.820
-
2.8 x 10s 6.443
-
-
-
-
-
-
— —
Ambersorb XE-340
FBTVg(20«C) 10*
U/q) FETVq
0.009 -2.046
0.229 -0.640
5.33 0.727
106 2.025
7500 3.875
-
-
4 x 10s 5.602
-
-
-
-
-
-
-
-
-
-
-
-
-
-
- -
SKC charcoal
FBTVg(20'C) log
0.047 -1.328
2.40 0.380
162 2.210
12 x 10" 4.079
2 x 10s 5.301
-
-
-
-
-
-
_
_ _
'-
-
-
-
_
-
_
_
_
-
Halogenated.
Potentially large experimental error.
-------
the use of backup tubes and varying sampling volumes, would be an appropri-
ate manner of obtaining valid samples in the event of highly concentrated
samples.
As it is a long and arduous task to determine the capacities of a large
number of compounds on several sorbent materials by the method just described,
it was thought that a means of correlating sorbent capacities with compound
properties would be highly desirable. Such a means of correlation would per-
mit the estimation of the FET ..-„ . of any compound on any sorbent by
knowing the value of the particular property or properties, and how this prop-
erty is related to sorbent capacity. Then, if a change or addition should
occur in the list of compounds of interest, one could state whether the new
compound is probably, possibly, or not likely to be quantitatively trapped
by a particular sorbent under certain conditions. If sorbent materials were
used in series for sample collection, one would also have an idea of on which
sorbent the majority of a certain compound is likely to appear. The general
advantage of a means of correlating sorbent capacity and compound properties
would be to eliminate the necessity of experimentally determining the capacity
of every compound on every sorbent.
The forces that determine the interaction of an organic compound with
other materials (neglecting vapor-to-liquid phenomena of nucleation and growth)
are: E., the dispersion or London forces; E , the permanent dipole/dipole
forces; and E the hydrogen-bonding forces. These forces are additive, and
the total interaction energy may be expressed as E « E . 4- E + E, . Dividing
both sides by the nuclear volume of the material, one obtains:
E, + E + E.
Since 6 + \\i] - cohesive energy density
where 6 is the solubility parameter, then
The solubility parameter has been well described in the literature (1).
Many experimental methods exist to determine $ for a compound, and many more
methods exist for estimating 6 from compound properties such as surface tension.
A very useful method of estimating 6 from the structural formula, density,
and molecular weight of a compound has been developed by Small (4).
392
-------
Accordingly, 6^, 6 6^, and 6 were examined for a number of compounds.
No correlation of the separate or total forces with the FET (2QO . was found,
One would expect a correlation with the dominant force factor, if one should
exist, and a correlation with 6 would seem even more reasonable. However,
of two compounds with similar 6 values, the compound with the higher molecular
weight (or size) would be expected to have a larger FET (2QO . on a given
sorbent due to its lesser volatility. Therefore, various molecular weight
adjustments of 6 were tried. The simple expedient of multiplying 6 by the
molecular weight gives a relative size dependent factor, 6 - 6 x MW, which
has the units of (g x cal)^/(cm x mole) . The molecular weight modified
solubility parameters ( fi^) for the test matrix and low molecular weight ali-
phatic compounds, both from literature and calculated (2) solubility parameter
values, are given in Table 4 along with sorbent capacity data. The data for
« are plotted versus the log FETVg/2o° c) for SKC charcoal» Amb' rsorb XE-340,
Porapak N, and Tenax-GC in Figure 8, and for Porapaks R and N in Figure 9.
The correlation coefficients for the "best" lines in these figures are given
in Table 5.
Note that the most divergent results occur for a few halogenated com-
pounds on Tenax-GC. Unusual behavior of such compounds on Tenax-GC had been
noted previously during capacity studies. It was postulated that some sort
of solubility effect was possible occurring, since Tenax-GC has a solubility
parameter similar to that of halogenated compounds and is known to be soluble
in such halogenated solvents as chloroform, carbon tetrachloride, and methy-
lene chloride.
Desorption Properties
A number of experiments were conducted to determine how amenable the
candidate sorbents are to thermal desorption. These experiments were of a
preliminary nature, since desorption properties are compound dependent, and
the test matrix compounds are not necessarily the compounds that will be of
interest in future field studies. The preliminary experiments that were con-
ducted attempted to evaluate the sorbents for efficient compound desorption
and extraneous background due to contamination and/or sorbent characteristics.
For the desorption efficiency experiments, 6-in long, 1/4 in O.D., 4 mm
I.D. glass sampling tubes were packed with the sorbent materials listed in
Table 6 and evaluated on the desorption/analytical system depicted in Figure
10. Note that the Chromalytics Concentrator® oven contains a six-port, two-
position valve which is sketched in Figure 11. This valve offers the alter-
393
-------
o TENAX
PORAPAKN
O AMBERSORB XE-340
a SKC ACTIVATED CHARCOAL
m FROM LIT 5
mFROMCALC3
* HALOGENATED
* POTENTIALLY LARGE
EXPERIMENTAL ERROR
1000
2000
3000
4000
5000
FIGURE 8. Correlation of 6 and log FET_, ,«ft0 «\ for test compounds on sor-
m VgllU UJ
bent materials. Entries correspond to key in Table 4.
* POTENTIALLY LARGE
EXPERIMENTAL ERROR
FIGURE 9. Correlation of «B and log FETy ,20« c» for selected test compounds
on Porapaks R and N. Entries correspond to key in Table 4.
394
-------
TABLE 5
Correlation Coefficients for the "Best" Lines of
versus Log FET
Vg(2Q
Plots (Figures 8 and 9)
SORBENT MATERIAL
FETVg(20° C)
CORRELATION COEFFICIENT
SKC charcoal
Ambersorb XE-340
Porapak N
Porapak R
Tenax-GC
Tenax-GC (excluding
halogenated compounds)
0.996
0.999
0.993
0.944
0.806
0.916
native of direct syringe injection of a standard or thermal desorption of
a sampling tube. Standards were prepared with a 1,000 pg/ml concentration
in acetone and stored in septum-capped vials. Chromatographic conditions
were established by direct injections of standards using a 7 ft, 1/4 in O.D.,
2 mm I.D. glass analytical column containing 1.125 g of Tenax, which was
conditioned at 320° C overnight. For statistical determination, replicate,
direct injections (
-------
TABLE 6
Sampling Tube Data (All Sorbent Filled Tubes Have Glass Wool Plugs)
Sorbent material
Tenax (60/80 mesh)
Tenax (60/80 mesh)
Tenax (60/80 mesh)
Porapak R (50/80 mesh)
Porapak R (50/80 mesh)
Porapak N (50/80 mesh)
Porapak N (50/80 mesh)
SKC activated charcoal
SKC activated charcoal
SKC activated charcoal
Ambersorb XE-340
Ambersorb XE-340
Ambersorb XE-340
Ambersorb XE-340
Tube
No.
38
7
33
26
15
40
30
34
27
17
41
43
839
847
Soxhlet
extraction information
None
Overnight with MeOH
Overnight with each
MeOH, EtOAc and pcntane
None
Overnight with MeOH
None
Overnight with MeOH
None
None
None
None
None
None
Overnight with each
MeOH and distilled H30
Amount of Manufacturer's
sorbent temperature Conditioning Desorption
material limit temperature temperature
(g) ("C) (»c) (*C>
0.1218
0.1507
0.1399
0.2604
0.2805
0.3735
0.3386
0.4165
0.5176
0.5507
0.6114
0.5234
0.7179
0.7201
400 325
400 325
400 325
250 175 and 240
250 175 and 240
190 175
190 175
325
320
320
320
320
325
325
300
300
300
170
170
170
170
300
300
300
300
300
300
300
TABLE 7
Chromatographic Conditions and Raw Data for
the Determination of Desorption Efficiencies
Compound
ChroBatoaraphle
condition!
Avaraaa Avaraga «r«« Com).
W Of COIt/Ill SaBpHna taBp.
atandarda for atandard tuba (»C)
Daa.
taap. Ml
I'd Trial »td.
Daaorptlon
Araa affielaney
oounta {%)
TaBparatura PrograBBad
froB SO'C t 2-C/Bln
for 10 Bin than t
!~" 32»C/Bln to a final
octMn* 250*C taaparatura
and hald thare for
alght Blnutaa
TeBparature PrograBBed
frOB 150'C to 250*C
8 8*C/Bln and hald
temperature for
4 Binutaa
TeBp. Prog. froB 200 -C
Phananthrana to 100*c ( 12'C/Bin and
hald 4 Binutaa
TaBparetura PrograBBed
n-Hexadacana fr~ '^.nS n!?d%
2SO*C for 4 Blnutaa
2.98 15694
(Ha carrier)
1.14 9376
3.32 14713
10.85 346086
11.33 350729
11.30 341814
7.72 205658
9.00 291098
8.95 292206
Tenax 17 300 300
Porapak H 235 150
126
Porapak N 175 150
110
Tanax 17 300 300
Porapak R> 235 220
115
Porapak N* 175 150
130
Tenax 17 300 300
Tanax 17 100 300
1
2
1
1
2
3
1
2
1
1
2
1
4
1
1
1
2
3
1
2
3
4
1.10
1.15
1.10
1.05
1.15
1.09
1.15
1.15
1.11
1.10
1.10
1.00
1.00
1.19
1.16
0.80
0.65
0.80
1.00
1.10
1.15
1.10
.59
.15
.91
.95
.73
.05
3.74
4.07
4.07
10.88
10.89
10.89
10.88
>30 Bin
>30 Bin
7.85
8.01
7.96
9.25
9.21
9.11
9.10
1680S
20929
17984
11075
11288
10805
19062
18906
18759
368397
355569
334466
327426
_ _
_ _
182183
139996
181463
270196
112449
111698
122291
97%
116%
104%
112%
105%
106%
113%
112%
113%
97%
93%
97%
95%
1
7
111%
105%
110%
95%
98%
99%
loot
*Mo Indication of a aaapla daaorptlon undar axparlBantal eondltlona
396
-------
5710A HEWLETT PACKARD GAS CHROMATOGRAPH
7132A HEWLETT PACKARD CHART RECORDER
CHROMALYTICS1* THERMAL CONTROLLER TO 1047
CONCENTRATOR SYSTEM
CHROMALYTICS* TUBE DESORPTION CHAMBER
TO 1047 CONCENTRATOR SYSTEM
THERMOCOUPLE CONNECTION FROM DESORPTION
CHAMBER TO THERMAL CONTROLLER
CHROMALYTICS* OVEN WITH VALVE TO 1047
CONCENTRATOR SYSTEM (200 °C)
INJECTION PORT FOR DIRECT INJECTIONS
THERMOCOUPLE CONNECTION FROM OVEN TO THERMAL
CONTROLLER
NITROGEN CARRIER GAS (30 min/ml) INTO CHROMALYTICS
VALVE
CHROMALYTICS* OVEN/GC INJECTION PORT (250 °CI
CONNECTION
GCOVEN CONTAINING 2.1 m.0.6cm O.D..GLASS
COLUMN WITH L125 g OF TENAX (60/80 MESH)
FID DETECTOR 1350 °C)
GC CABLE TO CENTRAL 3554 HEWLETT PACKARD
COMPUTER SYSTEM
FIGURE 10. Desorption/analytical system used in desorption efficiency evalu-
atlons.
SORBENT TUBE IN TUBE FURNACE
SWITCH IN "TRAP"
POSITION
(DIRECT) INJECTION PORT
CURRENTLY UNUSED (CAPPED)
CARRIER GAS SOURCE TOGC
DIRECT INJECTION OF STANDARDS INTO CC
SWITCH IN
"BACKFLUSH"
POSITION
SORBENT TUBE IN TUBE FURNACE
CURRENTLY UNUSED (CAPPED)
(DIRECT) INJECTION PORT
CARRIER GAS SOURCE TOGC
THERMAL DESORPTION OF TUBES INTO GC
FIGURE 11. Diagram of six-port, two-position valve within Chromalytics® oven.
397
-------
Since these experiments were of a preliminary nature, only a few of the
test matrix compounds were used in the evaluation of the desorption proper-
ties of the sorbents. However, by relating desorption efficiency to reten-
tion time data found previously (for capacity studies using 3 ft, 2 mm I.D.,
1/4 in O.D. glass columns filled with the sorbents) at or near desorption
temperatures, an idea of the types of compounds that are readily thermally
desorbed from the selected sorbents may be obtained. Table 7 gives the
chromatographic conditions and raw data for the determinations with the porous
polymer type sorbent materials, while Table 8 presents retention time data
along with experimentally determined desorption efficiencies. Note that
several values are above 100 percent efficiency. This may be due to either
background contributions to peak areas (especially for Porapaks), or slight
differences in peak shapes between direct injections and tube desorptions
resulting in different peak areas. In relationship to the indicated retention
times, the desorption efficiency data suggest potentially easy quantitative
desorption of compounds with retention times (Table 8) of less than a few
(
-------
TABLE 8
Retention Time Data and Desorption Efficiencies at or
near Desorption Temperature for Sorbent Materials
Test compound
n-Butane
Propylene oxide
Acrylonitrile
Benzene
iso-Octane
Ethylene glycol
Succinonitrile
Phenol
Benzyl chloride
Naphthalene
bis- (2-Chloroethyl) ether
Nitroaniline
Nitroanisole
Phenanthrene
n-Hexadecane
1,2, 4-Trichlorobenzene
4-Bromodiphenyl ether
Hexachloro-1 , 2-butadiene
Retention time (min)
. Porapak N Porapak R
m @ 150°C @ 150°C @ 222°C
395 0.51 0.50 0.17
594 1.03 0.68 0.20
557 1.93 1.00 0,24
719 4.48 3.23 0.47
788 12.1 10.33 0.85
(113±l%)a (108±4%) (>132%)
906 -
1073 -
1176 -
1253 110
1269 -
(?)C (?)°
1402 165
1657 -
1684 -
1747 -
1811 -
2014 -
2616 -
2783 -
Tenax
@ 302 °C
0.10
0.11
0.08
0.12
0.11
(106±10%)
0.11
0.17
0.17
0.16
0.22
(95±2%)
0.15
0.41
0.33
1.02
(109±4%)
0.21
(98±3%)
0.20
0.61
0.18
lumbers in parentheses are desorption efficiencies.
y.
Significant contribution from sorbent background.
"No indication of sample desorption after 30 min at experimental
conditions.
399
-------
*«
8
TABLE 9
Qualitative Evaluation of Two Sorbent Properties Compared to 6m
to Determine Ranges of Sorbent Utility
6 6
m m
Key Name (lit) (calc)
A Methane 89
B Ethane 180
C Propane 282 282
D(7) n-Butane 395 401
E n-Pentane 505 519
8 Propylene Oxide 534
9 Acrylonitrile 557 573
F n-Hexane 629 638
16 Benzene 719 719
4 iso-Octane 788 834
6 Ethylene Glycol 906
3 Succinonitrile - 1073
18 Phenol " 1176
17 Benzyl chloride - 1253
13 Naphthalene 1269 1410
5 Bis-(2-chloroethyl) 1402 1402
Ether
12 o-Nitroaniline - 1657
15 m-Nitroanisole - 1684
10 Phenanthrene 1747
1 n-Hexadecane 1811 1766
14 1,2,4-Trichloro- - 2014
benzene
11 4-Bromodiphenyl - 2616
Ether
2 Hexachloro-1,3- - 2783
butadiene
Tenax-GC
Trap Des
00
00
00
00
00
00
00
00
00
00
00
/
/
/
/
/
/
/
/
/
/
/ 1
^ 1
Porapak 1
orb Trap De:
00
00
00
00
00
00
00
00
00
/
/
/
/
/ 1
/
/
/ )
/ )
/ J
/ )
/ >
/ J
/ >
% Porapak 1
sorb Trap De!
00
00
00
00
00
00
00
00
00
/
/
/
? /
? /
f J
? /
C / 3
C / )
C / )
C / )
C / )
t / )
C / J
* Ambersorb
sorb Trap Desorb
00 1
00 !
00 I
00 !
/ 1?
/ 1?
/ 1?
/ 1?
l_ / 1?
/ X
^ X
/ X
7 / X
? / X
I? / X
? / X
C / X
C / X
t / X
C / X
C / X
t ^ X
t / X
SKC Charcoal
Trap DesorJ
00 1
00 1
00 1
/ 1?
/ !?
/ I?
/ 1?
/ X
/ X
/ X
/ X
/ X
/ X
/ X
/ X
/ X
/ X
/ X
/ X
/ X
/ X
/ X
/ X
Key to Table
Probably Possibly Not Likely
Trap Quantitatively
Desorb Quantitatively
I
I?
00 (Vg<480 1/g)
X
-------
TABLE 10
Ranges of Utility of Solid Sorbents Based on fim
SORBENT 6 (Trap) To 6 (Desorb)
m m
SKC charcoal
Ambersorb
Porapak N
Porapak R
Tenax-GC
^350
^50
^750
^750
^950
to
to
to
to
to
*600
^750
^1,500
^•1,500
>2,800
materials may prove to be more desirable.
In addition to desorptlon efficiencies and retention time data at or
near desorption temperature, Table 8 also gives 6 values for the compounds
listed. This table indicates a relationship between these retention times
and 6 . especially for Porapaks R and N. This relationship suggests that 6
m m
may be used to determine which compounds will be quantitatively desorbed from
sorbent materials.
Since a fair correlation has been demonstrated for 6 and sorbent capacity,
m
and a relationship potentially exists for 6 and desorption efficiency, then
6 may be useful in determining which compounds are likely to be quantitatively
m
adsorbed on and subsequently desorbed from a particular sorbent material.
A qualitative comparison of 6 with sorbent capacity and desorption efficiency
is given in Table 9. The entries in this table are defined in the key beneath
it and are based upon a combination of experimental data, demonstrated cor-
relations, and chemical intuition. The enclosed regions indicate compounds
which are probably or possibly quantitatively trapped at a high-volume condi-
tion (480 1, corresponding to 1 1/min for 8 hr) and are probably or possibly
quantitatively desorbed from the sorbent materials indicated. These regions
correspond to ranges of 6 values which are listed in Table 10.
Based on these results, a sorbent material may be used to sample most
compounds with £ values falling within its fi^ range. Alternatively, a
sorbent material may be selected for sampling studies with a particular com-
pound which has a 6 value within the 6m range of utility of the sorbent.
For example, a compound with a 6 value of 2,000 should probably be sampled
using Tenax-GC. A compound with a «m value of 1,400 falls within the ranges
of utility of Porapak N, Porapak R, and Tenax-GC. Since 1,400 is close to
401
-------
the 1,500 6 desorption limit of the Porapaks, Tenax-GC would again be the best
sorbent (of these five) to evaluate first for sampling this compound. However,
a compound with a 6 value of 1,000 would probably be easier to sample using
one of the Porapaks, since this value is near the 6 trapping limit of Tenax-GC,
A problem potentially exists for compounds with 6 values around 750, since
m
this is the 6 desorption limit of Ambersorb XE-340 and the 6 trapping limit
of Porapaks R and N. Therefore, for a complex organic sample, some overlap
exists for the ranges of utility (and the types of compound sampled) of
Tenax-GC and the Porapaks, but a potential gap exists between the ranges of
utility of these polymeric adsorbents and the carbonaceous adsorbents. It
should be emphasized that these ranges are only estimates of sorbent utility,
and it is likely that some compounds may not adhere to this scheme.
The other area of interest during the evaluation of the thermal desorp-
tion properties of the selected sorbent materials was potential extraneous
background resulting from contamination and/or sorbent characteristics.
Sorbent backgrounds can be composed of a variety of contaminants from a
number of different sources. Depending upon the degree and nature of these
contaminants, they can lead to complications during both sample collection
and analysis. In order to minimize problems from background contamination,
it is best to know as much as possible about what types of contamination can
arise, how they usually occur, and how best to minimize all sources of con-
tamination. In this way, complications—such as in situ reactions and inter-
ference during analysis—can be minimized and possibly avoided.
Generally, all commercial sorbent materials as received from suppliers
contain significant levels of background contamination as the result of pro-
duction, packaging, and/or transportation. Although most of this initial
contamination may be removed by solvent (before packing in tubes) and/or
thermal (usually after packing in tubes) conditioning, such conditioning may
also Introduce contaminants. Backgrounds may be introduced from trace im-
purities in the solvent and the gas stream, and also from decomposition pro-
ducts of the polymer. Obviously one does not heat a polymer above its tem-
perature limit or extract it in a solubilizlng solvent, but some polymeric
breakdown can occur under other situations as well. Each sorbent will have
thermal properties that are unique, and, therefore, conditioning procedures
should be validated and optimized for each sorbent material. As a precaution,
one should also be aware of the types of compounds each sorbent produces as
the result of thermal and/or chemical degradation. Table 11 lists several
of the major thermal decomposition products that could be expected from the
selected sorbent materials, as well as the chemical compositions and tempera-
402
-------
TABLE 11
Expected Thermal Decomposition Behavior
of Selected Sorbent Materials
Sorbent
Chemical composition
Temperature Major thermal
limit (°C) decomposition products
Porapak N
Porapak R
Tenax-GC
N-vinyl pyrrolidone
N-vinyl pyrrolidone
2 , 6-Diphenyl-p-phenylene oxide
Ambersorb XE-340 Carbonized styrene-divinyl
benzene
SKC activated
charcoal
Carbonized organics
190
250
400
>350
>400
Vinyl pyrrolidone
Pyrrolidone
Pyrrilidiene
Vinyl pyrrolidone
Pyrrolidone
Pyrrilidiene
Alkyl benzenes
Styrene
Benzene
Alkyl phenols
ture limits of the sorbents. Since the temperature limit of Ambersorb XE-340
was not stated by its manufacturer, a freshly packed 3 ft, 1/4 in O.D., 2 mm
I.D. glass column of this sorbent was prepared, conditioned, and analyzed by
GC/MS to verify that thermal decomposition was not occurring at the condition-
ing temperature of 350° C. This column was placed in the GC oven of a Hewlett-
Packard Model 5982A GC/MS system and subjected to stepwise temperature in-
creases (50° C intervals) up to 250° C. The effluent from the column was
continuously monitored by mass spectrometry and showed none of the expected
thermal decomposition products of the styrene-divlnyl benzene polymer. In-
deed, the only effluents observed were C02, S02» argon, and traces of a few
low molecular weight aliphatics. Therefore, thermal decomposition of Amber-
sorb XE-340 does not occur at 350° C, which is above the anticipated operating
temperatures.
Once the conditioning procedure for a particular sorbent has been estab-
lished, care must be taken to prevent additional contamination during sub-
sequent handling. The handling and storing of sampling tubes should be
optimized without being unreasonably complicated or expensive. The techniques
developed should also ensure the integrity of all samples collected (i.e.,
no sample loss).
Finally, backgrounds from other sources in the desorption/analytical
system should be eliminated or reduced to the greatest extent possible.
These can arise not only from the usual sources of chromatographic background
403
-------
contamination (e.g., column and septum bleed), but also from sources that are
unique to the method of desorption and sample introduction. These less obvious
difficulties could include dust being introduced into the desorption chamber,
or fingerprints on the sample tube, depending upon the desorption chamber
design. Generally, background contamination introduced by a desorption/analyt-
ical system are best minimized by using forethought when designing the system.
A series of experiments was conducted to evaluate the background levels
of the materials being studied and possible sources of background within the
desorption/analytical system. Sampling tube backgrounds were evaluated by us-
ing the desorption/analytical system sketched in Figure 12 and the sampling
tubes listed previously in Table 6. The following are some of the findings
determined during these evaluations of sorbent backgrounds.
Conditioning.
• No difference was noted between solvent extracted and nonsolvent ex-
tracted sorbents (for the sorbents studied and the experimental system used).
• For Porapak R, conditioning at 240° C produced less background upon
desorbing at 170° C than with conditioning at 175° C and desorbing at 170° C.
• Thermal conditioning removed a great deal of contamination, most with-
in the first hour.
• After conditioning, the backgrounds of Porapak R and N tubes were above
the background of a blank (empty) control tube, while the backgrounds of
Tenax-GC, Ambersorb XE-340, and SKC activated charcoal matched the background
level of the blank control tube.
Handling and Storage.
• A desorption system designed to eliminate the exterior of the sampling
tube from analytical desorption greatly diminishes problems with handling and
storage.
• Capping tubes with metal fittings and storing them in culture tubes
with Teflon-lined caps seems to be the best method of tube storage to elimi-
nate extraneous contamination.
• Glass sampling tubes offer a more inert surface than stainless steel,
404
-------
40
© 571QA HEWLETT PACKARD GAS CHROMATOGRAPH
© 7132A HEWLETT PACKARD CHART RECORDER
® CHROMALYTICS THERMAL CONTROLLER TO 1047
CONCENTRATOR SYSTEM
© CHROMALYTICS TUBE DESORPTION CHAMBER TO
1047 CONCENTRATOR SYSTEM
© THERMOCOUPLE CONNECTION FROM DESORPTION
CHAMBER TO THERMAL CONTROLLER
© DESORPTION CHAMBER ENTRANCE AND (0-RINGI SEAL
© NITROGEN CARRIER GAS (30 ml/mini
© DESORPTION CHAMBER/GC INJECTION PORT (300°CI
.CONNECTION
® GC OVEN 1320 °C) CONTAINING EMPTY a 9m, a 6 cm O.D..
2 mm I. D. GLASS COLUMN
® FID DETECTOR (350 °C)
® GC CABLE TO CENTRAL 3554 HEWLETT PACKARD
COMPUTER SYSTEM
FIGURE 12. Desorption/analytlcal system used in tube
background evaluations.
•sr
_a.
CL
20
10
NOTE:lPSIG = 6.9xl03Pa
TENAX-PORAPAK-
AMBERSORB
IN SERIES
SS*.'.S^ B——
&•& e GLASS w
>•%- r : _ •—
AMBERSORB XE-340
WOOL
3.0
l/min
FIGURE 13. Pressure drop versus flow rates for
15 cm, 0.6 cm O.D., 4 mm I.D. glass sampling
tubes filled with sorbent materials.
o
Ul
-------
and have fewer contamination and reactivity problems.
Evaluations of Sampling Tube Pressure Drops and Design
One limitation that automatically applies to any portable air sampling
system is the ability of a portable pump to pull air through sorbent-filled
sampling tubes at a desired rate. This ability is directly related to the
pressure drop across the sampling tube. For a particular pump to pull air
through a sampling tube system at a specific rate (0.5 to 3 1/mln for this
project), the pressure drop across these tubes must be equal to or less than
a certain maximum value. This corresponds to the rated capacity of the pump
at a particular pressure drop. Sampling tube parameters which affect the
magnitude of the pressure drop include: type of sorbent material packing,
mesh size of sorbent material packing, amount of glass wool plug, diameter
of tube, and amount of sorbent material packing.
Of these parameters, the types and amounts of sorbent material packings
will be mainly determined by the capacity of these sorbents for atmospheric
pollutants under the anticipated sampling conditions. The mesh size of the
sorbent materials offers some versatility, but there are limitations to the
mesh sizes available. The amount of glass wool used to contain the sorbent
material within the tube can be a critical factor in determining the pressure
drop, so that care should be taken to ensure that the minimum amount of glass
wool is used. In larger diameter tubing, a method of restraining the glass
wool plug may be necessary when minimal amounts of glass wool are used.
Tapering the ends of the tube or inserting a stainless steel screen are two
possible ways to secure the glass wool plugs.
The experimental parameter that offers the most flexibility in determin-
ing the pressure drop is the tube diameter. The only restriction on the di-
ameter of the tube is the necessity to achieve rapid and uniform heating of
the sorbent bed during the thermal desorption process. This becomes increas-
ingly difficult with increasing sampling tube diameter.
The pressure drops across sampling tubes of various shapes, diameters,
and sorbent beddings were measured using a differential pressure gauge. Flow
rates were set by using a Brooks Model 5841 thermal mass flow sensor/con-
troller. An example of the type of data generated during these pressure stud-
ies is given in Table 12 and depicted in Figure 13.
These pressure drop studies led to the conclusion that a 10-mm diameter
406
-------
TABLE 12
Pressure Drop Data for Glass Sampling Tubesa (pslg)
Tenax GCTenax GCPorapak NAmbersorb XE-340Glass tube~
60/80 mesh 35/60 mesh 50/80 mesh (not sieved) without Tenax GC (35/60),
Plow 0.1953 g 0.2014 g 0.2018 g 0.1964 g sorbent Porapak N, and
rate w/34.3 mg w/34.3 mg w/38.9 mg w/36.1 mg w/36.2 mg Ambersorb XE-340
3
2
1
0.5
0.25
23.2
15.8
6.4
3.0
1.5
20.3
12.3
5.1
2.2
1.0
14.8
9.0
3.8
1.6
0.8
3.0 1.1 to 1.2
1.6 0.6
0.4 0.1
0.1
M)
31.8
19.9
8.8
4.0
2.0
Other conditions
Transfer lines only at 3 i/rain show M) psig pressure drop.
Inlet pressure: 62 psig; downstream pressure: 9 psig.
TABLE 13
Adsorbent Properties Chart
Taap. Oond. Daa.
llaUt t««p. tan*. Ctwalcal
Adaorbant CO I'CI (*CI eoBwwitlon
Tanu-GC 400 120 100 2,6-oiphanyl-
(15/60 a»an) p-phaaylana
OKida
Porapak P. 250 215 150 n-Vlnyl
(50/10 aaah) to ryrrolidoaa
220
Porapak H 190 175 150 a-Vinyl
(50/10 Man) Pyrrolldona
ABfearaorb* >400 120 100 carbonlaad
O-140 ftyrana-
divinyl
•XC Aoti- »400 120 loo carbonltad
vatad Organlea
rharooal
Hijor tharaal
product!
Alkyl ununa
Btyrana
Bantana
Alkyl Phanola
Vinyl Pyrroli-
dooa
Pyrrolldona
Pyrrllldlana
Vinyl ryrroli-
doaa
Pyrrolldona
Pyrri lidiana
nona obaar-
vad laftar
conditioning
at JJO'C •» ob-
aarviBg on
OC/Mf)
vad
Background ap*
GOOD 160
(nona dataotad
afaova ayataat
background)
.
Attar condl- ^.l"
tinning at
2J5-C, back-
ground upon
daaorbiag lat
POM t JJO'C
(wall abova
ayat. baok-
ground)
PAIH 0 150*C
ayat. baok-
aroiiBd)
poo* 1.1
(^•ii abova
ayataai back-
ground)
0000 u>ft
(DOM datac-
tad abova
ayata* baek-
gnund)
V)."
(noon datao-
tad abova
background)
Capacity
Would afCUiantly
trap IntanMdlataly
(t laaa) volatila
oowounda wlttt
allghtly laaa affi-
nity for polar OOB-
pounda.
•bould affielantly
trap latanadlauly
(( laa»l voUtlla
coipounda vith
allghtly graatar
affinity for polar
ooapouoda.
Should afflctantly
tup intaraadiatatly
(t laaa) volatlla
coapounda with
aligbtly graatar
affinity for polar
oocpounda.
fbould afflalaBtly
trap bigbly (t all
laaa) volatlla oora-
P^jmt^ vitb graatar
affinity for polar
coBpounda.
•bould affioiaotly
trap highly (t all
laaa) volatila eo*~
pouaoa Mtn aucn
graatar affinity far
polar compnuiKla.
Oaaorptlon
Vary aaanabla to
tnarMal daaorp-
tlon for Intar-
••diataly (t all
hlgbar) volatila
OOBpOUOdfl*
Vary MiniliU Co
thttn.*..! dvatorptioo
COT lAfcMaMdiAMly
U *11 blflhw)
volatila ooapounda*
Vary laanihla to
tbanal daaorption
for lataraadlataly
(i all higbar)
voUtlla oMPnuMa.
guaatioaabla
aainibltlty to
tbanal daaorption
for all but higply
volatlla bydro-
oarboaa.
bllity to tnaoal
daaorption for all
but Uglily volatila
bydrooarboaa
Rang* of utility
v»io to >J«00
•V750 to «15OO
M50 to 1-1500
i rat.
407
-------
represents a reasonable compromise between the requirement to have the small-
est possible diameter for efficient thermal desorption and yet maintain an
acceptable pressure drop across sorbent-filled tubes. Two designs, straight
and tapered, with 10-mm cross sections, were evaluated taking into account
the desirable design features of the miniature collection system. Although
the tapered tubes had higher pressure drops than the straight tubes, the
difference was not significant. Furthermore, the tapered design offered ad-
vantages for the containment of the sorbent, since smaller amounts of glass
wool can be used with no "blowouts" of sorbent material. Finally, lighter,
less expensive (one-quarter inch) fittings can be used with the tapered tubes,
which is an Important factor in the design and construction of a miniature
collector. The specifications for the cartridge design determined to be most
desirable is given in Figure 14, along with a sketch of a sampling tube.
Evaluation of Sorbent Package
Five sorbent materials have been evaluated to determine their basic
properties, including special abilities and potential problems.
Table 13 is a compilation of the major sorbent material properties eval-
uated. Along with the name of the adsorbent is included:
• The manufacturer's stated temperature limit (or >400° C).
• The temperature used for sorbent conditioning.
• The temperature used for sorbent desorption.
• Some of the major thermal decomposition products.
• A qualitative description of the background to be expected from the
sorbent material.
• The pressure drop across tapered tubes containing 1.0 g of adsorbent
at a 3 1/mln flow rate.
• A qualitative description of the type of compounds that will potenti-
ally be quantitatively trapped by the adsorbent (capacity >480 1/g).
• A qualitative description of the type of compounds that will potenti-
ally be quantitatively thermally desorbed for analysis.
• The range of utility based on fi (described previously).
m
Of these five sorbents, a combination of three has been selected for
use in the miniature collection system. These three sorbents are listed be-
low along with the major reasons for their selection.
Tenax-GC. The only high-temperature (400° C) adsorbent available which
allows the quantitative thermal desorption of low volatility organic compounds.
408
-------
«
*-2.5cm-»
[
7-
^£
i^
14
6cm
- 7
• /.
12 mm 0. D.
Ull
CiH *
10 mm I.D.
%a ^^^^M^S
?
A
6cm
*-2.5cm
6.5mm
4mm 1.
•iM
0.
D.
})
D
r&v%-
GLASS WOOL
f
SORBENT MATERIAL
GLASS WOOL
FIGURE 14. Specifications for tapered sampling tube design.
Porapak R. One of the highest-capacity polymeric absorbents with a
reasonable background level (better than Porapak N) and with an overlap in
range of utility (6 ) with Tenax-GC.
Ambersorb XE-340. Less difficulty anticipated with the desorption of
compounds of intermediate volatility, fewer detrimental effects by water and
reactivity with collected samples than with charcoal. Also, its range of
utility (6 ) leaves the smallest gap between polymeric and carbonaceous ad-
m
sorbents in the types of compounds collected.
These sorbent materials will be packed into three separate tapered glass
tubes for sampling, with flow being directed either in series or in parallel.
If sampling is done with the sorbent tubes in series, the arrangement will
be Tenax-GC at the air intake, Ambersorb XE-340 at the air exhaust to the pump,
and Porapak R in the middle. In terms of total range of utility (6 ) of the
sorbent package, it should quantitatively trap and desorb compounds ranging
from ^450 to >2,800 (fi ) with a possible "qualitative only"
gap at *750 (6 ).
m
ACKNOWLEDGEMENT
This research was sponsored by the U.S.
under Contract No. 68-02-2774.
Environmental Protection Agency
409
-------
REFERENCES
1. Burrell, H., Immergut, B. Solubility Parameter Values. In: Polymer
Handbook (Brandup, J., ed.). New York, Interscience Publishers, 1966.
2. Gallant, R.F., King, J.W., Levins, P.L., Piecewicz, J.F. Characteri-
zation of Sorbent Resins for Use in Environmental Sampling. EPA-600/7-
78-054, pp. 79-92. March 1978.
3. Holzer, G., Shanfield, H., Zlatkis, A., Bertsch, W., Juarez, P.,
Mayfield, H., Liebich, H.M. Collection and Analysis of Trace Organic
Emissions from Natural Sources. J Chromatogr 142:755-764, 1977.
4. Small, P.A. Some Factors Affecting the Solubility of Polymers. J Appl
Chem 3:71-80, 1953.
MAILING ADDRESSES OF AUTHORS
Joseph J. Brooks, Ph.D., Diana S. West, and Donald J. David
Monsanto Research Corporation
Station B, Box 8
Dayton, Ohio 45407
James D. Mulik
Organic Pollutant Analysis Branch
Environmental Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
Discussion
SCHEIDE: Gene Scheide, Environmetries. What was the temperature used
in the thermal preparation of your adsorbent material?
BROOKS: It varies with sorbent material. Of course, it is based on
what the upper temperature limit is. We used about 350 degrees Centigrade
for the Tenax, for the Ambersorb and the charcoal.
We used about 175° C for the Porapak N, and about 240° C for the Porapak
R. Again, these are related to what their upper thermal limit is.
I should say we will be evaluating these sorbents in the second year
against 20 possible and probable carcinogenic compounds that have been iden-
tified as being of interest.
410
-------
SPENGLER: I understand you have not used all of these in the field,
yet. The Tenax is currently being used by Lawrence Berkeley Labs on indoor-
outdoor measurements, to look at organics.
But we would like to relate someone else's experience: that of
Peter Mueller from Environmental Research and Technology who also used a
Tenax collector in ambient conditions. He related that they had some ser-
ious problems with blank contaminations with the Tenax, and they were totally
frustrated with the its use.
I don't know if you have any comments on what would cause that, but he
said that oftentimes the blanks would have more material on them than the
exposed Tenax. They are disenchanted with it.
MEIER: Gene Meier, EPA, Las Vegas. The problem with Tenax traps is
aging. As your trap ages, it degrades, and you can't hold a trap for more
than 3 weeks; otherwise, you get a significant hydrocarbon background from
two sources—either just contamination from the normal environment on your
Tenax, or also it can be the composition of the Tenax itself.
If you look at your gas chromatogram, you will see a typical hydrocarbon
response, along with the chromatogram of the various alkanes as they break
down off the Tenax itself. That's why I would like to see some of the data
on the Ambersorbs, because we have done some work at Las Vegas—not our lab
personally, but the people at the University—and the Ainbersorb seems to be
a lot cleaner than the Tenax in trapping all the organics from water samples,
which I would expect would hold true here.
BROOKS: The reason that we are using three different materials is be-
cause we have to cover the range of compounds. You might have problems re-
covering a lot of the heavier, less volatile materials—if you were just
using Ainbersorb.
MEIER: Have you actually physically collected the samples and tested,
or are these hypothetical results?
BROOKS: We have done a limited amount of sampling with test compounds.
Right now, in the second year, we will be working with the actual 20 com-
pounds that we have selected to determine what the collection and adsorption
efficiencies are.
MEIER: The people out at Research Triangle Park have been using the
Tenax traps for their monitoring program and have been quite successful in
trapping a wide range of hydrocarbons, including your heavier molecules.
BROOKS: With Tenax, right, but I am saying that with Ambersorb, you
are not going to get them back.
MEIER: I realize the differences there, but I am saying that you work
in a whole series and one of the questions I am asking is why is the Tenax
acceptable, while you are looking for the three solvents?
411
-------
BROOKS: Because when you are talking about sampling, say, at a liter-
per-tninute for 8 hours, you are going to get significant breakthrough of the
higher volatility compounds—they will not be trapped.
MEIER: Well, they have been collecting 100 liter samples on 5/8-inch
diameter and I would say about 4 inches long tubes, and have been quite suc-
cessful. They use it in the quality assurance program where they spike
their traps before they go out in the field, so they can verify when they
have a breakthrough.
BROOKS: I doubt that they are successful for the really highly vola-
tile compounds. Let me say just one other thing. We do have first annual
reports available on two contracts that relate to this type of sampling and
that will be out very shortly.
MAGE: I just might add from my own personal experience that so much
depends on the method of preparation. One batch of Tenax may not be the same
as the other. There is a lot to be done to maintain quality.
412
-------
Adapting Commercial Voltammetric Sensors
to Personal Monitoring Applications
Manny Shaw, Ph.D.
InterScan Corporation
Chatsworth, California
Of recent concern to industrial hygienists and safety engineers is the
exposure of workers to harmful levels of noxious gases and vapors. Apart
from the survey type or fixed-station monitor, there is a need for an in-
expensive but accurate personal monitor with real time indication—one that
is wearable without being burdensome. The one proven analytical technique
meeting these requirements is the electrochemical voltammetric method of
instrumental analysis.
PRINCIPLE OF OPERATION
The voltammetric method differs from other instrumental methods of gas
analysis, such as the coulometric, conductimetrie, or colorimetric techniques,
which require that the sample gas react with chemical reagents. In the volt-
ammetric technique, sample gas is electro-oxidized (or electroreduced) di-
rectly at an electrode. This makes it possible to design a simple and prac-
tical portable monitor using a dry technique.
The voltammetric sensor operates under diffusion-controlled conditions.
The gas sample is drawn through the sensor, passing over an electrocatalytic
sensing electrode of the gas diffusion type. Some of the gas molecules dif-
fuse into and are adsorbed on the electrode, where they are electrochemically
oxidized or reduced (depending on the sensor) at an appropriate electrode
potential. This electrochemical reaction results in an electric current,
directly proportional to the gas concentration.
413
-------
To understand the concept of a diffusion-controlled reaction, picture
a single pore within the porous surface of the sensing electrode. Within each
such pore, a thin film of electrolyte constitutes a microscopic meniscus in
contact with the sample gas, creating a three-phase junction of gas, liquid,
and solid (electrode surface), shown schematically in Figure 1. The total
electro-oxidation reaction of a sample gas includes dissolution of gaseous
molecules in this thin liquid film, diffusion or mass transfer of the dis-
solved gas through the film, adsorption of the gas on the electrode, and trans-
fer of the electron charge to the metal surface. The reaction becomes dif-
fusion-limited when the gas is consumed at a greater rate than can be re-
plenished at the reaction site; that is, when the charge transfer reaction
is faster than the mass transfer reaction. The limiting diffusion current
is linearily proportional to the gas concentration according to the simpli-
fied equation
where i is the limiting diffusion current in amps, F is the Faraday constant
o
(96,500 coulombs), A is the reaction interface area in cm , n is the number
of electrons per mole reactant, L is the diffusion gradient in cm within the
o
thin liquid film, C is the concentration (moles/cm ) of gas molecules dis-
2
solved in the thin liquid film, and D is the diffusion coefficient (cm /sec)
of the gas. To be an analytical device having linear readout with gas concen-
tration, the voltammetric sensor must be biased so that the electrode reaction
occurs within the diffusion-limited region of the voltammetric curve. This
is illustrated in Figure 2, showing typical voltammetric curves for several
gases. Electrochemical current is plotted as ordinate, and the sensing
electrode potential as abscissa, relative to the reversible hydrogen elec-
trode (RHE) at zero potential. Increasing oxidation potential (more positive
values—Stockholm-Gibbs convention) is towards the right. Oxidation current
is arbitrarily chosen as positive.
Taking SO. as an example, no reaction occurs until a minimum oxidation
potential is reached at a, at which point current begins to flow, increasing
until it attains a limiting value at b. Since the region b to c represents
the diffusion-limited region of the current, the sensing electrode in the SO-
sensor is held at an oxidation potential of V. volts. This is accomplished
by applying the appropriate bias voltage to the sensing electrode relative
to the reference counterelectrode. Similar voltammetric curves are shown
for H.S and CO oxidation. NO- is unique in that it exhibits both oxidation
and reduction characteristics.
414
-------
SOLID
PHASE -
(electrode)
GAS PHASE
LIQUID
PHASE
FIGURE 1. Electrode-electrolyte
interface.
RHE
Ou
u
Dry?
^^^
8Pd
5
ELECTRODE
POTENTIAL
FIGURE 2. Voltammetric curves of several gases.
415
-------
These curves also show that In certain cases, interferences may be elimi-
nated by biasing the sensor at an oxidation potential below that of the inter-
fering gas. For instance, if the H2S sensor is biased at V2t below the oxi-
dation potential for S(>2, then S02 will not interfere in the HgS sensor. HjS
will, however, interfere in an S02 sensor. The extent of this interference
depends upon the specific output of the sensor in its response to the inter-
fering gas. In certain cases, choice of electrode material may virtually
eliminate interference from certain gases. Selective filters are generally
used when a potential interferent cannot be electrochemically scrubbed.
SENSOR DESCRIPTION
Figure 3 is a schematic representation of a voltammetric sensor used in
present commercial survey monitors. Sample air, drawn into the sensor by a
pump, streams over the backside of the sensing electrode. A portion of the
sample diffuses into the body of the electrode, adsorbing on its electro-
catalytic surface moistened with electrolyte. The bulk of the electrolyte
is immobilized in a matrix comprising the reservoir, which also contains the
reference counterelectrode. A small banana jack in the sensor head and a
metal strip fastened to the sensor near its bottom make connections to the
sensing electrode and to the nonpolarizable reference counterelectrode,
respectively. The sensor is secured by a clamp permanently mounted to the
base of the portable analyzer, the clamp also serving as an electrical con-
tact to the metal strip attached to the reference counterelectrode.
The use of a nonpolarizable counterelectrode allows it to serve the dual
function as reference electrode, so that a third electrode is not required.
The three-electrode sensor offers no advantages in sensitivity, response time,
drift, linearity, or interference rejection—these parameters being a function
of the sensing electrode only.
SENSOR CHARACTERISTICS
Response Time
Response times of properly designed voltammetric sensors are relatively
fast, ranging from 3 to 20 seconds to 90 percent of final value, depending
on sensor type. Rise and fall times are approximately equivalent, although
the fall time of CO sensors tends to tail the last 5 to 10 percent. Excessive
416
-------
SAMPLE
INLET
SENSING /
ELECTRODE
• • • <
• • •
ELECTROLYTE ,
.•.•.*.• BOUND IN MATRIX,
(150 ml volume)
ft'fi'!'!'!'!'!'ffi'!-!yffi • " • *
•" ~ • • ^^^^9t^^^T^9^9^9t9mm 9 9 9
TO
PUMP
SE BANANA JACK
j
REFERENCE
COUNTERELECTRODE
EXTERNAL REC
CONTACT TO
SENSOR CLAMP
FIGURE 3. Voltammetric sensor in portable monitor.
POTENTIAL
FIGURE 4. Background current of sensor,
417
-------
drying out of some sensors, particularly the CO type, Increases the response
time, due to significant increases in internal resistance.
Sensor Range
The specific output of voltammetric sensors, using high reaction rate
sensing electrodes, is high—on the order of microamps-per-ppm. This permits
measurements over a broad range. For practical reasons, determined by zero
drift and interference, the lowest recommended range is 0 to 1 ppm full scale.
The upper limit is determined by the current and voltage characteristics of
the current amplifier. Excessive current, due to gas concentration well in
excess of the meter range, may cause amplifier saturation, clipping the
output voltage—resulting in a fixed, meaningless meter reading. The measur-
ing range of the instrument is determined by the appropriate feedback resistor
associated with the current amplifier. Because of power supply limitations,
feedback resistors of different values are used to cover a broad range of
concentration. Multlrange units have a range switch to select the particular
feedback resistor. Special sensors can be formulated to give a low specific
output, permitting their use in high-concentration applications.
Zero Drift
A key performance parameter of a practical sensor is its zero drift
characteristic. In voltammetric sensors, this phenomenon is caused strictly
by the temperature effect on the background current. Figure 4 shows the back-
ground current of the sensor as a function of oxidation potential. The rising
positive current at higher potentials is due to electro-oxidation of the elec-
trocatalyst, followed by oxidation of water to oxygen at the highest potentials,
The rising negative current at lower potentials is caused by electroreduction
of dissolved oxygen in the electrolyte.
The zero control in the instrument provides a compensating voltage, which
nulls out this background signal. With change in temperature, this current
increases or decreases, resulting in an uncompensated signal. This drift is
measurable in microamps and is a sensor phenomenon only, remaining constant
irrespective of the amplifier gain characteristics and, hence, the meter
range. Percent drift must therefore increase with decreasing full-scale con-
centration range. As an example, a sensor has an output of 10 yA/ppm and a
zero drift of 0.1 nA per ° C, equivalent to 0.01 ppm per ° C. On a 0 to 10
ppm range, this corresponds to a change of 0.05 ppm for a 5° C change in
temperature, giving a zero drift of 0.5 percent of full scale. This corre-
418
-------
sponds to 5 percent drift on the 0 to 1 ppm range and 0.5 percent drift on the
0 to 100 ppm range.
Sample Flow Rate
Sensor output is flow dependent at flow rates below 2 liters-per-
minute, as illustrated in Figure 5. This is not a pressure effect, as demon-
strated by data obtained by pushing the sample through the sensor from a
pressurized cylinder, or pulling it through using the internal pump and a
sample bag. This flow effect is a result of the rapid consumption of gas at
the high reaction rate sensing electrode. As the flow rate is decreased,
there is less tendency for new gas molecules to replenish those consumed at
the electrode; i.e., the flow rate becomes less and less sufficient to fully
sustain the reaction. Figure 5 shows that a decrease of flow rate from 940
to 740 ml/minute decreases the sensor output by 5 percent.
Actually, the flow rate effect is an advantage because no purge of the
sensor is required. One merely shuts off the pump for zeroing. The portable
InterScan analyzers have a constant flow pump so that the flow rate is fixed,
independent of the state of battery charge. Calibration with a sample bag
ensures that the same flow rate will be used for the sample measurements.
PERSONAL MONITORING
The electrochemical voltammetric technique is highly suited to real
time air quality monitoring and integrated exposure measurement. It is prob-
ably one of the few available techniques offering a combination of small
size, low cost, minimal maintenance, and accurate linear output. The scaling
down in size from a portable monitor to a personal monitor requires no basic
development effort, but is rather one of design engineering. A large re-
duction in sensor volume can be accomplished with only a relatively small
reduction in area of the active elements—the electrodes.
The sensor in the portable, survey-type monitor has been reduced from
3 3
a volume of 24 in to 1 in for the personal monitor. The total volume
3 3
of the personal monitor is less than 20 in compared with 525 in for the
portable monitor. This drastic reduction in size in done by reducing the size
of the reservoir. The trade-off is the necessity for the frequent addition of
water to the personal monitor reservoir. (No addition of water is required
in the sensor shown in Figure 3, which has a sufficiently large reservoir
to give a sensor life of a year or more of normal use.)
419
-------
Internal pump -f
sample bag
0.70
500
1000 1500
FLOW RATE IN ML/MIN
2000
FIGURE 5. Effect of sample flow rate on sensor output.
"8
8 SECONDS TO 95%
CO DOSIMETER RESPONSE CURVE
PMMTUMU*
1 INCH= 30 SECONDS
FIGURE 6. CO response in personal monitor.
420
-------
Such reduction of size does not affect sensor performance. Figure 6
shows the response curve of the 1 cubic inch sensor in the CO personal monitor,
Rise and fall times are rapid. Rise time is 8 seconds to 95 percent (chart
speed shown is 1 inch equals 30 seconds).
PERSONAL DOSIMETERS
The voltammetric technique is particularly suitable for personal dosi-
meters which give an accumulated exposure over a time period. Using coulo-
metric or electronic integrators, the total dosage in ppm-hours is obtained
in a separate read-back unit. Read-back may be done at the end of an 8-hour
shift, and the time-weighted average (TWA) calculated from the ppm-hours. If
desired, read-back can be done at any time during a given period to identify
the existence of high-dosage periods.
The disadvantage of this approach is that in many cases the read-back
reading is an after-the-fact event, the wearer of the dosimeter already having
been exposed to a TWA greatly in excess of the threshold limit value (TLV).
Even though some dosimeters have an alarm indicator, it is only for indicating
the ppm level at a given moment. A more practical device would be a dosimeter
capable of being set to alarm at a TWA equivalent to the TLV. This concept
has been developed, and is presently being used by a major steel manufacturer
as an area monitor equipped with a TLV alarm. The electronics necessary to
accomplish this can be packaged in a pocket-sized dosimeter. The availability
of low-current logic components permit their usage in battery-powered circuits.
Figure 7 shows a block diagram of a personal dosimeter using this new
concept. Shown are the more standard components such as reference voltage,
zero and span circuits, amplifier, power supply, and low-battery indicator.
A plug-in meter is used for calibration and ppm level measurement. The block
diagram entitled TWA & ALARM CIRCUITRY represents the logic package designed
to accomplish the TLV alarm. This is detailed in Figure 8.
The analog output voltage is converted to a digital format. A clock
(square wave oscillator) regulates the feeding of information through the
gate into memory storage. If and when the TLV is exceeded, a visual (LED)
and audible (buzzer) alarm is actuated. The TLV is set at the factory, specif-
ic for that type of dosimeter. A second circuit permits a second alarm to
activate, based on exceeding the Short-Term Exposure Limit (STEL). This is
Indicated by a different color LED and the buzzer.
421
-------
To Calibration Indicator
Sample ]•-——-
Flowmeter
Power
Supply
Low
Battery
Indicator
FIGURE 7. Block diagram of TLV alarm dosimeter.
r
To Optional
Readout
FIGURE 8. Block diagram of TWA Integrator.
422
-------
An important feature of this dosimeter is the TEST circuit, which allows
the user to check the operation of the TLV alarm. By flipping a switch, a
signal is generated, which is designed to actuate the alarm in a given specif-
ic time, such as 30 seconds. The timing of the alarm is precise, within
+ 1 second. The timing is so precise that the test should be repeated three
or four times to be certain that the timepiece is being read correctly. (The
RESET control is used to clear the memory.) If the alarm is actuated too soon
or too late, relative to the 30+1 seconds, the unit is faulty. This simple
test, performed in the dosimeter itself, gives an excellent quick check for
reliability.
The concept of a TLV alarm dosimeter has obvious advantages. No auxil-
iary read-back unit is required—the dosimeter is complete in itself. A re-
set button in the dosimeter allows its transfer from one worker to another
during a shift, without the necessity of going to a separate erasing unit.
Although an optional TWA unit will become available, there is the practical
question as to its need. The main purpose in determining the ppm-hours of ex-
posure, or the TWA, is to prevent a worker from being exposed to a dosage in
excess of the TLV. If such is the case, then it seems that a logical way to
do this Is with a TLV alarm dosimeter.
MAILING ADDRESS OF AUTHOR
Manny Shaw, Ph.D.
InterScan Corporation
9614 Cozycroft Avenue
Chatsworth, California 91311
Discussion
PETROVICK: You illustrated a slide there where you have the electro-
lytes bound within a matrix. Could you give me an idea why you used a ma-
trix and what its particular features are in that design?
SHAW: Well, I am an old battery man besides being a fuel cell man,
and I don't see the logic of taking the sensor and putting in free acid,
because if the electrodes which are rupturable diaphragms are ruptured,
you have got free acid all over the Instrumentation.
423
-------
I used to meet electronic engineers and when they would look at such
devices they would exclaim: "Oh, gee, we would never put that into our
instrumentation—having an acid electrolyte in there." They don't stop to
think: they do the same thing with NiCd batteries all the time. It has
got strong alkali like the material you clean up a toilet with. It's the
same type of alkali; it is that strong—23 percent potassium hydroxide. But
it isn't sitting around there loosely, slushing around. It is in a matrix,
bound up. So, we simply make the sensor the same way.
424
-------
Solid Sorbent for Acrolein and
Formaldehyde in Air
Avram Gold, Ph.D., Thomas J. Smith, Ph.D., Christoph E. Dube, and
John J. Cafarella
Kresge Center for Environmental Health
Harvard School of Public Health
Boston, Massachusetts
INTRODUCTION
Acrolein and formaldehyde are toxic and irritating volatile aldehydes
of increasing interest In industrial hygiene and environmental settings.
Outdoor sources of acrolein are combustion and diesel exhaust, while indoor
sources may be cooking and smoking. Formaldehyde exposure in residences
from particle board and blown-in urea-formaldehyde foam have recently gen-
erated concern.
Current sampling methods for both aldehydes (7,8) involve the use of
liquid-filled impingers and are not particularly well-suited to personal
sampling. Additionally, the acrolein analysis must be performed within sev-
eral hours after sampling, and the effect of storage on formaldehyde samples
is unknown. Studies on stability of formaldehyde solutions of low concen-
tration, however, strongly suggest that storage will present problems (11).
Since our initial interest in the aldehydes was for inclusion of a sampler
in a package to be used by Boston firefighters on-the-job, we desired a
solid sorbent which would have a large specific capacity and provide sta-
bility for stored samples.
DISCUSSION
Activated molecular sieves have been used extensively in industry to
purify gas streams (1,6) and, unlike currently available porous polymers,
425
-------
have large capacities for adsorbates—20 to 30 percent by weight. Despite
the clearly Indicated potential for air sampling, molecular sieves have not
found much application for this purpose. We therefore undertook an investi-
gation to determine the suitability of molecular sieves for sampling low
molecular weight aldehydes in air. For this study, 13X sieves were chosen
because large pore size would ensure efficient mass transfer. Sieves were
ground to 12/30 mesh and activated by heating slowly to 400° C under vacuum and
maintaining temperature and vacuum overnight. Because acrolein is more toxic
than formaldehyde and the problem of obtaining constant concentrations in air
much more straightforward, verification of sieves as a sampling medium for
acrolein received priority.
Acrolein
Since some labile compounds react on sieves even at ambient temperatures
(2,9,10), efforts were initially directed at determining the yield of recovery
from sieves. When known amounts of acrolein were loaded onto sieves as vapor,
recovery by desorption with chilled distilled water (sieves added to water)
was quantitative: 97 + 11 percent for 3 to 8 ug acrolein/g sieves, 90+7
percent for 60 to 200 yg/g. Analysis of desorbate was performed by gas chro-
ma tog raphy on Tenax-GC with a flame ionizatlon detector. Sample tubes loaded
with equal volumes of vapor, stored in a refrigerator, and analyzed serially
over 4 weeks showed no losses.
The performance of sieves was assessed by determining the breakthrough
characteristics of acrolein. We determined that the Theory of Statistical
Moments (TSM) (3-5) would describe the behavior of acrolein on sieves and
extrapolated breakthrough performance from moderate to low concentrations
by TSM. In this manner, problems inherent in working with low concentrations
of a reactive compound were avoided. The apparatus in Figure 1, shown in a
configuration for breakthrough testing, was capable of producing constant
concentrations in the range 400 to 3,000 ppm for periods of up to 4 hours.
Typical breakthrough data obtained with 1 g of sieves in a 10 mm I.D. sampling
tube at a sampling rate of 1 1/min are given in Figure 2.
As the solid curves indicate, breakthrough is satisfactorily described
by curves constructed from the o's (standard deviation) and tn 's (break-
u »j
through time of 50 percent of input concentration) derived from the data.
Table 1, Column 3, indicates that the relative standard deviation a* (*0/tQ e)
is
-------
Rotameters
Septa
N
25° Bath
FIGURE 1. Dynamic uiluiion apparatus
1.00r
Sampling pump
•V
—Sieves
To exhaust
60
80 100
Time (min)
FIGURE 2. Representative breakthrough experiments for the following input
concentrations: a) 6.31 mg/1, b) 4.68 mg/1, c) 3.08 mg/1, d) 2.79 mg/1,
e) 1.66 mg/1.
427
-------
10
00
TABLE 1
Breakthrough Data for Acrolein and Water on 13X Sieves
c^ mg/L
Gravimetric Desorption GC
0.903a
1.66a 2.45
1.96a
2.79a 2.73 2.25
3.08a
3.22* 3.68
3.53a .3.39 3.52
4.68 5.55
4.81* 5.11
5.08* 4.24
6.31* 6.94 6.42
21.3
6.6
acrolein
A, mg/g
Gravimetric Desorption
121a
169* 166
148*
179*
151*
166a
174a
179* 197
water
260
230
GC
76a
178
147a
136
127a
17C
179
178
176
146
182
a* = o/t0>5
0.18
0.18
0.15
0.21
0.24
0.20
0.21
0.21
0.19
0.39
0.21
0.18
0.29
t0.5>min
84
69
67
54
39
46
43
31
32
33
25
22
18.3
F, L/min
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
2.0 •
used in least squares fit to Langmuir isotherm. Accuracy of results was assumed to be gravimetry > desorption
> GC.
-------
through data (Table 1) by a least squares fit to the best Langmuir isotherm.
The fit is quite good, with a correlation coefficient of 0.94 and standard
error of estimate +_ 19 percent. In addition, the calculated saturation capa-
city (dashed line, Figure 3) of 236 mg/g is in good agreement with the experi-
mental value of 226 mg/g determined in static experiments.
With the assumption from TSM of concentration independent a*, the break-
through curve for any concentration can be constructed from the corresponding
tQ - determined from the isotherm by the relation
.£ —
C0.5 " GI X F
where a - capacity, mg/g
c. « input, concentration, mg/1
w * weight of sieve bed, g
F - flow rate, 1/min
and o « a* x tn e
u «->
Calculated 5 percent breakthrough times for various acrolein concen-
trations sampled in dry air at 1 1/min with 1 g sieve beds are given in Table
2. Since 2 ug acrolein/g sieves can be readily determined by GC analysis, the
sensitivity for acrolein in dry air is 0.01 ppm for an 80-liter sample.
Because water will displace acrolein from the sieves, the effect of hu-
midity on acrolein breakthrough had to be defined. Breakthrough of 1,500
ppm acrolein at 30 percent relative humidity superimposed on the water break-
through curve is shown in Figure 4. Figure 5 shows results of a similar
experiment at 100 percent relative humidity. The acrolein elutes from the
sieve bed with the water front in the form of a GC peak, having a variance
similar to the water breakthrough curve and a concentration maximum at ap-
proximately tn _ of water. At 100 percent relative humidity, 5 percent
breakthrough occurs in *8 min. With a sensitivity of 2 ug acrolein/g sieves,
a concentration of 0.1 ppm should be detectable in an 8-liter sample on 1 g of
sieves. Since the capacity of sieves for water is constant to very low rel-
ative humidities, sample volume and therefore sensitivity will increase
directly in proportion to decrease in relative humidity.
Formaldehyde
Formaldehyde is more difficult to handle. To date, the recovery of
429
-------
f
J
o
240
200
160
120
80
40
0
•i ^ 1-
;l 1- 1-
I | | | | | | | |
2.0 4.0 6.0 8.0 10O 12.0 W.O 16.0 18.0 200
FIGURE 3. Dynamic adsorption isotherm of acrolein at 21° C.
Time (rmn)
FIGURE 4. Acrolein breakthrough, 30 percent relative humidity.
Imtn)
FIGURE 5. Acrolein breakthrough, 100 percent relative humidity.
430
-------
TABLE 2
Breakthrough Times of 5 Percent of Acroleln Input Concentration In Dry Air
t (mln)
4.57 20
2.29 43
0.229 72
0.023 82
0.0023 82
0.0002 82
formaldehyde from sieves has been established when It Is loaded as vapor from
formalin headspace. Relatively high concentrations were used so that analysis
of desorptlon solutions could be performed by GC on Carbowax 20 M with a flame
lonlzatlon detector. The chromatograms of formalin and the headspace show
two peaks in addition to methanol (present as a preservative). The major
peak, preparatlvely chromatographed and collected In water, gave a chromo-
phore with chromotropic acid and was assumed to be monomeric formaldehyde
(and/or the hemiacetal with methanol). This peak was used as a standard for
determination of formaldehyde in desorption solutions. The presence of the
monomeric aldehyde in headspace was qualitatively demonstrated by observing
the formaldehyde carbonyl absorbance bands in the UV on bubbling headspace
into heptane in a sample cuvette.
Recovery of formaldehyde from sieves was determined by comparing total
formaldehyde content of distilled water through which a known volume of dilut-
ed headspace had been bubbled with that in desorbate from sieves loaded with
an equal volume of diluted headspace. For loadings of 100 to 200 yg formalde-
hyde/g sieves, recovery was 98+5 percent; for 0.9 to 1.1 mg/g, 108 + 5 per-
cent. It was also determined that formaldehyde in desorbate could be analyzed
colorimetrically with chromotropic acid, but only with desorption volumes >IQ
ml/g sieves. More concentrated desorbate gave irregular color development
with yellow interference. For a 10-ml desorption volume and the sensitivity
reported in Reference 8 for the final colorimetrie solution, 0.2 ppm formal-
dehyde could be detected In an 8-liter sample on 1 g sieves at 100 percent rel-
ative humidity. We have assumed that breakthrough characteristics of form-
aldehyde will be similar to those of acrolein; however, work is currently in
progress to describe breakthrough behavior.
-------
FIGURE 6. Gas chromatogram of a 2.5-liter field sample collected over 12 min at
a sampling rate of 208 ml/min. The following concentrations were calculated
on the basis of a comparison of peak heights with those of standard solutions:
1) methanol, 110 ppm; 2) acetaldehyde, 10 ppm; 3) ethanol, 3 ppm; 4) acrolein,
16 ppm; 5) acetone, 66 ppm.
ACROLEIN
100.
50,
20,
-10.
c
i 5.
ir
K
UJ
I2-
1.
0.5
0.2,
0.1
» •- IMMEDIATELY OANGEWHIS TO LIFE OR HFALTH-
" O
••SHORT Te?n EXPOSURE LIMIT-
1 10 25 5C 75 90 99
PERCENTAGE OF SAMPLES WITH LEVELS LESS THAN STATED VALUE
99.9 99.99X
FIGURE 7- Frequency distribution of acrolein concentrations at fires, total
118 samples.
432
-------
Field Measurements
Molecular sieve sampling tubes were contained In a sampling package
deployed on the rescue squads of the Boston Fire Department. A gas chro-
matogram typical of the sample desorbates is shown in Figure 6. Formaldehyde
did not elute from Tenax-GC, but its presence was confirmed by chromotropic
acid analysis of the desorbate. To our knowledge, these data are the first
confirmation of the presence of acrolein at urban residential fires. The dis-
tribution of acrolein concentrations in fire samples, shown in Figure 7.
indicates that acrolein exposures are of concern as a potential hazard.
Formaldehyde was not present in sufficient concentration to justify allocation
of technician time for routine analysis. Analyses were performed on a spot
basis on samples which indicated severe exposure to other contaminants. Max-
imum recorded formaldehyde exposure was 11 ppm.
REFERENCES
1. Anderson, R.A. Mol. Sieves II. ACS Symp Ser 40:637, 1977.
2. Barrer, R.M., Reucroft, P.J. Proc R Soc London, Ser A 258:431, 1960.
3. Grubner, 0., Zikanova, A., Ralek, M. J Chromalogr 28:209, 1967.
4. Grubner, 0. Adv Chromatogr 6:173, 1968.
5. Grubner, 0., Underbill, D. Sep Sci 5:555, 1970.
6. Lee, H. Adv Chem Ser 121:311, 1973.
7- NIOSH Manual of Analytical Methods, 2nd Edition. U.S. Department of
Health, Education, and Welfare, Center for Disease Control, NIOSH.
Cincinnati, Ohio. Publication #77-157-A P and CAM 118.
8. Ibid., P and CAM 125.
9. Poutsma, M.L. Zeolite Chem and Catalysis, ACS Monogr 171:529, 1967.
10. Venuto, P.B., Landis, R.S. Adv Catal 18:259, 1968.
11. Walker, J.F. Formaldehyde. New York, R.E. Krieger Co., 1975 Ch. 3, 5, 8
433
-------
MAILING ADDRESS OF PRIMARY AUTHOR
Avram Gold, Ph.D.
Harvard School of Public Health
Kresge Center for Environmental Health
665 Huntlngton Avenue
Boston, Massachusetts 02115
Discussion
DEBBRECHT: I would like to Just make one comment and possibly a sugges-
tion. The one comment Is: I think you are very justified In watching out
for the volatile fume that obviously you became aware of. You had to put
these materials on your molecular sieve when the vapor condenses to a liquid
form.
I don't know how well known this fact is, but one runs into the same
problem with charcoal tubes in industrial hygiene work. It makes a difference
between your efficiencies and recovery.
The second thing Is that certainly the flame ionization has extreme im-
portance to formaldehyde. One possibility is using the technique that is
currently available on a GO system for carbon monoxide, which is also not
detected by flame. And that is to convert the carbon monoxide to methane
at the GC separation, when that occurs, using a nickel and hydrogen atmosphere.
This should certainly work with formaldehyde and at least give you methane-
sensitive formaldehyde.
GOLD: Yes, there are several possibilities. They are interesting
possibilities, and Dr. Lin here has suggested, for example, a photo ionization
detector. We do not have that capability and would not have it in the near
future.
DEBBRECHT: 1 don*t think the photo ionization detector has enough energy
to get the formaldehyde; I might be wrong.
GOLD: 1 have not had any personal experience with that. I understand that
it is high enough in energy, so that it would attach hydrocarbons, if the
formaldehyde is present as an aldehyde, when it enters the detector—we have
some evidence that it is. We are very worried about the form of the form-
aldehyde because of the fact that if it appears in a gas stream as a mono-
mer—or anything that has a molecular diameter smaller than the pores of the
sieves—it won't be collected; it will pass right through. So, we were very
worried about whether we had monomer or polymer. We had some interesting
experiences with the effluents from permeation tubes, using paraformaldehyde.
434
-------
Also, there is a possibility perhaps of doing the analysis by high
performance liquid chromatography. One has a very good chromophore in the
dinitrophenolhydrazine group. The concentration of the desorbate which
would occur in a prechromatographic step on some sub-packing could also be
used. I don't think there is any doubt that the method could be improved
considerably.
I also have talked to other people who have had problems with the chromo-
trophic acid determinations. We used it, because at least as far as our
verification experiments were concerned, we knew we were dealing with form-
aldehyde or something like formaldehyde.
I can't remember whether I have said that we do have some evidence that
the formaldehyde in the headspace of the analyzer contains at least some of
the aldehyde, because we bubble the headspace vapor into heptane in a UV
spectrophotometer, and in fact, we're able to see the fine structure of
formaldehyde in the UV.
So, at least some formaldehyde is present as monomer.
MEIER: I would caution you about extrapolating from high concentrations
to low concentrations. Past experience on other studies that we have done
indicate that the small amounts or irreversible adsorption that do take place
on things such as molecular sieves become more and more significant as your
concentration becomes less and less, and can result in errors of 100 to 200
percent or false-negative results indicating nothing is there when indeed
there is.
GOLD: 1 guess my answer to that would be that I think that for the ap-
plications which most people would be interested in, errors are tolerable of 100
percent at really low levels, if you are talking parts-per—billion.
MEIER: If you are talking about criteria level—and I am just using a
hypothetical case—of parts-per-million, and you irreversibly adsorb at that
level so that you are actually getting results of zero, it becomes very
significant.
GOLD: That's true. At those parts-per-million levels we are OK. We
can take enough of a sample so that irreversible adsorption in the small
pores, or whatever, of the sieves would not significantly impair our accuracy.
If one worries about trace analysis, that is another story, and at this
point, I wouldn't care to comment.
435
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Passive Membrane-Limited Dosimeters
Using Specific Ion Electrode Analysis
Charles E. Amass
Orion Research, Inc.
Cambridge, Massachusetts
INTRODUCTION
In recent years, many workers have described systems using permeation
techniques for detecting and determining toxic gases in the atmosphere.
Kenneth E. Reiszner and Philip W. West (8) described a method using a sill-
cone rubber membrane with a liquid collection medium for measuring sulfur
dioxide at ambient levels (7).
Similarly, B.I. Ferber, F.D. Sharp, and P.W. Freidman at the Bureau of
Mines used a silicons membrane, a liquid collecting medium, and an ion spe-
cific electrode readout for determining oxides of nitrogen (2).
Methods have been developed for vinyl chloride, carbon monoxide, nitrogen
oxide, sulfur dioxide, hydrocarbons, and ammonia utilizing diffusion prin-
ciples (1-8,10). This report describes the development of a system for
detecting a number of inorganic gases in the air and a rapid method for de-
termining their levels.
SYSTEM REQUIREMENTS
In designing the systems, a number of requirements were formulated as
being necessary for successful performance. The membrane must be mechanically
strong, uniform, and be free of reaction with solution chemistries. The
437
-------
membrane permeability must be uniform from piece to piece and slow enough to
be the limiting layer; that is, free from effects of changes in flow pattern
around the dosimeter. In addition, the permeability should be relatively low
for water (and high for the contaminant), combined with a rapid time response
for integrating peak values, and low sensitivity to temperature change. Per-
haps most importantly, the membrane/solution combination should exhibit
linearity with respect to both time and concentration.
The solution chemistries must be stable for 6 months before exposure,
and the stoichiometrically formed products must be invariant for at least 2
days. A rapid and complete reaction to form the product is necessary to ensure
proper integration—that is, maintain a zero partial pressure for the contami-
nant within the dosimeter. In addition, the reagent and analytical method must
be selective, sensitive, and capable of covering a wide concentration range.
Theoretical Background
Although much attention has been given to a theoretical model for geo-
metrically limited diffusion for dosimeter designs (3,5,6,9), no work has
clearly outlined the theoretical design criteria for a successful membrane-
limited dosimeter.
The past several years have seen a rapid advance in gas-permeable mem-
brane technology. This technology has been applied with great success at
Orion Research, Inc., in the development of a large number of gas-sensing
electrodes. The use of these membranes in dosimeters, while apparently quite
different, involves the same problems and theoretical analysis which were
developed for the gas-sensing electrodes (9).
On exposure to an atmosphere containing the sensed species, a steady
state will be attained in a short time (less than 1 minute), and steady state
solutions to Pick's Law of Diffusion can be applied. Concentration gradients
of a diffusing gas under steady state conditions are shown in Figure 1.
There are three diffusion phases: a boundary layer outside the membrane of
thickness 1D which depends on the aerodynamics of the sample atmosphere; the
D
actual membrane whose thickness is 1..; and an internal absorption liquid.
M
Within any phase, the concentration gradients are linear, and the flux of the
2
diffusing species per cm is given by:
438
-------
Cs
»b-*f— 'm—H
k. rm
Ca
SAMPLE
ABSORBING
SOLUTION
FIGURE 1. Membrane-limited diffusion.model. Cs atmospheric concentration, 1.
boundary layer, 1 membrane layer, Ca concentration in boundary layer at mem-
brane surface, Cm concentration in membrane at outer surface.
where F is the flux in moles/cm /sec
2
0 is the diffusion coefficient in cm /sec
1 is the phase thickness in cm
AC is the concentration difference between the phase boundaries in
3
moles/cm .
A concentration discontinuity may exist at the outer surface of the mem-
brane because of the partition of the diffusing gas between air and the mem-
brane phase* Such partition reactions are rapid for most gases, and it is
permissible to assume that equilibrium exists at the interface; i.e.,
C = k C
m a
[2]
where C and C are the boundary concentrations of the diffusing gas in the
m a
membrane and in air, respectively, and k is the partition coefficient (i.e.,
the Henry's Law constant for the gas expressed in dimenslonless units).
439
-------
At the membrane-absorbing solution Interface, the concentration of the
diffusing gas is zero, since the absorbing solution is designed to contain
a sufficiently high concentration of a fast-reacting species to destroy every
molecule of diffusing gas which reaches the absorbing solution surface.
The overall flux of diffusing gas into the dosimeter can be obtained
by combining Equations 1 and 2 and noting that the flux in the boundary layer
must be equal to that in the membrane in the steady state.
Dmk C, [3]
1m + D kl.
m b
D
a
where D and D are the diffusion coefficients of the gas in the membrane
ma
and in the air, respectively, and C is the sample concentration in moles
3 ®
per cm .
If the gas reacts with the absorbing solution to produce s moles of
product per mole of gas, then the final concentration of the product after
an exposure time t is
P- v
Fdt [4]
where V is the volume of the absorbing solution, and C is the concentration
of the product sensed by the ion specific electrode in the absorbing solution.
Thus, C is proportional to the integrated exposure to the reacting gas
p
concentration C in the environment.
8
AERODYNAMIC EFFECTS
The constant of proportionality in Equation 5 includes a term involving
1. , the boundary layer thickness. In normal use, the dosimeter will be ex-
posed to atmospheres which vary from completely static to high flow-rate
situations. As a consequence of the variable rates of stirring, the effective
boundary layer thickness JL will vary. Virtually no design data are avail-
able regarding air flow patterns in the Immediate neighborhood of a human
440
-------
subject, and exact predictions of 1, are therefore not possible* Measurements
D
In our own laboratory, however, under static conditions yield values of 1,
on the order of 10 cm. Extrapolations of published engineering data on
"gas side resistance'' in absorption columns suggest that 1, has a value around
10 at flow velocities of 1 mph, and that this thickness decreases rapidly
with further increase in flow velocity. It was necessary, therefore, to
select a membrane with appropriate values of 1 , D , and k, such that
m m
m *. ,n b for 10 percent accuracy [6]
D~k ? 10 D~
m a
Values of D for gases of intermediate molecular weight (20 to 100) in air at
2
atmospheric pressure at room temperature are on the order of 0.1 cm /sec,
and for the membrane, D^k = 2 x 10 cm /sec for SO-, MR., and H2S and
1 " 2.54 x 10* cm. Thus, substituting for D , D k, 1 , and for 1. , the
m ^i a' m * m' b*
worst case static condition value of 10 cm, we have:
2.54 x 10"3 IQCIO"1) [7]
2 x 10~4 .1
thus 13>10
The condition on accuracy imposed by Equation 5 is therefore met, and dosi-
meters of the type proposed can operate with negligible interference from
variable aerodynamic states in the environment. Laboratory tests have con-
firmed this result.
SOLUTION CHEMISTRY
Sulfur Dioxide System
An acid buffer assures that all sulfur dioxide is trapped on entering
the solution in the form of bisulfite ion.
H20 + SO, + NaX •*• HX + NaHSOg [8]
Sulfur dioxide is complexed in such a way that an ion which can be sensed by
electrode is stoichiometrically released.
Ammonia, Hydrogen Fluoride, Hydrogen Chloride
The dosimeter filling solution consists of a buffer which provides the
441
-------
necessary trapping pH and antibacterial action. The pH is on the acid side;
this converts all ammonia entering the dosimeter into ammonium ions. An am-
monium specific ion electrode using a macrotetralide antibiotic as the ion
selective element is used in combination with a single Junction reference
electrode to complete the measurement cell. Similarly, hydrogen fluoride
or hydrogen chloride are also trapped at this pH, and readout is by means of
the corresponding ion specific electrode.
Hydrogen Sulfide
The approach taken is to utilize the extreme insolubility of a metal
sulfide, even in the presence of an enormous excess of a strong complexing
agent. Hydrogen sulfide dissolves to form hydrosulfide ion which reacts with
metal ion. An electrode sensitive to the metal ion is used for the readout.
This method is a so-called subtractive one, and in order to obtain a usable
balance between sensitivity and range, the metal concentration of the dosi-
meter is set at two times the expected consumption for the point of maximum
required accuracy.
Hydrogen Cyanide
The hydrogen cyanide filling solution consists of a known amount of a
cyanide complex dissolved in a buffer at a high pH. At this pfl, any hydrogen
cyanide entering the solution will form cyanide ion. Cyanide ion further
complexes the small amount of uncomplexed metal in the solution in proportion
to the cyanide added. The readout cell consists of a metal ion electrode and
a reference electrode.
Dosimeter Design
The prototype dosimeter units used in our experiments are shown in Fig-
ures 2A and 2B. All pieces except the 0-ring were machined from linear poly-
ethylene. The 0-ring is solid Teflon.
The diffusion-limiting membrane construction is still proprietary at
this time. The dosimeter is designed to contain 2 ml of absorbing solution,
which leaves a small headspace. Full contact with the membrane is not neces-
sary for accurate integration.
442
-------
BODY
MEMBRANE
GRID
GAS COLLECTION
FLUID CAVITY
2.2ml VOLUME
1.247" DIA.x
.115" DEPTH
SEALINE
CAP
RETAINING
SCREW RING
SECTION A-A
NON TURNING LOCKING RING
BODY
CAP
TEFLON -0-RING
MEMBRANE
.115" DEPTH
1.247" DIA.
2.2cm3 VOLUME
FIGURE 2. Prototype dosimeters: (A) with grid over membrane and locking no-
turn washer, and (B) simplified design incorporating Teflon 0-ring.
-------
Equipment for Generating Test Atmosphere
A schematic diagram of the test equipment is shown in Figures 3A and 38.
Permeation tubes were used to generate test atmospheres for sulfur dioxide,
ammonia, and hydrogen sulfide. For hydrogen chloride, a gas phase permeation
device was used. The gas phase permeation device consists of a stainless
steel cylinder with connections to a HC1 tank. Nitrogen gas or air is passed
through a length of porous Teflon tubing which enters the cylinder and exits
from it. For this type of device, an air oven was used for temperature control
because of the danger of water contamination and the relative insensitivity of
the gas phase device to temperature changes.
The dosimeter test chamber consisted of a pyrex autoclave (2,200 ml) with
the seal modified by incorporation of a large 0-ring and retainer. A blending
device (Figure 3B) allowed mixing either dry or humidified diluent air with
the permeation tube output, and then splitting the gas stream into two parts
to allow for varying the flow rate through the chamber at constant concen-
tration. All connections were made with ball and socket joints with a thin
film of vacuum grease. Bubblers on all downstream lines were provided to give
the complete integrated analysis of the contaminant atmosphere concentration
during the course of the experiment*
The entire chamber was placed inside a constant-temperature air oven
to allow temperatures in the range of 0° to 50° C to be generated. It was
found that even a short length of tubing would equilibrate the sample gas to
the temperature of the test chamber. Humidification was supplied by passing
compressed air through a bubbler in a water bath at reduced temperature and
then through a suitable filter to remove micro droplets, or by a diffusion
tube technique.
Method
A volume of the dosimeter solution is pipetted into the dosimeter body
and sealed in place. The dosimeter is then stored with a protective cover
until exposure. After exposure, the cover is removed and a pair of electrodes
are placed into the solution. A potential is developed between the electrodes
which can be measured by a specific ion electrode meter. A calibration curve
is constructed (Figure 4) by adding known amounts of the ion of interest to
a sample of the dosimeter filling solution. A stable reading Is usually ob-
tained in less than 1 minute. In the hydrogen sulfide system, solutions are
444
-------
VENTED TO
ATMOSPHERE
DUAL
STAGE
REGULATOR
ALL THERMOMETERS
.fC DIVISIONS)
VERNIER
HIGH PRECISION
VALVES
SOAP BUBBLE
FLOWMETER
DOSIMETER
TEST CHAMBER
BUBBLER STAGES
OIL&
PARTICLE
TRAP
WATER BATH «
. o o . o
0 AIR OVEN
.800
m i mi • mt i §• i !• • tm i §• im
DRYING TUBE
COMPRESSED
GAS
PERMEATION TUBE
HOLDER/EQUILIBRATOR
VERNIER
NEEDLE
VALVE
LIQUID TRAP
FIGURE 3A. Test apparatus—permeation tube and temperature control system.
m
-------
"KENICS"
GAS BLENDER
SPLIT STREAM OR
BUBBLER TAKE-OFF
IN
OUT
BUBBLER
WATER BATH
FIGURE 3B. Test apparatus—gas blending and humidification system.
icr3
+70 +90 +110
MILLIVOLTS
30 *I50 +170
FIGURE 4. Electrode calibration curves for sulfur dioxide (0) -1 x 10 M,
reagent (background for current OSHA standards); (a) 1 x 10 M. reagent
(background for current EPA standards).
446
-------
prepared with progressively lower concentrations by diluting the filling
solution with ion buffer.
Calculations
Regular checks of permeation tube output are compared to the bubbler-
integrated value to determine system holdup or leaks. Calculation of ppm
exposure is based on the bubbler values corrected by the amount of gas trapped
by the dosimeters and the volume of gas remaining in the chamber which does
not pass through the bubblers. A permeation rate was calculated according to
the formula
[9]
P « 1 lO^ (ml gas [RTF]) x (cm thickness of membrane)
2
(seconds exposure) (cm area membrane) (cm Hg partial pressure
of contaminant - 0).
Permeation rates calculated in this fashion should be constant, and indepen-
dent of variations in time, concentration of exposure, and pressure. Once
such permeation values have been obtained for a series of different exposure
parameters, the range in these values is reduced using an average permeability
to decrease the error for measurements under unknown conditions. Thus, in
actual use, an average permeation value is selected for the particular gas of
interest, and that value is used as a constant to convert the moles of species
found in the dosimeter to ppm-hours. Dividing by the exposure time then gives
the average ppm level.
RESULTS
Membrane Selection
The membrane used offers a significant advantage over the silicone mem-
branes used by other workers. Although it is somewhat less permeable than
silicone rubber membrane, we gain the advantage of less interference from
windage effects. In addition to this, however, the membrane's mechanical
properties allow it to be used without the individual calibration of each dosi-
meter. If reasonable care is used in assembly, the values obtained with a
sample of the membrane are reproducible without prior calibration. All that is
necessary to know is the membrane area and the solution volume. This membrane
area-to-solution volume ratio is the only determinant of the concentration to
447
-------
be found In the dosimeter, for a given exposure time and concentration of gas.
This substantial advantage allows mass production of the dosimeters without
individual testing. Therefore, they can be disposable, since their manufacture
is not labor intensive.
All data in this report were obtained using a fresh piece of membrane
for each exposure. Thus, any variation in membrane permeability due to thick-
ness or composition is inherent in the data.
RESULTS
Linearity
System linearity is a function of electrode slope and the permeation
rate variation with concentration, time, temperature, or humidity. Typical
calibration curves are shown in Figure 4 for the ion selective electrode
used with the SO- filling solution. Figures 5A, 5B, and 5C show linearity
with respect to time at various selected constant concentration levels for the
ammonia, hydrogen chloride, and hydrogen sulfide systems. The regression line
calculated for the hydrogen sulfide system suggests a high blank. Actually,
the deviation is caused by a slight fall off in permeation rate at longer
exposure times (discussed below). Each point represents a group of from four
to six dosimeters.
Concentration linearity at various typical constant exposure times are
shown in Figures 6A, 6B, and 6C) for the ammonia, hydrogen chloride, and hydro-
gen sulfide systems. The regression line for the hydrogen sulfide system
was calculated using only values below 25 ppm. The high exposure levels
produce a falling off in permeability, probably due to back diffusion (see
discussion below).
An overall response to variation of temperature, concentration, and ex-
posure time is shown for sulfur dioxide in Figure 7. This graph of concen-
tration of exposure versus concentration predicted by the dosimeter shows a
close correlation with the theoretical 45° slope. Reproducibility of the
systems is indicated in Table 1, where statistical data are presented for each
of the systems currently tested. For this table, an average permeation rate
was selected based on the entire group data, and the value was then used to
calculate ppm levels.
448
-------
O MEAN
I ERROR RANGE AT THE 95%
CONFIDENCE INTERVAL FOR A
GROUP OF 4-6 DOSIMETERS
7 2
2
TIME (MRS.)
FIGURE 5A. Time linearity—exposure time versus dosimeter concentration,
5 ppm ammonia 20° C.
Ill
i
O MEAN
T ERROR RANGE AT THE 95%
CONFIDENCE INTERVAL FOR A
1 GROUP OF 4-6 DOSIMETERS
2
TIME(HRS)
FIGURE 5B. Time linearity—exposure time versus dosimeter concentration,
10 ppm hydrogen chloride 20° C.
ERROR RANGE AT THE 95%
CONFIDENCE INTERVAL FOR A
GROUP OF4-6 DOSIMETERS
FIGURE 5C. Time linearity—exposure time versus dosimeter concentration,^
20 ppm hydrogen sulfide 20° C.
-------
o 5
O MEAN
ERROR RANGE AT THE 95%
CONFIDENCE INTERVAL FOR A
GROUP OF 4-6 DOSIMETERS
FIGURE 6A. Concentration linearity—exposure time versus dosimeter concen-
tration, 1 hour ammonia*
ERROR RANGE AT THE 95%
CONFIDENCE INTERVAL FOR A
GROUP OF 4-8 DOSIMETERS
24
PPM
FIGURE 6B. Concentration linearity—exposure time versus dosimeter concen-
tration, 4 hours hydrogen chloride.
O MEAN
ERROR RANGE AT THE 95%
CONFIDENCE INTERVAL FOR A
GROUP OF 4-6 DOSIMETERS
90
PPM
J
n
100
FIGURE 6C. Concentration linearity—exposure time versus dosimeter concen-
tration, 8 hours hydrogen sulfide.
450
-------
24
I 20
12
O MEAN
I ERROR RANGE AT THE 95%
CONFIDENCE INTERVAL FOR A
GROUP OF 4-6 DOSIMETERS
12 16 20 24 26
EXPOSURE CONCENTRATION (PPM)
32
36
40
FIGURE 7. Overall system response for sulfur dioxide—test atmosphere concen-
tration versus dosimeter calculated value using average permeation rate.
260
240
1 200
x
t
d 160
g
120
80
40
263
O
- O
197
220
O
182.5
O
0)254
0239
234
D
D
2035
203
Q
0
1915
& 185
O 164
O(25.KT8
D(2.9»IO"* )
O.I 0.25 09 I
I I I L
10 1520 100
TIMEIMIN )
FIGURE 8. Response times for hydrogen sulfide. (0) 2.5 x 10 M. metal Ion,
(Q) 2.5 x 10~* M. metal ion, (A) 2.5 x 10 M. metal ion. (•) dilute buffer,
( ) concentrated buffer.
so
25
s
B-
V
J L
O MEAN
T ERROR RANGE AT THE 95% CONFIDENCE
. INTERVAL FOR A OROUP OF 4-6 DOSIMETERS
_L
9 «
TIME (MRS)
1
10
FIGURE 9. Membrane response for hydrogen sulfide—exposure time versus ppm-
hour found in dosimeter. 451
-------
TABLE 1
Systems Performance
DOSIMETER
EXPOSURE
S02 a:
b
H S cr
HC1 d:
SYSTEMATIC
ERROR
-0.4%
-3.9%
-3.2%
-2.8%
RELATIVE
STANDARD
DEVIATION
5.3%
4.6%
4.3%
4.3%
ERROR RANGE AT
95% CONFIDENCE
LEVEL BASED ON
SYSTEMATIC ERROR
-10.8% to 10.0%
-12.9% to 5.1%
-11.6% to 5.2%
-11.1% to 5.5%
a = four exposures of five dosimeters each at 0% humidity range, 1 to 9 ppm
range and 20° to 40° C temperature range.
b = four exposures of five dosimeters each at 0% humidity range, 5 to 70 ppm
range and 20° to 40° C temperature range.
c = 18 exposures of five dosimeters each at 0% humidity range, 4 to 210 ppm
range and 20° C temperature range.
d = 12 exposures of six dosimeters each at 0% to 45% humidity range, 1.5 to
26 ppm range and 5° C to 40° C temperature range.
Response Time
Other investigators have suggested response time for silicone rubber
membrane in the range of 30 seconds to 10 minutes for various gases (1,5,8).
Hydrogen sulfide was selected for response time tests since the solution used
adapted itself well to adjustment for quantitating low concentrations, and the
OSHA ceiling limit for H_S requires a sampling time of under 10 minutes. A
tank of 210 ppm hydrogen sulfide in nitrogen was used to generate the test
atmosphere in the test chamber. A 28/15 socket on the test chamber was adapt-
ed to an earlier prototype dosimeter by means of a standard clamp. Dosimeters
could be placed over the orifice and clamped in place for a set period of time.
When a dosimeter was about to be placed over the orifice, the exiting gas (300
ml/min) would ensure that rapid contact between the test atmosphere and the
dosimeter membrane would occur. A bleed was provided for escaping gas during
exposure. For the extremely low levels, multiple exposures of the dosimeter,
with a relaxation time between exposures, were used to build up a sufficient
452
-------
level of the sulfide in the test solution. Figure 8 illustrates the results
of these tests. It should be noted that the extremely short-range tests
were done with ion buffering at two concentrations. The lower values for
permeation rate at short times can be related to back diffusion of H.S from
the dosimeter before reaction could occur, since higher permeation rates were
obtained over the same exposure times (.1 to 1 minute) by adjusting the buffer
concentration, which, by reducing complexation, raises the available metal
ion concentration to that used for times from 5 to 20 minutes. This change
in concentration increases the rate of reaction with hydrogen sulfide dis-
solving in the solution. The high gas concentration utilized, over 20 times
the TLV, could readily exhaust a thin film of dilute metal ion concentration
near the membrane.
Trapping Efficiency
As Indicated above, for accurate integration the partial pressure of
the contaminant in the dosimeter must be zero, or substantially 100 to 1,OOOX
lower than the partial pressure of the contaminant in the atmosphere. The
hydrogen sulfide system Indicates some of the problems that can be encountered.
With one membrane construction, a somewhat erratic and large variation in
permeation rate is found, as shown in Figure 9, where exposure time versus
concentration found in dosimeter is graphed for 25 ppm H.S. The deposition
of a precipitate on the interior of the membrane causes a decrease In permea-
tion with time. Modification of the membrane construction corrected most of
the change, as shown in Figure 5C, although, as pointed out above, some de-
crease is noted at the high end. It should be noted that the ppm-hours for
typical government limits occur In the linear portion of the curve.
In addition, the hydrogen sulfide system showed some lowering of trap-
ping efficiency with high concentration of H_S at short exposure times, as
shown in Figure 10, where the variation of permeability as a function of ppm
level at constant ppm-hours is shown. High levels of H.S probably exhaust a
thin layer of buffer solution near the membrane surface and cause measurable
back diffusion. The effect is minor in light of the low standard of accuracy
proposed for dosimeters.
Humidity
Figure 11 shows the water loss from the dosimeters for an 8-hour exposure
period at various relative humidity levels as a percentage of total solution
volume. Unlike systems that use solid absorbents, one of the main limitations
453
-------
250
£ 200
£
150
I I I I I I I I
10 20 30 4O 50
70 80 *2IO
PPM H2S
FIGURE 10. Membrane response—ppm exposure level versus membrane permeability
at constant ppm-hours.
3*C
IO*C
I3*C ZO-C Z5'C
TEMPERATURE
30'C
35*C
40*C
FIGURE 11. Water loss of prototype dosimeter—temperature versus percent
water loss. (0) 0 percent relative humidity, (D) 40 percent relative humidity,
2
(A) 100 percent relative humidity. Membrane area 8.6 cm , solution volume
2.2 milliliters.
600
500
5400
m
<
tu
i 300
200-
O MEAN
T ERROR RANGE AT THE 95%
CONFIDENCE INTERVAL FOR A
,[_ 1 GROUP OF4-6 DOSIMETERS
5*C IO«C IS'C 20"C 25*C
TEMPERATURE
, i _.
35-C
FIGURE 12. Permeability of hydrogen chloride—temperature versus permeati
rate.
454
on
-------
of the Orion system is water loss with a resultant change in dosimeter com-
position. Even under the most rigorous conditions, water loss is acceptable.
In addition, a simple means of correction can be provided by weighing the
dosimeter at the end of the exposure period and correcting the concentration
by an appropriate factor.
The literature has indicated that membrane permeabilities can be affected
by humidity. The hydrogen chloride dosimeter was selected as a worst case
test for humidity problems with the dosimeter. The average permeability of
all hydrogen chloride tests was 440. For a test at 40 percent relative hu-
midity, the permeation rate was 415~a small difference from the average value.
It might be noted that the dosimeters themselves can generate local
humidity levels in the chamber. Flow rates were kept high in mc^t tests to
keep the relative humidity below 5 percent.
Windage Effects
As noted above, the dosimeter theoretically would have very little wind-
age effect. Tests on the sulfur dioxide system at face velocities of between
30 to 16,000 cm-per-minute showed no effects, other than slightly higher
H_0 loss. A test on the hydrogen sulfide system in which dosimeters were
twirled in the chamber at speeds of about 5 miles-per-hour showed no differ-
ence with those exposed to a flow of 0.001 miles-per-hour. On the other hand,
dosimeters using microporous Teflon as the only diffusion-limiting layer
showed erratic response in a similar test.
Dosimeters containing a grid (Figures 2A and 2B) did show about a 10 per-
cent across-the-board decrease in permeability versus the dosimeter without
such a covering (Figure IB). This effect is ascribed to an increase in L, ,
the static boundary layer (discussed above).
Temperature Effects
The literature has indicated that the effect of the permeation rate with
temperature varies with the gas of interest. Reiszner (8) indicated sulfur
dioxide to have a negligible temperature coefficient in silicone rubber, for
example, while carbon monoxide (4) had a large temperature dependence.
The hydrogen chloride system permeation rate at constant ppm levels
versus temperature is shown in Figure 12. The variation is within other
455
-------
TABLE 2
Permeation Rate Variation with Temperature
SYSTEM
VALUE:
FOR: Px 5° C 20° C 30° C 40° C
S02 330 - 285 - 370
NH3 290 - 300 - 275
H2S 220 220 -
HC1 440 530 >440 475 <440
experimental variables. Less data is available on other systems. Spot tests
are summarized in Table 2, where permeabilities at various temperatures are
shown versus the average permeability for the systems.
Interferences
The hydrogen sulfide system was designed to avoid interference by HC1.
HCN would be a strong interference for this system. The H_S dosimeter was
tested in ozone at 2.5 ppm for 8 hours and nitrous oxide at 22.8 ppm for 8
hours with no change in the dosimeter solution.
The ammonium electrode is somewhat sensitive to other cationic species*
Hydrazine and other low-boiling amines can pass through the membrane, but no
data are available at this time on this interference level. Buffering pre-
vents changes in the hydrogen ion concentration—the only other significant
variable caused by dissolution of acid gases.
The sulfur dioxide system is sensitive to hydrogen cyanide and hydrogen
sulfide gases, both of which can liberate the sensing ion. However, trap-
ping efficiency for these gases will be very low due to the low pH of the
trapping solutions relative to the pKa's. >
The hydrogen chloride system would be affected by hydrogen cyanide,
hydrogen sulfide, and ammonia. Hydrogen sulfide and hydrogen cyanide, however,
would not be trapped efficiently by the buffer. Ammonia would be trapped as
ammonium ion, which does not interfere.
456
-------
The hydrogen cyanide system would have a slight Interference from hy-
drogen sulfide. The hydrogen fluoride system has no Interferences.
Storage Stability
A significant problem in designing dosimeter systems of this kind is the
necessity for extremely dilute reagents and standards to remain stable for
periods of 6 months or more. All the solutions used in our program have been
tested in polyethylene for at least 6 months, including the standards which
are generally at the 10* 1(T M. level. It is hoped that some of the solutions
may be stable for as long as a year. The main limitation is water loss in
the dosimeter, which, due to the experimental nature of the dosimeter pro-
totypes, has not been significantly tested. A good seal is all that is re-
quired.
Limit of Detection
The limits of detection for the current dosimeter systems are outlined
in Table 3. Being of special interest to ambient air quality, an attempt
was made to extend the sulfur dioxide system to its ultimate limit within
the confines of the current geometry. By adjusting the internal solution
concentration downward, the sensitivity was increased as shown in the cali-
bration chart, Figure 4 above. It is possible and convenient to quantitate
at the .1-ppm level for a 24-hour exposure or at the .5-ppm level for a 3-
hour exposure, as suggested on the graph by the indicated levels of concen-
tration to be expected.
The sensitivity of the SCL system can be increased by a factor of 2 by
heating the dosimeters. Water loss at low humidities and high temperatures
would put a time limitation on the device, for 24-hour exposures.
It might be possible to reduce water loss for a special application by
use of a nonaqueous solvent or addition of neutral salts to the dosimeter
solution.
CONCLUSIONS
A passive membrane dosimeter has been developed that requires no individ-
ual calibration, is lightweight, durable, and has no moving parts. When com-
bined with various solution chemistries and specific ion electrodes, the dosi-
meter provides a system for integration of trace quantities of hydrogen sul-
fide, sulfur dioxide, ammonia, hydrogen cyanide, and hydrogen fluoride. The
457
-------
TABLE 3
Sensitivity Limits*
pom hours
b
S02 .25
8C
HC1 1.6
NH R
H2S 16d
.16e
3
a) using 2.0 ml solution and a membrane area of 8.6 cm
-4
b) 1 x 10 molar reagent
-3
c) 1 x 10 molar reagent
_3
d) 2.5 x 10 M. reactant
e) 2.5 x 10 M. reactant
analysis method is simple enough for less skilled personnel and can be done
in a few minutes. The basic method can be extended to carbon dioxide and
other gases amenable to electrode or other methods of analysis.
Exposure tests for various concentration, time, humidity, flow, and
temperature conditions have been performed on hydrogen sulfide, sulfur dioxide,
ammonia, and hydrogen chloride with results more accurate and sensitive than
the current monitoring procedures required in government standards.
ACKNOWLEDGEMENTS
The author wishes to acknowledge the work of other past and present Orion
458
-------
staff members: Martin Frant, who originated the concept and developed many
of the chemistries; James Ross, who provided the theoretical work on diffusion;
Jon Soderberg, responsible for development of the hydrogen sulfide and sulfur
dioxide systems; and Nelson Perry, who patiently carried out the test program
for the other gases and provided the graphs for this manuscript.
REFERENCES
1. Bell, D.K., Reiszner, K.D., West, P.W. A Permeation Method for the De-
termination of Average Concentrations of Carbon Monoxide in the Atmos-
phere. Anal Chim Acta 77:245-254, 1975.
2. Ferber, B.I., Sharp, F.A., Freedman, R.W. Dosimeter for Oxides of Ni-
trogen. Am Ind Hyg Assoc J 37:32-36, 1976.
3. Frant, M.S., Ross, J.W., Riseman, J.H. Electrode Indicator Technique
for Measuring Low Levels of Cyanide. Anal Chem 44:2227-2230, 1972.
4. Mazur, J.F., Bamberger, R.L., Podolak, 6.E., Esposito, G.G. Develop-
ment and Evaluation of an Ammonia Dosimeter. Am Ind Hyg Assoc J 39:
749-753, 1978.
5. Nelms, L.H., Reiszner, K.D., West, P.W. Personal Vinyl Chloride Moni-
toring Device with Permeation Technique for Sampling. Anal Chem 49:
994-998, 1977.
6. Palmes, E.D., Gunnison, A.F. Personal Monitoring Device for Gaseous
Contaminants. Amer Ind Hyg Assoc J 34:78-81, 1973.
7. Palmes, E.D., Gunnison, A.F. Personal Sampler for Nitrogen Dioxide.
Am Ind Hyg Assoc J 37:570-577, 1976.
8. Reiszner, K.D., West, P.W. Collection and Determination of Sulfur
Dioxide Incorporating Permeation and West-Gaeke Procedure. Environ
Scl Technol 7:526-532, 1973.
9. Ross, J.W., Riseman, J.H., Krueger, J.A. Potentiometric Gas Sensing
Electrodes* In: International Symposium on Selective Ion-Sensitive
Electrodes (Moody, G.J., ed.). Cardiff, The University of Wales, 1973,
pp. 473-487.
10. Tompkins, F.C., Jr., Goldsmith, R.L. A New Personal Dosimeter for the
Monitoring of Industrial Pollutants. Am Ind Hyg Assoc J 38:371-377,
1977.
459
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MAILING ADDRESS OF AUTHOR
Charles E. Amass
Orion Research, Inc.
380 Putnam Avenue
Cambridge, Massachusetts 02139
Discussion
SCHEIDE: Do you see any advantages that you would have on using this
liquid solution collecting medium as opposed to a solid collector?
AMASS: We could use a solid collector. We just felt that from the point
of view of analysis, it would be easier. We were looking, possibly, even at
having field people do this work rather than having to train personnel to do
it.
460
-------
Personal Monitoring by Means of Gas
Permeation
Phlljp W. West, Ph.D., and Kenneth D. Reiszner, Ph.D.
Environmental Sciences Institute
Louisiana State University
Baton Rouge, Louisiana
There is an obvious need for personal monitors that are suitable for
determining exposures to toxic agents in residential areas as well as in the
workplace. For such broad applications, convenience and low costs, together
with sensitivity, accuracy, and reliability, are prime requirements. Passive
monitors are especially attractive because they can be produced at a relatively
low cost and are the ultimate in simplicity. Passive devices for sample col-
lection employing gas permeation through polymer membranes are especially
attractive because environmental variations Induce little if any error, and
the total analytic process can be so designed as to accommodate the study of
almost any and all gaseous hazards.
Although permeation-type monitors are the subject of this discussion,
there are other passive systems that have merit for certain applications.
Monitors based on effects response can be used where qualitative results are
sufficient and low cost and convenience are important. Although quantitative
sampling is not possible, relative concentrations are indicated by the degree
of the induced effect. A second type of passive sampling is that based on
the use of evacuated vessels. With such devices, a known volume of sample
can be collected by simply opening the evacuated bottled or flask in the
atmosphere under study to provide a grab sample. Such an approach can also
be used for the collection of integrated samples over a predetermined time
if the sample inlet is provided with a rate-controlling orifice. Evacuated
vessels are limited as to the volume of sample that can be collected and
therefore lack the necessary sensitivity for most work that is involved in
personal monitoring.
461
-------
Diffusion has been introduced as a convenient means of sampling. The
diffusion technique was first introduced as a means of preparing standard
gas atmospheres (1), and where conditions can be kept reasonably constant,
such as in the laboratory, this approach has proven to be quite successful
(2,3). For the preparation of standard gas mixtures, the liquid form of the
reference material is allowed to diffuse into a dilute matrix system. The
resultant conversion of a concentrated reference material to a dilute standard
mixture can be reliable and convenient. The application of diffusion to the
reverse problem—that is, the sampling of a dilute system with the quantitative
collection of a minor constituent—has been advocated by the 3M Company
and the Abcor Development Corporation, as well as by the British Defense
Ministry at Porton Down. To date, the diffusion-type samplers have employed
adsorption for the capture of the diffused sample. After the sample is col-
lected, it is desorbed by suitable means and determined by conventional an-
alytic processes such as gas chromatography. The badge is usually discarded
after a single sample collection. In our experience, sample collection by
means of diffusion is subject to some degree of error due to variations in
humidity as well as by variations in the relative rates of movement of the
collection device and the ambient atmosphere.
Permeation was introduced by O'Keeffe and Ortman (4) in 1966 as a means
of preparing standard gas mixtures. This technique has been widely accepted
as a method of choice for accurately Introducing known amounts of sample gas
into appropriate volumes of diluting atmospheres. The reverse of this process
was introduced by Reiszner and West in 1973 (5) as a means for quantitatively
collecting sulfur dioxide from ambient atmospheres. In this approach the
ambient air was sampled by means of a simple cell containing a solution of
tetrachloromercurate(II), stoppered at the top and enclosed on the bottom
by means of a permeable membrane of a silicone polymer. The permeated 802
was absorbed and fixed as the sulfItodichloromercurate(II) complex which was
subsequently analyzed by the well known West-Gaeke procedure (6). By prior
determination of the calibration constant for a given membrane, the rate of
permeation for SO- was determined; and, thus, the time-weighted average con-
centration for SO- for a known exposure could be established.
Permeation of a given gas through a given membrane is a function of the
concentration of that gas. In general, permeation of a gas can be compared
with dissolution. That is, a gas molecule coming in contact with a liquid
dissolves and permeates into that liquid without the benefit of stirring.
Instead of liquids, polymeric membranes can also serve as a permeation medium.
Gas molecules coming into contact with such membranes dissolve and pass into
462
-------
the barrier until saturation is achieved. If a receiving system is introduced
on the other side of the barrier, equilibrium is disturbed and the permeating
molecules are removed, thus providing a means for quantitative mass transfer.
Because of the fixed relationship between a given gas and a given membrane, the
passage of a gas through membranes can be described by the equation:
w
where k = the permeation constant
C « concentration of the gas of interest, ppm
t « time of exposure
w - amount of gas absorbed, yg.
For use in personal monitoring, the above concepts can be applied, and knowing
the permeation constant, or more properly, the calibration constant for an
individual gas, sampling can be achieved and the concentrations of the gas
of interest in unknown atmospheres for a given exposure period can be calcu-
lated,
C = wh
t
where C = the time-weighted average for the gas, ppm.
At this point it is proper to point out the difference between diffusion
and permeation. Although there are similarities, there are subtle differences
which may be significant in adjudging characteristics and, thus, applications.
Unlike permeation, which is essentially a solution process as discussed above,
diffusion represents the passage of molecules through holes in a discrete
barrier where turbulence is minimized. Beyond the barrier, mass transfer
across a stagnant space to a collecting surface provides a means for quanti-
fying the transport process. The quantitative relationship is given by Pick's
Law of Diffusion,
N - - DA (DC/DX)
where N » rate of diffusive transport, moles/ sec
o
D » diffusivlty of species, cm /sec
A » area of diffusion path, cm
C = concentration of species, moles/cm
X = path length, cm.
463
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There are a number of general advantages to the permeation technique for
sample collection. A unique advantage that has been disclosed over the past
8 years of laboratory and field experience is the almost indestructible na-
ture of permeation-type devices. Since there is nothing to wear out or other-
wise degrade, months or even years of service can be expected. Only the sorp-
tion medium needs to be replaced, and thus the cost for collecting any in-
dividual sample amounts to only a few cents. The long-term performance, to-
gether with the low cost of the original devices themselves, make this the
lowest cost approach for reliable monitoring of gaseous pollutants. It is
important to note also that the badge-type monitors are the ultimate in con-
venience and that they present no more hazard than the typical identification
badge worn by plant personnel. This is in contrast to the impediment to mo-
tion and the danger of entanglement presented by the conventional battery,
motor, pump, and tube personal monitors.
The versatility of the permeation approach for personal monitors pro-
vides a variety of options for the solution of different monitoring problems.
Solid adsorbers such as silica gel and activated charcoal are of course well
suited for use in the monitors. In addition, liquid systems are readily us-
able, as, for example, utilization of tetrachloromercurate(Il) for S0« sam-
pling and the use of solutions containing bromide and fluorescein for the
simultaneous collection and determination of chlorine.
Permeation-type monitors have been widely field tested over the past
6 years, and in all cases excellent results have been obtained. Colleagues
in the United Kingdom, Europe, Canada, and various parts of the United States
have cooperated in the field tests, and their results have generally confirmed
the results of the extensive testing that has gone into the original develop-
ment of the individual monitor types.
Field use of any type of monitor emphasizes problems associated with
environmental variations and stresses. The first problem faced in the develop-
ment of permeation-type devices was that of temperature effects* The char-
acter of most polymeric membranes is very susceptible to changes in tempera-
ture, but silicone polymers were found to exhibit minimiurn variation over
normal temperature ranges, and for some gases, such as vinyl chloride and
chlorine, no errors were found over the range of 0° to. 40° C. In general,
therefore, temperature effects were found to be of little significance when
the proper membrane was used. In general, the presence or absence of sun-
light has been without effect, and humidity and relative air movement have
been of no significance. The presence of a wide variety of copollutants
464
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in industrial atmospheres has presented no problems with any of the monitors
developed so far.
The following discussion summarizes the essential make-up of five dif-
ferent devices that have been developed for the monitoring of sulfur dioxide,
chlorine, alkyl lead, benzene, and vinyl chloride, respectively. In each
case, the monitor itself is basically a hollow badge having a selected mem-
brane enclosure and containing a sorption medium chosen especially for the
collection and stabilization of the toxic gas of interest.
SULFUR DIOXIDE (5)
Membrane—dimethyl silicone, single backed
Sorber—sodium tetrachloromercurate(II), 1M
Analytic finish—conventional West-Gaeke spectrophotometric
determination
Interferences—none
Temperature effect 0.5 percent * C increase
Humidity effect—none
Relative air movement—no effect
Sensitivity for 8 hours exposure—0.01 ppm
Remarks—a catalytic stabilization can be used that permits sample
collection over l-to-4-week periods.
CHLORINE (7)
Membrane—dimethyl silicone, single backed
Sorber—buffered (pH 7) solution of fluorescein (0.005 to 0.0005 percent)
and sodium bromide (0.31 percent)
Analytic finish—spectrophotometric or colorimetric measure of the
color produced by the Cl_-oxidation of bromide and resultant bromination
of fluorescein to produce eosin
Interferences—none of significance
Temperature effect—none
Humidity effect—none
Relative air movement—no effect
Sensitivity for 8 hours exposure: 0.013 ppm
Remarks—sampling and simultaneous estimation of exposure results
are possible by on-the-spot colorimetry.
ALKYL LEAD (8)
Membrane—dimethyl silicone, unbacked
Sorber—silica gel with desorption by means of IC1
465
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Analytic finish—spectrophotometric measure of color produced with
dlthlzone or an atonic absorption spectrophotometric determination
Interference—none; errors due to lead Impurities In reagents minimized
by use of silica gel rather than charcoal
Temperature effect-- -0.66 percent * C for TEL and +0.81 percent
per * C for TML, thus essentially compensating for the usual plant
mixtures
Humidity effect—none
Relative air movement—no effect
3
Sen8itivity~0.2 yg, range 5 to 300 yg Pb/m
Remarks—analysis time only a fraction of that required in previous
methods.
VINYL CHLORIDE (9)
Membrane—dimethyl sllicone, single backed
Sorber—activated charcoal with desorption using CS.
Analytic finish—gas chromatography
Interferences—none
Temperature effect—none
Humidity effect—none
Relative air movement—no effect
Sensitivity—0.02 ppm, range linear to at least 50 ppm
Remarks—widely field tested with excellent results.
BENZENE (10)
Membrane—-sllicone polycarbonate copolymer
Sorber—activated charcoal with desorption using CS-
Analytic finish—gas chromatography
Interferences—none
Temperature effect— -1.2 percent/* C
Humidity effect—none
Relative air movement—no effect
Sensitivity—0.02 ppm 8 hours, linear to at least 20 ppm
Remarks—analysis dependent on the purity of the CS. used for
desorption.
SUMMARY AND CONCLUSIONS
Passive sampling of toxic gases for monitoring personal exposures can
be accomplished reliably, conveniently, and at low cost by means of badge-type
466
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TABLE 1
Reaulta of Typical Field Teata
Sulfur Dioxide (area monitoring),
Permeation Device
<5
<5
156
17
156
132
6
386
Coulometrlc
<25
<25
144
<25
Weat-Caeke
<2
<2
158
128
14
382
Vinyl Chloride, ppm
Permeation Device
0.98
0.17
0.12; 0.11
0.05; 0.08
0.92; 0.97
Pump-Charcoal Tube
0.83
0.10
0.07
0.07
0.88
Chlorine, ppm (preliminary data)
Permeation Device
0.52; 0.67; 0.56
1.10; 0.20; 1.15
0.44; 0.49; 0.52
2.70; 2.60
2.80; 2.10
*NI08H methyl orange procedure
Sane aa above ualng saturated aolutiona
Impinger
0.47*
1.10*
0.28a
>0.40b
>0.40b
467
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FIGURE 1. The MinlMonitor.
devices utilizing permeation for quantifying sample collection. Samples col-
lected over periods of hours, weeks, or in some cases even months, are an-
alyzed by conventional means to give the time-weighted average exposures.
Permeation-type monitors are indefinitely reusable because there are
no moving parts to wear out, nor is there anything to degrade with time.
The collected samples are adsorbed or absorbed by suitable means, removed
after the sampling period, and analyzed. All that is required for repeated
use of the monitor is to replace the sorber after each exposure; thus, these
devices are the ultimate on the basis of convenience, cost, and reliability.
The convenience is obvious because the monitors are single units having a
size and weight comparable to that of an identification badge. The cost
advantage is based on an initial cost of less than $80, which can be amortized
over months or years of service—the only operational cost being a few cents
for recharging with the appropriate sorber plus the cost of the subsequent
analytical procedure. The reliability is attested to by extensive laboratory
experience verified by widespread, independent, cooperative field studies
(Table 1).
Permeation-type personal monitors, "The MiniMonitor" (see Figure 1), are
available for a number of toxic gases with additional monitors currently
under development. REAL, P.O. Box 3341, Baton Rouge, La. 70821.
468
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REFERENCES
1. McKelvey, J.W., Hollscher, H.E. Anal Chem 29:123, 1959.
2. Allshuller, A.P., Choen, I.R. Anal Chem 32:802, i960.
3. Saltzman, B.E., Gilbert, N. Am Ind Hyg Assoc 20:379, 1959.
4. O'Keeffe, A.E., Ortman, G.C. Anal Chem 38:760, 1966.
5. Reiszner, K.D., West, P.W. Environ Sci Technol 7:526, 1973.
6. West, P.W., Gaeke, G.C. Anal Chem 28:1816, 1956.
7. Hardy, J.K., Dasgupta, P.K., Reiszner, K.D., West, P.W. Submitted to
Anal Chem, 1978.
8. Dasgupta, P.K., Pitts, W.D., Reiszner, K.D., Wolcott, J.W., West, P.W.
Submitted to Anal Chem, 1978.
9. West, P.W., Reiszner, K.D. Am Ind Hyg J 39:645, 1978.
10. Reiszner, K.D., West, P.W. In preparation.
MAILING ADDRESS OF AUTHORS
Philip W. West, Ph.D., and Kenneth D. Reiszner, Ph.D.
Environmental Sciences Institute
Chemistry Department
Louisiana State University
Baton Rouge, Louisiana 70803
Discussion
SYKES: Dr. West, would you comment on the calibration procedures in
these permeation-type adsorbers—specifically, on your system for calibrat-
ing?
WEST: We have standard gas atmospheres. So, we generate our standard
atmospheres by diffusion for the alkyl lead, and for the rest of them I think
we uniformly used permeation tube standards for generating our standard
atmospheres.
We have a dynamic system in which the standard gas passes through the
calibration device, which is something that we have published. If you look
469
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back at some of the publications you can see the details on that. We just
simply insert or expose our monitors or our membranes to the dynamic standard
gas atmosphere, and from that, determine the calibration constant.
MAGE: Dr. West, does any Government agency support your research right
now?
WEST: Yes, I must give credit to the National Institutes of Health.
We have had some support from them, and we have had some support from industry,
and the university also supported it. Unfortunately, the support we have
from N1H will be terminated in August. I am ready for any support you could
give me, and I am open to any suggestions as to what you would like to have
worked on.
BERLAND1: Dr. West, there has been a number of these gas badges at the
conference that you have talked about. Are there any physical features of
the badge that you have developed that allows it to volumetrically sample
more air, or are all these badges essentially similar? Is the membrane some-
what unique in that it allows for more precision?
WEST: Incidentally, to impress some people, we can provide them with
gold plating, so it will cost a little bit more if that is important.
At any rate, as far as the unique features of this particular badge
go, yes, we have more capacity. If we are using adsorbents such as charcoal,
we have somewhat more charcoal, and therefore greater capacity. There is no
breakthrough, by the way, on these.
I certainly am not running down the other badges, but, the thing is
is that these badges cost more than the 3M badge or the Gasbadge. These will
run, say, anywhere from $40 to $80. But they are usable indefinitely. We
have had one or two of these successfully performing, I guess, after more than
4 years. There is nothing to wear out, and since the sorber is poured out
for the analysis and then replaced, that is the only cost after the initial
cost of the badge. Then you pay a few pennies for whatever sorber you have
to use in refilling it.
PETERS: Edward Peters, York Research. Perhaps I missed something
earlier, but I notice that there is no effect from the movement of air.
WEST: That Is right.
PETERS: The way I see it, the higher the movement of air, the more one
might ingest these gases, and yet your instrument shows a constant level.
Can you comment on that?
WEST: Well, what we are doing is that we are collecting the air at that
particular spot and we are getting a time-weighted average of that particular
exposure. Now, the rate at which the sample is collected here corresponds
quite closely with the sample rajte obtained, say, with a charcoal tube and
pump. So, any variation that might be due to that would be, I think, char-
acteristic of any sampling system.
470
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SCHEIDE: I think the point to make is that you want those badges to
be diffusion or permeation limited so that if the person is sitting still
or walking down the hall, it should sample at the same rate. That, in effect,
is what the membrane does.
471
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Personal Air Pollution Monitors:
New Developments
Robert W. Miller and Byron Denenberg
MDA Scientific, Inc.
Park Ridge, Illinois
With the advent of increasing awareness by the research community and
the public at large of the potential short-term and long-term health hazards
associated with airborne toxic contaminants, great emphasis has been placed
on the development of new instrumental monitoring techniques to measure these
hazards. In many cases, laws have been established to limit human exposures
to various contaminants, regarding both occupational and ambient levels.
Historically, most ambient monitoring has been area monitoring, done
with relatively sophisticated, expensive, and sensitive analytical devices
that are hardly one step removed from the typical laboratory devices that
require great care and attention in calibration and operation to obtain
optimal performance. The use of this kind of analytical equipment for pollu-
tion monitoring in ambient air is dictated by the low concentration being
measured.
In the occupational environment, quite different approaches have been
undertaken. Typically, the toxic levels being measured are one to three
orders of magnitude higher than permissible ambient levels, and, therefore,
the choice of analytical technique, with adequate sensitivity, is greater.
As additional toxicological and clinical evidence becomes available, there is
a constant downward trend in permissible exposure levels of various contami-
nants. Typical examples of this process are vinyl chloride, acrylonitrile,
and benzene. There is an ever-increasing body of data suggesting strongly
that a very large percentage of the ambient and occupationally exposed popu-
lation exhibits a multitude of subtle deleterious symptoms of exposure.
473
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Many instances are documented of the effects of very low levels of pollutants
causing significant changes in behavior and hormone-enzyme balance that re-
sult in numerous symptoms that are difficult to treat because the industrial
physicians involved are not aware of the causative agent.
The need to accurately define what an individual is actually exposed to,
and to comply with OSHA requirements, has added Impetus to develop personal
monitoring systems for toxic substances. Oftentimes, standards are based
on the limitation of sampling techniques, as well as toxicologlcal data*
For example, most OSHA exposure limits are time-weighted averages, based on
averaging air concentration over a prolonged sampling period—i.e., 15 minutes,
2 hours, 4 hours, etc. Obviously, liquid implnger and charcoal tube tech-
niques with typical sampling times, as suggested above, will have poor time
resolution of changes in concentrations. The use of continuous, instantaneous
readout monitors for substances (for which they are available), Indicates
that it is not unusual to see marked concentration flux over periods of 15
minutes or less in the occupational environment, as well as in ambient en-
vironments.
Since a short-term peak concentration may be as Important as total dose
in its effect on humans, it becomes Important to define these exposures,
where possible, and to provide immediate indication of concentration so that
protective action can be taken to avoid excessive exposures. A number of
passive monitoring techniques have recently been developed, including small,
lightweight adsorption badges. Although these devices can be useful as diag-
nostic or screening agents, they cannot provide an exposure profile, and,
most importantly, they only provide historical information—i.e., after it is
too late to do anything about the exposure. To detect peak concentration
requires, first, a sensing device small and lightweight enough to be readily
worn by an individual in or near his or her breathing zone, with the capa-
bility of providing maximum time resolution and a continuous concentration
output. A number of analytical techniques can meet these criteria, but not
without limitations. Electrochemical cells and semiconductors are attractive
techniques for personnel devices but oftentimes are limited by sensitivity
and/or specificity problems. In these cases, the application often dictates
success or failure of measurements relative Co possible interferences.
One technique that offers great promise for further development and ap-
plication is the detection of toxic gases using chemically impregnated paper
tapes. In this case, contaminants which are collected on the tape react with
the chemicals on the tape to produce a stain proportional to the mass con-
centrations of the contaminant. The strength of this technique is that not
474
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only can it provide time resolution (as short as 30 seconds), but also that
the chemistry can be manipulated to obtain remarkable sensitivity (low ppb)
and a high degree of specificity.
A personal sampling system using this detection principle (the MCM)
has been commercially available for several years, and is capable of provid-
ing both a time versus concentration curve and total dose information for
accurately defining personnel exposures. A modified MCM system, referred
to as the Chromatox System, is currently in the final stages of development;
it will expand even further the time resolution capabilities, as well as the
overall versatility In utilizing new tape detection systems as they are de-
veloped from an ongoing research program. This system is analogous to hi-fi
tape recorders, with the difference being that a chemical signal instead of
an audio signal is recorded and played back.
To immediately increase the capabilities of the MCM and other personal
detection devices that have a continuous output, a unique mircoprocessor pro-
file alarm dosimeter (Chronotoximeter) has been developed. The Chronotoxi-
meter is designed to accept an output signal from any detection system. The
microprocessor takes a reading every second (this feature is adaptable to
the sensor) and stores that datum in a temporary memory. At the end of 90
seconds, the data are processed and a 90-second average value is stored in
a permanent memory. At the end of the exposure period, the Chronotoximeter
Is then interrogated to provide a time versus concentration curve and/or a
digital printout of the stored data. The microprocessor can be programed
to accept the input from other detection systems, in addition to the MCM.
In fact, it has been designed with this intent so that a user would have maxi-
mum choice of detectors for data gathering. As detectors are changed, a
"FROM" (programmable read only memory), calibrated to the detector calibration
curve, is inserted into the Chronotoximeter, and the system is then totally
compatible.
For ambient personal monitoring, the tape detection technique offers
the greatest promise because of the ppb sensitivity and because of the in-
finite possibilities of chemical reactions to choose from to obtain appro-
priate specificity. An ongoing research program is continuing to develop new
detection systems. The capability to begin meaningful surveys of general
population exposures to compounds such as CO, N02» and SO,, with the Chronotox
System should provide a fruitful ground for research in the next several years.
The Chronotoximeter will also incorporate digital real time readout
with high level and total dose alarm capability In one embodiment. This
475
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further enhances its usefulness, from a protection standpoint, to the in-
dividual wearing the device* Later phases of the development program will
provide telemetry output of the Chronotoximeter so the data produced can be
telemetered back to a central data center and appropriate warnings given to
the wearer, when warranted. Such telemetry systems are already operational
for measuring individual motion and heartbeat in hazardous occupational
environments.
MAILING ADDRESS OF AUTHORS
Robert W. Miller and Byron Denenberg
MDA Scientific, Inc.
808 Busse Highway
Park Ridge, Illinois 60068
Discussion
PETROVICK: Would you tell us what you are using and what the memory
capacity of it is?
MILLER: Both answers at this point are proprietary.
PETROVICK: Another comment: I am pleased to see that someone is moving
in that direction, because of the extrapolations from your hydrobodies to a
true, physiological monitoring and and response type capacity. I commend
you for that; I think that is the way to go*
MILLER: Just to comment in reference to what you say: I really didn't
come here to talk about the physiological approach, but associated with this
system, there is also a radio-operative system, and that radio-operative
physiological system is one that an individual can wear, which will provide
a heartbeat, that is tied into this complete system where you can radio the
signal back to a central location.
So, if you have an individual out in an industrial environment—which
would be a primary application here—where they may encounter an extremely
high concentration of something that they cannot physically remove themselves
from immediately, you will get an alarm signal as well as a direct heartbeat
and respiration signal, sent back to a central control panel where individuals
are continually monitoring, and then you can immediately take steps to send
someone up. That system also now exists and is available, in conjunction
with this.
476
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PETROVICK: I would like to come back to that. That is very interesting,
because if you pick up this week's US News and World Report, there is an ar-
ticle in there on cardiac heart attacks. It alludes to a 23 percent drop in
fatalities from coronary attacks in the last 5 years with the implementation
of some kinds of technology, particularly the emergency health care of the
kind where help can get to the person within an hour. It is that crucial
hour-long-period that I think you have* And if someone may have problems,
even as simple as a bee sting, there are enzymes within the heart muscle
that reside there that release themselves and partly are responsible for a
coronary event. That is not my opinion—it is in the US News and World Report.
I urge you to read it.
LIN: Will particulates be a strong interfering agent in the tape sampler?
MILLER: Generally speaking, we have found that not to be the case—
actually, even in foundry operations where you have high ambient dust levels.
And the reason is that the tape is continuously moving. It is not stopped
on one spot. So primarily the stain that develops there is a function of
the organics or whatever compound you are measuring and not of the particu-
lates.
Also, most of the heavies drop out because of the relatively low flow
rates that we are using, so you don't pick up a lot of the heavy particulates.
Most of the submicron particles, because of the tape movement, don't create
enough darkening of the tape system to make a significant difference.
Now, realistically speaking, that is not universally true, because I
have found one or two situations where in fact the ambient dust level was
so high that it did cause a significant background reading. In which case
you had to correct for it by compensating your baseline. But that also,
you know, can be done.
I might also add that in those situations the ambient dust level was so
far above anything remotely approaching permissible exposures that it was a
necessity, really, to correct the ambient dust levels before they worried
about some of the other things they were sampling.
SHAW: What is the operating principle of this cell?
MILLER: I think it is best construed as an amperometric cell.
WEST: I believe you mentioned you have gotten away from the lead ace-
tate. What do you use?
MILLER: I will tell you that we do use lead acetate. However, a little
modern chemistry and engineering has, let's say, taken the basic lead acetate
and made it workable, in effect, in a real-world environment.
There are units available that use the old lead acetate that require
all kinds of unbelievably complex humidification schemes. Our system does
not require that. Again, it is proprietary, but suffice it to say that we
build the water into the tape.
477
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WEST: We'll take your word for that, because that is important.
MILLER: That is critical. The sensitivity is tremendous, but it has
always been the humidity effects that have really been the problem one has to
cope with.
478
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A New Sampling Tool for Monitoring
Exposures to Toxic Gases and Vapors
John C. Gillespie and Leah B. Daniel
Abcor Development Corporation
Wilmington, Massachusetts
INTRODUCTION
Air sampling devices are needed to provide a variety of exposure infor-
mation, including:
1) Occupational exposure information concerning employees in a plant
and environmental exposure information of the population in an area sur-
rounding a given plant.
2) Personal and fixed-station (area) exposure information.
3) Information concerning immediate (acute) versus long-term (chronic)
health hazards.
4) Peak versus time-weighted average exposure data (or episode versus
average concentrations)•
5) Continuous versus integrated sample measurements.
These various applications require a number of different sampling de-
vices, each having certain advantages and limitations. A comprehensive sum-
mary of the uses of air quality monitors in measuring the exposure of the gen-
eral public to air pollution is explored by Lance Wallace in Reference 1.
The purpose of this paper is to discuss a passive sampling device, the
479
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»*
GASBADGE dosimeter, and Its applications to date (primarily In occupational
health monitoring), and to suggest which of the exposure Information needs
presented above It can best satisfy*
THE GASBADGE ORGANIC VAPOR DOSIMETER
The GASBADGE organic vapor dosimeter is a 1 and 1/2-ounce sampling device
which can easily be worn by an Individual to collect time-weighted average
exposures to organic vapors. Since it requires no air sampling pump, it is
often referred to as a "passive" sampler. The GASBADGE dosimeter Is analogous
to and as convenient to wear as the radiation film badge.
The dosimeter (Figure 1) contains an activated carbon collection element
which is removed after exposure for subsequent analysis. To determine the
time-weighted average exposure, the element is removed from the dosimeter and
placed in a sealed vial. The organic material collected on the element is
then desorbed using carbon disulfide or another appropriate solvent and an-
alyzed by gas chromatography. The dosimeter is reusable and can be easily
reloaded with a new collection element. Additional elements (other than char-
coal) can be used to collect other gases and vapors.
The components of the dosimeter (Figure 2) include (from bottom to top):
1) A sliding cover to prevent contamination, or exposure, for short
periods of time.
2) A dosimeter front with a carefully defined opening to allow diffusion
of gas or vapors into the dosimeter.
3) A draft shield made from a nonreactive porous material.
4) An open grid to define the diffusion geometry and minimize internal
mixing.
5) A replaceable collection element.
6) A caseback with a spring clip for attachment to the individual.
OPERATING PRINCIPLES
Generally, the first reaction to the GASBADGE dosimeter centers around
*GASBADGE is a trademark and registered servicemark of Abcor Development
Corporation, Wilmington, Mass.
480
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GASBADGE
4MKAMCVMKM
FIGURE 1. The GASBADGE Organic
Vapor Dosimeter.
FIGURE 2 (right). GASBADGE compo-
nents and specifications.
COMPONENTS
Sliding protective cover prevents contam-
ination or exposure for short periods of
time
Badge front with opening allows diffusion of
gas or vapors into dosimeter
Draft shield made from nonreactive porous
material
Open grid defines diffusion geometry,
minimizes internal mixing
Replaceable collection element
Dosimeter back with spring clip
SPECIFICATIONS
Dimensions:
Weight:
Power:
Collection Element:
Analysis Method:
Sampling Time:
Sampling Range:
Accuracy:
Shelf Life:
Air Velocity:
Patent:
2x2 9/16 x 5/8 in.
(5.1 x6.5x 1.6cm)
1.5oz. (43g)
None
Activated carbon
NIOSH P&CAM 127
(modified)
8 hr nominal
0.2-160 ppm/8-hr TWA
(benzene)
+ 25%
2 years
15fpm (0.08 m/s)
minimum. Normal
industrial plant
air velocity exceeds
20fpm (0.1 m/s)
U.S. Patent 3,985,017
481
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the absence of an air sampling pump. The reaction is either positive or neg-
ative. The positive reaction is: "Now I won't have to spend all my time
calibrating my pumps, charging batteries, or Just trying to keep the pumps
running." The negative side of the "no pump" response is this: "If it doesn't
have a pump to control the air flow into the device, how will I know the volume
of air sampled?"
What these two responses point out is that:
1) There is a fundamental difference between collecting samples using
sampling tubes and an air sampling pump and using the GASBADGE dosimeter be-
cause the GASBADGE dosimeter does not depend on the volume concept associated
with air sampling pumps; and
2) Since the GASBADGE dosimeter has no rotometer, makes no noise, and
has no moving parts, it is impossible to physically see the sample collection
in process.
The GASBADGE dosimeter is based on controlling the random but predictable
molecular movement of gas molecules rather than controlling air flow. What
Abcor has done with the organic vapor dosimeter is to utilize physical chem-
istry principles of vapor diffusion to control the amount of material col-
lected by the collection element.
Figure 3 shows a comparison of the two equations used to calculate the
ppm concentration of an organic vapor exposure using either a diffusion dosi-
meter or a pump sampler. Both equations are time dependent In that more ma-
terial will be collected for longer exposures at a given concentration (up to
the capacity of the device).
The first two parts of each equation are basically the same. The dif-
ference between the two equations is in Section III, or what is labeled the
"Transport Force." In Section III, the flow-rate or volume component of the
pump sampler equation is replaced by three physical constants which control
the mass of material collected by a diffusion-based sampler, namely:
1) The length of the diffusion path;
2) The cross-sectional area onto which the gas or vapor is diffusing;
3) The diffusion rate of the gas or vapor in air, determined by ex-
perimental methods.
To accurately determine measurements of employee exposures using a char-
coal tube sample collected with an air sampling pump, the flow rate must be
precisely controlled at a known constant level throughout the sampling period.
482
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1
Measurement of
Collected Sample
Diffusion Dosimeters
Kample-Wblank'
desorptlon efficiency
Pumped Sampler
foSsample-Wblank'
desorptlon efficiency
II
Standard Conditions and
Molar Conversions
1 *«**» , , T°K 760mmHg
•* __, v *JV Afm\ f**»/mnlM v " v *.
' mw X 22''100cc/mo"' x 273o K x PmmHg *
— r 224S/mol0 * ^ K « 7""'inH8
mw x22'4B/m°'«' x2?30|C x pmmHfl >
III
Transport Force
X(cm) .
CD/cm2\ Afcm2)t««o)
\»/
1
Flow Rate(fi/min) x T(mln)
X - Diffusion Length (cm)
D - Diffusion Coefficient
A " Cross-sectional Area (cm2)
FIGURE 3. Diffusion and air sampling pump equations*
8 12 16
HiLLICRAMS ADSORBED
20
FIGURE 4. Percent recovery versus milligrams adsorbed. (Source: Mazur, J.F.
et al. A New Personal Sampler for Organic Vapors. Paper presented at the AIHA
conference, May 1977.)
483
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If the flow rate changes during sampling, or it is not verified before and
after sampling, the calculated results will be in error.
Passive samplers, operating on the diffusion principles, are dependent
not on flow but on careful definition of the physical dimension of the sam-
pling device and on making certain that the only force causing the collector to
operate is gaseous diffusion. The GASBADGE dosimeter does this by creating
a dead air space that is relatively unaffected by changes in air velocity
between the draft shield and the collection element. The GASBADGE dosimeter
works, in effect, because the draft shield prevents air flow into the device,
thereby ensuring that the amount of gas or vapor collected is determined only
on the diffusion rate (molecular movement) of gas or vapor in the air being
monitored.
PERFORMANCE TEST RESULTS
Two types of performance testing are:
1) Testing under carefully controlled laboratory conditions with a
known concentration and environment.
2) Testing primarily in industrial (occupational) environments under
field conditions which present more variability and essentially unknown
concentrations.
The advantage of performance testing under controlled laboratory con-
ditions is that one can measure the accuracy and precision of the sampling
method when compared to a known concentration. The disadvantage is that
testing under laboratory conditions does not necessarily duplicate the real
world.
While field testing is the real world, determination of accuracy and
precision is much more difficult because the actual concentration is generally
unknown and varying and can be measured only by the use of other secondary
sampling devices such as charcoal tubes which also have variations in their
accuracy. In other words, when comparing two sampling methods under field
conditions, one may be comparing one sampling method with a potential error
of plus or minus 25 percent with another device which has a similar error
range. This means one could expect variations between the results of two
such sampling methods of as much as plus or minus 50 percent.
For these reasons, Abcor has relied on controlled exposure testing by
Abcor and other groups to determine the accuracy of the GASBADGE dosimeter
484
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for various organic materials. Correlations between side-by-side field samples
collected using organic vapor dosimeters and other suitable sampling methods
verify that there is general agreement between two (or more) sampling methods
under varying field conditions*
The U.S. Army Environmental Hygiene Agency (USAEHA) conducted an exten-
sive evaluation of this monitoring device (2). Table 1 shows the percent
recovery and relative concentration obtained by the USAEHA for seven different
organic compounds. The compounds tested represent seven different classes
of organlcs; namely, an aromatic, an alkane, an alcohol, a ketone, an ester,
a halogenated alkane, and a halogenated alkene. The compounds were Individu-
ally sampled to determine percent recoveries for each in the 1/4, 1, and 2x
the TLV concentration range, and to determine if the dosimeter compared favor-
ably with the recoveries previously obtained by the USAEHA for charcoal tubes.
Since the dosimeter data were so reproducible, the U.S. Army Environmental
Hygiene Agency felt that the results could easily be corrected for the slight-
ly lower percent recovery levels for absorption/desorption efficiencies,
just as charcoal tube data are corrected.
Figure 4, again from the USAEHA study, shows a plot of percent recovery
versus total mg adsorbed for iso-octane, trichloroethylene, methyl chloroform,
n-butanol, and MIBK. The results of this experiment indicated that the per-
cent recovery was relatively independent of ambient concentration when less
than 10 mg of material is loaded on the collection element. For this reason,
Abcor recommends that the maximum loading of GASBADGE collection elements not
exceed 10 mg total solvent.
Many customers have asked if the GASBADGE dosimeter measures mixtures as
well as single-component vapors. The data in Table 2, again from the USAEHA
study, show that diffusion operates effectively for mixtures of organic com-
pounds as well as when the compounds are each monitored separately. This
holds true as long as the mixture does not exceed the maximum recommended
loading of 10 mg total solvent.
Tables 3 and 4 show the accuracy and precision of the GAS BADGE dosimeter
for benzene and acrylonitrile monitoring. Table 3 was compiled from performance
testing conducted by Abcor for benzene exposures varying from 0.28 ppm to
4.69 ppm. It shows the mean dosimeter concentrations, systematic error, and
relative standard deviation for the GASBADGE organic vapor dosimeter at var-
ious levels. The pooled values of the individual test levels are a measure
of the overall accuracy of the device for all exposure runs combined and in-
485
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TABLE 1
Percent Recovery Versus Relative Concentration
COMPOUND
Benzene
Iso-Octane
n-Butanol
MIBK
n- Butyl
Acetate
Methyl
Chloroform
Trichloro-
ethylene
AMBIENT
CONC. (PPM)
2.5
10.0
20.0
75
300
600
12.5
50.0
100.0
25
100
200
37.5
150.0
300.0
87.5
350.0
700.0
25
100
200
TOTAL MG
ADSORBED
0.076(a) »
0.37
0.71
3.0
11.5, .
20.5(C)
0.28
1.5
2.9
i.O
3.8
7.5
1.5
5.8
10.5
4.7, .
15.8 c
25.5(c>
1.4
5.7
11.1
AVERAGE
% RECOVERY
(b) 76
94 + 4
89 + 4
104 + 3
101 + 3
90
64
84 + 3
84 + 5
79 + 4
80 + 6
80 + 2
93 + 3
88 + 4
84 + 4
85 + 2
77 + 3
58
90 + 2
90 + 3
89 + 3
CHARCOAL
TUBE
97
NA
88 + 5+"
93
95*
100
95
Too low for accurate quantitation.
' Percent recovery improved by Abcor to 94 percent by modifying the an-
alytical technique used in the USAEHA study.
( c j
v ' Overload conditions.
+ From the literature.
Source: Mazur, J.F. et al. A New Personal Sampler for Organic Vapors.
Paper presented at the AIHA conference, May 1977.
486
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TABLE 2
Percent Recoveries for a Four-Component Mixture
COMPONENTS
Iso-Octane
Benzene
MIBK
Butyl Acetate
AMBIENT
CONC. (PPM)
46.1
80.0
56.6
54.0
% RECOVERY
102
86
75
90
REFERENCE ^
% RECOVERIES
101-104
89-94
79-80
84-93
k
Percent recovery In the absence of other components
Source: Mazur, J.F. et al. A New Personal Sampler for Organic Vapors.
Paper presented at the AIHA conference, May 1977.
dlcate that the GASBADGE dosimeter Is within plus or minus 20 percent at a 95
percent confidence level.
Similar accuracy for the GASBADGE dosimeter is demonstrated in Table 4,
which summarizes data collected by Dow Badlsche (3) for monitoring exposures
to known concentrations of acrylonitrile. After conducting laboratory meas-
urements to determine the accuracy of the GASBADGE dosimeter, Dow Badische
performed field tests on a side-by-side basis with charcoal tube samples.
The data from the field testing demonstrated that the GASBADGE organic vapor
dosimeter is comparable to the charcoal tube technique.
CURRENT APPLICATIONS OF PASSIVE SAMPLERS FOR PERSONAL EXPOSURE MONITORING
The major uses of the GASBADGE organic vapor dosimeter have centered
around potential occupational exposures, including:
1) Monitoring employee exposures to benzene in petroleum refineries,
benzene manufacturing facilities, pharmaceutical companies, laboratories, and
other similar industries.
2) Monitoring exposures of field personnel to benzene in remote pe-
troleum pipeline and pumping station locations where the dosimeters are dis-
487
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oo
oo
TABLE 3
GASBADGE™ Organic Vapor Dosimeter Performance Data
Benzene Monitoring
(8-Hour TWA Exposures)
Exposure
Concentration
(ppm)
0.28 ppm
0.5 ppm
0.5 ppm
0.56 ppm
0.56 ppm
0.97 ppm
1 .90 ppm
4.69 ppm
Number of
Dosimeters
4
5
5
9
10
20
15
20
Pooled
Mean Dosimeter
Concentration
0.25 ppm
0.56 ppm
0.49 ppm
0.64 ppm
0.60 ppm
0.98 ppm
2.24 ppm
5.25 ppm
Values
Standard
Deviation
(ppm)
0.01 ppm
0.01 ppm
0.01 ppm
0.03 ppm
0.04 ppm
0.04 ppm
0.10 ppm
0.30 ppm
Systematic
Error
-11%
+12%
- 2%
+14%
+ 7%
+ 1.0%
+17.9%
+11.9%
+ 8.5%*
Relative
Standard
Deviation
(RSD)
4.0%
1.7%
2.0%
4.7%
6.7%
4.1%
4.5%
5.7%
4.8%**
Error Range to
a Confidence Level
of 95% Based on
Systematic Error
±RSD
-19.0% to- 3.0%
+ 8.6% to +15.4%
- 6.0% to + 2.0%
+ 4.6% to +23.4%
- 6.4% to +20.4%
- 7.2% to + 9.2%
+ 8.9% to +26.9%
+ 0.5% to +23.3%
- 1.1% to +18.1%
Systematic Error
Mean Dosimeter Concentration - Exposure Concentration
Relative Standard Deviation
Exposure Concentration
Standard Deviation
Mean Dosimeter Concentration
'Calculated using a weighted systematic error.
*'Calculated using the technique specified by NIOSH for evaluating the accuracy of methods for the standards completion pro-
gram. Summary of Statistical Terms and Formulas, S112-D1 (Attachment D). The mathematical equation is expressed as:
where:
Z fi (RSDj)2
RSD
f j
RSD|
f
RSD
Pooled Relative Standard Deviations (Coefficient of Variation)
degrees of freedom, equal to number of observations minus one. at the Ith level
Relative Standard Deviation of the observations at the Ith level
n
Z fj
-------
TABLE 4
GASBADGE* Organic Vapor Dosimeter Performance Data
Acrylonitrlle Monitoring
Exposure Number of Mean Dosimeter Standard
Concentration Dosimeters Concentration Deviation
0.74 ppm 10 0.75 ppm 0.03 ppm
8.9 ppm 16 8.67 ppm 0.83 ppm
19 ppm 7 19. 14 ppm 2.41 ppm
Pooled Values
This data demonstrates that the GASBADGE organic vapor dosimeter meets
Standard for Acrylonitrile issued by OSHA on January 17, 1978.
Systematic
4 Error
+1.4%
-2.6%
-0.7%
Relative
Standard
Deviation
(RSD)
4.0%
9.6%
12.6%
-1.0%* 9.1%**
the accuracy requirements of the
Error Range to
a Confidence Level
of 95% Based on
Systematic Error
±2 RSD
- 6.6% to + 9.4%
-21. 8% to +16.6%
-25.9% to +24.5%
-19.2% to +17.2%
Temporary Emergency
The above data is a summary of results of a study conducted by the Dow Badische Company, exposing the dosimeters in a dynamic test
chamber for 6-8 hours. As a further check, eighteen GASBADGE dosimeters were worn, side-by-side with charcoal tube samples under
field conditions. The data from both the dynamic testing and field testing show the GASBAOGE technique is accurate, reproducible
and comparable to the charcoal tube technique. A copy of the complete test data is available from Abcor Development Corporation or
W. O. Calhoun, Quality Control Laboratory, Dow Badische Company, Post Office Drawer D, Williamsburg, Virginia 23185.
Systematic Error
Mean Dosimeter Concentration - Exposure Concentration
Relative Standard Deviation
Exposure Concentration
Standard Deviation
Mean Dosimeter Concentration
•Calculated using a weighted systematic error.
• 'Calculated using the technique specified by NIOSH for evaluating the accuracy of methods for the standards completion pro-
gram. Summary of Statistical Terms and Formulas, SI 12-D1 (Attachment D). The mathematical equation is expressed as:
RSD = /.£ fj (RSDj)2
where:
RSD
fj
RSDj
f
Pooled Relative Standard Deviations (Coefficient of Variation)
degrees of freedom, equal to number of observations minus one, at the itn level
Relative Standard Deviation of the observations at the itn level
n
£
£
-------
tributed to the field, reloaded in the field, and samples sent in vials
to central laboratories for analysis.
3) Monitoring employee exposures to various chlorinated solvents used
in metal degreasing and other cleaning operations, such as trichloroethylene.
4) Monitoring employee exposures to acrylonitrile from the manufactur-
ing of the basic material through its use in ABS injection molding operations.
In addition to its use in a traditional industrial hygiene sampling
program of a large plant under the supervision of an industrial hygienist,
the GASBADGE dosimeter lends itself to "self-administered" sampling of per-
sonnel at remote locations or in plants where there is no industrial hygien-
ist. The GASBADGE dosimeter makes sampling easier and even possible in areas
where air sampling pumps cannot practically be sent or used due to the lack
of trained personnel.
Additional areas in which the GASBADGE dosimeter has or will be used
include:
1) Evaluations of hospital personnel having exposure to various anes-
thetic gases and other gases and vapors.
2) A study of vocational education students to determine qualitative
exposure information for a variety of organic vapors found in painting and
decorating, plastic technology, and auto body shops.
3) An evaluation of the exposures of Individuals to various dry clean-
Ing solvents
4) A study of the exposure of college art students to various solvent
vapors present in silk screening operations.
POTENTIAL APPLICATIONS OF PASSIVE SAMPLERS FOR MONITORING COMMUNITY EXPOSURES
The GASBADGE dosimeter provides a sampling device which can be used to ob-
tain personal exposure information related to health effect studies for en-
vironmental as well as occupational exposures*
The primary purpose of this sampling device is for personal monitoring,
although it could be used to obtain area monitoring information. Since it
490
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Is not direct reading and has no alarm to warn of overexposure, it should
be used for monitoring chronic rather than acute health hazards. While it
is effective for short-term monitoring (1 hour or less), it should normally
be used for obtaining time-weighted exposure information over several hours.
It should be used for obtaining integrated sample measurements rather than
as a continuous monitor to measure changes in concentrations.
Since the GASBADGE dosimeter does not require an expensive air sampling
pump nor the calibration and training requirements associated with pumps,
it can be distributed and collected in a number of ways (mail, a central
distribution point, or by personal visit). In other words, it is both eco-
nomical and relatively easy to use in a large-scale population study.
Performance data indicate the success of passive samplers for monitoring
occupational exposures to a variety of gases and vapors. It would be ap-
propriate and necessary to conduct similar performance tests to determine
the effectiveness of the GASBADGE dosimeter for monitoring exposures over
days or weeks (rather than 8 hours) at levels in the parts-per-billion rather
than the parts-per-million sampling range. We believe such testing will
demonstrate that this sampling approach has the ability to provide valuable
exposure Information for a variety of population groups in the home and out-
side environment as well as in the workplace.
REFERENCES
1. Wallace, L. Personal Air Quality Monitors: Past Uses and Present
Prospects* Paper presented at the 4th Joint Conference on Sensing of
Environmental Pollutants, American Chemical Society, 1978.
2. Mazur, J.F. et al. A New Personal Sampler for Organic Vapors. Paper
presented at the American Industrial Hygiene Conference, New Orleans, La.,
May 1977.
3. Calhoun, W.O., Silverstein, L.G. Personal Monitoring for Acrylonitrlle
Using the Abcor GASBADGE". Dow Badische Company, Williamsburg, Va.,
September 1977.
MAILING ADDRESS OF AUTHORS
John C. Glllespie and Leah B. Daniel
Abcor Development Corporation
Wilmington, Massachusetts 01887
491
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Panel Discussion
Panel members for the following discussion were: Dr. David Mage, En-
vironmental Monitoring and Support Laboratory, U.S. Environmental Protection
Agency (EPA); Dr. Lance Wallace, Office of Monitoring and Technical Support,
EPA; Mr. Otto White, Brookhaven National Laboratories; Mr. Mathew Petrovick,
Health Effects Research Laboratory, EPA; and Dr. Manny Shaw, InterScan Cor-
poration.
MAGE: Thank you very much for returning this afternoon. We are going
to try to summarize for the benefit of the record, as well as for the dis-
cussants, our impressions and conclusions of what we have learned, and the
directions that we feel we should be going in.
You will have an opportunity to make remarks for the record after the
panel members have given their summary.
I am going to start off by recognizing the panel members—Dr. Lance Wallace,
Mr. Otto White, Mr. Matt Petrovick, Dr. Manny Shaw, and finally, myself.
WALLACE: I don't have any prepared remarks. I am still trying to come
to grips with everything that I have learned the last few days, which has
been a large amount of information to try to take in.
Frankly, my horizons have been broadened. I came into this conference
thinking of personal monitors basically on the physical-chemical side of it
493
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and of making that type of measurement. I now see that the advances in the
methods of measuring physiological responses are great enough that they have
opened up to us a possibility of dose response measurements that I hadn* t
really envisioned before.
The microcomputer aspects, that would enable us to take these continuous
measurements of both dose and response and provide complete 8-hour or 24-
hour readout, appear to be extremely promising for the future.
So, these three aspects—the physical-chemical side, the physiological
side, and the microcomputer side—appear to be very promising.
Among the monitors that are available now, 1 see several obvious repre-
sentatives: one is the electrochemical family for CO for which we already
have the ESI instrument, the GE Instrument, and we have a promise from our
industry representative of an InterScan instrument in the next year or so.
For NO., the Palmes effort has been field tested and is getting indoor
levels in the 50 parts-per-million range near gas stoves.
In another area, the organics area, it is clear that we have several
specific monitors. Dr. West has benzene, toluene, alkyl lead, vinyl chloride,
and halogenated hydrocarbons. These monitors have been used in both the
workplace and home environments.
Both Minnesota Mining and Manufacturing (3M) and Abcor have special
activated charcoal elements that can adsorb any organic materials that can't
be absorbed on activated carbon. Those dosimeters are available right now
so that we can monitor out in the field. That is what they have been doing—
monitoring a wide range of organics.
Each badge is not specific for a particular organic. You can use one
badge and monitor a wide variety of them. You just break it down in the analy-
sis. So, those are available now for workplace monitoring.
These badges have not been tested at the parts-per-million levels found
in ambient air, since there has been no need to do so up to this time.
I have the feeling at the moment that we do not have available personal
monitors for ozone, although we did see the Mast instrument, which is a port-
able one.
494
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In regard to fine particulates, the Harvard group does have a set of
instruments that they have adapted themselves. I am not certain whether
we can call these instruments working personal monitors or not, because they
are rather bulky. In their study that they described previously, one third
of the persons in the first sample group who tried it gave it up on the first
day. Apparently, more work is needed here.
In regard to S02> it is no problem at all. Dr. Philip West has been
doing that for some time, not really as a personal monitor, but for workplace
and ambient area monitoring in general. Personal monitoring can be done with
the permeation approach, and it can be done over long periods of time.
Stability is ensured by converting the SO,, to sulfuric acid, and the analysis
proceeds from there. This provides a completely stable system. These badges
can be used for levels of 0.01 ppm and below.
The one remaining thing that I would like to mention is the prospects for
the future in the development of personal monitors. It appears from what
we have heard in the last 2 or 3 days that the most emphasis and the largest
payoff in the future may be the area of fine or respirable particulates.
We have a great interest in that within EPA. A particulate dosimeter pre-
sents a possibility of collecting the material and then subjecting it to analy-
sis for a spectrum of individual pollutants. And the other main aspect would
be the organic monitors that we heard about from Dr. Joseph Brooks,
Leah Daniel, Dr. Phil West, and other people here. We may be able to do
classes of organics. We may be able to do individual organics of interest.
Monsanto staff are going to check 20 carcinogens. They have a 3-year program
of which they have completed the first year. This may be an area in which we
can expect great advances in the future.
MAGE: Thank you very much, Dr. Wallace.
WHITE: Certainly, this week has been enlightening to me, and hopefully
the information from this meeting will help formalize the final report that
my committee is working on. Certainly we are aware of pollution conditions
that exist, not only in the occupational environment, but also in the general
environment, that resulted in the conditions of black lung, the Donora, Pa.,
episode, and the London air pollution situation.
One does not have to ponder long in thinking in terms of why we need to
monitor from the epidemiclogical standpoint or the compliance standpoint.
We need to determine whether or not the workplace or the environment is in-
deed safe. These represent challenging areas for not only the industrial
495
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hygienlst, but also for the environmentalist—that is, to develop the instru-
mentation to perform that monitoring.
As I see it, we are still on the threshold of trying to develop instru-
mentation for some of the more common pollutants such as CO and oxides of
nitrogen. We have yet to begin tackling what may Indeed be the more difficult
components of the environment. We can look at the incidence of cancer per
county as published by HEW.
It has been reported in the literature that a high percentage of cancers
are environmentally or anthropogenically induced. This represents a more
challenging area of monitoring than our traditional oxidants, NO's, CD's,
total particulates, and hydrocarbons.
So, 1 think yes, there is a need for defining where the instrumentation
development should come from and what should be analyzed. 1 think there has
been a lot of discussion in terms of the physical-chemical aspects of moni-
toring. There has been some discussion about monitoring the physiological
stress on the individual.
1 personally am concerned about long-term effects, as to whether or not
that kind of data per individual would allow us to explain some of the long-
term effects. Maybe it is going to be necessary to perform these exposure
monitoring activities for a long period of time. I guess 1 am Just not in-
formed as to what health effects you are going to be looking for over a short
term for some of the ambient ranges of pollutants.
But 1 also think we should probably search the horizon for the types of
tools that we are looking for. Almost no comment has been made on some of
the biological systems, bioassay systems. I recall about 12 years ago when
1 was here at the University of North Carolina, and we were looking for bio-
Indicators for oxidant and ozone, using white pine seedlings.
Although the Ames test was not intended to be a bioindicator, I certainly
think it represents an area where research and development may be warranted
in terms of defining whether or not that tool can be used as an indicator.
That may be of particular interest for some of these organics where there
is a potential of there being a large host of compounds. Some decision is
going to have to be made as to which compounds represent types of interest.
Maybe what is significant is a measurement of biological activity of the
atmosphere as opposed to measurement of benzopyrenes and benzene soluble
fraction.
496
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There are a lot of biological screening tests. At Brookhaven we have
been using tradescantia, which is a plant system. Our tradescantia has been
cloned to be very sensitive to chemical mutagens. It has been used in a test
system trailer which has been going around the country with an EPA air pollution
monitoring system. That is an area where there may be some development in
terms of a personal monitor.
1 know that you can take the buds from the tradescantia system and wear
it on the lapel. As a proposal, maybe this is something—maybe we could de-
vise a corsage or something that could be worn on an individual1s lapel and
after a week of use and with some hydroponlc solution to keep this system wet
and moist, you would be able to score this. I think this is a very easy
system to score by continuing visible mutations. This may indeed give you an
indication of the biological activity of the atmosphere.
I think that in terms of my own concerns for identifying those kinds of
pollutants that are of interest for the coal conversion and oil shale industries,
we are looking at the occupational environment now. Unless these systems are
quite tight and enclosed, the emissions may be your CO and oxides of nitrogen
of the future. The commercialization and applications of these systems are
expected to come on line within the next 4 or 5 years, and they thus represent
a concern to us all.
The monitoring technology is there. We are in trouble in terms of de-
fining what to measure and in terms of Identifying health effects. If we are
going to try to eliminate Workmen1s Compensation claims that are comparable
to the claims for black lung, which have been reported to be $1 billion annually,
then we are behind in our efforts to develop the technology.
In regard to the comments made by the developers and manufacturers of
these personal monitors, one question that came up repeatedly is, "Where is
the market?" I think that as pollutant standards are developed, in terms of
defining what is a safe environment and the frequency and the type of precision
that is required in order to ensure that environment, that at least in the
occupational environment the instrumentation need is going to be quite high.
So, I think that there is that particular market area. There is a man-
date to make sure that instrumentation is simple, uncum her some for the individ-
ual to wear, and cheap. If you are talking about sampling some representative
fraction of the work force, you can't afford to stay in business and buy
$5,000, high technology devices to monitor a representative component of that
work force. But you are going to have to have simple, lightweight devices.
That is where I think the passive dosimeters are needed.
497
-------
I think, however, that there are other areas where you need more in-
formation than passive dosimeters can provide, such as special survey devices
for high hazards and potentially acute exposures.
And there are areas where area monitors are appropriate. If the work-
place conditions are fairly stable and you are protected, say, from micro-
meterological episodic conditions, area monitors can provide the type of
monitoring that is required.
This particular meeting has been enlightening for me. It has provided
me with an insight in terms of the fact that not only in the occupational
environment, but also in the ambient environment, are there instrumentation needs.
I think there should be a unified effort addressed to the suppliers so
that what technology is developed is useful to all sectors.
MAGE: Thank you very much, Otto. Our next speaker is Matt Petrovick,
from EPA's Health Effects Research Laboratory.
PETROVICK: I would like to reflect a little on my impression of this
conference. I think I agree with the other panelists in that it has been
quite an enlightening and an exciting educational experience.
I see a number of opportunities in so many areas that we are not going
to be able to talk about them all. But I would just like to reflect on a few.
Specifically, in this morning's initial session, Dr. Mage mentioned a
wide variety of the types of sensors that we are going to look at. He touched
on the topic of agricultural pesticides. Perhaps I might have missed a few
sessions, but I didn't hear too much other comment in that direction. Maybe
I have a lot to learn on the sensors that are used in this area.
However, I would like to identify for this group an area where the badge-
type membrane devices and sensors that I have heard about here today can be
very effectively applied in terms of manufacturers' motivation, health effects
monitoring, and dosimeter measuring. And that is specifically in the area of
agricultural spraying; that is, agricultural spraying with aircraft. If I
can just briefly give you some background information on this. The Federal
Aviation Administration (FAA) happens to be in a great state of alarm at the
present time due to the increased incidence of agricultural aircraft accidents.
Not only are the pilots having problems in the flying of these aircraft,
498
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but the manpower that happens to be coordinating with these people have
problems. The farmer's wife standing at the end of a row that is to be
sprayed, a coworker filling the spray tanks of the plane, and the field workers
are all exposed to the atomized droplets by direct skin contact. When the
pilot finishes a summer of spraying, he might have acquired a significant
build-up of these pesticides, without being aware of it. It is suspected
by the FAA that the pilots' perceptive and cognitive judgments may suffer.
For example, there could be central nervous system disorders which have to
do with motor reaction, sensory perception of the visual tract, and judgment.
It is that particular aspect that the FAA feels might be responsible for the
pilot losing control of the aircraft and going in. That is only one aspect.
The other aspect is that there is not enough attention being given to
the person on the ground who is getting belted with a lot more pesticide than
the pilot. Over a summer of this kind of activity, there is widespread op-
portunity to look at a population that is exposed and isn't being monitored
very well.
On the other side of the coin, from the research standpoint and from the
clinical epidemiologlcal standpoint, EPA has invested a large sum of money
into design and development of a clinical-environmental laboratory here in
Chapel Hill—a clean air facility and a controlled atmosphere facility. It
just seems illogical that we can*t transpose some form of clinical protocol
out of a laboratory of this kind and, in this specific instance, into a small,
single-cockpit laboratory where that pilot is sitting. These are air condi-
tioned cockpits which leak like a sieve. The air conditioning flows back
through, picks up the pesticide, passes it through the cockpit, and the pilot
sits there and breathes it.
Some of the pilots wear oxygen masks; some of them don't. But it seems
to me that we can create an effective payback to the taxpayer for the invest-
ments in these kinds of research facilities by addressing problems like that
and actually performing an epidemiologic study in the area of pesticides where
a man sits in a fixed chamber and you have the opportunity to look at phys-
iological responses*
As experimenters, we are very fortunate. The man is sitting in a seat
relatively still. The EEC, respiration, and cardiac functions can be monitored
quite easily. The Air Force has 30 years of clinical background experience
in this kind of an area.
I am advocating that we take other Interdisciplinary sciences and join
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them into the health effects area to look at the types of dosimeters and ex-
posure devices we have here today, to merge medicine into computer science
and into epidemiology, and to bring these disciplines together in a coordinated
fashion in a public health initiative.
I would like to identify that one area that stands out here, because I
see a lot of opportunity for a simple study with immediate payoff. 1 see a
lot of technology here, and it gives me the Impression that it is untapped
and unapplied, yet the potential is staring us in the eye. I think it is
incumbent upon this conference to somehow pull these attributes together.
A second point might be: How could we pull these attributes together;
that is, to take advantage of the knowledge that we all have to offer and that
we all have to gain and learn? I might like to make a suggestion here because
1 have had the feeling that many of us are doing our own thing. Many of us
appear to be running in opposite directions. We have the organic chemist who
is in the corner doing his thing, and we have the physiologist in his corner
doing his own thing. Wouldn't it be more effective if we could all communicate
in a professional manner through the formation of—for a better choice of words—
a society for personal monitoring in health effects? Why not have an organi-
zation of the interdisciplinary sciences of medicine, epidemiology, computer
science, biomedical engineering, organic chemistry, biochemistry, and micro-
biology? Why would we advocate such a position? 1 can reflect over the last
20 years. 1 have seen many new disciplines come into being, which showed
the same symptoms that this conference is showing here today; that is, there
being a somewhat unfocused direction and the embryonic signs that here is a
whole new discipline emerging before us.
So, I would think that one of the ways to pull this together would be
to establish such a society and to follow it up with a professional journal,
where the experience and research results can be published, at least on a
quarterly basis. It would also help to have the different Federal agencies
and industries provide a society of this kind with seed money to help it along
and to further implement the educational processes of that new interdisciplinary
hybrid, the environmental scientist. For example, the environmental scientist
who may have an organic chemistry background may also have an epidemiologic
background.
So, if we can shape and train these people in an academic environment,
10 years from now we will have the kinds of disciplines and the kinds of talent
out in the field that can effectively respond in a coordinated fashion to
solving problems in environmental health effects.
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It is rather obvious to me that we are not going to come up with solutions
overnight. I see this as a long-term effort. And the need will exist as long
as technological man walks the earth.
So, I think it is incumbent upon this conference and future conferences
to seriously consider formally organizing such a society so we can provide
feedback to the Federal agencies which might be providing the funds to do
this kind of work and to do this kind of research for the increase of knowl-
edge in health effects.
I must also Include the area of microcomputers. I think that there
lies in this area a great opportunity for all of the disciplines, particularly
in organic chemistry and membrane technology. From that standpoint, we should
be looking at the other disciplines to learn what has been done in the last
20 years.
For example, there has been a lot of membrane technology displayed here
today. But if we look into the field of medicine, you will find that in the
design of artificial kidneys, in the design of blood oxygenators and artificial
hearts, there is a widespread knowledge of membrane technology and ion specific
electrodes.
In summary, that is my recommendation and observation. Thank you.
MAGE: Thank you very much, Matt. Our next speaker is Dr. Manny Shaw
of the InterScan Corporation.
SHAW: I do have a few things that I want to say. But just before I
get into that, I would like to say that in regard to the SO. dosimeter—as
soon as we have a CO dosimeter, we will have an SO- dosimeter. The S02
instrument we are now making is a portable monitor. It is our second largest
selling instrument. So, there is no problem—not just for us, but for some
of the people who are making this type of a device. It is here now if you
want it.
It has been stated by a few of the people here who are the Instrument
makers that they had hoped that the purpose of this meeting would be to make
a beginning of an understanding between EPA and we who have to make, develop,
and market these instruments. I think they are leaving today with a notion
that that hasn't been done as yet. Hopefully, in the last hour or so that
remains with us, and possibly with the idea that Mr. Petrovick had expressed
of working together through an actual society, that might be the way to go.
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Even prior to that, however, there are some things that can be done.
Now, I have been in the instrument world for some time. Long before I ever
got into the instrument world, I was in the technical research world. One of
the things that I have noticed in particular with instruments, going back a
decade in regard to instruments that have been developed for air monitoring,
is that there is a very large credibility gap between such agencies as EPA
and other agencies who are responsible for this type of monitoring and the
industry which is |