EPA-600/1-77-048
October 1977
Environmental Health Effects Research Series
HUMAN EXPOSURE SYSTEM FOR CONTROLLED
OZONE ATMOSPHERES
Health Effects Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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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 cate-
gories were established to facilitate further development and application of en-
vironmental 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
This report has been assigned to the ENVIRONMENTAL HEALTH EFFECTS RE-
SEARCH series, This series describes projects and studies relating to the toler-
ances of man for unhealthful substances or conditions. This work is generally
assessed from a medical viewpoint, including physiological or psychological
studies. In addition to toxicology and other medical specialities, study areas in-
clude biomedical instrumentation and health research techniques utilizing ani-
mals — but always with intended application to human health measures.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/1-77-048
October 1977
HUMAN EXPOSURE SYSTEM
FOR CONTROLLED OZONE ATMOSPHERES
Arthur A. Strong, Robert Penley,
and
John H. Knelson
Clinical Studies Division
Health Effects Research Laboratory
United States Environmental Protection Agency
Research Triangle Park, N. C. 27711
U.S. Environmental Protection Agency
Health Effects Research Laboratory
Office of Research and Development
Research Triangle Park, North Carolina
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DISCLAIMER
This report has been reviewed by the Health Effects Research Laboratory,
U.S. Environmental Protection Agency, and approved for publication. Mention
of trade names or commercial products does not constitute endorsement or
recommendation for use.
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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
establishment of sound regulatory policy. These regulations serve to
enhance the quality of our environment in order to promote the public
health and welfare and the productive capacity of our Nation's population.
The Health Effects Research Laboratory, Research Triangle Park,
conducts a coordinated environmental health research program in toxicology,
epidemiology, and clinical studies using human volunteer subjects. These
studies address problems in air pollution, non-ionizing radiation,
environmental carcinogenesis and the toxicology of pesticides as well as
other chemical pollutants. The Laboratory develops and revises 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 preparing the health basis for
non-ionizing radiation standards. Direct support to the regulatory function
of the Agency is provided in the form 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 endangerment of their health.
Research involving human subjects must be conducted under the most
carefully controlled conditions. The human exposure system described in
this publication assures a high degree of reliability with many safety
features. The controlled laboratory environment produced by the system
accurately simulates exposures occurring in urban areas, allowing the
researcher to determine effects on a variety of health indicators. These
research results, when compared to the information from animal studies
and population surveys provide a sound basis for establishing environmental
standards.
John H. Knelson, M.D.
Director,
Health Effects Research Laboratory
m
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ABSTRACT
An experimental exposure system for health effects research in environ-
mental pollutants that permits the introduction and control of ozone (03) to
an acrylic plastic chamber in which a human subject actively resides is des-
cribed. Ozone is introduced into the chamber air intake and is controlled
by an electro-mechanical feedback system operating from the electrical output
of an 03 gas analyzer.
A continuous record of 03 concentration, temperature, and dew point is
provided by an analog multipoint strip chart recorder. If the chamber 03
levels exceed preset limits, an alarm system automatically stops the 03 flow
and switches the chamber exhaust to purge operation.
A complete air exchange occurs every 72 seconds. In an emergency, the
chamber can be purged in 190 seconds. Chamber temperature and humidity are
dependent upon conditioned laboratory air.
IV
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CUUTEnTS
Foreword iii
Abstract iv
1. Introduction 1
k.. Materials and Kethocs 2
3. Comment 12
Keferences 13
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SECTION 1
INTRODUCTION
Ideally experimental environmental exposure chambers for human suojects
should be precisely monitored with automatic control of the pollutant levels
and alarms that will stop the pollutant flow ^noer adverse conditions. The
intent here is to describe such a system where the pollutant level in trie
chamber is automatically controlled by the output signal of the pollutant
analyzer monitoring the atmosphere of the exposure chamber. Presented as an
example is the methodology used in establishing an experimental exposure
system that continuously generates and i.aintains the desired ozone concentra-
tion by including the exposure chamber in the gas delivery feedback control
loop. The exposure system consists of a spacious, transparent acrylic plastic
chamber to contain the exposure atmosphere, an exhaust fan to maintain a fresh
air supply, a method to inject known volumes of pollutant gases into the
chamber air supply, a system of calibrated gas analyzers to determine the
actual pollutant gas concentration in the chamber, and safety components to
shut down the pollutant gas supply and sound alarms to protect the exposure
subject. During exposure in the chamber, pollutant effects on human behavior-
al and physiological functions, such as visual motor coordination discrimina-
tion and cardiac, pulmonary, and peripheral circulatory response, can be
evaluated.
In recent chamber studies, volunteers have been exposed to an ozone (03)
atmosphere of 800 yg/m3 [0.4 part per million (ppm)] ± 1C percent. Further
exposure studies are planned for nitrogen dioxide (N02) and sulfur dioxide
(S02) atmospheres, both singly and combined with ozone.
The exposure chamber is located in EPA's health Effects Research Labora-
tory facilities on the campus of the University of North Carolina at Chapel
Hill and was developed as part of the Environmental Protection Agency's ef-
forts to assess the adverse health effects of air pollution on humans. All
human exposure experiments using the chamber are cooperative efforts between
the University arid EPA.
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SECTION 2
MATERIALS AND METHODS
EXPOSURE CHAMBER DESIGN
Initial requirements for the exposure chamber, illustrated in Figure 1,
involved keeping the design simple and the construction complexity minimal
with the safety of the exposure subject uppermost in mind. Because a trans-
parent chamber was desired, 1.2- x 2.4-meter (4- x 8-foot) transparent
acrylic plastic sheets 1.3 centimeters (cm) (1/2 inch) were selected for the
walls, floor, ceiling, and doors. To minimize cutting of the construction
material, the chamber was made as close to an 8-foot cube as permitted by the
space allocated in the laboratory facility. The corner and ceiling support
members were made from 3.8-centimeter (1-2/3 inch) thick aluminum "U" channel
stock. The closed backs and sides of the "U" shaped channels were bolted to-
gether so that adjoining sheets of plastic could be slipped into the open end
of the "U" and sealed with silicone calking to form a rigid airtight seam.
Seventeen 1.2- x 2.4-meter plastic sheets and 137.2 linear meters (450 feet)
of "U" channel were required for the chamber.
The finished chamber interior provides a 2.44 x 2.44 meter (8x8 foot)
floor area with a 2.23 meter (7 foot 4 inch) ceiling which represents a total
enclosed volume of 13,282 liters (469 cubic feet). An 850-liter (30 cubic
feet), stand-up, whole body plethysmograph was constructed inside and in one
corner of the chamber with the entrance opening into the exposure chamber.
Because the body plethysmograph door is normally closed, the instrument is
sealed from the exposure gas. The gaseous pollutant is thus confined to a
chamber volume of 12,432 liters (439 cubic feet). Dynamic pulmonary function
measurements are made in a body plethysmograph as one test for subtle effects
of pollutant gas exposure.
The doors to the body plethysmograph and exposure chamber were construct-
ed from 76.2- x 208.3-cm sheets of 1.3-cm thick acrylic plastic. The door
openings were made smaller than the doors to provide a surface around the
periphery of the opening where gasket material could be sandwiched between
the edges of the opening and the overlapping door. This provided a gas-leak-
proof door without an elaborate door jamb and threshold. Door hinges of the
type found on standard walk-in refrigerators were used with a cam door latch
that was operable from either side of the doors.
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CHAMBER AIR SUPPLY
The rear of the chamber was situated again.t -'n outsioe wall of the lab-
oratory thus permitting the location of the exhaust far. outside the buildiny.
A low speed industrial radial wheel exhaust fan was selected to draw ambient
laboratory air through the chamber. The noise produci-d by the exhauster is
negligible because of the low operating speed of 92U revolutions per minute
(rpm) and the remote location of the fan. A manufacturer-applied corrosion
resistant coating (LENKOTE) on the fan wheel anc, weather proof housing pro-
tects the exhauster from the pollutant gases. A 22.9-cm (9-inch) diameter
stainless steel vertical duct carries the output of the fan fror.i its ground
level location to 61 cm (2 feet) above the building roof line. Selection of
the exhaust fan was based on the requirements for a standard, commercially
available, low speed, weather proof fan that could produce a complete air
exchange in the chamber within 2 minutes at an estimated differential air
pressure of 5.1 centimeters (2 inches) of water across the cnamber and air
supply subsystem. A 2-speed, 0.5 horsepower, 115-volt, single phase motor
was selected to drive the fan. Motor speeds of 1140 and 172b rpm drive the
fan at speeds of 920 and 1392 rpm. High speed operation of the fan is used
only to purge the chamber, a process that can be accomplished in approxi-
mately 190 seconds under alarm conditions. Under normal low speed operation,
the exhaust fan develops an actual pressure of 2.7 cm (1.0£> inches) of water
to move air at a rate of 10,393 liters per minute (367 cutic feet per minute
(cfm)) through the air supply duct, the chamber, anc the exnaust duct; there-
fore, one air exchange occurs in the chamber every 72 seconds.
The fan input is connected by a 22.9-cm (9-inch) diameter stainless steel
duct to the center of the chamber back wall at the floor line. A 12.7- x
22.9-cm (5- x 9-inch) rectangular exhaust duct at the junction of the chamber
floor and walls contain six registers; two on each side wall and two on the
back wall. Each register has an adjustable 7.6- x 17.8-cr.: (3- x 7-inch) open-
ing to provide a means of controlling the air flow within the chamber. Clos-
ing the register openings increases the resistance of the duct system and
results in a reduced airflow. In the .present study, the registers were placed
in the maximum open position.
A perforated aluminum yriTl in the ceiling of the chamber covers a 71.1-
x 71.1-cm (28- x 28-inch) square by 10.2-cm (4-inch) high dispersion box. The
grill (available at most hardware stores) has a 3.^-millimeter (mm) diarr.eter
(1/8-inch) holes on 7.1-mm (9/32 cm) centers and 1.6-m,' (1/16-incn) diameter
holes en 2.4-mii! (3/32-inch) centers between ihe larger holes.
An air supply duct with inside dimensions of 10.L x 71.1 centimeters
(4 x 28 inches) extends from the dispersion box 2A meters (8 feet) into the
laboratory where the exposure chamber is located. The supply air is drawn
through the duct and through the dispersion box by the negative chamber pres-
sure generated by the exhaust fan. A removable orifice plate with a 6.4- x
29.2-cm (2-1/i: x 11-1/2 inch) rectangular opening is positioned midway in the
2.4-meter-long air supply duct. The orifice plate is useu with a differential
pressure-meter to indicate the air flow to the chai.iber. The air supply duct
and orifice plate were constructed from the Sctfie acrylic i/tastic material
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used for the construction of the chamber. The available space above the
chamber and the thickness of the plastic had to be considered in designing
the size of the duct and dispersion box.
The static pressure tap locations for the rectangular orifice plate were
found experimentally using a magnehelic pressure gauge with a 6.4-mm (1/4-
inch) diameter tube probe. An inexpensive water manometer could have been
used for the pressure gauge, however. From the center line of the rectangular
orifice plate, the high pressure tap was located 20.3 cm (8 inches) upstream
and the low pressure tap at a point 10.2 cm (4 inches) downstream. The dif-
ferential pressure measured between the pressure taps was 14.5 mm (0.57 inch)
of water for an air flow rate of 367 cfm measured with a Velometer. All of
the equipment that was available to measure air velocities and pressure drops
used the British system of units; therefore, conversion to metric units was
made after all air velocities and pressure drop measurements were made and
the airflow calculated.
If a Velometer is not available, the approximate air flow through the
orifice can be computed from the simplified equation:
Q = 60A /1705Pd
Where: "Q" is the approximate air flow (in cubic feet per minute).
"A" is the area of the orifice opening (in square feet).
"P.," is the pressure drop between the high and low pressure
taps for the orifice (in inches of water).
For a round orifice of diameter D, the duct diameter should be 2D, the low
pressure tap should be the distance D downstream, and the high pressure tap
should be a distance 2D upstream from the orifice.1'2
>
The air flow through the chamber determined from the above formula is
373 cfm where the Velometer-measured air flow was 367 cfm or 367 cfm times
28.32 liters per cfm which equals 10,393 liters per minute.
Because the ambient pollutant concentrations in Chapel Hill are less than
10 percent of the chamber exposure levels, the cost of an absolute filter
system for the chamber air supply duct was not justified. A standard furnace
type dust filter was placed across the entrance of the air supply duct, how-
ever, to remove normal airborne dust.
The air resistance of the dust filter and orifice plate creates a nega-
tive pressure of 0.67 inch of water in the chamber when referenced to the
outside air pressure. A drop in pressure of 0.67 inch of water is equal to
0.0235 pound per square inch reduction in pressure.
The temperature and humidity conditions in the chamber are dependent on
the conditioned makeup air supply to the laboratory area in which the chamber
is housed. Solid state thermistor and lithium chloride sensors,3 located in
the chamber, through electronic signal conditioners provide linear 0 to 1
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volt DC signals that are directly proportional to the- temperature and
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As a safety precaution, two devices are used to restrict the flow of 02
gas and, consequently, the 63 gas. A normally closed solenoid valve is used
to shut off the flow of gas to the chamber in the event of a power failure or
an alarm condition. Power must be applied to this valve for it to remain
open. (The conditions for an alarm will be explained later). A 20-turn
micrometer valve with a coefficient of velocity (CV) of 0.028 is the second
flow restrictor. Used as a throttling device, the valve was adjusted to a
setting of three turns restricting the 02 flow to 600 cm3/min with all other
valves in the maximum open position. The limited 02 flow through the 03 gen-
era tor. will prevent a chamber 03 concentration above 0.6 ppm.
All components in the 02 gas flow path are maintained as fixed value
passive elements except for the servo-driven micrometer valve on the output
of the "Pollutant Level Error Detector and Processor." (See Figure 2).
Changes in the 02 flow are made by the servo-motor-driven valve inversely to
changes in the analogue DC voltage output of the 03 gas analyzer monitoring
the chamber atmosphere. Except for the motor drive coupling, this valve is
identical to the flow restrictor valve. Uncontrolled variables in the expo-
sure chamber system that may influence the chamber pollutant level are com-
pensated for by the negative feed back of the "Pollutant Level Error Detector
and Processor" between the output of the 03 gas analyzer and the servo-motor-
driven valve. Typical of the uncontrolled variables are:
1. Changes in the air flow through the chamber resulting from
outside wind conditions, fan speed, leaks, and filter loading.
2. Absorption of the pollutant gas by the subjects, particulates, and
materials in the chamber.
3. Changes in the gas generation system.
With automatic closed loop control of the 02 flow and subsequently the
03 flow, the 03 concentration at any point in the chamber can be held within
± 10 percent of 0.4 ppm exclusive of the accuracy of the 03 analyzer. Any
inaccuracies or drift in the calibration of the 03 analyzer directly affect
the chamber concentration through control of the 02 servo-driven valve.
The block diagram of the "Pollutant Level Error Detector and Processor,"
Figure 3, and the discussion that follows will give an idea of the operation
of the pollutant flow controller. The input device to the flow controller
circuit is a meter relay with the meter movement electrically activated by
the 1-volt DC output of the gas analyzer that monitors the chamber atmos-
phere.5 The two set point switches, which are photoelectrically operated by
the meter movement, are set at 5 percent below and at 5 percent above the de-
sired 03 exposure level. For the present exposure level of 0.4 ppm, the full
scale output range of the 03 analyzer is set at 1 volt DC, which is equiva-
lent to 0.5 ppm at the input. The meter relay set point switches determine
the direction of rotation of the valve servo motor by applying a 5-volt DC
positive logic level to the data input of the clockwise (CW) or counter-
clockwise (CCW) Flip-Flop.
If the meter relay indication is higher than the upper set point, a
logic high 5-volt DC level will appear on the data input of the counterclock-
wise Flip-Flop. When a clock pulse arrives at the clock input, the Flip-
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Flop will be triggered, resulting in a logic high level on the output. An
electronic switch connected to the output of the Flip-Flop will apply power
to the CCW rotation input power phase of the motor. The servo valve will be
driven in a CW direction toward the closed position with a reduction in the
flow of 02 gas to the 03 generator. The valve rotation is opposite that of
the motor because of the gear reduction coupling between the motor and the
valve. If the meter relay indication was below the lower set point, the CW
Flip-Flop would be triggered by the clock pulse resulting in the servo valve
being driven further open.
An astable multivibrator, or Correction Interval Clock, with an adjust-
able period of 1 to 3 minutes provides the clock pulses for the CW and CCW
Flip-Flops. The clock period is set to exceed the measured time between a
step change in the 03 flow to the chamber and the indication of the step
change on the 03 gas analyzer monitoring the chamber. Thus, incremental
changes in the 03 flow are time-spaced to allow the 03 analyzer to detect the
chamber concentration. For an 03 chamber concentration of 0.4 ppm, the mea-
sured time between the start of the 03 flow to the chamber and the point at
which the concentration reached 63% of 0.4 ppm was 2 minutes, 32 seconds.
After stabilizing at 0.4 ppm, the 03 concentration dropped to 37% of 0.4 ppm
in 1 minute, 50 seconds after the 03 flow had stopped. Thus, the astable
multivibrator period was set for 3 minutes. The accuracy of this setting is
not important as long as the period is longer than the detected step change
in the 03 flow to the chamber.
To generate incremental changes in the 03 flow, the "Correction Incre-
ment Monostable" multivibrator is triggered by the outputs of the CW and CCW
Flip-Flops through an AND gate that subsequently resets the Flip-Flops 0.1
to 3.0 seconds after the clock pulse (Figure 3). This delay time or cor-
rection time is set to allow the servo-motor-driven valve to rotate suffi-
ciently to permit an incremental change in the 02 flow to the ozonator, and
consequently the 03 flow, that will bring the meter relay indicator from a
limit reading to a value midway between the limits. With a valve rotation
speed of 1 revolution every 6 seconds, a reset dalay time of 0.6 seconds will
change the 220 cm3/min 02 flow 8 percent for the desired 5 percent change in
the chamber 0.4 ppm 03 concentration. Figure 4 indicates the relationship
between the rotation of the servo-motor-driven valve and the 02 flow through
the 03 generator with the resulting 03 chamber concentration. Intermittent
operation of the servo motor is necessary because the servo-driven valve can
change the 03 flow at a faster rate than the gas measurement subsystem can
follow.
High and low limit comparators detect the limits of the feed back
potentiometer on the valve servo motor shaft and present a logic low reset
level through the OR gate to the Flip-Flop that causes the servo motor to be
driven beyond the limit (Figure 3). A high limit alarm is also set off when
the servo valve is driven to the maximum 03 flow limit. For the present ex-
posure study, this limit was 5 turns of the valve for a maximum flow of 590
cm3/min. Rotation of the valve beyond 5 turns increased the flow only 10
cm3/min because of the low 02 line operating pressure. If a servo-driven
valve'with a lower CV was available, a larger number of valve turns would be
usuable.
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To adjust the initial 03 flow to the chamber, the input of the servo
valve motor drive amplifier is switched by the double-pole, double-throw
switch to the output of an analogue servo amplifier. A manually operated,
10-turn potentiometer is positioned to the required flow setting. If the
feedback potentiometer on the valve servo motor shaft is in a different posi-
tion, an error voltage will occur at the summing point of the servo amplifier.
The amplified error voltage will activate the motor drive amplifier thereby
energizing the motor phase to rotate the feedback potentiometer in the direc-
tion that will reduce the error signal.
The 02 flow controller (shown in Figure 2) is followed by a rotameter
that is used as a relative 02 flow indicator for the 03 generator. Cali-
bration of the rotameter is not actually required because the flow of 02
is based on the quantity of 03 in the chamber and the rotameter is used
only as an indicator of flow.
Finally, 02 is converted into 03 in a corona silent discharge arc ozon-
ator in which the 02 is subjected to a 60-hertz alternating electric field
between electrodes connected to a high voltage transformer. Ozone is
formed by collision of a free oxygen atom with an 02 molecule. The high
electric field provides the medium for the transfer of energy to form a
stable 03 molecule.6
In order that the oxygen flow will be the major factor in controlling the
03 concentration, the two variables of power input and temperature of the ozo-
nator are held reasonably constant. A 40-watt incadescent lamp is used as a
fixed ballast on the power input to the ozonator. The lamp provides some reg-
ulation by holding the ozonator input voltage within 5 percent for a 10 per-
cent line voltage change. The temperature of the cooling water for the ozona-
tor is held at a constant 22°C within a half degree by a water bath. Without.
the water bath, a 5°C change will alter the 0.4 ppm chamber concentration
by 1 percent. >
A 6.4-mm (1/4-inch) outside diameter stainless steel tube 4.6 meters (15
feet) long is used to transport the 03 directly from the ozonator the the lo-
cation of the low pressure tap of the orifice plate in the chamber air supply.
CHAMBER OZONE LEVEL MEASUREMENT
The pollutant level in the chamber is measured by drawing chamber air
samples through 6.1 meters (20 feet) of 6.4-mm (1/4-inch) diameter Teflon
tubing with a vacuum pump connected to the output of a cnemiluminescence 03
analyzer.6 The upstream input end of the sample tube is located 1.5 meters
(5 feet) from the floor of the chamber and normal to the center of the alumi-
num dispersion grill in the ceiling of the chamber. This sampling location
was selected because it places the input end of the sample tube at the center
of the chamber input air stream and at the height of the nose of the average
subject sitting on a bicycle ergometer. The subject's electrocardiogram is
measured at rest and during periods of exercise on a bicycle ergometer during
the 03 exposure.
8
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Calibration of the 03 analyzer is accomplished by the gas phase titra-
tion method as described in Tentative Method for the Calibration of Nitric
Oxide, Nitrogen Dioxide, and Ozone Analyzers, an EPA publication.7
The 1-volt DC electrical output signals from the 03 gas analyzer are re-
corded concurrently with the temperature and dew point sensor signals on a
multipoint strip chart recorder. A digital voltmeter is also used to display
the output of the analyzer, thus improving the reliability of the meter read-
ing by the operator.
SAFETY ALARM SYSTEM
Electrical signals from the ozone gas analyzer, the chamber air supply
flow monitor, the pollutant gas flow controller, and the fire and combus-
tion gas level monitors are used to set off audible alarms and turn on indi-
cator lamps under the following conditions:
1. If a fire develops in the chamber, the area around the chamber, or
in the outside gas cylinder storage house, the gas supply and
chamber air supply will be automatically shut off to help prevent
spreading the fire. When activated, heat and explosive gas de-
tectors close normally open switches.
2. If the flow rate of the fresh air supply to the chamber drops below
a preset level or if the chamber door is opened when the 03 gas is
flowing, the alarm will sound, the 03 gas will be shut off, and the
exhaust fan will go into high speed purge operation. A differen-
tial pressure gauge connected to the high and low pressure taps
of the chamber air supply duct orifice plate will close a
switch when the pressure drop goes to zero.
3. If the 03 pollutant gas concentration in the chamber goes above the
0.5 ppm limit set for a normal exposure level of 0.4 ppm, a switch
connected to the multipoint strip chart recorder pen drive will
activate an alarm stopping the pollutant gas flow.
4. When the 03 pollutant gas flow controller has reached the maximum
preset gas flow limit of 590 cm3/nrin into the chamber, an alarm
switch is closed and the gas flow is stopped. This will occur
when the servo driven valve has rotated open 5 turns. Thus the
alarm will sound even in the 03 gas analyzer output signal to the
meter relay remains below the low chamber concentration limit
causing the flow controller to compensate by increasing the 03 flow
when in reality the 03 concentration was above the limit.
Under all of the above alarm conditions, power will be removed from the
03 generator and the normally closed solenoid valve on the 02 gas supply
cylinder thereby stopping the flow of 03 gas.
MEASURED PERFORMANCE CHARACTERIZATION
Before human subjects were permitted in the chamber, sequential valida-
tion and characterization tests were performed to measure the air supply
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volumetric flow rate and to determine the pollutant flow volume so that
the desired chamber concentration, the required incremental change in
pollutant flow rate to adjust for system variables, and the necessary distri-
bution the pollutant throughout the chamber would be provided.8
The volumetric air flow of 10,393 liters/minute through the chamber was
determined by averaging six velocity measurements with a Velometer in front
of the chamber air supply duct filter and multiplying by the cross sec-
tional area of the duct. For the exposure volume of 12,432 liters, one
complete air exchange will occur every 72 seconds. Five-percent variations
in the pressure drop across the orifice plate caused by outside wind condi-
tions have been observed. Any adjustments required in the chamber pollutant
concentration attributable to wind-caused air flow deviations were well
within the ± 5 percent of 0.4 ppm correction range of the automatic pollu-
tant gas flow controller, however.
Before the oxygen flow through the ozone generator could be determined
for the required exposure level, the power line input current to the genera-
tor had to be set at a stable value. The initial step in the procedure was
to adjust the 02 gas cylinder output pressure to the 10 psig maximum operat-
ing pressure of the generator.
With the input current set at zero, the 02 flow was adjusted to pro-
vide 1 liter/nrin through the generator. The input current was then in-
creased slowly from zero until the chamber concentration reached approxi-
mately the design limit of 1 ppm, which occurred at a value of 0.16 amperes.
Both the generator current and the chamber concentration were monitored for
at least 2 hours. Compensation for slight adjustments made in the generator
to improve the input current stability was accomplished by altering the 02
flow.
After calibration of the ozone gas analyzer, ozone was introduced to
the chamber for evaluation and characterization of gas control subsystem.
The flow controller valve was adjusted to the maximum open position, and
the micrometer flow restrictor valve was adjusted to produce a flow that
created a chamber pollutant level at the experimental design safety limit.
For a maximum chamber 03 concentration limit of 0.6 ppm, the valve was
opened 3 turns, which allowed an 02 flow through the gas subsystem of 6000
cm3/min with an 02 cylinder line pressure of 10 psig.
A curve of 03 flow and the chamber 03 concentration versus rotation of
the servo driven valve was plotted for the flow controller (Figure 4).
Information from this curve was used to determine the initial flow setting
and the length of the correction time that the servo motor is energized.
The correction time was computed from the formula:
%.
.t - Af X S/r
At AR
Where: "At" is the correction time (in seconds).
"Af" is the cc/min change in 03 flow (in cubic centi-
meters per minute) that will produce a 5 percent
10
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change in the part per million chamber con-
centration of ozone.
"S/r" is the time (in seconds) for each revolution.
"AR" is the change in 03 flow (in cubic centimeters per
revolution) for each revolution of the 20-turn
servo valve.
The period between correction times of the controller is a matter of
minutes based on the chamber air exchange rate, the pollutant monitoring
cycle or settling time, the transport time of the pollutant gas to the cham-
ber and the time for a gas sample to flow from the chamber to the pollutant
monitor.
Two calibrated ozone gas analyzers were used to define the profile of
the exposure chamber from six locations equally spaced on two planes (2 feet
and 5 feet above the floor respectively). The sample probe for the reference
analyzer remained stationary 5 feet above the floor at the center line of the
perforated aluminum grill covering the dispersion box. At the start, the
movable probe for the second analyzer was placed at the stationary location
to ascertain differences between the two 03 analyzers. When the movable probe
was placed at other locations, a lower concentration was measured with a mean
distribtuion deviation of 3.4 percent of 0.4 ppm. If space had permitted a
larger input grill area, the distribution would have been better. No hot
spots of highly concentrated gas were found even with a probe at the exit of
the chamber supply duct. The gas and air supply were well mixed by the tur-
bulence in the rectangular supply duct.
11
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SECTION 3
COMMENT
The exposure system described here is presently used for 4-hour expo-
sures of human subjects to an 03 concentration of 0.4 pprr> ± 10 percent. The
major concern in designing the system was the safety of the exposure subjects
Safety features of the system include the automatic closed loop control of
the pollutant flow, the alarms to alert operating personnel, and the auto-
matic shutdown of the pollutant flow if out-of-tolerance conditions develop.
Controls similar to those described for 03 will be employed when human volun-
teers are exposed to concentrations of N02 and S02 in future exposure
chamber studies. A procedure similar to that described for 03 will also be
used for N02 and S02 characterization of the chamber system. An additional
step will be to determine the interaction of one residual gas on the other
when switching between pollutants. In all cases, the chamber atmosphere
will be monitored simultaneously for 03, NO, N02, NUX, and S02.
12
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REFERENCES
1. Hinners, R., Burkart J. K., Punte C. L. Animal inhalation exposure
chambers. Arch. Environ. Health 16:194-206, 1968.
2. Oxford, C. W. How To Determine Fluid-Flow Rates - 2. Oil and Gas
Equipment, The Petroleum Publishing Co., October 1956.
3. Leithe, W. The Analysis of Air Pollutants. Ann Arbor - Humphrey
Science Publishers, Ann Arbor, Michigan, 1970, Library of Congress
Catalog No. 70-120994. pp 126-127, 14K
4. Baker, W., Mossman, A. L. Matheson Gas Data Book. Matheson Gas
Products, 5th ed., 1971, pp" 451-454.
5. Johnson, B. L., Strong, A. A. The design of an automatic control system
for laboratory produced automobile exhaust concentrations. Presented at
Air Pollution Control Association Annual Meeting, June 1965.
6. Air Quality Criteria for Photochemical Oxidants. US Department of
Health, Education and Welfare,- National Air Pollution Control Admin-
istration, Washington, D. C., No. AP-63, March 1970, pp 23-24, 55.
7. Tentative Method for Calibration of Nitric'Oxide, Nitrogen Dioxide, and
Ozone Analyzers by Gas Phase Titration. US Environmental Protection
Agency, Research Triangle Park, NC, No. EPA-R2-73-246, March 1974.
Federal Register 36(84), April 30, 1971.
•
8. Hinners, R. G., Burkart, J. K., Coutner, G. L. Animal exposure chambers
in air pollution studies, Arch. Environ. Health, 13:609-615, 1966.
13
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ALUMINUM "U" CHANNEL
PERFORATED GRILL
ORIFICE PLATE
AIR SUPPLY
OUCT
10.16 cm
(4 in.)
(8ft)
Figure 1. Ozone and nitrogen dioxide human exposure chamber.
-------
en
02
GAS
CYLINDER
THREE-
WAY
VALVE
DOUBLE
REGULATOR
> ^-*\ ^~^ CUTOFF
r * VALVE
02
GAS
CYLINDER
ALARM
BELL AND
HORNS
120 VAC
120 VAC
C2H4
GAS
CYLINDER
WATER
BATH ^J
CONSTANT-
TEMPERATURE
WATER SUPPLY
72° WATER
I
ROTAMETER
MICRO-
METERING
VALVE
MICRO-
METER
SERVO VALVE
OZONE
GENERATOR
1 liter/min, 1% 03
TO CHAMBER FOR
1 ppm MAX.
5 VDC LIMIT SIG.
POLLUTANT
LEVEL ERROR
DETECTOR AND
PROCESSOR
1 VDC 03 LEVEL SIGNAL
ALARM SYSTEM;
POLLUTANT LEAK,
FIRE, SMOKE, AND
COMBUSTIBLE GAS
MONITORS
LIMIT SIGNALS
120 VAC
DATA
RECORDING
STRIP CHART
RECORDER
1 VDC 03
LEVEL SIGNAL
CHAMBER
AIRFLOW
INFORMATION
DIGITAL
VOLTMETER
OZONE
ANALYZER
AMBIENT
LAB. AIR
SAMPLE
OZONE
ANALYZER
SAMPLE
FROM
CHAMBER
Figure 2. Ozone generation and control system.
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MANUAL
POTENTIOMETER
MANUAL
IIS VAC
J_
MICROMETERING
VALVE
MOTOR
DRIVE
AMPLIFIER
TEN-TURN
COUNTER
DIAL
-•*• —-o
CW ROTATION
TO OPEN VALVE
LOW VALUE CORRECT
HIGH VALUE CORRECT
HIGH LIMIT
COMPARATOR
1 »
HIGH LIMIT
ALARM
1 OR V
J GATE /
LOW LIMIT
COMPARATOR
TIME
ADJUSTMENT
1 TO 3 min
CORRECTION
INTERVAL
CLOCK
OSCILLATOR
RESET PULSE AFTER
CORRECTION TIME
CHAMBER GAS
SAMPLE
CORRECTION
INCREMENT
MONOSTABLE
FEEDBACK
POTENTIOMETER
CW
FLIP-FLOP
DATA a
OUTPUT
CLOCK
RESET
CCW
FLIP-FLOP
DATA Q
OUTPUT
CLOCK
RESET
TIME ADJUSTMENT
0.1 TO 3.0 sec AFTER
RESET IS REMOVED
Figure 3. Pollutant level error detector and processor.
-------
O 02 FLOW TO OZONATOR
A 03 CHAMBER CONCENTRATION
0.1 S
0.10
0.05
12345
NUMBER OF TURNS SERVO VALVE HAS ROTATED OPEN
Figure 4. Measured oxygen flow to the ozonatpr and the ozone chamber
concentration as a result of the rotational position of the servo-driven valve.
17
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TECHNICAL REPORT DATA
<• rcaJ Instj;irtii>its mi //;<• reverse bcfmv i\>inptctinx)
P four NO.
EPA-600/1-77-048
. i II LL AND SUf3Tl ri.fc
HUMAN EXPOSURE SYSTEM FOR CONTROLLED OZONE ATMOSPHERES
. AUIHOR(S)
Arthur A. Strong, Robert Penley and John H. Knelson
. PERFORMING ORGANIZATION NAMtl AND ADDRESS
Clinical Studies Division
Health Effects Research Laboratory
Research Triangle Park, N.C. 27711
3. RECIPIENT'S ACCESSION-NO.
5. REPORT DATE
October 1977
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
1AA601
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Health Effects Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, N.C. 27711
13. TYPE OF REPORT AND PERIOD COVERED
RTP.NC
14. SPONSORING AGENCY CODE
EPA 600/11
15. SUPPLEMENTARY NOTES
16. ABSTRACT
An experimental exposure system for health effects research in environmental
pollutants that permits the introduction and control of ozone (03) to an acrylic
plastic chamber in which a human subject actively resides is described. Ozone
is introduced into the chamber air intake and is controlled by an electro-mechanical
feedback system operating from the electrical output of an 03 gas analyzer.
A continuous record of 03 concentration, temperature, and dew point is provided
by an analog multipoint strip chart recorder. If the chamber 03 levels exceed
preset limits, an alarm system automatically stops the 03 flow and switches the
chamber exhaust to purge operation.
A complete air excharige occurs every 72 seconds. In an emergency, the chamber
can be purged in 190 seconds. Chamber temperature and humidity are dependent upon
conditoned laboratory air.
17.
a.
KEY WORDS AND DOCUMENT ANALYSIS
DLSCHIPTORS
test chambers
environmental tests
ozone
tests
humans
b. IDENTIFIERS/OPEN ENDED TERMS
U. COSATI Held/Group
06 F, L
14 B
18. DISTRIBUTION V.TATEMEN T
RELEASE TO PUBLIC
19. SECURITY CLASS (Tills Report)
UNCLASS^EFIED
20 SECURITY"CLASS fT/i/i pane")
UNCLASSIFIED
21. NO. OF PAGES
22
Form 2220-1 (9-73)
18
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