EPA-650/2-73-016
June 1973
ENVIRONMENTAL PROTECTION TECHNOLOGY SERIES
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EPA-650/2-73-016
DEVELOPMENT OF AN INSTRUMENTAL
MONITORING METHOD FOR MEASUREMENT
OF ASBESTOS CONCENTRATIONS
IN OR NEAR SOURCES
by
Amitav Pattnaik and John D. Meakin
The Franklin Institute Research Laboratories
Benjamin Franklin Parkway
Philadelphia, Pennsylvania 19103
Contract No. 68-02-0544
Program Element No. 1AA010
EPA Project Officer: Jack Wagman
Chemistry and Physics Laboratory
National Environmental Research Center
Research Triangle Park, North Carolina 27711
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
June 1973
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This report has been reviewed by the Environmental Protection Agency and
approved for publication. Approval does not signify that the contents
necessarily reflect the views and policies of the Agency, nor does
mention of trade names or commercial products constitute endorsement
or recommendation for use.
11
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F-C3415
ABSTRACT
A methodology has been developed for the determination of the amount
and size distribution of asbestos fibers and fibrils in air at point
sources and near point sources. The technique can also be applied to
ambient air samples.
This report describes the effort on the development of an analytical
method which employs a scanning electron microscope with microprobe
capability and an image analyzing system. Complete details for manual
operation have been worked out. Feasibility study for automated oper-
ation has been completed also.
Preliminary results of the analysis of samples collected at point
sources and near point sources are also included.
iii
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F-C3415
CONTENTS
Section Tit1e Page
ABSTRACT iii
1 INTRODUCTION 1-1
2 EXPERIMENTAL PROCEDURE 2-1
2.1 Statement of the Problem 2-1
2.2 Summary of Research Leading to Specimen
Preparation Technique 2-1
2.3 Description of Methodology for the Analysis of
Asbestos in Air. ......... 2-3
2.3.1 Sampling. ......... 2-3
2.3.2 Specimen Preparation for Scanning Electron
Microscopy and Microprobe Analysis . . . 2-4
2.3.3 Specimen Preparation for TEM 2-7
2.3.4 Measurement Techniques 2-7
2.3.5 Analysis of Microscopic Data 2-9
3 EXPERIMENTAL RESULTS 3-1
3.1 SEM Observations 3-1
3.2 Microprobe Analysis. ........ 3-4
3.3 Image Analysis 3-7
3.4 Analysis of Actual Air Samples 3-14
3.5 TEM Observations 3-17
4 DISCUSSION 4-1
4.1 Feasibility Study - Manual Method 4-1
4.2 Feasibility Study - Automated Method .... 4-2
5 FUTURE WORK 5-1
5.1 Pre-concentration of Asbestos in Samples of Ambient
Air 5-J
v
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CONTENTS (Cont'd)
Section Titles Page
5.2 Field Survey 5-2
6 ACKNOWLEDGEMENTS 6-1
7 REFERENCES 7-1
vi
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FIGURES
Number Title Page
1 Schematic Diagram of the Steps Involved in Specimen
Preparation 2-5
2 SEM Photographs of Millipore Filter with Standard
Crocidolite; (a) Blank, (b) with Crocidolite; both
X10.000 3-2
3 SEM Photographs of Standard and Point-Source Samples;
(a) Standard Amosite; O.A5y Filter; X3.000, (b) Point
Source, 0.8y Fiber, XI,000 3-3
4 SEM Photographs of Near-Point-Source Samples; (a) X300,
(b) XI,000 3-5
5 X-ray Spectrum from a 0.5p Diameter Chrysotile Fiber . 3-6
6 X-ray Spectrum from a O.lp Diameter Chrysotile Fiber . 3-8
o
7 X-ray Spectrum from a 500 A Diameter Chrysotile Fiber . 3-9
8 SEM Photographs of Chrysotile Fibers from which X-Ray
Spectra0were Obtained; (a) O.ly Diameter Fiber; XlO.OOO,
(b) 500A Diameter Fiber; X10,000 ...... 3-10
9 SEM Photograph of Standard Crocidolite and Its Corres-
ponding IMANCO Images; (a) Image, XI, 000, (b) IMANCO
Image Counting All Particles ....... 3-11
(c) IMANCO Image Counting Fibers Only, (d) IMANCO Image
with Perimeter Display, (e) IMANCO Image with "Count
10 SEM Photograph of Air Sample and Its Corresponding
IMANCO Image, (a) XI, 000 ........ 3-15
11 Cumulative Distribution of Fiber Lengths in Point-
Source and Near-Point-Source Samples ..... 3-18
12 TEM Photographs: Carbon Extraction Replica of Aspira-
ted Standard Chrysotile and Selected Area Electron
Diffraction, (a) X3,000 ......... 3-19
vii
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F-C3415
1. INTRODUCTION
The carcinogenic properties of asbestos are now well accepted [1-7].
Langer et al [4] have recently reviewed the incidence of asbestos fibers
in human lung tissue and it has been experimentally verified that "asbestos
bodies" do contain asbestos fibers in their cores [8, 9], Occupational
exposure to asbestos dust is associated with serious risks of lung scarring
and neoplastic disease [10, 12]. Under certain circumstances, although
to a lesser degree, similar hazards may exist with indirect occupational
exposure [13, 14], with family contact [15, 16] and as a result of neigh-
borhood and environmental exposure [15, 16]. For example chrysotile asbestos
has been identified in the lungs of persons in New York City [3].
However, the influence of type of asbestos, fiber size and cofactors
on biologic effects is not well documented [7]. Fiber size is critically
important in determining respirability, deposition, retention and clear-
ance from the pulmonary tract and is probably an important determinant of
the site and nature of biologic action. Little is known about the movement
of fibers within the human body, including their potential for entry through
the gastrointestinal tract. The aerodynamic properties of fibers depend
largely on their diameter; fibers below 3.5y in diameter are regarded as
being in the respirable range [17]. Fiber length affects deposition,
longer fibers apparently having greater fibrogenic effects [18]. Hence,
ambiguities exist as to the effect of size and shape of asbestos fibers in
creating lung cancer. Very recently, Stanton and Wrench [19] have found
that asbestos fibers with diameters in the range of O.Sp to 5y and up to
80)j in length create cancer in hamsters; fibers either smaller or larger
than this range are harmless. This is the only experimental study [19]
which proves the importance of size and shape of asbestos fibers in
o
causing cancer. However, chrysotile fibrils with diameters -400A have
been observed in human lung tissue [3, 4],
1-1
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F-C3415
For the promulgation of any asbestos standard by EPA, asbestos fibers
that can be airborne and inhaled by human beings have to be identifiable
and countable. From the aforesaid, it is obvious that a method(s) need
to be developed which can give the amount of asbestos and their size dis-
tribution (fibers and fibrils included) in ambient air and in or near
asbestos sources.
Several experimental techniques have been studied to determine the
asbestos content of air. There are, however, many uncertainties as to
the best methods of sampling, identifying and quantifying airborne asbestos
and interpreting the data so obtained [7]. The monitoring problem lies in
identifying a very small number of asbestos fibers against a background of
a very large number and variety of other particles in the same sample.
Only within recent years have methods for determining concentrations of
fibers for industrial hygiene purposes been standardized [20]; they use
samples collected on membrane filters in which fibers are counted with
phase-contrast illumination in an optical microscope. However, only fibers
having diameters 0.5p and larger can be determined by this technique. This
is a critical limitation of this technique.
X-ray diffraction techniques [21] can only give the total amount of
asbestos in a sample; moreover, only amounts greater than ~10yg can be
determined by this technique. The amount of asbestos in ambient air is
3
believed to lie in the range of 0 to 5,000 ng/m . Depending on the air
being analysed the necessary volume of air to produce a useable sample
may become prohibitive.
Transmission electron microscopy (TEM) has been successfully applied
[22-25] in the determination of the asbestos content in ambient air.
However, there are two limitations in this technique, namely, only the
total amount of asbestos is determined and this technique is not easily
amenable to automation. The counting is very often based on a morphology
identification only with this technique. Selected area electron diffraction
patterns obtained in the TEM can be used to identify asbestos fibers from
all others, but diffraction cannot be used to differentiate among various
1-2
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F-C3415
amphibole types [26].
The electron beam microprobe has been applied [8. 9] to identify
asbestos fibers in lung tissues but the resolution limits it to fibers
having diameters larger than ~ly.
Recently, Maggiore and Rubin [27] have employed a scanning electron
microscope (SEM) with a field emission source to identify asbestos fibers
o
using x-ray fluorescence analysis. Asbestos fibrils -500A in diameter
could be identified in -200 sees. However, no attempt was made to develop
a sampling system which could be used for automated identification and
counting of asbestos fibers.
Urban particulate identification and characterization by combining
transmission electron microscopy and x-ray microanalysis (EMMA) has been
attempted recently [28] but we feel that applying any form of transmission
microscopy for the identification and counting of asbestos particles in
air is unlikely to ever be "commercially" feasible.
As a step towards solution to this particulate monitoring problem, a
methodology has now been developed in our laboratory. The newly developed
technique employs SEM and characteristic x-ray emission analysis to identify
asbestos particles even in the presence of other particles. The specimen
preparation is done in such a way that automated identification and count-
ing of asbestos particles is believed to be feasible. As it stands, samples
from point sources (inside an asbestos factory) and near point sources
can be analysed. Further research is needed to perfect the technique for
ambient air. A method for concentrating asbestos and removing other par-
ticulates must be developed.
1-3
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2. EXPERIMENTAL PROCEDURE
2.1 STATEMENT OF THE PROBLEM
The monitoring problem can be stated as "identifying and counting a
very small number of asbestos fibers against a background of a large number
and variety of other particles". This implies that one is interested in
determining both the amount and the size distribution of asbestos particles
as they exist in ambient air. The technique used in conjunction with TEM
[22-25] could satisfy the first requirement but as it destroys the original
size distribution of asbestos particles in air through ashing and ultra-
sonification there is no way of meeting the second requirement.
The present technique aims ultimately at identifying and counting
asbestos in air in an automated way. Initial sample collection is by
absolute filtration using a membrane filter. The final SEM specimen
prepared from the airborne particles should be on a featureless background
so that the particles can be detected unequivocally by an image analyzing
system [29-31]. Furthermore the x-ray emission from the asbestos particles
should be without either a significant background or any extraneous x-ray
emission from other particles or the substrate. Hence, the amount of air
collected should be such that little superposition of particles takes
place. Overcrowding of the particles not only hampers image analysis but
also makes the x-ray emission from the asbestos ambiguous. All operating
features of the final system should be compatible with automated image
analysis and x-ray fluorescence [29].
2.2 SUMMARY OF RESEARCH LEADING TO SPECIMEN PREPARATION TECHNIQUE
Initially two types of standard membrane filters were considered,
namely, Millipore and Nuclepore filters. To assist in the developmental
stage standard asbestos samples were obtained. To simulate air samples
2-1
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F-C3415
the standard asbestos fibers were dispersed in deionized water and aspir-
ated onto filters.
Some SEM micrographs of asbestos collected on Nuclepore filter were
sent for image analysis by a Quantimet 720 system. The fibres were seen
to be very bright on a dark background and were felt to be very suitable
for image analysis. However, f bright crescent exists around each pore
in the SEM image and although the human operator can readily ignore this
it is impossible for the Quantimet system to distinguish between the pore
and the bright asbestos fiber. Consequently, a method to close, or elim-
inate the pores of the filters after sample collection was sought.
After some experimentation a method was developed to eliminate the
interfering effects of the pores in the Nuclepore filter by solvent vapour
attack. The resulting SEM photographs were amenable to image analysis by
a Quantimet 720 system and also the solvent treated Nuclepore filter was
sufficiently stable under the electron beam for x-ray analysis. The only
disadvantage was that during solvent vapour attack the Nuclepore softens
and the asbestos fibers get imbedded in the polycarbonate film. This
results in a suppression of the soft x-rays (Si and Mg peaks) from the
asbestos fibers, particularly for fibers with diameters in the vicinity
of O.lu.
A similar approach with Millipore filters had failed because although
the solvent vapour treated Millipore is featureless, it Is extremely
sensitive to the electron beam and virtually disintegrates on exposure.
The next development was to completely eliminate the filter leaving
the particles on a featureless substrate. An optically polished pyrolytic
graphite (PG) surface parallel to the c-axis is featureless when observed
by the SEM at magnifications in the range of x 1,000 to x 30,000. Moreover,
carbon is not detectable by E.D. x-ray analysis and gives insignificant
white radiation. Pyrolytic graphite was preferred to a possible alter-
native beryllium because of toxicity problems. The final approach was to
mount the Nuclepore filter with collected airborne particles on an optically
polished PG and then completely dissolve the filter by solvent vapour
2-2
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F-C3415
attack. This method was successful to a considerable extent but certain reser-
vations remained as follows:
(1) It takes more than 40 hours of solvent vapour (chloroform) attack
in order to dissolve the filter to a thickness which does not
suppress soft x-ray emission from asbestos significantly. X-ray
o o
emission from fibrils (500A - 1,OOOA) was still significantly
suppressed.
(2) It will take a significantly longer time to completely eliminate
the Nuclepore filter. Moreover, the particle distribution could
be unstable when the Nuclepore filter is completely dissolved.
(3) A Cl peak from an undissolved filter appears along with Si, Mg,
and Fe peaks from the asbestos during microprobe analysis.
A solvent attack in the liquid state was not thought to be possible
as the fibers or particles are not restrained as the filter dissolves.
Attempts to use a similar approach with Millipore filter failed because
even a very thin layer of Millipore filter left behind after the vapour
attack disintegrated under the electron beam.
Following considerable experimentation a satisfactory technique to
study airborne particles by SEM along with energy dispersive x-ray analysis
and image analysis was finallv developed. The technique is based on the
system described above but with one or two critical variations. The details
of the technique are described in the following Section 2.3. We believe
that this technique is reliable and could be repeated in any laboratory
without undue expense or difficulty.
2.3 DESCRIPTION OF METHODOLOGY FOR THE ANALYSIS OF ASBESTOS IN AIR
2.3.1 Sampling
Airborne particulates are first collected on a Millipore filter of
either 0.45y or 0.8y pore size. The pore size of the Millipore filter is
not a critical variable but does influence the superposition of particles.
2-3
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F-C3415
Using a 0.45y Millipore filter a large number of ~0.1y size spherical
particles are collected on the filter. These airborne particles are not
asbestos and are not collected with a 0.8)j Millipore filter. For the
determination of asbestos in the air the 0.8)j Millipore is therefore
preferable. One can sample a larger volume of air with a 0.8y size filters
than with a 0.45y size filters without overcrowding the background with
the small spherical particles. Minor differences in image analysis that
arise with different size Millipore filters will be discussed further in
Section 3.1 on SEM Observations. Virtually all fibers are collected with
the 0.8p size Millipore filter [25] even though the 0.8y pore size is
larger than the largest dimension of some asbestos fibrils. It has been
found [25] that the surface charge properties of the filter and the asbestos,
as well as the circuitous path through the filter result in virtually
complete collection of all asbestos material.
3 3
The volume of air filtered lies in the range of O.lm to 0.15m .
3
If the sample volume exceeds 0.15m , overcrowding of particles occurs and
3
if the volume is much less than O.lm , the number of asbestos fibers is
too few to permit reasonable counting statistics. The rate of air collec-
tion is not thought to be an important variable.
The above discussion is for point source (inside an asbestos factory)
or near point source (adjacent to an asbestos source) sampling. As will
be discussed in Section 5.1, further research is needed to perfect a system
for ambient air samples. A process of concentrating asbestos fibers and
eliminating extraneous particles is needed for ambienc air samples.
2.3.2 Specimen Preparation for Scanning Electron Microscopy and
Microprobe Analysis
The steps involved in specimen preparation are shown schematically
in Figure 1. The Millipore filter is mounted on a clean metal disc;
mounting is done with rubber cement which is put only at the periphery
o
of the filter. A very thin carbon layer (-100A) is evaporated onto the
filter in a vacuum evaporator. (The thickness of the carbon layer is
monitored by observing the surface of a drop of oil resting on glazed
2-4
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PARTICLES
CARBON
o p p
/7//?
-MILLIPORE
FILTER
F-C3415
CARBON EXTRACTION
REPLICA ON PG
(IV)
(Q)
Mechanical Mounting
MILLIPORE FILTER
BRASS RING
BOLT
ACETONE LEVEL
IN PETRI DISH
(b)
Figure 1. Schematic Diagram of the Steps Involved in Specimen Prepara-
tion
2-5
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F-C3415
ceramic. As soon as the oil drop is distinctly visible with respect to
the darkened glazed surface, evaporation is stopped.) A thicker carbon
layer embeds the asbestos fibrils and suppresses x-ray emission from them.
A 1/2" diameter circular piece of the "composite" film is now cut
out with a sharpened hollow tool (hardened tool steel). Four such
specimens can be made from a standard 47mm Millipore filter. The "composite"
film is put on optically polished pyrolytic graphite* stud and mounted
mechanically with carbon side down as shown in Figure l(b). As stated
before the surface parallel to the c-axis can be polished to a featureless
finish at magnifications in the range of xl.OOO to x30,000.
The PG stud (Figure l(b)) is next put in a covered petri dish con-
taining acetone. Care should be taken to see that the level of acetone
in the petri dish is such that the liquid does not attack the filter paper
directly. The specimen undergoes acetone vapour attack for about half an
hour. Initially, the composite film swells due to the vapour attack but
then settles down on to the PG.
The brass ring serves to keep the film in position while swelling
occurs. During vapour attack the Millipore filter becomes transparent.
Occasionally, a few bubbles form when the film is settling on the PG
causing breaks in the continuous film. This does not affect the general
procedure and on average, 90% of the film remains continuous.
After the film has completely settled on the PG (as observed visually),
the stud is totally immersed in acetone for a minimum of 2 hours. Accel-
erating the dissolution by slow stirring is not recommended because of the
fragile nature of the carbon replica.
After the brass ring is removed, the specimen is ready for SEM obser-
vation. A thin layer of Millipore filter is left behind on the PG around
the periphery of the carbon extraction replica, (Figure l(b)). A line of
silver paint is put over this to avoid charging under the electron beam.
* Obtained from Union Carbide
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PG studs can be used repeatedly if the carbon extraction replica is
removed by ultrasonic cleaning in acetone.
To summarize the technique produces a carbon extraction replica of
all airborne particles lying on polished PG. All airborne particles are
retained unless there is excessive overcrowding of particles leading
superposition. The carbon layer preserves the original distribution of
the particles as collected on the Millipore filter. The carbon extraction
replica adheres well to the PG, so that the stud can be handled with ease.
2.3.3 Specimen Preparation TEM
Although transmission electron microscopy was not specifically ex-
plored in this project, a modification of the above specimen preparation
technique was shown to be a convenient method of sample preparation for
transmission microscopy.
The specimen is prepared in the same way as described in Section
2.3.2 up to the acetone vapour attack. At this stage, the brass ring is
removed and the composite film peeled from the PG with a pair of tweezers.
The film is put on a clean glass slide and sections to fit a copper TEM
grid are cut out. The composite film with carbon side down is placed on
a copper grid and dipped into acetone for half an hour. The Millipore
filter completely dissolves in the acetone and the copper grid (200 mesh)
supports a carbon extraction replica containing the airborne particles.
This technique is complementary to other similar techniques [22, 32].
2.3.4 Measurement Techniques
The following summarizes the counting proceedure in a totally manual
mode. Operational modes for automatic operation will be described and
discussed in Section 4.2 on Feasibility Study - Automated. Operational
modes are described for a scanning electron microscope JSM-50A with a
o
guaranteed resolution of 100A. The E. D. x-ray analyzer is based on a
detector having a 0.0007mm Be window with a resolution of 160 ev.
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The specimen is first observed in the picture-mode at a condenser
lens setting which gives an electron beam current of -2x10 amps. At
o
this setting, the resolution is -100A. The carbon replica does possess a
surface structure which is a replica of Millipore filer, but at a beam
current of 2x10 amps (normal picture mode operation) the replica is
featureless. Asbestos fibers appear as bright images against a dull back-
ground with an intensity that depends on their size. Fibers with larger
diameters appear brighter than "hose with smaller diameters. To observe
o
asbestos fibrils (-500A in diameter), the contrast has to be increased by
increasing the electron beam current thus enhancing the secondary electron
yield. This also results in the appearance of the background structure
from the carbon replica but this can be suppressed by the image analyzer
for particle counting.
A magnification of xl,000 or x3,000 is suitable for observing and
counting asbestos fibers in air samples. Fibrils can be detected at about
x3,000. The optimum magnification depends on the concentration of fibers
or particles and is such that about 5 to 10 fibers are within a field of
view. Twenty five random areas are selected and the fibers in them counted
for statistical analysis.
The x-ray microprobe analysis for positive identification of asbestos
is done in the following way. First, the number of fibers and fibrils are
counted on the viewing screen and the size (diameter and length) of the
fibers recorded. Each fiber is then brought to the center of the screen
-9
and the beam current increased to 1.5x10 amp. by adjusting the condenser
lens. At this current, the resolution is adequate and fibers and fibrils
are still observed distinctly. The microscope is now brought to the
spot-mode and the spot centered on the fiber. X-ray counts are accumulated
for 5 sees, to 60 sees, depending on the fiber size; smaller fibers take
a longer time to yield significant Si, Mg, and Fe peaks. The same pro-
cedure is repeated for other fibers in the field of view. Fibers which
do not show Si, Mg, and Fe peaks are rejected as being non-asbestos material.
The field of view is then changed to another area.
2-?
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9
The reason for getting an image first at a current of 1.5x10 amp
and then changing to spot-mode is that there is a shift in the picture
when the beam current is changed. One could operate at a current of
-9
1.5x10 amp during the whole operation but two difficulties arise.
Firstly, as the resolution is degraded the accuracy of determining the
diameter of the fiber is decreased considereably. Secondly, the back-
ground structure due to the carbon replica becomes less desirable at a
-9
current of 1.5x10 amp.
2.3.5 Analysis of Microscopic Data
The technique developed aims at identifying and quantitating the
asbestos in air samples. The identification of the asbestos is by means
of the characteristic x-ray emission spectra, Si, Mg, and Fe are the vital
elements. Langer et al [8, 9] have used the intensity ratios of Si, Mg,
and Fe peaks to classify asbestos into chrysotile and amosite, etc. However,
such a classification was not stressed in the manual approach as it is
quite time consuming. The present technique aims at identifying and quan-
tifying asbestos in air rapidly. With our present capabilities, asbestos
fibers down to 0.2y diameter can be identified in 5 sees; fibers with
diameters less than 0.2y need counting time up to 60 sees.
The total amount of asbestos and its size distribution are determined
in the present technique. Twenty-five random areas are counted at a con-
venient magnification, preferably x3000, for a statistical measurement
using the following two formulae:
Average number of fibers x K , ,,,-., / 3 ,n.
° = Number of fibers/m (1)
Volume of air collected (m )
Average weight of fibers x K . 3 ,-,
r = Weight of fibers/m (2;
Volume of air collected (m )
2
, ,, Filter area (mm )
where, K = s -
Field area (mm )
2-9
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F-C3415
As noted earlier, the length and diameter of each fiber are recorded
at a given magnification; the weight of each fiber is calculated knowing
its density [33, 34].
The size distribution of asbestos fibers is represented by a cumula-
tive frequency distribution of length of fibers. The diameter of the
fibers is also another important variable; however, the length distribution
is the criterion that will be used in the present work. Most of the fibers
in air samples have diameters less than 5p whereas their length variation
is considerable. Moreover, longer fibers apparently have greater fibro-
genic effects [18]. One could use an equivalent (spherical) radius for
asbestos fibers. Recognizing that no conclusive results exist to deter-
mine which physical parameters for asbestos controls the health hazard
we have chosen to present a cumulative frequency distribution asbestos
fibers lengths.
The total number of particles that need to be counted for presenting
a statistically reliable cumulative frequency distribution is debatable
and depends on the technique used to count them [35]. We believe that
the total number should be about 100 for a good distribution plot. This
is achievable xvithout making the counting very time consuming. Counting
is continued in the present technique until about 100 asbestos fibers are
counted, generally involving surveying rather more than 25 random areas.
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F-C3415
3. EXPERIMENTAL RESULTS
3.1 SEM OBSERVATIONS
The surface structure of 0.45y pore size Millipore filter is shown
in Figure 2(a). Unlike Nuclepore filter, both sides of a Millipore filter
show identical structure. Figure 2(b) illustrates standard crocidolite
fibers aspirated onto the Millipore filter.
Figure 3(a) shows standard amosite fibers aspirated onto a Millipore
filter; the specimen has been prepared according to Section 2.3.2. The
brightness of the fibers with respect to the background depends on the
diameter of the fiber. The picture, Figure 3(a), was taken under high
contrast condition and a surface structure of the carbon extraction replica
(0.45u Millipore filter) is observed. Airborne particles with chrysotile
fibers from a point source are shown in Figure 3(b).
An air sample was collected on a 0.8p pore size Millipore filter
inside an asbestos factory dealing with chrysotile fibers only; the volume
3
of air collected was 0.135m . As was mentioned in Section 2.3.A, the
background structure of the carbon extraction replica from a 0.8p pore
size Millipore filter is worse than that from a 0.45y pore size Millipore
filter (compare Figures 3(a) and 3(b)) particularly at high magnifications.
However, this background structure is easily suppressed by the Quantimet
720 image analyzer, and does not hinder counting of fibers either manually
or by the contemplated automated operation.
SEM photographs of near-point-source and ambient air samples are
shown in Figure 4 and Figure 10(a) respectively. Comparison of Figures
3(b), 4(a) and 10(a) indicates that the ratio of asbestos particles to
extraneous particles decreases progressively from the point source to
ambient air samples. The air sample in Figure 10(a) was obtained with a
0.45)J pore size Millipore filter, and the point-source and near-point-source
3-1
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F-C3415
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3-2
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F-C3415
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3-3
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F-C3415
samples in Figures 3(b) and 4(a) respectively, were obtained with a 0.8u
size filter. A large number of -O.lp size extraneous particles are visible
in the air sample, Figure 10(a), but not in Figures 3(b) and 4(a) . For
present purposes a 0.8y Millipore filter is preferable. Occasionally3
asbestos fibers are seen in conglomeration with other particles as shown
in Figure 4(b); although an operator can cope with such a situation,
automated counting in such an area would present difficulties.
3.2 MICROPROBE ANALYSIS
For x-ray fluorescence analysis the JSM-50A is operated at a beam
-9
current of -1.5x10 amp. Voltage and current can be optimized for the
best count rate from asbestos fibers [27] but all data presented in the
-9
following were obtained at 25 KV and at -1.5x10 amp. X-ray emission
data is obtained in the spot-mode rather than picture-mode as the back-
ground radiation is high in picture-mode. The energy dispersive spec-
trometer is equipped with a detector having a 0.0007mm Be window thus
allowing a high counting rate at the soft X-ray end of the spectrum (Mg
and Si).
Most of the counting was done on chrysotile which is the most common
type of asbestos used in the U.S.A. [33]. Moreover, chrysotile asbestos
o
fibers easily break down to fibrils of -500A diameter when subjected to
ultrasonic vibration. Mg is leached out of chrysotile asbestos in many
environments [25]; hence, our x-ray studies were mostly done on chrysotile
collected from air at a point source. However, the standard crysotile
was used after ultrasonification in order to get asbestos fibrils whose
diameters are less than O.ljj. This was necessary in determining the limit
of detection of the smallest fibrils with the present capabilities.
A distinct x-ray spectrum of chrysotile asbestos is obtained in 5
sees from fibers having diameters greater than 0.2p; an example for a 0.5y
diameter fiber is shown in Figure 5. To know the limit of detection, x-ray
o
spectra from O.lp and 500A diameter fibers were also obtained and are
presented in Figures 6 and 7 respectively; corresponding SEM photographs are
3-4
-------
F-C3415
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F-C3415
CHRYSOTILE FIBER
DIAMETER : 0.5/i
SPECIMEN CURRENT- 1.4 x IO~9AMP
COUNTING TIME 5 SEC
(SPOT- MODE)
4 6
ENERGY (kev)
10
Figure 5. X-ray Spectrum from a 0.5u Diameter Chrysotile Fiber
3-6
-------
F-C3415
shown in Figures 8(a) and 8(b). Photographs were taken after the x-ray
counts were recorded and the white spots represent the points at which
the electron beam was directed. As can be seen in Figures 6 and 7, the
count rate is not good and the peak to background ratio is rather low.
The count rate could be improved considerably by avoiding charging effects
on the fibers, which is manifested as bright spots after irradiation
(Figures 8(a) and 8(b)). Charging of the fibers leads to an effective
reduction of the applied vcltage and hence a low count rate. This aspect
o
needs further investigation and we believe, a 500^ fibril could be detected
in less thar 30 sees with our present system if the charging effect is
removed. A thir, layer of carbon coating after final specimen preparation
(Section 2.3.2) should remove the charging effect.
3.3 IMAGE ANALYSIS
For an automated determination of the amount and size distribution of
asbestos in air samples, it was planned to use an Image Analysing System
(e.g. Quantimet 720 [30, ?!]). For the feasibility study, SEM photographs
cf standard asbestos and air samples were sent to IMANCO*. The following
questions were raised to assess the plausibility of a fully automated
operation, Section 4.2.
1. The total count of distinguishable particles of all aspect ratios.
2. What are the total number of fibers with an aspect ratio of
greater than 3 to 1?
3. Are you able to generate automatically a histogram of the size
distribution?
4. What x, y coordinates would be available from the IMANCO system
to locate an individual fiber?
5. Are there problems with variations in brightness that make it
impossible to count all the fibers without generating extra counts?
*Manufacturer: IMANCO, Image Analysing Computers, 40 Robert Pitt Drive,
Monsey, New York 10952.
3-7
-------
F-C3415
1000
800
600
400
200
Si
CHRYSOTILE FIBER
DIAMETER 0.1/x
SPECIMEN CURRENT !4xlO"9AMP
COUNTING TIME 60 sec
(SPOT- MODE )
6 8
ENERGY (kev)
10
12
Figure 6. X-ray Spectrum from a O.lp Diameter Chrysotile Fiber
3-8
-------
F-C3415
250
200
150
o
o
o
100
CHRYSOTILE FIBER
DIAMETER- 500A
SPECIMEN CURRENT: 1.4 x IO"9 AMP
COUNTING TIME 120 SEC
(SPOT-MODE)
Si
Fe
Figure 7. X-ray Spectrum from a 500 A Diameter Chrysotile Fiber
3-9
-------
F-C3415
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F-C3415
The results are very encouraging with regard to automated counting.
The results, presented in the following, are based on certain image
analyzing concepts which are dealt with in detail by Jesse [31] and will
not be repeated here.
Figure 9(a) shows a SEM image of an aspirated standard crocidolite.
The IMANCO image showing the total number of all particles is shown in
Figure 9(b). The system was run "wide open" and there are 193 particles of
all aspect ratios within the measuring frame. Figure 9(c) shows the total
number of fibers with a greater than 3 to 1 aspect ratio. The fibers were
identified from other particles using the Form Separator [31] having an
2
Area/Perimeter ratio of 0.050 or less. This resulted in a count of 58
fibers. After isolation of "fibers" on the basis of their form factor,
artifacts were sized out using an area discrimination factor of 50 picture
points. This resulted in a count of 51 acceptable fibers. Figure 9(d)
shows the perimeter display of all acceptable fibers; a perimeter distri-
bution is easily obtained from Figure 9(d). A length distribution of
the fibers is in turn easily found from the perimeter distribution as the
perimeter of a fiber is twice the length approximately. A small error is
introduced by the fact that some are wider than others but this is not
enough to skew the curve. Later, the IMANCO analyzing computer can be
asked to find the shortest dimension of each fiber; this will give the
approximate diameter of each fiber assuming that the fibers do not have
varying diameters. Figures 9(a), 10(a) and 3(b) show that in fact asbestos
fibers have nearly constant diameters. From the diameter and length of
each fiber, the volume of each fiber can be determined; this is required
to determine the average weight of asbestos fibers. Moreover, a histogram
of length distribution can be plotted automatically.
In order to carry out microanalysis on each fiber on an automated
basis, the coordinates of each fiber need to be known. This is also
accomplished by the Quantimet 720 system. Each fiber is assigned a "count
flag" as evidenced as a tiny white spot at the bottom of each feature
accepted by the pattern recognition logic. The X-Y coordinates are avail-
able via the Feature Data Interface which is compatible with most mini-
3-13
-------
F-C3415
computer systems. The X is available as the digital value (1-880) of
the picture-point at the leading edge of the flag (there are 880 picture-
points on each scan line). The Y is available as the line (1-688) number
on which the flag is located (there are 688 lines per frame). The "count
flags" are not visible in Figures 9(c) and 9(d); but are made visible in
Figures 9(e) and 9(b). Knowing the X-Y coordinates of each fiber the
computer can guide the electron beam to the fiber for x-ray microprobe
analysis.
There is some problem with the brightness of different fibers (see
Figure 9(a)). However the operator has a number of variables with which
to deal with this problem when actual interfacing is done between a Quan-
timet 720 and a JSM-50A.
Figure 10 shows a SEM photograph of an air sample and its IMANCO
image. There is a single asbestos fiber in the presence of innumberable
extraneous particles. After going through the procedures described
earlier with respect to Figure 9, the Quantimet 720 counts 1 fiber as seen
in Figure 10(b). This result is very encouraging as actual air samples are
similar to Figure 10(a). It is obvious that point-source and near-point-
source photographs (Figures 3(b) and A(a) respectively) will be analyzed by
the Quantimet 720 system with ease.
3.4 ANALYSIS OF ACTUAL AIR SAMPLES
Point-source, near-point-source, and air samples were collected on
Millipore filters and specimens from these were prepared for SEM obser-
vation. Manual counting was done on the point-source and near-point-source
samples; all the fibers counted in these samples were not confirmed as
asbestos for the following preliminary results. Total number of fibers
3 3
per m and total weight of asbestos per m were determined according to
Eqs. 1 and 2; the data is presented in Table I. In order to gain confi-
dence in the technique, one specimen was prepared with a known amount of
asbestos, i.e, 10x10 gms. A statistical count gave a value of 8.1x10
gms., which is in excellent agreement. Also included in Table 1 is a
3-14
-------
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data point from the Battelle Report [22] for comparison with our values
of mass concentration.
To illustrate the possible importance of size distribution specimens
3
A-226 and A-227 were chosen for comparison. Specimen A-226 has 1140x10
fibers/m3 and 50,OOOxlO~9gm/m3 whereas A-227 has 1040xlQ3 fibers/m3 and
-9 3
130,000x10 gm/m . Although the number concentrations of fibers are
approximately equal a weight difference arises because of their respective
size distributions as is rhown in Figure 11. According to Stanton [19],
the critical length of the hazardous asbestos fibers is put at 80y (tenta-
tive only). From a plot similar to Figure 11, one can draw many conclu-
sions. For example, 90% of the asbestos fibers in A-227 is in the
"harzardous" region whereas all of A-226 is in this hazardous region.
Considering only the total weight of asbestos in the two samples, A-227
would seem worse than A-226 from a health hazards point of view. The
above analysis is speculative but is used to illustrate the potential
significance of size distribution.
Air samples collected at FIRL had very few asbestos fibers and hence
a statistical analysis could not be carried out. However, asbestos fibers
have been identified positively in air samples and an example is shown in
Figure 10(a). A process of concentrating asbestos fibers in air samples
has to be devised to permit meaningful statistical counts.
3.5 TEM OBSERVATIONS
Carbon extraction replicas of standard asbestos and air samples were
successfully made as described in Section 2.3.3. An example of a standard
chrysotile specimen is represented in Figure 12. The replicas were observed
at 100KV in a JEM-7 Electron Microscope. It is interesting to note that
the carbon extraction replica has a surface structure (replica of Millipore
filter) which is distinctly visible in the TEM, Figure 12(a); but does not
appear nearly as distinctly in the SEM. Selected area electron diffraction
patterns were difficult to obtain because the fiber has to be thin enough
to be electron transparent. We believe that this represents a serious
3-17
-------
F-C3415
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80
70
60
o
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50
40
30
20
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A-227
A-266 fl!40x I03 fibers/m3
(Near Point Source) ^50,000 X IO"9 gm/m3
A-227 fl040x!03 fibers/m3
(Point Source) [130,000 x IO'9 gm/m3
DANGEROUS
SAFE
j L
20
40 60 80
FIBER LENGTH (
100
120
140
Figure 11.
Cumulative Distribution of Fiber Lengths in Point-Source and
Near-Point Source Samples
3-18
-------
F-C3415
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F-C3415
limitation to identifying asbestos fibers by TEM which could perhaps be
offset by using high voltage transmission microscopy. Another limitation
is the difficulty of differentiating between amphibole asbestos fibers by
their electron diffraction patterns [26].
3-20
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F-C3415
4. DISCUSSION
4.1 FEASIBILITY STUDY-MANUAL METHOD
A technique has been developed to determine the total amount of
asbestos and its size distribution in air at point sources and near point
sources. The size distribution of the asbestos fibers which is obtained
by the present technique corresponds to the distribution of the fibers as
they actually existed in the air. No steps are involved which might dis-
turb the original fiber distribution. In contrast the techniques which
employ current TEM techniques destroy the original distribution of fibers;
the fibers are broken into fibrils by ultrasonification [22-25]. Also
violent procedures like ashing, ultrasonification and aliquoting are not
involved in the present technique.
All the problems relating to a manual operation have been solved. A
systematic counting of asbestos fibers can be done for point-source and
near-point-source samples. For ambient air samples, a process of concen-
trating asbestos fibers has to be investigated. Even if suitable tech-
nique for concentrating asbestos fibers could not be developed the amount
of asbestos in ambient air samples could probably be determined by scanning
all the areas in a prepared specimen instead of a limited number such as
25.
Unlike optical microscopic techniques [18], the present technique
permits positive identification and counting of asbestos fibers and fibrils
in the same sample (fibrils cannot be observed in optical microscopes).
TEM techniques [22-25] can be used to count fibers and fibrils; however,
unambiguous identification of asbestos, particularly the amphibole types,
is not possible. The salient advantage of the present technique is that
it is amenable to automated identification and counting. Maggiore and
Rubin [27] have developed a technique very similar to the present one but,
their technique appears much less amenable to automated counting.
4-1
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F-C3415
To date, the present technique is the only method available for
determining the total amount of asbestos and its size distribution either
manually or automatically. At the present stage of development the tech-
nique is only applicable to point-source and near-point-source samples;
however, ambient air samples could be handled with the following two
modifications: (1) a pre-concentration of asbestos in air samples or,
(2) scanning all areas in a specimen instead of a limited number of
random areas.
4.2 FEASIBILITY STUDY-AUTOMATED METHOD
A feasibility study for an automatic determination of the amount and
size distribution of asbestos fibers in or near sources has been completed.
In the original proposal we contemplated to use a SEM with microprobe
facility in conjunction with an image analyzing system. The image analyzing
system would have been interfaced directly with SEM viewing screen and a
minicomputer with certain software would have controller the whole oper-
ation. The details of the steps involved in the development of such a
system have been worked out and will be described in the following. Given
suitable financial resources such a system will be developed at FIRL.
1. Specimen Preparation:
Air is collected on 0.8p pore size Millipore filter; the required
3 3
volume of sampled air lies in the range of 0.10m to 0.15m for point
sources and near point sources. The volume of air collected is determined to
by the need to avoid overlapping at the high end and to have sufficient
fibers to count at the low end.
The details of the specimen preparation for SEM observation are
described in Section 2.3.2. Basically, a carbon extraction replica of
airborne particles is carefully mounted on an optically polished pyrolytic
graphite stud. Asbestos fibers appear as bright features in either a
clear background or a background of extraneous particles. It has been
4-2
-------
F-C3415
shown, in the present investigation, that image analysis by the Quantimet
720 system can be performed on specimens prepared according to Section
2.3.2.
2. Automated Operation:
The following are the steps contemplated for an automated analysis.
The proposed analytical system would typically consist of a Scanning
Electron Microscope (JSM-50A) with E. D. X-ray analyzing capability (NS-
880), an Image Analyzing System (Quantimet 720) directly interfaced with
the SEM, software to manipulate the SEM for automatic shifting of the
sample and the electron beam (from picture-mode to spot-mode etc.), and
a minicomputer with input and output terminals to control the whole
operation.
A suitable magnification is chosen for counting; our experience shows
a magnification of x3,000 is most suitable. Depending on the specimen
size and shape, the computer can guide the system to choose 25 random
areas for counting, alternatively the computer could guide the system to
scan all the areas instead of a few random areas. For a particular field
of view, the Quanitmet 720 detects and counts "fibers", records the length
and diameter of each fiber, and gives X, Y coordinates of each fiber to
the computer. The "picture-mode" is now changed to "spot-mode" on the
SEM and the electron beam is guided on to a fiber knowing its X, Y co-
ordinates. At this stage an x-ray spectrum of the fiber is taken for, say,
30 sees, and compared with standard asbestos spectra; if the spectrum
matches with one of the four possible spectra the computer counts that
"fiber" as an "asbestos fiber". This is repeated for all the "fibers" in
the field of view. Then the field of view is changed to another by shift-
ing the specimen automatically.
The computer can now calculate the total number of asbestos fibers
3 3
and total weight of asbestos from which fibers/m and weight/in of asbestos
can be determined. Moreover, a histogram of size distribution (either
length or diameter) can be automatically plotted.
4-3
-------
F-C3415
It is our conclusion that the feasibility of a fully automated system
for determining the amount and size distribution of asbestos fibers in
air has now been established.
4-4
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F-C3415
5. FUTURE WORK
5.1 PRE-CONCENTRATION OF ASBESTOS IN SAMPLES OF AMBIENT AIR
As pointed out in Section 2.3.5, a statistical determination of the
amount and size distribution of asbestos fibers in point-source and near-
point-source samples is readily done by the present technique. However,
the amount of asbestos fibers in ambient air samples (in a volume of 0.100
3 3
m to 0.150m ) is such that an unsatisfactory statistical determination is
gained by scanning a few random areas. Two variations are possible. Firstly,
all the filter area can be scanned instead of a few random areas. Secondly,
the asbestos fibers can be concentrated so that the ratio of asbestos fibers
to extraneous particles is increased.
No experimental work has been done in this laboratory towards such
a goal but some possibilities are immediately evident. Ambient air parti-
culate samples can contain up to 30% of organic matter. A suitable solvent
can be chosen which will remove these organics from airborne particulates.
Some research has been done [36] in this direction. Ideally, the organics
should be removed without disturbing inorganic particulates on the Milli-
pore. If the Millipore filter dissolves in the solvent then a solvent
exchange could be effected and the inorganic residue filtered through
another Millipore filter. This might well be enough to concentrate the
asbestos particles to such an extent that a statistical count can be made
by the present technique. Failing this some further approaches could be
investigated based on preliminary research that was carried out to con-
centrate asbestos fibers in airborne particulates at Battelle Laboratories
[22]. Dielectric separation, electrophoretc batch separation, continuous
particle electrophoresis and density separation were tried out. All these
techniques met partial success and need further research to make them
workable. We firmly believe that a workable technique can be developed
to concentrate asbestos fibers. For the present analytical technique to
5-1
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F-C3415
be workable, only partial concentration is sufficient.
5.2 FIELD SURVEY
Due to limited time, the present technique could not be applied
systematically to field samples. However a field survey on the following
samples would be a most desirable and logical follow-on subsequent to
the present work.
1. Point Source:
Air samples would be collected at different sites inside an asbestos
plant. There may well be a wide variation in the amount of asbestos at
the different sites. A complete size distribution of the fibers will be
obtained as well as total fiber concentration.
This survey will be done at different asbestos plants if funds allow.
2. Near Point Source:
Air samples will be collected outside an asbestos plant; the main
variable will be the distance from the source, for example, 20 ft, 1/2
mile, 2 miles, etc.. Construction or demolition sites may also be included
in this experimental study.
5-2
-------
F-C3415
6. ACKNOWLEDGEMENTS
The authors gratefully acknowledge Mrs. L. Fallen for initiating
experimental work on this project and her continued interest thereafter.
Valuable discussions with colleagues are acknowledged. Personal
interest taken by Ur. J. Wagman of Environmental Protection Agency is
gratefully acknowledged. Acknowledgements are also due to Mr. R. L. Lanz
and to IMANCO, Image Analyzing Computers, New York, for free service in
conducting image analysis.
Submitted by
Amitav Pattnaik
Research Metallurgist
Approved by
J. D./Meakin
Manager, Physics of Materials Laboratory
6-1
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F-C3415
7. REFERENCES
1. Whipple, H. E., Biological Effects of Asbestos; Annals of the New
York Academy of Sciences, 132, 1 (1965).
2. Tabershaw, I. R., Asbestos as an Environmental Hazard; J. Occup.
Med. , 3j6, 32 (1968).
3. Langer, A. M., Selikoff, I. J. and Sastre, A., Chrysotile Asbestos
in the Lungs of Persons in New York City; Arch. Environ. Health,
7/1, 348 (1971).
4. Langer, A. M., et al. , Identification of Asbestos in Human Tissues;
J. Occup. Med., March 1973.
5. Gilson, J. C., Health Hazards of Asbestos; Composites, 2^, 59 (1972).
6. Sherrill, R., Asbestos, the Saver of Lives has a Deadly Side;
New York Times Magazine, Jan. 21, p:12 (1973).
7. Asbestos-The Need for and Feasibility of Air Pollution Controls;
Committee on Biological Effects of Atmospheric Pollutants, Publ.
by National Academy of Sciences, 1971.
8. Langer, A. M., Rubin, I. B. and Selikoff, I. J., Chemical Charac-
terization of Asbestos Body Cores by Electron Microprobe Analysis;
J. Histochemistry and Cytochemistry, 20, 723 (1972).
9. Langer, A. M., et al., Chemical Characterization of Uncoated Asbestos
Fibers from the Lungs of Asbestos Workers by Electron Microprobe
Analysis; ibid, 2Q, 735 (1972).
10. Selikoff, I. J., et al., Asbestosis and Neoplasia; Amer. J. Med.,
42^ 487 (1967).
11. Enticknap, I. B., and Smither, W. J., Peritorial Tumors in Asbestosis,
Brit. J. Indust. Med., 21, 20 (1964).
12. Selikoff, I. J., Hammond, E. C. and Chung, J., Asbestos Exposure,
Smoking and Neoplasia; JAAIA, 204, 20 (1968).
13. Harris, P. G., Asbestos Hazards in Naval Shipyards; Ann. Occup. Hyg.,
11., 135 (1968).
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F-C3415
14. McEwen, J., et al., Mesothelioma in Scotland, Brit. Med. Jour., 4^
575 (1970).
15. Newhouse, M. and Thomson, H., Mesothelioma of Pleura and Peritoneum
Following Exposure to Asbestos in the London Area; Bri. J. Indust.
Med., _22, 261 (1965).
16. Lieben, I. and Pistawka, H., Mesothelioma and Asbestos Exposure;
Arch. Environ. Health, L4, 599 (1967).
17. Timbrell, V., The Inhalation of Fibrous Dusts; Ann. N. Y. Acad,
Sci., 132, 255 (1965).
18. Vorwald, A. J., Durkan, T. M. and Pratt, P. C., Experimental Studies
of Asbestosis; A.M.A. Arch. Ind. Hug. Occup. Med., _3_, 1 (1951).
19- Stanton, M. F. and Wrench, C., Mechanism of Mesothelioma Induction
with Asbestos and Fibrous Glass; J. National Cancer Inst., 48, 797
(1972).
20. Edwards, G. H., and Lynch, J. R., The Method Used by the U.S. Public
Health Service for Enumeration of Asbestos Dust on Membrane Filters;
Ann. Occup. Hug., 11, 1 (1969).
21. Richards, A. L., Estimation of Trace Amounts of Chrysotile Asbestos
by X-ray Diffraction; Anal Chem, 44. 1872 (1972).
22. Henry, W. H., et al., Development of a Rapid Survey Method of Sampling
and Analysis for Asbestos in Ambient Air; Final Report, Battelle
Columbus Laboratories, Feb., (1972).
23. Richards, A. L., Estimation of Submicron Quantities of Chrysotile
Asbestos by Electron Microscopy; Anal. Chem., 45, 809 (1973).
24. Staff, Collodion Film Method for the Determination of Asbestos in
Ambient Atmospheres, Air and Industrial Hygiene Laboratory,
California State Department of Public Health, private communication
(1972).
25. Selikoff, I. J., Nicholson, W. J. and Langer, A. M., Asbestos Air
Pollution in Urban Areas; paper presented at AMA's Air Pollution
Medical Research Conf., New Orleans, Oct. 6, 1970.
26. Anderson, C. A., An Introduction to the Electron Probe Microanalyzer
and its Application to Biochemistry; Methods of Biochem. Anal.,
Click, D., Ed., Interscience Publ. N. Y., 15, 147 (1967).
7-2
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F-C3415
27. Maggiore, E. J. and Rubin, I. B., Optimization of an SEM X-ray
Spectrometer System for the Identification and Characterization of
Ultramicroscopic Particles; Scanning Electron Microscopy/1973,
IITRI Conf., Ed. Johari Om and Corvin, I; p. 129 (1973).
28. Yakowitz, H., Jacobs, M. H., and Hunneyball, P. D., Analysis of
Urban Particulates by Means of Combined Electron Microscopy and X-ray
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Recognition on the Quantimet, 720; The Microscope, 20, 39 (1972).
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Technology; Environ. Res., 2, 166 (1969).
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Reference Asbestos Samples, N.R.I.O.D. Johannesburg, South Africa,
(1972).
35. Corn, M., Statistical Reliability of Particle Size Distributions
Determined by Microscope Techniques; Amer. Indust. Hyg. Assoc. J.,
2_6, 8 (1965).
36. Stanley, T. W., Meeker, J. E. and Morgan, M. J., Extraction of Organics
from Airborne Particulates; Environmental Science and Technology, I,
927 (1967).
7-3
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BIBLIOGRAPHIC DATA
SHEET
1. Report No.
EPA-650/2-73-016
3. Recipient's Accession No.
I
4. Title and Subtitle
Development of an Instrumental Monitoring Method for
Measurement of Asbestos Concentrations In or Near
Sources
5. Report Date
June 1975 fdate of prep
6.
7. Author(s)
Amitav Pattnaik and John D. Meakin
8- Performing Organization Kept.
N°- F - C 3415
9. Performing Organization Name and Address
The Franklin Institute Research Laboratories
Benjamin Franklin Parkway
Philadelphia, PA 19103
10. Project/Task/Work Unit No.
ROAP 26 AAN. Task 02
11. Contract/Grant No.
68-02-0544
12. Sponsoring Organisation Name .Hid Address
Office of Research and Development
U. S. Environmental Protection Agency
Washington, DC 20460
13. Type of Report & Period
Covered Final
Year ending June 1973
14.
15. Supplementary Notes
16. Abstracts
A methodology has been developed for the determination of amount and size distribu-
tion of asbestos fibers and fibrils in air at point sources and near point sources.
The technique can also be applied to ambient air samples. The method employs a
scanning electron microscope with microprobe capability and an image analyzing
system. Complete details for manual operation have been worked out. Feasibility
study for automated operation has been completed also. Preliminary results of
analysis of samples collected at point sources and near point sources are also
included.
17. Key Words and Document Analysis 17a. IV.st riptors
Asbestos
Asbestos measurements
Asbestos fibers
Monitoring of pollution
Air pollution
Source emissions
Scanning electron microscope
Microprobe analysis
Image analyzing system
17b. Identifiers/Open-Ended Terms
17c. COSAT1 Field/Group
18. Availability Statement
Release unlimited
19. Security C lass (This
Report)
UNCLASSIFIED
20. Security C lass (This
Page
UNCLASSIFIED
21. No. of I'age.s
54
22. Pri
FORM NTIS-3S (REV. 3-72)
USCOMV-DC M8>i2-P72
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FORM NTIS-35 IREV. 3-721 USCOMM-DC I4952-P72
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