ASTM D6281-98

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Designation: D 6281 – 98
Standard Test Method for
Airborne Asbestos Concentration in Ambient and Indoor
Atmospheres as Determined by Transmission Electron
Microscopy Direct Transfer (TEM)
This standard is issued under the fixed designation D 6281; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope priate safety and health practices and determine the applica-
2 bility of regulatory limitations prior to use.
1.1 This test method is an analytical procedure using
transmission electron microscopy (TEM) for the determination
2. Referenced Documents
of the concentration of asbestos structures in ambient atmo-
2.1 ASTM Standards:
spheres and includes measurement of the dimension of struc-
D 1193 Specification for Reagent Water
tures and of the asbestos fibers found in the structures from
D 1356 Terminology Relating to Sampling and Analysis of
which aspect ratios are calculated.
Atmospheres
1.1.1 This test method allows determination of the type(s)
D 1357 Practice for Planning the Sampling of the Ambient
of asbestos fibers present.
Atmosphere
1.1.2 This test method cannot always discriminate between
2.2 ISO Standard:
individual fibers of the asbestos and non-asbestos analogues of
ISO 10312 Ambient air - Determination of asbestos fibres -
the same amphibole mineral.
Direct-transfer transmission electron microscopy method
1.2 This test method is suitable for determination of asbes-
tos in both ambient (outdoor) and building atmospheres.
3. Terminology
1.2.1 This test method is defined for polycarbonate
3.1 For definitions of general terms used in this test method,
capillary-pore filters or cellulose ester (either mixed esters of
refer to Terminology D 1356 (see 2.1).
cellulose or cellulose nitrate) filters through which a known
3.2 Definitions of Terms Specific to This Standard:
volume of air has been drawn and for blank filters.
3.2.1 acicular—the shape shown by an extremely slender
1.3 The upper range of concentrations that can be deter-
2 crystal with cross-sectional dimensions that are small relative
mined by this test method is 7000 s/mm . The air concentration
to its length, that is, needle-like.
represented by this value is a function of the volume of air
3.2.2 amphibole—a group of more than 60 different silicate
sampled.
minerals with similar crystal structures and complex composi-
1.3.1 There is no lower limit to the dimensions of asbestos
tions that conform to the nominal formula:
fibers that can be detected. In practice, microscopists vary in
their ability to detect very small asbestos fibers. Therefore, a A B C T O ~OH,F,Cl! (1)
0–1 2 5 8 22 2
minimum length of 0.5 μm has been defined as the shortest
where:
fiber to be incorporated in the reported results.
A = K, Na, Ca,
1.4 The direct analytical method cannot be used if the
2+
B =Fe , Mn, Mg, Ca, Na,
general particulate matter loading of the sample collection filter
3+ 2+
C = Al, Cr, Ti, Fe , Mg, Fe , Mn, and
3+
as analyzed exceeds approximately 10 % coverage of the
T = Si, Al, Cr, Fe ,Ti.
collection filter by particulate matter.
In some varieties of amphibole, these elements can be
1.5 This standard does not purport to address all of the
partially substituted by Li, Pb, Zn, Be, Ba, or Ni. Amphiboles
safety concerns, if any, associated with its use. It is the
are characterized by a complex monoclinic or orthorhombic
responsibility of the user of this standard to establish appro-
structure that includes a double chain of T-O tetrahedra with a
T:O ratio of approximately 4:11; a variable morphology that
ranges from columnar to prismatic to acicular to fibrous; and
This test method is under the jurisdiction of ASTM Committee D-22 on
Sampling and Analysis of Atmospheres and is the direct responsibility of Subcom-
mittee D22.07 on Asbestos.
Current edition approved July 10, 1998. Published October 1998. Annual Book of ASTM Standards, Vol 11.01.
2 4
This test method was adapted from International Standard ISO 10312 “Air Annual Book of ASTM Standards, Vol 11.03.
5 nd th
quality - Determination of asbestos fibres - Direct transfer transmission electron Available from American National Standards Institute, 11 West 42 St., 13
microscopy method.” floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 6281
good prismatic cleavage at angles of about 56 and 124°. The 3.2.14 cluster—a structure in which two or more fibers or
cleavage may not be readily exhibited by small crystals that are fiber bundles are randomly oriented in a connected grouping.
bound by irregular growth and fracture surfaces (1) .
3.2.15 d-value or interplanar spacing—the perpendicular
3.2.3 amphibole asbestos—amphibole in an asbestiform
distance between identical adjacent and parallel planes of
habit.
atoms in a crystal.
3.2.4 analytical sensitivity—the calculated airborne asbes-
3.2.16 electron diffraction—techniques in electron micros-
tos structure concentration in asbestos structures/L, equivalent
copy, including selected area electron diffraction (SAED) and
to the counting of one asbestos structure in the analysis.
microdiffraction, by which the crystal structure of a specimen
3.2.5 asbestiform—a specific type of fibrous habit in which
is examined.
the fibers are separable into thinner fibers and ultimately into
3.2.17 electron scattering power—the extent to which a
fibrils. This habit accounts for greater flexibility and higher
substance scatters electrons from their original courses.
tensile strength than other habits of the same mineral.
3.2.18 energy dispersive X-ray analysis—measurement of
3.2.6 asbestos—a collective term that describes a group of
the energies and intensities of X-rays by use of a solid state
naturally occurring, inorganic, highly-fibrous, silicate minerals
detector and multichannel analyzer system.
that are easily separated into long, thin, flexible, strong fibers
3.2.19 eucentric—the condition when the area of interest of
when crushed or processed.
an object is placed on a tilting axis at the intersection of the
3.2.6.1 Discussion—Included in the definition are the as-
electron beam with that axis and is in the plane of focus.
bestiform varieties of serpentine (chrysotile); riebeckite (cro-
3.2.20 field blank—a filter cassette that has been taken to the
cidolite); grunerite (grunerite asbestos [Amosite]); anthophyl-
sampling site, opened, and then closed. Such a filter is used to
lite (anthophyllite asbestos); tremolite (tremolite asbestos); and
determine the background structure count for the measurement.
actinolite (actinolite asbestos). The amphibole mineral compo-
3.2.21 fibril—a single fiber of chrysotile that cannot be
sitions are defined according to the nomenclature of the
further separated longitudinally into smaller components with-
International Mineralogical Association.
7 out losing its fibrous properties or appearances.
Asbestos Chemical Abstracts Service Registry No.
Chrysotile 12001-29-5
3.2.22 fiber—an elongated particle that has parallel or
Crocidolite 12001-28-4
stepped sides. For the purposes of this test method, a fiber is
Grunerite Asbestos [Amosite] 12172-73-5
Anthophyllite Asbestos 77536-67-5 defined as having an aspect ratio equal to or greater than 5:1
Tremolite Asbestos 77536-68-6
and a minimum length of 0.5 μm.
Actinolite Asbestos 77536-66-4
3.2.23 fiber bundle—a structure composed of parallel,
3.2.7 asbestos structure—a term applied to isolated fibers or
smaller-diameter fibers attached along its length. A fiber bundle
to any connected or overlapping grouping of asbestos fibers or
may exhibit diverging fibers at one or both ends.
bundles, with or without other nonasbestos particles.
3.2.24 fibrous structure—a fiber or connected grouping of
3.2.8 aspect ratio—the ratio of length to width of a particle.
fibers with or without other particles.
3.2.9 blank—a structure count made on TEM specimens
3.2.25 habit—the characteristic crystal growth form or
prepared from an unused filter to determine the background
combination of these forms of a mineral, including character-
measurement.
istic irregularities.
3.2.10 camera length—the equivalent projection length be-
3.2.26 limit of detection—the calculated airborne asbestos
tween the specimen and its electron diffraction pattern, in the
structure concentration in structures/L, equivalent to counting
absence of lens action.
2.99 asbestos structures in the analysis. The detection limit has
3.2.11 chrysotile—a group of fibrous minerals of the ser-
been set at 2.99 structures counted in any area of any filter
pentine group that have the nominal composition
because of concerns that false positives (counting a structure
Mg Si O (OH) and have the crystal structure of either cli-
2 5 4
when none exists) may occur in both blanks and sample filters.
nochrysotile, orthochrysotile, or parachrysotile. Most natural
Based on the assumption of a Poisson distribution of false
chrysotile deviates little from this nominal composition.
positives, the detection limit of 2.99 would protect against a
Chrysotile may be partially dehydrated or magnesium-leached,
false positive rate as high as 5 % (5 false positive structures per
both in nature and in building materials. In some varieties of
3 100 blank filters counted). This level is very conservative,
chrysotile, minor substitution of silicon by Al + may occur.
since the actual false positive rate is believed to be 2 % or
Chrysotile is the most prevalent type of asbestos.
lower. Thus, many of the samples reported as being below the
3.2.12 cleavage—the breaking of a mineral along one of its
detection limit (less than three structures counted) will actually
crystallographic directions.
contain true positives. Note that concentration values are
3.2.13 cleavage fragment—a fragment of a crystal that is
included in the test report, even if they are below the limit of
bounded in whole or in part by cleavage faces. Some cleavage
detection.
fragments would be included in the fiber definition used in this
3.2.27 matrix—a structure in which one or more fibers or
method.
fiber bundles touch, are attached to, or partially concealed by a
single particle or connected group of nonfibrous particles.
The boldface numbers in parentheses refer to the list of references at the end of
3.2.28 miller index—a set of three integer numbers used to
this standard.
specify the orientation of a crystallographic plane in relation to
The non-asbestiform variations of the minerals indicated in 5.2.6 have different
Chemical Abstracts Service (CAS) numbers. the crystal axes.
D 6281
3.2.29 PCM equivalent fiber—a particle of aspect ratio that cellulose nitrate) membrane filter of maximum pore size 0.45
is greater than or equal to 3:1, is longer than 5 μm, and that has μm by means of a battery-powered or mains-powered pump.
a diameter between 0.2 and 3.0 μm TEM specimens are prepared from polycarbonate filters by
3.2.30 PCM equivalent structure—a fibrous structure of applying a thin film of carbon to the filter surface by vacuum
aspect ratio that is greater than or equal to 3:1, is longer than evaporation. Small areas are cut from the carbon-coated filter,
5 μm, and has a diameter between 0.2 and 3.0 μm. supported on TEM specimen grids, and the filter medium is
3.2.31 primary structure—a fibrous structure that is a sepa- dissolved away by a solvent extraction procedure. This proce-
rate entity in the TEM image. dure leaves a thin film of carbon that bridges the openings in
3.2.32 replication—a procedure in electron microscopy the TEM specimen grid and that supports each particle from
specimen preparation in which a thin copy, or replica, of a the original filter in its original position. Cellulose ester filters
surface is made. are chemically treated to collapse the pore structure of the
3.2.33 residual structure—matrix or cluster material con- filter, and the surface of the collapsed filter is then etched in an
taining asbestos fibers that remains after accounting for the oxygen plasma to try to expose particles embedded in the
prominent component fibers or bundles, or both. collapsed filter. A thin film of carbon is evaporated onto the
3.2.34 serpentine—a group of common rock-forming min- filter surface and small areas are cut from the filter. These
erals having the nominal formula: Mg Si O (OH) . sections are supported on TEM specimen grids, and the filter
3 2 5 4
3.2.35 structure—a single fiber, fiber bundle, cluster, or medium is dissolved by a solvent extraction procedure.
matrix. 4.2 The TEM specimen grids from either preparation
3.2.36 twinning—the occurrence of crystals of the same method are examined at both low and high magnifications to
species joined together at a particular mutual orientation, and check that they are suitable for analysis before carrying out a
such that the relative orientations are related by a definite law. quantitative structure count on randomly-selected grid open-
3.2.37 unopened fiber bundle—a large-diameter asbestos ings. In the TEM analysis, electron diffraction (ED) is used to
fiber bundle that has not been separated into its constituent examine the crystal structure of a fiber, and its elemental
fibrils or fibers. composition is determined by energy dispersive X-ray analysis
3.2.38 zone-axis—the crystallographic direction parallel to (EDXA). For a number of reasons, it is not possible to identify
the intersection edges of the crystal faces defining the crystal each fiber unequivocally and fibers are classified according to
zone. the techniques that have been used to identify them. For each
3.3 Symbols: fiber, a simple code is used to record the manner in which it
was classified. The fiber classification procedure is based on
successive inspection of the morphology, the ED pattern, and
eV = electron volt
the qualitative and quantitative EDXA. Confirmation of the
kV = kilovolt
identification of chrysotile is only by quantitative ED, and
L/min = liters per minute
–6 confirmation of amphibole is only by quantitative EDXA and
μg = micrograms (10 g)
–6 quantitative zone axis ED.
μm = micrometer (10 m)
–9 4.3 In addition to isolated fibers, ambient air samples often
nm = nanometer (10 m)
contain more complex aggregates of fibers, with or without
W = watt
other particles. Some particles are composites of asbestos
Pa = Pascals
fibers with other materials. Individual fibers and these more
3.4 Abbreviations:Abbreviations:
complex structures are referred to as asbestos structures.A
coding system is used to record the type of fibrous structure
DMF = dime
...