SIST ISO 13794:2002
(Main)Ambient air -- Determination of asbestos fibres -- Indirect-transfer transmission electron microscopy method
Ambient air -- Determination of asbestos fibres -- Indirect-transfer transmission electron microscopy method
Air ambiant -- Dosage des fibres d'amiante -- Méthode par microscopie électronique à transmission par transfert indirect
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INTERNATIONAL ISO
STANDARD 13794
First edition
1999-07-15
Ambient air — Determination of asbestos
fibres — Indirect-transfer transmission
electron microscopy method
Air ambiant — Dosage des fibres d'amiante — Méthode par microscopie
électronique à transmission par transfert indirect
A Reference number
ISO 13794:1999(E)
---------------------- Page: 1 ----------------------
ISO 13794:1999(E)
Contents
Page
1 Scope .1
1.1 Substance determined .1
1.2 Type of sample.1
1.3 Range.1
1.4 Limit of detection.1
2 Terms and definitions .2
3 Abbreviated terms .6
4 Principle.6
5 Apparatus .7
5.1 Air sampling .7
5.2 Specimen preparation laboratory .8
5.3 Equipment for analysis .8
5.4 Consumable supplies.13
6 Reagents.14
7 Air sample collection.14
7.1 Calculation of analytical sensitivity .14
7.2 Sample collection procedure.15
8 Procedure for analysis .15
8.1 General.15
8.2 Cleaning of sample cassettes .16
8.3 Preparation of analytical filters .16
8.4 Preparation of TEM specimens from PC analytical filters.17
© ISO 1999
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
or mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 • CH-1211 Genève 20 • Switzerland
Internet iso@iso.ch
Printed in Switzerland
ii
---------------------- Page: 2 ----------------------
© ISO
ISO 13794:1999(E)
8.5 Preparation of TEM specimens from cellulose ester analytical filters. 19
8.6 Criteria for acceptable TEM specimen grids. 20
8.7 Procedure for structure counting by TEM . 21
8.8 Blank and quality control determinations. 24
8.9 Calculation of results . 25
9 Performance characteristics . 25
9.1 General . 25
9.2 Interferences and limitations of fibre identification. 25
9.3 Precision and accuracy. 26
9.4 Limit of detection. 26
10 Test report . 27
Annex A (normative) Determination of operating conditions for plasma asher. 30
Annex B (normative) Determination and standardization of operating conditions for ultrasonic bath. 31
(normative)
Annex C Calibration procedures . 33
Annex D (normative) Structure-counting criteria . 36
Annex E (normative) Fibre identification procedure . 44
Annex F (normative) Determination of concentrations of asbestos fibres and bundles longer than 5 mm,
and of PCM-equivalent asbestos fibres . 53
Annex G (normative) Calculation of results . 54
Annex H (normative) Test procedure to determine suitability of cellulose ester sample collection filters. 60
Annex I (informative) Strategies for collection of air samples . 61
Bibliography. 62
iii
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© ISO
ISO 13794:1999(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
International Standard ISO 13794 was prepared by Technical Committee ISO/TC 146, Air quality, Subcommittee
SC 3, Ambient atmospheres.
Annexes A to H form a normative part of this International Standard. Annex I is for information only.
iv
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© ISO
ISO 13794:1999(E)
Introduction
This International Standard is applicable to the measurement of airborne asbestos in a wide range of ambient air
situations, including the interior atmospheres of buildings, and for detailed evaluation of any atmosphere in which
asbestos fibres are likely to be present. Because the best available medical evidence indicates that the numerical
fibre concentration and the fibre size and type are the relevant parameters for evaluation of the inhalation hazards,
a fibre counting and measuring technique is the only logical approach. Most fibres in ambient atmospheres are not
asbestos, and therefore there is a requirement for fibres to be identified. Many airborne asbestos fibres in ambient
atmospheres have diameters below the resolution limit of the optical microscope. This International Standard is
based on transmission electron microscopy, which has adequate resolution to allow detection of small fibres and is
currently the only technique capable of unequivocal identification of the majority of individual fibres of asbestos. The
fibres found suspended in an ambient atmosphere can often be identified unequivocally, if sufficient measurement
effort is expended. However, if each fibre were to be identified in this way, the analysis becomes prohibitively
expensive. Because of instrumental deficiencies or because of the nature of the particulate, some fibres cannot be
positively identified as asbestos, even though the measurements all indicate that they could be asbestos. Subjective
and instrumental factors therefore contribute to this measurement, and consequently a very precise definition of the
procedure for identification and enumeration of asbestos fibres is required.
In addition to single fibres and bundles, asbestos is often found in air samples as very complex, aggregated
structures which may or may not be also aggregated with other particles. The number of asbestos fibres and
bundles incorporated in these complex structures often exceeds the number of isolated fibres and bundles
observed, and many of them may be completely obscured in direct-transfer TEM preparations. The method defined
in this International Standard incorporates specimen preparation procedures that result in selective concentration of
asbestos fibres, and removal of organic and water-soluble materials. These procedures have the effect of
dispersing the majority of the complex clusters and aggregates of fibres into their component fibres and bundles so
that the asbestos in the air sample can be more accurately quantified. All of the feasible specimen preparation
techniques result in some modification of the airborne particulate. Even the collection of particles from a
three-dimensional airborne dispersion on to a two-dimensional filter surface can be considered a modification of the
particulate, and some of the particles in most samples are modified by the specimen preparation procedures.
Although this method results in dispersal of complex clusters and aggregates, it minimizes other effects on the size
distribution of fibres and fibre bundles.
This International Standard is necessarily complex, because the instrumental techniques used are complex, and
also because a very detailed and logical procedure must be specified to reduce the subjective aspects of the
measurement. The method of data recording specified in this International Standard is designed to allow
re-evaluation of the fibre counting data as new medical evidence becomes available.
This International Standard describes the method of analysis for a single air filter. However, one of the largest
potential errors in characterizing asbestos in ambient atmospheres is associated with the variability between filter
samples. For this reason, it is necessary to design a replicate sampling scheme in order to determine the standard's
accuracy and precision.
Comparison of results obtained using this indirect-transfer procedure with those from the direct-transfer procedure
may not be done a priori. A site-specific intercomparison study must be done which takes into account the fibre size
and type of asbestos, and also the nature of the source of the airborne asbestos.
v
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INTERNATIONAL STANDARD © ISO ISO 13794:1999(E)
Ambient air — Determination of asbestos fibres — Indirect-
transfer transmission electron microscopy method
1 Scope
1.1 Substance determined
This International Standard specifies a reference method using transmission electron microscopy (TEM) for
determination of the concentration of asbestos structures in ambient atmospheres. The specimen preparation
procedure incorporates ashing and dispersion of the collected particulate, so that all asbestos is measured,
including the asbestos originally incorporated in particle aggregates or particles of composite materials. The lengths,
widths and aspect ratios of the asbestos fibres and bundles are measured, and these, together with the density of
the type of asbestos, also allow the total mass concentration of airborne asbestos to be calculated. The method
allows determination of the type(s) of asbestos fibre present. The method cannot discriminate between individual
fibres of the asbestos and non-asbestos analogues of the same amphibole mineral.
1.2 Type of sample
The method is defined for polycarbonate capillary-pore filters or cellulose ester (either mixed esters of cellulose or
cellulose nitrate) filters through which a known volume of air has been drawn. The method is suitable for
determination of asbestos in both exterior and building atmospheres.
1.3 Range
2
The upper limit for the range of concentration that can be measured on the analytical filter is 7 000 structures/mm .
The lower limit of the range that can be measured on the analytical filter corresponds to detection of 2,99 structures
in the area of specimen examined. The air concentrations represented by these values are a function of the volume
of air sampled and the degree of dilution or concentration selected during the specimen preparation procedures.
The method is particularly applicable for measurements in areas with high suspended-particulate concentrations
3
(exceeding 10 μg/m ), or where detection and identification of asbestos fibres are likely to be prevented or hindered
by other types of particulate in direct-transfer TEM preparations. In theory, there is no lower limit to the dimensions
of asbestos fibres which can be detected. In practice, microscopists vary in their ability to detect very small
asbestos fibres. Therefore, a minimum length of 0,5 μm has been defined as the shortest fibre to be incorporated in
the reported results.
1.4 Limit of detection
The limit of detection theoretically can be lowered indefinitely by filtration of progressively larger volumes of air,
concentrating the sample during specimen preparation, and by extending the examination of the specimens in the
electron microscope. In practice, the lowest achievable limit of detection for a particular area of TEM specimen
examined is controlled by the total suspended particulate concentration remaining after the ashing and aqueous
dispersal steps, and this depends on the chemical nature of the suspended particulate. For total suspended
3
particulate concentrations of approximately 10 μg/m , corresponding to clean, rural atmospheres, and assuming
filtration of 4 000 litres of air, an analytical sensitivity of 0,5 structure/litre can be obtained, equivalent to a limit of
2
detection of 1,8 structures/litre, if an area of 0,195 mm of the TEM specimens is examined. Lower limits of
detection can be achieved by increasing the area of the TEM specimen that is examined, or by concentration of the
sample during specimen preparation. In order to achieve lower limits of detection for fibres and bundles longer than
5 μm, and for PCM-equivalent fibres, lower magnifications are specified which permit more rapid examination of
larger areas of the TEM specimens when the examination is limited to these dimensions of fibre.
1
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© ISO
ISO 13794:1999(E)
2 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply.
2.1
acicular
shape shown by an extremely slender crystal with cross-sectional dimensions which are small relative to its length,
i.e. needle-like
2.2
amphibole
group of rock-forming ferromagnesium silicate minerals, closely related in crystal form and composition, and having
the nominal formula:
A B C T O (OH,F,Cl)
0-1 2 5 8 22 2
where
A is K, Na
21
B is Fe , Mn, Mg, Ca, Na
3 2
1 1
C is Al, Cr, Ti, Fe , Mg, Fe
31
T is Si, Al, Cr, Fe , Ti
NOTE In some varieties of amphibole, these elements can be partially substituted by Li, Pb, or Zn. Amphibole is
characterized by a cross-linked double chain of Si-O tetrahedra with a silicon:oxygen ratio of 4:11, by columnar or fibrous
prismatic crystals and by good prismatic cleavage in two directions parallel to the crystal faces and intersecting at angles of
about 56° and 124°.
2.3
amphibole asbestos
amphibole in an asbestiform habit
2.4
analytical filter
filter through which an aqueous dispersion of ash from the sample collection filter is passed, and from which TEM
specimen grids are prepared
2.5
analytical sensitivity
calculated airborne asbestos structure concentration, equivalent to counting of one asbestos structure in the
analysis
NOTE 1 It is expressed in structures/litre.
NOTE 2 The method given in this International Standard does not specify an analytical sensitivity.
2.6
asbestiform
specific type of mineral fibrosity in which the fibres and fibrils possess high tensile strength and flexibility
2.7
asbestos
term applied to a group of silicate minerals belonging to the serpentine and amphibole groups which have
crystallized in the asbestiform habit, causing them to be easily separated into long, thin, flexible, strong fibres when
crushed or processed
NOTE The Chemical Abstracts Service Registry Numbers of the most common asbestos varieties are: chrysotile
(12001-29-5), crocidolite (12001-28-4), grunerite asbestos (Amosite) (12172-73-5), anthophyllite asbestos (77536-67-5),
tremolite asbestos (77536-68-6) and actinolite asbestos (77536-66-4).
2
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© ISO
ISO 13794:1999(E)
2.8
asbestos structure
term applied to an individual asbestos fibre, or any connected or overlapping grouping of asbestos fibres or bundles,
with or without other particles
2.9
ashed filter blank
fibre count made on TEM specimens prepared by the indirect procedure from a blank membrane filter of the type
used for collection of air samples
2.10
aspect ratio
ratio of length to width of a particle
2.11
blank
structure count made on TEM specimens prepared from an unused filter in order to determine the background
measurement
2.12
camera length
equivalent projection length between the specimen and its electron diffraction pattern, in the absence of lens action
2.13
chrysotile
fibrous mineral of the serpentine group which has the nominal composition
Mg Si O (OH)
3 2 5 4
NOTE Most natural chrysotile deviates little from this nominal composition. In some varieties of chrysotile, minor
31 31 21 31 21 21 21
substitution of silicon by Al may occur. Minor substitution of magnesium by Al , Fe , Fe , Ni , Mn and Co may
also be present. Chrysotile is the most prevalent type of asbestos.
2.14
cleavage
breaking of a mineral along one of its crystallographic directions
2.15
cleavage fragment
fragment of a crystal that is bounded by cleavage faces
2.16
cluster
structure in which two or more fibres, or fibre bundles, are randomly oriented in a connected grouping
2.17
direct-transfer blank
structure count made on TEM specimens prepared by the direct-transfer procedure from a blank filter of the type
used for filtration of aqueous dispersions of ash
2.18
d-spacing
distance between identical adjacent and parallel planes of atoms in a crystal
2.19
electron diffraction
technique in electron microscopy by which the crystal structure of a specimen is examined
2.20
electron scattering power
extent to which a thin layer of substance scatters impinging electrons from their original directions
3
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© ISO
ISO 13794:1999(E)
2.21
empty beaker blank
fibre count made on TEM specimens prepared by the indirect procedure, using an empty beaker as the initial
sample
2.22
energy-dispersive X-ray analysis
EDXA
measurement of the energies and intensities of X-rays by use of a solid-state detector and multichannel analyzer
system
2.23
eucentric
condition in which the area of interest of an object is placed on a tilting axis, at the intersection of the electron beam
with that axis, and is in the plane of focus
2.24
field blank
filter cassette which has been taken to the sampling site, opened and then closed, and the filter subsequently used
to determine the background structure count for the measurement
2.25
fibril
single fibre of asbestos which cannot be further separated longitudinally into smaller components without losing its
fibrous properties or appearances
2.26
fibre
elongated particle which has parallel or stepped sides
NOTE For the purposes of this International Standard, a fibre is defined to have an aspect ratio equal to or greater than 5:1
and a minimum length of 0,5 μm.
2.27
fibre bundle
structure composed of parallel, smaller-diameter fibres attached along their lengths
NOTE A fibre bundle may exhibit diverging fibres at one or both ends.
2.28
fibrous structure
fibre, or connected grouping of fibres, with or without other particles
2.29
funnel blank
structure count made on TEM specimens prepared by the direct-transfer method from a filter used for filtration
of a sample of distilled water
2.30
habit
characteristic crystal growth form, or combination of these forms, of a mineral, including characteristic irregularities
2.31
limit of detection
calculated airborne asbestos structure concentration, equivalent to counting of 2,99 asbestos structures in the
analysis
NOTE It is expressed in structures/litre.
4
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© ISO
ISO 13794:1999(E)
2.32
matrix
structure in which one or more fibres, or fibre bundles, touch, are attached to or partially concealed by, a single
particle or connected group of nonfibrous particles
2.33
Miller index
set of either three or four integer numbers used to specify the orientation of a crystallographic plane in relation to the
crystal axes
2.34
PCM-equivalent fibre
fibre of aspect ratio greater than or equal to 3:1, longer than 5 μm, and which has a diameter between 0,2 μm and
3,0 μm
NOTE For the purposes of this International Standard, PCM is the abbreviated term for phase-contrast optical microscopy.
2.35
PCM-equivalent structure
fibrous structure of aspect ratio greater than or equal to 3:1, longer than 5 μm, and which has a diameter between
0,2 μm and 3,0 μm
NOTE For the purposes of this International Standard, PCM is the abbreviated term for phase-contrast optical microscopy.
2.36
primary structure
fibrous structure that is a separate entity in the TEM image
2.37
replication
procedure in electron microscopy specimen preparation in which a thin copy, or replica, of a surface is made
2.38
selected area electron diffraction
technique in electron microscopy in which the crystal structure of a small area of a sample is examined
2.39
serpentine
group of common rock-forming minerals having the nominal formula
Mg Si O (OH)
3 2 5 4
2.40
structure
single fibre, fibre bundle, cluster or matrix
2.41
twinning
occurrence of crystals of the same species joined together at a particular mutual orientation, and such that the
relative orientations are related by a definite law
2.42
unopened fibre
large diameter asbestos fibre bundle which has not been separated into its constituent fibrils or fibres
2.43
zone-axis
line or crystallographic direction through the centre of a crystal which is parallel to the intersection edges of the
crystal faces defining the crystal zone
5
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© ISO
ISO 13794:1999(E)
3 Abbreviated terms
DMF Dimethylformamide
ED Electron diffraction
EDXA Energy dispersive X-ray analysis
FWHM Full width, half maximum
HEPA High efficiency particle absolute
MEC Mixed esters of cellulose
PC Polycarbonate
PCM Phase-contrast optical microscopy
SAED Selected area electron diffraction
SEM Scanning electron microscope
STEM Scanning transmission electron microscope
TEM Transmission electron microscope
UICC Union Internationale Contre le Cancer
4 Principle
A sample of airborne particulate is collected by drawing a measured volume of air through either a capillary-pore
polycarbonate (PC) membrane filter of maximum pore size 0,4 μm or a cellulose ester (either mixed esters of
cellulose or cellulose nitrate) membrane filter of maximum pore size 0,8 μm by means of a battery-powered or
mains-powered pump. A portion of the filter is ashed in an oxygen plasma, and the residual ash is dispersed in
distilled water with adjustment of the pH to between 3,0 and 4,0 using acetic acid. Analytical filters are then
prepared by filtration of known volumes of this aqueous dispersion through either capillary-pore PC membrane
filters of maximum pore size 0,2 μm or cellulose ester membrane filters of maximum pore size 0,22 μm.
TEM specimens are prepared from PC analytical filters by applying a thin film of carbon to the filter surface by
vacuum evaporation. Small areas are cut from the carbon-coated filter, supported on TEM specimen grids, and the
filter medium is dissolved away by a solvent extraction procedure. This procedure leaves a thin film of carbon which
bridges the openings in the TEM specimen grid, and which supports each particle from the original filter in its
original position.
Cellulose ester analytical filters are chemically treated to collapse the pore structure of the filter, and the surface of
the collapsed filter is then etched in an oxygen plasma to ensure that all particles are exposed. A thin film of carbon
is evaporated onto the filter surface and small areas are cut from the filter. These sections are supported on TEM
specimen grids and the filter medium is dissolved away by a solvent extraction procedure.
The TEM specimen grids from either preparation method are examined at both low and high magnifications to
check that they are suitable for analysis before carrying out a quantitative fibre count on randomly-selected grid
openings. If the selected TEM specimen grid has too high a particulate or fibre loading, another specimen grid with
a lower filtered aliquot shall be selected for analysis. In the TEM analysis, electron diffraction (ED) is used to
examine the crystal structure of a fibre, and its elemental composition is determined by energy-dispersive X-ray
analysis (EDXA). For a number of reasons, it is not possible to identify each fibre unequivocally, and fibres are
classified according to the techniques which have been used to identify them. A simple code is used to record, for
each fibre, the manner in which it was classified. The fibre classification procedure is based on successive
inspection of the morphology, the selected area ED pattern, and the qualitative and quantitative EDXAs.
Confirmation of the identification of chrysotile is only by quantitative ED, and confirmation of amphibole is only by
quantitative EDXA and quantitative zone-axis ED.
6
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© ISO
ISO 13794:1999(E)
In addition to isolated fibres, ambient air samples often contain more complex aggregates of fibres, with or without
other particles. Some particles are composites of asbestos fibres with other materials. Individual fibres and these
more complex structures are referred to as "asbestos structures". The indirect specimen preparation procedure
permits the majority of these complex structures to be dispersed into their constituent fibres and fibre bundles,
allowing more precise quantification than is possible using the direct-transfer procedure.
A coding system is used to record the type of fibrous structure, and also to provide the optimum morphological
description of each structure. The two codes remove from the microscopist the requirement to interpret the fibre
counting data, and allow this evaluation to be made later without the requirement for re-examination of the TEM
specimens. Several levels of analysis are specified, the higher levels providing a more rigorous approach to the
identification of fibres. The procedure permits a minimum required fibre identification criterion to be defined on the
basis of previous knowledge, or
...
SLOVENSKI STANDARD
SIST ISO 13794:2002
01-maj-2002
=XQDQML]UDN±'RORþHYDQMHD]EHVWQLKYODNHQ±0HWRGDWUDQVPLVLMVNHHOHNWURQVNH
PLNURVNRSLMH
Ambient air -- Determination of asbestos fibres -- Indirect-transfer transmission electron
microscopy method
Air ambiant -- Dosage des fibres d'amiante -- Méthode par microscopie électronique à
transmission par transfert indirect
Ta slovenski standard je istoveten z: ISO 13794:1999
ICS:
13.040.20 Kakovost okoljskega zraka Ambient atmospheres
SIST ISO 13794:2002 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
SIST ISO 13794:2002
---------------------- Page: 2 ----------------------
SIST ISO 13794:2002
INTERNATIONAL ISO
STANDARD 13794
First edition
1999-07-15
Ambient air — Determination of asbestos
fibres — Indirect-transfer transmission
electron microscopy method
Air ambiant — Dosage des fibres d'amiante — Méthode par microscopie
électronique à transmission par transfert indirect
A Reference number
ISO 13794:1999(E)
---------------------- Page: 3 ----------------------
SIST ISO 13794:2002
ISO 13794:1999(E)
Contents
Page
1 Scope .1
1.1 Substance determined .1
1.2 Type of sample.1
1.3 Range.1
1.4 Limit of detection.1
2 Terms and definitions .2
3 Abbreviated terms .6
4 Principle.6
5 Apparatus .7
5.1 Air sampling .7
5.2 Specimen preparation laboratory .8
5.3 Equipment for analysis .8
5.4 Consumable supplies.13
6 Reagents.14
7 Air sample collection.14
7.1 Calculation of analytical sensitivity .14
7.2 Sample collection procedure.15
8 Procedure for analysis .15
8.1 General.15
8.2 Cleaning of sample cassettes .16
8.3 Preparation of analytical filters .16
8.4 Preparation of TEM specimens from PC analytical filters.17
© ISO 1999
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
or mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 • CH-1211 Genève 20 • Switzerland
Internet iso@iso.ch
Printed in Switzerland
ii
---------------------- Page: 4 ----------------------
SIST ISO 13794:2002
© ISO
ISO 13794:1999(E)
8.5 Preparation of TEM specimens from cellulose ester analytical filters. 19
8.6 Criteria for acceptable TEM specimen grids. 20
8.7 Procedure for structure counting by TEM . 21
8.8 Blank and quality control determinations. 24
8.9 Calculation of results . 25
9 Performance characteristics . 25
9.1 General . 25
9.2 Interferences and limitations of fibre identification. 25
9.3 Precision and accuracy. 26
9.4 Limit of detection. 26
10 Test report . 27
Annex A (normative) Determination of operating conditions for plasma asher. 30
Annex B (normative) Determination and standardization of operating conditions for ultrasonic bath. 31
(normative)
Annex C Calibration procedures . 33
Annex D (normative) Structure-counting criteria . 36
Annex E (normative) Fibre identification procedure . 44
Annex F (normative) Determination of concentrations of asbestos fibres and bundles longer than 5 mm,
and of PCM-equivalent asbestos fibres . 53
Annex G (normative) Calculation of results . 54
Annex H (normative) Test procedure to determine suitability of cellulose ester sample collection filters. 60
Annex I (informative) Strategies for collection of air samples . 61
Bibliography. 62
iii
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SIST ISO 13794:2002
© ISO
ISO 13794:1999(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
International Standard ISO 13794 was prepared by Technical Committee ISO/TC 146, Air quality, Subcommittee
SC 3, Ambient atmospheres.
Annexes A to H form a normative part of this International Standard. Annex I is for information only.
iv
---------------------- Page: 6 ----------------------
SIST ISO 13794:2002
© ISO
ISO 13794:1999(E)
Introduction
This International Standard is applicable to the measurement of airborne asbestos in a wide range of ambient air
situations, including the interior atmospheres of buildings, and for detailed evaluation of any atmosphere in which
asbestos fibres are likely to be present. Because the best available medical evidence indicates that the numerical
fibre concentration and the fibre size and type are the relevant parameters for evaluation of the inhalation hazards,
a fibre counting and measuring technique is the only logical approach. Most fibres in ambient atmospheres are not
asbestos, and therefore there is a requirement for fibres to be identified. Many airborne asbestos fibres in ambient
atmospheres have diameters below the resolution limit of the optical microscope. This International Standard is
based on transmission electron microscopy, which has adequate resolution to allow detection of small fibres and is
currently the only technique capable of unequivocal identification of the majority of individual fibres of asbestos. The
fibres found suspended in an ambient atmosphere can often be identified unequivocally, if sufficient measurement
effort is expended. However, if each fibre were to be identified in this way, the analysis becomes prohibitively
expensive. Because of instrumental deficiencies or because of the nature of the particulate, some fibres cannot be
positively identified as asbestos, even though the measurements all indicate that they could be asbestos. Subjective
and instrumental factors therefore contribute to this measurement, and consequently a very precise definition of the
procedure for identification and enumeration of asbestos fibres is required.
In addition to single fibres and bundles, asbestos is often found in air samples as very complex, aggregated
structures which may or may not be also aggregated with other particles. The number of asbestos fibres and
bundles incorporated in these complex structures often exceeds the number of isolated fibres and bundles
observed, and many of them may be completely obscured in direct-transfer TEM preparations. The method defined
in this International Standard incorporates specimen preparation procedures that result in selective concentration of
asbestos fibres, and removal of organic and water-soluble materials. These procedures have the effect of
dispersing the majority of the complex clusters and aggregates of fibres into their component fibres and bundles so
that the asbestos in the air sample can be more accurately quantified. All of the feasible specimen preparation
techniques result in some modification of the airborne particulate. Even the collection of particles from a
three-dimensional airborne dispersion on to a two-dimensional filter surface can be considered a modification of the
particulate, and some of the particles in most samples are modified by the specimen preparation procedures.
Although this method results in dispersal of complex clusters and aggregates, it minimizes other effects on the size
distribution of fibres and fibre bundles.
This International Standard is necessarily complex, because the instrumental techniques used are complex, and
also because a very detailed and logical procedure must be specified to reduce the subjective aspects of the
measurement. The method of data recording specified in this International Standard is designed to allow
re-evaluation of the fibre counting data as new medical evidence becomes available.
This International Standard describes the method of analysis for a single air filter. However, one of the largest
potential errors in characterizing asbestos in ambient atmospheres is associated with the variability between filter
samples. For this reason, it is necessary to design a replicate sampling scheme in order to determine the standard's
accuracy and precision.
Comparison of results obtained using this indirect-transfer procedure with those from the direct-transfer procedure
may not be done a priori. A site-specific intercomparison study must be done which takes into account the fibre size
and type of asbestos, and also the nature of the source of the airborne asbestos.
v
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SIST ISO 13794:2002
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SIST ISO 13794:2002
INTERNATIONAL STANDARD © ISO ISO 13794:1999(E)
Ambient air — Determination of asbestos fibres — Indirect-
transfer transmission electron microscopy method
1 Scope
1.1 Substance determined
This International Standard specifies a reference method using transmission electron microscopy (TEM) for
determination of the concentration of asbestos structures in ambient atmospheres. The specimen preparation
procedure incorporates ashing and dispersion of the collected particulate, so that all asbestos is measured,
including the asbestos originally incorporated in particle aggregates or particles of composite materials. The lengths,
widths and aspect ratios of the asbestos fibres and bundles are measured, and these, together with the density of
the type of asbestos, also allow the total mass concentration of airborne asbestos to be calculated. The method
allows determination of the type(s) of asbestos fibre present. The method cannot discriminate between individual
fibres of the asbestos and non-asbestos analogues of the same amphibole mineral.
1.2 Type of sample
The method is defined for polycarbonate capillary-pore filters or cellulose ester (either mixed esters of cellulose or
cellulose nitrate) filters through which a known volume of air has been drawn. The method is suitable for
determination of asbestos in both exterior and building atmospheres.
1.3 Range
2
The upper limit for the range of concentration that can be measured on the analytical filter is 7 000 structures/mm .
The lower limit of the range that can be measured on the analytical filter corresponds to detection of 2,99 structures
in the area of specimen examined. The air concentrations represented by these values are a function of the volume
of air sampled and the degree of dilution or concentration selected during the specimen preparation procedures.
The method is particularly applicable for measurements in areas with high suspended-particulate concentrations
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(exceeding 10 μg/m ), or where detection and identification of asbestos fibres are likely to be prevented or hindered
by other types of particulate in direct-transfer TEM preparations. In theory, there is no lower limit to the dimensions
of asbestos fibres which can be detected. In practice, microscopists vary in their ability to detect very small
asbestos fibres. Therefore, a minimum length of 0,5 μm has been defined as the shortest fibre to be incorporated in
the reported results.
1.4 Limit of detection
The limit of detection theoretically can be lowered indefinitely by filtration of progressively larger volumes of air,
concentrating the sample during specimen preparation, and by extending the examination of the specimens in the
electron microscope. In practice, the lowest achievable limit of detection for a particular area of TEM specimen
examined is controlled by the total suspended particulate concentration remaining after the ashing and aqueous
dispersal steps, and this depends on the chemical nature of the suspended particulate. For total suspended
3
particulate concentrations of approximately 10 μg/m , corresponding to clean, rural atmospheres, and assuming
filtration of 4 000 litres of air, an analytical sensitivity of 0,5 structure/litre can be obtained, equivalent to a limit of
2
detection of 1,8 structures/litre, if an area of 0,195 mm of the TEM specimens is examined. Lower limits of
detection can be achieved by increasing the area of the TEM specimen that is examined, or by concentration of the
sample during specimen preparation. In order to achieve lower limits of detection for fibres and bundles longer than
5 μm, and for PCM-equivalent fibres, lower magnifications are specified which permit more rapid examination of
larger areas of the TEM specimens when the examination is limited to these dimensions of fibre.
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ISO 13794:1999(E)
2 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply.
2.1
acicular
shape shown by an extremely slender crystal with cross-sectional dimensions which are small relative to its length,
i.e. needle-like
2.2
amphibole
group of rock-forming ferromagnesium silicate minerals, closely related in crystal form and composition, and having
the nominal formula:
A B C T O (OH,F,Cl)
0-1 2 5 8 22 2
where
A is K, Na
21
B is Fe , Mn, Mg, Ca, Na
3 2
1 1
C is Al, Cr, Ti, Fe , Mg, Fe
31
T is Si, Al, Cr, Fe , Ti
NOTE In some varieties of amphibole, these elements can be partially substituted by Li, Pb, or Zn. Amphibole is
characterized by a cross-linked double chain of Si-O tetrahedra with a silicon:oxygen ratio of 4:11, by columnar or fibrous
prismatic crystals and by good prismatic cleavage in two directions parallel to the crystal faces and intersecting at angles of
about 56° and 124°.
2.3
amphibole asbestos
amphibole in an asbestiform habit
2.4
analytical filter
filter through which an aqueous dispersion of ash from the sample collection filter is passed, and from which TEM
specimen grids are prepared
2.5
analytical sensitivity
calculated airborne asbestos structure concentration, equivalent to counting of one asbestos structure in the
analysis
NOTE 1 It is expressed in structures/litre.
NOTE 2 The method given in this International Standard does not specify an analytical sensitivity.
2.6
asbestiform
specific type of mineral fibrosity in which the fibres and fibrils possess high tensile strength and flexibility
2.7
asbestos
term applied to a group of silicate minerals belonging to the serpentine and amphibole groups which have
crystallized in the asbestiform habit, causing them to be easily separated into long, thin, flexible, strong fibres when
crushed or processed
NOTE The Chemical Abstracts Service Registry Numbers of the most common asbestos varieties are: chrysotile
(12001-29-5), crocidolite (12001-28-4), grunerite asbestos (Amosite) (12172-73-5), anthophyllite asbestos (77536-67-5),
tremolite asbestos (77536-68-6) and actinolite asbestos (77536-66-4).
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2.8
asbestos structure
term applied to an individual asbestos fibre, or any connected or overlapping grouping of asbestos fibres or bundles,
with or without other particles
2.9
ashed filter blank
fibre count made on TEM specimens prepared by the indirect procedure from a blank membrane filter of the type
used for collection of air samples
2.10
aspect ratio
ratio of length to width of a particle
2.11
blank
structure count made on TEM specimens prepared from an unused filter in order to determine the background
measurement
2.12
camera length
equivalent projection length between the specimen and its electron diffraction pattern, in the absence of lens action
2.13
chrysotile
fibrous mineral of the serpentine group which has the nominal composition
Mg Si O (OH)
3 2 5 4
NOTE Most natural chrysotile deviates little from this nominal composition. In some varieties of chrysotile, minor
31 31 21 31 21 21 21
substitution of silicon by Al may occur. Minor substitution of magnesium by Al , Fe , Fe , Ni , Mn and Co may
also be present. Chrysotile is the most prevalent type of asbestos.
2.14
cleavage
breaking of a mineral along one of its crystallographic directions
2.15
cleavage fragment
fragment of a crystal that is bounded by cleavage faces
2.16
cluster
structure in which two or more fibres, or fibre bundles, are randomly oriented in a connected grouping
2.17
direct-transfer blank
structure count made on TEM specimens prepared by the direct-transfer procedure from a blank filter of the type
used for filtration of aqueous dispersions of ash
2.18
d-spacing
distance between identical adjacent and parallel planes of atoms in a crystal
2.19
electron diffraction
technique in electron microscopy by which the crystal structure of a specimen is examined
2.20
electron scattering power
extent to which a thin layer of substance scatters impinging electrons from their original directions
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2.21
empty beaker blank
fibre count made on TEM specimens prepared by the indirect procedure, using an empty beaker as the initial
sample
2.22
energy-dispersive X-ray analysis
EDXA
measurement of the energies and intensities of X-rays by use of a solid-state detector and multichannel analyzer
system
2.23
eucentric
condition in which the area of interest of an object is placed on a tilting axis, at the intersection of the electron beam
with that axis, and is in the plane of focus
2.24
field blank
filter cassette which has been taken to the sampling site, opened and then closed, and the filter subsequently used
to determine the background structure count for the measurement
2.25
fibril
single fibre of asbestos which cannot be further separated longitudinally into smaller components without losing its
fibrous properties or appearances
2.26
fibre
elongated particle which has parallel or stepped sides
NOTE For the purposes of this International Standard, a fibre is defined to have an aspect ratio equal to or greater than 5:1
and a minimum length of 0,5 μm.
2.27
fibre bundle
structure composed of parallel, smaller-diameter fibres attached along their lengths
NOTE A fibre bundle may exhibit diverging fibres at one or both ends.
2.28
fibrous structure
fibre, or connected grouping of fibres, with or without other particles
2.29
funnel blank
structure count made on TEM specimens prepared by the direct-transfer method from a filter used for filtration
of a sample of distilled water
2.30
habit
characteristic crystal growth form, or combination of these forms, of a mineral, including characteristic irregularities
2.31
limit of detection
calculated airborne asbestos structure concentration, equivalent to counting of 2,99 asbestos structures in the
analysis
NOTE It is expressed in structures/litre.
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2.32
matrix
structure in which one or more fibres, or fibre bundles, touch, are attached to or partially concealed by, a single
particle or connected group of nonfibrous particles
2.33
Miller index
set of either three or four integer numbers used to specify the orientation of a crystallographic plane in relation to the
crystal axes
2.34
PCM-equivalent fibre
fibre of aspect ratio greater than or equal to 3:1, longer than 5 μm, and which has a diameter between 0,2 μm and
3,0 μm
NOTE For the purposes of this International Standard, PCM is the abbreviated term for phase-contrast optical microscopy.
2.35
PCM-equivalent structure
fibrous structure of aspect ratio greater than or equal to 3:1, longer than 5 μm, and which has a diameter between
0,2 μm and 3,0 μm
NOTE For the purposes of this International Standard, PCM is the abbreviated term for phase-contrast optical microscopy.
2.36
primary structure
fibrous structure that is a separate entity in the TEM image
2.37
replication
procedure in electron microscopy specimen preparation in which a thin copy, or replica, of a surface is made
2.38
selected area electron diffraction
technique in electron microscopy in which the crystal structure of a small area of a sample is examined
2.39
serpentine
group of common rock-forming minerals having the nominal formula
Mg Si O (OH)
3 2 5 4
2.40
structure
single fibre, fibre bundle, cluster or matrix
2.41
twinning
occurrence of crystals of the same species joined together at a particular mutual orientation, and such that the
relative orientations are related by a definite law
2.42
unopened fibre
large diameter asbestos fibre bundle which has not been separated into its constituent fibrils or fibres
2.43
zone-axis
line or crystallographic direction through the centre of a crystal which is parallel to the intersection edges of the
crystal faces defining the crystal zone
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3 Abbreviated terms
DMF Dimethylformamide
ED Electron diffraction
EDXA Energy dispersive X-ray analysis
FWHM Full width, half maximum
HEPA High efficiency particle absolute
MEC Mixed esters of cellulose
PC Polycarbonate
PCM Phase-contrast optical microscopy
SAED Selected area electron diffraction
SEM Scanning electron microscope
STEM Scanning transmission electron microscope
TEM Transmission electron microscope
UICC Union Internationale Contre le Cancer
4 Principle
A sample of airborne particulate is collected by drawing a measured volume of air through either a capillary-pore
polycarbonate (PC) membrane filter of maximum pore size 0,4 μm or a cellulose ester (either mixed esters of
cellulose or cellulose nitrate) membrane filter of maximum pore size 0,8 μm by means of a battery-powered or
mains-powered pump. A portion of the filter is ashed in an oxygen plasma, and the residual ash is dispersed in
distilled water with adjustment of the pH to between 3,0 and 4,0 using acetic acid. Analytical filters are then
prepared by filtration of known volumes of this aqueous dispersion through either capillary-pore PC membrane
filters of maximum pore size 0,2 μm or cellulose ester membrane filters of maximum pore size 0,22 μm.
TEM specimens are prepared from PC analytical filters by applying a thin film of carbon to the filter surface by
vacuum evaporation. Small areas are cut from the carbon-coated filter, supported on TEM specimen grids, and the
filter medium is dissolved away by a solvent extraction procedure. This procedure leaves a thin film of carbon which
bridges the openings in the TEM specimen grid, and which supports each particle from the original filter in its
original position.
Cellulose ester analytical filters are chemically treated to collapse the pore structure of the filter, and the surface of
the collapsed filter is then etched in an oxygen plasma to ensure that all particles are exposed. A thin film of carbon
is evaporated onto the filter surface and small areas are cut from the filter. These sections are supported on TEM
specimen grids and the filter medium is dissolved away by a solvent extraction procedure.
The TEM specimen grids from either preparation method are examined at both low and high magnifications to
check that they are suitable for analysis before carrying out a quantitative fibre count on randomly-selected grid
openings. If the selected TEM specimen grid has too high a particulate or fibre loading, another specimen grid with
a lower filtered aliquot shall be selected for analysis. In the TEM analysis, electron diffraction (ED) is used to
examine the crystal structure of a fibre, and its elemental composition is determined by energy-dispersive X-ray
analysis (EDXA). For a number of reasons, it is not possible to identify each fibre unequivocally, and fibres are
classified according to the techniques which have been used to identify them. A simple code is used to record, for
each fibre, the manner in which it was classified. The fibre classification procedure is based on successive
inspection of the morphology, the selected area ED pattern, and the qualitative and quantitative EDXAs.
Confirmation of the identification of chrysotile is only by quantitative ED, and confirmation of amphibole is only by
quantitative EDXA and quantitative zone-axis ED.
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In addition to isolated fibres, ambient air
...
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