ISO 14966:2019

Ambient air - Determination of numerical concentration of inorganic fibrous particles - Scanning electron microscopy method

This document specifies a method using scanning electron microscopy for determination of the concentration of inorganic fibrous particles in the air. The method specifies the use of gold-coated, capillary-pore, track-etched membrane filters, through which a known volume of air has been drawn. Using energy-dispersive X-ray analysis, the method can discriminate between fibres with compositions consistent with those of the asbestos varieties (e.g. serpentine and amphibole), gypsum, and other inorganic fibres. Annex C provides a summary of fibre types which can be measured. This document is applicable to the measurement of the concentrations of inorganic fibrous particles in ambient air. The method is also applicable for determining the numerical concentrations of inorganic fibrous particles in the interior atmospheres of buildings, for example to determine the concentration of airborne inorganic fibrous particles remaining after the removal of asbestos-containing products. The range of concentrations for fibres with lengths greater than 5 µm, in the range of widths which can be detected under standard measurement conditions (see 7.2), is approximately 3 fibres to 200 fibres per square millimetre of filter area. The air concentrations, in fibres per cubic metre, represented by these values are a function of the volume of air sampled. The ability of the method to detect and classify fibres with widths lower than 0,2 µm is limited. If airborne fibres in the atmosphere being sampled are predominantly [8] can be used to determine the smaller fibres.

Air ambiant — Détermination de la concentration en nombre des particules inorganiques fibreuses — Méthode par microscopie électronique à balayage

Zunanji zrak - Določevanje numerične koncentracije anorganskih vlaknastih delcev - Metoda štetja z elektronskim mikroskopom

General Information

• Status: Published
• Publication Date: 12-Dec-2019
• ICS: 13.040.20 - Ambient atmospheres
• Technical Committee: ISO/TC 146/SC 3 - Ambient atmospheres
• Drafting Committee: ISO/TC 146/SC 3/WG 1 - Determination of asbestos fibre content
• Current Stage: 9093 - International Standard confirmed
• Start Date: 04-Aug-2025
• Completion Date: 13-Dec-2025
• Ref Project: SIST ISO 14966:2020 - Ambient air - Determination of numerical concentration of inorganic fibrous particles - Scanning electron microscopy method

Relations

• Revises: ISO 14966:2002/Cor 1:2007 - Ambient air - Determination of numerical concentration of inorganic fibrous particles - Scanning electron microscopy method - Technical Corrigendum 1
• Effective Date: 22-Mar-2018
• Revises: ISO 14966:2002 - Ambient air - Determination of numerical concentration of inorganic fibrous particles - Scanning electron microscopy method
• Effective Date: 22-Mar-2018

Overview

ISO 14966:2019 specifies a standardized scanning electron microscopy (SEM) method for determining the numerical concentration of inorganic fibrous particles in ambient air. The method uses gold‑coated, capillary‑pore, track‑etched membrane filters onto which a known volume of air is drawn. With energy‑dispersive X‑ray analysis (EDXA) the procedure discriminates fibres that have compositions consistent with asbestos varieties (serpentine and amphibole), gypsum (calcium sulfate), and other inorganic fibres. Annex C summarizes measurable fibre types and the document includes procedures for sampling, SEM analysis, calibration and reporting.

Key technical topics and requirements

• Sampling media and preparation: use of gold‑coated capillary‑pore polycarbonate filters and plasma ashing to remove organics before SEM examination.
• Instrumentation: requirements and calibration of SEM and EDXA systems; magnification and resolution checks (Annex B).
• Counting and classification: fibre counting criteria (minimum aspect ratio 3:1), lengths counted ( > 5 µm ), and width detection limits (detection and classification become limited below ~0.2 µm). Calcium sulfate fibres are identified separately and excluded from final asbestos counts.
• Analytical performance: calculation of mean fibre concentration, 95% confidence intervals, limit of detection, and assessment of measurement uncertainty and random/systematic errors.
• Range and sensitivity: typical filter densities for fibres > 5 µm correspond roughly to 3–200 fibres/mm² of filter area; corresponding air concentrations depend on sampled air volume.
• Quality control: procedures for SEM calibration, possible early termination rules for filter evaluation, and requirements for the test report.

Practical applications and users

• Environmental air monitoring: measurement of asbestos and other inorganic fibre concentrations in ambient outdoor air.
• Indoor air assessment: post‑abatement verification following removal of asbestos‑containing materials in buildings; assessment of residual airborne inorganic fibres.
• Occupational and public health laboratories: SEM/EDXA laboratories performing fibre identification and numerical concentration reporting.
• Regulatory agencies and consultants: air quality specialists, industrial hygienists, environmental consultants, and authorities defining compliance or remediation endpoints.

Keywords: ISO 14966:2019, ambient air, inorganic fibrous particles, scanning electron microscopy, SEM, EDXA, asbestos, capillary‑pore filters, fibre counting, measurement uncertainty.

Related standards

• VDI 3492 (basis for this method)
• ISO 14966:2002 (previous edition) and its corrigenda (incorporated updates)
• References to WHO membrane filter counting recommendations and PCM (phase‑contrast microscopy) methods where applicable for comparison.

Standards Content (Sample)

SLOVENSKI STANDARD
01-april-2020
Nadomešča:
SIST ISO 14966:2004
SIST ISO 14966:2004/Cor 1:2011
Zunanji zrak - Določevanje numerične koncentracije anorganskih vlaknastih
delcev - Metoda štetja z elektronskim mikroskopom
Ambient air - Determination of numerical concentration of inorganic fibrous particles -
Scanning electron microscopy method
Air ambiant - Détermination de la concentration en nombre des particules inorganiques
fibreuses - Méthode par microscopie électronique à balayage
Ta slovenski standard je istoveten z: ISO 14966:2019
ICS:
13.040.20 Kakovost okoljskega zraka Ambient atmospheres
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

INTERNATIONAL ISO
STANDARD 14966
Second edition
2019-12
Ambient air — Determination of
numerical concentration of inorganic
fibrous particles — Scanning electron
microscopy method
Air ambiant — Détermination de la concentration en nombre des
particules inorganiques fibreuses — Méthode par microscopie
électronique à balayage
Reference number
©
ISO 2019
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
ii © ISO 2019 – All rights reserved

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 4
5 Principle . 4
6 Apparatus and materials. 4
6.1 Air sampling . 4
6.1.1 Sampling head . 4
6.1.2 Sampling train . 5
6.1.3 Sampling pump . 5
6.1.4 Needle valve . 6
6.1.5 Volumetric flowmeter (rotameter) . 6
6.1.6 Timer . 6
6.1.7 Dry type gas meter (optional) . 6
6.1.8 Meteorological instruments (optional) . 6
6.1.9 Instruments for unattended sampling (optional) . 7
6.2 Preparation of filters . 7
6.2.1 Vacuum evaporator . . 7
6.2.2 Plasma asher . 8
6.3 Sample analysis . 8
6.3.1 Scanning electron microscope (SEM) . 8
6.3.2 Energy-dispersive X-ray system . 8
6.3.3 Stereo-microscope . . 9
6.3.4 Gold-coated capillary-pore polycarbonate filters. 9
6.3.5 Backing filters . 9
6.3.6 Disposable plastic field monitors (optional) . 9
6.3.7 Technically pure oxygen . 9
6.3.8 Rubber connecting hoses . 9
6.3.9 Filter containers . 9
6.3.10 Routine electron microscopy tools and supplies . 9
6.3.11 Sample for resolution adjustment . 9
6.3.12 Sample for magnification calibration .10
7 Air sample collection and analysis .10
7.1 Measurement planning .10
7.2 Collection of air samples .10
7.3 SEM specimen preparation .13
7.4 Analysis in the scanning electron microscope .13
7.4.1 General instructions.13
7.4.2 Fibre-counting criteria .14
7.4.3 Fibre classification .19
7.4.4 Analysis using reference spectra and peak height ratios .26
7.4.5 Measurement of fibre dimensions .28
7.4.6 Recording of data on the fibre counting form .28
8 Calculation of results .28
8.1 Calculation of the mean fibre concentration .28
8.2 Calculation of the 95 % confidence interval .30
9 Performance characteristics .30
9.1 General .30
9.2 Measurement uncertainty .30
9.2.1 Systematic errors . . .30
9.2.2 Random errors .30
9.2.3 Errors due to sampling .31
9.2.4 Errors associated with the SEM examination .31
9.2.5 Total error of the measurement.31
9.2.6 Random errors due to fibre counting .32
9.3 Limit of detection .34
10 Test report .35
Annex A (normative) Preparation of filters for air sampling .37
Annex B (normative) Procedures for calibration and adjustment of the SEM .38
Annex C (informative) Characteristics and chemical composition of inorganic fibres .40
Annex D (informative) Poisson variability as a function of fibre density on sampling filter
and area of filter analysed .45
Annex E (informative) Combination of the results from multiple samples .47
Bibliography .48
iv © ISO 2019 – All rights reserved

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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 146, Air quality, Subcommittee SC 3,
Ambient atmospheres.
This second edition cancels and replaces the first edition (ISO 14966:2002), which has been technically
revised. It also incorporates the corrected version ISO 14699:2002/Cor 1:2007. The main changes
compared to the previous edition are as follows:
— Counting rules, changed to the recommended method (membrane filter method) of the WHO
(World Health Organization);
— Analytical procedure (classification), using normalized peak height ratios in addition to the method
of the previous edition;
— Rule for early termination of filter evaluation (counting and analysis). A formula is given to terminate
the filter evaluation, if the calculated (asbestos) fibre concentration is above a set limit value for this
fibre concentration.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
Introduction
This document describes a method for measurement of the numerical concentration of inorganic fibrous
[1]
particles in ambient air using the scanning electron microscope. This document is based on VDI 3492 .
The method is also suitable for determining the numerical concentrations of inorganic fibres in the
interior atmospheres of buildings, for example measurement of residual airborne fibre concentrations
after the removal of asbestos-containing building materials.
Biological research has shown that the fibrogenic or carcinogenic effect of a fibre is related to its
length, diameter and its resistance to dissolution in a biological environment. The point at which
fibres are too short, too thick or of insufficient durability to produce a fibrogenic or carcinogenic effect
is uncertain. Fibres with lengths greater than 10 µm and diameters of a few tenths of 1 µm, which
also have durabilities such that they remain unchanged for many years in the body, are regarded as
particularly carcinogenic. Based on current knowledge, fibres shorter than 5 µm are thought to have a
[2]‒[5]
lower carcinogenic potential .
For the purposes of this document, a fibre is defined as a particle which has a minimum length to width
(aspect) ratio of 3:1. Fibres with lengths greater than 5 µm and widths extending from the lower limit of
visibility up to 3 µm are counted. Fibres with diameters less than 3 µm are considered to be respirable.
Since the method requires recording the lengths and widths of all fibres, the data can be re-evaluated if
[6]
it is required to derive concentrations for fibres with a higher minimum aspect ratio .
The range of concentration to be measured extends from that found in clean air environments, in which
the mean value of a large number of individual measurements of asbestos fibre concentrations has
been found to be generally lower than 100 fibres/m (fibres longer than 5 µm), up to higher exposure
[4][6]
scenarios in which concentrations as much as two orders of magnitude higher have been found .
This method is used to measure the numerical concentration of inorganic fibres with widths smaller
than 3 µm and lengths exceeding 5 µm up to a maximum of 100 µm. Using energy-dispersive X-ray
analysis (EDXA), fibres are classified as fibres with compositions consistent with those of asbestos
fibres, calcium sulfate fibres and other inorganic fibres.
Calcium sulfate fibres are separated from other inorganic fibres and are not included in the final result,
because on the basis of current knowledge, they do not represent any health hazard. Nevertheless, the
numerical concentration of calcium sulfate fibres should be determined, since a high concentration of
these fibres can negatively bias the results for probable asbestos fibres, and in some circumstances the
[7]
sample may have to be rejected . In addition, knowledge of the numerical concentration of calcium
sulfate fibres is of importance in the interpretation of fibre concentrations in ambient atmospheres.
Detection and identification of fibres becomes progressively more uncertain as the fibre width is
reduced below 0,2 µm. Identification of a fibre as a specific species is more confident if the source of
emission is known or suspected, such as in a building for which bulk materials are available for analysis.
In order to facilitate the scanning electron microscope examination, organic particles collected on the
filter are almost completely removed by a plasma ashing treatment.
Except in situations where fibre identification is difficult, there should be only minor differences
between fibre counting results obtained by this method and those obtained using the procedures for
determination of PCM-equivalent fibres in Annex E of the transmission electron microscopy method
[8]
ISO 10312 .
vi © ISO 2019 – All rights reserved

INTERNATIONAL STANDARD ISO 14966:2019(E)
Ambient air — Determination of numerical concentration
of inorganic fibrous particles — Scanning electron
microscopy method
1 Scope
This document specifies a method using scanning electron microscopy for determination of the
concentration of inorganic fibrous particles in the air. The method specifies the use of gold-coated,
capillary-pore, track-etched membrane filters, through which a known volume of air has been drawn.
Using energy-dispersive X-ray analysis, the method can discriminate between fibres with compositions
consistent with those of the asbestos varieties (e.g. serpentine and amphibole), gypsum, and other
inorganic fibres. Annex C provides a summary of fibre types which can be measured.
This document is applicable to the measurement of the concentrations of inorganic fibrous particles in
ambient air. The method is also applicable for determining the numerical concentrations of inorganic
fibrous particles in the interior atmospheres of buildings, for example to determine the concentration
of airborne inorganic fibrous particles remaining after the removal of asbestos-containing products.
The range of concentrations for fibres with lengths greater than 5 µm, in the range of widths which can
be detected under standard measurement conditions (see 7.2), is approximately 3 fibres to 200 fibres
per square millimetre of filter area. The air concentrations, in fibres per cubic metre, represented by
these values are a function of the volume of air sampled.
The ability of the method to detect and classify fibres with widths lower than 0,2 µm is limited. If
airborne fibres in the atmosphere being sampled are predominantly <0,2 µm in width, a transmission
[8]
electron microscopy method such as ISO 10312 can be used to determine the smaller fibres.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
acicular
shape shown by an extremely slender crystal with cross-sectional dimensions which are small relative
to its length, i.e. needle-like
3.2
amphibole
any of a group of rock-forming double-chain 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 = K, Na;
2+
B = Fe , Mn, Mg, Ca, Na;
3+ 2+
C = Al, Cr, Ti, Fe , Mg, Fe ;
3+
T = Si, Al, Cr, Fe , Ti
Note 1 to entry: 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°.
3.3
amphibole asbestos
amphibole (3.2) in an asbestiform (3.5) habit (3.17)
3.4
analytical sensitivity
calculated airborne fibre (3.13) concentration equivalent to counting one fibre in the analysis
Note 1 to entry: The analytical sensitivity is expressed in fibres per cubic metre.
Note 2 to entry: This method does not specify a unique analytical sensitivity. The analytical sensitivity is
determined by the needs of the measurement and the conditions found on the prepared sample.
3.5
asbestiform
specific type of mineral fibrosity in which the fibres (3.13) and fibrils possess high tensile strength and
flexibility
3.6
asbestos
any of a group of silicate minerals belonging to the serpentine and amphibole fibres (3.2) groups which
have crystallized in the asbestiform (3.5) habit (3.17), causing them to be easily separated into long,
thin, flexible, strong fibres (3.13) when crushed or processed
Note 1 to entry: 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).
3.7
aspect ratio
ratio of length of a particle to its width
3.8
chrysotile
fibrous variety of the mineral serpentine, which has the nominal composition:
Mg Si O (OH)
3 2 5 4
Note 1 to entry: Most natural chrysotile deviates little from this nominal composition. In some varieties of
3+ 2+ 3+
chrysotile, minor substitution of silicon by Al + can occur. Minor substitution of magnesium by Al , Fe , Fe ,
2+ 2+ 2+
Ni , Mn and Co can also be present. Chrysotile is the most prevalent type of asbestos.
3.9
cleavage
breaking of a mineral along one of its crystallographic directions
2 © ISO 2019 – All rights reserved

3.10
cluster
fibrous structure in which two or more fibres (3.13), or fibre bundles (3.14) are randomly oriented in a
connected grouping
3.11
countable fibre
any object longer than 5 µm, having a maximum width less than 3 µm and a minimum aspect ratio of 3:1
3.12
energy-dispersive X-ray analysis
measurement of the energies and intensities of X-rays by use of a solid-state detector and multi-channel
analyser system
3.13
fibre
elongated particle which has parallel or stepped sides and a minimum aspect ratio of 3:1
3.14
fibre bundle
structure composed of apparently attached, parallel fibres (3.13)
Note 1 to entry: A fibre bundle can exhibit diverging fibres at one or both ends. The length is defined as equal
to the maximum length of the structure, and the diameter is defined as equal to the maximum width in the
compact region.
3.15
fibril
single fibre (3.13) of asbestos which cannot be further separated longitudinally into smaller components
without losing its fibrous properties or appearances
3.16
fibrous structure
fibre (3.13), or connected grouping of fibres, with or without other particles
3.17
habit
the characteristic crystal growth form or combination of these forms of a mineral, including
characteristic irregularities
3.18
image field
the area on the filter sample which is shown on the screen
3.19
limit of detection
calculated airborne fibre (3.13) concentration equivalent to the upper 95 % confidence limit of 2,99
fibres predicted by the Poisson distribution for a count of zero fibres
Note 1 to entry: The limit of detection is expressed in fibres per cubic metre.
3.20
magnification
ratio of the size of the image of an object on the observation screen to the actual size of the object
Note 1 to entry: For the purposes of this document, magnification values always refer to that applicable to the
observation screen.
3.21
matrix
structure in which one or more fibres (3.13) or fibre bundles (3.14) touch, are attached to, or partially
concealed by a single particle or connected group of non-fibrous particle
3.22
serpentine
any of a group of common rock-forming minerals having the nominal formula:
Mg Si O (OH)
3 2 5 4
3.23
split fibre
agglomeration of fibres (3.13) which, at one or several points along its length, appears to be compact
and undivided, whilst at other points appears to separate into separate fibres
3.24
structure
single fibre (3.13), fibre bundle (3.14), cluster (3.10)or matrix
4 Abbreviated terms
EDXA Energy-dispersive X-ray analysis
FWHM Full width, half maximum
PTFE Polytetrafluoroethylene
SEM Scanning electron microscope
5 Principle
A sample of airborne particulate is collected by drawing a measured volume of air through a gold-
coated, capillary pore track-etched membrane filter with a maximum nominal pore size of 0,8 µm,
which is subsequently examined in the scanning electron microscope (SEM). Before analysis, the gold-
coated filter is treated in a plasma asher to remove organic particles, to the extent that this is possible.
The individual fibrous particles and constituent fibres in a randomly-selected area of the filter are
then counted at a magnification of approximately 2 000×. If a fibre is detected at the magnification of
approximately 2 000×, it is examined at a higher magnification of approximately 10 000× to measure
its dimensions. At the higher magnification of approximately 10 000×, energy-dispersive X-ray analysis
(EDXA) is used to classify the fibre according to the chemical composition.
The limit of detection for this method is defined as the numerical fibre concentration below which, with
95 % confidence, the actual concentration lies when no fibres are found during the SEM examination.
The limit of detection theoretically can be lowered indefinitely by filtration of progressively larger
volumes of air and by examination of a larger area of the specimen in the SEM. In practice, the lowest
achievable limit of detection for a particular area of SEM specimen examined is controlled by the total
suspended particulate concentration remaining after the plasma ashing step.
3 3
A limit of detection of approximately 300 fibres/m is obtained if an air volume of 1 m per square
centimetre of filter surface area passes through the filter, and an area of 1 mm of the filter area is
examined in the SEM. This corresponds to an evaluated sample air volume of 0,01 m .
6 Apparatus and materials
6.1 Air sampling
6.1.1 Sampling head
A disposable, 3-piece, conductive plastic field monitor cassette may be used as the sampling head,
provided that the design is such that significant leakage around the filter does not occur. A re-usable
4 © ISO 2019 – All rights reserved

unit may also be used as the sampling head, consisting of a cylindrical cowl and a filter holder with
backing filter. Figure 1 shows an example of a suitable sampling head. The cowl and the filter holder
should be made from a corrosion-resistant material. The filter shall be clamped in such a manner that
significant leaks around the filter do not occur at differential pressures up to approximately 50 kPa
as described in B.4. The length of the cowl should be 0,5 to 2,5 times the effective filter diameter (the
diameter of the exposed circular filter area through which the air is drawn). If it is possible that wind
velocities greater than 5 m/s could occur during sampling, use a long cowl with a ratio of length to
effective diameter of 2,5.
6.1.2 Sampling train
Figure 2 shows an example of a suitable sampling train. Control of the volumetric flowrate can be
achieved either by the use of a throttle valve (3) or a volumetric flow controller (8) in conjunction with
a regulator valve (4).
6.1.3 Sampling pump
Pulse-free or pulsation-damped, capable of maintaining, at a pressure differential across the filter of at
least 50 kPa, a volumetric flow of between 8 l/min and 30 l/min, depending on the diameter of filter used.
In order to achieve the required analytical sensitivity, a flowrate of 8 l/min is required if a 25 mm
diameter filter is used. This flowrate is equivalent to a filter face velocity of approximately 35 cm/s.
The sampling pump shall be capable of maintaining the intended flowrate within ±10 % throughout the
whole sampling period.
Key
1 cowl 6 suction hose
2 filter holder 7 clamping roller
3 backing filter 8 clamping ring
4 track-etched membrane filter 9 PTFE gaskets
5 supporting mesh
Figure 1 — Example of design of sampling head
6.1.4 Needle valve
With a fine adjustment mechanism, for setting the volumetric flowrate.
6.1.5 Volumetric flowmeter (rotameter)
For measuring the volumetric flowrate.
6.1.6 Timer
For measuring the sampling time.
6.1.7 Dry type gas meter (optional)
For volumetric measurement, calibrated, designed for a maximum volumetric flowrate of 2 m /h.
6.1.8 Meteorological instruments (optional)
For recording of meteorological conditions during sampling. Instruments such as a thermometer, a
hygrometer, a barometer and a wind speed and direction recorder will be required.
6 © ISO 2019 – All rights reserved

6.1.9 Instruments for unattended sampling (optional)
For unattended sampling, a volumetric flow controller is required for regulation of the flowrate
to within ±10 % of the nominal rate, with an automatic switch to turn off the sampling pump if the
flowrate exceeds or falls below the pre-set tolerance band. The flow controller can be integrated into
the suction unit.
A programmable switch is required for pre-setting the air sampling cycle. A pressure gauge which
incorporates a switching contact is required to switch off the sampling pump if the pressure differential
across the sampling filter increases to a pre-set value.
Key
1 sampling head or cassette 8 volumetric flow controller (optional)
2 pressure gauge 9 sampling-time recorder (optional)
3 throttle valve (optional) 10 programmer (optional)
4 regulator valve (optional) 11 timer
5 pump 12 thermometer (optional)
6 variable-area flowmeter 13 barometer (optional)
7 gas meter (optional) with thermometer 14 hygrometer (optional)
Figure 2 — Example of a suitable sampling train
6.2 Preparation of filters
6.2.1 Vacuum evaporator
Capable of producing a vacuum better than 0,013 Pa.
A vacuum coating unit is required for vacuum deposition of gold onto the capillary-pore membrane
filters, and for carbon coating of SEM specimens if the particulate loading is such that excessive
charging of the specimen occurs.
A sputter coating unit has also been found to meet the requirements for gold coating of the capillary-
pore filters.
6.2.2 Plasma asher
Supplied with oxygen, to oxidize organic particles on the SEM specimen.
An example of the configuration of a suitable plasma asher is shown in Figure 3. The chamber of the
plasma asher may be coupled either capacitatively or inductively. Care shall be taken not to damage the
specimen during the plasma ashing process. A calibration procedure to determine suitable operating
conditions for the plasma asher is described in B.3.
Key
1 bell jar 5 connection for vacuum pump
2 filter in mounting ring 6 air inlet
3 oxygen inlet 7 cooling-water inlet
4 power supply from plasma generator 8 cooling-water outlet
Figure 3 — Example of a configuration of a plasma asher
6.3 Sample analysis
6.3.1 Scanning electron microscope (SEM)
With an accelerating voltage of at least 15 kV, is required for fibre counting and identification.
6.3.2 Energy-dispersive X-ray system
For the SEM, capable of achieving a resolution better than 140 eV (FWHM) on the MnK peak.
α
The performance of an individual combination of SEM and solid-state X-ray detector is dependent on a
number of geometrical factors. Accordingly, the required performance of the combination of the SEM
and X-ray analyser is specified in terms of the measured X-ray intensity obtained from a chrysotile fibre
of width 0,2 µm, under the operating conditions used during the analysis. Solid-state X-ray detectors
are least sensitive in the low energy region, and so detection of sodium in crocidolite is an additional
performance criterion.
The instrumental combination shall satisfy the minimum requirements with regard to the visibility of
fibres, as specified in 7.4.1, and identification of the fibres, as specified in 7.4.3.
8 © ISO 2019 – All rights reserved

6.3.3 Stereo-microscope
With a magnification of approximately 20×, for visual examination of the particulate deposit on the filter.
6.3.4 Gold-coated capillary-pore polycarbonate filters
Maximum nominal pore size 0,8 µm, for collection of air samples. The gold coating shall be approximately
30 nm thick applied to the shiny side of the filter. The procedure for preparation of the gold-coated
filters is described in Annex A.
NOTE Optionally, a 20 nm thick layer of gold can be evaporated on to the reverse side of the filter. This coating
serves to protect the filter during plasma ashing and can help to improve the contrast of fibres in the SEM image.
6.3.5 Backing filters
Cellulose ester membrane, or absorbent pads, with a porosity of approximately 5 µm to be used as
diffusing filters behind the sample collection filters.
6.3.6 Disposable plastic field monitors (optional)
If disposable plastic field monitors are used, they shall consist of 25 mm to 50 mm diameter, three-piece
cassettes, which conform to the requirements of 6.1.1. The cassette shall be loaded with a gold-coated,
capillary-pore polycarbonate filter of maximum nominal pore size 0,8 µm, backed by a cellulose ester
filter of 5 µm porosity or an absorbent pad. Suitable precautions shall be taken to ensure that the filters
are tightly clamped in the assembly so that significant air leakage around the filter cannot occur.
Re-use of disposable plastic field monitors is not recommended.
6.3.7 Technically pure oxygen
For operation of the plasma asher.
6.3.8 Rubber connecting hoses
For connecting the sampling head to the pump, and other equipment in the sampling train.
The hose shall have a wall thickness such that it does not collapse under a vacuum of 50 kPa. Silicone
rubber hose has been found to meet the requirements.
6.3.9 Filter containers
For transport and storage of filters if disposable field monitors are not used.
6.3.10 Routine electron microscopy tools and supplies
Fine point tweezers, scalpel holders and blades, double-coated adhesive tape, SEM specimen stubs
and colloidal carbon paint and other routine supplies are required. If a vacuum evaporator is used
for preparation of gold-coated filters, gold wire and tungsten filaments are required. For carbon
evaporation, spectroscopically pure carbon rods and a means of sharpening the rods is required.
6.3.11 Sample for resolution adjustment
A gold-coated polycarbonate filter, on which chrysotile fibres with a width of ≥0,2 µm have been
deposited, is required for adjustment of the operating conditions of the SEM.
6.3.12 Sample for magnification calibration
A test sample is required to calibrate the magnification of the SEM. The magnification standard
SRM484e (U.S. National Institute of Standards and Technology) is an example of a sample which meets
the requirement.
7 Air sample collection and analysis
7.1 Measurement planning
When determining the spatial and temporal scope of the measurements, it is important to take into
consideration the special aspects of the situation. It is therefore essential to define the objective of
the measurements before samples are collected. Any available information on emission sources,
meteorological conditions and the local situation should be taken into account in order to obtain the
maximum information from the measurements. The number of individual measurements to be made
should be selected according to the particular task. In particular, prior to collection of the samples,
the required accuracy for the mean concentration of the inorganic fibres should be specified, since the
error of each individual measurement needs to be taken into consideration in determining the number
of samples to be collected. Measurement uncertainty is discussed in Clause 9.
7.2 Collection of air samples
Figure 2 shows an example of a sampling train. Position the sampling head approximately 1,5 m above
ground level.
If a re-usable sampling head is used, place a 5 µm porosity cellulose ester backing filter on to the filter
support in the sampling head. Place a gold-coated filter on top of the backing filter, with the shiny side
facing into the direction of the airflow. Clamp the filters in the sampling head so that the gold-coated
filter lies flush against the backing filter and is tightly fitted. Ensure that damage does not occur to the
filter during clamping, and that the filter is not twisted.
Before air sampling is commenced, perform a brief test with the tube to the sampling head closed, to
determine if any leaks exist in the complete sampling system. Under the conditions of this test, the
flowrate indicated by the volumetric flowmeter shall be less than 10 % of the unimpeded flowrate.
Open the tube only after the pump has been switched off, in order to avoid sudden pressure surges.
Leaks around the filter can also occur if the filter is inadequately sealed on the low-pressure side, or if
the filter has been damaged. Observation of a lower differential pressure at the start of the air sampling
indicates that a serious leak exists. If, after sampling, particulate deposits are observed around the
edge of the backing filter or on the unexposed edges of the sampling filter, a leak around the filter has
occurred and the sample shall be rejected.
When sampling is to be commenced, start the pump and the timer simultaneously.
Within 2 min of the start of sampling, adjust the volume flowrate to approximately 2 l/min per square
centimetre of effective filter area (this value shall not vary by more than ±10 % for the period of
sampling). This corresponds to a filter loading of 1 000 l per square centimetre of effective filter area
over a sampling period of approximately 8 h. Sampling in an environment with high dust concentrations
in the air, the loading of particulate material on the sample collection filter can be too high for adequate
analysis after 8 h sampling. In such cases, it is permissible to use a shorter sampling time.
At the end of the sampling period, switch off the sampling apparatus. If a programmer was used, confirm
that the sampler operated within the required parameters for the preset sampling period. Taking care
not to disturb the particulate deposits on the filter surface, remove the sample collection filter and
store it upright in a dust-tight sample container.
Record all sampling data which can be of significance for later interpretation. An example of a form for
recording of air sampling data is shown in Figure 4. The location of the sampling apparatus shall be
documented in the form of a sketch and, if possible, a photograph.
10 © ISO 2019 – All rights reserved

In fog, a thick coating (including calcium sulfate fibres) on the sampling filter can occur, resulting in a
rapid increase in the pressure differential across the filter. Under these conditions, it will be necessary
to take several sequential samples, each collected over a shorter sampling time, in order to obtain filters
suitable for analysis. Annex E shows the procedure for calculation of a mean value from the results of
several sequential short-term samples.
Figure 4 — Example of a sampling log form for recording of sampling data
12 © ISO 2019 – All rights reserved

7.3 SEM specimen preparation
Before sample analysis, examine the uniformity of the particulate depos
...

INTERNATIONAL ISO
STANDARD 14966
Second edition
2019-12
Ambient air — Determination of
numerical concentration of inorganic
fibrous particles — Scanning electron
microscopy method
Air ambiant — Détermination de la concentration en nombre des
particules inorganiques fibreuses — Méthode par microscopie
électronique à balayage
Reference number
©
ISO 2019
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 4
5 Principle . 4
6 Apparatus and materials. 4
6.1 Air sampling . 4
6.1.1 Sampling head . 4
6.1.2 Sampling train . 5
6.1.3 Sampling pump . 5
6.1.4 Needle valve . 6
6.1.5 Volumetric flowmeter (rotameter) . 6
6.1.6 Timer . 6
6.1.7 Dry type gas meter (optional) . 6
6.1.8 Meteorological instruments (optional) . 6
6.1.9 Instruments for unattended sampling (optional) . 7
6.2 Preparation of filters . 7
6.2.1 Vacuum evaporator . . 7
6.2.2 Plasma asher . 8
6.3 Sample analysis . 8
6.3.1 Scanning electron microscope (SEM) . 8
6.3.2 Energy-dispersive X-ray system . 8
6.3.3 Stereo-microscope . . 9
6.3.4 Gold-coated capillary-pore polycarbonate filters. 9
6.3.5 Backing filters . 9
6.3.6 Disposable plastic field monitors (optional) . 9
6.3.7 Technically pure oxygen . 9
6.3.8 Rubber connecting hoses . 9
6.3.9 Filter containers . 9
6.3.10 Routine electron microscopy tools and supplies . 9
6.3.11 Sample for resolution adjustment . 9
6.3.12 Sample for magnification calibration .10
7 Air sample collection and analysis .10
7.1 Measurement planning .10
7.2 Collection of air samples .10
7.3 SEM specimen preparation .13
7.4 Analysis in the scanning electron microscope .13
7.4.1 General instructions.13
7.4.2 Fibre-counting criteria .14
7.4.3 Fibre classification .19
7.4.4 Analysis using reference spectra and peak height ratios .26
7.4.5 Measurement of fibre dimensions .28
7.4.6 Recording of data on the fibre counting form .28
8 Calculation of results .28
8.1 Calculation of the mean fibre concentration .28
8.2 Calculation of the 95 % confidence interval .30
9 Performance characteristics .30
9.1 General .30
9.2 Measurement uncertainty .30
9.2.1 Systematic errors . . .30
9.2.2 Random errors .30
9.2.3 Errors due to sampling .31
9.2.4 Errors associated with the SEM examination .31
9.2.5 Total error of the measurement.31
9.2.6 Random errors due to fibre counting .32
9.3 Limit of detection .34
10 Test report .35
Annex A (normative) Preparation of filters for air sampling .37
Annex B (normative) Procedures for calibration and adjustment of the SEM .38
Annex C (informative) Characteristics and chemical composition of inorganic fibres .40
Annex D (informative) Poisson variability as a function of fibre density on sampling filter
and area of filter analysed .45
Annex E (informative) Combination of the results from multiple samples .47
Bibliography .48
iv © ISO 2019 – All rights reserved

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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 146, Air quality, Subcommittee SC 3,
Ambient atmospheres.
This second edition cancels and replaces the first edition (ISO 14966:2002), which has been technically
revised. It also incorporates the corrected version ISO 14699:2002/Cor 1:2007. The main changes
compared to the previous edition are as follows:
— Counting rules, changed to the recommended method (membrane filter method) of the WHO
(World Health Organization);
— Analytical procedure (classification), using normalized peak height ratios in addition to the method
of the previous edition;
— Rule for early termination of filter evaluation (counting and analysis). A formula is given to terminate
the filter evaluation, if the calculated (asbestos) fibre concentration is above a set limit value for this
fibre concentration.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
Introduction
This document describes a method for measurement of the numerical concentration of inorganic fibrous
[1]
particles in ambient air using the scanning electron microscope. This document is based on VDI 3492 .
The method is also suitable for determining the numerical concentrations of inorganic fibres in the
interior atmospheres of buildings, for example measurement of residual airborne fibre concentrations
after the removal of asbestos-containing building materials.
Biological research has shown that the fibrogenic or carcinogenic effect of a fibre is related to its
length, diameter and its resistance to dissolution in a biological environment. The point at which
fibres are too short, too thick or of insufficient durability to produce a fibrogenic or carcinogenic effect
is uncertain. Fibres with lengths greater than 10 µm and diameters of a few tenths of 1 µm, which
also have durabilities such that they remain unchanged for many years in the body, are regarded as
particularly carcinogenic. Based on current knowledge, fibres shorter than 5 µm are thought to have a
[2]‒[5]
lower carcinogenic potential .
For the purposes of this document, a fibre is defined as a particle which has a minimum length to width
(aspect) ratio of 3:1. Fibres with lengths greater than 5 µm and widths extending from the lower limit of
visibility up to 3 µm are counted. Fibres with diameters less than 3 µm are considered to be respirable.
Since the method requires recording the lengths and widths of all fibres, the data can be re-evaluated if
[6]
it is required to derive concentrations for fibres with a higher minimum aspect ratio .
The range of concentration to be measured extends from that found in clean air environments, in which
the mean value of a large number of individual measurements of asbestos fibre concentrations has
been found to be generally lower than 100 fibres/m (fibres longer than 5 µm), up to higher exposure
[4][6]
scenarios in which concentrations as much as two orders of magnitude higher have been found .
This method is used to measure the numerical concentration of inorganic fibres with widths smaller
than 3 µm and lengths exceeding 5 µm up to a maximum of 100 µm. Using energy-dispersive X-ray
analysis (EDXA), fibres are classified as fibres with compositions consistent with those of asbestos
fibres, calcium sulfate fibres and other inorganic fibres.
Calcium sulfate fibres are separated from other inorganic fibres and are not included in the final result,
because on the basis of current knowledge, they do not represent any health hazard. Nevertheless, the
numerical concentration of calcium sulfate fibres should be determined, since a high concentration of
these fibres can negatively bias the results for probable asbestos fibres, and in some circumstances the
[7]
sample may have to be rejected . In addition, knowledge of the numerical concentration of calcium
sulfate fibres is of importance in the interpretation of fibre concentrations in ambient atmospheres.
Detection and identification of fibres becomes progressively more uncertain as the fibre width is
reduced below 0,2 µm. Identification of a fibre as a specific species is more confident if the source of
emission is known or suspected, such as in a building for which bulk materials are available for analysis.
In order to facilitate the scanning electron microscope examination, organic particles collected on the
filter are almost completely removed by a plasma ashing treatment.
Except in situations where fibre identification is difficult, there should be only minor differences
between fibre counting results obtained by this method and those obtained using the procedures for
determination of PCM-equivalent fibres in Annex E of the transmission electron microscopy method
[8]
ISO 10312 .
vi © ISO 2019 – All rights reserved

INTERNATIONAL STANDARD ISO 14966:2019(E)
Ambient air — Determination of numerical concentration
of inorganic fibrous particles — Scanning electron
microscopy method
1 Scope
This document specifies a method using scanning electron microscopy for determination of the
concentration of inorganic fibrous particles in the air. The method specifies the use of gold-coated,
capillary-pore, track-etched membrane filters, through which a known volume of air has been drawn.
Using energy-dispersive X-ray analysis, the method can discriminate between fibres with compositions
consistent with those of the asbestos varieties (e.g. serpentine and amphibole), gypsum, and other
inorganic fibres. Annex C provides a summary of fibre types which can be measured.
This document is applicable to the measurement of the concentrations of inorganic fibrous particles in
ambient air. The method is also applicable for determining the numerical concentrations of inorganic
fibrous particles in the interior atmospheres of buildings, for example to determine the concentration
of airborne inorganic fibrous particles remaining after the removal of asbestos-containing products.
The range of concentrations for fibres with lengths greater than 5 µm, in the range of widths which can
be detected under standard measurement conditions (see 7.2), is approximately 3 fibres to 200 fibres
per square millimetre of filter area. The air concentrations, in fibres per cubic metre, represented by
these values are a function of the volume of air sampled.
The ability of the method to detect and classify fibres with widths lower than 0,2 µm is limited. If
airborne fibres in the atmosphere being sampled are predominantly <0,2 µm in width, a transmission
[8]
electron microscopy method such as ISO 10312 can be used to determine the smaller fibres.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
acicular
shape shown by an extremely slender crystal with cross-sectional dimensions which are small relative
to its length, i.e. needle-like
3.2
amphibole
any of a group of rock-forming double-chain 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 = K, Na;
2+
B = Fe , Mn, Mg, Ca, Na;
3+ 2+
C = Al, Cr, Ti, Fe , Mg, Fe ;
3+
T = Si, Al, Cr, Fe , Ti
Note 1 to entry: 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°.
3.3
amphibole asbestos
amphibole (3.2) in an asbestiform (3.5) habit (3.17)
3.4
analytical sensitivity
calculated airborne fibre (3.13) concentration equivalent to counting one fibre in the analysis
Note 1 to entry: The analytical sensitivity is expressed in fibres per cubic metre.
Note 2 to entry: This method does not specify a unique analytical sensitivity. The analytical sensitivity is
determined by the needs of the measurement and the conditions found on the prepared sample.
3.5
asbestiform
specific type of mineral fibrosity in which the fibres (3.13) and fibrils possess high tensile strength and
flexibility
3.6
asbestos
any of a group of silicate minerals belonging to the serpentine and amphibole fibres (3.2) groups which
have crystallized in the asbestiform (3.5) habit (3.17), causing them to be easily separated into long,
thin, flexible, strong fibres (3.13) when crushed or processed
Note 1 to entry: 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).
3.7
aspect ratio
ratio of length of a particle to its width
3.8
chrysotile
fibrous variety of the mineral serpentine, which has the nominal composition:
Mg Si O (OH)
3 2 5 4
Note 1 to entry: Most natural chrysotile deviates little from this nominal composition. In some varieties of
3+ 2+ 3+
chrysotile, minor substitution of silicon by Al + can occur. Minor substitution of magnesium by Al , Fe , Fe ,
2+ 2+ 2+
Ni , Mn and Co can also be present. Chrysotile is the most prevalent type of asbestos.
3.9
cleavage
breaking of a mineral along one of its crystallographic directions
2 © ISO 2019 – All rights reserved

3.10
cluster
fibrous structure in which two or more fibres (3.13), or fibre bundles (3.14) are randomly oriented in a
connected grouping
3.11
countable fibre
any object longer than 5 µm, having a maximum width less than 3 µm and a minimum aspect ratio of 3:1
3.12
energy-dispersive X-ray analysis
measurement of the energies and intensities of X-rays by use of a solid-state detector and multi-channel
analyser system
3.13
fibre
elongated particle which has parallel or stepped sides and a minimum aspect ratio of 3:1
3.14
fibre bundle
structure composed of apparently attached, parallel fibres (3.13)
Note 1 to entry: A fibre bundle can exhibit diverging fibres at one or both ends. The length is defined as equal
to the maximum length of the structure, and the diameter is defined as equal to the maximum width in the
compact region.
3.15
fibril
single fibre (3.13) of asbestos which cannot be further separated longitudinally into smaller components
without losing its fibrous properties or appearances
3.16
fibrous structure
fibre (3.13), or connected grouping of fibres, with or without other particles
3.17
habit
the characteristic crystal growth form or combination of these forms of a mineral, including
characteristic irregularities
3.18
image field
the area on the filter sample which is shown on the screen
3.19
limit of detection
calculated airborne fibre (3.13) concentration equivalent to the upper 95 % confidence limit of 2,99
fibres predicted by the Poisson distribution for a count of zero fibres
Note 1 to entry: The limit of detection is expressed in fibres per cubic metre.
3.20
magnification
ratio of the size of the image of an object on the observation screen to the actual size of the object
Note 1 to entry: For the purposes of this document, magnification values always refer to that applicable to the
observation screen.
3.21
matrix
structure in which one or more fibres (3.13) or fibre bundles (3.14) touch, are attached to, or partially
concealed by a single particle or connected group of non-fibrous particle
3.22
serpentine
any of a group of common rock-forming minerals having the nominal formula:
Mg Si O (OH)
3 2 5 4
3.23
split fibre
agglomeration of fibres (3.13) which, at one or several points along its length, appears to be compact
and undivided, whilst at other points appears to separate into separate fibres
3.24
structure
single fibre (3.13), fibre bundle (3.14), cluster (3.10)or matrix
4 Abbreviated terms
EDXA Energy-dispersive X-ray analysis
FWHM Full width, half maximum
PTFE Polytetrafluoroethylene
SEM Scanning electron microscope
5 Principle
A sample of airborne particulate is collected by drawing a measured volume of air through a gold-
coated, capillary pore track-etched membrane filter with a maximum nominal pore size of 0,8 µm,
which is subsequently examined in the scanning electron microscope (SEM). Before analysis, the gold-
coated filter is treated in a plasma asher to remove organic particles, to the extent that this is possible.
The individual fibrous particles and constituent fibres in a randomly-selected area of the filter are
then counted at a magnification of approximately 2 000×. If a fibre is detected at the magnification of
approximately 2 000×, it is examined at a higher magnification of approximately 10 000× to measure
its dimensions. At the higher magnification of approximately 10 000×, energy-dispersive X-ray analysis
(EDXA) is used to classify the fibre according to the chemical composition.
The limit of detection for this method is defined as the numerical fibre concentration below which, with
95 % confidence, the actual concentration lies when no fibres are found during the SEM examination.
The limit of detection theoretically can be lowered indefinitely by filtration of progressively larger
volumes of air and by examination of a larger area of the specimen in the SEM. In practice, the lowest
achievable limit of detection for a particular area of SEM specimen examined is controlled by the total
suspended particulate concentration remaining after the plasma ashing step.
3 3
A limit of detection of approximately 300 fibres/m is obtained if an air volume of 1 m per square
centimetre of filter surface area passes through the filter, and an area of 1 mm of the filter area is
examined in the SEM. This corresponds to an evaluated sample air volume of 0,01 m .
6 Apparatus and materials
6.1 Air sampling
6.1.1 Sampling head
A disposable, 3-piece, conductive plastic field monitor cassette may be used as the sampling head,
provided that the design is such that significant leakage around the filter does not occur. A re-usable
4 © ISO 2019 – All rights reserved

unit may also be used as the sampling head, consisting of a cylindrical cowl and a filter holder with
backing filter. Figure 1 shows an example of a suitable sampling head. The cowl and the filter holder
should be made from a corrosion-resistant material. The filter shall be clamped in such a manner that
significant leaks around the filter do not occur at differential pressures up to approximately 50 kPa
as described in B.4. The length of the cowl should be 0,5 to 2,5 times the effective filter diameter (the
diameter of the exposed circular filter area through which the air is drawn). If it is possible that wind
velocities greater than 5 m/s could occur during sampling, use a long cowl with a ratio of length to
effective diameter of 2,5.
6.1.2 Sampling train
Figure 2 shows an example of a suitable sampling train. Control of the volumetric flowrate can be
achieved either by the use of a throttle valve (3) or a volumetric flow controller (8) in conjunction with
a regulator valve (4).
6.1.3 Sampling pump
Pulse-free or pulsation-damped, capable of maintaining, at a pressure differential across the filter of at
least 50 kPa, a volumetric flow of between 8 l/min and 30 l/min, depending on the diameter of filter used.
In order to achieve the required analytical sensitivity, a flowrate of 8 l/min is required if a 25 mm
diameter filter is used. This flowrate is equivalent to a filter face velocity of approximately 35 cm/s.
The sampling pump shall be capable of maintaining the intended flowrate within ±10 % throughout the
whole sampling period.
Key
1 cowl 6 suction hose
2 filter holder 7 clamping roller
3 backing filter 8 clamping ring
4 track-etched membrane filter 9 PTFE gaskets
5 supporting mesh
Figure 1 — Example of design of sampling head
6.1.4 Needle valve
With a fine adjustment mechanism, for setting the volumetric flowrate.
6.1.5 Volumetric flowmeter (rotameter)
For measuring the volumetric flowrate.
6.1.6 Timer
For measuring the sampling time.
6.1.7 Dry type gas meter (optional)
For volumetric measurement, calibrated, designed for a maximum volumetric flowrate of 2 m /h.
6.1.8 Meteorological instruments (optional)
For recording of meteorological conditions during sampling. Instruments such as a thermometer, a
hygrometer, a barometer and a wind speed and direction recorder will be required.
6 © ISO 2019 – All rights reserved

6.1.9 Instruments for unattended sampling (optional)
For unattended sampling, a volumetric flow controller is required for regulation of the flowrate
to within ±10 % of the nominal rate, with an automatic switch to turn off the sampling pump if the
flowrate exceeds or falls below the pre-set tolerance band. The flow controller can be integrated into
the suction unit.
A programmable switch is required for pre-setting the air sampling cycle. A pressure gauge which
incorporates a switching contact is required to switch off the sampling pump if the pressure differential
across the sampling filter increases to a pre-set value.
Key
1 sampling head or cassette 8 volumetric flow controller (optional)
2 pressure gauge 9 sampling-time recorder (optional)
3 throttle valve (optional) 10 programmer (optional)
4 regulator valve (optional) 11 timer
5 pump 12 thermometer (optional)
6 variable-area flowmeter 13 barometer (optional)
7 gas meter (optional) with thermometer 14 hygrometer (optional)
Figure 2 — Example of a suitable sampling train
6.2 Preparation of filters
6.2.1 Vacuum evaporator
Capable of producing a vacuum better than 0,013 Pa.
A vacuum coating unit is required for vacuum deposition of gold onto the capillary-pore membrane
filters, and for carbon coating of SEM specimens if the particulate loading is such that excessive
charging of the specimen occurs.
A sputter coating unit has also been found to meet the requirements for gold coating of the capillary-
pore filters.
6.2.2 Plasma asher
Supplied with oxygen, to oxidize organic particles on the SEM specimen.
An example of the configuration of a suitable plasma asher is shown in Figure 3. The chamber of the
plasma asher may be coupled either capacitatively or inductively. Care shall be taken not to damage the
specimen during the plasma ashing process. A calibration procedure to determine suitable operating
conditions for the plasma asher is described in B.3.
Key
1 bell jar 5 connection for vacuum pump
2 filter in mounting ring 6 air inlet
3 oxygen inlet 7 cooling-water inlet
4 power supply from plasma generator 8 cooling-water outlet
Figure 3 — Example of a configuration of a plasma asher
6.3 Sample analysis
6.3.1 Scanning electron microscope (SEM)
With an accelerating voltage of at least 15 kV, is required for fibre counting and identification.
6.3.2 Energy-dispersive X-ray system
For the SEM, capable of achieving a resolution better than 140 eV (FWHM) on the MnK peak.
α
The performance of an individual combination of SEM and solid-state X-ray detector is dependent on a
number of geometrical factors. Accordingly, the required performance of the combination of the SEM
and X-ray analyser is specified in terms of the measured X-ray intensity obtained from a chrysotile fibre
of width 0,2 µm, under the operating conditions used during the analysis. Solid-state X-ray detectors
are least sensitive in the low energy region, and so detection of sodium in crocidolite is an additional
performance criterion.
The instrumental combination shall satisfy the minimum requirements with regard to the visibility of
fibres, as specified in 7.4.1, and identification of the fibres, as specified in 7.4.3.
8 © ISO 2019 – All rights reserved

6.3.3 Stereo-microscope
With a magnification of approximately 20×, for visual examination of the particulate deposit on the filter.
6.3.4 Gold-coated capillary-pore polycarbonate filters
Maximum nominal pore size 0,8 µm, for collection of air samples. The gold coating shall be approximately
30 nm thick applied to the shiny side of the filter. The procedure for preparation of the gold-coated
filters is described in Annex A.
NOTE Optionally, a 20 nm thick layer of gold can be evaporated on to the reverse side of the filter. This coating
serves to protect the filter during plasma ashing and can help to improve the contrast of fibres in the SEM image.
6.3.5 Backing filters
Cellulose ester membrane, or absorbent pads, with a porosity of approximately 5 µm to be used as
diffusing filters behind the sample collection filters.
6.3.6 Disposable plastic field monitors (optional)
If disposable plastic field monitors are used, they shall consist of 25 mm to 50 mm diameter, three-piece
cassettes, which conform to the requirements of 6.1.1. The cassette shall be loaded with a gold-coated,
capillary-pore polycarbonate filter of maximum nominal pore size 0,8 µm, backed by a cellulose ester
filter of 5 µm porosity or an absorbent pad. Suitable precautions shall be taken to ensure that the filters
are tightly clamped in the assembly so that significant air leakage around the filter cannot occur.
Re-use of disposable plastic field monitors is not recommended.
6.3.7 Technically pure oxygen
For operation of the plasma asher.
6.3.8 Rubber connecting hoses
For connecting the sampling head to the pump, and other equipment in the sampling train.
The hose shall have a wall thickness such that it does not collapse under a vacuum of 50 kPa. Silicone
rubber hose has been found to meet the requirements.
6.3.9 Filter containers
For transport and storage of filters if disposable field monitors are not used.
6.3.10 Routine electron microscopy tools and supplies
Fine point tweezers, scalpel holders and blades, double-coated adhesive tape, SEM specimen stubs
and colloidal carbon paint and other routine supplies are required. If a vacuum evaporator is used
for preparation of gold-coated filters, gold wire and tungsten filaments are required. For carbon
evaporation, spectroscopically pure carbon rods and a means of sharpening the rods is required.
6.3.11 Sample for resolution adjustment
A gold-coated polycarbonate filter, on which chrysotile fibres with a width of ≥0,2 µm have been
deposited, is required for adjustment of the operating conditions of the SEM.
6.3.12 Sample for magnification calibration
A test sample is required to calibrate the magnification of the SEM. The magnification standard
SRM484e (U.S. National Institute of Standards and Technology) is an example of a sample which meets
the requirement.
7 Air sample collection and analysis
7.1 Measurement planning
When determining the spatial and temporal scope of the measurements, it is important to take into
consideration the special aspects of the situation. It is therefore essential to define the objective of
the measurements before samples are collected. Any available information on emission sources,
meteorological conditions and the local situation should be taken into account in order to obtain the
maximum information from the measurements. The number of individual measurements to be made
should be selected according to the particular task. In particular, prior to collection of the samples,
the required accuracy for the mean concentration of the inorganic fibres should be specified, since the
error of each individual measurement needs to be taken into consideration in determining the number
of samples to be collected. Measurement uncertainty is discussed in Clause 9.
7.2 Collection of air samples
Figure 2 shows an example of a sampling train. Position the sampling head approximately 1,5 m above
ground level.
If a re-usable sampling head is used, place a 5 µm porosity cellulose ester backing filter on to the filter
support in the sampling head. Place a gold-coated filter on top of the backing filter, with the shiny side
facing into the direction of the airflow. Clamp the filters in the sampling head so that the gold-coated
filter lies flush against the backing filter and is tightly fitted. Ensure that damage does not occur to the
filter during clamping, and that the filter is not twisted.
Before air sampling is commenced, perform a brief test with the tube to the sampling head closed, to
determine if any leaks exist in the complete sampling system. Under the conditions of this test, the
flowrate indicated by the volumetric flowmeter shall be less than 10 % of the unimpeded flowrate.
Open the tube only after the pump has been switched off, in order to avoid sudden pressure surges.
Leaks around the filter can also occur if the filter is inadequately sealed on the low-pressure side, or if
the filter has been damaged. Observation of a lower differential pressure at the start of the air sampling
indicates that a serious leak exists. If, after sampling, particulate deposits are observed around the
edge of the backing filter or on the unexposed edges of the sampling filter, a leak around the filter has
occurred and the sample shall be rejected.
When sampling is to be commenced, start the pump and the timer simultaneously.
Within 2 min of the start of sampling, adjust the volume flowrate to approximately 2 l/min per square
centimetre of effective filter area (this value shall not vary by more than ±10 % for the period of
sampling). This corresponds to a filter loading of 1 000 l per square centimetre of effective filter area
over a sampling period of approximately 8 h. Sampling in an environment with high dust concentrations
in the air, the loading of particulate material on the sample collection filter can be too high for adequate
analysis after 8 h sampling. In such cases, it is permissible to use a shorter sampling time.
At the end of the sampling period, switch off the sampling apparatus. If a programmer was used, confirm
that the sampler operated within the required parameters for the preset sampling period. Taking care
not to disturb the particulate deposits on the filter surface, remove the sample collection filter and
store it upright in a dust-tight sample container.
Record all sampling data which can be of significance for later interpretation. An example of a form for
recording of air sampling data is shown in Figure 4. The location of the sampling apparatus shall be
documented in the form of a sketch and, if possible, a photograph.
10 © ISO 2019 – All rights reserved

In fog, a thick coating (including calcium sulfate fibres) on the sampling filter can occur, resulting in a
rapid increase in the pressure differential across the filter. Under these conditions, it will be necessary
to take several sequential samples, each collected over a shorter sampling time, in order to obtain filters
suitable for analysis. Annex E shows the procedure for calculation of a mean value from the results of
several sequential short-term samples.
Figure 4 — Example of a sampling log form for recording of sampling data
12 © ISO 2019 – All rights reserved

7.3 SEM specimen preparation
Before sample analysis, examine the uniformity of the particulate deposit on the filter. If the particulate
deposit shows evidence of non-uniformity, reject the filter.
If the particulate deposit is uniform, place the filter into the holder of the mounting ring, and position
it in the plasma asher, as shown in Figure 3. The plasma ashing treatment removes the majority of
the organic material on the filter, and this considerably facilitates the SEM analysis of the sample.
Adjustment of the plasma asher see Annex B.3.
The rate of oxidation of the organic material on the filter by the oxygen plasma is enhanced by the
electrical conductivity of the filter and the sample holder. Under the specified operating conditions, the
plasma ashing treatment is generally completed after approximately 30 min. After the plasma ashing
treatment, either the whole filter or a part thereof is mounted on an SEM specimen stub, without any
further preparation, for SEM analysis. For adjustment of the plasma asher see Annex B.3.
NOTE 1 The portion of the filter to be analysed can be mounted on the SEM specimen stub either before or
after the plasma ashing treatment.
NOTE 2 Double-sided conductive adhesive tape has been found to be an effective means of mounting the filter.
If, during SEM analysis, fibres are detected which appear to be organic, the
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