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

ISO 14966 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 electron microscopy method such as ISO 10312[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
Public Enquiry End Date
09-Oct-2019
Publication Date
12-Mar-2020
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
17-Feb-2020
Due Date
23-Apr-2020
Completion Date
13-Mar-2020

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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 14966:2019(E)
ISO 2019
---------------------- Page: 1 ----------------------
ISO 14966:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© 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: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 14966:2019(E)
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

© ISO 2019 – All rights reserved iii
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ISO 14966:2019(E)

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
---------------------- Page: 4 ----------------------
ISO 14966:2019(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.

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.
© ISO 2019 – All rights reserved v
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ISO 14966:2019(E)
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
---------------------- Page: 6 ----------------------
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
© ISO 2019 – All rights reserved 1
---------------------- Page: 7 ----------------------
ISO 14966:2019(E)
A = K, Na;
B = Fe , Mn, Mg, Ca, Na;
3+ 2+
C = Al, Cr, Ti, Fe , Mg, Fe ;
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
---------------------- Page: 8 ----------------------
ISO 14966:2019(E)
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
© ISO 2019 – All rights reserved 3
---------------------- Page: 9 ----------------------
ISO 14966:2019(E)
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
---------------------- Page: 10 ----------------------
ISO 14966:2019(E)
unit may also be used as the
...

SLOVENSKI STANDARD
SIST ISO 14966:2020
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
SIST ISO 14966:2020 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST ISO 14966:2020
---------------------- Page: 2 ----------------------
SIST ISO 14966:2020
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 14966:2019(E)
ISO 2019
---------------------- Page: 3 ----------------------
SIST ISO 14966:2020
ISO 14966:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© 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: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
---------------------- Page: 4 ----------------------
SIST ISO 14966:2020
ISO 14966:2019(E)
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

© ISO 2019 – All rights reserved iii
---------------------- Page: 5 ----------------------
SIST ISO 14966:2020
ISO 14966:2019(E)

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

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SIST ISO 14966:2020
ISO 14966:2019(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.

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.
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SIST ISO 14966:2020
ISO 14966:2019(E)
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 .
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SIST ISO 14966:2020
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
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ISO 14966:2019(E)
A = K, Na;
B = Fe , Mn, Mg, Ca, Na;
3+ 2+
C = Al, Cr, Ti, Fe , Mg, Fe ;
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
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ISO 14966:2019(E)
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
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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 examinat

...

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