ISO 20552:2007

Workplace air - Determination of mercury vapour - Method using gold-amalgam collection and analysis by atomic absorption spectrometry or atomic fluorescence spectrometry

ISO 20552:2007 specifies a procedure for determination of the mass concentration of mercury vapour in workplace air using a method of gold-amalgam collection with analysis by either cold vapour atomic absorption spectrometry (CVAAS) or cold vapour atomic fluorescence spectrometry (CVAFS). The procedure specifies a number of sampling methods for different applications. The procedure is suitable for making short-term measurements (e.g. 15 min) when sampling at a flow rate of between 100 ml per min and 1 000 ml per min. For assessment of long-term exposure, such as 8 h, this procedure can be used with sampling flow rate of 100 ml per min in workplaces where the concentration of mercury vapour is expected to be lower than 20 micrograms per cubic metre. If the expected concentration of mercury vapour is higher than 20 micrograms per cubic metre, it is necessary to use the procedure prescribed in ISO 17733. ISO 20552:2007 is unsuitable for making measurements of mercury vapour in air when chlorine is present in the atmosphere, e.g. in chloralkali works. Gaseous organo-mercury compounds can cause a positive interference.

Air des lieux de travail — Détermination de la vapeur de mercure — Méthode combinant un prélèvement par amalgamation à l'or et une détection par spectrométrie d'absorption atomique ou par spectrométrie de fluorescence atomique

General Information

• Status: Published
• Publication Date: 05-Feb-2007
• ICS: 13.040.30 - Workplace atmospheres
• Technical Committee: ISO/TC 146/SC 2 - Workplace atmospheres
• Drafting Committee: ISO/TC 146/SC 2/WG 2 - Inorganic particulate matter
• Current Stage: 9093 - International Standard confirmed
• Start Date: 12-Sep-2022
• Completion Date: 13-Dec-2025

Overview

ISO 20552:2007 specifies a validated laboratory and field procedure for determination of mercury vapour in workplace air using gold‑amalgam collection on sorbent tubes followed by instrumental analysis by either cold‑vapour atomic absorption spectrometry (CVAAS) or cold‑vapour atomic fluorescence spectrometry (CVAFS). The method covers static (area) and short‑term personal sampling and defines sampling rates, sorbent materials and analytical performance characteristics for occupational exposure assessment and mercury monitoring.

Key topics and technical requirements

• Sampling medium: pumped sorbent tubes containing porous gold‑coated diatomaceous earth (gold‑amalgam collection).
• Particle removal: optional quartz‑fibre prefilter when particulate inorganic mercury may be present.
• Analysis: CVAAS or CVAFS of the desorbed mercury from sorbent tubes.
• Sampling flow rates: recommended 100–1 000 ml·min‑1 for short‑term measurements (e.g., 15 min). For long‑term (8 h) sampling, use 100 ml·min‑1 where concentrations are expected < 20 µg·m‑3.
• Working range & limits: analytical lower limit ~0.01 ng Hg per 80 mg sorbent; upper analytical range ~1 µg Hg; typical sorbent tube capacity >2 µg.
• Interferences & limitations: unsuitable in atmospheres containing chlorine (e.g., chlor‑alkali plants); gaseous organo‑mercury compounds can cause positive interference.
• Performance/quality control: guidance on detection/quantification limits, blanks, bias and precision, storage stability, breakthrough volume, collection efficiency and transport of samples.
• Sampling types: static (area) sampling and personal sampling in the breathing zone.

Applications

• Routine occupational exposure monitoring for elemental mercury vapour in industrial settings.
• Short‑term task‑based assessments (e.g., 15‑minute exposure peaks) and limited long‑term (8‑hour) monitoring where concentrations are low.
• Verification of engineering controls, ventilation effectiveness and worker protection measures.
• Analytical laboratories performing mercury analysis using CVAAS/CVAFS and industrial hygienists conducting field sampling.

Who should use ISO 20552:2007

• Industrial hygienists and occupational health professionals
• Environmental and analytical laboratories performing mercury vapour analysis
• Safety and compliance officers in industries using mercury or mercury compounds
• Regulatory agencies and consultants involved in workplace air quality and mercury monitoring

Related standards

• ISO 17733 - recommended when expected mercury vapour concentrations exceed 20 µg·m‑3 or when particulate inorganic mercury is a primary concern.

Keywords: ISO 20552:2007, mercury vapour, workplace air, gold‑amalgam, CVAAS, CVAFS, sorbent tube, occupational exposure, mercury monitoring, industrial hygiene.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 20552
First edition
2007-02-15
Workplace air — Determination of
mercury vapour — Method using gold-
amalgam collection and analysis by
atomic absorption spectrometry or atomic
fluorescence spectrometry
Air des lieux de travail — Détermination de la vapeur de mercure —
Méthode combinant un prélèvement par amalgamation à l'or et une
détection par spectrométrie d'absorption atomique ou par spectrométrie
de fluorescence atomique
Reference number
©
ISO 2007
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©
ii ISO 2007 – All rights reserved

Contents Page
1 Scope . 1
2 Normative references . 2
3 Terms and definitions . 2
4 Principle . 4
5 Reactions . 4
6 Requirement . 5
7 Reagents . 5
8 Apparatus . 5
8.1 Sampling equipment . 5
8.2 Analytical instrumentation . 7
9 Occupational exposure assessment . 7
9.1 General . 7
9.2 Static (area) sampling . 7
9.3 Personal sampling . 7
9.4 Selection of measurement conditions and measurement pattern . 7
10 Sampling . 9
10.1 Preliminary considerations . 9
10.2 Preparation for sampling . 10
10.3 Sampling position . 11
10.4 Collection of samples . 11
10.5 Transportation of samples . 12
11 Analysis . 12
12 Expression of results . 13
12.1 Calculation of the air sample volumes . 13
12.2 Calculation of airborne mercury concentrations . 13
13 Method performance . 13
13.1 Detection and quantification limits . 13
13.2 Upper limits of the analytical range . 14
13.3 Blank values . 14
13.4 Bias and precision . 14
13.5 Effects on sampler performance . 14
13.6 Collection efficiency, breakthrough volume and sampling capacity of sorbent tubes . 14
13.7 Storage stability . 15
13.8 Interferences . 15
14 Test report . 15
Annex A (informative) Temperature and pressure correction . 17
Annex B (informative) Figures . 19
Bibliography . 23
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ISO 2007 – All rights reserved iii

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International
Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 20552 was prepared by Technical Committee ISO/TC 146, Air quality, Subcommittee SC 2, Workplace
atmospheres.
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iv ISO 2007 – All rights reserved

Introduction
The health of workers in many industries is at risk through exposure by inhalation of mercury and inorganic
mercury compounds. Industrial hygienists and other public health professionals need to determine the
effectiveness of measures taken to control workers' exposure, and this is generally achieved by making
workplace air measurements. This International Standard has been published in order to make available a
method for making measurements of mercury vapour in the workplace environment, i.e. by static sampling. It is
also of use for making short-term personal exposure measurements. The standard will be of benefit to:
agencies concerned with health and safety at work; industrial hygienists and other public health professionals;
analytical laboratories; industrial users of mercury and inorganic mercury compounds and their workers, etc.
[1][2][3][4][5][6]
The procedure described in this International Standard is based upon several published papers
that describe methodology for the determination of mercury vapour in air. This procedure has been fully
validated and the resulting back-up data are presented in this standard.
It has been assumed in the drafting of this International Standard that the execution of its provisions and the
interpretation of the results obtained, is entrusted to appropriately qualified and experienced people.
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ISO 2007 – All rights reserved v

INTERNATIONAL STANDARD ISO 20552:2007(E)
Workplace air — Determination of mercury vapour — Method
using gold-amalgam collection and analysis by atomic
absorption spectrometry or atomic fluorescence spectrometry
1Scope
This International Standard specifies a procedure for determination of the mass concentration of mercury
vapour in workplace air using a method of gold-amalgam collection with analysis by either cold vapour atomic
absorption spectrometry (CVAAS) or cold vapour atomic fluorescence spectrometry (CVAFS).
The procedure specifies a number of sampling methods for different applications.
a) When it is known that no particulate inorganic mercury compounds are used in the workplace and that none
are produced in the processes carried out, samples of mercury vapour are collected using a pumped
sorbent tube containing porous gold-coated diatomaceous earth. Suitable sorbent tubes are commercially
available or they can be made from sorbent prepared by pyro-decomposition of chloroauric acid [hydrogen
tetrachloroaurate(III)] sintered on diatomaceous earth.
b) When both mercury vapour and particulate inorganic mercury compounds could be present in the test
atmosphere, samples of mercury vapour are collected using a pumped sorbent tube fitted with a quartz fibre
prefilter to remove particulate inorganic mercury compounds. If desired, the procedure described in
ISO 17733 can be used to collect and analyse separate samples for measurement of particulate inorganic
mercury compounds.
c) When it is known that no elemental mercury is used in the workplace and that no mercury vapour is
produced in the processes carried out, the procedure described in ISO 17733 can be used, if desired, to
collect and analyse samples for measurement of particulate inorganic mercury compounds.
The procedure is highly sensitive and suitable for static sampling or for determination of short-term personal
exposure to mercury vapour in workplace air. The lower limit of the working range of the procedure is governed
by the lower limit of the analytical range of the CVAAS or CVAFS instrument, which is approximately 0,01 ng of
mercury for a sorbent tube containing 80 mg of sorbent (see 13.1). The upper limit of the working range of the
procedure is governed by the upper limit of the analytical range of the CVAAS or CVAFS instrument, e.g. about
1µg of mercury (see 13.2). The sampling capacity of one commercially available sorbent tube has been shown
to be greater than 2µg. The concentration ranges of mercury in air for which the procedure is applicable are
determined in part by the sampling method selected by the user.
The procedure is suitable for making short-term measurements (e.g. 15 min) when sampling at a flow rate of
−1 −1
between 100 ml min and 1 000 ml min using a commercially available sorbent tube. For assessment of
−1
long-term exposure, such as 8h, this procedure can be used with sampling flow rate of 100 ml min in
−3
workplaces where the concentration of mercury vapour is expected to be lower than 20µgm . If the expected
−3
concentration of mercury vapour is higher than 20µgm , it is necessary to use the procedure prescribed in
ISO 17733.
The method is unsuitable for making measurements of mercury vapour in air when chlorine is present in the
atmosphere, e.g. in chloralkali works (see 13.8.1). Gaseous organo-mercury compounds can cause a positive
interference (see 13.8.2).
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ISO 2007 – All rights reserved 1

2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced document
(including any amendments) applies.
ISO 17733, Workplace air — Determination of mercury and inorganic mercury compounds — Method by cold-
vapour atomic absorption spectrometry or atomic fluorescence spectrometry
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1 General definitions
3.1.1
chemical agent
any chemical element or compound, on its own or admixed as it occurs in the natural state or as produced by
any work activity, whether or not produced intentionally and whether or not placed on the market
[7]
[EN 1540:1998]
3.1.2
breathing zone
〈general definition〉 space around the worker's face from where he or she takes his or her breath
3.1.3
breathing zone
〈technical definition〉 hemisphere (generally accepted to be 0,3 m in radius) extending in front of the human face,
centred on the mid-point of a line joining the ears; the base of the hemisphere is a plane through this line, the
top of the head and the larynx
NOTE 1 The definition is not applicable when respiratory protective equipment is used.
[7]
NOTE 2 Adapted from EN 1540 .
3.1.4
exposure (by inhalation)
situation in which a chemical agent is present in air, which is inhaled by a person
3.1.5
measuring procedure
procedure for sampling and analysing one or more chemical agents in the air, and including storage and
transportation of the sample
3.1.6
operating time
period during which a sampling pump can be operated at specified flow rate and back pressure without
recharging or replacing the battery
[8]
[EN 1232:1997]
3.1.7
limit value
reference figure for concentration of a chemical agent in air
�
NOTE An example is the Threshold Limit Value (TLV) for a given substance in workplace air, as established by the
[9] �
ACGIH . (Threshold Limit Value is an example of a suitable product available commercially. This information is given for
the convenience of users of this International Standard and does not constitute an endorsement by ISO of this product.)
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3.1.8
reference period
specified period of time stated for the limit value of a specific chemical agent
NOTE Examples of limit values for different reference periods are short-term and long-term exposure limits, such as those
[9]
established by the ACGIH .
3.1.9
workplace
defined area or areas in which the work activities are carried out
[7]
[EN 1540:1998]
3.2 Sampling definitions
3.2.1
personal sampler
device attached to a person that samples air in the breathing zone
[7]
[EN 1540:1998]
3.2.2
personal sampling
process of sampling carried out using a personal sampler
[7]
[EN 1540:1998]
3.2.3
sampling instrument
sampler
device for collecting airborne particles or gaseous materials (vapour), or both
3.2.4
sorbent tube, pumped
tube, usually made of metal or glass, containing an active sorbent or reagent-impregnated support, through
which sampled atmosphere is passed at a rate controlled by an air sampling pump
[10]
[EN 1076:1997]
3.2.5
static sampler
area sampler
device, not attached to a person, that samples air in a particular location
3.2.6
static sampling
area sampling
process of air sampling carried out using a static (area) sampler
3.3 Statistical terms
3.3.1
analytical recovery
ratio of the mass of analyte measured when a sample is analysed, to the known mass of analyte in that sample,
expressed as a percentage
3.3.2
bias
consistent deviation of the results of a measurement process from the true value of the air quality characteristic
itself
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ISO 2007 – All rights reserved 3

3.3.3
precision
closeness of agreement of results obtained by applying the method several times under prescribed conditions
3.3.4
true value
value which characterizes a quantity or quantitative characteristic, perfectly defined in the conditions which exist
when that quantity or quantitative characteristic is considered
NOTE The true value of a quantity or quantitative characteristic is a theoretical concept and, in general, cannot be known
exactly.
[11]
[ISO 3534-2:2006, definition 3.2.5]
3.3.5
uncertainty (of measurement)
parameter associated with the result of a measurement that characterizes the dispersion of the values that
could reasonably be attributed to the measurand
NOTE 1 The parameter may be, for example, a standard deviation (or a given multiple of it), or the width of a confidence
interval.
NOTE 2 Uncertainty of measurement comprises, in general, many components. Some of these components may be
evaluated from the statistical distribution of the results of a series of measurements, and can be characterized by standard
deviations. The other components, which also can be characterized by standard deviations, are evaluated from assumed
probability distributions based on experience or other information. The Guide to the expression of uncertainty in
[12]
measurement (GUM) refers to these different cases as Type A and Type B evaluations of uncertainty, respectively.
[13]
NOTE 3 Adapted from the International vocabulary of basic and general terms in metrology (VIM) .
4Principle
Mercury vapour is collected by drawing a known volume of air through a sorbent tube containing porous gold-
coated diatomaceous earth using a pump. The sorbent tube is preceded by a quartz fibre filter to trap
particulate inorganic mercury compounds when these could be present in the test atmosphere. If desired, the
procedure described in ISO 17733 is used to collect and analyse separate samples for measurement of
particulate inorganic mercury compounds.
The sample tube is transported to the laboratory and installed in a mercury analyser, consisting of a double
gold-amalgam unit, or sample applicator unit, and a CVAAS or CVAFS analyser unit. The sample applicator unit
comprises two heaters, separated by a gas washer, and a charcoal filter. The sample tube used for sampling
◦
mercury vapour is installed in the first heating unit and the temperature is raised to about 300 C. At this
temperature any volatile organic compounds collected with the mercury vapour are driven off, but the mercury
is retained on the sample tube. The released volatile organic compounds pass through a second gold sorbent
◦
tube, which is preheated to 150 C in the other heating unit, before being exhausted through the charcoal filter.
◦
The sample tube is then heated to the vaporisation temperature of mercury (about 700 C) and the mercury
vapour released is trapped on the second gold sorbent tube (a mercury-gold amalgam is formed up to about
◦ ◦
200 C). Finally, the trapping tube is heated to 700 C and the mercury vapour is released into the CVAAS or
CVAFS analyser unit. An important characteristic of double gold-amalgam technique is that the mercury peak is
sharp and stable due to the reproducible analysis conditions that result from repeated use of the same gold trap.
Sample tubes can be reused up to 3 000 times if no damage occurs from exposure to chlorine or ammonia.
[14]
The results may be used for the assessment of workplace exposure to mercury vapour (see EN 689 ).
5 Reactions
The porous gold-coated sorbent used in the method described in this International Standard has been shown to
have a reversible affinity for mercury. The trapped mercury forms an alloy, called an amalgam, from which
mercury vapour is easily released by heating.
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4 ISO 2007 – All rights reserved

NOTE Other amalgam-based mercury sorbents are known, e.g. silver wool and gold wool. However, silver wool has many
problems. It is easily oxidized, has a low sorption capacity and poor collection and recovery efficiencies. Similarly, mercury
[1]
is not released efficiently from gold wool by heating and does not give sharp analytical peaks .
6 Requirement
The measuring procedure shall comply with any relevant International, European or national standard that
specifies performance requirements for procedures for measuring chemical agents in workplace air.
7Reagents
During the analysis of mercury vapour by this method, only analytical grade mercury reagent is needed for
generation of a standard mercury vapour to make a calibration curve.
7.1 Argon, suitable for use in CVAAS.
7.2 Mercury, for preparation of a mercury vapour standard.
8 Apparatus
8.1 Sampling equipment
8.1.1 Sorbent tubes, glass, containing a single section of porous gold-coated diatomaceous earth, stored in
a glass tube sealed with a butyl rubber stopper.
The construction of such a sorbent tube is illustrated in Figure B.1.
[2][3][15]
NOTE A sorbent tube suitable for use in this method is commercially available . This is 160 mm long, with a 6mm
outer diameter and a 4mm internal diameter, and contains 80 mg of porous granular gold sorbent retained by small quartz
wool plugs. Similar custom-made sorbent tubes can also be used if it can be demonstrated that they give equivalent
performance. Custom-made sorbent tubes can be manufactured from porous gold-coated sorbent consisting of
◦
diatomaceous earth on which pyro-decomposition of chloroauric acid has been carried out by sintering at about 800 C.
8.1.2 Sorbent tube and prefilter assemblies, consisting of a quartz fibre filter (8.1.3) mounted in a suitable
sampler, connected to the inlet of a sorbent tube (8.1.1) with a minimum length of inert plastic tubing, e.g.
polytetrafluoroethylene (PTFE) or modified polyvinyl chloride tubing.
NOTE A sorbent tube and prefilter assembly is only required if the concentration of airborne particles could be so high that
there is a risk of blockage of the quartz wool plugs that retain the gold-coated sorbent in the tubes.
8.1.3 Quartz fibre filters, of a diameter suitable for use in the samplers used for construction of prefilter
assemblies (see 8.1.2), with a collection efficiency of not less than 99,5 % for particles with a 0,3µm diffusion
[16]
diameter (see 2.2 of ISO 7708 ).
[17]
NOTE Quartz fibre filters have been shown not to absorb mercury vapour from the sampled air. They are therefore
[18]
suitable for use as prefilters. It has been reported that there can be significant loss of mercury vapour if mixed cellulose
[19]
ester filters are used as prefilters, although these findings were not reproduced in later work .
8.1.4 Sampling pumps, with an adjustable flow rate, capable of maintaining the selected flow rate
±5%
(see 10.1.3) to within of the nominal value throughout the sampling period (see 10.1.4).
NOTE 1 A flow-stabilized pump may be required to maintain the flow rate within the specified limits.
For personal sampling the pumps shall be capable of being worn by the worker without impeding normal work
activity. Sampling pump flow meters shall be calibrated using either a primary or secondary standard; if a
secondary standard is used, it shall be calibrated using a primary standard.
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ISO 2007 – All rights reserved 5

The pump should have, as a minimum, the following features:
— an automatic control that keeps the volume flow rate constant in the case of a changing back pressure;
— either a malfunction indicator which, following completion of sampling, indicates that the air flow has been
reduced or interrupted during sampling; or an automatic cut-out, which stops the pump if the flow rate is
reduced or interrupted; and
— a facility for the adjustment of flow rate, such that it can only be actuated with the aid of a tool (e.g.
screwdriver) or requires special knowledge for operation (e.g. via software), so as to preclude inadvertent
readjustment of the flow rate during use.
An integral timer is a highly desirable additional feature.
[8]
NOTE 2 EN 1232 requires that the performance of the pumps is such that:
— the pulsation of the flow rate does not exceed 10 %;
— a flow rate set within the nominal range does not deviate by more than ±5% from the initial value under increasing
back pressure;
◦ ◦
— within the range of ambient temperatures from 5 C to 40 C, the flow rate measured under operating conditions does
◦
not deviate by more than from the flow rate at ;
±5% 20 C
— the operating time is at least 2h, and preferably 8h; and
— the flow rate does not deviate by more than ±5% from the initial value during the operating time.
[8]
If the sampling pump is used outside the range of conditions specified in EN 1232 , appropriate action should
be taken to ensure that the performance requirements are met. For instance, at sub-zero temperatures it might
be necessary to keep the pump warm by placing it under the worker's clothes.
8.1.5 Flow meter, portable, with an accuracy that is sufficient to enable the volume flow rate (see 10.1.3) to be
measured to within ±5%.
The calibration of the flow meter shall be checked against a primary standard, i.e. a flow meter whose accuracy
is traceable to national standards. If appropriate (see 10.1.2), record the atmospheric temperature and pressure
at which the calibration of the flow meter was checked.
It is advisable that the flow meter used is capable of measuring the volume flow rate to within ±2% or better.
8.1.6 Ancillary equipment.
8.1.6.1 Flexible tubing, of a diameter and length suitable for making a leak-proof connection between the
sampling pumps and the sorbent tubes and/or the samplers.
8.1.6.2 Belts or harnesses, to which the sampling pumps can conveniently be fixed for personal sampling
(except where the sampling pumps are small enough to fit inside worker's pockets).
8.1.6.3 Forceps, flat-tipped, for loading and unloading of filters and sorbent capsules into and out of samplers.
8.1.6.4 Filter transport cassettes, or similar, if required to transport samples for laboratory analysis.
8.1.6.5 Barometer, suitable for measurement of atmospheric pressure, if required (see 10.1.2).
◦ ◦ ◦
8.1.6.6 Thermometer, 0 C to 50 C, graduated in divisions of 1 C or better, for measurement of
atmospheric temperature, if required (see 10.1.2).
For applications at temperatures below freezing, the range of the thermometer shall extend to the appropriate
desired range.
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8.2 Analytical instrumentation
A mercury analyser consisting of a double gold-amalgam unit (or sample applicator unit), comprising two
heaters, a gas washer and a charcoal filter, connected to an analyser unit employing a cold vapour atomic
absorption spectrometer or cold vapour atomic fluorescence spectrometer. A block diagram of an instrument
employing a double gold amalgam system with CVAAS is illustrated in Figure B.2.
[2][3][15]
NOTE A mercury analyser suitable for use in this method is commercially available .
9 Occupational exposure assessment
9.1 General
This standard pertains to the taking both of static (area) and personal samples. Refer to relevant International,
[14] [20]
European or national standards (e.g. EN 689 , ASTM E 1370-96 , etc.) for guidance on how to develop
an appropriate assessment strategy and for general guidance on measurement strategy.
9.2 Static (area) sampling
Static (area) sampling may be carried out, if appropriate, at points systemically selected in the workplace for
one or more of the following purposes:
a) to assess the concentration of mercury vapour in the working environment,
b) to give an indication of the efficiency of ventilation or other engineering controls,
c) to characterize or to provide information on the location and intensity of an emission source, and/or
d) to estimate the exposure of workers in situations where personal sampling is not possible.
9.3 Personal sampling
Exposure of workers to mercury shall normally be determined by personal sampling, since the concentration of
mercury vapour in the breathing zone can be different from the background level in the workplace.
9.4 Selection of measurement conditions and measurement pattern
9.4.1 General
9.4.1.1 Sampling shall be carried out in such a way as to cause the least possible interference with the worker
during the normal performance of the job, and to provide samples that are representative of normal working
conditions and that are compatible with the analytical method.
9.4.1.2 The pattern of sampling shall take into consideration practical issues, such as the nature of the
measurement task and the frequency and duration of particular work activities.
9.4.2 Screening measurements of variation of concentration in time and/or space
Screening measurements of variation of concentration in time and/or space may be performed to provide
information on the likely pattern of concentration of chemical agents. They can be used to identify locations and
periods of elevated exposure, and to set the duration and frequency of sampling for measurements for
comparison with limit values. Emission sources can be located and the effectiveness of ventilation or other
[21]
technical measures can be estimated (see 4.3 of EN 482:1994 ).
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ISO 2007 – All rights reserved 7

9.4.3 Screening measurements of time-weighted average concentration and worst case
measurements
9.4.3.1 Screening measurements of time-weighted average concentration may be performed to obtain
relatively crude information on the exposure level in order to decide whether an exposure problem exists at all,
and if so to appraise its possible seriousness. They may also be used to determine if the exposure is well below
[21]
or well above the limit value (see 4.2 of EN 482:1994 ).
9.4.3.2 Screening measurements of time-weighted average concentration are typically carried out in the initial
stages of a survey to assess the effectiveness of control measures. Sampling may be carried out during
representative work episodes to obtain clear information about the level and pattern of exposure, or worst case
measurements may be made.
NOTE Screening measurements of time weighted average concentration made to clearly identify work episodes during
[14]
which highest exposure occurs are typically referred to as “worst case measurements” (see 5.2.3.2 of EN 689:1995 ).
9.4.4 Measurements near an emission source
Measurements may be performed near an emission source to provide information on the location and intensity
of the source. In association with other information they can allow the elimination of a suspected source as a
[21]
significant contributor to exposure (see 4.4 of EN 482:1994 ).
9.4.5 Measurements for comparison with limit values and periodic measurements
9.4.5.1 Measurements for comparison with limit values
9.4.5.1.1 Measurements for comparison with limit values are performed to provide accurate and reliable
information on, or allow the prediction of, the time-weighted average concentration of a specific chemical agent
[21]
in the air, which could be inhaled (see 4.5 of EN 482:1994 ).
9.4.5.1.2 For making measurements for comparison with a long-term exposure limit, samples shall be
collected for the entire working period, if possible, or during a number of representative work episodes
(see 10.1.4.1 for the minimum sampling time).
9.4.5.1.3 For making measurements for comparison with a short-term exposure limit, the sampling time shall
be as close as possible to the reference period, which is typically 15 min, but can be anything between 5 min
and 30 min (see 10.1.4.2).
NOTE The best estimate of long-term exposure is obtained by taking samples for the entire working period, although this
might not always be practicable.
9.4.5.2 Periodic measurements
Periodic measurements are performed to determine whether exposure conditions have changed since
measurements for comparison with limit values were made, or whether control measures remain effective.
[21]
(see 4.6 of EN 482:1994 ).
©
8 ISO 2007 – All rights reserved

10 Sampling
10.1 Preliminary considerations
10.1.1 Selection of sampling method
10.1.1.1 Measurement of mercury vapour
For measurement of mercury vapour, or for measurement of total inorganic mercury (mercury vapour and
inorganic mercury compounds) when it is known that no particulate inorganic mercury compounds are used in
the workplace and that none are produced in the processes carried out, use the pumped sorbent tube method
specified in this International Standard to collect samples.
10.1.1.2 Measurement of mercury vapour and particulate inorganic mercury compounds
When both mercury vapour and particulate inorganic mercury compounds could be present in the test
atmosphere, use the pumped sorbent tube method specified in this International Standard to collect samples of
mercury vapour and, if desired, use the procedure described in ISO 17733 to collect and analyse separate
samples for measurement of particulate inorganic mercury compounds.
10.1.1.3 Measurement of particulate inorganic mercury compounds
For measurement of inorganic mercury compounds, or for measurement of total inorganic mercury (mercury
and inorganic mercury compounds) when it is known that no elemental mercury is used in the workplace and
that no mercury vapour is produced in the processes carried out, use the procedure described in ISO 17733, if
desired, to collect and analyse samples.
10.1.2 Consideration of temperature and pressure effects
10.1.2.1 Effect of temperature and pressure on volume flow rate
Refer to the manufacturer's instructions to determine if the indicated volume flow rate of the flow meter (8.1.5)
is dependent upon temperature and pressure. Consider whether the difference between the atmospheric
temperature and pressure at the time of calibration of the flow meter and during sampling, is likely to be great
enough to justify applying a correction to take this into account, e.g. if the error could be greater than ±5%. If
a correction is necessary, measure and record the atmospheric temperature and pressure at which the
calibration of the flow meter was checked (see 8.1.5), and measure and record the atmospheric temperature
and pressure at the start and at the end of the sampling period (10.4.1 and 10.4.3). Then calculate a
temperature and pressure corrected volume flow rate following the procedure given in A.1.
10.1.2.2 Expression of results
Consider whether it is necessary to recalculate mercury in air concentrations to reference conditions (such as
in high altitude situations). If so, measure and record the atmospheric temperature and pressure at the start and
at the end of the sampling period (10.4.1 and 10.4.3) and follow the procedure given in A.2 to apply the
necessary correction to the mercury in air concentrations calculated in 12.2.1.
NOTE The concentration of mercury in air is generally stated for actual environmental conditions (temperature, pressure)
at the workplace during the sampling period.
10.1.3 Volume flow rate
Select a flow rate within the range recommended by the manufacturer of the sorbent tube (normally between
−1 −1
100 ml min and 1 000 ml min ).
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ISO 2007 – All rights reserved 9

10.1.4 Sampling period
10.1.4.1 Select a sampling period that is appropriate for the measurement task (see 9.4), but ensure that it is
long enough to enable mercury to be determined with acceptable uncertainty (see 3.3.5) at levels of industrial
hygiene significance. For example, estimate the minimum sampling time required to ensure that the amount of
mercury collected is above the lower limit of the working range of the analytical method when it is present in the
test atmosphere at a concentration of 0,1 times its limit value, using the following equation:
m
lower
t =
min
q × 0,1× ρ
V LV
where
t is the minimum sampling time, in minutes;
min
m is the lower limit of the analytical range, in nanograms;
lower
q is the design flow rate of the sampler, in millilitres per minute;
V
ρ is the limit value, in milligrams per cubic metre.
LV
15 min
10.1.4.2 The sampling time shall not be less than when the sorbent tube is used at a flow rate of
−1
100 ml min .
10.1.4.3 Sample handling
To minimize the risk of damage or contamination, only handle sorbent tubes (8.1.1) and quartz fibre filters
(8.1.3), if used, in a clean area where the concentration of mercury in air minimal, and only handle quartz fibre
filters using flat-tipped forceps (8.1.6.3).
10.2 Preparation for sampling
10.2.1 Preconditioning of sorbent tubes
Take out the required number of sorbent tubes (8.1.1) from their sealed glass tubes. Precondition the sorbent
◦
tubes prior to sampling by heating to 700 C in the mercury analyser and passing air through them at a flow rate
−1
of 500 ml min for 2 min to reduce the mercury blank. Replace each sorbent tube in its stoppered glass tube
and label the glass tube uniquely.
Preconditioning of sorbent tubes to reduce the mercury blank may be done automatically by commercial
instruments.
10.2.2 Setting the volume flow rate
Perform the following in a clean area, where the concentration of mercury in air is minimal.
Remove each sorbent tube (8.1.1) from its storage tube and connect it to a sampling pump (8.1.4) using flexible
tubing (8.1.6.1), ensuring that no leaks can occur. Switch on the sampling pump, attach the flow meter (8.1.5) to
the sorbent tube so that it measures the flow through the inlet orifice, and set the required volume flow rate
(see 10.1.3). Switch off the sampling pump, replace each sorbent tube in its storage tube and close with a butyl
rubber stopper to prevent contamination during transport to the sampling position.
If necessary, allow the sampling pump operating conditions to stabilize before setting the volume flow rate (refer
to the manufacturer's instructions).
©
10 ISO 2007 – All rights reserved

10.2.3 Field blanks
Retain as blanks, one unused sorbent tube (10.2.1) from each batch of ten prepared, subject to a minimum of
two. Treat these in the same manner as those used for sampling with respect to storage and transport to and
from the sampling position, but draw no air through them.
10.2.4 Sorbent tube and prefilter assemblies
If required, construct sorbent tube and prefilter assemblies (see 8.1.2).
10.3 Sampling position
10.3.1 Static (area) sampling
10.3.1.1 If static sampling is carried out to assess the exposure of a worker in a situation where personal
sampling is not possible (e.g. due to the need to sample in confined spaces), position a sorbent tube (10.2.1) or
sorbent tube and prefilter assembly (10.2.4) in the immediate vicinity of the worker and at breathing height. If in
doubt, take the sampling position to be the point where the risk of exposure is considered to be greatest.
10.3.1.2 If static sampling is carried out to assess the background level of mercury in the workplace, select a
sampling position that is sufficiently remote from the work processes, such that results will not be directly
affected by mercury from emission sources.
10.3.1.3 If static sampling is carried out to characterize the concentration of mercury in the working
environment, select a number of sampling points systematically to cover the workplace.
NOTE This working environment measurement employing static sampling has been performed in some countries by
regulation, comparing the measured concentration values statistically with a specific value which is established by an
authority, e.g. an administrative control level (ACL) by the Japanese government (see
http://www.jicosh.gr.jp/english/index.html).
10.3.2 Personal sampling
Position the sorbent tube (10.2.1) or sorbent tube and prefilter assembly (10.2.4) in the worker's breathing zone,
as close to the mouth and nose as is reasonably practicable, e.g. fastened to the worker's lapel or collar. Attach
the sampling pump to the worker in a manner that causes minimum inconvenience, e.g. to a belt (8.1.6.2)
around the waist or place it in a convenient pocket.
10.4 Collection of samples
10.4.1 When ready to begin sampling, switch on the sampling pump. Record the time and volume flow rate at
the start of the sampling period. If the sampling pump is fitted with an integral timer, check that this is reset to
zero. If appropriate (see 10.1.2), measure the atmospheric temperature and pressure at the start of the
sampling period using the thermometer and barometer, and record the measured values.
Integral timers built into sampling pumps can be imprecise and should only be used to provide evidence that the
sampler has been operating properly throughout the sampling period (see 10.4.3).
If the temperature or pressure at the sampling position is different from that where the volume flow rate was set
(see 10.2.2), the volume flow rate could change and it might need to be re-adjusted before sampling.
10.4.2 Monitor the performance of the pumps frequently, a minimum of once every two hours. Measure the
flow rate using the flow meter (8.1.5) and record the measured value. Terminate sampling and consider the
sample to be invalid if the flow rate is not maintained to within ±5% of the nominal value throughout the
sampling period.
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ISO 2007 – All rights reserved 11

10.4.3 At the end of the sampling period (see 10.1.4), record the time. Check the malfunction indicator and/or
the reading on the integral timer, if fitted, and consider the sample to be invalid if there is evidence that the
sampling pump was not operating properly throughout the sampling period. Measure the volume flow rate at the
end of the sampling period using the flow meter (8.1.5), and record the measured value. If appropriate
(see 10.1.2), measure the atmospheric temperature and pressure at the end of the sampling period using the
thermometer and barometer, and record the measured values.
10.4.4 Carefully record the sample identity and all relevant sampling data (see Clause 14). Calculate the mean
volume flow rate by averaging the volume flow rates at the start and at the end of the sampling period and, if
appropriate (see 10.1.2), calculate the mean atmospheric temperature and pressure. Calculate the volume of
air sampled, in litres, at atmospheric temperature and pressure, by mul
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