SIST EN 838:2010
(Main)Workplace exposure - Procedures for measuring gases and vapours using diffusive samplers - Requirements and test methods
Workplace exposure - Procedures for measuring gases and vapours using diffusive samplers - Requirements and test methods
This European Standard specifies performance requirements and test methods under prescribed laboratory conditions for the evaluation of diffusive samplers and of procedures using these samplers for the determination of gases and vapours in workplace atmospheres. This European Standard is applicable to diffusive samplers and measuring procedures using these samplers in which sampling and analysis are carried out in separate stages. This European Standard is not applicable to: diffusive samplers which are used for the direct determination of concentrations; diffusive samplers which rely on sorption into a liquid.
Exposition am Arbeitsplatz - Messung von Gasen und Dämpfen mit Diffusionssammlern - Anforderungen und Prüfverfahren
Diese Europäische Norm legt Anforderungen an die Leistungsfähigkeit und Prüfverfahren für die Evaluierung
von Diffusionssammlern ("Passivsammlern") unter vorgegebenen Laborbedingungen fest, sowie Verfahren,
die diese Probenahmeeinrichtungen zur Bestimmung von Gasen und Dämpfen in der Arbeitsplatzatmosphäre
verwenden.
Diese Europäische Norm gilt für Diffusionssammler und Messverfahren, die Sammler, bei denen Probenahme
und Analyse in getrennten Schritten vorgenommen werden, verwenden.
Zusätzliche Prüfungen, um festzustellen, ob die Leistungsmerkmale der Diffusionssammler durch irgend
welche Umwelteinflüsse beeinträchtigt werden, die bei der Felderprobung angetroffen werden können,
werden in den Anhängen D und E beschrieben. Diese Anhänge richten sich in erster Linie an die Benutzer
solcher Sammler, die am besten in der Lage sind, die spezifischen Faktoren zu erkennen, welche die
Leistungsfähigkeit eines Sammlers signifikant beeinflussen können.
Exposition sur les lieux de travail - Procédures pour le mesurage des gaz et vapeurs à l'aide de dispositifs de prélèvement par diffusion - Exigences et méthodes d'essai
La présente norme européenne spécifie les exigences de performances et les méthodes d'essai, dans des conditions de laboratoire prescrites, pour l’évaluation de dispositifs de prélèvement par diffusion et des procédures utilisant ces dispositifs de prélèvement pour la détermination des gaz et des vapeurs présents dans l'atmosphère des lieux de travail.
La présente Norme européenne s'applique aux dispositifs de prélèvement par diffusion et aux procédures de mesurage utilisant ces dispositifs de prélèvement qui dissocient l'étape de prélèvement de l'étape d'analyse.
Les annexes D et E décrivent des essais supplémentaires, conçus pour déterminer si les caractéristiques de performances du dispositif de prélèvement par diffusion sont affectées par les conditions environnementales plus variées, pouvant être rencontrées sur le terrain. Ces annexes s'adressent principalement aux utilisateurs de tels dispositifs, lesquels sont les mieux placés pour connaître les facteurs spécifiques qui peuvent affecter de façon significative les performances du dispositif de prélèvement.
Izpostavljenost na delovnem mestu - Postopki za merjenje plinov in par z difuzijskimi vzorčevalniki - Zahteve in preskusne metode
Ta evropski standard določa zahteve za zmogljivost in preskusne metode pod predpisanimi laboratorijskimi pogoji za vrednotenje difuzijskih vzorčevalnikov in postopkov, pri katerih se uporabljajo ti vzorčevalniki za določevanje plinov in par v delovnih atmosferah. Ta evropski standard se uporablja za difuzijske vzorčevalnike in postopke za merjenje, pri katerih se uporabljajo ti vzorčevalniki, pri katerih se vzorčenje in analiza opravita v ločenih fazah. Ta evropski standard se ne uporablja za: difuzijske vzorčevalnike, ki se uporabljajo za neposredno določevanje koncentracij; difuzijske vzorčevalnike, ki se opirajo na sorpcijo v tekočino.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 838:2010
01-april-2010
1DGRPHãþD
SIST EN 838:1998
,]SRVWDYOMHQRVWQDGHORYQHPPHVWX3RVWRSNL]DPHUMHQMHSOLQRYLQSDU]
GLIX]LMVNLPLY]RUþHYDOQLNL=DKWHYHLQSUHVNXVQHPHWRGH
Workplace exposure - Procedures for measuring gases and vapours using diffusive
samplers - Requirements and test methods
Exposition am Arbeitsplatz - Messung von Gasen und Dämpfen mit Diffusionssammlern -
Anforderungen und Prüfverfahren
Exposition sur les lieux de travail - Procédures pour le mesurage des gaz et vapeurs à
l'aide de dispositifs de prélèvement par diffusion - Exigences et méthodes d'essai
Ta slovenski standard je istoveten z: EN 838:2010
ICS:
13.040.30 Kakovost zraka na delovnem Workplace atmospheres
mestu
SIST EN 838:2010 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN 838:2010
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SIST EN 838:2010
EUROPEAN STANDARD
EN 838
NORME EUROPÉENNE
EUROPÄISCHE NORM
January 2010
ICS 13.040.30 Supersedes EN 838:1995
English Version
Workplace exposure - Procedures for measuring gases and
vapours using diffusive samplers - Requirements and test
methods
Exposition sur les lieux de travail - Procédures pour le Exposition am Arbeitsplatz - Messung von Gasen und
mesurage des gaz et vapeurs à l'aide de dispositifs de Dämpfen mit Diffusionssammlern - Anforderungen und
prélèvement par diffusion - Exigences et méthodes d'essai Prüfverfahren
This European Standard was approved by CEN on 11 December 2009.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2010 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 838:2010: E
worldwide for CEN national Members.
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EN 838:2010 (E)
Contents Page
Foreword .3
Introduction .4
1 Scope .5
2 Normative references .5
3 Terms and definitions .5
4 Symbols and abbreviations .5
5 Types of samplers .7
6 Requirements .7
6.1 General .7
6.2 Sampler requirements .8
6.3 Measuring procedure requirements .9
7 General test conditions . 11
7.1 Reagents . 11
7.2 Apparatus . 11
7.3 Independent method . 12
7.4 Generation of a calibration gas mixture . 12
8 Test methods . 13
8.1 General . 13
8.2 Sampler test methods . 13
8.3 Measuring procedure test methods . 16
8.4 Uncertainty of measurement . 21
9 Test report . 23
Annex A (informative) Fundamentals of diffusive sampling. 24
Annex B (informative) Estimation of uncertainty of measurement . 26
Annex C (informative) Example of estimation of expanded uncertainty . 36
Bibliography . 39
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EN 838:2010 (E)
Foreword
This document (EN 838:2010) has been prepared by Technical Committee CEN/TC 137 “Assessment of
workplace exposure to chemical and biological agents”, the secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by July 2010, and conflicting national standards shall be withdrawn at the
latest by July 2010.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 838:1995.
The major technical changes between this European Standard and the previous edition are as follows:
a) adaptation of the framework for assessing the performance of procedures for measuring gases and
vapours against the general requirements for the performance of procedures for measuring chemical
agents in workplace atmospheres as specified in EN 482;
b) revision of the calculation model for the uncertainty of measurement to comply with EN 482 and
ENV 13005;
c) modification of the classification scheme for sampler types;
d) deletion of the informative annexes on the evaluation of diffusive samplers by means of field tests.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
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Introduction
This European Standard provides a framework for assessing the performance of procedures for measuring
gases and vapours against the general requirements for the performance of procedures for measuring
chemical agents in workplace atmospheres as specified in EN 482. These performance criteria include
maximum values of expanded uncertainty achievable under prescribed laboratory conditions for the methods
to be used. In addition, the performance criteria should also be met under a wider variety of environmental
influences, representative of workplace conditions.
This European Standard enables manufacturers and users of diffusive samplers and developers and users of
procedures for measuring gases and vapours to adopt a consistent approach to method validation.
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1 Scope
This European Standard specifies performance requirements and test methods under prescribed laboratory
conditions for the evaluation of diffusive samplers and of procedures using these samplers for the
determination of gases and vapours in workplace atmospheres.
This European Standard is applicable to diffusive samplers and measuring procedures using these samplers
in which sampling and analysis are carried out in separate stages.
This European Standard is not applicable to:
diffusive samplers which are used for the direct determination of concentrations;
diffusive samplers which rely on sorption into a liquid.
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.
EN 482:2006, Workplace atmospheres ― General requirements for the performance of procedures for the
measurement of chemical agents
EN 1076, Workplace exposure ― Procedures for measuring gases and vapours using pumped samplers ―
Requirements and test methods
EN 1540, Workplace atmospheres ― Terminology
EN ISO 8655-2, Piston-operated volumetric apparatus ― Part 2: Piston pipettes (ISO 8655-2:2002)
EN ISO 8655-6, Piston-operated volumetric apparatus ― Part 6: Gravimetric methods for the determination of
measurement error (ISO 8655-6:2002)
3 Terms and definitions
1)
For the purposes of this document, the terms and definitions given in EN 482:2006 and EN 1540 apply.
4 Symbols and abbreviations
For the purposes of this document, the following symbols and abbreviations apply.
NOTE See 8.4 and Annex C for symbols used in conjunction with uncertainty of measurement only.
A cross-sectional area of sorption surface, in square centimetres (cm²)
CRM certified reference material
1) EN 1540:1998 is currently subject to revision. Until the revised EN is published the definitions given in EN 482:2006
take precedence.
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D diffusion coefficient of an analyte, in square centimetres per minute (cm²/min)
a
D diffusion coefficient of analyte 1, in square centimetres per minute (cm²/min)
a1
D diffusion coefficient of analyte 2, in square centimetres per minute (cm²/min)
a2
l length of static air layer in sampler (or equivalent for permeation types), in centimetres (cm)
LV limit value
m mass of analyte desorbed from blank sampler, in nanograms (ng)
b
m mass of analyte desorbed, in nanograms (ng)
d
m mass of the analyte which can diffuse to a suitable sorbent within a certain time, i.e. the mass uptake
s
of a diffusive sampler, in nanograms (ng)
m& mass loss from permeation tube, in micrograms per minute (µg/min)
1
M molar mass of analyte, in grams per mole (g/mol)
a
n number of replicate samples
p actual pressure of the test atmosphere sampled, in kilopascals (kPa)
at
R recovery
R analytical recovery
an
RH relative humidity of the test atmosphere sampled, in percent (%)
t exposure time, in minutes (min)
e
T temperature of the test atmosphere sampled, in Kelvin (K)
at
&
U uptake rate, in cubic centimetres per minute (cm³/min)
d
-1 -1
&
(U )' uptake rate, in nanograms per parts per million (volume fraction) per minute (ng ppm min )
d
&
U uptake rate of analyte 1, in cubic centimetres per minute (cm³/min)
d1
&
U uptake rate of analyte 2, in cubic centimetres per minute (cm³/min)
d2
&
v flow rate into the exposure chamber, for example, in litres per minute (l/min)
β mass concentration of the analyte in the calibration gas mixture, in milligrams per cubic metre
a
(mg/m³)
(β )' mass concentration in parts per million (ppm);
a
β mass concentration of the given analyte at the beginning of the diffusion layer (i.e. at the distance l
a1
from the surface of the sorbent), in milligrams per cubic metre (mg/m³)
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β mass concentration of the given analyte at the end of the diffusion layer (i.e. at the surface of the
a2
sorbent), in milligrams per cubic metre (mg/m³)
β mean mass concentration of the analyte recovered from the test gas atmosphere, in milligrams per
a,R
cubic metre (mg/m³);
β mass concentration of the calibration gas mixture, in milligrams per cubic metre (mg/m³)
cg
ϑ temperature of the test atmosphere sampled, in degree Celsius (°C)
at
2)
Κ coefficient of variation (CV)
v
φ volume fraction of the analyte, in microlitres per litre (µl/l)
a
5 Types of samplers
Samplers for gases and vapours can be divided into type A samplers and type B samplers:
Type A samplers rely on sorption onto a solid or onto a support impregnated with a reagent, desorption with
solvent, and subsequent analysis of the desorbate. They are usually made of glass and consist of two beds of
sorbent in series, i.e. with a back-up section, and contain an active sorbent (e.g. activated carbon) or a
support impregnated with reagent.
Type B samplers rely on sorption onto a solid or onto a support impregnated with a reagent, thermal
desorption, and analysis of the desorbate. They are usually made of glass or metal, are sealed with
removable fittings and consist of one or more beds of sorbent (e.g. porous polymer resin).
6 Requirements
NOTE If there is no procedure for measuring a particular chemical agent which meets the requirements of this
European Standard, a procedure whose performance is nearest to the specified requirements should be used.
6.1 General
Some requirements (see 6.2) shall be verified once for each type of sampler. Other requirements (see 6.3)
shall be verified for each combination sampler/chemical agent.
It is the responsibility of the manufacturer to meet the requirements specified in 6.2. It is also the responsibility
of the manufacturer or the developer of the measuring procedure to meet the requirements specified in 6.3
when use of a sampler for measurement of a particular gas or vapour is claimed.
NOTE 1 No useful performance requirements can be given for the effect of interferents (with the exception of water
vapour). The effect of interferents is difficult to predict for a non ideal sorbent without adsorption isotherm data on mixed
systems which is normally unavailable. However the user of diffusive samplers should be cautioned that the adsorption of
water vapour on certain sorbents, e.g. activated carbon and silica gel, can have a large effect on sampler capacity and
analytical recovery.
NOTE 2 Because of the known effect of pressure on diffusion coefficients, a pressure test is not necessary.
2) The predecessor term "relative standard deviation" is deprecated by the term "coefficient of variation". See also
ISO 3534-1:2006, 2.38, Note 2.
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6.2 Sampler requirements
6.2.1 Nominal uptake rate
3)
The nominal uptake rate and the coefficient of variation shall be provided by the manufacturer. If it is
possible to calculate the ideal steady-state value in accordance with 8.2.1.1, the nominal uptake rate,
determined in accordance with 8.2.1.2, shall be within ± 25 % of the steady-state value.
6.2.2 Air velocity/sampler orientation
The manufacturer shall test the working range of air velocity and the influence of sampler orientation in
accordance with 8.2.2.
6.2.3 Sampler leak test
When tested in accordance with 8.2.3, any additional analyte determined above the blank value (see 6.3.2.3)
shall be less the one-third of the calculated mass uptake by the sampler for 30 min exposure to a
concentration of 0,1 LV.
6.2.4 Shelf life (for impregnated supports)
The manufacturer shall specify the shelf life of the diffusive sampler when stored in its original package.
During this period the sampler shall fulfil all requirements.
6.2.5 Sample identification (for commercially available diffusive samplers)
The diffusive sampler shall have a suitable area for sample identification by the user.
6.2.6 Marking
Diffusive samplers shall be marked with at least the following:
manufacturer's name;
product identification;
batch identification;
shelf life (if applicable);
number of this European Standard.
If required due to limited space, the marking may be placed on the packaging of the diffusive sampler.
However, the manufacturer's name and product identification shall be indicated on the diffusive sampler.
6.2.7 Instructions for use
The instructions for use supplied with the diffusive sampler shall be in the language(s) of the country where
the diffusive sampler is to placed on the market. They shall contain at least the following information:
a) designated use (general purpose for a number of gases and vapours or, specific, for a particular gas or
vapour, see 6.1);
3) The predecessor term "relative standard deviation" is deprecated by the term "coefficient of variation". See also
ISO 3534-1:2006, 2.38, Note 2.
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b) blank value (only when used for a particular gas or vapour, see 6.1;
c) nominal uptake rate for the substances for which the diffusive sampler is intended to use;
d) directions for proper handling of the diffusive sampler, including opening and closing;
e) general information on the principle of use, for example, sorbent type, reaction of the reagent
impregnated solid, desorption method;
f) information on storage and transport;
g) working range of air velocity;
h) orientation;
i) information on health or environmental hazards and method of disposal.
The general information on the principle of use can be given in additional literature.
6.3 Measuring procedure requirements
6.3.1 Sampling procedure requirements
6.3.1.1 Sampling time
Sampling time shall be established according to concentration range of the compounds of interest over which
measurements are to be made, i.e. up to two times the limit value (see EN 482), and taking into account the
nominal or theoretical uptake rate.
6.3.1.2 Bias due to the selection of a non ideal sorbent (back diffusion)
When tested in accordance with 8.3.1.1, the bias shall be ≤ 10 %.
6.3.1.3 Uptake rate
If it is possible to calculate the ideal steady-state value in accordance with 8.2.1.1, the nominal uptake rate,
determined in accordance with 8.2.1.2, shall be within ± 25 % of the steady-state value.
6.3.1.4 Storage conditions after sampling
The storage conditions after sampling shall be specified. When tested in accordance with 8.3.1.3, the mean
value of the recovery after storage shall not differ by more than 10 % from the value before storage.
6.3.2 Analytical procedure requirements
6.3.2.1 Analytical quantification limit
The quantification limit shall be lower than or equal to one-third of the calculated mass uptake by the sampler
for 30 min exposure to a concentration of 0,1 LV.
6.3.2.2 Analytical recovery
When tested in accordance with 8.3.2.2 the analytical recovery R shall be:
an
For type A samplers: R ≥ 75 % with Κ ≤ 10 % at each loading;
an v
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For type B samplers: R ≥ 95 % with Κ ≤ 10 % at each loading.
an v
6.3.2.3 Blank value
When tested in accordance with 8.3.2.3 the blank value shall be less than one-tenth of the calculated mass
uptake by the sampler for 30 min exposure to a concentration of 0,1 LV.
Where it is known that the blank value is significant and varies between batches of samplers, it shall be
checked regularly.
Type B samplers which are not thermally sealed should be cleaned before sampling to eliminate any
contamination which could occur during storage before use.
NOTE 1 In order to eliminate any contamination which could occur during storage before use, Type B samplers should
be cleaned by taking them through the thermal desorption procedure. This cleaning process should be carried out as close
as possible to the time when the samplers will be used.
NOTE 2 In order to obtain acceptable values for the quantification limit of the method, the blank value of the sampling
media should be as low as technically possible.
6.3.3 Expanded uncertainty
When tested in accordance with 8.3 the expanded uncertainty calculated in accordance with 8.4 shall meet
the requirements given in EN 482.
The expanded uncertainty requirement shall be met from 10 ºC to 40 ºC and at relative humidities from 20 %
to 80 %. Above 30 ºC the use of correction factors is permitted to meet this requirement.
6.3.4 Method description
6.3.4.1 Scope of the measurement procedure
The scope of the measuring procedure shall give information about the following:
principle of the method;
chemical agents covered by the measuring procedure;
analytical technique used;
working ranges;
chemical agents for which the measuring procedure is known to be adequate but not completely validated
according to this European Standard, especially in case of compounds of the same chemical family or
homologous series;
chemical agents for which the measuring procedure is known to be inadequate;
any known interferences.
6.3.4.2 Method performance
The measuring procedure shall give information about method performance, including the following:
the chemical agents for which measurement method has been shown to be effective;
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the range of concentrations of chemical agents in air, sample volume, uptake rates, exposure time and
range of environmental conditions over which the measurement method has been shown to meet the
performance criteria for expanded uncertainty prescribed in EN 482;
the quantification limit of the analytical method for chemical agents of interest;
full details of any known interferences, including suitable and sufficient information on how to minimise
their effects.
6.3.4.3 Apparatus
The measuring procedure shall:
specify that the diffusive sampler complies with the provisions of this European Standard;
define the required characteristics of analytical instruments to be used;
specify the quality of the reagents to be used.
6.3.4.4 Safety information
The measuring procedure shall provide suitable and sufficient information on the safety hazards associated
with the reagents and equipment used in the procedure.
7 General test conditions
7.1 Reagents
Use reagents of analytical grade, where possible.
7.2 Apparatus
Usual laboratory apparatus and the following:
7.2.1 A dynamic system for generating, pre-mixing and delivering a known concentration of a test gas or
vapour in air (see EN ISO 6145-1, EN ISO 6145-4 and EN ISO 6145-6), including at least:
an exposure chamber constructed of inert materials such as glass or polytetrafluorethylene (PTFE),
through which the generated test atmosphere is passed, of sufficient capacity to accommodate
simultaneously at least six test samplers and six samplers of one independent method (see 7.3)
positioned in such a manner that there is no interference between each sampler;
provisions for measuring, controlling and varying the air flow rate through the chamber and the
concentration, temperature and relative humidity of the calibration gas mixture.
NOTE It is also possible to use a smaller exposure chamber and to carry out repeat experiments to obtain at least six
pairs of data.
7.2.2 Micropipettes or syringes, for applying known volumes of standard solutions, complying with the
requirements of EN ISO 8655-2 and with a calibration checked in accordance with EN ISO 8655-6.
7.2.3 Instruments for analysing the gas, vapour or a characteristic reaction product collected by either the
test sampler or an independent sampling method.
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7.3 Independent method
The concentration of the generated calibration gas mixture in the exposure chamber shall be verified as
follows:
a) by an independent method, which has been validated using an established protocol, for example a
pumped sampler method, bubbler method, or a different diffusive sampler method; or
b) by using an independently calibrated on-line instrument, e.g. a flame ionization detector, or an infrared
spectrometer.
If a pumped sampler procedure is used as the independent method, the method shall comply with all
requirements of EN 1076.
7.4 Generation of a calibration gas mixture
7.4.1 General
Set up a calibration gas mixture at the concentration and values of temperature, relative humidity, etc.
specified in the appropriate test methods in Clause 8.
Ensure that the flow rate into the exposure chamber exceeds the combined sampling rate of all samplers by at
least 25 %.
7.4.2 Calibration gas mixture
7.4.2.1 Calculate the mass concentration of the calibration gas mixture, β , given in milligrams per cubic
cg
metre (mg/m³), from the test atmosphere generation parameters. For example, for a permeation cell system,
the delivered mass concentration is:
&
m
1
β = (1)
cg
&
v
where
&
m is the mass loss from permeation tube, in micrograms per minute (µg/min);
1
&
v is the flow rate into the exposure chamber, for example, in litres per minute (l/min).
NOTE 1 The example does not give a preference for permeation systems for generating calibration gas mixtures of
gases and vapours.
NOTE 2 This value is the calculated inlet value of the exposure chamber concentration.
7.4.2.2 Measure the mass concentrations at the inlet and outlet of the exposure chamber using the
independent method described in 7.3 with all samplers within the test chamber, including both the test and
independent method functioning.
Determine whether the measured outlet mass concentration differs by more than 5 % from the measured inlet
mass concentration. If it does, then the generation system shall be changed e.g. by increasing the flow rate or
chamber volume, until the difference is less than 5 %.
When the difference is less than 5 %, calculate the mean mass concentration in the test atmosphere within
the exposure chamber either from the mean of the calculated inlet and outlet values, or from the mean
calculated inlet value adjusted for (half of) the experimentally determined depletion.
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7.4.2.3 Determine the mean mass concentration of the test atmosphere within the exposure chamber
experimentally using the results of the independent method described in 7.3. A correction may be applied for
any known bias in the independent method.
Compare the determined mass concentration with the calculated value (see 7.4.2.2). If the experimentally
determined value is within ± 10 % of the calculated value of the mass concentration of the delivered test
atmosphere, take the calculated value as the true value. If this requirement is not met, then make adjustments
or use an alternative generation method or verify the independent method.
If it is not possible to calculate a mass concentration of the calibration gas, for example, for reactive gases, the
value determined by the independent method shall be used as the true value.
8 Test methods
8.1 General
If it is known in advance that a certain type of diffusive sampler is unaffected by an environmental influence
then the relevant tests in 8.3.3.1 to 8.3.3.5 may be modified to examine only the factors likely to have an
influence.
If not otherwise specified in the test procedure, the s
...
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