WORKPLACE ATMOSPHERES - GENERAL REQUIREMENTS FOR THE PERFORMANCE OF PROCEDURES FOR THE MEASUREMENT OF CHEMICAL AGENTS I.S./EN 482:1995

Forfás in exercise of the power conferred by section 20 (3) of the Industrial Research and Standards Act, 1961 (No. 20 of 1961) and the Industrial Development Act, 1993 (No. 19 of 1993), and with the consent of the Minister for Enterprise and Employment, hereby declares as follows:

1. This instrument may be cited as the Standard Specification (Workplace Atmospheres - General Requirements for the Performance of Procedures for the Measurement of Chemical Agents) Declaration, 1995.

2. (1) The Specification set forth in the Schedule to this declaration is hereby declared to be the standard specification for Workplace Atmospheres - General Requirements for the Performance of Procedures for the Measurement of Chemical Agents. The Schedule comprises the text of EN 482 : 1994.

(2) The said standard specification may be cited as Irish Standard/EN 482:1995 or as I.S./EN 482:1995.

EUROPEAN STANDARD

EN 482

July 1994

UDC 628.511/.512:331.4:620.1

Descriptors: air, quality, air pollution, workroom, measurements, concentration, dangerous materials, classification, tests

English version

Workplace atmospheres - General requirements for the performance of procedures for the measurement of chemical agents

This European Standard was approved by CEN on 1994-07-27. 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 Central Secretariat or to any CEN member.

The European Standards exist 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 Central Secretariat has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.

Foreword

This European Standard has been prepared by Technical Committee CEN/TC 137 “Assessment of workplace exposure”, 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 January 1995, and conflicting national standards shall be withdrawn at the latest by January 1995.

In accordance with the CEN/CENELEC Internal Regulations, following countries are bound to implement this European Standard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.

0 Introduction

National laws and regulations based on European Directives require the assessment of the potential exposure of workers to chemical agents in workplace air. One way of assessing such exposure is to measure the concentration of the chemical agent in air in the worker’s breathing area. The procedures used for such measurements shall give reliable and valid results so that when compared with set limit values a correct decision can be made, for instance, as to whether the exposure level is acceptable or control measures need to be applied.

Because of their importance in the process of exposure assessment, the measurement procedures shall fulfil some general requirements, which are given in this European Standard. Specific standards will be prepared for different types of measuring procedures and measuring devices. These include standards for dust samplers, diffusive samplers, sorption tubes for active sampling, detector tubes, sampling pumps and direct reading instruments. In these specific standards additional requirements will be included for the procedure or device in question, such that the general requirements of this standard are not compromised. Where no specific standard exists, only the general requirements apply.

Performance requirements given in this standard include unambiguity, selectivity, overall uncertainty (a combination of precision and bias) for minimum specified measuring ranges, averaging time, etc. These requirements should ideally also apply under environmental conditions present at the workplace. Because of the wide range of these environmental conditions the requirements laid down in this European Standard shall be fulfilled by the measuring procedures under prescribed laboratory conditions.

For some workplaces it may be necessary for the measuring procedures to meet the performance requirements over a wider range of environmental influences. This shall be decided from case to case and cannot be covered by this general standard.

The test methods for the measuring procedures are given in this standard in general terms. As test methods depend on the specific measuring procedures or devices, detailed test methods will be specified in the specific standards. These detailed test methods shall be consistent with the general test methods given in this European Standard.

It is the user’s primary responsibility to choose appropriate procedures or devices that meet the requirements in this European Standard. One way of doing this is to obtain information or confirmation from the manufacturer. Type-testing, or more generally, the assessment of performance criteria of procedures or devices, may be undertaken by the manufacturer, user, test house or research and development laboratory, as is most appropriate. Guidance on the most appropriate of these options in specific cases will be given in the specific standards.

This standard is a basis for forthcoming standards for specific procedures and devices for workplace measurements. These specific standards will contain more detailed requirements and test methods for specific measuring procedures or devices which may necessitate elaboration of the requirements laid down in this standard. However, reasons for specific changes will be given while the basic level of requirements in this standard shall not be reduced.

Note:

A number of existing procedures for workplace measurements have been tested over part of the required minimum specified measuring range but not over the entire range (see table 1) or have not been tested for all environmental influences and potential interferences. If these procedures meet the performance requirements of this standard they may nevertheless be used at present. It is recommended that these procedures are tested over the full ranges as soon as is reasonably practicable. If there is no measuring procedure for a chemical agent, which meets the requirements of this standard, it is recommended to use a procedure, whose performance is nearest the specified requirements.

1 Scope

This standard specifies general performance requirements for procedures for determining the concentration of chemical agents in workplace air. Such requirements apply to all measuring procedures, irrespective of the chemical nature or physical form (gas, vapour, suspended matter) of the agent, and irrespective of the sampling method or analytical method used.

This standard is applicable to all stages of a measuring procedure, including transportation and storage of the sample where appropriate.

This standard is applicable to measuring procedures with separate sampling and analysis stages, and also to direct-reading devices.

2 Normative references

This European Standard incorporates by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies.


EN 481	Workplace atmospheres - Size fraction definition for measurement of airborne particles
prEN 889	Workplace atmospheres - Guidance for the assessment of exposure to chemical agents for comparison with limit values and measurement strategy
ISO 78/2	Layouts for standards - Part 2: Standard for chemical analysis. 1982
ISO 3534-1	Statistics - Vocabulary and symbols - Part 1: Probability and general statistical terms
ISO 6879	Air quality - Performance characteristics and related concepts for air quality measuring methods 1983

3 Definitions

For the purpose of this standard the following definitions apply:

3.1 averaging time: A period of time for which the measuring procedure yields a single value.

Note:

For direct reading instruments the averaging time is related to the internal electrical time constant. For other procedures it is normally equal to the sampling time.

3.2 bias: consistent deviation of the results of a measurement process from the true value of the air quality characteristic itself (ISO 6879).

Note:

In this European Standard “Air quality characteristic” means the concentration of a chemical agent in air.

3.3 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.

Note:

This definition is taken from a proposal for a European Directive.

3.4 exposure (by inhalation): A situation in which a chemical agent is present in air which is inhaled by a person.

3.5 limit value: Reference figure for the concentration of a chemical agent in air.

Note:

Limit values are mostly set for reference periods of 8 h, but may also be set for shorter periods or concentration excursions.

The limit values for gases and vapours are stated in terms independent of temperature and air pressure variables in ml/m³ (ppm V/V) and in terms dependent on those variables in mg/m³ for a temperature of 20 °C and a pressure of 101,3 kPa.

The limit values for suspended matter are given in mg/m³ or multiples of that for actual environmental conditions (temperature, pressure) at the workplace. The limit values of fibres are given in fibres/m³ or fibres/cm³ for actual environmental conditions (temperature, pressure) at the workplace.

3.6 measuring procedure: Procedure for sampling and analysing one or more chemical agents in the air including storage and transportation of the sample.

3.7 overall uncertainty (of a measuring procedure or of an instrument): Quantity used to characterize as a whole the uncertainty of the result given by an apparatus or a measuring procedure. It is expressed, as a percentage, by a combination of bias and precision usually according to the formula

|x − x_ref| + 2s

x_ref

× 100

where:

x is the mean value of results of a number n of repeated measurements;
x_ref is the true or accepted reference value of concentration;
s is the standard deviation of measurements.

Note:

In strict mathematical terms there is no way to combine precision (a variance) and bias (an absolute number). However by occupational hygiene precedent and time honoured convention they have been combined according to the above formula.

3.8 precision: The closeness of agreement between the results obtained by applying the method several times under prescribed conditions. (ISO 6879)

3.9 selectivity: Degree of independence from interferents.

3.10 species: The different forms in which a chemical agent may be present, each form being defined by its chemical composition and/or detailed physical characteristics.

3.11 specified measuring range: The set of values of the concentration for which the overall uncertainty of a measurement procedure is intended to lie within specified limits.

3.12 true value (of a quantity): The value which characterizes a quantity perfectly defined in the conditions which exist at the moment when that quantity is considered.

Note:

The true value of a quantity is a theoretical concept and, in general, cannot be known exactly. (ISO 3534-1)

3.13 validation: The process of evaluating the performance of a measuring procedure and checking that the performance meets certain pre-set criteria.

4 Classification

4.1 General
The measurement procedures are classified with regard to measurement tasks. As a result of the measurement strategy, as laid down in prEN 689, the following measurement tasks are specified and explained (see also table 1).

prEN 689 also describes a number of measurement strategies which involve a combination of these measurement tasks (see annex A).

4.2 Screening measurements of time weighted average concentration
These are performed to obtain relatively crude quantitative information on the exposure level in order to decide whether an exposure problem exists at all and if so to appraise its possible seriousness. These measurements can also be used to determine if the exposure is well below or well above the limit value.

4.3 Screening measurements of variation of concentration in time end/or space
These measurements are used in order to:

- provide information on the likely pattern of concentration of chemical agents;
- identify locations and periods of elevated exposure;
- set the duration and frequency of sampling for measurements for comparison with limit values;
- locate emission sources;
- estimate the effectiveness of ventilation or other technical measures.

4.4 Measurements near an emission source
These may provide information on the location and the intensity of the source. In association with other information they may allow the elimination of a suspected source as a significant contributor to exposure.

4.5 Measurements for comparison with limit values
These provide accurate and reliable information on, or allow the prediction of, the time-weighted average concentration of a specific chemical agent in the air which may be inhaled.

4.6 Periodic measurements
These are used to determine whether the exposure conditions have changed since the comparison with limit values, or whether control measures remain effective.

Note:

Since the composition of the workplace atmosphere and the environmental conditions will have been investigated during the initial occupational exposure assessment it may be appropriate for periodic measurements to use procedures with lower selectivity.

5 Performance requirements

5.1 Unambiguity
Every measurement procedure in the specified measuring range shall produce an unambiguous measurement result of the concentration of the chemical agent being measured. This means that an analytically determined value shall correspond to one concentration only.

5.2 Selectivity
Selectivity requirements will vary from case to case, depending on what is known in advance about the air composition. If the air composition is not fully known in advance then the measuring procedure shall have a high selectivity taking into account the measuring uncertainty and the likely interferences.

If the composition of the atmosphere is known, qualitatively, prior to the measurement, then the selectivity requirement will be low, as long as the full value recorded is counted as applying to the chemical agent being measured and provided that the result is not lowered by the presence of the other components.

Procedures for measuring suspended matter shall make possible a selection of that particle fraction, for which the chemical agents limit value is set. (see EN 481)

If different limit values are set for different species of an agent, then the measuring procedure shall enable the determination of the individual species if necessary for the assessment.

5.3 Overall uncertainty, minimum specified measuring range, averaging time
5.3.1 Depending on the measurement task the specifications of the overall uncertainty, for minimum specified measuring ranges and averaging times, shall be as given in table 1.

5.3.2 In some specific standards performance requirements shall be specified for minimum measuring range and/or averaging time as is appropriate for the specific measuring procedure or device.

5.3.3 To cover the required minimum specified measuring range a combination of two procedures with restricted but complementary and overlapping specified measuring ranges may also be used.

**Table 1: Specification of performance requirements depending on the measurement task (LV = limit value)**
Measurement task	relative overall uncertainty	minimum specified measuring range	averaging time	see clause
screening measurement of time weighted average concentration	<= 50%	0,1 to 5 LV	less than or equal to limit value reference period	5.3.3
screening measurement of variation of concentration
a) in time	<= 20%	dynamic range ≥ 10:1 ¹)	<= 5 min	5.3.4
b) in space	<= 40%	dynamic range ≥ 10:1 ¹)	<= 15 min	5.3.3 5.3.5
measurement near an emission source	<= 50%	0,5 to 10 LV	source dependent	5.3.3
measurement for comparison with limit values	<= 50%	0,1 to 0,5 LV	less than or equal to limit value reference period	5.3.3
measurement for comparison with limit values	<= 30%	0,5 to 2 LV	less than or equal to limit value reference period	5.3.3
periodic measurements	<= 50%	0,1 to 0,5 LV	less than or equal to limit value reference period	5.3.3
periodic measurements	<= 30%	0,5 to 2 LV	less than or equal to limit value reference period	5.3.3

¹) A minimum measuring range is not specified. The required measuring range of the concentration can be decided for each particular application. Nevertheless, a minimum span between the upper and lower limits of the measuring range of concentration is specified.

5.3.4 For this type of measurement only the precision shall be used in the calculation of the overall uncertainty, provided it can be shown that the variation in the bias is small.

5.3.5 If relative concentrations only are of interest in screening measurements of variation of concentration in space bias is unimportant and the overall uncertainty requirement may be replaced by a precision requirement of <= 20 %, provided it can be shown that the variation in the bias is small.

5.4 Composite procedures
Performance requirements detailed in 5.3 shall be fulfilled for the whole procedure even if the procedure consists of several distinct steps.

Storage and transportation of a sample, which is collected as part of a measuring procedure, shall be carried out in such a way, that the physical and chemical integrity is not changed.

5.5 Environmental conditions
Performance requirements concerning unambiguity, selectivity, overall uncertainty, minimum specified measuring range and averaging time shall be fulfilled under the environmental conditions present at the workplace and typical of the intended use of the procedure. However, the testing of a procedure shall be carried out under laboratory conditions. Appropriate test methods and criteria can only be specified for laboratory tests at present. It may be necessary to consider influences of climate (temperature, humidity, pressure), interferences and other environmental conditions.

For each measuring procedure the range of climate conditions, under which the performance requirements of 5.1, 5.2, 5.3 and 5.4 are fulfilled by this procedure shall be specified.

5.6 Description of measuring procedure
There shall be a description for each procedure (see ISO 78/2). The description shall contain all necessary information to carry out the procedure, information about the attainable overall uncertainty, specified measuring range, averaging time, interferences and information on environmental or any other conditions, which can influence the performance of the procedure.

5.7 Dimension of result
The final result of a measuring procedure shall be expressed in the same units as those of the limit value. This may be achieved directly or by means of a suitable conversion.

This requirement is not obligatory for screening measurements of the variation of concentration.

6 Test methods

6.1 Detailed test methods for unambiguity, selectivity, overall uncertainty, minimum specified measuring range, averaging time and environmental influences depend on the specific procedure or device used for workplace measurement. These test methods are given in the standards detailing specific performance requirements for these individual procedures or devices (see clause 0).

Note:

As requirements for field testing are not yet available, it is necessary to limit testing to laboratory conditions (see also 5.5).

6.2 For measuring procedures consisting of several independent steps (preparation of equipment, sampling, transportation and storage of sample, analysis) as an alternative to testing the whole procedure it may be more convenient to test the independent steps of a procedure individually. The relative overall uncertainty of the whole procedure shall then be calculated by an appropriate combination of the uncertainties of all the independent steps.

Note:

The detailed calculation method is specified in the appropriate specific standards.

6.3 To determine the overall uncertainty of a measuring procedure, repeated measurements under defined conditions shall be carried out. These test conditions shall be as given in the specific standards. The overall uncertainty under these defined conditions shall be determined by the same analyst, in the same laboratory, repeating the procedure on the same day. The minimum number of repeated measurements for a given set of conditions shall be 6. The relative overall uncertainty shall be calculated according to 3.7.

The number of measurements on which the relative overall uncertainty is based upon shall be specified in the specific standards.

The result shall be compared with the requirements of 5.3.

6.4 As a minimum requirement the relative overall uncertainty shall be determined at concentrations at the lower and upper ends of the minimum specified measuring range of table 1 and at least at one intermediate concentration.

6.5 The influence of environmental parameters and interferences which may influence the measurement results, depending on the principle of the method, shall be tested (see 5.5). Further influences may also occur and shall be taken into account if necessary. These include for example wind speed and wind direction and direction of sampling probe. If correction factors are applied for known and explainable bias due to environmental influences, these shall be justified and recorded in the test.

7 Test report

A test report shall be prepared for each measurement procedure tested containing at least the method and conditions of test and the results obtained.

Annex A (informative)

Measurement categories described in prEN 689 and involving a combination of measurement tasks

A.1 Worst case measurements
Screening measurements in time and space (see 4.3) may clearly identify episodes where higher exposures occur, e.g. high emissions due to certain working activities. Sampling periods can be selected containing these episodes. This approach is called worst-case sampling. Subsequently, monitoring may be required either as a screening measurement of time-weighted average concentration (see 4.2) or for comparison with limit values (see 4.5).

A.2 Fixed point measurements
Fixed point measurements may be used for comparison with limit values (see 4.5) if the results are representative for the exposure concentration. In other uses, the initial measurement task is the same as for emission sources (see 4.4) and any subsequent monitoring will be a screening measurement of time-weighted average concentration (see 4.2) or periodic measurements (see 4.6).

A.3 Short-term peak measurements
Screening measurements of variation of time (see 4.3) may find short-term peaks. These measurements may be followed by screening measurements of time-weighted average concentration (see 4.2). Where the measurements are of exposure concentration, these may be compared within limit values (see 4.5) Short-term limit values may be important in these cases.