Bsi bs en 14412 2004 (2009)

en covers fm BRITISH STANDARD BS EN 14412 2004 Indoor air quality — Diffusive samplers for the determination of concentration of gases and vapours — Guide for selection, use and maintenance Confirmed[.]

Indoor air quality —

Diffusive samplers for

the determination of

concentration of gases

and vapours — Guide

for selection, use and

This British Standard was

published under the authority

of the Standards Policy and

A list of organizations represented on this subcommittee can be obtained on request to its secretary

Cross-references

The British Standards which implement international or European

publications referred to in this document may be found in the BSI Catalogue

under the section entitled “International Standards Correspondence Index”, or

by using the “Search” facility of the BSI Electronic Catalogue or of British

— aid enquirers to understand the text;

— present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the

Amendments issued since publication

EUROPÄISCHE NORM September 2004

ICS 13.040.20

English version

Indoor air quality - Diffusive samplers for the determination of

concentrations of gases and vapours - Guide for selection, use

and maintenance

Qualité de l'air intérieur - Echantillonneurs par diffusion

pour la détermination de la concentration des gaz et des

vapeurs - Guide pour la sélection, l'utilisation et la

maintenance

Innenraumluftqualität - Passivsammler zur Bestimmung der Konzentrationen von Gasen und Dämpfen - Anleitung zur Auswahl, Anwendung und Handhabung

This European Standard was approved by CEN on 9 July 2004.

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.

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 Central Secretariat has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION

C O M I T É E U R O P É E N D E N O R M A L I S A T I O N

E U R O P Ä I S C H E S K O M I T E E F Ü R N O R M U N G

Management Centre: rue de Stassart, 36 B-1050 Brussels

© 2004 CEN All rights of exploitation in any form and by any means reserved

worldwide for CEN national Members.

Ref No EN 14412:2004: E

Contents

page

Foreword 4

1 Scope 6

2 Normative references 6

3 Terms and definitions 6

4 Symbols and abbreviations 9

5 Operating principles 9

5.1 Principle of diffusive sampling 9

5.2 Dimensions of diffusive uptake rate 10

5.3 Bias due to the selection of a non-ideal sorbent 11

5.4 Environmental factors affecting sampler performance 11

5.4.1 Temperature and pressure 11

5.4.2 Humidity 11

5.4.3 Transients 12

5.4.4 The influence of air velocity 12

5.4.5 Transportation 13

6 Measurement objectives 13

6.1 General 13

6.2 Identification of causes of complaints about poor indoor air quality 13

6.3 Determination of reference values for indoor air quality 13

6.4 Compliance with limit or guideline values for indoor air 14

6.5 Identification of indoor pollutant sources 14

6.6 Testing of effectiveness of remedial action 14

6.7 Analysis of trends in indoor air quality 14

6.8 Assessment of concentrations in indoor air at abnormal or "worst-case" conditions 14

6.9 Personal monitoring 14

6.10 Validation of indoor pollution models 14

6.11 Measurement of mean ventilation rates 14

6.12 Aim of quality control with parallel measurements involving different methods 15

7 Measurement strategy 15

7.1 General 15

7.2 Elements of sampling strategy 15

7.2.1 General 15

7.2.2 Time of sampling 15

7.2.3 Sampling duration and sampling frequency 16

7.2.4 Location of samplers 17

7.2.5 Simultaneous ambient air measurements 17

7.2.6 Supplementary information 18

7.2.7 Uncertainty 18

7.3 Measurement strategy with respect to defined measurement objectives 18

7.3.1 General 18

7.3.2 Identification of causes of complaints about poor indoor air quality 18

7.3.3 Determining reference values of indoor air quality 20

7.3.4 Control of limit and guideline values 21

7.3.5 Identification of air pollutant sources 22

7.3.6 Testing of effectiveness of remedial actions 23

7.3.10 Validation of indoor pollution models 27

7.3.11 Measurement of mean ventilation rates 28

7.3.12 Aim of quality control with parallel measurements involving different methods 28

8 Selection of a sampling method 29

8.1 Sources of information on the maintenance of diffusive samplers 29

8.2 Selection of a sampler 29

9 Requirements for training 30

10 Quality assurance and quality control 30

Annex A (informative) Types of diffusive samplers 33

Annex B (informative) Limit values/Guideline values 36

Annex C (informative) Calculation of diffusion coefficients and uptake rates 38

C.1 Calculation of diffusion coefficients 38

C.2 Simple method to calculate uptake rates 41

C.3 Literature on values of diffusive coefficients 43

Annex D (informative) Characteristics of some diffusive samplers 44

Bibliography 46

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom

Introduction

European Standard EN 13528 specifies requirements and test methods for the determination of performance characteristics of diffusive samplers used for the determination of concentrations of gases and vapours in ambient and indoor atmospheres Additionally this document provides a guidance for the user when selecting an appropriate type of sampler, measurement strategy and maintenance procedure

EN 13528 is a multi-part standard having the following parts:

— Part 1 (Ambient air quality – Diffusive samplers for the determination of concentrations of gases and vapours – Requirements and test methods): General requirements

— Part 2 (Ambient air quality – Diffusive samplers for the determination of concentrations of gases and vapours – Requirements and test methods): Specific requirements and test methods

— Part 3 (Ambient air quality – Diffusive samplers for the determination of concentrations of gases and vapours – Requirements and test methods): Guide to selection, use and maintenance

Because of the importance of these samplers in the process of monitoring, diffusive samplers used to measure indoor air quality have to fulfil some general requirements related to the sampling objective These requirements are given in EN 13528-1 for measuring ambient air quality The same principles apply to measuring indoor air although the target values have yet to be set by the Regulatory Authorities

at either National, European or International level

These requirements include unambiguity, selectivity and data quality objectives, including uncertainty

In addition, diffusive samplers used to measure ambient and indoor air quality have to also fulfil some specific requirements in addition to those specified in EN 13528-1 These specific requirements are given in EN 13528-2 for measuring ambient air quality The same principles apply to measuring indoor air These requirements include desorption efficiency, diffusive uptake rate and sensitivity to air velocity Such general and specific requirements may also be appropriate for other measuring objectives used in the assessment of indoor air quality

It is the user's primary responsibility to choose appropriate procedures or devices that meet the requirements of this document 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

EN 13528-3 gives guidance on the selection, use and maintenance of diffusive samplers used to measure ambient air quality

For the special tasks of sampling workplace air, the regulations of the European Standard EN 482 [1] and EN 838 apply This document on the use of diffusive samplers for indoor air has been created in addition to those for workplace air because the measurement strategies, the underlying European Directives for ambient air [2], limit and guideline values and the consequent definitions and practical applications of the estimation of the uncertainty of measurements are different

In contrast to typical ambient air measurements the appearance of unexpected compounds in indoor air environments is quite common Procedures to calculate specific uptake rates of these compounds are needed more often as there is only a limited number of uptake rates validated by experiments (see EN 13528-2 and EN 13528-3) to assess the respective concentration values In addition to the general calculation procedure of the individual uptake rate as given in EN 13528-2 and EN 13528-3 detailed procedures to calculate diffusion coefficients and the uptake rate are given in annex C of this document

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 13528-2:2002, Ambient air quality – Diffusive samplers for the determination of concentrations of

gases and vapours – Requirements and test methods – Part 2: Specific requirements and test methods

ISO 16000-1, Indoor air – Part 1: General aspects of sampling strategy

3 Terms and definitions

For the purposes of this document, the following terms and definitions apply

cross-sectional area of the diffusion path

cross-sectional area of the space inside the diffusive sampler, which is available for the diffusion process, expressed in square centimetres This cross-sectional area may be identical to the intake opening

3.4

diffusive sampler

a device which is capable of taking samples of gases or vapours from the atmosphere at a rate controlled by a physical process such as gaseous diffusion through a static air layer or a porous material and/or permeation through a membrane, but which does not involve the active movement of pumped air through the device

[EN 13528-1:2002]

NOTE Active normally refers to the pumped movement of air

3.5

diffusive uptake rate

rate at which the diffusive sampler collects a particular gas or vapour from the atmosphere, expressed

in cubic centimetres per minute (cm3 min-1)

3.6

indoor air

air in indoor environment, i.e dwellings having living rooms, bedrooms, DIY (do-it-yourself) rooms, recreation rooms and cellars, kitchens and bathrooms; workrooms or work places in buildings which are not subject to health and safety inspections in regard to air pollutants (for example, offices, sales premises); public buildings (for example hospitals, schools, kindergartens, sports halls, libraries, restaurants and bars, theatres, cinemas and other function rooms), and also cabins of vehicles

NOTE In some countries workplaces like offices and sales premises are subject to health and safety inspections with regard to air pollutants

u is the uptake rate (ml/min);

t is the time of exposure (min);

ρ is the concentration of analyte (µg/m³)

uncertainty (of measurement)

parameter, associated with the results of a measurement, that characterises the dispersion of values that could reasonably be attributed to the measurand

NOTE 1 The parameter may be, for example, a standard deviation (or given multiple of it), or the half width of an interval having a stated level of confidence

NOTE 2 Uncertainty of measurement comprises, in general, of many components Some of these components may be evaluated from the statistical distribution of the results of a series of measurements and can be characterised by experimental standard deviations The other components, which can also be characterised by standard deviations, are evaluated from assumed probability distributions based on experience or other information NOTE 3 It is understood that the result of a measurement is the best estimate of the value of a measurand, and that all components of uncertainty, including those arising from systematic effects, such as components associated with corrections and reference standards, contribute to this dispersion

3.16

validation

process of evaluating the performance of a measuring procedure and checking that the performance meets certain pre-set criteria

4 Symbols and abbreviations

A cross-sectional area of the diffusion path, or equivalent sorption surface, in square centimetres

D diffusion coefficient of analyte, in square centimetres per minute

k correction factor for non-ideal behaviour

l length of static air layer in sampler (or equivalent for permeation types), in centimetres

M molar mass of analyte, in grams per mol

m s mass of the analyte which is sorbed by diffusion, in picograms

P pressure of the sampled atmosphere during sampling, in kilopascals

t exposure time, in minutes

T temperature of the atmosphere sampled, in Kelvin

U diffusive uptake rate, in cubic centimetres per minute

ρ delivered concentration, in micrograms per cubic meter

ρ1 the concentration of the given analyte at the beginning of the diffusion layer (l = 0), in

micrograms per cubic meter

ρ2 the concentration of the given analyte at the end of the diffusion layer, in micrograms per cubic

meter

τ the time constant of the diffusive sampler, in seconds

5 Operating principles

5.1 Principle of diffusive sampling

The mass of the analyte which can diffuse to a suitable sorbent within a certain time is determined by

the equation which is derived from Fick's first law of diffusion:

l

t D

A

This equation differs from equation (4) in EN 13528-2:2002, because it refers to the more general

situation where ρ2 may be non-zero Ideally ρ1 is equal to the concentration of the given analyte in the

air outside the diffusive sampler (ρ), and ρ2 equals zero ("zero sink"-condition) In that case the

magnitude of the diffusive uptake rate, D ⋅ A/l, is dependent only on the diffusion coefficient of the given

analyte and on the geometry of the diffusive sampler used

Figure 1 – Diagram of diffusion process

The inlet of a sampler with cross-section A at position 1 defines the beginning of the diffusion path of an

analyte with a concentration of ρ1.A sorbent at position 2, which will reduce the concentration of the

analyte, ρ2, to zero (ideally) due to sorption or chemical reaction, serves as the driving force for the

diffusion along l

In practice, there are a number of factors that can give rise to non-ideal behaviour, so that:

l

k t D A

ms = × × ρ × ×

(3)

NOTE The correction factor k can be a function of concentration and time of exposure (see 5.3)

A general overview of the principles of diffusive sampling is given in [3]

5.2 Dimensions of diffusive uptake rate

For a given concentration ρ in micrograms per cubic metre of gas or vapour, the diffusive uptake rate is

NOTE Although the uptake rate, U, has dimensions of volume per unit time, this does not indicate a real

volumetric flow of (analyte in) air

5.3 Bias due to the selection of a non-ideal sorbent

The performance of a diffusive sampler depends critically on the selection and use of a sorbent or collection medium If the sorbent has a high sorption efficiency, the residual vapour pressure and the respective concentration (ρ2) of the sampled compound at the sorbent surface will then be very small in comparison to the ambient concentration, and the observed uptake rate will be close to its ideal steady-state value, which can usually be calculated from the geometry of the sampler and the diffusion coefficient of the analyte in air

In the case where a weak sorbent is used, then ρ2 in equation (2) is non-zero and ms/t will decrease with the time of sampling In the alternative expression, equation (3), k has a value significantly less than unity Hence U in equation (4) will also decrease with the time of sampling The concentration of the sampled pollutant can also have a (lesser) effect on ms/t and hence on U The magnitude of these

effects is dependent on the adsorption isotherm of the analyte and sorbent concerned, and may be calculated with the aid of computer models [4,5]

Another manifestation of the same effect is back-diffusion, sometimes called reverse diffusion This can happen where, some time after sampling has started, the vapour pressure of the analyte at the sorbent surface, ρ2, is greater than the external concentration, ρ1, for example if a sampler is first exposed to a high concentration and then to a much lower or even zero concentration This type of exposure profile can occur in certain applications, and the magnitude of any error introduced will depend on whether the period of high concentration occurs at the beginning, middle, or end of the sampling period The phenomenon has been discussed in detail by Bartley and others [6-8] and a simple test is proposed [9]

to give an estimate of the maximum bias to be expected between a pulsed exposure and an exposure

to a constant concentration, which latter normally provides the basis for the sampler calibration This test is 30 min exposure to a high concentration, followed by 7,5 h of clean air, and has been adopted in

EN 838 For ambient air applications (EN 13528-2:2002, 7.3.1), however, it is considered that an exposure profile of alternate equal periods of high and low exposure for a 24h cycle is more typical of the intended application, where diurnal variations in concentration are common Generally in indoor environments both types of exposure profiles may occur The extent of back-diffusion can also be modelled theoretically [5,10]

To reduce these effects as much as possible, it is desirable to choose a sorbent with high sorption capacity and low vapour pressure of the sorbed analyte or of the reaction product formed by a reactive sorbent

5.4 Environmental factors affecting sampler performance

5.4.1 Temperature and pressure

For an ideal diffusive sampler, the dependence of U on absolute temperature and pressure is governed

by that of the diffusion coefficient of the analyte The latter dependence is given by:

5.4.3 Transients

Simple derivations of Fick's Law assume steady state conditions, but in the practical use of diffusive samplers, the ambient level of pollutants is likely to vary widely The question then arises whether a sampler will give a truly integrated response (ignoring sorbent effects, see 5.3) or will "miss" short-lived transients before they have had a chance to be trapped by the sorbent The problem has been discussed theoretically [6, 13-15] and practically [13, 16-17] and shown not to be a problem provided the total sampling time is well in excess of (say 10 times) the time constant, τ, of the diffusive sampler,

i.e the time a molecule takes to diffuse into the sampler under steady-state conditions The time constant is given by:

Most commercial samplers, as described in annex D, exhibit time constants with values between about

1 s and 10 s When using these types of sampler at low concentrations and respective sampling duration (days and weeks) transients are of no concern

5.4.4 The influence of air velocity

5.4.4.1 Effect of low and high wind speeds

Air face velocity and the way a diffusive sampler is oriented in a room can affect its performance because both parameters may influence the effective diffusion path length [18-21] The diffusive mass

uptake of a sampler (equation 2) is a function of the length, l, and the cross-sectional area, A, the

diffusion gap within the sampler The nominal diffusion path length is defined by the geometry of the sampler and is the distance between the sorbent surface and the external face of the sampler The effective length is not necessarily the same as the nominal length, and may be greater or less, depending on circumstances The cross-sectional area is also defined by the geometry of the sampler and if the cross-section of the diffusion gap is not constant along its length, is defined by the narrowest portion

Under conditions of low wind speeds, the effective diffusion path length may be increased [20,21] This

is because a 'boundary layer' [18,19] exists between the stagnant air within the sampler and the moving

air outside and contributes to the effective diffusion path length, l In reality, there is a space outside the

sampler where there is a transition between static air and moving air: this space defines an extra length

(∆l) of static air which shall be included in the value of l The value of ∆l depends on the external

geometry of the sampler It also decreases with increasing air velocity Its significance depends on the value of the nominal path length of the diffusive sampler Thus a sampler with a small cross-section and long internal air gap will be relatively unaffected by air velocity, whilst a short, broad sampler will be significantly affected This is borne out in practice, as has been demonstrated with samplers of varying length [20,21] Low sampling rates are observed at low air velocities, but increase to a plateau value as the boundary layer effect becomes insignificant

Under conditions of high wind speeds, the effective diffusion path length may be decreased [22-27] This is because external high air flows disturb the static air layer within the sampler, which reduces the

effective air gap by a (different) factor ∆l The value of ∆l is small, provided the length to diameter ratio

of the sampler air gap is greater than 2,5 to 3 [22], or it can be avoided, or greatly reduced, by incorporating a draught shield, e.g a stainless steel screen or plastic membrane

The overall effect is therefore an s-shaped curve (see EN 13528-2:2002, 7.4, Figure 1)

5.4.4.2 Consequence for different sampler geometries

Tube-type samplers are typically unaffected by low air velocities [13,28,29] but those without a draught shield may be affected by high air velocities

Badge-type samplers generally have a large surface area and a reduced length of static air layer, so that they may be more affected by air velocity than tube designs and typically require a minimum face velocity of between 0,5 m⋅s-1 and 0,2 m⋅s-1 [30-33] Some badges with an inadequate draught shield are also affected at high air velocities [29,31,34]

Radial diffusive samplers [35,36] require a minimum face velocity of about 0,25 m⋅s-1

— place the samplers in inert closed containers to minimise the ingress of external contamination;

— if air-freighting samples, ensure that they are not subjected to negative pressure, e.g in the baggage hold;

— avoid exposure to high temperatures during transit, e.g in the boot of a car;

— if possible, keep the samplers at low temperature and away from contamination sources e.g petroleum or aviation fuel, but avoiding condensation on the sample;

— ensure that adequate sample blanks are transported with the samples so that any of the above problems can be identified

6 Measurement objectives

6.1 General

The primary objective of taking indoor air is to determine the quality of indoor air with the aim of assessing any risks to the health of the population and of individuals due to indoor air pollution This may include personal sampling In addition diffusive sampling is a cost effective way to gain knowledge

of parameters influencing the indoor environment, e.g ventilation rate

6.2 Identification of causes of complaints about poor indoor air quality

In many cases investigations of the indoor air are carried out as a consequence of complaints, which are made by persons living or working indoors Such complaints may be the perception of unknown or unpleasant odours, headache, irritation of the eyes, nose and throat, dryness of the skin or symptoms like tiredness, lack of concentration and unspecific hypersensitivity reactions Investigations resulting from observed or suspected health problems of occupants are quite similar and require the same sampling strategy

6.3 Determination of reference values for indoor air quality

Reference values describe the status of a defined set of rooms at a given period in terms of their expected level of indoor pollutants These are useful to assess whether the levels of indoor pollutants are outside the normal range of occurrence

6.4 Compliance with limit or guideline values for indoor air

This objective requires measurements for checking whether specified limit or guideline values are being exceeded

Examples of limit and guideline values (except workplace atmospheres and ambient air) for indoor environments are given in Table B.1 and Table B.2 in annex B

6.5 Identification of indoor pollutant sources

Emission from point sources generate a pronounced concentration gradient in the vicinity of the source The existence of such concentration gradients may be used to trace the source in an indoor environment by a careful selection of sampling sites This strategy can lead to recommendations on how to improve indoor air quality e.g removing identified materials and strong emitters

6.6 Testing of effectiveness of remedial action

Remedial actions are modifications to a building, its systems or equipment aimed at reducing indoor air pollution The measurements for testing their effectiveness are comparison measurements before and after the remedial actions

6.7 Analysis of trends in indoor air quality

It is important to document intermediate and long-term trends of indoor air pollution concentration Respective analysis of trends will help to maintain, improve and establish abatement or risk management procedures

6.8 Assessment of concentrations in indoor air at abnormal or "worst-case" conditions

Beside screening measurements it can be very helpful to evaluate indoor air concentrations at abnormal

or "worst-case" conditions of the indoor climate (temperature, humidity, ventilation etc.) and during particular activities

6.9 Personal monitoring

Personal monitoring is the measurement of pollutants in the air that is breathed In general diffusive samplers for stationary measurements may be used for personal monitoring provided that the sampler design (size, fixing) is appropriate

6.10 Validation of indoor pollution models

Indoor air pollution models can be used to predict the concentration of pollutant in a building at a design stage based on an understanding of ventilation, air movement, source strength and sink effects Modelling can also be applied to predict the effectiveness of remedial or control measures The models need to be validated with experimental data

6.11 Measurement of mean ventilation rates

Ventilation rates in buildings can be determined using tracer gases Tracer gas is released into the building at a controlled rate and its concentration measured in the indoor air

Diffusive samplers can be used to measure some tracer gases for the determination of the mean ventilation rate over a period of days or weeks

6.12 Aim of quality control with parallel measurements involving different methods

The aim of this objective is to control and improve the quality of indoor measurements This can be achieved very effectively by parallel sampling with different sampling methods and/or different analytical methods

7 Measurement strategy

7.1 General

An appropriate measurement strategy is needed to reliably assess the defined objectives of indoor air quality (see above clauses) The measurement procedure is based on this strategy and includes an appropriate diffusive sampler (see 8.2), an analytical method and an associated quality assurance system (see clause 10)

Diffusive sampling of indoor air constituents is typically used for long-term sampling over periods of one day to several weeks Therefore the application of diffusive samplers has to be considered very carefully with respect to specific variations of the source strength and potential health effects of targeted compounds When using diffusive samplers the assessment of indoor air quality will require the development of a measurement strategy which may be different to the strategy for short-term measurements The strategy will take into account the monitoring objectives, the pollutants to be assessed, the required detection limit and the source emission characteristics Basically it has to be specified where, how, and how often measurements shall be taken The total measuring effort will be dependent on:

— the variation of pollutant concentrations in space and time;

— the availability of supplementary information;

— the required measurement uncertainty of the estimate

7.2 Elements of sampling strategy

of these parameters is fundamental and diffusive sampling is especially appropriate to study variations

in indoor air quality because of the moderate cost and effort required

If the substance to be determined is emitted constantly and continuously, for example by building materials or furnishings, several hours shall be allowed for the establishment of equilibrium after ventilating by opening a window In principle this effect is important for all types of sampling However, it

is less important for diffusive sampling, especially if the sampling is carried out for a long time under actual living conditions The assessment of the respective ventilation regime of the room under investigation will give valuable information when interpreting the results

If the building or room is equipped with a heating, ventilation and air-conditioning (HVAC) system, additional aspects shall be considered For example, undesirable emissions may result from the HVAC system itself (e.g., from sealing materials, humidifier water, dust deposits) and from sources of other rooms being distributed throughout the entire building, especially if the HVAC has a high recirculation rate

When indoor air pollutants have to be assessed due to emissions from intermittent sources the time of sampling will depend on the monitoring objectives It may correspond to the peak exposure period which can be measured only by continuous monitoring with a high time resolution or short-term sampling with exact timing But diffusive sampling can favourably be used to obtain the average exposure over a longer period

In some cases, the emission characteristics of suspected sources are initially unknown In such cases,

a continuous recording of measured quantities (for example total gaseous organic compounds using a flame ionisation detector (FID) or photoionization detector (PID)) for a limited time may provide useful information for estimating the sampling time and sampling duration (7.2.3)

7.2.3 Sampling duration and sampling frequency

The duration of sampling is determined by:

— nature of the substances under consideration;

— emission characteristics of the source;

— limits of quantification of the analytical method;

— occupant activities;

— environmental conditions in the building;

— definition of limit and guideline values

In many cases, particularly if only a few measurements are made, it is necessary to make compromises

that are not optimum for the first five aspects at the same time The sampling duration chosen is

particularly important in relation to the potential health effects of the targeted substance For substances having acute health effects, successive short-term sampling with a high time resolution shall be used, whereas long-term sampling shall be used for substances having chronic effects on health Long-term sampling methods do not detect short-term concentration peaks This may result in difficulties in interpretation of the measurement results, particularly if a substance also has a short-term effect on health

In relation to the emission characteristics of the source, it is clear that emissions from a source that emits only for a short time can only reasonably be determined by a short-term measurement correctly timed Conversely, sources with long-term emissions are best dealt with by long-term measurements However, it is quite possible that there are deviations from this general rule For example, the short-term peak concentration of a substance due to aerosol spraying can only be determined with a short-term measurement, but long-term sampling may be quite appropriate after spraying if residual concentration levels in the room are of primary interest

The sampling duration is determined by the limit of quantification of the chosen analytical method, i.e the mass of the analyte collected during sampling shall make possible an unambiguous identification and a reliable quantitative determination At the same time, it shall be remembered that the amount of analyte collected is not necessarily substantially increased by extending the sampling time over a longer period When the intention is to determine the concentration of a compound originating from an intermittent source that is activated only on rare occasions and for short intervals, nearly as much substance may be collected in a 1 h sampling period as in 24 h

For checking compliance with national or international limit and guideline values the sampling duration shall correspond to the time of exposure period stated in the limit/guideline definition (see annex B) Considering the expense and the resource available, the sampling frequency is generally low Moreover there is a tendency to take the result of one (or only a few) measurement(s) as a representative of the

on bookshelves, surfaces of furniture shall be avoided

Samples shall be taken about 1,5 m above the floor since this is the approximate height of the average breathing zone A convenient way is to suspend the sampler from the ceiling or a lamp by a thread Alternate sites may be required in specific circumstances; for example in the case of steep concentration gradients or thermal movement

The prevailing movement of air in a room, which depends on the nature and extent of the ventilation, may also be of great importance in specifying the measurement point Locations near openable windows and chimneys for example may have a higher local ventilation rate than the room as whole On the other hand a sampling error may result when using diffusive samplers having a large cross-section (badge-type samplers) if the face air velocity is too low, as it is possible particularly in niches and the corners of rooms

To find out the distribution of pollutants inside a building can be helpful especially when tracing frequent health complaints, e.g in an office building Respective data can be obtained conveniently by sampling with diffusive samplers simultaneously at representative sites in the building, e.g at the same site in different floors, at all quarters of a floor, in rooms respective to their activity patterns, age of renovation, building material etc Again a careful and comprehensive documentation of all parameters is a prerequisite for a successful interpretation of the results

In occupied premises, care shall be taken to assure that the sampling equipment is protected as much

as possible from accidental or unauthorized intervention (e.g from children and pets) Furthermore it is important that measurements shall not impair the normal use of the room

7.2.5 Simultaneous ambient air measurements

Due to the permanent exchange between indoor and ambient air caused by infiltration and ventilation processes, it may be important to supplement indoor air measurements with a simultaneous measurement of the ambient air [37,38] Depending on the circumstances this will provide further useful information on the sources of the indoor pollutants The ambient air samples shall be taken in the vicinity of the building preferably outside the window of the room under investigation but avoiding any source of contamination In making such measurements, it shall be remembered that vertical concentration gradients may occur; for example, for the components of vehicle exhaust gases in street canyons If the building is equipped with an HVAC system, the ambient air shall be sampled near the air intake

7.2.6 Supplementary information

It is a prerequisite of a successful sampling strategy to obtain all relevant supplementary information regarding the measurement objectives A careful observation of the sampling site by an experienced interviewer will help to obtain the information To record the information needed a questionnaire according to annex D of ISO 16000-1 will be beneficial Information about building and maintenance materials, furniture and other equipments, time of construction and/or renovation, location of the building

(influence of ambient air quality, e.g due to traffic and industrial emissions), location of the room in the

building and possible interferences with other rooms, physical parameters of the indoor environment (e.g temperature, humidity, air exchange rate), activities and health status of the occupants and last but not least social/psychological aspects are needed to support and to interpret analytical data with respect

to the measurement objectives of clause 6

The operating parameters and the state of maintenance of the HVAC system, if used, shall always be included in the report relating to an indoor air sample, and if operation is intermittent or restricted

Information on mean weather conditions at the time of sampling may be of interest as well

7.2.7 Uncertainty

The degree of uncertainty needed to meet different sampling objectives has direct consequences on the effort, time and manpower involved The resource required is influenced by the nature of the target

compound, the types of sampling and the analytical procedure available The requirements for

measuring one or a few target compounds as e.g in objective "control of limit and guideline values" (see 7.3.4) are generally higher than for "identification of causes of complaints about poor indoor air quality" (see 7.3.2) as in the latter case most often target compounds are unknown The demand to find out a cause-effect relationship will override the necessity of maximum uncertainty

7.3 Measurement strategy with respect to defined measurement objectives

7.3.1 General

Practical examples of the development of a strategy for the measurement of VOC in indoor air are given

in various reports and guidelines [39-44] As these papers are mainly aimed at short term active sampling some additional information will be given in this guideline with special emphasis on diffusive sampling for the objectives given in clause 6

7.3.2 Identification of causes of complaints about poor indoor air quality

The causes of the complaints and health effects are difficult to discover because the cause may be multifactorial; pollutants, temperature, humidity, lighting, noise, work related stress etc Information on the environmental conditions associated with the occurrence of the complaint is often inadequate or misleading Quick changing conditions with corresponding changes in concentrations of pollutants and changes of assumed health effects (odour, irritations etc.) may not be traceable by diffusive sampling due to the inherent long sampling period Thus, in assessing the health implications of strong irritants, the maximum exposure over short periods of time tends to be of interest Ideally a continuous measurement with a high resolution in time rather than an integrating sampling method like diffusive sampling would be used In the case of compounds which have long-term effects, for example carcinogenic, mutagenic and teratogenic compounds and compounds leading to disorder of metabolic and central nervous systems, it is generally the mean exposure over fairly long periods of time which is

of interest and this may favour the use of diffusive sampling

There are many different circumstances encountered in such investigations and so it is not appropriate

to set strict rules for the sampling strategy Judgement is required based on the site specific situation, type of information required and previous experiences A progressive strategy involving additional compounds and parameters and finally a long term experience in this field of measurement The nature

of a substance, its concentration and its effect on the occupants may also have a considerable influence

on the strategy/boundary conditions chosen for the measurement Therefore it is strongly recommended

to start with pilot or screening measurements to determine a large variety of compounds to assess the indoor environmental conditions The pilot measurements as well as further measurements shall be supported by the results of questionnaires either distributed to all building occupants or completed by an interviewer The use of diffusive samplers has been described to measure formaldehyde and other volatile organic compounds in more than 100 buildings where occupants were concerned about poor indoor air quality [45]

If possible, during long term sampling, ventilation of the room and the behaviour of the occupants shall

be the same as when health effects occurred

The concentration of a compound can be influenced by the room temperature and air humidity (e.g formaldehyde which is emitted from chip boards) Therefore it is necessary to carry out the sampling under normal room conditions at which the room is usually used When complaints occur at other conditions an additional sampling shall be carried out at these specific conditions (also see 7.3.8) If these conditions are outside of the range of comfort [46] it shall be recommended that remedial action is undertaken to meet these criteria before any other measures are undertaken to reduce the concentration of the pollutant in the indoor air

To determine causes of complaints and possible health effects the elements of the sampling strategy shall be used as follows in addition to the basic information as given in 7.2.2 to 7.2.7:

— Time of sampling

The time of sampling shall be as soon as possible after complaints or health effects had become evident However, for sampling of duration of ≥ one week, the choice of sampling time tends to be less important

— Sampling duration and sampling frequency

The duration of sampling has to be set in a way that the limits of determination for all compounds of interest are exceeded and that representativity is guaranteed It is necessary to maintain a sampling duration of one week or a multiple to achieve a maximum of representativity per sampling site This

is to assess all different pollution loads that occur on the different days a week of at least once One sampling per site is adequate

— Sampling site and determinations with resolution in space

For screening measurements the diffusive sampler shall be placed in room assigned by the complaining occupant The sampler has to be fixed in the centre of the room in the breathing zone at

a height of approximately 1,5 m It has to be taken care, that no radiation heat influences the sampling characteristic of the diffusive sampler The distance from any wall shall be at least 1 m When occupants complain about poor air quality in a room screening measurements with diffusive samplers can be carried out in single rooms as well as in different rooms of a building at the same time

— Simultaneous ambient air measurements

Simultaneous ambient measurements are recommended as well

— Supplementary information

Any supplementary information (see 7.2.6) is needed to gain insight in a particular situation of indoor air quality, especially with regard to any time dependency of emission or concentration events and health complaints If there are changes in occupant activity during the sampling period these have to

be recorded Very important is the knowledge of the activity of intermittent sources This careful but critical assessment of supplementary information is a prerequisite of success

— Uncertainty

One of the main tasks of screening measurements is to get qualitative information about the composition of the indoor air and a good estimate of the concentration level Therefore an exceptional low uncertainty of the method is not required When compounds are determined for which diffusion coefficients are not available, these can be calculated by the formula described in annex C In this way the concentrations of compounds, which are not analysed routinely, can be estimated

7.3.3 Determining reference values of indoor air quality

If the choice of sampling sites and the number of samples fulfil the criteria of representativity reference values can be obtained, typically 95 percentiles per convention [47] According to an IUPAC guideline [48] it is recommended, especially for a limited number of values, to introduce the 0,95 expectation tolerance interval supplemented with information on the coverage with a confidence probability of at least 0,95 If the presence of a normal distribution has to be significantly rejected, the 0,95 confidence interval for the 0,05 and 0,95 percentiles based on the noncentral t-distribution have to be provided

To determine reference values of indoor air pollutants the following elements of sampling strategy shall

be used as follows in addition to the basic information given in 7.2.2 to 7.2.7:

— Time of sampling

To rule out any seasonal effects the individual sampling events shall be evenly distributed over the year The time of individual sampling shall be fixed in a way that representative concentration values can be assessed However, for sampling for ≥ one week, the choice of sampling time tends to be less important

— Sampling duration and sampling frequency

The duration of sampling has to be set in a way that the limits of determination for all compounds of interest are exceeded and that representative readings are obtained It is necessary to maintain a sampling duration of one week or a multiple to achieve a maximum of representativity per sampling site This is to assess all different pollution loads that occur on the different days of the week at least once One sampling per site is adequate

— Sampling site and determinations with resolution in space

The sampling site shall be representative, e.g the centre of the room most inhabited by all occupants shall be used

— Simultaneous ambient air measurements

Simultaneous ambient measurements are usually not necessary

— Supplementary information

The documentation of the criteria defining the population under study and the selection of samples is compulsory This will include the procedure of selecting random samples distributed all over the country or the area to be referred corrected by the population density, including all types of population agglomeration according to their presence The total number of samples shall be large enough to include different strata of building ages and their types of construction, of traffic density, of industrialization, of smoking habits and of other known confounders

— Uncertainty

Establishing reference values requires good analytical repeatability and trueness Both shall be as good as reasonably achievable and external intercomparison exercises, preferably at field conditions, shall be incorporated into the study Further intercomparison studies can be used to compare reference methods with the diffusive sampling method used All QA/QC procedures of the achieved level of uncertainty have to be documented completely

7.3.4 Control of limit and guideline values

Few guideline values applicable to indoor air exist at present [49] Moreover a common feature of most published indoor air quality guideline values is the fact that only limited instruction has been provided about the method of testing compliance with these values Essential to the use of the diffusive sampling method is a sampler characteristic (see annex D, Table D.1) with a resulting detection limit which meets the given values within their time base in a sufficient manner

In addition to the general principles for selection and use of diffusive samplers for the control of limit and guideline values, the following items shall be observed:

Before carrying out the sampling procedure, it has to be decided whether compliance with the limits given is to be considered under "ordinary usage" or "worst case" conditions Usually "worst case" conditions are utilized for short-term measurements, e.g in order to estimate a maximum load (also see 7.3.8)

Long-term sampling with diffusive samplers is used mainly for measurements in indoor environments under "normal conditions of occupancy" This sampling procedure shall have as little influence as possible upon normal room usage and lifestyle of the people who are living or working there Accordingly, the same activities and typical conditions shall continue throughout the measurement period

To control limit and guideline values the elements of sampling strategy shall be used as follows in addition to the basic information as given in 7.2.2 to 7.2.7:

— Time of sampling

In principle the time of sampling is not a prerequisite parameter because limit values have to be met all the time But a full understanding of potential and relevant source characteristics will help to survey limit and guideline values even under unfavourable circumstances

— Sampling duration and sampling frequency

The sampling duration (averaging time) shall be stipulated by the limit value (see B.1) Some guideline values show a less stringent definition of the sampling time In this case only the limits of determination for all compounds of interest have to be exceeded If there is no definition of the sampling frequency the representativity of a single measurement has to be proven

— Sampling site and determinations with resolution in space

The selection of the sampling site shall ensure results which are as representative as possible This

is usually done by placing the sampler in the investigated room as centrally as possible Tests on the limit value control of tetrachloroethene have shown that placement of diffusive samplers

at the most central site possible and at an approximate height of around 1,5 m (e.g while suspended from a thread) is optimal

Usually, rooms where people spend most of their time are chosen (e.g bedrooms or living rooms)

On the other hand, in the case of the testing of rooms in the vicinity of a dry cleaning establishment, for example, rooms which are closest to the dry cleaners shall be the first chosen (Sampling site is mainly dependent on the proximity of the pollutant source in relation to the investigated rooms.)

— Simultaneous ambient air measurements

Ambient measurements are not necessary

— Supplementary information

Especially in the case where limit values shall be controlled and where legal consequences could otherwise be pending, a clear and complete documentation of the sampling procedure is required

— Uncertainty

The utilization of diffusive samplers, especially with regard to measurements to ensure that limit values are not exceeded, shall be carried out by professional personnel (also see clause 9) who are familiar with the sampling device, the measurement task and its marginal conditions Only the precise knowledge of all parameters affecting the concentration of gases and vapours in the indoor environment and the function of the sampling device allow for accurate results which provide a representative picture of the indoor air pollution

To obtain a low degree of uncertainty it is recommended to incorporate comprehensive measurements for internal quality control e.g the use of field blanks and duplicate samples, external quality control with intercomparison measurements and to keep the analytical procedure traceable

7.3.5 Identification of air pollutant sources

Examples of identification of air pollution sources by a large field study involving diffusive samplers and questionnaires are given in [38,50,51] To identify air pollutant sources the elements of sampling strategy shall be used as follows in addition to the basic information as given in [52] and 7.2.2 to 7.2.7:

— Time of sampling

Simultaneous sampling is required to rule out the dependency of pollutant concentrations with all time related conditions The sampling time is less important

— Sampling duration and sampling frequency

The duration of sampling is less important provided the limits of determination for all compounds of interest are exceeded Sampling frequency depends on the degree of success and the resource available

— Sampling site and determinations with resolution in space

To identify the source it is advisable to divide the room into different areas and to simultaneously sample at a site in each area However, such a procedure will only be successful if the individual areas of the room can be classified as similar in terms of ventilation, which is not always the case, particularly in artificially ventilated rooms

Furthermore, diffusive samplers can be sited as near as possible to suspected sources, e.g on book shelves, at the outlet of ventilation systems, near the vent of electronic devices and floor or wall coverings, in cabinets Substantially elevated concentrations at these sites relative to the concentration simultaneously gained at a representative site in the room will identify a source But it shall be kept in mind that due to a spatial influence of the object under investigation on the uptake rate of the diffusive sampler (excessive or reduced air movement, see 5.4.4.1 and 5.4.4.2) the quantification of the measurements may be influenced

More detailed study would involve an investigation of the emission characteristics of material suspected to be a relevant pollutant source using respective guidelines [53] These will provide traceable and reproducible results of emission characteristics of material and products

— Simultaneous ambient air measurements

If there are indications of substantial pollutant sources outside the indoor environments, e.g odour or special activities like dry cleaning, painting, printing, degrassing etc., it is recommended to undertake simultaneous ambient air measurements in order to trace respective pollutants

— Supplementary information

An in-depth collection of typical information on indoor climate, activities etc are less necessary However, a careful description of individual sampling sites and an investigation and description of the chemical nature of the material in the nearest neighbourhood of each sampling site are prerequisite to understanding the analytical results and to effective countermeasures if necessary

— Uncertainty

7.3.6 Testing of effectiveness of remedial actions

The remedial actions for reducing indoor air pollution will consist of either the removal or modification of the source or improvement to the ventilation conditions Such remedial actions are considered to the extent that pollutants have been identified and are used as indicators of their effectiveness

Obviously, the most important feature of the measurement aimed at evaluating the effectiveness of remedial actions is that samples have to be collected before and after the remedial actions under identical or as much the same conditions as possible This implies that the measurement strategy shall

be chosen in such a way that the success or failure of the remedial actions is demonstrated as clearly

as possible by the result of the measurement

Notice that the success of the measurements for testing the effectiveness of remedial treatments depends on a critical and documented choice of the sampling conditions before the beginning of the remedial actions The two samplings (before and after the actions) shall consider as an unity

To test effectiveness of remedial actions the elements of sampling strategy shall be used as follows in addition to the basic information as given in 7.2.2 to 7.2.7:

— Time of sampling

For planning the sampling time care shall be taken of the identity of the sampling conditions which are not included in the remedial actions Therefore these conditions (e.g temperature, humidity and ventilation) shall be as similar as possible for both measurements E.g., identical sampling conditions are not realised if one measurement takes place in the summer (high temperature, good ventilation,

no room-heating) and the second measurement takes place in winter (low temperature, poor ventilation, room-heating)

The decay of the pollutants after removal or reduction of an emission source will govern the time of the second sampling event If the decay is known the time of the second sampling event has to be scheduled beforehand Otherwise successive samples have to be taken

— Sampling duration and sampling frequency

For the selection of these parameters the type and objective of the remedial action has to be taken into consideration, however the sampling duration of both measurements shall be equal Diffusive sampling is particularly suitable for long-term sampling if the remedial action is aimed at reducing average concentrations or exposures For short-term sampling aimed at assessing the effect of source modification or other actions to reduce peak concentrations of pollutants the diffusive sampling may be of limited value

Duplicate sampling is recommended for optimal quality control because of the inherent juridical and financial consequences

of the 95 % confidence interval of the measured mean concentrations are higher than the target concentrations

Within an indoor environment all spaces in which a remedial action has been taken or which shall benefit from the remedial action shall in principle be included in the pollutant measurement program For the selection of these spaces similar rationales hold as for the selection of the indoor

environments themselves If a source is removed or modified which, although polluting several spaces, causes highest pollutant levels in a distinct space, measurements in this space may be sufficient

In the case of the remedial action involving modification or removal of a source of pollutants, the source position is appropriate for assessing the result of the remedial action

However, the breathing zone position (1 m to 2 m above the floor level) will be more appropriate if the remedial action is intended to significantly reduce occupant exposure to a pollutant which may have other possible sources in the environment

If the remedial action is aimed at improving the ventilation efficiency at least two sampling positions

in a space shall be selected which before the remedial action yield the largest pollutant concentration For other remedial actions the breathing zone position shall be considered

— Simultaneous ambient air measurements

If the indoor air pollution is high due to ambient concentrations, parallel ambient air measurements are necessary both before and after the remedial actions to control the effectiveness of those actions

If the ventilation conditions change, ambient air measurements are useful to describe the influence

of ambient pollution on the indoor air concentrations

— Supplementary information

Furthermore notice has to be taken of the following conditions provided that these conditions are not included in the remedial actions:

— use of the room;

— activities of the occupants (e.g using of solvents and detergents, hobbies, renovations);

— use of fuels (wood, gas, oil, coal), kind and duration of heating;

— ambient sources and their variability (daily, weekly, seasonally)

— Uncertainty

These measurements require a high reproducibility because they are based on a critical comparison

of the results before and after the remedial actions

For testing of effectiveness of remedial treatments the requirements for the uncertainty are the same

as 7.3.2 A calculation of the diffusion coefficients is also possible If the measured mean pollutant concentration after the remedial action is near to the specified limit or guideline value a further measurement to check the observance of these values described in 7.3.4 is necessary

7.3.7 Analysis of trends in indoor air quality

It is important to know trends of indoor air pollutants in order to understand the mechanisms of their occurrence [54] and to reconsider measures undertaken in the past to improve indoor air quality This can be achieved by studying indoor air pollutants e.g benzene, formaldehyde, tetrachloroethene, dichloromethane or other pollutants which had been regulated or discussed critically in the past Also important is to recognise any appearance or increase of compounds which have been recently introduced in the indoor environment by new technologies and occupants behaviour or by substitution for other compounds of concern In the UK a study has been undertaken of 860 homes in order to establish a baseline for concentrations of indoor air pollutants in order that the UK Government can evaluate trends in indoor air quality by undertaking repeat surveys at approximately 5 year intervals [55]

To analyse trends in indoor air quality the elements of sampling strategy shall be used as follows in

— Time of sampling

To rule out any seasonal effects the individual sampling events shall be evenly distributed throughout the year The time of individual sampling shall be fixed in a way that representative concentration values can be assessed However, for sampling of duration ≥ one week the settings of sampling time tend to be less important

— Sampling duration and sampling frequency

The duration of sampling is less important providing that the limits of determination for all compounds of interest are exceeded and representativity is guaranteed The frequency of one sampling per site within one study is quite sufficient The long-term frequency of studies to investigate trends depends upon available resources A frequency of one study per five years seems

to be optimal

— Sampling site and determinations with resolution in space

The sampling site shall be representative, e.g the centre of the room most inhabited by all occupants shall be used

— Simultaneous ambient air measurements

Simultaneous ambient measurements are not necessary

— Supplementary information

The documentation of all conditions influencing the concentration of indoor air compounds by a standard questionnaire is a prerequisite to analyse trends This will include indoor climatic parameters, activities and the introduction of new material and products into the indoor environment

— Uncertainty

When analyzing long-term trends all aspects of quality control and quality assessment have to be addressed with a particular care If comparing new data with historic data, it is important to relate the performance of the method previously used with that being applied in the new study The trueness of all assessment procedures shall be as good as reasonably achievable and external intercomparison exercises, preferably at field conditions, shall be incorporated into the studies If external intercomparison exercises don’t involve diffusive samplers but a reference method, a second intercomparison study can be used to compare the reference method with the diffusive sampling method used in the trend study The repeatability shall be well documented and all QA/QC documentation of the level needed shall cover the total time frame of trend analysis

7.3.8 Assessment of concentrations in indoor air at abnormal or "worst-case" conditions

Most often there is a relationship between the source strength and the indoor environmental conditions The principle outcome of the application of a worst case measurement strategy may provide information about the nature of sources of indoor pollutants

In addition to this diffusive samplers are especially useful to assess particular conditions, e.g very low air exchange rates (e.g building constructions aimed at low energy consumption) or strong sink effects (influence of special building material leading to large additional reduction of indoor air concentrations)

or the reverse of it, the function of secondary sources (release of formerly adsorbed compounds) or the reactivity of special compounds indoors

The respective results may lead to a recommendation to adjust unfavourable conditions to normal values [56] in order to maintain good indoor air quality prior to removal of material suspected to be a pollutant source which may incur substantial costs

Most important, it shall be emphasized that the results of this sampling strategy shall not be used to

assess possible health impairments at normal conditions

To assess concentrations in indoor air at abnormal or "worst-case" conditions the elements of sampling strategy shall be used as follows in addition to the basic information as given in 7.2.2 to 7.2.7:

— Time of sampling

The sampling time is less important provided there is a link with the conditions under investigation

— Sampling duration and sampling frequency

The sampling duration is less important provided the limits of determination for all compounds of interest are exceeded Sampling frequency is a matter of degree of success and/or the resource available

— Sampling site and determinations with resolution in space

The sampling site shall be standardized, e.g in the centre of the room under investigation and not particularly influenced by emission sources

— Simultaneous ambient air measurements

Simultaneous ambient air measurements will only provide information of background concentrations not related to special indoor environmental conditions They are less necessary

— Supplementary information

The prerequisite of a successful assessment is the control and/or at least the documentation of all conditions influencing the concentration of compounds in indoor air over the total of the sampling duration

— Uncertainty

The uncertainty in terms of repeatability and trueness have to be well documented, but there is less requirement to maintain best values of both parameters as provided the statistical results to be discussed differentiate significantly from values at normal indoor conditions

7.3.9 Personal monitoring

Personal monitoring is a very useful objective to get information of the direct burden of a person with regard to selected compounds [37,57,58] In contrast to stationary diffusive sampling personal (mobile) samplers are usually exposed to much higher variations in air velocity, air temperature, humidity and

CO2 concentrations Personal samplers may be exposed to indoor, ambient and workplace air To differentiate between distinct exposure situations the temporary use of personal samplers will be useful Hence one or several samplers have to be opened and closed according to the situation or a determined schedule The increase of information will be beneficial but it shall be kept in mind that this multi sampling procedure is very complicated and therefore not recommended for a large collective

To monitor personal exposure the elements of sampling strategy shall be used as follows in addition to the basic information as given in 7.2.2 to 7.2.7:

— Time of sampling

The sampling time is less important providing that specific situations and activities are of no concern

— Sampling duration and sampling frequency

The duration of sampling is less important providing that the limits of determination for most compounds of interest are exceeded The successive sampling which is a matter of resource available will provide information on variation of the personal exposure

— Sampling site and determinations with resolution in space

The personal sampler shall be as close as possible to the inhaled air but not directly exposed to the expired air It is favourable to fix the personal sampler to items of clothing below mouth and nose The position has to be recorded During sleep and showering/bathing the personal sampler shall be placed nearby The site shall be representative for inhaled air and not subject to local sources or sinks (open window, evaporating fluids, etc.)!

— Supplementary information

Parallel monitoring of air, temperature and humidity (e.g by miniature data loggers) gives additional information to interpret results and to check reliability Continuous daily records (time, site, activities, incidents, sources, etc.) shall be made in order to make the data from personal monitoring with diffuse samplers valuable for exposure assessment (example of a appropriate form see Table 1)