Bsi bs en 13725 2003 (2006)

page Foreword...3 Introduction ...4 1 Scope ...4 2 Normative references ...5 3 Terms, definitions and symbols ...5 4 Principle of measurement ...19 5 Performance quality requirements...1

Incorporating Corrigendum No 1

This British Standard was

published under the authority

of the Standards Policy and

Strategy Committee on

15 May 2003

© BSI 2006

National foreword

This British Standard is the official English language version of

EN 13725:2003, including Corrigendum January 2006

The UK participation in its preparation was entrusted by Technical Committee EH/2, Air quality, to Subcommittee EH/2/1, Stationary source emissions, which has the responsibility to:

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

Amendments issued since publication

16253

Corrigendum No 1 28 April 2006 Replacement of Tables D.1 and E.1,

and Equations 36 and 43

Qualité de l'air - Détermination de la concentration d'une

odeur par olfactométrie dynamique Geruchsstoffkonzentration mit dynamischer OlfaktometrieLuftbeschaffenheit - Bestimmung der

This European Standard was approved by CEN on 6 December 2002.

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 Management Centre or to any CEN member.

This European Standard exists in three official versions (English, French, German) A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, 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 IS C H E S K O M IT E E FÜ R N O R M U N G

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

© 2003 CEN All rights of exploitation in any form and by any means reserved

worldwide for CEN national Members. Ref No EN 13725:2003 E

Including Corrigendum January 2006

page

Foreword 3

Introduction 4

1 Scope 4

2 Normative references 5

3 Terms, definitions and symbols 5

4 Principle of measurement 19

5 Performance quality requirements 19

6 Materials, gases and panel members 27

7 Sampling 35

8 Presentation of odorants to assessors 38

9 Data recording, calculation and reporting 40

Annex A (normative) Working conditions and working platform for sampling 46

Annex B (informative) Physiological principles 47

Annex C (informative) Example of calculation of instrumental accuracy and instability 51

Annex D (informative) Example of calculation of odour measurements within one laboratory 53

Annex E (informative) Example of calculations for panel selection 55

Annex F (informative) Example of the calculation of the odour concentration from a set of panel member responses 56

Annex G (informative) Example of the calculation used to determine the number of odour concentration measurements required to achieve a defined precision 60

Annex H (informative) Example of the calculation used to determine the number of odour concentration measurements required to detect a difference between two means 62

Annex I (informative) Example of the calculation of the odour flow rate (standard conditions) for a wet emission 65

Annex J (informative) Sampling strategy 66

Bibliography 70

This document (EN 13725:2003) has been prepared by Technical Committee CEN/TC 264 "Air quality", thesecretariat 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 October 2003, and conflicting national standards shall be withdrawn at the latest

by October 2003

Annex A is normative Annexes B, C, D, E, F, G, H, I and J are informative

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

1 Scope

This European Standard specifies a method for the objective determination of the odour concentration of a

gaseous sample using dynamic olfactometry with human assessors and the emission rate of odours emanatingfrom point sources, area sources with outward flow and area sources without outward flow The primary application

is to provide a common basis for evaluation of odour emissions in the member states of the European Union.This European Standard is applicable to the measurement of odour concentration of pure substances, definedmixtures and undefined mixtures of gaseous odorants in air or nitrogen, using dynamic olfactometry with a panel ofhuman assessors being the sensor The unit of measurement is the European odour unit per cubic metre: ouE/m3.The odour concentration is measured by determining the dilution factor required to reach the detection threshold.The odour concentration at the detection threshold is by definition 1 ouE/m3 The odour concentration is thenexpressed in terms of multiples of the detection threshold The range of measurement is typically from 101 ouE/m3

to 107 ouE/m3 (including pre-dilution).

The field of application of this European Standard includes:

 the measurement of the mass concentration at the detection threshold of pure odorous substances in g/m3;

 the measurement of the odour concentration of mixtures of odorants in ouE/m3;

 the measurement of the emission rate of odorous emissions from point sources and surface sources (with andwithout an outward flow), including pre-dilution during sampling;

 the sampling of odorants from emissions of high humidity and temperature (up to 200 °C);

 the determination of effectiveness of end-of-pipe devices used to reduce odour emissions

The characterisation of odour emissions requires detailed measurement of the gas velocity, that shall be performedaccording to the relevant standards included in the normative references

This European Standard is not applicable to:

 the measurement of odours potentially released by particles of odorous solids or droplets of odorous fluidssuspended in emissions;

 the measuring strategy to be applied in case of variable emission rates;

 the measurement of the relationship between odour stimulus and assessor response above detection

threshold;

 direct measurement of hedonic tone (or (un)pleasantness) or direct assessment of potential annoyance;

 measurement of identification thresholds.

Although the ultimate application of odour measurement is in reducing odour nuisance, the relation between

measured thresholds of odour according to this standard and the occurrence of odour nuisance is highly complex

It is profoundly influenced by the atmospheric processes determining the dispersion of odours, the quality of theodour (hedonic tone) and finally by the receptor characteristics of those exposed to the odour These

characteristics not only vary strongly between individuals, but also in time within one individual The relation

between emissions, dispersion, exposure and annoyance is not within the scope of this European Standard

2 Normative references

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

ISO 10780, Stationary source emissions - Measurement of velocity and volume flowrate of gas streams in

ducts

3 Terms, definitions and symbols

3.1 Terms and definitions

For the purposes of this European Standard, the following terms and definitions apply

3.1.1

accepted reference value

value that serves as an agreed upon reference for comparison, and which is derived as a consensus or certifiedvalue, based on collaborative experimental work under the auspices of a scientific or engineering group (derivedfrom ISO 5725-1)

certified reference material, CRM

reference material of which one or more property values are certified by a technically valid procedure accompanied

by or traceable to a certificate or other documentation which is issued by a certifying body

detection threshold (for a reference material)

odorant concentration which has a probability of 0,5 of being detected under the conditions of the test

3.1.11

detection threshold (for an environmental sample)

dilution factor at which the sample has a probability of 0,5 of being detected under the conditions of the test

NOTE One dilution series can consist of:

One series of presentations, at odour concentrations in ascending or random order, where, when sorted in order of descendingconcentrations, a significant change from consistently TRUE responses to a FALSE response occurs (see also Figure 1)

3.1.15

direct olfactometry

European Odour unit

that amount of odorant(s) that, when evaporated into 1 cubic metre of neutral gas at standard conditions, elicits aphysiological response from a panel (detection threshold) equivalent to that elicited by one European ReferenceOdour Mass (EROM), evaporated in one cubic metre of neutral gas at standard conditions

3.1.20

accepted reference value for the European odour unit, equal to a defined mass of a certified reference material.One EROM is equivalent to 123 µg n-butanol (CAS-Nr 71-36-3) Evaporated in 1 cubic metre of neutral gas thisproduces a concentration of 0,040 µmol/mol

3.1.21

expanded uncertainty

quantity defining an interval about the result of a measurement that may be expected to encompass a large fraction

of the distribution of values that could reasonably be attributed to the measurand

forced choice method

for this standard the following definition applies: An olfactometric method in which assessors are forced to make achoice out of two or more air flows, one of which is the diluted sample, even if no difference is observed

detection threshold applying to an individual estimated on the basis of one dilution series

instrumental dilution range

range between the minimum and maximum dilution factor

3.1.32

instrumental lag time

time taken for the output signal to reach 10 % (by convention) of the final change in reading (derived from

ISO 6879)

3.1.33

instrumental response time

time taken for an instrument to respond to an abrupt change in value of the air quality characteristic It is the sum ofthe lag time and rise time (rising mode) or lag time and fall time (falling mode) (derived from ISO 6879)

3.1.34

instrumental rise time (fall time)

time taken for the reading to pass from (by convention) 10 % to (by convention) 90 % of the final change in outputsignal reading (derived from ISO 6879) For instruments where transient oscillations occur in the approach to thefinal output signal reading, the rise time is the time taken for the instrument reading to pass from (by convention)

10 % of the final change in instrument reading until the oscillations fall to less than (by convention) 10 % of the finalchange in instrument reading

3.1.35

maximum dilution factor

maximum settable dilution factor of the olfactometer; an instrument property

measuring range comprises all odour concentrations which can be measured by a specific olfactometer It depends

on the minimum and maximum dilution factor and the step factor The numerical values defining the measuringrange are the minimum dilution factor multiplied with the step factor to the power 1,5 and the maximum dilutionfactor divided by the step factor to the power 1,5

neutral gas

air or nitrogen that is treated in such a way that it is as odourless as technically possible and that does, according

to panel members, not interfere with the odour under investigation

SAFETY WARNING Nitrogen is only used to predilute the sample itself For the olfactometer the neutral gas used to dilutethe sample and present a reference shall be air

odour flow rate

odour flow rate is the quantity of European odour units which crosses a given surface divided by time It is theproduct of the odour concentration cod, the outlet velocity v and the outlet area A or the product of the odour

concentration cod and the pertinent volume flow rate V
Its unit is ouE/h (or ouE/min or ouE/s, respectively)

NOTE The odour (emission) flow rate, expressed in units ouE/s, is the quantity equivalent to the emission mass flow rate,expressed in kg/s, as used in dispersion models for example

odour abatement efficiency

reduction of the odour concentration or the odour flow rate due to an abatement technique, expressed as a fraction(or percentage) of the odour concentration in or the odour flow rate of the untreated gas stream

3.1.46

odour concentration

number of European odour units in a cubic metre of gas at standard conditions

NOTE The odour concentration is not a linear measure for the intensity of an odour Steven’s Law describes the a-linearrelation between odour stimulus and its perceived intensity When using odour concentrations in dispersion modelling, the issue

is complicated by the effects of the averaging time of the dispersion model, further complicating the use of the odour

concentration as a direct measure for dose To define a ‘no nuisance level’, the entire method of dosage evaluation, includingthe dispersion model, will yield a ‘dose’ The relation between this ‘dose’ and its effect (odour annoyance) should be validated inpractical situations to be a useful predictive tool for occurrence of odour nuisance

population (detection) threshold

detection threshold applying to the general population, if this population is not specified

in a manner not influenced by any previous result on the same or similar material

presented gas flow

gas flow presented to the assessor It may be:

 a diluted odour sample;

 neutral gas (e.g as a blank or reference air)

in the context of this standard, the sample is the odorous gas sample It is an amount of gas which is assumed to

be representative of the gas mass or gas flow under investigation, and which is examined for odour concentration[ISO 6879]

standard conditions for olfactometry

at room temperature (293 K), normal atmospheric pressure (101,3 kPa) on a wet basis (derived from ISO 10780)NOTE This applies both to olfactometric measurements and volume flow rates of emissions The conditions were chosen

by convention, to reflect typical conditions for smell perception

property of the result of a measurement that can be related through an unbroken chain of comparisons to

appropriate reference materials, generally national or international reference materials, using measurement

standards of successively increasing accuracy

[ISO 6879]

NOTE In practice, the value of the air quality characteristic is considered to be zero

Figure 1 - Diagram of various terms describing the elements of one (single) measurement for

yes/no method and forced choice method3.2 Symbols and units

The symbols used in this standard are listed in the table below Those parameters that are calculated from testresults obtained after log10 conversion of the underlying test results, see 5.3, are marked in the last column

Table 1 — Symbols and units

results to log 10

required?

Ad Accuracy of dilution instruments

Aod Accuracy of the odour measurement

Aw Statistical factor for calculation of accuracy

Aw,d Statistical factor for calculation of accuracy of dilution

B Laboratory component of bias

CRM Certified Reference Material

dw Trueness expressed as the estimate of within-laboratory

bias

dw,d Trueness expressed as the estimate of the dilution setting

biasD50 The dose of odorant that 50 % of a population that can

detect as a sensory stimulus

e Random error of test result

n Number of test results

oj Observation number j (instrumental calibration)

ouE European odour unit

R Limit value for reproducibility

r Limit value for repeatability

rd Limit value for repeatability of dilution

sI,d Standard deviation for the calculation of instability

szero Standard deviation of measurement results for zero samples

sr,d Standard deviation for calculation of repeatability of dilution

t Statistical factor (Students’ t)

Table 1 — Symbols and units (continued)

yi,d Value of a test result of a dilution setting

Z50 Dilution factor at the 50 % detection threshold

ZITE Individual threshold estimate, expressed as a dilution factor

Z Geometric mean of ZITE of all valid panel members in one

measurement, after retrospective screening

Zmax Maximum dilution factor of dilution instrument

Zmin Minimum dilution factor of dilution instrument

∆Z Panel screening parameter

δ Bias of a test method

δw Within-laboratory bias of a test method

δw,d Within-laboratory bias of a test method for dilutions

µd Reference value for a dilution setting

3.3 The unit of measurement

The European odour unit [ouE] is that amount of odorant(s) that, when evaporated into 1 m3 of neutral gas atstandard conditions, elicits a physiological response from a panel (detection threshold) equivalent to that elicited byone European Reference Odour Mass (EROM), evaporated in 1 m3 of neutral gas at standard conditions

One EROM, evaporated into 1 m3 of neutral gas at standard conditions, is the mass of substance that will elicit the

D50 physiological response (detection threshold), assessed by an odour panel in conformity with this standard, andhas, by definition, a concentration of 1 ouE/m3

For n-butanol (CAS-Nr 71-36-3) one EROM is 123 µg Evaporated in 1 m3 of neutral gas, at standard conditions,this produces a concentration of 0,040 µmol/mol (which is equal to a volume fraction of 40 parts per billion)

There is one relationship between the ouE for the reference odorant and that for any mixture of odorants Thisrelationship is defined only at the D50 physiological response level (detection threshold), where:

1 EROM≡ 123 µg n-butanol ≡ 1 ouE for the mixture of odorants

This linkage is the basis of traceability of odour units for any odorant to that of the reference odorant It effectivelyexpresses odour concentrations in terms of ‘n-butanol mass equivalents’

The odour concentration can only be assessed at a presented concentration of 1 ouE/m3 As a consequence theodour concentration is expressed as a multiple of one ouE in 1 m3 of neutral gas The odour concentration,

in ouE/m3, can be used in the same manner as mass concentrations (kg/m3)

NOTE 1 The odour unit is a difficult unit to define, because it relates a physiological effect to the stimulus that caused it Thestimulus, in this case, can be a multitude of substances In that sense the odour unit is very similar to the LD50, as used intoxicology assessments, indicating the dose that causes a lethal effect in 50 % of a well-defined test population The

physiological reaction is the unifying reaction that can be caused by a wide range of substances, at an equally wide range ofdosages The potential of a certain amount of a substance to cause the physiological effect can be expressed as a multiple ofthe dose that would cause an effect in 50 % of a population The concept underlying the definition and use of the unit are highlyanalogous to that of the odour unit In odour research the D50 could be described as the dose that 50 % of a population candetect as a sensory stimulus

In the past odour researchers have not used populations of standard test subjects, and have only related the physiologicalresponse to the number of dilutions of the dose of a sample to be measured That practice implies a fundamental inability tocompare the dosage of the samples through other means than the population itself This can only be justified if the researcher isconvinced that the samples of the population are sufficiently large to compensate for biological variability within this population.This assumption, however, cannot be fulfilled in the practice of odour measurement The sample from the population (4 to 8subjects, more or less randomly chosen) is far too limited a sample to be representative, knowing the variability of sensitivitywithin the population This practice does not comply with statistical requirements as used in toxicological experimental design,

as the sample size from the population required to be representative is far larger than the usual number of panel members used

in olfactometry

The solution is to standardise the test subjects, used to assess the physiological effect, by selecting panel members with aknown sensitivity to an accepted reference material (now n-butanol [CAS -Nr 71-36-3]) The assumption made is that thesensitivity for the reference will be a predictor for sensitivity to other substances The dose of other substances and mixtures isthen expressed in multiples of the dose that would elicit a physiological reaction equivalent to that of the reference

NOTE 2 When using odour concentrations one should be aware that the relationship between the odour intensity and theodour concentration is not linear, and can be a different relationship for different (mixtures of) odorants

NOTE 3 The relation between the stimulus and the perceived intensity is logarithmic, see B.2 To express odour

concentrations in a unit that reflects the odour intensity rather than the odour concentration, an approach in analogy withexpressing the sound pressure level in decibels is suggested The ‘odour level’ can be expressed in odour-related decibel dBodwhich is the decimal logarithm (log10) of the odour concentration, multiplied by 10

4 Principle of measurement

The odour concentration of a gaseous sample of odorants is determined by presenting a panel of selected andscreened human subjects with that sample, varying the concentration by diluting with neutral gas, in order todetermine the dilution factor at the 50 % detection threshold (Z50≡ ZITE,pan)

At that dilution factor the odour concentration is 1 ouE/m3 by definition The odour concentration of the examinedsample is then expressed as a multiple (equal to the dilution factor at Z50) of one European odour unit per

cubic metre [ouE/m3] at standard conditions for olfactometry

5 Performance quality requirements

5.1 General

The most important requirement of this European Standard concerns quality criteria for the overall performance ofthe sensory measurement method A testing laboratory shall comply with all the quality criteria specified in thisclause and can only claim compliance with this standard if it has assessed the quality of its performance by means

of performance testing

NOTE Performance testing is best done in a proficiency test coordinated by an external organisation

The requirements for the quality of the performance of a laboratory focus on quality assessment within one

laboratory, using reference material By setting an accepted reference value for the reference material n-butanol inthis standard, the reproducibility of results between laboratories is assured implicitly

The quality criteria a laboratory shall meet to comply with this standard are defined on the basis of parametersdescribing both trueness and precision These parameters shall be assessed using reference material The

laboratory shall comply with the quality criteria as defined in 5.3

The calibration of the dilution equipment shall be done regularly using a tracer gas and a physical/chemical method

of analysis In addition to accuracy and precision the instability is determined The dilution equipment shall complywith the quality criteria as defined in 5.4

The calibration of the sensor of the sensory measurement, in this case the odour panel, shall be done on the basis

of a reference odorant Thus traceability to the accepted reference odorant is achieved

The assumption is made that the performance characteristics as determined on reference materials are

transferable to other odours

NOTE 1 To confirm this point interlaboratory testing should be undertaken, in order to assess precision The precision fornon-reference odorants should be compatible with the criteria set for the reference material For the procedure for

interlaboratory comparisons this standard refers to ISO 5725-2

NOTE 2 The quality requirements for the performance of the analytical method as a whole and of equipment used to presentthe sample to the assessor are the core of this standard

To formulate quality requirements for this sensory measurement, the approach is identical to that for other analytical methods,chemical or physical To formulate the quality parameters and to set the performance criteria in this standard, the internationalstandard ISO 5725 has been applied to the sensory measurement and the dilution instruments used To define instability ofdilutions produced by olfactometers, ISO 9169 has been applied As a true value for odour measurements as such is notavailable, an accepted reference value for a reference odorant has been defined in this standard To give values to the quality oftest results, these are assigned a measure of accuracy (see 3.1)

Two terms are used to describe accuracy: precision and trueness

The need to consider precision arises because tests performed on presumably identical materials in presumably identicalcircumstances do not, in general, yield identical results This is attributed to unavoidable random errors, inherent in every testprocedure Two measures of precision, termed repeatability and reproducibility have been found necessary and, for manypractical cases, useful for describing the variability of a measurement method Repeatability is a measure for the quality of the

measurements within one laboratory, whereas reproducibility is a measure for the quality of test results when comparing results

of different laboratories

Repeatability conditions as defined in ISO 5725 cannot be achieved for olfactometry, strictly speaking The measurements take

a relatively long time, so that a series of repeated measurements can stretch over more than one day Also, due to practicalconsiderations, the composition of the panel can change between sessions As these variations occur in the analytical practicethey are accepted, and considered to fall within repeatability conditions

The trueness of a measurement method is of interest when it is possible to conceive of a true value for the property beingmeasured The trueness of the measurement method can be investigated by comparing the accepted reference value with thelevel of the results given by the measurement method Trueness is normally expressed in terms of bias The general termaccuracy is used to refer to trueness and precision combined

5.2 Accuracy - statistical model

The general concept and the statistical model for accuracy is described in ISO 5725-1:1994, clause 5 and

ISO 5725-4:1994, 4.1 The statistical model is applied in this standard as follows

A test result y can be described as:

e B

where

B is the laboratory component of bias;

e is the random error of test result;

δ is the bias of the test method;

µ is theaccepted reference value

For odour measurements on reference material n-butanol, where the accepted reference value is defined implicitly

in the method, the bias of the test method is not of interest In this case the laboratory bias, δw, is given by:

where δw is the within-laboratory bias

5.3 Overall sensory quality requirements

correcting measurement results on the basis of the relation between the actual panel threshold and the acceptedreference value.

To determine whether a laboratory complies with this European Standard only criteria applying to accuracy,

trueness and precision for reference materials are considered In addition, the precision expressed as repeatabilityfor non-reference odorants can be assessed and should comply with the same criterion as set for the referenceodorant

For environmental odours, however, an accepted reference value is not available This implies that for

non-reference odorants, such as environmental odours, only precision can be tested Trueness cannot be

determined in these cases

If a laboratory complies with the overall sensory quality criteria for the reference material, this standard assumesthat this quality level is transferable to other, environmental, odours (van Harreveld, Heeres 1995, see

Bibliography)

NOTE 1 To confirm this assumption on environmental odours, interlaboratory comparisons should be conducted to assessprecision and compare precision with that obtained for reference material

When conducting inter-laboratory comparisons the precision shall be assessed in terms of repeatability and

reproducibility and in terms of trueness (laboratory bias) These values for a laboratory shall be compatible with thevalues found for the reference material

'When calculating statistical parameters the decimal logarithms of the measured odour concentration values shall

be used To obtain a value of non-logarithmic units, the value can be re-converted into its antilog For assessinginstrumental quality requirements a logarithmic conversion shall not be used

NOTE 2 Examples of the calculations for performance testing are given in annex D

NOTE 3 The frequency distribution for detection thresholds for an odorant is log-normal The exponential nature of the datacan be understood by realising that thresholds are determined by presenting an odour panel with a sequence of dilutions thatare a fixed factor apart The multiplication of dilution factors can be expressed on a linear scale after logarithmic transformation.NOTE 4 It is useful to plot test results obtained on reference material on quality control charts, enabling a visual check toassess whether the quality is sufficiently under control

5.3.2 Quality criteria for the performance within one laboratory on reference material (odorant)

The accuracy reflects both the trueness (expressed as bias) and the precision (random error) The test variable foraccuracy is Aod

To assess if a laboratory complies with the accuracy criterion, the 95 % confidence interval for the within-laboratorybias δw is first calculated as:

r A d r

Aw is a statistical factor;

dw is the trueness, expressed as the estimate of within-laboratory bias;

n is the number of test results;

r is the repeatability limit

The calculations of trueness and precision are described in 5.3.2.4 and 5.3.2.5

The test variable Aod is then calculated The criterion for accuracy of the odour concentration is:

w

od = d + A ⋅ r ≤

NOTE Examples of the calculations for performance testing are given in annex D

In addition to the overall accuracy criterion, the precision, expressed as repeatability limit, shall comply with:

10r ≤

NOTE 1 This requirement implies that the factor that expresses the difference between two consecutive single

measurements, performed on the same testing material in one laboratory under repeatability conditions, will not be larger than afactor 3 in 95 % of cases

NOTE 2 Examples of the calculations for performance testing are given in annex D

To assess if a laboratory complies with the criteria for accuracy and precision, expressed as repeatability, thefollowing procedure applies Odour concentration measurements shall be performed on a certified reference

material of the reference odorant, under repeatability conditions, using one or more concentration levels compatiblewith the measuring range At least 10 test results, all measured within the most recent twelve months, shall beused for testing compliance

The expanded uncertainty of the concentration of the reference material shall be ± 5 % or less in terms of

concentration The operator should not be aware of the concentration of the samples

NOTE The test results can be obtained on reference material at one concentration, as the dilution performance of theolfactometer is assessed in a separate procedure However, to obtain an overall quality assessment the use of multiple

concentration levels within the measuring range is advisable

First the repeatability limit r is calculated from the test results

The repeatability standard deviation for the laboratory sr is calculated using:

) 1 (

) (

1

2 w

n

i

i

(7)where

n is the number of test results;

w

y is the average of test results;

yi is the test result

The repeatability limit r is then calculated using:

t is a factor from the Student's t-distribution for n - 1 degrees of freedom, and a confidence

level of 95 %, (Lide, see Bibliography)

The repeatability limit is then compared with the quality criterion

The within-laboratory bias δw is estimated by:

where ywis the average of the test results

5.3.3 Assessment of the performance on non-reference materials (odorants)

5.3.3.1 General

The accuracy reflects both the trueness (expressed as bias) and the precision (random error) However, for reference odorants, for which no accepted reference value is available, the bias of the measurement method (theterm δ in the statistical model) cannot be assessed

non-The precision expressed as repeatability and as reproducibility however can be assessed and shall be calculated

as specified below The results shall comply with the same criteria as those for reference materials

Performance testing to assess compliance with the criterion for precision (expressed as repeatability) is done byperforming measurements on identical samples of the odorant(s) concerned, under repeatability conditions Atleast 10 test results are required

The calculation of the repeatability limit from the test results is identical to that in 5.3.2.4

The repeatability limit shall comply with the same quality criterion that applies to the reference odorant:

5.3.3.3 Assessment of precision between laboratories (reproducibility)

For non-reference odorants an accepted reference value is not available Consequently the bias of the

measurement method cannot be quantified To assess accuracy for odorants or environmental odours when noagreed reference value is available an interlaboratory comparison should be held where a suitable number oflaboratories all analyse identical samples

The geometric mean of the odour concentrations in ouE/m3 of all the participating laboratories is then considered to

be the best estimate of the reference value µ

Using that best estimate the analysis of accuracy can be made along the same lines as for the reference material.However, the precision in this analysis will be expressed in terms of reproducibility

To carry out assessment of trueness (laboratory bias) and precision (expressed as reproducibility) measurementsare performed on identical samples under reproducibility conditions These samples can be produced for

environmental odours by diluting a concentrated sample using a calibrated dilution apparatus At least 10 testresults per laboratory are required Such results should be obtained in a proficiency test, following the guidance ofISO 5725-2

5.4 Quality requirements for dilution apparatus

The quality requirements are defined for two parameters: accuracy and instability The requirements have been set

on the basis of the required performance in relation to odour testing, and take into account that these requirementsshould be appropriate in relation to other sources of error in the odour concentration measurement process

The tracer concentrations as produced by the dilution equipment are considered to have a normal distribution ofprobability Therefore conversion to logarithms of the test results is not required

The dilution equipment shall comply with both the criterion for accuracy (see 5.4.2.1) and the criterion for instability5.4.3

Compliance of the dilution equipment used by a laboratory to the instrumental quality requirements shall be testedand demonstrated regularly The appropriate calibration frequency shall be based on the performance history of theequipment, but shall be at least once a year

Compliance testing shall involve the full dilution range of the instrument, with at least two points for each decade ofdilution factor Z For instruments with discrete dilution settings, every setting shall be tested for compliance

For an assessment the settings of the olfactometer shall be calibrated using a suitable tracer, and a monitor thathas a proven accuracy of an order of magnitude better than the required level of accuracy for the dilution

equipment For the reference materials used as tracers see 6.4.3 The monitor that is used for calibration shall becalibrated over its full range of measurement at a suitable frequency, depending on the actual calibration history(see 5.4), but not less frequent than once a year, using reference materials with an expanded uncertainty of ± 3 %

or less

As the ‘accepted reference value’ for a dilution setting (µd) the dilution factor measured at the previous calibrationshall be used to calculate trueness The procedure for compliance testing and the data to be collected are

5.4.2 Quality criteria for the performance of dilution apparatus

The accuracy of dilution reflects both the dilution bias and the random error The test variable for accuracy ofdilution is Ad

To assess compliance of a dilution setting with the accuracy criterion, first, the 95 % confidence interval for thedilution setting bias estimate is calculated

d d w, d w, , d d w,

dw,d is the trueness, expressed as the estimate of the dilution setting bias;

∆δ w,d is the trueness, expressed as the dilution setting bias;

n is the number of test results;

rd is the repeatability limit

Trueness and precision are then calculated as defined in 5.4.2.2 and 5.4.2.3 The accuracy of a dilution settingshall comply with:

20 , 0 ) (

d

d d w, d

w,

µ

r A d

where

µd is the reference value for a dilution setting (usually derived from previous calibration)

The repeatability limit shall be calculated from the repeatability standard deviation for dilution instruments sr,d using:

) 1 (

) (

1

2 d w, d , d

n

i

i

(13)

n is the number of test results;

yi,d is one test result;

d

w

y , is the average of test results

The repeatability limit rd then is:

d r,

The bias of the dilution setting δw,d is estimated by:

d d w,

d

w, = y − µ

where yw,d is the average of the test results (one test result y being the average of observed values for one

setting; one setting is calibrated repeatedly, see 6.5.5.)

To assess if a dilution setting complies with the accuracy criterion the dilution setting shall be evaluated repeatedlyusing tracer gases and a monitor, yielding a number of test results yi,d (for details see 6.5.5) Compliance shall beassessed as often as prudently necessary The frequency of calibration and assessment shall be determined onthe basis of the actual calibration history of the equipment, but shall be no less than once a year

5.4.3 Quality criterion for instability of dilution apparatus

The quality criterion for dilution instability Id is:

% 5

d ≤

I

Instability for the purpose of this standard is calculated from measurements obtained by setting a dilution, using atracer and a continuous gas monitor Starting at the moment where the assessor would normally be signalled tostart smelling, at least 10 concentration observations are obtained, which are the test values yi for the calculation ofinstability This procedure is repeated five times, simulating five presentations For each presentation the instability

is calculated, and the values obtained for the presentations are ultimately averaged to obtain the instability

For each series of n observations obtained in one ‘presentation’, the instability standard deviation is calculated:

) 1 (

) (

1

2 d , d

n

(16)

n is the number of observations;

oj is the observation number j;

yi,d is the average of n observations oj in ‘presentation’ i

The instability Id for ‘presentation’ i is then calculated for a two tailed confidence level of 95 % using:

% 100 96

,

1

d ,

d ,

The instability criterion is tested using the mean of at least five values of Id, for five ‘presentations’

NOTE 1 An example of the calculation of instrumental instability is given in annex C

NOTE 2 As the perception of the assessor is a fast process, involving a number of inhalations in a time span of 20 s, it isimportant that the concentration produced remains sufficiently constant To ensure this, the quality parameter instability is used,that only considers a random part of variation This is a simplified approach to instability, compared with the approach in

ISO 9169:1994, 6.2.2 As the time of presentation to a panel member is short, it is assumed that the systematic component ofinstability (drift) does not apply to this requirement

For assessment of instability the continuous monitor used in combination with its sampling system has to have asufficiently fast response to provide meaningful data The rise time and lag time have to be of the same order asthe interval between observations, i.e about 5 s

5.5 Quality requirements for sampling equipment

If sampling equipment can be used to achieve pre-dilution of the gas stream to be sampled, the equipment shallcomply with the same requirements for accuracy and instability as those that apply to dilution apparatus, see 5.4.The method of calibration shall ensure that the results obtained are valid for the conditions in which the instrument

6 Materials, gases and panel members

6.1 General properties of materials

Materials used for olfactometry shall have the following general properties:

 shall be odourless: the materials shall not add odorants to the sample;

 shall be selected to minimise the physical or chemical interaction between sample components and samplingmaterials;

 shall have low permeability in order to minimise loss of sample caused by diffusion;

 shall have smooth surface

6.2 Sampling equipment

6.2.1 General

The sampling equipment has to comply with the criteria set for the accuracy of the olfactometer The calibration ofsampling equipment is necessary and specified for the equipment used to sample the different types of sourcesdescribed in this standard

6.2.2 Materials for sample equipment

Appropriate materials1 shall be used for those parts of the sampling equipment that are in contact with the odorantsample The following materials are appropriate:

 PTFE (polytetrafluoroethylene);

 tetrafluoroethylene hexafluoropropylene copolymer (FEP);

 polyethyleneterephthalate (PET, Nalophan );

 stainless steel;

 glass;

 materials listed in 6.3.1

Each material has specific advantages determined by its mechanical, chemical and thermal properties

Inappropriate materials shall not be allowed to get into contact with the sample, even in minor parts like seals orjoints Such materials are, for example:

 silicone rubber;

 natural rubber

Sampling probes and tubes that are exposed to odorant sample during a sampling session, shall not be re-usedunless they are effectively cleaned and odourless before re-use

6.2.3 Conditioning of sample equipment

The sampling equipment is inherently conditioned by the procedure described in 6.3.2 for taking samples from anodorous source

6.2.4 Cleaning and re-use of sample equipment

Sampling equipment shall be cleaned to become odourless No residues of any cleaning or rinsing agent shall beallowed to remain on the surfaces Products and substances for cleaning and rinsing that have a strong odour shall

be avoided The last step of the cleaning process shall be drying and flushing using neutral gas

NOTE An effective cleaning procedure is submerging the parts in an ultrasonic bath, filled with a solution of dishwashercleaning product (alkaline + some detergent) in water The parts remain in the bath for at least 15 min at a temperature of 70 °C

or higher Then, the products are rinsed with water, preferably de-mineralised, and blown dry using neutral gas As a last stepthe parts can be flushed with neutral gas for sufficient time to become odourless

6.3 Sample container

6.3.1 Materials for sample container (bags)

So far the following materials2 are considered appropriate for making sample containers:

 tetrafluoroethylene hexafluoropropylene copolymer (FEP);

 polyvinylfluoride (PVF, Tedlar );

 polyethyleneterephthalate (PET, Nalophan NA )

Materials shall be tested for suitability, by assessing if they are odourless and if they can hold a mixture of odorantswith minimal changes for periods of storage as indicated in 7.3.3

NOTE In PVF background concentrations of over 100 ouE/m3 have been noted in some batches, due to release of a solventfrom the film

6.3.2 Conditioning and testing of sample containers

New bag materials (or new batches of bag materials) shall be tested for their background odour concentrationbefore being put into service Before use, bags shall be tested for leakage

NOTE Sometimes a new batch can be of a different quality from previous batches, and has to be evaluated as if it were anew material

The test for background odour concentration of the bag material shall be carried out by filling at least 3 bags made

of the material to be tested with neutral gas and storing them for 30 h Then perform an odour measurement oneach bag to determine odour concentration A bag material shall be considered odourless if no threshold can bemeasured for all of the bags, or when the highest odour concentration measured in these bags is at least a factor

Fs4 lower than that of the samples that will be stored in the bags

The bag should be conditioned by filling it with sample at least once and evacuating it again, or by flushing it withthe sample flow for an appropriate amount of time (depending on the capacity of the bag) If dynamic pre-dilution isnecessary, the bag shall be conditioned by filling it once with the diluted sample

6.3.3 Cleaning and re-use of containers

Sampling bags shall not be re-used, unless each bag is tested in accordance with the procedures of 6.3.2 Theconnectors used in sampling bags can be re-used, after cleaning as described in cleaning of sampling equipment

6.4 Gases

6.4.1 Neutral gas

Neutral gas shall be safe for breathing and perceived as odourless, according to the panel members and operator,

so that it does not interfere with the perception of the odour under investigation

The neutral gas shall be tested before any measurement procedure is started by asking the panel to smell theneutral gas and ask if they perceive it as odourless or not If the panel perceives an odour (or a change in theperceived odour) in the neutral gas, systematic testing has to be done to trace and eliminate the source of theodour

2Tedlar is a trademark of Dupont de Nemours Nalophan is a trademark of Kalle Nalo GmbH This information is given forthe convenience of users of this European Standard and does not constitute an endorsement by CEN of the materials named

Neutral gas shall be used:

 to dilute odorant samples within the olfactometer (air);

 to pre-dilute highly odorous samples (nitrogen or air);

 as a diluting gas in reference materials (nitrogen);

 as the sensory reference in the presentation (air)

NOTE It is recommended that the source of neutral gas is provided in the following way:

 compressed air generated using a compressor (oil-free compressors are recommended), followed by

particulate filtration, air cooling and drying to remove particulate material and prevent condensation and

final treatment with activated carbon filter to remove residual odours, followed by a fine particle filter to

remove activated carbon particles;

 nitrogen from a cylinder or from a liquid nitrogen evaporating unit;

 ambient air from the air conditioned odour room (for treatment of odour room air, see 6.6.2);

 synthetic air from a cylinder

6.4.2 Reference material: odorant (n-butanol)

A certified reference material with an expanded uncertainty of ± 5 % or less of n-butanol (CAS-Nr 71-36-3)innitrogen shall be used as the reference odorant The stability of the reference material CRM shall be known

For preparation of standards of odorants, the highest purity that is commercially available shall be used For

n-butanol this is specified as n-butanol 99,9 %, spectroscopy quality

NOTE 1 The uncertainty of the reference material contributes to the total uncertainty of the measurement of odourconcentration

NOTE 2 n-butanol was selected as reference material because of the history of usage and the availability of metrologicalinfrastructure providing a traceable reference material A reference mixture would however be preferable Interaboratorycomparisons of both n-butanol and environmental odours and fundamental research have demonstrated that the repeatabilitylimit for mixtures of odorants is better than for single components Development of a reference mixture would be welcome.NOTE 3 The Netherlands Measurement Institute (NMi) in Delft maintains primary standards of n-butanol in nitrogen againstwhich reference materials can be certified as CRM’s

6.4.3 Reference material for calibration of dilution equipment

SAFETY WARNING Since tracers can be toxic, such as carbon monoxide, safety requirements shall be drawn up andimplemented when working with tracers for instrumental calibration

To calibrate dilution equipment and assess compliance with the criteria set in this standard a suitable analyticalmethod shall be applied Two types of reference material are needed for the tracer chosen:

 to ensure stability of the analytical method: reference materials with an expanded uncertainty of ± 3 % or less,

at approximately 15 % and 90 % of the measuring ranges shall be used;

 to be used as tracer gas: reference material with an expanded uncertainty of ± 3 % or less shall be used.NOTE Carbon monoxide has proved to be a suitable tracer, with good availability of traceable reference materials and astable analytical method (NDIR) The advantage of carbon monoxide is that it does not cause mass flow controllers to responddifferently from their normal characteristics, regulating air The serious disadvantage of carbon monoxide is its toxicity and theassociated acute risks Alternatives for dilution instruments that do not use mass flow controllers are propane (with FID) or SF6

6.5 Dilution apparatus

6.5.1 Construction of the olfactometer

The general requirements for materials that are in contact with neutral or odorous gases are detailed in 6.1 Thedesign of olfactometers should apply the following precautions:

 the length and diameter of internal tubing and residence time should be minimised to prevent contamination bythe odorant;

 orifices should be sized to prevent blockage by particulate contamination;

 devices that change the gas characteristics shall be avoided, for example hot-wire anemometers;

 devices which affect the odorant sample, e.g by changes in temperature etc should be avoided

The temperature of the reference gas or odour from the olfactometer presented to the panel, should differ no morethan 3 °C from the measurement room temperature

The olfactometer shall be constructed so that the noise or other stimuli do not disclose information to the assessor

as to the location or concentration of the stimuli

6.5.2 Dilution range of olfactometer

The olfactometer shall be capable of producing a dilution range from less than 27 up to at least 214, with a range of

at least 213 between the maximum and minimum dilution The step factor Fs should be adjusted to comply with therequirements of 8.3

Pre-dilution can be applied to bring the concentration of a sample within the measurement range of the instrument(see 7.3.2)

6.5.3 Interface between nose and olfactometer

The air or air/odorant mixtures are made available to the assessor for sensory evaluation using various types ofports Only general principles for the design of ports are described in this standard:

 the design shall allow the assessor to smell with ease, and should in no way distract the assessor whenevaluating the odour;

 the air flow emanating from a port shall be at least 20,0 l/min;

NOTE The port should be shaped in such a way that the air velocity across its opening is at least 0,2 m/s The velocity of airfrom the cup is usually kept below 0,5 m/s to avoid discomfort of the assessor

 the port shall provide an even distribution of air velocity across its opening, with differences at cross sectionsnot more than 10 % different from the average velocity, measured at a distance of at least 0,005 m from thewall of the cup The odour concentration for a type of cup shall be checked using tracers, and shall be required

to show a uniform distribution across its opening, with differences at various points of the cross section notexceeding 10 % of the average concentration When sampling tracer from the cup cross section, the velocity ofextraction of the sample shall be equal or less than that of the air/tracer mixture flowing out of the cup Thesampling should be done on a grid pattern;

 when using breathing masks the airflow shall be sufficient to allow for normal breathing

6.5.4 Decision limit of the olfactometric measurement

The decision limit for odour measurement is the lowest odour concentration that can be determined to be differentfrom a zero sample with 95 % statistical confidence It shall be determined by filling an odour sampling bag withneutral gas, leaving the sample for the maximum storage time (see 7.3.3) and then analysing the sample using thenormal procedure

When an odour sample is taken by means of a stack sampling equipment and pre-dilution equipment, this

equipment becomes part of the system to determine the decision limit In that case the decision limitof the wholesampling and measurement system shall be determined by taking a sample from neutral gas using the samplingprobe and the sample container The sample container filled with this gas is subsequently analysed for determiningthe decision limit of the system

At least six independent measurements have to be carried out to determine the decision limit, which is then

calculated as follows:

DECISION LIMIT = 10y zero + 10t0 , 95 ⋅s zero [ouE/m3] (18)where

szero is the standard deviation of the test results on zero samples;

t0,95 is the student factor for n - 1 degrees of freedom;

zero

y is the average of test results on zero samples

If the measurement does not produce individual thresholds in the responses, the decision limit can be assumedequal to the lower limit of the measuring range:

6.5.5 Calibration procedure

To ensure correct dilution characteristics, the settings of the olfactometer shall be calibrated using a suitable tracer,and a monitor that has a proven accuracy of an order of magnitude better than the required level of accuracy forthe dilution equipment The monitor that is used for calibration shall be calibrated over the full range at a suitablefrequency, but not less frequent than once a year, using reference materials

When using tracers in dilution systems with mass flow controllers one has to be aware that the tracer mixture maynot have the same calibration characteristics as the gas for which the mass flow controller was calibrated

Five test results shall be collected for every dilution setting, Between measurement for each test result the controls

of the dilution instrument, if this is applicable, are set to another setting Each test result yi,d shall consist of at leastten observations oj with a sampling frequency no less than once in every 10 s This is relevant for the

determination of instability The lag time of the monitor, including the sampling system, shall not be more than onecycle of the sampling frequency To obtain one test result, at least 10 observations shall be recorded

To obtain a test result yi,d the value is calculated as the average of the observations oj within that setting

measurement See 5.4 for the calculation of accuracy and instability

6.6 Environment for observations by assessors

 mobile units, purpose built into a truck, van or container;

 specially adapted rooms at or near testing sites, which have been put at the disposal of the testing team for alimited time

The working environment for assessors shall be pleasant and odourless Any odour emissions from equipment,furnishings and materials installed (i.e paints, wall and floor coverings, furniture etc.) into the odour room shall beavoided, as well as any release of the odorous components to be measured

The room shall be kept well aired When the assessors are equipped with a sensory mask, constantly being

flushed with neutral gas, the requirements for the ambient air are of secondary importance Temperature

fluctuations during the measuring process shall be less than ± 3 °C The maximum temperature in the room should

be 25 °C

Exposing the assessors to direct sunlight shall be avoided

The room shall be free of any sources with regard to noise and light that could negatively effect the measurement

in progress

NOTE The neutral gas should be tested by the panel before any measurement is made by asking the panel if they perceive

it as odourless or not If the panel perceives an odour or a change in the perceived odour of the neutral gas, systematic testingshould be done to trace and eliminate the source of the odour

6.6.2 Air conditioning for the odour room

The odour room shall be ventilated to maintain an odourless environment and to provide fresh air to the panelmembers In order to maintain a comfortable working environment the CO2 volume fraction in the odour room shall

be less than 0,15 %

The room air should be ventilated and passed through an active carbon filter before entering the room Shouldassessors not be in a position to progress with measurements under conditions of neutral gas supply, suitablearrangements should be made to present an odourless atmosphere (i.e activated carbon filter, particulate filtrationetc.)

6.7 Panel

6.7.1 Code of behaviour for assessors and panel members

When recruiting panels the following conditions shall be met:

 panel members shall be at least 16 years of age and willing and able to follow instructions

To qualify as a panel member, assessors shall observe the following code of behaviour

 the panel member shall be motivated to carry out his/her job conscientiously;

 the panel member shall be available for a complete measurement session (series of measurements on a day,interrupted by short breaks only);

 the panel member shall be engaged for a sufficient period to build up and monitor a history of measurement;

 from 30 min before and during olfactometric measurement panel members shall not be allowed to smoke, eat,drink (except water) or use chewing gum or sweets;

 panel members shall take great care not to cause any interference with their own perception or that of others

in the odour rooms by lack of personal hygiene or the use of perfumes, deodorants, body lotions or cosmetics;

 panel members suffering of a cold or any other ailment affecting their perception of smell (e.g allergic fits,sinusitis) shall be excluded from participating in measurements;

 panel members shall be present in the odour room or in a room with comparable conditions 15 min before themeasurements start in order to get adapted to the actual odour environment of the measuring room;

 during measurements panel members shall not communicate with each other about the results of their

choices When using ‘forced choice’ mode, informing them of the correctness of their choices after the

measurement can enhance the motivation of the assessors during the measurements

The operator shall ensure that the code of conduct is fully known to each panel member The enforcement of thecode of conduct is a direct influence on the test results, and therefore of great importance The operator shallensure that the motivation of panel members is maintained throughout the measurements, and corrective actionshall be taken when required

6.7.2 Selection of assessors on individual variability and sensitivity

In order to obtain a reliable sensor, composed of a number of panel members, assessors with specific qualitiesshall be selected from the general population to serve as panel members

In order to ensure repeatability of their result, their olfactory responses should be as constant as possible from day

to day, and within a day

In order to ensure repeatability of the sensor, formed by a panel composed of individual panel members, theirolfactory sensitivity shall be within a defined bandwidth, much narrower than the variability within the population Toachieve this aim assessors with a specific sensitivity to the reference odorant n-butanol are selected to be panelmembers

To make new assessors familiar with the olfactometric procedures they shall first be trained by performing at leastone single measurement These results are discarded

Then at least 10 individual threshold estimates (ITE) for the reference gas shall be collected for selection purposes

As a reference n-butanol in nitrogen shall be used The data for each assessor shall be collected in at least

3 sessions on separate days with a pause of at least one day between sessions

To become a panel member, the data collected for that assessor shall comply with the following criteria:

 the antilog of the standard deviation sITE calculated from the logarithms (log10) of the individual thresholdestimates, expressed in mass concentration units of the reference gas, has to be less than 2,3;

 the geometric mean of the individual threshold estimates ITEsubstance, expressed in mass concentration units ofthe reference gas, has to fall between 0,5 times and 2 times the accepted reference value for that referencematerial (for n-butanol 62 µg/m3 to 246 µg/m3 ≡ 0,020 µmol/mol to 0,080 µmol/mol)

NOTE 1 An example of such a calculation is given in annex E

A measuring history for each panel member shall be recorded and maintained by determining one individualthreshold estimate for the reference odorant for at least once for each twelve regular measurements in which thepanel member is used Each time such an individual threshold estimate for the reference odorant is collected, themeasuring history of the panel member in question shall be completed and evaluated Evaluation shall be done bycalculating the selection parameters as defined above from at least the 10 and at most 20 most recent individualthreshold estimates, and comparing the results with the selection criteria If the panel member does not comply,he/she is excluded from all further measurements until compliance is established once again

NOTE 2 An example of panel selection calculations is presented in annex E

The minimum panel size in any measurement shall be no less than four after retrospective screening (see 9.2.3)

7 Sampling

7.1 General

When collecting samples proper care shall be taken to ensure that the health and safety of sampling techniciansshall not be put at risk at the sampling location To achieve this, the sampling site should comply with conditions asoutlined in annex A

7.2 Choice of sampling method

The choice of sampling method to be used depends on the type of olfactometry that is to be applied

Two types of sampling can be considered:

 dynamic sampling;

 sampling for delayed olfactometry

Selecting one or the other of these two methods will depend on the source that is to be examined Whatever thecircumstances, a defined methodology of sampling shall be used, appropriately conditioning the sample andtransferring it to the olfactometer or container in such a way that the sample taken is representative of the total flow

of gas to be analysed

NOTE Sampling is an important step in the process in measuring the odour concentration of a gaseous effluent; it will affectthe quality and reliability of the result

7.2.1 Sampling for direct olfactometry

With dynamic sampling the sample is ducted directly to the olfactometer, without storage in a sample container.This method shall only be applied to emissions with a constant concentration level throughout the duration ofsampling This sampling technique applies to cases of odorous atmospheres arising from sources that are, or could

be, channelled (stack release, breathing of storage tanks, biofilters, mixed liquid volumes such as in waste watercollection stations)

NOTE The advantage of direct olfactometry is that the short time elapsing between sample and measurement effectivelyreduces the risks of a modification in the composition of the gaseous sample through chemical reactions or adsorption Thedisadvantage of direct olfactometry is that it requires the use of ventilated measuring rooms in order to isolate the panel

members from the ambient environment, which is always odorous to some extent Such equipment is difficult to implement andoften requires very long sampling lines liable to disturb the sample (condensation, adsorption, admission of air)

Delayed olfactometry improves measurement accuracy by placing the assessors in the best possible environmental conditions

7.2.2 Sampling for delayed olfactometry

In sampling for delayed olfactometry a sample is collected and transferred into a sample container for analysis bydelayed olfactometry This sampling technique shall be applied if the odour room conditions required for assessorscannot be maintained on site, or for sources where odour concentration can vary with time, which is typically thecase Sampling for delayed olfactometry can be applied to all sources emitting odorants, whether diffuse,

channelled or those that can be channelled for sampling

NOTE It is recommended that one of the following two methods of sample collection is used:

 the 'lung principle' where the sample bag is placed in a rigid container, the air is removed from the container using avacuum pump, the under pressure in the container causes the bag to fill with a volume of sample equal to that which hasbeen removed from the container;

 direct pumping, where the sample is pumped directly into the sample bag, has to be used with caution in order that thesample being collected is not contaminated by odours previously adsorbed onto the pump and sample tube being

desorbed into the sample Sampling lines have to be replaced between samples and the pump flushed with neutral gasuntil all contamination is removed