VDI 3882 refers to the German standards and methods of olfactometry, which is split into 2 major parts detailed below:

VDI3882 Part 1

Part 1 describes an olfactometric method of investigation. It can be used to assess inhaled samples having odorant concentrations above the odour threshold (suprathreshold concentrations). This is in relation to the sensation intensity they induce in human beings. For a given odourant concentration, this sensation intensity is substantially dependent on the substance and/or mixture. This means that height can be used in variation intensity calculations as a characteristic of that sample. The investigation of the odour intensity of individual concentration levels using an olfactometer makes it possible to assess it under field conditions.

Above all, with the field of emission reduction, the determination of the intensity of an untreated waste provides guide values. These can be used for the reduction in odorant concentration needed to maintain certain odour intensity at the source. In this connection, the assessment will be all the more reliable, the less the untreated gas composition is altered by the reduction technique used.

The relationship between the odour intensity and the odorant concentration makes it possible to use intensity determinations carried out on clean gas samples and dispersion calculations for odorants [6] to make forecasts of the theoretically remaining odour intensi¬ ty in the field (ambient air). Perceptible interfering actions due to synergistic effects with other odorant emissions are not allowed for in this connection since they cannot be included in the calculations.

However, the variation in intensity cannot be used to describe the nuisance potential of an odourant sample.

Odour Guideline Standards

The Standards set by this Guideline apply to odour intensity determinations carried out on the following samples :

a) emission samples obtained from a source of the odour
b) individual substances or specified mixtures of substances in neutral air,
c) Above all, emission samples provided their odorant concentration is high enough for an olfactometer to be used

VDI3882 Part 2

Part 2 of Guideline VDI 3882 describes an olfactometric method of evaluating the hedonic tone of odorous samples. These samples are above-threshold odourant concentrations according to the sensation scale “pleasant – unpleasant”. The hedonic tone of an odour is contingent on the nature or mixture of the odorous substance or substances. These are on the odourant concentration – the perceived intensity of the odour – and on the background experience of the individual. This means that, by evaluating several above-threshold stages of concentration of a specific odorous sample. However, it is possible to plot the hedonic odour tone as a characteristic curve of the sample under investigation.

The hedonic tone of an odour, most importantly, must not be confused with its quality (fragrant, pungent, stale, or smell like…)

In conclusion, with regards to the methods recommended in VDI 3881 for determining odourant concentration (odour threshold) and odour intensity, the additional determination of the hedonic odour tone of an emission sample frequently permits an assessment of its nuisance effect. This occurs under ambient air conditions, though a conclusive assessment of the actual degree of nuisance is not possible with olfactometric methods alone. In cases where it is necessary to ascertain the nuisance effect, additional sociological methods (e.g. neighbourhood surveys) can be helpful

Hedonic Tone Guidelines

This guideline is valid for the determination of the hedonic odour tone of the following types of sample :

a) Above all, emission samples come from a source of the smell
b) Single substances or defined mixtures in a neutral gas,
c) Ambient air samples, with regards to their odorant concentration, is high enough for detection by the olfactometer

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A Clean Air Act requirement that state implementation plans must include a permit review, which applies to the construction and operation of new and modified stationary sources in non-attainment areas, to ensure attainment of national ambient air quality standards. The two major requirements of NSR are emission offsets & the best available control technology.

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The International Organization for Standardization is a collective group of international representatives that agree upon various standards for numerous organizations worldwide. With relation to odour, ISO 13301 was initiated to provide a set of guidelines and procedures on the topic of odour. ISO provides specific guidelines on:
• Obtaining data on the detection of chemical stimuli that evoke responses to odour, flavour and taste by a 3-AFC (three alternatives forced-choice) procedure;
• The processing of the data to estimate the value of a threshold and its error bounds, and other statistics related to the detection of the stimulus.
The set of standards encompass the sensitivities of many groups of people around the world, taking into consideration age, gender, physiological condition, disease, administration of drugs, and ambient conditions of sensitivities.

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See EN13725 standard Standard on Determination of Odour Concentration by Dynamic Olfactometry

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There are a number of ASTM standards related to odour assessment and regulation:

• ASTM E679-04 United States ‘standard practice for determination of odour and taste threshold by a forced-choice ascending concentration series method of limits’
• D1292 test method for odour in the water
• E544 practices for referencing suprathreshold odour intensity
• E1432 practice for defining and calculating individual and group sensory thresholds from forced-choice data sets of intermediate size

The ASTME679-04 is the most commonly used standard in the USA for olfactometry, however, outside of the USA, EN13725 standard is more commonly accepted.

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ASTM E679-04, the United States standard for the “determination of odour and taste threshold by a forced-choice ascending concentration series method of limits”, provides guidance on both olfactometry and sampling.

The ASTM E679-04 is the most commonly used standard in the USA for olfactometry, however, outside of USA standard EN13725 is more commonly accepted.

Differences between ASTM E679-04 and EN13725 is mostly on panellist screening and on minor details of olfactometry. One highly controversial difference is the presentation flow, which is set at only a minimum of 5 litres per minute in ASTM E679-04 and 20 litres per minute in EN13725. It is however technically possible to run at 20 litres per minute and still comply with the ASTM standard.

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A federal law passed in 1970 and amended in 1974, 1977, and 1990 which forms the basis for the national air pollution control effort. Basic elements of the act include national ambient air quality standards for major air pollutants, mobile and stationary control measures, air toxics standards, acid rain control measures, and enforcement provisions.

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European Dynamic olfactometry is described in detail by the standard EN 13725. This standard was last released in 2003 and is currently under review for revision. As of 2020, an updated version is still waiting to be finalized in the UK. Key elements of this standard are the focus on quality criteria for precision and repeatability. The EN13725 tries to link these values to standard values of n-butanol in nitrogen. It is assumed in this standard that whenever a laboratory complies with the overall sensory quality criteria for n-butanol, the quality level is transferable to other, environmental, odours.

The Standard describes the different test modes such as Triangular Forced Choice, Binary Forced Choice, and Yes/No method for determining the true odour concentration of a sample bag.

Testing Requirements

Many aspects of testing are defined including:

• Number of panellists (min. 4)
• Acceptance criteria of each panellist
• Airflow (20 litres per minute) design of the olfactometer, presentation airspeed, minimum dilution, maximum dilution, and maximum step size
• Calculation of individual detection thresholds and overall detection threshold
• Design of the testing room including temperature and humidity
• materials used in the olfactometer

One of the main objectives of the EN13725 standard is inter-laboratory testing and panellist screening.

While the EN13725 does cover sampling, it is generally accepted that sampling techniques require much greater attention in the next revision of the standard. The standard does provide guidance on the type of sample bags (nalophan, Tedlar, PTFE, etc) and on the dilution devices required (stack diluting sampler, flux chamber, static hood, etc).

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