Members are evaluated to determine if they are fit candidates for odour measurement.  Specific criteria must be met, for example, age etc.  In the EN13725 standard, n-butanol is used to determine what a person’s olfactory response may be. 

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An average or mean calculated by taking the nth root of the product of n numbers. The geometric mean is used in the EN13725 and E679-04 standards in order to calculate the odour concentration. The geometric mean is used (and not the arithmetic mean) because a constant factor (step factor) is used to calculate the dilutions for the analysis. Example: (5724x5724x5724x8918x13891x13891)^1/6 = 8282

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The assessor is presented with two or more ports, of which one presents the stimulus and the other(s) neutral gas. The location of the stimulus in the consecutive presentation is randomly distributed over the two or more ports. The assessor is asked to indicate which of ports is the one with the stimulus. When the assessor expresses doubt, he/she is asked to indicate a port ” at random”. To reduce variability and achieve convergence with the yes/no choice mode, the following procedure is applied to distinguish False from True responses. The assessor is asked whether his/her choice was a guess, an inkling or certain. From the combination of the choice result and the indicated level of certainty, the response is classified to be False or True.

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The assessor is asked to evaluate gas presented from a specific port and to indicate if an odour is perceived (YES/NO). The assessor is aware that in some cases blanks (only neutral gas) are presented. A second part always presenting neutral gas may be made available to the assessor to provide a reference.

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EN13725 defines the following criteria for panellist screening:

• Have a detection threshold of n-butanol between 20ppb to 80ppb
• requires the assessor to be at least 16 years of age
• must be motivated and diligent to carry out duties
• available for the complete measurement session
• participated sufficiently to build a history of measurements
• may not eat, drink (except water), or smoke 30 min before the measurement
• not create interference from personal hygiene or perfume products
• refrain from participating in measurements if the assessor’s perception of odour is diminished (i.e. cold, allergies, etc.)
• assessors will remain in the odour room for 15min prior to beginning measurement to adapt to the room
• Panel members shall not communicate or influence one another

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Certain criteria must be met in order to perform odour measurements.  For instance, EN13725 essentially outlines the following criteria:

• Have a detection threshold of n-butanol between 20ppb to 80ppb
• requires the assessor to be at least 16 years of age
• must be motivated and diligent to carry out duties
• available for the complete measurement session
• participated sufficiently to build a history of measurements
• may not eat, drink (except water), or smoke 30 minutes before the measurement
• not create interference from personal hygiene or perfume products
• refrain from participating in measurements if the assessor’s perception of odour is diminished (i.e. cold, allergies, etc.)
• assessors will remain in the odour room for 15 minutes prior to beginning measurement to adapt to the room
• Panel members shall not communicate or influence one another

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A ratio of diluting neutral gas to odorous sample gas.  According to ASTM E679, this is a ratio of diluting gas to the odour sample. According to EN13725, this is a ratio of the sum of the diluting gas and odour sample, to the odour sample.  It is calculated based on the flow rate.

Example

5 parts of diluting air to 1 part of sample

ASTM E679:  Diluting gas/odourous sample = 5:1 = 5

EN 13725:  (diluting gas + odourous sample)/odourous sample = 6:1 = 6

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A time-lag between sampling and measuring of odour concentration where the odour sample is preserved in an appropriate container (odour-neutral material). It can also be referred to as static sampling. Delayed olfactometry is the analytical technique used in the UK. EN13725 stipulates a maximum temperature during storage of 25°C and samples must be analyzed within 30 hours from the moment of collection. This temperature can be exceeded when working in hot environments provided the deviation is justified in the final report.

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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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