Dynamic olfactometer is a device for estimating the intensity of the sense of smell by presenting diluted air samples to panelists.

The principle of olfactometry measurement is determining odour concentration of a gaseous sample by presenting a panel of selected and screened human subjects with that sample and varying the concentration by diluting with neutral gas (normally fresh air), in order to determine the dilution factor at the 50% detection threshold.

There are some important aspects that affect the accuracy (repeatability and reproducibility) of odour measurements ( odour strength and odour concentration): calibrate dynamic olfactometer regularly, keep testing environment odour-free and ensure the panelists trained and screened.

Instrument calibration
The calibration of olfactometer needs to be done regularly using a tracer gas such as carbon monoxide (CO). In addition to accuracy and precision, the instability is determined. The statistics of calibrated results of olfactometer should comply with the quality criteria as defined in the standard (Australia/NZ Standard).

Panelist screening - selection of assessors
Reliable assessors are important to ensure the accuracy of olfactometry measurement. Panelists should be trained and screened from normal people before they are qualified to be panelists. Panelist screening tests uses standard odorous gas (such as n-butanol) to check the performance of each panelist candidate and select those whose responses are statistically meet the defined criteria to be panelists for real odour test.

The standard odorous gas n-butanol sample at the known concentration should also be measured firstly in each odour panel to check the validility of the olfactometry results and the performance of the panellists. The statistic n-butanol odour threshold measurements of UNSW odour laboratory is shown HERE.

Odour-free testing environment
An odour-free testing environment is required for odour measurement. Contamination or disturbance of background odours can be avoided in an odour-free testing room. To keep a testing laboratory odour-free, the following efforts are useful:

• No renovation materials should have any kind of smell.
• The furniture and equipments inside the room should not release any odour.
• No odorous compounds or chemicals should be stored in the laboratory.
• Installation of an effective activated carbon filter at the inlet of air-conditioning system.
• Keep the ventilation rate of the laboratory high than the minimum requirement.

The odour measurement results can be used to calculate odour emission rates from the sources where the samples were collected. With the calculated odour emission rates, odour dispersion modeling and odour impact assessment can be performed.