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Core Lab - Odor and Emissions Research FAQ's

Odor and Emissions Research FAQ’s

What is Olfactometry?
Olfactometry is the measurement of the response of assessors to olfactory stimuli. The odor is measured as DT, Intensity, and Hedonic Tone.

What is an Olfactometer and how does it work?
An Olfactometer is a device which dilutes a sample of odorous air with clean air. The odor panel will sniff the sample beginning with a very high dilution (small amount of sample to large amount of clean air). If the panelist cannot determine the difference in three presentations, the panel leader will then decrease the dilution by increasing the amount of sample air and the process will begin again. This will continue until the panelist can detect a difference in the three presentations.

The WTAMU Olfactometery Lab uses a dynamic triangular forced choice olfactometer. This means that panelists are given 3 presentations, one of which contains the sample, and two of which are clean air. The assessor must choose which of the 3 presentations he/she believes the sample to be. If the assessor does not know which is the sample, a 'guess' is selected. If the assessor detects a difference in the presentations, a 'detect' is selected. If the assessor recognizes the sample and can place a characterization with it, a 'recognize' is selected. For most applications, the panel leader will stop the presentation when the assessor correctly determines two consecutive detects. However, for the the results to be counted, the assessor must first select a guess. This lets the panel leader know that the dilutions were high enough that the assessor did not detect the sample at the beginning of the round.

Olfactometer Front 

Panelist Sniffing Sample


What is an "Odor Panel"?
An Odor Panel is a group of trained odor assessors who analyze the odor samples by using olfactometry. These people are the actual instruments. They tell the panel leader when they can detect an odor. WTAMU uses a wide variety of panelists both in age and ethnicity. They are student workers and people from the local community.

 Image of Odor panel

What are the qualifications for a person to become a trained panelist?
In order to be a panelist, a person must meet certain criteria. They must be at least 18 years of age so their olfactory system is fully developed. They cannot smoke, use smokeless tobacco, or live in the environment of a smoker. They should not have a chronic allergy which affects the olfactory system. If female, the panelist should not be pregnant. Pregnancy causes changes in a woman's hormonal levels which can affect her sense of smell. They must also agree to the Code of Behavior.

If all the above is acceptable, the person must determine their individual threshold estimates for a reference gas. The reference gas used is 40 ppm n-butanol in nitrogen. The data must be collected in at least 3 sessions on separate days with at least one day of rest between each session. In order to assure repeatability, each panelist must fall in a range of sensitivity for the n-butanol. These are the people selected for the odor panel.

The WTAMU Olfactometry Lab uses a sensitivity range of 1 part n-butanol to 256 parts clean air (1:256) to 1 part n-butanol to 2048 parts clean air (1:2048). Persons able to detect the reference gas at these levels are the correct sensitivity. These numbers are based on the European Standard (CEN / TC264) target of 20 to 80 ppb 40 ppm n-butanol/volume of nitrogen.


What is the Code of Behavior?
The Code of Behavior is a list of rules which all odor assessors must follow. There are not many of them, but they must be adhered to so the resulting data is reliable and accurate. They are split into two parts.

Part 1: Before a Panel Session

  • Must approach duties as a panelist with a professional attitude.
  • Punctuality: must arrive 10 minutes before the first sample to be analyzed to allow the olfactory senses to acclimate to the odor lab.
  • Report absences in advance if at all possible.
  • Acknowledge colds or physical conditions which can affect your sense of smell.
  • Maintain an acceptable level of personal hygiene to prevent any personal odor.
  • No personal scents such as perfume, cologne, aftershave, scented shampoos, body washes, or hand lotions the day of the lab session.
  • No spicy foods at least 6 hours prior to a lab session.
  • No alcohol at least 6 hours prior to a lab session.
  • No gum or flavored drinks like coffee, tea, or soft drinks, for at least 1 hour prior to a lab session (may drink water).
  • Must be available for the complete session.
  • Cannot work in livestock facilities for at least 24 hours prior to a lab session.

Part 2: During a Panel Session

  • Stay in the odor lab (may leave for bathroom breaks).
  • Do not discuss odor selections with other panelists.
  • Drink only bottled water (supplied).
  • No phone calls during a panel session (cell phones and pagers must be turned off, emergency calls must be made outside the room).
  • These rules must be followed exactly, or the data from that session will not be good data.

How do you collect an odor sample?
Odor Samples are collected in Tedlar® bags which are contained in a vacuum chamber. The samples can then be transported to the odor lab for analysis.

Image of Tedlar Bag

What is a vacuum chamber?
A vacuum chamber is a suitcase sized hard cased box with a pump attached. The pump, when activated, will pump air out of the chamber. The sample bag, located in the chamber, with a sample line running outside, will fill as the air in the chamber is evacuated. This way the sample air is not fouled by passing through the pump mechanism.

Image of Vacuum chamber

What are the quality controls that are used in the odor lab?
Olfactometer flow rates are checked twice per odor panel, once before the panel begins, and after the end of the session. If flow rates are not within specified limits, the olfactometer is calibrated. With each odor session, a machine blank (bag with sample air taken from the olfactometer) and a bag blank (a pre-conditioned bag taken from the same batch of bags used for the odor samples and filled with zero-air) is run. This will assure that no odor from the machine or the bag is contaminating the odor samples. At least one n-butanol sample is presented to the odor panel to ensure that each panelist is within the specified sensitivity range required by the standards.