Assessment of Air Velocity and Flow at the Sniff Port on Odor Panel Evaluations

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The EN 13725 European Standard for the evaluation of odor samples by dynamic olfactometry specifies that the air flow rate emanating from individual panelist sniff ports must be at least 20 L/min and that the air velocity at the opening must be between 0.2 m/s and 0.5 m/s. The AWMA EE-6 Guideline (2002), recommends a minimum flow rate of 5 L/min, with a velocity at the opening between 0.01m/s and 0.1 m/s.

The flow rate and the velocity settings provided in the AWMA EE-6 Guideline were based on the settings of other laboratories at that time and even ORTECH recommended 8-10 L/min flow rate at the port which was the flow we used in our laboratory. The same applied to the port design. The diameterand a shape of the port was chosen based on various laboratories designs without consideration forany detailed research.

The ASTM E679-04 (2004) standard does not specify a flow rate or velocity. It is almost impossibleto imagine that when you compare EN13725 European Standard with AWMA EE-6 Guideline that a factor of 20 times difference in velocity profile is allowable. Which method is appropriate? Obviously you are not able to comply with both methods.

There are other differences between European and US approaches. Therefore, this paper is not basedon the European or US approach, but use some of the sections from both the standards and guidelines. For example, the European Standard EN 13725 and AWMA EE-6 Guidelines allow the use of a binary system, whereas the ASTM E 679-04 does not, and this may be is the time to change the ASTM E 679-04 method.

The importance of setting the flow rate and the velocity at the port opening is critical. For example, the Ontario Ministry of the Environment (MOE) is moving towards an odor detection threshold value standard of 1 odor unit (ou) beyond a plant property, without realizing that the flow rate and velocity must be specified alongside this standard. Without such specifications, variations of up to 10 times in the odor detection threshold values obtained by different olfactometers could be expected.

The Ontario Ministry of the Environment defines optimum conditions for odor testing as those conditions which give the highest odor detection threshold value.

Based on the huge difference between European recommendations and the AWMA EE-6 Odor Committee recommendations, there is urgency in Ontario to optimize the flow rate and the velocity across the port in order to obtain the highest odor detection threshold value. Based on consultationwith the Ontario Ministry of the Environment the optimum flow rate and the optimum velocity for the ORTECH's olfactometer were chosen based on the results of this study. Three different port diameters were used: 3.0 cm, 3.7 cm and 4.0 cm in order to create different velocities across the portusing different flow rates.

This paper is based on a series of studies performed at the ORTECH laboratory in Mississauga, Ontario to determine the optimum air flow emanating from a sniff port and the optimum air velocity across the port during the determination of the odor detection threshold values by the ORTECH olfactometer. The optimum flow rate and optimum velocity terminology used in this paper reflects such flow rate and velocity settings, that the highest odor detection threshold value is obtained.

This paper also compares the odor detection threshold values obtained for different concentrationsof n-butanol with the results obtained from the 2003 Robin International Test for olfactometry performance based on different n- butanol concentrations.

Document Type: Research Article


Publication date: January 1, 2006

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