Source Emission Odor Measurement by a Dynamic Forced-Choice Triangle Olfactometer

Abstract

Current odor emission control regulations specify a syringe dilution technique to determine odor concentration level of exhaust stack emissions. This procedure in practice is cumbersome, slow, and subject to improvisations. Further, there is no satisfactory provision to check reliability of positive-negative responses of panel. An approach is desired where the diluted odor sample is presented to the panel for discrimination from samples of non-odorous air and results can be related to statistically significant confidence levels.An olfactometer based upon forced-choice triangle statistical design was designed and constructed. One diluted odor sample and two non-odorous air blanks are presented dynamically at each dilution level. Each panelist is required to judge which of three ports is odorous and to signal a choice. The three ports are arranged in a circular symmetrical pattern to achieve a double-blind sample presentation since neither panelists nor panel leader know the correct choice until after the judgment is made. Dynamically diluted stimuli are presented at constant flow in ascending concentration order, increasing by a factor of 3 per step. Three odor dilution steps are available on a continuous basis during the evaluation. Evaluation of one sample is routinely completed by a panel of 9 within less than 15 minutes. Statistical data compilation is achieved by ranking procedures to obtain the average panel odor threshold for each sample. Testing of rendering plant odor emissions resulted in a satisfactory correlation between the dynamic olfactometer and syringe dilution methods.