Chemicals & Odor Threshold-Environmental Health & Safety - Carnegie Mellon University

Wednesday, September 26, 2012

Chemicals & Odor Threshold

If there is one thing a scientist needs to know about hazardous chemicals is that there is really no relation between type and level of odor and the hazard that the odor represents from the chemical in question.

Some very serious hazards have no odor at all, such as carbon monoxide. Some very serious hazards, such as benzene, have quite pleasant odors (well, most people agree on that!) Other high hazard items, such as hydrogen sulfide, have a pretty unpleasant odor, which is detected at very low levels. The problem with H2S, though, it is that it “deadens” one’s sense of smell fairly quickly, and you may think the odor is gone when in reality, you just can’t smell it any longer.

The odor threshold for a material is defined as the concentration in the air of a particular material, when the typical person should first be able to detect it. As you might suspect, the odor threshold is NOT a good mechanism for determining whether the concentration of a chemical is a hazard to one’s health or not. Many chemicals have good detection properties and you can detect the odor long before the concentrations become hazardous. Of course, there are others where the threshold is well above the hazard level and, by the time you detect the odor, you are already in a hazardous exposure situation.

Information on odor threshold and its relation to hazard levels is available in any good Material Safety Data Sheet, so be sure to check them out before using a chemical or evaluating a hazard level. EH&S can always provide assistance with this as well.

By: Mark Banister,, 412-268-1493