Environmental Issue & Sick Building Syndrome Blog

The scientific literature describes the sense of smell as a built-in warning system to alert humans and other animals of hazards that frequently cannot be seen or otherwise sensed. The American Conference of Government Industrial Hygienists (ACGIH) has been a leader in the expert determination of minimum odor threshold ranges for humans for the purpose of determining whether the sensing of an odor may be associated with a worker health hazard, particularly in industrial settings. One fact that has become clear based on an extensive number of ACGIH surveys is that the minimum concentration level (odor threshold) at which an odor can be discerned is highly variable from person to person, with the range on most substances being a full order of magnitude. Some chemical vapors, such as mercury, are odorless, and therefore are absent of any odor warning properties. Carbon monoxide is also odorless; however, in many cases, other hydrocarbon combustion odors are discernible, thereby providing a good indication of the potential presence of hazardous levels of carbon monoxide.

Other chemicals, such as anhydrous ammonia, can cause almost immediate olfactory fatigue, such that a person’s ability to perceive this highly toxic chemical vapor hazard is very rapidly vanquished. Still other hazardous chemicals, such as DBCP (dioxin), are highly toxic at very low concentrations that are much lower than the minimum odor detection thresholds for humans.

Other commonly reported odor complaints that investigators have been responding to for many years include chemical vapors/odors released as a result of fuel oil spills, soil vapor intrusion problems related to hydrocarbon based solvent vapors (VOC’s) often resulting from a building’s prior use as a manufacturing or dry cleaning facility where chemicals have been spilled, rotten egg-type odors that are frequently related to damaged or infrequently used drain lines, and odors related to clandestine illicit drug production. Most people when asked acknowledge that they recognize the smell of an odor that they would characterize as musty or moldy. Such odors provide a very good warning indicator of there being mold growth conditions in the indoor environment. Mold odors are caused by the volatilization of very caustic enzymes that are secreted through the mycelia (similar to a root system) of mold, which is the process by which molds dissolve organic materials such that the nutrients can be absorbed to provide sustenance and growth. It should be noted that mold will secrete digestive enzymes only when there is sufficient moisture, and therefore, the presence of a mold-related odor strongly suggests that there is an active moisture intrusion, plumbing leak or condensation problem.