Odor threshold

Some chemicals can be smelled at levels far below any harmful exposure, which makes odor a handy early warning. Others have a threshold well above the level that can cause harm, so by the time you smell them you are already overexposed. SDS figures are often given as a range or may be missing entirely.

Smell fades with time. Olfactory fatigue means the nose adapts to a constant odor, and some gases, such as hydrogen sulfide, can deaden the sense of smell at higher concentrations, leaving the worker unaware of growing danger. Colds, age, smoking and individual differences also change what people notice.

For this reason, the absence of odor does not mean the air is safe, and the presence of odor does not necessarily mean it is hazardous. Odor is not an accepted basis for choosing respirators or deciding that a work area is acceptable. Exposure assessment relies on air monitoring compared against Occupational exposure limit (OEL) values.

Odor can still be useful in a limited way. Gas suppliers add odorants to otherwise odorless fuel gases so leaks are noticed. If a worker reports an unexpected smell, treat it as a signal to check ventilation and containers, and to measure if there is any doubt.