Working recently with an industrial hygienist at a facility where we were doing some respiratory training, hydrogen sulfide (H2S ) was prevalent in the atmosphere. Despite this, workers we interviewed told us that they could not smell the H2S, which was at concentrations that nearly made us nauseous.
Hydrogen sulfide has an offensive "rotten egg" odor that is easily detectable by smell even at low concentrations. However, with prolonged exposure one can become accustomed, or desensitized, to its smell. This occurrence is known as olfactory fatigue. Workers that become desensitized may not be aware of their exposures above permissible levels, which could lead to respiratory health concerns.