Low concentration exposures (under 10 PPM) Hydrogen Sulfide is noticeable by its offensive odor (similar to rotten eggs) even in low concentrations. The sense of smell cannot be relied upon to warn a worker of a dangerous concentration of the gas, because the gas rapidly paralyzes the olfactory nerves causing a loss of the sense of smell. A longer exposure to a low concentration of the gas may result in the loss of the sense of smell as well.

Higher concentration exposures (10 PPM and above)
Low concentrations that are prolonged or a short term exposure to higher concentrations may lead to death. It is a well known fact that the sense of smell will be rendered ineffective by hydrogen sulfide and that can result in an individual failing to recognize the presence of dangerously high concentrations. Exposure to hydrogen sulfide causes death by asphyxiation.