Hydrogen sulfide H2S is a colorless chalcogen hydride gas with the characteristic foul odor. It is poisonous, corrosive, and flammable. Hydrogen sulfide is often produced from the microbial breakdown of organic matter in the absence of oxygen gas, such as in swamps and sewers; this process is commonly known as anaerobic digestion which is done by sulfate-reducing microorganisms. H2S also occurs in volcanic gases, natural gas, and in some sources of well water. The human body produces small amounts of H2S and uses it as a signaling molecule.


Hydrogen Sulfide

Time-weighted average

150 (0.01) - 40 (0.03) µg/Nm3 (ppm)

Averaging time

24 hour - Annual

Time –weighted average Averaging Time Number of allowable exceedances
100 ppb 24-hour 10 times per annum
30 ppb annually None
Number of allowable exceedances

10 times per annum - N/A