Hydrogen sulphide occurs naturally in crude petroleum, natural gas, volcanic gases, and hot springs. It can also result from bacterial breakdown of organic matter. Although it can remain in the air from 1 to 42 days, depending on the season, people can usually smell hydrogen sulphide at low concentrations in air ranging from 0.0005 to 0.3 parts per million (ppm).
Hydrogen sulphide is a flammable, colourless gas that smells like rotten eggs
Respiratory protection is recommended when entering an H2S environment, due to the toxic effects of the gas
Exposure to low concentrations of hydrogen sulphide may cause headaches, poor memory, tiredness, and balance problems