Hydrogen Sulfide Gas and Monitors

July 9, 2021

Hydrogen Sulfide (H2S) gas is one of the most toxic and deadly hazards found in industry. H2S is a natural constituent of crude oil and natural gas. It can result from full recovery coke production, iron making, oil refineries, and occurs naturally in volcanic gases and hot springs, and it can be evolved from the refining or manufacturing of other substances such as molybdenum, pulp and paper, rayon textile or leather tanning. H2S is also commonly found in sewers and is known as “Sewer Gas”. Workers in the oil and gas industry are very aware of its lethal properties. Found in formations that are being drilled for oil, the gas is formed by decomposition of organic matter containing sulfur in low oxygen environments.

Hydrogen sulfide is a highly toxic, colorless, flammable gas. It is heavier than air (at standard temperature and pressure) so this invisible gas can collect in depressions in the ground and in confined spaces and it has the unmistakable odor of rotten eggs. However, the sense of smell is not a reliable warning because exposure to this gas quickly deadens the sense of smell. If you smell rotten eggs and then the smell goes away it is possible that the exposure has deadened your sense of smell. Loss of consciousness can occur within seconds of exposure to a high concentration of this gas. The only positive means of determining the amount of H2S present is by testing with approved detectors.

Toxicity and Effects

H2S - Classified as a chemical asphyxiate, is similar to carbon monoxide and cyanide gases. It inhibits cellular respiration and uptake of oxygen, causing biochemical suffocation.

Typical exposure symptoms include:






Lowest level detectable by odor


8 Hour Exposure Limit (TLV)



Irritation of the eyes and nose - generally accepted maximum exposure limit - alarm set-point on



Deadens sense of smell in 3 -15 minutes: headache, dizziness, nausea and vomiting, coughing

and breathing difficulty - At this level it is considered immediately dangerous to life and health




Deadens sense of smell quickly, stings the eyes and throat



Loss of reasoning and balance - will lose consciousness within 30 minutes



Will become unconscious very quickly, death will result if not promptly rescued



Loss of consciousness is immediate; breathing stops