Hydrogen sulfide, a colorless gas that smells like rotten eggs, is produced naturally from decaying matter. This gas is lethal to breathe in, and hydrogen sulfide present in high concentrations can cause death very rapidly.

Its relative density is also greater than air, causing it to accumulate at lower altitudes and posing an enormous threat to workers at sites, such as manholes, sewage systems and mining operations.

Why is hydrogen sulfide so dangerous? It binds strongly to the heme-containing cytochrome c oxidase (CcO) enzyme and blocks the cellular process of aerobic (oxygen-dependent) respiration.

Source Paper:

Detoxification of hydrogen sulfide by synthetic heme model compounds

https://www.nature.com/articles/s41598-024-80511-1