Hydrogen sulfide (H2S) is a deadly gas common at many industrial work sites. It must be handled carefully because its toxicity is similar to cyanide, and even slight exposure comes with a host of health concerns. Where does it come from? H2S has few industrial applications on its own, but can be used to harvest sulfur, one of the most useful and versatile elements in the industry. It is commonly sourced from natural gas and petroleum deposits for this purpose. Even if you don’t work at a gas refinery, you aren’t out of the woods. Hydrogen sulfide occurs in any place where organic matter breaks down in the absence of oxygen. Significant quantities of H2S often build up in sewers, basements, manholes and manure pits. Okay, so how is it dangerous? Hydrogen sulfide can ignite when mixed with air, even at small concentrations. Any operations where the gas is likely to build up should be carried out with safety equipment. In addition to being flammable, H2S is an asphyxiant and an irritant. At low levels, H2S gas affects the mucous membranes. Medium concentrations cause stronger symptoms in addition to difficulty breathing, coughing and respiratory distress. High concentrations produce convulsions, shock, choking, coma and death. These symptoms can be delayed for up to 72 hours. Prolonged level exposure can lead to chronic health issues. Protecting yourself Though H2S smells like rotten eggs, it also contains a molecule that can paralyze the olfactory nerve, which would prevent you from smelling the gas. This is why OSHA regulations require applicable locations to be tested prior to entry. Multi-gas monitors can tell you if a space is dangerous, but because H2S is heavier than air, gas checks need to be done at all heights in a confined space. If H2S is found in high concentrations, ventilation or a breathing apparatus will be needed. (Buy a Multi-Gas monitor.) In short, hydrogen sulfide is extremely dangerous, but as long as you test for it properly and follow regulations regarding breathing apparatuses, you can still work in confined spaces safely.