Hydrogen sulfide

Sewers, manure pits, landfills, hot springs/volcanoes, and industries such as oil and gas, wastewater treatment, and pulp and paper [1][4].

Mainly by breathing air at work or near sources; it can quickly build up in enclosed or low-lying spaces. You can lose the ability to smell it at high levels, so odor is not a safe warning [1][2].

Short-term exposure can cause eye/throat irritation, headache, nausea, and coughing; high levels can cause collapse, lung injury, and death within minutes [1][2]. Long-term effects from low levels are less certain. Not classifiable as to carcinogenicity (IARC) [3].

Workers in oil/gas, wastewater, agriculture, and pulp/paper; people near sewage, landfills, or large animal operations; those with asthma or lung disease [1][2][4].

Avoid entering sewers, tanks, or manure pits; ensure ventilation and use gas monitors at work; follow local advisories and move upwind during odor events. Don’t rely on smell; seek medical care after significant exposure [1][2].