Hydrogen Sulfide

Hydrogen sulfide \(H_2S\) is a colorless, highly toxic, corrosive, and flammable gas infamous for its distinctive rotten-egg odor at low concentrations.  Often referred to as sewer gas, swamp gas, or stink damp, it is slightly denser than air and can accumulate in low-lying and enclosed spaces, posing a significant hazard in poorly ventilated areas like sewers, manholes, and underground vaults.  \(H_2S\) occurs naturally from the bacterial decomposition of organic matter in the absence of oxygen, such as in swamps, bogs, and sewage.  It is also found in crude petroleum, natural gas, volcanic gases, and hot springs.  Industrially, it is a byproduct of processes like oil refining, mining, tanning, and pulp and paper manufacturing.

 

While its strong odor serves as a warning at low levels, prolonged exposure or higher concentrations can quickly lead to "olfactory fatigue," where the sense of smell is lost, giving a false sense of safety.  Exposure to hydrogen sulfide primarily occurs through inhalation, and its health effects vary greatly depending on concentration and duration.  At low levels, it can cause eye and respiratory irritation, headaches, and nausea.  However, at higher concentrations, \(H_2S\) can rapidly inhibit cellular respiration, leading to more severe symptoms like dizziness, confusion, unconsciousness, and even death, making it one of the leading causes of workplace gas inhalation fatalities.  Despite its toxicity, hydrogen sulfide plays a role in various natural cycles and is even produced endogenously in the human body, where it acts as a neuromodulator.