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Hydrogen Sulfide Safety

Hydrogen sulfide is a compound with the molecular formula H2S. It's colorless, flammable, toxic and extremely malodorous. Hydrogen sulfide is perhaps best known as the chemical that gives rotten eggs their unforgettable odor. In trace concentrations, it's unpleasant and nothing more, but at higher levels it causes unconsciousness, respiratory failure, coma and death. At one point in 2008, hydrogen sulfide reportedly enjoyed a brief popularity in Japan as a way for those seeking to end their lives to commit suicide.

  1. Low Concentrations

    • The foul odor of hydrogen sulfide becomes perceptible at levels well below 1 part per million (ppm). At levels of 10 to 20 ppm, the gas causes eye irritation; concentrations from 50 to 100 ppm cause blurred vision and can even result in permanent eye damage. Hydrogen sulfide can quickly deaden the sense of smell so that, after a short length of time, those exposed to the gas cease to notice the scent.

    High Concentrations

    • Prolonged exposure to levels of 250 ppm or above can cause pulmonary edema, a condition where fluid accumulates in the lungs. When concentrations exceed 800 ppm, exposure for a mere 5 minutes is fatal; and concentrations of 1,000 ppm and above can kill with a single breath. Hydrogen sulfide is also flammable and can auto-ignite in air at 500 degrees Fahrenheit.

    Occurrence

    • Certain anaerobic bacteria (bacteria that live without oxygen) break down decaying organic matter and release hydrogen sulfide as waste. Other bacteria can actually use hydrogen sulfide as fuel. Consequently, hydrogen sulfide is typically found in decaying organic matter such as manure, sewage sludge and some deposits of natural gas. Hydrogen sulfide is sometimes released during the mining of sulfide ores or while refining petroleum with a high sulfur content. It's also a byproduct of some industrial processes.

    Staying Safe

    • Hydrogen sulfide is most likely to pose a hazard when allowed to accumulate in a confined space or when suddenly released at high concentrations. In 2007, for example, the Journal of Clinical Toxicology reported a case where a dairy farmer was poisoned with hydrogen sulfide after entering a tank containing rotting eggs; the gas had accumulated in the confined space until it reached dangerous levels.

      If you or your employees work under conditions where high levels of hydrogen sulfide might build up--with manure lagoons and holding tanks, for example--you should take precautions, including monitoring hydrogen sulfide levels, ensuring proper ventilation, and using appropriate protective equipment such as respirators. The Occupational Health Guideline for hydrogen sulfide has more complete information.

    Use in Suicide

    • In 2008, according to an article in Wired magazine, a mixture of bath sulfur and toilet bowl cleaner that released hydrogen sulfide became popular with people seeking to end their lives in Japan. A related USA Today article reported that 517 Japanese people killed themselves using hydrogen sulfide during the first half of the year. Wired reported that the a similar technique was later in vogue with suicides in the U.S. as well. Hydrogen sulfide is an extremely dangerous way to commit suicide because people who later enter the room or other residents of the same building may also be exposed to toxic concentrations of the gas and become unintended victims.

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