Hydrogen Sulfide (H2S)

Hydrogen sulfide has a chemical formula as H2S.
H2S is a gas that forms naturally in crude oil, natural gas, and water with high sulfur concentrations (sour water).
  • H2S is soluble in water, and may be released out of the water if there is change in the pH, line pressure, and /or temperature.
  • Some of the process areas may generate potentially fatal concentrations of H2S. These sources could be from raw materials, process reactions, or exposure of materials during a fire.
  • Flare systems handle large volumes of H2S. Any process flare or vent equipment entry could expose personnel to deadly concentrations of H2S.
    Some streams downstream of refineries may also contain potentially fatal concentrations of H2S. (Contact your local facility safety representatives for a list of specific equipment, which may contain H2S)
H2S is a flammable substance, incomplete combustion of H2S may cause the formation of Sulfur Dioxide (SO2). SO2 is also very toxic, and precautions should be taken to avoid exposure.

Characteristics of SO2 include:
-Colorless gas
-Corrosive
-Moderately soluble in water

Exposure to SO2 causes:
-Eye, nose, and throat irritation
-Cough, choking, and decreased respiration
-Forms sulfurous acid upon contact with moisture in mucous membranes

DANGER
EXTREME TOXICITY

  • H2S can kill in seconds at high enough concentrations
  • H2S usually enters the body via the lungs during inhalation of the gas.
  • The toxic effect depends upon–concentration of the gas in the air–duration of exposure.
  • H2S odor becomes detectable in concentrations as low as 0.008 ppm. It has a distinct rotten odor.
  • At as little as 50 ppm, the poison may deaden a persons sense of smell after only 2-15 minutes, making the individual unaware that he or she continues to be exposed to H2S.
  • Therefore, odor MUST NOT BE CONSIDERED AS A SAFE MEANS OF DETECTION.
  • At low levels, eye, nose and throat irritation occurs.
  • Moderate levels can cause headaches, dizziness, nausea and vomiting as well as cough and breathing difficulty.
  • High levels can cause shock, convulsions, coma and death.

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