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Physical Effects of Hydrogen Sulfide
(H₂S)

The way hydrogen sulfide (H₂S) affects you depends on three things. They are (1) how much you are exposed to (dosage or concentration); (2) how long you are exposed to it; and (3) each individual’s body tolerance. Studies show that exposure to H2S by different individuals may have different effects or symptoms for each individual. In general:

• Exposure to H2S in low concentrations may cause irritation of the eyes, nose, and throat
• Exposure to H2S in moderate concentrations causes headaches, dizziness, nausea, vomiting, and coughing
• Exposure to H2S in high concentrations causes loss of consciousness rapidly and death

H2S is measured in parts per million (ppm) or in percentages (%). The number of parts per million of H2S is equal to the number of parts of H2S per million parts of air by volume. In other words, if you had one million marbles in a barrel and those marbles represented H2S, one of those marbles would be equal to one ppm or 0.0001%. Half of those marbles would represent 500,000 ppm or 50%. As another example, if one inch represents one ppm of H2S, this would be like comparing one inch to over 15 miles.

The following information has been obtained from American National Standards Institute (ANSI) Z37.2 – 1972 Acceptable Concentrations of Hydrogen Sulfide:

• 0.13 ppm: Minimal perceptible odor
• 4.60 ppm: Easily detectable, moderate odor
• 10 ppm: Beginning eye irritation
• 27 ppm: Strong, unpleasant odor, but not intolerable
• 100 ppm: Coughing, eye irritation, loss of sense of smell after two to 15 minutes
• 200-300 ppm: Marked conjunctivitis (eye inflammation) and respiratory tract irritation after one hour of exposure
• 500-700 ppm: Loss of consciousness and possibly death in 30 minutes to one hour
• 700-1000 ppm: Rapid unconsciousness, cessation (stopping or pausing) of respiration, and death
• 1000-2000 ppm: Unconsciousness at once, with early cessation of respiration and death in a few minutes; death may occur even if individual is removed to fresh air at once
  

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