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Job Safety Analysis (JSA)
General Safety and Health >> Hydrogen Sulfide Gas >> Appendix A
Physical Properties and Physiological Effects of Hydrogen Sulfide

A.1 Physical Data
  • Chemical Name: Hydrogen Sulfide
  • CAS Number: 7783-06-4
  • Synonyms: Sulfureted hydrogen, hydrosulfuric acid, dihydrogen sulfide
  • Chemical Family: Inorganic sulfide
  • Chemical Formula: H2S
  • Normal Physical State: Colorless gas, slightly heavier than air. Vapor density (specific gravity) at 59°F (15°C) and 1 atmosphere = 1.189.
  • Auto ignition Temperature: 500º F
  • Boiling Point: -76º F
  • Melting Point: -117.2º F
  • Flammable Limits: 4.3-46 percent vapor by volume in air
  • Solubility: Soluble in water and oil: solubility decreases as the fluid temperature increases
  • Combustibility: Burns with a blue flame to produce sulfur dioxide (SO2). Refer to Appendix B Odor and Warning Properties: Hydrogen sulfide has an extremely unpleasant odor, characteristic of rotten eggs, and is easily detected at low concentrations: however, due to rapid onset of olfactory fatigue and paralysis (inability to smell) ODOR SHALL NOT BE USED AS A WARNING MEASURE.
A.2 Exposure Limits

The American Conference of Governmental Industrial Hygienists recommends a Threshold Limit Value of 10ppm and a short-term exposure (STEL) limit of 15 ppm averaged over 15 minutes. Exposure at the STEL should not be repeated more than four times per day with at least 60 minutes between successive exposures in this range.

 A.3 Physiological Effects

Inhalation at certain concentrations can lead to injury of death. The 300 ppm is considered by the ACGIH as Immediately Dangerous to Life and Health. Hydrogen sulfide is an extremely toxic, flammable gas that may be encountered in the production of gas well gas, high-sulfide, high sulfur content crude oil, crude oil fractions, associated gas, and waters. Since hydrogen sulfide is heavier than air, it can collect in low places. It is colorless and has a foul rotten egg odor. In low concentrations, H2S sometimes can be detectable by its characteristic odor; however, the smell cannot be relied upon to forewarn of dangerous concentrations (greater than 100ppm) of the gas because it rapidly paralyzes the sense of smell due to paralysis of the olfactory nerve. A longer exposure to the lower concentrations has a similar desensitizing effect on the sense of smell.

It should be well understood that the sense of smell will be rendered ineffective by hydrogen sulfide, which can result in an individual failing to recognize the presence of dangerously high concentrations. Exposure to hydrogen sulfide causes death by poisoning the respiratory system at the cellular level. Symptoms from repeated exposures to low concentrations usually disappear after not being exposed for a period of time. Repeated exposures to low concentrations that do not produce effects eventually may lead to irritation if the exposures are frequent.

A.4 Respiratory Protection

Respiratory protection shall be worn above the action level. Refer to 6.6 for proper breathing equipment recommendations for oil and gas well drilling and servicing operations involving hydrogen sulfide.


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