Note: It is not the intent of this section to create an H2S contingency plan.
Hydrogen Sulfide or sour gas (H2S) is a flammable, colorless gas that is toxic at extremely low concentrations. It is heavier than air, and may accumulate in low-lying areas. It smells like "rotten eggs" at low concentrations and causes you to quickly lose your sense of smell. Many areas where the gas is found have been identified, but pockets of the gas can occur anywhere. [More]
Iron sulfide is a byproduct of many production operations and may spontaneously combust with air.
Flaring operations associated with H2S production will generate Sulfur Dioxide (S02), another toxic gas.
Active monitoring for hydrogen sulfide gas and good planning and training programs for workers are the best ways to prevent injury and death.
Also see: NIOSH Classification of H2S Hazard Areas.
Hazards may include and/or be related to the following:
All personnel working in an area where concentrations of Hydrogen Sulfide may exceed the 10 Parts Per Million (PPM) should be provided with training before beginning work assignments.
Implement an H2S contingency plan (see API) including, but not limited to:
For emergency response information, see Hazardous Waste and Emergency Response (HAZWOPER) Standard, [29 CFR 1910.120].
Comprehensive training should be provided for workers in H2S operations. Example topics include:
Metal fatigue, including hydrogen embrittlement or sulfide stress cracking, can result in a release of hydrogen sulfide gas.
It is possible for hydrogen sulfide gas to accumulate in any low or enclosed area, such as a gas venting system, mud system, cellars, pits, and tanks.
Additional guidance materials are available from:
H2S Training and Information Links
A.1 Physical Data
A.2 Exposure Limits
The American Conference of Governmental Industrial Hygienists recommends a Threshold Limit Value of 1 ppm and a short-term exposure (STEL) limit of 5 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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