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    Safety Tips | Workplace exposure

    Prevent hydrogen sulfide exposure

    April 1, 2010

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    Hydrogen sulfide is a highly flammable hazardous gas that occurs naturally in crude petroleum and natural gas. It also is present in sewage, created through the breakdown of organic matter, and can cause negative health effects when inhaled. Hydrogen sulfide is heavier than air so it tends to be more highly concentrated in low-lying areas that are poorly ventilated, such as basements, manholes, sewer lines, and underground telephone or electrical vaults.

    Health effects

    Hydrogen sulfide’s effect on individuals varies depending on the levels of exposure. For most individuals (asthmatics may be at greater risk for ill health effects from exposure):

    • Low concentrations cause irritation of the eyes, nose, throat and respiratory system. This reaction can be delayed.
    • Moderate concentrations cause more severe eye and respiratory effects, headache, dizziness, nausea, vomiting, coughing and difficulty breathing.
    • High concentrations can lead to shock, convulsions and inability to breathe. In some instances, high levels of exposure can lead to coma and death. This effect can take place very rapidly, after only a few breaths.

    Detecting the presence

    Although low levels of concentration hydrogen sulfide may be detected by a “rotten egg” smell, high levels of concentration or being exposed to low levels for an extended period of time can cause a worker to lose the ability to smell the gas. Sense of smell alone is not a reliable method to indicate the presence of hydrogen sulfide.

    Avoiding exposure

    Before entering areas where hydrogen sulfide may be present, have a qualified person test the air. This will indicate whether fire or explosion precautions are necessary.

    If the gas is present, the area should be ventilated. If the gas cannot be removed, workers should be equipped with proper personal protective, rescue and communication equipment. A self-contained breathing apparatus is required in spaces with a concentration higher than 100 parts per million.

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