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    Utility workers such as sewage and wastewater treatment workers, face many dangers while working on the job. These include exposure to diseases, being confined in tight spaces, trench collapses, and even drowning. However, one such hazard that is often forgotten about is Hydrogen Sulfide (H2S). H2S is a toxic gas that is both colorless and flammable. It can be sensed by its distinct “rotten egg smell”. H2S is naturally occurring in crude petroleum and hot springs. It is also produced through the break-down of organic materials and wastes. H2S can be found in either liquid or gas forms.

    At what level does H2S become dangerous?

    H2S concentrations are measured using a system called Parts Per Million (PPM). As an example, 100 PPM H2S means that for every 999,900 molecules of air, there are 100 molecules of Hydrogen Sulfide. Exposure to H2S can result in a variety of health effects. These effects can occur very early on and are compounded as exposure to higher concentrations or the duration of exposure increases.

    • 0 PPM- Normal Fresh Air
    • 0.01-1.5 PPM- “Rotten egg” smell is first noticeable, becomes more noticeable at 3-5 PPM
    • 2-5 PPM- Nausea can occur from prolonged exposure
    • 20 PPM- Fatigue, headache, irritability, dizziness, and possible loss of appetite
    • 50-100 PPM- Conjunctivitis, and respiratory tract irritation after an hour of exposure. May upset digestion and cause loss of appetite
    • 100 PPM- Possible loss of smell after 2-15 minutes. Altered breathing after 15-30 minutes. Throat irritation after 1 hour. Death can occur after 48 hours of exposure.
    • 100-150 PPM- Loss of smell (fatigue or paralysis)
    • 200-300 PPM- Pulmonary edema can occur from increased exposure.
    • 500-700 PPM- Collapse within 5 minutes. Serious eye damage in 30 minutes. Death after 30-60 minutes.
    • 700-1000 PPM- Immediate collapse after 1 or 2 breaths, death within minutes.
    • 1000-2000- Death almost instantaneously

    Utilities worker and Inspector


    Following proper guidelines can help prevent or reduce the exposure to H2S and other harmful gases.

    • Evaluate the confined work spaces before starting work.
    • Ventilate the workspace if necessary
    • Ensure proper PPE resources are available
    • Monitor H2S levels consistently

    For further information please refer to our application notes: