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Air: Sewer Gas

Sewer gas is a complex mix of toxic and nontoxic gases that forms when household and industrial waste decay. The concentration of sewer gas typically varies depending on the source. Highly toxic components of sewer gas include hydrogen sulfide and ammonia.

Sewer gas also contains:

  • Carbon dioxide.
  • Methane.
  • Nitrous oxides.
  • Sulfur dioxide.

Municipal and privately owned treatment systems can also contain:

  • Chlorine bleaches.
  • Gasoline.
  • Industrial solvents.

Exposure information

Sewer gas can enter a home through a floor drain, from a leaking or blocked plumbing roof vent, or (if the gases are in soil next to the house) through cracks in the foundation. Sanitary and farm workers can be exposed to sewer gas when cleaning and maintaining:

  • Home septic tanks.
  • Manure storage tanks.
  • Municipal sewers.

How can I avoid exposure to sewer gas?

  • Flush floor and sink drains with water to prevent the traps in sewer pipes from drying out.
  • Never enter a municipal sewer line, manure-storage tank, or any other large storage tank without proper training and equipment.
  • Occasionally check the roof plumbing vent for debris like leaves or bird nests.

What should I do if I suspect a problem?

First, try to follow the odor. Locate the point of entry, if possible, such as a basement floor drain. Then, check for a blocked rooftop plumbing gas vent. By adding water to the floor drain or removing debris from a vent, you may be able to prevent sewer gas from entering your home.

If the leak is behind the wall, you may need to hire a plumber to find the source and fix it. Some local public health departments offer home inspections.

Certain symptoms suggest exposure to gases like methane or carbon monoxide, which are odorless, or hydrogen sulfide, which smells like rotten eggs. These symptoms include:

  • Headaches
  • Dizziness
  • Drowsiness
  • Nausea

If you experience these symptoms and suspect a sewer gas leak in your home, see a doctor.

If you believe there are high concentrations of sewer gas in an enclosed space, evacuate the building and call the fire department for help. Also, avoid creating an ignition source, such as a spark from an electrical appliance, match, or cigarette lighter.

Health effects

The health risks linked to sewer gas exposure include:

  • Hydrogen sulfide poisoning: Hydrogen sulfide smells like rotten eggs, even in low concentrations. Exposure to low levels of hydrogen sulfide can cause eye and respiratory irritation. Other symptoms include:
    • Dizziness
    • Drowsiness
    • Headaches
    • Nausea
    • Nervousness

At high concentrations, hydrogen sulfide can interfere with the sense of smell, making it harder to use the gas’s distinct odor as a warning sign. In extremely high concentrations, hydrogen sulfide can cause loss of consciousness and death.

  • Suffocation: High concentrations of methane in enclosed areas decrease the amount of oxygen in the air and can cause suffocation. Symptoms of a lack of oxygen include:
    • Dizziness
    • Headaches
    • Nausea
    • Unconsciousness

Very low oxygen concentration levels (less than 12%) can cause unconsciousness and death very quickly and without warning. The most concentrated levels of sewer gas collect where it’s entering the home, which is often in basements.

  • Explosion and fire: Methane and hydrogen sulfide gases are both flammable and highly explosive.

The severity of health risks can vary from person to person. A person’s reaction can depend on several things, such as:

  • Heredity.
  • Individual health.
  • Previous exposure to chemicals, including through medicines and habits like smoking and drinking.

Severity also depends on the length of the exposure, the concentration of the gas, and whether it was eaten, inhaled, or touched.

Last revised April 18, 2023