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What is sewer gas?
Sewer gas is a complex mixture of toxic and non-toxic gases that can be
present at varying levels depending upon the source. It is formed during the decay of household and
industrial waste. Highly toxic components of sewer gas include hydrogen
sulfide and ammonia.
Sewer gas also contains methane, carbon dioxide, sulfur dioxide, and nitrous oxides. In
addition, chlorine bleaches, industrial solvents, and gasoline are frequently present in
municipal and privately owned-sewage treatment systems.
How are people exposed to sewer gas?
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 adjacent to the
house) through cracks in foundations. Sanitary and farm workers can be exposed to
sewer gas during the cleaning and maintenance of municipal sewers, manure storage tanks,
and home septic tanks.
What are the effects of exposure to sewer gas?
The principal risks and effects associated
with exposure are:
- Hydrogen sulfide poisoning. Exposure to low levels of hydrogen sulfide causes irritation
of the eyes and respiratory tract. Other symptoms include nervousness, dizziness, nausea,
headache, and drowsiness. This gas smells like rotten eggs, even at
extremely low concentrations. Exposure to high concentrations can interfere with the sense of smell, making this warning signal unreliable. At
extremely high levels, hydrogen sulfide can cause immediate loss of consciousness and
Asphyxiation. High concentrations of methane in enclosed areas can lead to suffocation as large amounts of methane will decrease the amount of oxygen
in the air. The effects of oxygen deficiency include headache, nausea,
dizziness and unconsciousness. At very low oxygen concentrations (<12%), unconsciousness and death may occur very quickly and without
warning. Sewer gas diffuses and mixes with indoor air, and will be
most concentrated where it is entering the home. It can accumulate in basements.
Explosion and fire. Methane and hydrogen
sulfide are flammable and highly explosive.
How can I avoid being exposed to sewer gas?
What should I do if I suspect a problem?
First, following the odor, try to locate the point of entry, such as a basement floor drain.
Check for a blocked rooftop plumbing gas vent. By adding
water to the floor drain or removing debris from a roof plumbing stack vent you may be able to prevent sewer
gas from entering your home. In the unlikely event that a leak in gas
vent plumbing is behind walls, a plumber may be needed to find and fix
it. Some local public health
departments may be able to offer home inspections.
Symptoms of headache, nausea, dizziness, or drowsiness may indicate exposure to
an odorless gas like methane or carbon
monoxide, or to hydrogen sulfide, which smells of rotten eggs. Persons experiencing
severe symptoms should seek immediate
If you suspect that high
concentrations of sewer gas have accumulated in an enclosed space, you should evacuate the
area and contact the fire department for assistance. Avoid creating an ignition source
such a spark from an electrical appliance, match, or cigarette lighter.
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Last Revised: September 03, 2014