Sewer gas

Sewer gas is gases produced in sewers by decomposing sewage and other decomposing organic matter. It can refer to:

• Methane: explosion and anoxia risks, as with firedamp in a coalmine.
• Hydrogen sulfide

Sewer gas is a mixture of gases formed during the decomposition of household or industrial wastes. These include hydrogen sulfide, ammonia (which are toxic), as well as methane, carbon dioxide, sulfur dioxide and nitrogen oxides.

Causes

Plumbing drains' traps are used to create a water seal that prevents sewer gases from entering buildings. In addition, plumbing vents allow sewer gases to be exhausted outdoors. However, infrequently used plumbing fixtures may not pass enough water to keep their water seals from evaporating with time, especially in dry weather. The result is the most common means of sewage gas entering buildings, and can be solved easily by regularly using the fixtures or adding water to their drains. One of the most common traps to dry out, possibly unnoticed, are floor drains like those typically placed near home furnaces and water heaters. Infrequently used utility sinks, tubs, showers, and restrooms are also common culprits. Trap primers are available that automatically add water to remote or little used traps such as these. Blocked plumbing vents, typically at the roof, can also cause water seals to fail via siphoning of the water.

Exposure to sewer gas can also happen if the gas seeps in via a leaking plumbing drain or vent pipe or even through cracks in a building’s foundation. Sewer gas tends to accumulate in basements, but can mix with all the air in a house. Individuals who work in sanitation industries or on farms might be exposed on the job if they clean or maintain municipal sewers, manure storage tanks, or septic tanks.

Health effects

Sewer gas often has a “rotten eggs” smell, which comes from the hydrogen sulfide it contains. Exposure to low levels of this toxic chemical can irritate the eyes, cause a cough or sore throat, shortness of breath, and fluid accumulation in the lungs. Prolonged low-level exposure may cause fatigue, loss of appetite, headaches, irritability, poor memory and dizziness. High concentrations of hydrogen sulfide can interfere with the sense of smell so that you don’t sense the “rotten eggs” smell that warns of its presence; this effect is called olfactory fatigue. At very high concentrations, hydrogen sulfide can cause loss of consciousness and death.

What to do

If you suspect that sewer gas is leaking into your building first ventilate it and then fill all your traps with water. Also look for damaged or disconnected drains, like under sinks. If the problem is not solved, continue ventilating the building. If you are the owner, call a plumber to find and repair the problem; if leasing, contact the property management. For stubborn problems, like neighboring drainage fields, or when a landlord is unresponsive, contacting your local public health department may help. Because sewer gases are highly flammable, and might be confused with a natural gas or propane leak, don’t take chances. If the smell is strong, don't use appliances or do anything that produces sparks or flames, get everyone, including yourself, out of and away from the building, and call the local Fire Department from another building or a cell phone.

See also

• Plumbing
• Potable cold and hot water supply
• Rainwater, surface, and subsurface water drainage
• Septic systems
• Fire protection

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