Sewer gas

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Sewer gas is fundamentally methane gas, but in reality a complex mixture of toxic and non-toxic gases produced and collected in sewage systems by the decomposition of organic household or industrial wastes.^[1]

Sewer gases include hydrogen sulfide, ammonia, methane, carbon dioxide, sulfur dioxide and nitrogen oxides. Improper disposal of petroleum products such as gasoline and mineral spirits contribute to sewer gas hazards. Sewer gases are of concern due to their odor, health effects, and potential for creating fire or explosions.^[2]

Sewage gas in homes

Sewage gas is typically restricted from entering buildings through plumbing traps that create a water seal at potential points of entry. In addition, plumbing vents allow sewer gases to be exhausted outdoors. Infrequently used plumbing fixtures may allow sewer gas to enter a home due to evaporation of water in the trap, especially in dry weather. The result is the most common means of sewer gas entering buildings, and can be solved easily by using the fixtures regularly or adding water to their drains. One of the most common traps to dry out are floor drains such as those typically placed near home furnaces and water heaters. Infrequently used utility sinks, tubs, showers, and restrooms also are 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, also can cause water seals to fail via siphoning of the water.

Exposure to sewer gas also can 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 is typically denser than atmospheric gases and may accumulate in basements, but may eventually mix with surrounding air. 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.

In buildings with HVAC air handlers that admit outside air for ventilation, plumbing vents placed too closely to air intakes or windows can be a source of sewer gas odors. In some cases airflow around buildings and wind effects may contribute to sewer gas odor problems even with appropriately separated vents and air intakes. Increasing vent heights, adding vent pipe filters, or providing powered dilution and exhaust can help reduce occurrences.

Health effects

Sewer gas often has a “rotten egg” smell due to the hydrogen sulfide content, which can be detected by human olfactory senses in concentrations as low as parts per billion. Exposure to low levels of this 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, pnomia, loss of appetite, headaches, irritability, poor memory, and dizziness. High concentrations of hydrogen sulfide (>150 ppm) can produce olfactory fatigue, whereby the scent becomes undetectable. At very high concentrations (>300 ppm), hydrogen sulfide can cause loss of consciousness and death. See main article, Hydrogen sulfide.

Greenhouse gas contribution

Fully-vented sewer gases contribute to greenhouse gas emissions. Septic vent pipes can be fitted with filters that remove odors and reduce some greenhouse gas emissions.^{[citation needed]}

Sewer gas can be used as a power-source, thus reducing the consumption of fossil fuels.

See also

• Fire protection
• Indoor air quality
• Louisville sewer explosions
• Plumbing
• Potable cold and hot water supply
• Rainwater, surface, and subsurface water drainage
• Septic systems

References