Sewer gas
Encyclopedia
Sewer gas is a complex mixture of toxic and non-toxic gases produced and collected in sewage systems
by the decomposition of organic household or industrial wastes, typical components of Sewage
.
Sewer gases may 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.
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 fixture
s 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 furnace
s and water heaters. Infrequently used utility sinks, tubs, showers, and restrooms also are common culprits. Trap primer
s 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 sewer
s, manure
storage tanks, or septic tank
s.
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.
, among others, worked to prove that polluted water was the culprit, not the foul smells from sewage pipes. Subsequently, even as the Germ theory of disease
developed, society was slow to accept the idea that odors from sewers were relatively harmless when it came to the spread of disease.
, oxygen
, carbon dioxide
, etc.). Often, methane
is the gas of next highest concentration, but typically remains at non-toxic levels, especially in properly vented systems. However, if sewer gas has a distinct “rotten egg” smell, especially in sewage mains, septic tanks, or other sewage treatment facilities, it may be due to 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 lung
s. Prolonged low-level exposure may cause fatigue, pneumonia, 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.
emissions. Septic vent pipes can be fitted with filters that remove some odors.
Sewer gas can be used as a power-source, thus reducing the consumption of fossil fuels. The gas is piped into a cleaning system and then used as a fuel to power a generator or Combined Heat and Power (CHP) plant.
Sanitary sewer
A sanitary sewer is a separate underground carriage system specifically for transporting sewage from houses and commercial buildings to treatment or disposal. Sanitary sewers serving industrial areas also carry industrial wastewater...
by the decomposition of organic household or industrial wastes, typical components of Sewage
Sewage
Sewage is water-carried waste, in solution or suspension, that is intended to be removed from a community. Also known as wastewater, it is more than 99% water and is characterized by volume or rate of flow, physical condition, chemical constituents and the bacteriological organisms that it contains...
.
Sewer gases may include hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
, ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
, methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
, carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
, sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
and nitrogen oxides. Improper disposal of petroleum products such as gasoline
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...
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.
Sewage gas in homes
Sewer gas is typically restricted from entering buildings through plumbingPlumbing
Plumbing is the system of pipes and drains installed in a building for the distribution of potable drinking water and the removal of waterborne wastes, and the skilled trade of working with pipes, tubing and plumbing fixtures in such systems. A plumber is someone who installs or repairs piping...
traps
Trap (plumbing)
In plumbing, a trap is a U-, S-, or J-shaped pipe located below or within a plumbing fixture. An S-shaped trap is also known as the S-bend invented by Alexander Cummings in 1775 but became known as the U-bend following the introduction of the U-shaped trap by Thomas Crapper in 1880. The new U-bend...
that create a water seal at potential points of entry. In addition, plumbing vents
Plumbing drainage venting
In modern plumbing, a drain-waste-vent is part of a system that removes sewage and greywater from a building and regulates air pressure in the waste-system pipes, facilitating flow. Waste is produced at fixtures such as toilets, sinks and showers, and exits the fixtures through a trap, a dipped...
allow sewer gases to be exhausted outdoors. Infrequently used plumbing fixture
Plumbing fixture
A plumbing fixture is an exchangeable device which can be connected to an existing plumbing system to deliver and drain away water but which is also configured to enable a particular use.-Common fixtures:The most common plumbing fixtures are:*Bathtubs...
s may allow sewer gas to enter a home due to evaporation
Evaporation
Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....
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 furnace
Furnace
A furnace is a device used for heating. The name derives from Latin fornax, oven.In American English and Canadian English, the term furnace on its own is generally used to describe household heating systems based on a central furnace , and sometimes as a synonym for kiln, a device used in the...
s and water heaters. Infrequently used utility sinks, tubs, showers, and restrooms also are common culprits. Trap primer
Trap primer
A trap primer is a plumbing device or valve that adds water to traps. The water seals in traps are needed to prevent sewer gases from entering buildings, but because this water is exposed to the air, it is subject to evaporation over time in infrequently used floor drains, leading to the release...
s 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 sewer
Sanitary sewer
A sanitary sewer is a separate underground carriage system specifically for transporting sewage from houses and commercial buildings to treatment or disposal. Sanitary sewers serving industrial areas also carry industrial wastewater...
s, manure
Manure
Manure is organic matter used as organic fertilizer in agriculture. Manures contribute to the fertility of the soil by adding organic matter and nutrients, such as nitrogen, that are trapped by bacteria in the soil...
storage tanks, or septic tank
Septic tank
A septic tank is a key component of the septic system, a small-scale sewage treatment system common in areas with no connection to main sewage pipes provided by local governments or private corporations...
s.
In buildings with HVAC
HVAC
HVAC refers to technology of indoor or automotive environmental comfort. HVAC system design is a major subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer...
air handlers that admit outside air for ventilation
Ventilation (architecture)
Ventilating is the process of "changing" or replacing air in any space to provide high indoor air quality...
, 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.
History
During the mid 1800s, when indoor plumbing was being developed, it was believed by many that disease was spread by miasmas, or literally "bad air." Originally, traps in plumbing drain pipes were designed to help keep this bad air from passing back into living spaces within buildings. However, during the Broad Street cholera outbreak in London, in the Summer of 1854, physician John SnowJohn Snow (physician)
John Snow was an English physician and a leader in the adoption of anaesthesia and medical hygiene. He is considered to be one of the fathers of epidemiology, because of his work in tracing the source of a cholera outbreak in Soho, England, in 1854.-Early life and education:Snow was born 15 March...
, among others, worked to prove that polluted water was the culprit, not the foul smells from sewage pipes. Subsequently, even as the Germ theory of disease
Germ theory of disease
The germ theory of disease, also called the pathogenic theory of medicine, is a theory that proposes that microorganisms are the cause of many diseases...
developed, society was slow to accept the idea that odors from sewers were relatively harmless when it came to the spread of disease.
Health effects
In most homes, sewer gas may have a slightly unpleasant odor, but does not often pose a significant health hazard. Residential sewer pipes primarily contain the gases found in air (nitrogenNitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
, carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
, etc.). Often, methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
is the gas of next highest concentration, but typically remains at non-toxic levels, especially in properly vented systems. However, if sewer gas has a distinct “rotten egg” smell, especially in sewage mains, septic tanks, or other sewage treatment facilities, it may be due to hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
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
Hypoxia (medical)
Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...
, and fluid accumulation in the lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
s. Prolonged low-level exposure may cause fatigue, pneumonia, loss of appetite, headaches, irritability, poor memory, and dizziness. High concentrations of hydrogen sulfide (>150 ppm) can produce olfactory fatigue
Olfactory fatigue
Olfactory fatigue or adaptation is the temporary, normal inability to distinguish a particular odor after a prolonged exposure to that airborne compound. For example, when entering a restaurant initially the odor of food is often perceived as being very strong, but after time the awareness of the...
, whereby the scent becomes undetectable. At very high concentrations (>300 ppm), hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
can cause loss of consciousness and death.
Greenhouse gas contribution
Fully vented sewer gases contribute to greenhouse gasGreenhouse gas
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
emissions. Septic vent pipes can be fitted with filters that remove some odors.
Sewer gas can be used as a power-source, thus reducing the consumption of fossil fuels. The gas is piped into a cleaning system and then used as a fuel to power a generator or Combined Heat and Power (CHP) plant.
See also
- Fire protectionFire protectionFire protection is the study and practice of mitigating the unwanted effects of fires. It involves the study of the behaviour, compartmentalisation, suppression and investigation of fire and its related emergencies, as well as the research and development, production, testing and application of...
- Indoor air qualityIndoor air qualityIndoor air quality is a term referring to the air quality within and around buildings and structures, especially as it relates to the health and comfort of building occupants....
- Louisville sewer explosionsLouisville sewer explosionsThe Louisville sewer explosions were a series of explosions that destroyed more than two miles of streets in Louisville, Kentucky, United States on February 13, 1981. The blasts were caused by the ignition of hexane vapors which had been illegally discharged from a Ralston-Purina soybean...
- PlumbingPlumbingPlumbing is the system of pipes and drains installed in a building for the distribution of potable drinking water and the removal of waterborne wastes, and the skilled trade of working with pipes, tubing and plumbing fixtures in such systems. A plumber is someone who installs or repairs piping...
- Potable cold and hot water supply
- Rainwater, surface, and subsurface water drainageDrainageDrainage is the natural or artificial removal of surface and sub-surface water from an area. Many agricultural soils need drainage to improve production or to manage water supplies.-Early history:...
- Septic systems
- Sewer gas destructor lampSewer gas destructor lampThe main purpose of a sewer gas destructor lamp is to remove sewer gases and their hazards.- Background :Biogas forming in sewers via anaerobic digestion can be a potentially foul-smelling and explosive hazard . Unlike ordinary gas lamps for street lighting, the main purpose of sewer gas...