Sewer gas forms when solid waste from humans and animals decomposes. The gas contains ammonia, methane and hydrogen sulphide, all of which are toxic when inhaled in high concentrations. People can die through asphyxiation when exposed to very high concentrations of sewer gas. More common effects include eye irritation, nausea and breathing difficulty.
Who Is at Risk
Sanitation workers and farmers who work in and around animal waste storage facilities and ponds have the highest risks for encountering harmful concentrations of sewer gas. Others may get exposed to sewer gas if the drains on their toilets dry out or if vents installed on buildings to dissipate the gas become clogged or get installed incorrectly.
Home or office exposures to toxic levels of sewer gas occur rarely, but you should have persistent noxious smells from bathrooms investigated by trained plumbing professionals.
When sewer gas concentrations in regular air reach 0.0005 parts per million, they can be detected as a smell of rotten eggs or burning chemicals. At 0.01 ppm of sewer gas, the gas will cause nausea and eye discomfort.
Also at 0.01 ppm of sewer gas, people can start showing signs of physical and mental illness. Headaches, and increased heart rate and a loss of muscle coordination (ataxia) can set in. When concentrations reach 20 ppm, people can display memory loss, lose their appetite and become irritable.
Bacteria, viruses and fungi also travel through the air from raw sewage. These pathogens tend to die quickly in the atmosphere but could still infect people who inhale sewer gas.
The nitrogen in ammonia and methane, as well as the hydrogen in hydrogen sulphide, can rapidly replace oxygen in the lungs and blood streams of those exposed to sewer gas. Asthma symptoms like bronchial spasms begin occurring at gas concentrations of 5 ppm. Respiratory distress and loss of consciousness sets in at 500 ppm. Concentrations greater than 700 ppm can be fatal.
Hydrogen Sulfide Exposure
People who survive after inhaling large amounts of sewer gas can experience long-term health problems due to hydrogen sulphide poisoning. Exposure to concentrations of ydrogen sulphide of 500 ppm or greater have been associated with chronic headaches, short attention spans, memory problems and decreased motor function.