The dangers of breathing sewer gas are hydrogen sulfide poisoning and asphyxiation, according to the Wisconsin Department of Health Services. Inhaling very high levels of hydrogen sulfide can lead to immediate loss of consciousness and death.
Sewer gas consists of varying levels of toxic and non-toxic gases depending on the source, says the Wisconsin DHS. It results from the decomposition of household and industrial waste, and it smells like rotten eggs. Hydrogen sulfide and ammonia are highly toxic components of this gas. Exposure to small levels of hydrogen sulfide irritates the eyes and respiratory tract. It also causes headache, dizziness, drowsiness, nausea and nervousness. Exposure to high concentrations of hydrogen sulfide sometimes causes people to experience a loss of sense of smell. Sewer gas is fatal at extremely high levels. It contains methane, which decreases the amount of oxygen in the air and leads to suffocation. When oxygen deficiency occurs, a person is likely to experience headache, dizziness, nausea and unconsciousness. Death can occur immediately when a person is exposed to very low oxygen concentrations.
The Wisconsin DHS states that floor and sink drains must be flushed with water to prevent pipe traps to the sewer from drying. The roof plumbing vent should also be checked regularly for blockage from debris, such as bird nests or leaves.