Hydrogen sulfide poisoning. Exposure to low levels of hydrogen sulfide causes irritation of the eyes and respiratory tract. Other symptoms include nervousness, dizziness, nausea, headache, and drowsiness. At extremely high levels, hydrogen sulfide can cause immediate loss of consciousness and death. Carbon monoxide poisoning.
Carbon monoxide is a colorless, odorless gas that can cause suffocation and death at high levels.
Exposure to lower levels can produce flu-like symptoms such as headache, nausea, and drowsiness. Sewer gas is heavier than air and contains very little oxygen. Breathing sewer gas even for short periods can result in suffocation and death. Because sewer gas is heavier than air, it can accumulate in basements and is highest at floor level. This poses a high health risk to small children and pets.