Sometimes referred to as a "sewer gas", hydrogen sulfide has a strong offensive odour and is both colourless and flammable. At low concentrations, it can irritate the eyes and act as a depressant; at high concentrations it can cause irritation of the upper respiratory tract and, during long exposure, pulmonary edema.

A 30 minute exposure to 500ppm results in headache, dizziness, excitement, staggering gait and diarrhea, followed sometimes by bronchitis or bronchopneumonia.

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