Hydrogen sulfide is the chemical compound with the formula H 2 S. It is a color- less gas with the characteristic foul odor of rotten eggs; it is heavier than air, very poisonous, corrosive, flammable, and explosive. (Wikipedia) Concentration in parts per million (ppm)* Observations and health effects Less than 1 Most people smell “rotten eggs.” 3 to 5 Odour is strong. 20 to 150 Nose and throat feel dry and irritated. Eyes sting, itch, or water; and “gas eye” symptoms may occur. Prolonged exposure may cause coughing, hoarseness, shortness of breath, and runny nose. 150 to 200 Sense of smell is blocked. 200 to 250 Major irritation of the nose, throat, and lungs occurs, along with headache, nausea, vomiting, and dizziness. Prolonged exposure can cause fluid build-up in the lungs (pulmonary edema), which can be fatal. 300 to 500 S...