"CNS injury is immediate and significant after exposure to hydrogen sulfide. At high concentrations, only a few breaths can lead to immediate loss of consciousness, coma, respiratory paralysis, seizures, and death. . . . Hydrogen sulfide is a mucous membrane and respiratory tract irritant; pulmonary edema, which may be immediate or delayed, can occur after exposure to high concentrations." [ATSDR Medical Management] Like cyanide, causes cellular asphyxiation; Also a mucous membrane irritant; IDLH = 100 ppm; Pulmonary edema at 300-500 ppm; Rapidly fatal at 600-800 ppm; [Olson, p. 271] H2S is heavier than air; it displaces air in confined spaces. 80 fatalities were recorded by OSHA from 1984-94. Prevent deaths by using H2S detection equipment, air-supplied respirators, and confined space safety training. [Fuller DC, Suruda AJ. J Occup Environ Med. 2000;42:939-942] Possible frostbite from contact with liquid; [NIOSH] The following chemicals can release H2S when spilled in water: Sulfur chlorides; Phosphorus pentasulfide; and Sodium, Potassium, Calcium & Zinc hydrosulfite. [ERG 2016] "Measuring thiosulfate in urine allows health care providers to identify nonfatal H2S exposure, allowing life-saving prevention opportunities. Measuring thiosulfate in blood is the preferred method to confirm death from H2S exposure." [PMID 24164756
] See the Process, "Toxic Gas from Spilling Chemical in Water." Hydrogen sulfide is fibrogenic to the lungs in the context of an acute inhalation exposure complicated by bronchiolitis obliterans.