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Compilations of the concentrations of hydrogen sulfide that produce serious systemic toxic effects and death in humans and laboratory animals indicate that species differences in toxicity are not significant ( ATSDR 2006). Laboratory studies generally indicate that toxic effects observed in animals exposed to hydrogen sulfide at high concentrations are identical with those observed in humans who exhibit acute toxicity of the gas. Exposure at much higher concentrations (about 500 ppm) may result in coma, which is often rapidly reversed when the victim is evacuated, or persistent headaches, equilibrium loss, and memory loss. Symptoms become more severe with longer exposure and sometimes lead to pulmonary edema. In humans, inhalation of hydrogen sulfide at as low as 100-250 ppm for only a few minutes can result in incoordination, memory and motor dysfunction, and anosmia (so-called olfactory paralysis). However, people recovering from hydrogen sulfide exposure can have cough and a variety of effects on the sense of smell, including diminished function (hyposmia), altered sensation (dysosmia), and false odor recognition (phantosmia), for a few days to weeks. Those changes generally resolve on evacuation to fresh air. People acutely exposed to hydrogen sulfide at about 100 ppm commonly experience lacrimation, photophobia, corneal opacity, tachypnea, dyspnea, tracheobronchitis, nausea, vomiting, diarrhea, and cardiac arrhythmias ( ATSDR 2006). Adverse effects on the human eye after exposure at 20 ppm or less are often associated with concomitant exposure to other chemicals or irritants that would reduce the threshold of corneal irritation (ACGIH 2005). There is agreement in the literature that effects on the eye predominate at concentrations above 50 ppm (Beauchamp et al. Eye irritation is the most common complaint associated with single or repeated hydrogen sulfide exposure. Hydrogen sulfide is a contact irritant, causing inflammatory and irritant effects on the moist membranes of the eyes and respiratory tract respiratory tract inflammation can result with exposure at about 50 ppm. People exposed at low concentrations of hydrogen sulfide and other sulfur gases often report head aches, nausea, and other symptoms (Glass 1990 Shusterman 1992). The toxic effects of hydrogen sulfide are characteristically dose-related and most notably involve the nervous, cardiovascular, and respiratory systems ( ATSDR 2006). Most people readily perceive hydrogen sulfide because the olfactory detection limit for it is so low (for example, 0.3 ppb or greater as reported by Hoshika et al. Occupational exposure to hydrogen sulfide occurs in the agricultural, gas, oil-refining, and other industries, and workers often notice the characteristic rotten-egg odor associated with exposure. Hydrogen sulfide emissions are thought to arise from the sanitary system (Hagar 2008). Whether the reported concentrations are representative of the submarine fleet is not known few details were provided about the conditions on the submarines when the samples were taken. Data collected on three nuclear-powered attack submarines indicate a range of 2-22 ppb (Hagar 2008). Hydrogen sulfide has been measured in the submarine atmosphere. The ambient air concentration resulting from natural sources is estimated as 0.11-0.33 ppb ( ATSDR 2006). Hydrogen sulfide is a byproduct of many industrial processes and is used to make inorganic sulfides that are used to make such products as dyes, pesticides, polymers, and pharmaceuticals (Weil et al. It arises from bacterial reduction of sulfates and decomposition of proteins. Hydrogen sulfide is a component of the natural sulfur cycle and is produced endogenously in mammals (Weil et al.