of ammonia. The odor threshold for ammonia is reported at 5–50 ppm (parts per million); the perception threshold for irritation is reported at 30–50 ppm (Wands 1981; WHO 1986). Intense irritation to the eyes, nose, and throat can occur at 100 ppm, but at that concentration, there is no evidence of a decrease in pulmonary or central nervous system (CNS) function, nor is there evidence of injury or lasting effects (Ferguson et al. 1977). Adaptation to the odor and to the effects of ammonia at low concentrations (<100 ppm) has been demonstrated in occupational exposure studies of workers who were able to carry out job-related functions during extended periods of exposure (Vigliani and Zurlo 1955; Ferguson et al. 1977).
Ammonia is a colorless gas with a distinctive, penetrating, pungent odor that is often described as “drying urine.” Exposure to ammonia vapor can cause symptoms that range from mild eye and throat irritation at low concentrations to severe respiratory injury and death at high concentrations. Ammonia is highly soluble in water, forming ammonium hydroxide through an exothermic reaction (Budavari et al. 1996). Exothermic reaction of ammonia with water can cause thermal and chemical burns because of the alkalinity of ammonium hydroxide. Contact with refrigerated liquid ammonia can cause cryogenic skin injury (Hathaway et al. 1991). In addition to being a potent respiratory irritant, ammonia is a potent ocular irritant, and it can rapidly penetrate the corneal epithelium. Severe ocular exposures can lead to corneal ulceration, corneal perforations, and persistent corneal opacity (NRC 1979).
Heating ammonia to decomposition produces ammonia vapor, hydrogen gas, nitrogen gas, and oxides of nitrogen (OSHA 1992; Sax and Lewis 1987). Under some conditions, mixtures of ammonia and air will explode when ignited, and fires and explosions can occur upon mixing of ammonia with other chemicals, such as chlorine, hypochlorites, and chlorine bleach (OSHA 1992). The National Fire Protection Association has assigned the flammability rating of 1 (slight fire hazard) to ammonia (New Jersey Department of Health 1998). The chemical and physical properties of ammonia are shown in Table 2–1.
Ammonia is found in the environment as the result of natural and industrial processes. It is released into the environment by the breakdown of organic wastes, and it is a constituent of the soil, the atmosphere, and bodies of water. Ammonia is also a key intermediate in the nitrogen cycle and is a product of amino acid metabolism (WHO 1986). Anhydrous ammonia is used in the production of nitric acid, explosives, synthetic fibers, and fertilizers (Budavari 1989). It is used as a refrigerant; as a corrosion inhibitor; in the purification of water supplies; in steel production; as a catalyst for polymers; as a preservative for latex; and in the production of nitrocellulose, urea formaldehyde, sulfite cooking liquors, and nitroparaffins (ACGIH 1991; Lewis 1993). Ammonium hydroxide (10–35% ammonia) is a major constituent of many cleaning solutions. Ammonia