Ammonia

Ammonia is a compound with the formula NH3. It is normally encountered as a gas with a characteristic pungent odor. Although ammonia contributes significantly to the nutritional needs of Earth, the gas itself is caustic and can cause serious health damage. The United States Occupational Safety and Health Administration (OSHA) has set a 15-minute exposure limit for gaseous ammonia of 35 ppm by volume in the environmental air and an 8-hour exposure limit of 25 ppm by volume. Exposure to very high concentrations of gaseous ammonia can result in lung damage and death. Although ammonia is regulated in the United States as a non-flammable gas, it still meets the definition of a material that is toxic by inhalation and requires a hazardous safety permit when transported in quantities greater than 13,248 L (3,500 gallons).

Ammonia used commercially is usually named anhydrous ammonia. This term emphasizes the absence of water. Because NH3 boils at -33 °C, the liquid must be stored under pressure or at low temperature. Its heat of vaporization is, however, sufficiently high that NH3 can be readily handled in ordinary beakers in a fume hood. "Household ammonia" or "ammonium hydroxide" is a solution of NH3 in water. The strength of such solutions is measured in units of baume (density), with 26 degrees baume (about 30 weight percent ammonia at 15.5 °C) being the typical high concentration commercial product. Household ammonia ranges in concentration from 5 to 10 weight percent ammonia. See Baumé scale.