Anhydrous ammonia is used extensively throughout the United States for a variety of purposes. We find ammonia in agriculture, in the manufacture of synthetic fibers, plastics and explosives, in refrigeration plants, and in the manufacture of ammonium compound containing fertilizers. We also find ammonia in common household cleaners, metallurgical processes, and in power plants for emissions controls. Approximately eighty percent of manufactured ammonia is used for agricultural purposes, either as a direct application of anhydrous ammonia (about 33% of the total), application of an ammonium solution (e.g. ammonium hydroxide or aqua ammonia), or as a dry fertilizer product.
Ammonia is a naturally occurring colorless gas that is an inhalation hazard and has an extremely pungent odor; the odor threshold for ammonia vapor is between five and fifty parts per million (ppm). It is estimated that some 140 million metric tons are produced annually by commercial means, and that this total is approximately equal to the amount produced naturally.i The preponderance of naturally occurring ammonia is derived from decomposing animal excreta with the decay of organic materials (plants, dead animals, etc.) providing the balance.
Manufacture within the United States has been declining over the past three to four years, while production internationally has been increasing. The two primary reasons for the U. S. decline appear to be the cost of natural gas and labor expense. Commercial use of anhydrous ammonia is normally in the liquid form, and the physical characteristics and properties have inherent dangers to users. Liquid ammonia is colorless and is normally stored under pressure at about 130 to 160 psi in quantities of up to 50,000 gallons. The boiling point is -28 °F (-33 °C), and the freezing point is -108 °F (-78 °C); as a solid ammonia is white. Ammonia is extremely corrosive either as a liquid or vapor, and has a pH of about 12.ii Ammonia terminal facilities also store their product in atmospheric tanks of up to 25,000-ton capacity; in this case the product is stored at less than one pound of pressure (in our facility the norm is 0.3 psi in the tank vapor space).
Catastrophic releases are different for pressurized and atmospheric storage. A pressurized container that fails will provide a large visible, vapor cloud affecting the downwind zone with the size of the zone being dependent on the quantity of released product, prevailing wind conditions, amount of moisture in the air, temperature, and topography. The reason we can see this vapor cloud released under pressure is the affinity that ammonia has for water; the cold ammonia will freeze the water moisture in the air and we see a white cloud. During some uncontrolled releases these visible vapor clouds have been known to travel downwind for several miles and thus have a huge impact on the downwind zone.
