Anhydrous ammonia is a chemical compound consisting of one nitrogen atom and three hydrogen atoms, represented by the formula NH3. The term “anhydrous” literally means “without water,” distinguishing it from common household ammonia, which is an aqueous solution. Anhydrous ammonia is a foundational industrial chemical produced globally in massive quantities, primarily through the Haber-Bosch process. Its powerful chemical properties make it extremely useful in agriculture and manufacturing, but they also classify it as a toxic and corrosive substance requiring strict safety protocols.
Fundamental Chemical and Physical Properties
Anhydrous ammonia is a colorless gas at standard atmospheric temperature and pressure, possessing a distinct, intensely pungent odor. This smell provides an early warning system, as the odor threshold is very low. It is a lightweight gas, with a vapor density lower than that of air, though a large release can form a visible white cloud.
For transport and storage, the gas is compressed into a liquid under high pressure or cooled to its boiling point of approximately -28°F (-33°C). This compressed liquid state is necessary because one volume of liquid ammonia expands to about 850 times its volume when it rapidly vaporizes back into a gas. The defining chemical characteristic is its extreme affinity for water, meaning it is highly hygroscopic. When anhydrous ammonia contacts any moisture, it immediately reacts to form ammonium hydroxide, which is a caustic, alkaline solution.
Primary Uses in Industry and Agriculture
The most significant application of anhydrous ammonia is in agriculture, where it is a primary source of nitrogen for crop fertilization. The chemical composition of NH3 is approximately 82.5% nitrogen by weight, making it an extremely concentrated and efficient fertilizer. Farmers inject the liquid directly into the soil where it converts to a usable form for plants, supporting the growth of major crops like corn and wheat.
More than 70% of all industrially produced ammonia is used either in this direct application or as a precursor for other nitrogen-based fertilizers like urea and ammonium nitrate. Its thermodynamic characteristics, including efficient heat absorption, make it an excellent refrigerant for large-scale cooling systems. It is widely used in industrial freezers, cold storage warehouses, and ice-making plants.
Anhydrous ammonia is also a foundational building block in chemical manufacturing. It is synthesized into a vast array of products, including pharmaceuticals, plastics, explosives, and various synthetic fibers.
Health Hazards and Physiological Effects
Any exposed body tissue containing moisture, such as the eyes, mucous membranes, skin, and lungs, becomes the target for corrosive reaction. Contact with moisture in the body instantly forms the highly alkaline chemical ammonium hydroxide, causing severe chemical burns. Exposure to the gas, even at concentrations as low as 300 parts per million, is considered immediately dangerous to life and health.
Inhalation can lead to extensive damage throughout the respiratory tract, including the nasal passages, larynx, and trachea. This irritation can rapidly progress to severe respiratory injuries such as pulmonary edema (fluid accumulation in the lungs) and airway obstruction. Contact with the eyes is particularly hazardous, resulting in permanent vision loss or blindness as the alkaline solution rapidly penetrates the eye tissue.
Because liquid anhydrous ammonia is stored at a temperature of about -28°F, contact with the liquid causes severe frostbite or freezing burns alongside the chemical injury. If clothing is contaminated with the liquid, it may freeze to the skin. Attempting to remove frozen clothing without thawing can tear off tissue.
Safe Storage and Emergency Procedures
The storage of anhydrous ammonia requires specialized, heavy-duty equipment capable of withstanding the high pressures necessary to keep the substance in a liquid state. Storage tanks must be constructed from steel, as ammonia is corrosive to metals like copper, brass, and zinc. Tanks are typically painted white or silver to reflect heat, which helps prevent excessive pressure buildup inside the container. Safety devices, such as pressure relief valves, must be installed on all storage tanks to prevent rupturing in case of temperature increases.
Immediate action following exposure is focused on dilution and flushing the affected area with copious amounts of water. Water is often called the first responder’s primary tool because it dilutes the corrosive ammonium hydroxide. Anyone handling the substance must have a readily accessible, large supply of clean water, with a minimum of a five-gallon container required on nurse tanks and applicators.
In the event of an accidental release, personal protective equipment is required for anyone operating near the substance. This equipment includes chemical-resistant gloves, full-face splash-proof goggles, and long-sleeved clothing. For respiratory protection, a self-contained breathing apparatus is required for entry into highly concentrated ammonia atmospheres. Following any exposure, the victim must be flushed with water for at least 15 minutes, and immediate transport to a medical facility is necessary.