Anhydrous Ammonia

Last updated: November 25, 2018

What Does Anhydrous Ammonia Mean?

Anhydrous ammonia is a chemical compound with the formula NH3. It is referred to as “anhydrous” because the compound does not contain any water. Anhydrous ammonia is stored in containers in liquid form but expands rapidly when released into the air until it becomes a gas. It has a number of occupational uses, including laboratory uses, use as a refrigerant, and widespread use as an agricultural fertilizer.

It is a colorless but pungent gas that is toxic to humans, and it can be immediately dangerous to life or health (IDLH) in incidents resulting in high exposure to the chemical.

Safeopedia Explains Anhydrous Ammonia

Anhydrous ammonia poses a number of hazards to human health and safety. Governmental occupational health and safety authorities in the U.S. and other major countries impose a number of legal requirements for its safe handling, storage, and transport. The National Institute of Occupational Health and Safety (NIOSH) rates it as being immediately dangerous to life or health at 300 ppm, and it provides a recommended exposure limit of 25 ppm (18 mg/m3) as an eight-hour time-weighted average (TWA), as well as a short-term exposure limit of 35 ppm (27 mg/m3). The legally enforceable permissible exposure limit (PEL) set by OSHA is a TWA of 50 ppm (35 mg/m3).

Non-fatal exposure to anhydrous ammonia can still cause severe injury. Symptoms of exposure include eye, nose, and throat irritation, breathing difficulties, burns, blisters, and frostbite. Because anhydrous ammonia readily absorbs water, significant human exposure can result in the exposed person becoming rapidly dehydrated. Due to these hazards, workers exposed to significant concentrations of anhydrous ammonia must use personal protective equipment (PPE) including skin protection, eye protection, and respiratory protection. OSHA standard 1911.111 (general industry) provides specific legal requirements that must be followed within U.S. workplaces.

Anhydrous ammonia is also flammable when present in high concentrations and confined spaces, creating specific hazards related to its transport and storage. The U.S. Department of Transportation provides specific requirements for transporting anhydrous ammonia. These rules are compliant with the United Nations’ consensus guidelines for the transportation of anhydrous ammonia (UN1005), which are laid out under the UN Recommendations on the Transport of Dangerous Goods. Storage of anhydrous ammonia is also subject to various labeling requirements, including OSHA’s Hazard Communication Standard and the United Nations’ Globally Harmonized System of Classification and Labelling of Chemicals.


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