What it is:
Anhydrous (which means 'without water') ammonia is a liquid inorganic nitrogen compound, compressed under high pressure from pure ammonia gas (NH3)
Colourless, but pungent-smelling gas that will typically sting and irritate before posing a health risk
Commonly used as a nitrogen fertilizer, it is often referred to simply as ammonia or liquid ammonia
Preferred as an agricultural fertilizer because, when it's injected into the subsoil, it quickly returns to its gaseous state and dissolves in soil moisture
The highest-concentration nitrogen fertilizer, anhydrous ammonia is considered the most cost-effective and therefore used in the manufacture of a wide range of fertilizer products
Also used in the manufacture of other chemicals, synthetic fibres, refrigerants and cleaning solutions
Combining anhydrous ammonia with nitric acid triggers a reaction that results in ammonium nitrate (AN). In turn, AN can easily be mixed with hydrocarbons such as fuel oil to create ANFO, a powerful explosive typically used in the mining and construction industries
Because the components are so cheap and widely available in large quantities, it has been used in the manufacture of 'fertilizer bombs' including that used in Timothy McVeigh's 1995 Oklahoma City attack
Dangers:
Direct exposure to the liquid anhydrous ammonia can cause frostbite
At high enough concentrations, it can react with moisture in the skin, eyes and respiratory systems to cause tissue burns, blindness or potentially-fatal pulmonary edema (liquid in the lungs)
On its own, it is considered a low risk of explosion as the gas will only ignite between 16% and 25% vapour concentrations in air
That's enough to rate as a 'Slight' flammability risk on the U.S.-based National Fire Protection Rating (NFPA) fire rating scale
Flammability risk increases, however, in the presence of oil or other combustible materials
Precautions in Canada:
Handling, storage, transportation and application are all regulated under various provincial and federal codes including the Canadian Environmental Protection Act (CEPA) and the Canadian WHMIS Classification
A dangerous good under the Transportation of Dangerous Goods Regulations (TDG), it is now classified as a Class 2.3, Toxic Gas, subsidiary Class 8, Corrosive.
As a result, anhydrous ammonia tanks must display a placard bearing the UN1005 product identification number that alerts handlers, and first responders in the event of an emergency, to the presence of a toxic gas with corrosive properties.
In addition, the Canadian Fertilizer Institute Fertilizer Safety and Security Council's (FSSC) has developed an Ammonia Code of Practice that is mandatory for the transportation, storage and handling and agricultural end-use of the substance.
