Almost everyone has experienced the sharp, pungent odor of ammonia. It's the active ingredient in common glass cleaning solutions, bath and sickroom cleaners, and in more concentrated form, a stimulating sniff of ammonia can revive the victim of a fainting spell. Ammonia is a naturally occurring colorless gas with the chemical formula NH3 that is used to manufacture fertilizers, explosives, and plastics. It is plentiful and cheap, and a truly useful compound. For nearly two centuries it also has been used as a refrigerant.
Ammonia's one drawback is that in quantities much larger than a "sniff" it is poisonous. It dissolves in water, including the water in our lungs, to form a strong base (alkali), ammonium hydroxide. It is also corrosive. Wherever ammonia is used in bulk, including for refrigeration, careful precautions must be taken to educate and safeguard people in the area.