Ammonia compressor systems are among the oldest industrial refrigeration systems. They are still more efficient than modern refrigerants, but they are potentially dangerous becuase ammonia is toxic, and though not rated flammable, is explosive. (?)
United Fruit, a US flag shipping company before WWII used ammonia systems in thier ships to keep bananas cool on the way north from central america, many old ice houses still use it today. It was also commonly used in ice scating rinks.
Propane is used in eastern europe, where brains win out over lobbyists. a home refridgerator has about as much propane as a Bic lighter? Where are the horror stories of death and destruction from R290 propane reefers?
R290 is pure propane, a hydrocarbon and efficient naturally occurring refrigerant with similar properties to R22
No ozone depletion potential, ODP = 0 Extremely low global warming potential GWP = 3
Environmentally safe but highly flammable. Used only after careful consideration to safety.