I wouldn't want to be near if there is an accident! Any gas seems like it would work if the parameters are close. It's a simple system. Compress the gas...it heats up...run through a condenser to cool it off, then vent the gas back to normal atmospheric pressure....heat is absorbed and chilled air is made. you can do the same thing with an air compressor.
After 31 years in the fire service, I have seen a lot. A couple of years ago, a neighboring fire department charged a vehicle a/c system with propane and created a leak. They then provided an ignition source and videoed the results. The hood of the car flew about 100 feet after the explosion, which totalled the car. Nuff said.
I dabble in industrial fire fighting. (I spend most of my work time trying to prevent a fire from breaking out in the first place) Propane burns exceptionally well and to use it in a manner such as refrigerant is crazy. Believe me , at my girth I love cool as much as anybody . Just aint willing to burn smooth up over it.
As long as it's clean and dry all sorts of gasses can be used in refrigeration systems. Nothing new about using propane or natural gas for refrigeration. It's been done for years. These days it's much, much cheaper than freon.
Propane has been used as an alternate fuel for years now. Cars have large propane tanks mounted in the trunk. It’s not any more dangerous than 18 gallons of gasolene.