In the days of the industrial revolution propane was used as refrigerant. that was till a couple factory's blew up. Then there was a need to make non flammable refrigerant.
That's interesting, I didn't realize they used it like that in the old days. Propane is an approved refrigerant today, known as R209, and you can buy "pure" propane in refrigerant type cans, but it's not cheap. It's not approved for household use (in the US) and there is no way to add the stench to let you know it's leaking, the line filters just remove it. It is used in some industrial/commercial applications in the US and I think is more common for household use overseas.
Even while flammable, it's not that great of a danger in a small system, because it will only hold a few pounds of propane at most. But definitely needs to be in a well ventilated area.