A while ago (back when Google worked) I stumbled upon a refrigerant hacking page that detailed DIY retrofitting of refrigeration equipment to use propane as the refrigerant instead. Obviously the flammability is a problem, but as standard refrigerants seem to be pressing towards the flammable-with-harmful-combustion-products direction, I wonder why the industry isn't reconsidering. It seems nicer to have a plain fireball rather than one which creates hydrofluoric acid.