There are pictures floating around the web of a Porsche that had an underhood fire after the radiator fan sliced a refrigerant line. The system was charged with a propane mix. So it
is possible for bad things to happen. Can't say what the real-world risk of injury is.
I seriously considered it for my Cabriolet, which has an R12 system. I think for me the risks with a system that's in good shape might be acceptable, but I decided I would have to be crazy to put propane in a system that I already knew must be leaking.
