I have heard of people using propane in refrigerators and such but they aren't subject to high speed collisions. I wonder if there is any real risk of explosion using it in a car. There are a few companies now selling 60/40 propane/isobutane blends as R12/R134a alternatives so I figure it has to be relatively safe. They claim that the concentrations are low enough that it isn't dangerous. I was thinking about putting straight propane in my sister's 1989 honda accord because it's cheap and I already have a tank at home. Plus moisture in the system wouldn't be as big a deal because propane doesn't create an acid when it comes in contact with moisture like R12 does. I've heard that straight propane may cause problems though because it could get too cold and freeze the evaporator. That is supposedly why the blends contain isobutane. If that is the case then I guess I'll just pay a little more and get the blend. Just wondering if anyone here has experience with this stuff. I may try straight propane first just to see if the AC system even works at all.