[Johnny555]

Proponents of propane as refrigerant claim that it's not more dangerous than the 10 gallons of gasoline in the gas tank. I'm not sure I agree. Since propane is heavier than air, it doesn't dissipate as quickly as, say, natural gas would.

And while its true that you need the right mixture of propane and air for it to ignite, with the right-mixture, you've got a fuel-air explosive formed right next to an ignition source (the car's engine and battery).

[bigiain]

Like propane, gasoline fumes are also heavier than air. This becomes a problem in boats, where propane and/or gasoline fumes "collect" down in the hull with no natural ventilation path. Boats with propane stoves or gasoline motors need gas detectors and ventilation to ensure dangerous (suffocating or exploding) levels don't build up below decks...

[Spooky23]

Safe until it leaks.