Years ago I had a 10 gallon propane tank's relief valve pop off while driving down the road, with it in the front seat of my little Toyota pickup as I had the bed totally full already. The seat seemed like a good place for it, being empty and with a belt to secure it, but it was winter, and it had been overfilled a bit in the cold, and the heat in the truck....you can guess the rest, obvious now! Luckily I'm not a smoker, and the release was only a second, but it scared the heck out of me and almost made me wreck, my helper was driving behind me and asked "what was that all about" when we got to the jobsite.