The maine news was full of a incident where an individual hauling old propane tanks got in a lot of trouble. The state police and practically every other agency in Maine went ballistic and is citing the driver for every regulation they can think of. Its not much of a detailed link. http://bangordailynews.com/2012/04/03/news/portland/westbrook-man-sets-off-terror-scare-after-hauling-propane-tanks-behind-van/?ref=polbeat His claim is the tanks were empty and one of his friends who was interviewed on another channel said that they had been welding on the tanks. While a state official claims they were full of propane and were bombs waiting to go off. The state claims one of the tanks was stolen but I expect it will end up that there was a break in the chain of ownership going to a scrap yard. Nevertheless its something to keep in mind when buying a used propane tank for storage.