Meth lab? If the propane tanks were intact, what was the vapor cloud that blew up? If there was a leaking propane tank, the "Heating Mechanism" if it was on, would have consumed the vapor as it accumulated instead of waiting for the cloud density to get to a point of explosion. They may have turned the propane on for a couple minutes while they had trouble getting the lighter or matches to light and in that time the propane filled the house, but WOW would that take more than the usual amount of propane to fill a house enough to blow it up. I could easily believe something was going on where they had a cloud of something accumulate, then got cold and lit the heaters. BOOM!!! Either way, getting burned SUCKS!!!