There were those 'flubbed' propane-tank-based (I presume the small size used in outdoor grills) car bombs a couple months back (what actually burned were several containers of gasoline) - cnn.com had a CNN video of some experts they had called in to make such a bomb and explode it (they of course did not give the details of how to make the propane tank explode, which did NOT happen in the car-bomb attempts, and is apparently not as easy to do as the terrorists thought). It was impressive.
I haven't seen or heard of a tank itself explode at a residence, but I heard of a trailer fire where the firefighters were watering down the propane tank (which sits about a foot away from the trailer in that particular trailer park). I recall that these tanks were 100 gallon capacity and 'sat' vertically about five feet tall. Another trailer had gas leaking, perhaps a stove burner was left on without being lit, and it (the trailer) exploded big time (no one was in it at the time). I lived in the park, had gone to the grocery store when it happened and didn't hear it but noticed a fire truck down the street when I got back. There was fiberglass insulation everywhere. Someone a few trailers away said it was really loud and scary. I took pics the next day and have them around somewhere. This may be more dramatic than a tank exploding since the gas gets well-mixed with air before exploding.
