Back in the day, we stumbled upon dozens of abandoned dead 1lb propane cylinders and we used them for target practice--(glass bottles were no-no). Guess how many exploded? Zero.
We all assumed some were not 100% purged..so being young fools that we were, we shot at a few full tanks and guess what happened. Think bottle rockets; the tank propelled away rather fast then sputtered to a stop.
Exploding propane tanks is a Hollywood invention.
The risk of danger is probably greater traveling with the TT propane tanks turned on (which I regularly do, gotta keep our Tillamook Ice Creams frozen...pics of our favs).