My understanding from the fire dept., who inspect my store every year tell me to remove the propane so if there was a fire, the tanks will not be there to explode and kill fire firemen.
Interestingly enough, my old neighbor who was a firefighter told me
something else. I had my tanks chained to a heavy 4x4 post, they
told me that the biggest danger was the end of the tank igniting and
it acting like a torpedo. He said they seldom explode but can shoot
themselves through any number of things like cars, brick walls and
fire trucks.
Karen