He mighta just been cutting the straps holding the tank in place.

Even purged tanks explode.
Normally what happens is a cuts made to the edge of the tank (or drum) & what fuel that is still stuck in crevices boils & fumes,
filling the tank with fumes
& then it explodes.



I had a empty 55 gallon drum that used to be filled with a solvent & was cutting the lid off with a hammer & cold chisel with my earmuffs & glasses on.

At some point around the lid there was a light 'wump' & the lid lifted a bit & I kept cutting till I'd finished.

Then I noticed the small room I was in was a little warmer, so I felt inside the drum & smelt a burnt smell & the drum was warm.....