You basically have what sounds like a lower-explosive-limit vapour explosion
with multiple traces of 'medium petroleum distillates' (could be anything).

Had a similar case this week, timber restaurant went up
- total loss (just as few timber support poles remaining).
Eye-witness accounts say the fire started at the chips fryer,
but I can't guesstimate a fire origin based on remaining physical evidence.

Here, I'm taking the short cut, saying I have half a dozen solid witnesses
(with no particular vested interest) corroborating each other.