RIP. Very sad. On the barest of initial information, it does not seem to be the "normal" HEMS accident. Given the circumstances, I think it would be unwise to discount oxygen. If you do get enrichment it changes the whole game with fire. Things you would not think of turn into great fuels and innocuous ignition sources leap to start the thing up.
Forensic investigation should give us a clue, the fire spread is likely to be different if O2 is involved.