THEY DO NOT EXPLODE PERIOD
Sorry but you're just wrong. Pretty much every playthrough I
go into the ruins via the chapel entrance (kill off the 4 guys outside and pick the lock). Once inside I kill the guy immediately inside the door then sneak to the other door. I go into turn-based mode, open it and use minor illusion to get the 5 enemies as close to the oil barrel as possible and pass through the rest of the turns. As soon as they've moved, I have someone firebolt the oil barrel which promptly explodes killing at least 4 if not all 5 of the looters.
This is very repeatable and demonstrates that oil barrels do, in fact, explode.
Actually, the nautiloid tanks dealing force damage is an illustration that Larian do not actually understand what force damage is or represents. Mundane objects - not even highly explosive fuel, let alone goblin hand bombs - should never deal force damage under any circumstance. That's not what force damage is. Force damage is, specifically, raw magical energy; that is why it's so rare, and why so little has any kind of resistance or immunity to it.
Except the stuff in the tanks is otherworldly so who knows, maybe it would deal force damage. Not really seeing the issue here. I do agree that mundane explosions definitely would not deal force damage though.
