In my honest opinion I think fire can and always be able to pass through a grated door in real life and in game (
it just makes sense) unless it has an invisible force field or something.
I understand about not killing anyone before the match starts but a simple solution is not to get close to the door unless you want to get burned.
I personally don't mind getting killed if I am taunting the enemy from inside the door.
But like I said it is just my opinion and it does not represent a suggestion or a complain.