I think the point Tim is getting at is it's IN the cabin unlike any road car I know which has them under the car.
Mine is in the car then incased in a housing, wether I'd class it as a firewall or not is another matter but the tank itself is about 12 inches into the car so it would be a fair whack to crush that area.
Either way it's a good point raised, safety has to be the number one priority when building such a highly specced car.