I guess that switch is the same as used on a race car, just a battery shut off. Jegs or Summit has them. The threat of a fire starting in a collision is a real possibility. I think its rare, but it can still happen. I have seen a lot of torn up vehicles in 26 years in the collision business, yet I havent seen any in the shop that caught fire. I guess the ones that catch fire usuall burn to the ground and never see a body shop. BMW has a nice idea. A lot of times their battery is located in the trunk. Their main positive line running to the front has a big fusible link in it. If I understand correctly, this link blows with a certain amount of force, possibly blows along with the triggering of an airbag. We replace this harness all the time. Some models are a pain cause the harness is one piece all the way up front, some models its a very short harness that need replacing. I know germans tend to over-engineer a lot but this seems to be a good idea.