Adding my 2¢. One would suspect that the hybrid car engineers would use the same type of impact sensing relays, currently used to operate electric fuel pumps, to operate the contactors (really big relays) for the electric drive system. DIY electric car building guides strongly using using them (in pairs) so that in the event of an impact, the high current system is disabled. (Just don't use ones from late '80's Fords - they'd cut off when you closed the trunk lid!)

Oh and a fun thing for all you first responders out there, there is an outfit "upgrading" hybrid battery systems from NICad to Lithium Ion. There is a reason the car makers aren't using Li batteries yet, large Li batteries pose a significant exolpsion risk. They are working on ways to better contain the cells to make them safer because Li batteries offer significantly better performance in compairison to NiCAD's..

If it's not one thing it's another...

JimJr