Le Mans Disaster

The 300 SLR struck the mound at such speed and angle that it was launched into a somersault, which caused loosened and damaged parts of the car to be flung away from the car. This included the bonnet and the front axle, both of which separated from the frame and landed in the crowd. With the front of the spaceframe chassis—and thus crucial engine mounts—destroyed, the car's heavy engine block also broke free and hurtled into the crowd. Levegh was also thrown free of the somersaulting car, fatally crushing his skull when he landed.
As the remains of the 300 SLR slowed its somersault, the fuel tank, situated behind Levegh's seat, ruptured. The ensuing fuel fire raised the temperature of the remaining Elektron bodywork past its flashpoint, which due to its high magnesium content was already very low. Magnesium's properties mean that a combustion in oxygen is possible at relatively low temperatures, and the alloy burst into white hot flames, sending searing embers onto the track and into the crowd. Rescue workers attempting to put out the burning wreckage were initially unsuccessful, as they unknowingly used water on the magnesium fire, which only intensified the inferno. As a result, the car burned for several hours. In total, 80 spectators were killed either by flying parts and debris or from the fire.

http://en.wikipedia.org/wiki/1955_Le_Mans_disaster