Until recently I was blissfully unaware of the possibility of something called Thermite Sparking. It is a variety of the classic Thermite reaction, only it can happen inadvertently in the workplace by mechanical friction.
Thermite sparking is a circumstance wherein an aluminum part smartly strikes an oxidized iron component generating a momentary and highly localized spot of very hot metal. Normally, the thermite reaction is limited to the small mass of material in the impact zone and does not progress further.
What is useful to know is that aluminum and iron together constitute a sparking pair of materials and could serve as an ignition source for flammable liquids and vapor in the area. An aluminum cart or component could suffer an impact while in motion and provide an ignition source for a fire.
Lamentations on Chemistry 
Wow… sounds like a Homeland Insecurity Department what-if scenario: “Terrorists are planning to crash American cars into the rusting bridges of our failing infrastructure.”
Note: If they are driving a Delorean then don’t shoot. It’s okay…
Sounds fiendish. By the way, where do you live …
Have you heard of the thermite ball demonstration? If you take two rusty two-inch ball bearing, cover one in aluminum foil, and then smash them together then the friction provided gives enough heat to send thermite sparks in all directions. It’s pretty cool, see this video. http://www.youtube.com/watch?v=s4De8-B1CSk
Hey! Sounds cool. Thanks for the link!