Catastrophic Engine Failure By 'Diesel Runaway' Looks Like This

If you've never heard of it, diesel runaway usually occurs due to worn pistons. As the pistons no longer fit snugly in the bores, gases from the crankcase intake blow past them, bringing an oil mist with it. The engine will run on this mist, and a feedback loop is created, with more and more mist being forced through the pistons via the crankcase intake.

Scarily, turning the ignition off will make no difference, as the engine is essentially feeding itself fuel in the form of the mist. The revs will increase until the engine explodes, unless you shoot a CO2 fire extinguisher into the air intake, or plug it with something.