how do lipos go up in smoke/ flames?

Had one over on the E-savage forum recently where someone was charging some intellect NIMH cells in the bed of a pickup truck and they went off like a bomb, one cell punched through the side of the pickup and buried itself in the wall. Then again the 4200 cells are notorious for blowing due to inferior gas venting whilst charging.

Lipos are surrounded by a huge amount of safety and warnings, and generally people who buy them tend to be in the higher echelons of RC and so usually aren't too stupid, though accidents will always happen and no one is immune. It's when they start fitting them in RTR toys that it gets dodgy.

usually when lipos let go they just swell like a little balloon, or if you run them down too far, refuse to charge.