It's not the physical damage that causes fires in a battery, it is the electrochemistry in the electrodes.
Consider that in a typical chemistry you have lithium ions plus a metal oxide. Ever heard of a thermite reaction? That's what you get if the electro-potentials go wrong.
Lithium iron phoshate batteries are much safer because the oxygen is locked up in the phosphate radical, and can't enter a thermite reaction. Use Manganese oxide (or most other transition metal oxides) in the mix, and the lithium will try to steal the oxygen off the manganese, at the 'right' [wrong] electro-potentials. Titanates are much more stable, but both titanates and phosphate based lithium batteries have significantly lower specific capacity.
For all we know that might have been what happened in the infamous post-crash-test Volt. Perhaps it was physically damaged, but did not experience that sort of reaction until the cell voltage dropped to the 'dangerous' level.