[Wonder Warthog]

"Impact causes heat. That is just plain old ordinary run-of-the-mill physics."

It also causes a shock wave, which triggers detonation. There are explosives that you can actually set fire to and burn without triggering an explosion....it specifically requires a shock wave to be set off.

In this instance, shock wave is the more likely explanation.

[GingisK]

A shock wave causes heat, more so than does setting the material on fire.

Have you ever noticed the illuminated white sphere that expands from a high explosive detonation? That is the shock wave in the air; and, the air is heated white hot like the filament of a light bulb.

It is all about the heat. I have set off dynamite with a flashbulb.

Physics & chemistry are really certain about this.

[GingisK]

Try this: Get a block of hardwood and a large nail. Pound the nail into the wood with a hammer. When the nail sticks about 1/2 inch from the surface of the wood, stop hammering and immediately feel the heal of the nail. (It will burn you.) Impact (shock) converted to heat.