I had a protected ICR battery explode in a mechanical mod two years ago. The mod was too hot to touch. The battery caps blew off the tube, the plastic wrap melted from the heat, and the pants pocket that the mod was in (not wearing the pants this happened in) was burnt from the flames vented.
I've also had an IMR battery vent in a pocket when it came in contact with coins or keys in the pocket
*. Extreme heat was quickly felt and I barely had time to finagle it out of my pocket to keep from getting burnt. Venting was not nearly as dramatic as the ICR battery, with only hot gas being released. The venting gas is hot enough to cause first or second degree burns requiring immediate medical attention.
Recommendation: If you feel your mod or fire switch become hot, if you have time to open the battery cap and release the battery to the ground, do so. Walk away from the battery a safe distance of several feet away.
If the mod becomes too hot to touch, then drop the mod and again move away a safe distance of several feet away. The battery will quickly do its business within a few minutes.
Video of an ICR battery venting and then exploding; explosion occurs at the 3:30 mark.
* Carry spare batteries in a plastic battery case. These are only about $1 each and can be purchased from most B&M shops and online e-cig vendor websites.