Thankfully the "boom" failure mode is the most common these days. Back in the late 90s, when I worked full time for a company called "Battery Works" (no longer in business) we did everything from tiny 3 gram silver oxide watch
batteries up to multi-ton forklift and floor scrubber
batteries. Those were the days when lithium batteries had 2 modes of failure. I called them "firecracker and road flare" Road flare was more common. Basically it was just elemental lithium reacting with atmospheric water in a very bright and hot manner. Firecracker is what this thread is about. But always remember: It could be worse!
Personally whenever I get around to building/modifying things, I'm actually going to stick to Ni-CAD and Ni-MH cells. They can put out nearly inifnite current when needed, and love to be drained fully. Also cheaper. I could probably vape for a month on a stack of 3 8500mAh SAFT D-Cells. 3.6v@8500mAh
And don't get me wrong. Li-Ion and Li-Poly are great systems. I just prefer that they are designed and implemented in a controlled system by a team of paid engineers who know exactly how they're going to be used and charged.