Every battery can blow when too hot, overcharged or damaged. Lithium batteries release gases, and that's why they shouldn't be in a closed containers.
If they blow, and they are in let's say metal body flash light - you have a pipe bomb, and it will hurt.
High quality lithium batteries will be relatively safe to use, but many of us are using batteries or light sets from China. EBay deals are so sweet that are too hard to pass.
I always charge mine on fire proof surface, never leave the house when they are charging, and I never overcharge them. Both overcharging and discharging to less than 5-10% is not a good idea.
When on my bike - I keep my battery pack under my seat, away from my face.
There is a ton of online resources about these batteries. Overall, they are considered pretty dangerous, but when tested its not always the case.