I've got to second what debian said.

I have never heard of a lipo going up under normal use. You've got about as good a chance of setting off a lithium pack if it's properly taken care of, as you do of setting off a jug of fuel sitting in your garage.

While I don't have any real statistics to back it up, i'd say 99% of all lithium fires are user error.

Wrong settings, poor judgement on pack condition, pack abuse, or any combination therein.

That said, it certainly doesn't hurt to be cautious. I charge in a metal tin. It's enough to contain the flames should something happen. I've been using and selling lithium packs for quite a long time, and never personally experienced, or had someone mention to me something about a lithium based fire.