I dont charge in a container of any sort, but I am within sight/sound of the packs while charging. The nice thing about the TP balancer is it provides an audible alarm if any cell hits 4.3V.....if you hear that during charge you unplug the pack. The problems arise when you a) make a mistake during charge setup with cell count, or b) allow an overcharge (read imbalanced pack) situation to remain unchecked and the pack to continue charging.

Again with most stuff on the big electrics, attention to detail is paramount. Personally I have not found lipo charging to be of significant danger, its not like the packs explode instaneously....it takes a bit of time for an overcharge situation to progress to one of fire.

My biggest concern is one where a model crashes, the pack shorts and ignites. Where I live and fly grain fields are plentiful and the climate is very dry, an ignited pack in a farmers field could turn into a wildfire within a matter of minutes. Coming from a farm I have witnessed first hand what a burning crop that gets out of control can turn into on a windy day !!