Even though I'm about 95% Lipos myself I always find it funny the NIMH batteries get pretty hot while charging while my lipos stay nice and cool Even at 1C some of those NIMHs can pretty darn hot, hence my warning on charging inside the tank. I charge approximately 20-30 batteries a day on our chargers (3 of us here at work also RC after work so there is always something to charge) and while I always put Lipos in a fire bag I also treat the NIMHs the same way. If you guys haven't seen the Bat-Safe it is a great product for any type of battery really, it will mostly contain a fire and even filter it too, it isn't a catch-all but is definitely a step up in charging. My buddy also used refractory cement inside of an ammo can to separate and isolate batteries while charging too but it doesn't have all the neat features of the Bat-Safe.