The following advice is given by almost every US fire department. Though in the UK, the "danger" does not get a mention anywhere. It would be nice to know as I always have around 10kgs in a locker and spontaneous combustion there would be a bummer. Anybody else heard of this phenomenon? Or is it the American equivalent of the British "never draw 6 amps without completely unwinding your 25m cable or the whole campsite will ignite."