Was your friend charging a battery pack?

I have never heard of a fire starting from charging a battery pack when using the proper charger, I guess it's possible, but probably no more of a danger than any appliance in your house that is plugged in. I have had NiMh battery packs get warm during fast charge but not hot. I think you would be ok on overnight trickle charger. You might think twice before leaving one on fast charge for a long period of time.

I never store glow fuel near a possible source of ignition and I do store it in a vented area in case fumes escape.
Hope this helps.

WCB