There was a scuba-diving salvage fella killed in the late 1950s by a badly-handled flintlock/ black powder musketoon from the circa-1680 period. The muzzle, it seems, was found to have been blocked with a lead ball [big surprise there!] so since the proper *worm* for removal was unavailable, instead a torch was applied in attempt to melt the obstruction for removal. Shortly thereafter: BOOM!
It apparently never occurred to anyone that the watch on duty carried loaded weapons and that when the ship went down such niceties as unloading or discharging their hardware was not of a high priority to the surviving crew.
I doubt it's a *record* and am also aware of a Crimean War museum piece projectile [circa 1855] exploding during a storage facility fire, thankfully without resulting in human injury. But I'd bet that there have been occasions in which recovered explosive cannon shot were brought home to the family domicile and later exploded during residence fires have claimed more than a few unlucky or stupid folks, particularly in the days when homes were heated and cooking was done via open flames.
Imagine their suprise!