[JRandomFreeper]

Correct, it was a pile. And they were composting some high nitrogen stuff obviously. Your twirly composter with leaves and kitchen scraps shouldn't ever get hot. Unless you put chicken or horse poop in it.

/johnny

[ApplegateRanch]

Years ago, at a So-Cal apartment complex we lived at, a neighbor worked for Asplundh a commercial tree “trimming” (butchers!) service.
One afternoon, they finished loading the enclosed deuce and a half dump too late to dump it at the landfill, so he drove it home and parked it on the street to take & empty first thing next morning.
It was late spring or early summer, so the the branches going through their chipper had lots of succulent new growth, and was heavily leaved out.
A bit after midnight, the load spontaneously combusted. Heavy damage to the truck, but no other property damage.