hey mine also did this...did you figure out why this happens?

Bumping because mine also did this. Pretty pissed because we used our basement as a storage room

If you turn on cheats and fly above the basements, they are run by generators. I assume the mod doesn't take into account their degradation and they eventually explode.

If you want to prevent this, I found that deleting/removing the generators prevents any fires.

Additionally installing a battery bank with solar panels from a solar power mod provides safer power to a basement.

The battery you use "spawns" a generator with the same statistics, so if you're using a battery that has 20% or less condition, yeah your basement can catch fire.

Batteries degrade over time too, so just like with a normal generator you need to keep an eye on the condition and "fuel"