How dare you use common sense, reason, and rational thought. Possible causes after the workers leave for the day include spontaneous combustion from improperly stored cleaning rags or fluids; gas leak (i.e., welding gas); un-extinguished cigarette; spark that simmers in combustible materials; faulty wiring, etc.
“How dare you use common sense, reason, and rational thought.”
I know, but someone’s gotta do it