Debbie Rowe and the woman whose home she burned down learned a hard lesson about spontaneous combustion.

Michael Jackson's ex was in Vermont, recovering from breast cancer treatment at a friend's cottage. The cottage was awesome ... built in 1937. Debbie and the owner were refinishing crown molding with linseed oil.

Debbie decided to take a break last Thursday and left a rag soaked in the oil in the living room. She took a long break, went to the main house and started knitting. Unbeknownst to her ... the cottage erupted in flames. She didn't hear a thing because of the wind.

Turns out the fumes from linseed oil are highly flammable ... the process of the oil turning into fumes creates heat, and the combo of that on rags is a fire waiting to happen.

Debbie's friend is supremely understanding ... grateful that Deb wasn't hurt.

Extreme Flammable Home Makeover ... anyone?