My brother lived in Napa during the fires in that area. He said he was watching the fires in the distance and they appeared to be about 20 miles away when all of a sudden a spark ignited the corner of his roof and made immediately made its way across the roof to the other side.
This was a Spanish tile roof. You know the kind made with tiles baked at extremely high temperatures. You get a big insurance discount because these roofs are fireproof.
They got in the car and hightailed out of there!