Anything in the house could spark it.
Some of these houses, it's just ripped them apart. It's amazing we haven't had more people hurt than we had.
The door is probably what saved her. It would have protected her from the debris. She crawled up out of the rubble. A paramedic found her wandering around in a daze.
It was clear this person intended to bring the entire building down and a great deal of accelerant was used.