Or maybe two stray pieces of flint inside the backpack touched off the blaze when they were thrown together to cause a spark.
Authorities quickly determined there were no explosives in the bag, which contained no items that are banned on flights.
Phoenix police Lt. Rick Gehlbach said the backpack likely began to smoke after it got jammed between two larger pieces of luggage on a conveyor belt.
The impact probably caused toiletries containing alcohol to leak, and a combination of heat from the conveyor belt and its track rubbing against the backpack caused it to catch fire, Gehlbach said.
(East Valley Tribune)
I'm not saying I don't believe it, but that's a strange explanation.