I think alot of it has to do with the tiles and mortar being cracked therefore the fire spreads along the roof. Creosote fires can spill out of the chimney and flash into the house.
thats scary as fuck
reason i ask is cause i was drinking vodka with some tapout bros, and i spit it into the fire. old fire place, and we noticed that the vodka explosion ignited a fire above the damper. we waited and it went out but wtf?
thnx for all the info by the way!!!