A chimney fire is the burning of soot and chimney build-up called creosote on the inner surfaces of the chimney. Chimney fires start when the heat inside the chimney flue ignites the excess soot and creosote. Soot is highly combustible, so the fire quickly migrates up the chimney flue.
Chimney fires are explosive and produce loud cracking and popping noises. The sound is often compared to the rumbling of a freight train. These fires are dangerous because debris coming from the top of the chimney can ignite other parts of the house. Chimney fires also break down the interior structure of the chimney, displacing mortar and tiles. This exposes the flammable wooden frame of the house to the flames and compromises the entire structure.
Dirty chimneys cause chimney fires, so regular chimney cleaning is mandatory for prevention. The type of fuel a chimney uses determines how often it is swept. Chimneys using smokeless fuel should be swept once per year. Oil, gas and smokeless coal chimneys follow the same once a year rule. Bituminous coal chimneys require twice-yearly cleaning, and wood chimneys need to be cleaned four times per year.
If a chimney fire occurs, the structure of the chimney needs to be repaired. Certified chimney sweeps are qualified to inspect fireplaces and look for signs of damage. Signs that a chimney fire has occurred include warped metal inside the chimney, cracked flue tiles, discolored rain cap and creosote pieces on the roof.