Fireplaces and wood stoves are designed to safely contain wood fuel fires.The chimneys that serve them have the job of expelling the products of combustion-the substances produced when wood burns. These include smoke, water vapor,gases, unburned wood particles, hydrocarbon,tar fog and assorted minerals. As these substances exit the fireplace or wood stove and travel up into the relatively cooler chimney condensation occurs. The resulting residue that sticks to the inner walls of chimney is called creosote. Creosote is black or brown in appearance, it can be crusty and flaky, tar-like ,sticky, shiny and hardened. What ever form it takes, creosote is highly combustible. If it builds up in sufficient quantities and the internal flue temperature is high enough a chimney fire could result.
While some chimney fires sound like a freight train or produce a loud rumbling noise, some burn very slowly in the flue system and may be undetected by the homeowner while they are watching a football game on TV. Although these fires are less violent initially they are no less dangerous than the loud, rumbling chimney fire. Remember , it is very easy for the fire to move from being contained in the flue system to catching the roof, surrounding drywall,etc on fire so at the first sign of a chimney fire evacuate the family and the call the fire department.
Clean chimneys don’t catch fire. Make sure to have your chimney for your fireplace and wood stove swept and inspected by a Certified Chimney Sweep on a yearly basis or more frequently if you are a heavy burner-have it cleaned after every cord of wood. Your chimney professional can evaluate your flue system using video equipment to check for signs of a chimney fire,which include heavy creosote glazing, vertical or longitudinal cracks in the flue tiles or if the liner is stainless steel–the warping and buckling at the seams.
Proper maintenance is important in the prevention of chimney fires.