A chimney flue fire nearly became a catastrophe for a local homeowner, and a fire chief says creosote is the likely culprit.
The Gravois Fire Protection District responded to a 911 call to a flue fire at 3:02 p.m. on Saturday, Dec. 17 at 310 Dunwurkin Road in Gravois Mills. The GFPD responded with four units and four personnel.
Upon arrival, firefighters found that the home owner had the flue fire under control. According to Gravois Fire Protection District Deputy Chief Ron Anselmo, flue fires like that one can start due to a buildup of creosote inside of the flue.
“Creosote is caused by using green wood and newspaper, restricted air supply and cooler than normal surface temperatures in the flue (such as with a metal chimney),” Anselmo explained. Newspaper can also cause a fire by flying up into the flue and igniting the creosote.
Anselmo advises homeowners to keep their chimney clean and use wood that is seasoned for six months to one year. Professional services can be hired for this task.
At the Gravois Mills home, fire crews checked for an extension of the fire to the structure by using a thermal imaging camera on the flue and surrounding walls. The camera picks up extra heat and reveals fire behind the wall by reporting the temperatures inside the wall. “This way we don’t have to tear the walls apart to find out if there is fire in the wall,” Anselmo said. No additional fire was found. Firefighters also checked for cracks in the fireplace.
According to Anselmo, the homeowner took the fire out of the fire box and knocked flu fire down into the fireplace. He then used a chain to clear build up in the flue. There was no damage or injuries as a result of this fire.
Anselmo advises, “If you are experiencing a flue fire, call 911 and close all dampers so it doesn’t get air. A fire won’t burn unless it has oxygen.”
According to masterchimneysweep.com, what most people think of as "smoke" is better termed "flue gas." This "smoke" or flue gas is released by the initial fire: the "primary combustion." Flue gas consists of steam, and vaporized but unburned carbon based by-products (vaporized creosote). As the flue gas exits the fireplace or wood stove, it drafts upward into the relatively cool flue where condensation occurs. Like hot breath on a cold mirror, the cool surface temperature of the flue causes the carbon particles in the warm vapor to solidify. The actual cause of creosote condensation is the surface temperature of the flue in which the flue gas comes in contact. This resulting carbon based condensation which materializes inside the flue is creosote. It's usually black in appearance. It can be the fine black dust called soot, (1st stage creosote); or porous and crunchy, (2nd stage); or it can be tar-like: drippy and sticky, until it hardens into a shiny glaze, (3rd stage). All forms of creosote can occur in one chimney system. Whatever form it takes, creosote is highly combustible. If it builds up in sufficient quantities - and ignites inside the chimney flue: the result is a volcanic chimney fire.
