On January 19, 2010 local chimney sweep Gene Padgitt found something odd while getting ready to install a woodburning insert in a 1920’s Kansas City, Missouri home. Something that would likely have caused a house fire. The original builder of the home constructed an unlined chimney (a chimney without a clay tile flue liner) and put structural wood members inside the flue.
After Padgitt saw the wood inside the chimney he told the homeowner he had to open up the brick chimney in the attic area to remove the combustibles. There, he found double 2 x 4’s on one side and a header on the other side inside the chimney with brick built underneath and on top of the wood. Some of the wood had already been burned away by previous fires unknown to the homeowner, which probably smoldered but did not ignite due to lack of oxygen.
“We see crazy things like this more often than most people realize,” said Padgitt, who is also a State Certified Fire Investigator. “People don’t think about the inside of their chimney, and unless a professional chimney sweep inspects it, there is no way of knowing what the condition is. In this case, the house had been standing for 90 years without burning down, but the hazard was there and eventually would have been a serious problem.
Wood chemically changes when exposed to heat over a period of time, allowing it to ignite at a much lower temperature than normal without direct flame. The ignition point of wood is normally 500 degrees, but pyrolized wood can ignite at temperatures as low as 180 degrees. Internal flue gas temperatures of fireplaces can reach up to 400 degrees, but if a chimney fire occurs the temperature will be much higher. Some chimney fires in field testing by the Midwest Chimney Safety Council have caused temperature readings of 2,100 – 2,800 degrees. A masonry chimney will continue to heat up after a chimney fire is out, causing a secondary fire hazard. Often, fire departments are called back to a house several hours after leaving due to combustibles igniting after they extinguished the fire.
Note: The MCSC warns that most chimney fires go unnoticed by homeowners and damages by fire are found later by a chimney inspector.
Padgitt says that most of the fire hazards he sees having to do with the structure is wood framing placed right next to the exterior of the chimney chase. Code requires 1” clearance for exterior chimneys, and 2” clearance for interior chimneys, but this is often ignored, even in newer homes. The location where it is the biggest problem is right above the opening of the fireplace in front of the smoke chamber, where the facial wall may hide internal combustible wood framing. Most of the house fires he sees start in this area.
The Midwest Chimney Safety Council recommends that a Level II internal camera inspection be performed annually by a CSIA Certified Chimney Sweep.
For more information about chimney safety visit www.chimkc.com or the Midwest Chimney Safety Council website at www.mcsc-net.org.