Corry, Bob. Understanding and Investigating Chimney Fires. Fire and
Arson Investigator. March, 1992. pp. 22-24.
Abstract: This article discusses the formation and nature of creosote
and how the substance starts chimney fires. It also describes the building
codes concerning the installation of factory-built and masonry chimneys.
Creosote is an organic compound comprised of different pyrolytic decomposition
compounds that change states as they cool while traveling up a chimney.
The amount of creosote that condenses and accumulates on chimney walls is
increased with low temperature fires because creosote will not reach its
gas state and exit the chimney. Most fires in fireplaces and wood-burning
stoves are ventilation-controlled to conserve fuel and control the heat
production. This produces low temperature fires, which contributes to creosote
The article describes the conditions creosote requires to ignite. Most
tests conclude that temperatures of 1,000 degrees F lasting for three to
four minutes will ignite a fire in the flue. A chimney fire usually begins
in the lower half of the chimney and burns upwards. The oxygen supply for
the fire is usually the damper or the clean out door. The fire gradually
burns towards the top as it gains more oxygen. A chimney fire will usually
last 15 minutes, lasting longer if the chimney is larger.
To check a chimney for creosote levels, examine the chimney walls with
a mirror and a flashlight. If the walls appear black and dull, the chimney
is lined with soot and safe. If the walls are black and shiny, the walls
are covered with creosote and should be cleaned professionally. The article
describes the building codes concerning the installation of factory-built
and masonry chimneys.
For more information, contact:
International Association of Arson Investigators (IAAI)
300 Broadway Suite 100
St. Louis, MO 63102-2808