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SUMINSERTA 160309-20
Chimney Fires
The result of excessive creosote buildup is a chimney fire.
Chimney fires are dangerous. Chimney inside temperatures
can exceed 2000 degrees F. This causes much higher than
normal temperatures in the chimney and on its exterior sur-
faces thus ignition of nearby or touching combustible material
is more likely during a chimney fire. Proper clearances are
critical during such a fire.
Chimney fires are easy to detect; they usually involve one
or more of the following:
- Flames and sparks shooting out of the top of the
chimney
- A roaring sound
- Vibration of the chimney
In Case of a Chimney Fire
1. Prepare to evacuate to ensure everyone’s safety. Have
a well understood plan of action for evacuation. Have
a place outside where everyone is to meet.
2. Close air inlets on stove.
3. Call local fire department. Have a fire extinguisher handy.
Contact your local fire authority for further information on
how to handle a chimney fire. It is most important that
you have a clearly understood plan on how to handle a
chimney fire.
4. After the chimney fire is out, the chimney must be cleaned
and checked for stress and cracking before starting
another fire. Also check combustibles around chimney
and the roof.
- The services of a competent or certified installer, (certified
by the Wood Energy Technical Training program (WETT) -
in Canada, Hearth Education Foundation (HEARTH) - in
U.S.A.,) are strongly recommended.
Avoiding a Chimney Fire
There are two ways to avoid chimney fires:
1. Do not let creosote build up to a point where a big chim-
ney fire is possible.
2. Do not have fires in the heater that may ignite chimney
fires. These are hot fires, such as when burning house-
hold trash, cardboard, Christmas tree limbs, or even
ordinary fuel wood; (eg. with a full load on a hot bed of
coals and with the air inlet wide open).
Creosote
Formation and Need for Removal
When wood is burned slowly, it produces tar and other
organic vapours, which combine with expelled moisture
to form creosote. The creosote vapours condense in the
relatively cool chimney flue of a slow burning fire. As a
result, creosote residue accumulates on the flue lining.
When ignited, this creosote makes an extremely hot fire.
The chimney connector and chimney should be inspected
at least once every two months during the heating season
to determine if a creosote buildup has occurred. If creosote
has accumulated, it should be removed to reduce the risk
of a chimney fire.
1. Highest smoke densities occur when a large amount of
wood is added to a bed of hot coals and the air inlet is
closed. The heated wood generates smoke, but without
ample air, the smoke cannot burn. Smoke-free, clean
burning requires small fuel loads, two or three logs at a
time or 1/4 to 1/2 of a fuel load and leaving the air inlet
relatively wide open, especially during the first 10 to 30
minutes after each loading, when most of the smoke
generating reactions are occurring. After 30 minutes or
so, the air inlet can be turned down substantially without
excessive smoke generation. Wood coals create very
little creosote-producing smoke.
2. The cooler the surface over which wood smoke is pass-
ing, the more creosote will be condensed. Wet or green
wood contributes significantly to creosote formation as the
excess moisture that is boiled off cools the fire, making
it difficult for the tars and gasses to ignite, thus creating
dense smoke and poor combustion. This moisture-laden
smoke cools the chimney, compounding the problem by
offering the smoke the ideal place to condense.
In summary, a certain amount of creosote is inevitable and
must be lived with. Regular inspection and cleaning is the
solution. The use of dry, seasoned wood and ample com-
bustion air will help to minimize the buildup.