Chimney fire

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A chimney or chimney fire occurs when soot deposited in the chimney from incomplete combustion (soot fire) or condensed wood tar ignite .

Chimney / fireplace fire

General

Chimney / chimney fire photographed from the basket of a turntable ladder

Occurs from incomplete combustion

  • Smear soot , shiny soot or hard soot in solid fuels or
  • Flake soot in liquid and gaseous fuels.

In the first case, the actual soot (= pure carbon, dusty) is sticky bound in high-boiling condensate , in the other, the carbon is very finely distributed and with plenty of air. Both promote the ignition and the continued burning of soot.

Incomplete combustion takes place,

  • when burning wet wood or other unsuitable fuels (e.g. fats ) and / or
  • when fuels burn in a lack of oxygen.

This danger also exists with boilers that are too large for solid fuels: If no heat is drawn off, the boilers run into the partial load range ; If the air supply is restricted, the combustion is incomplete: carbon monoxide and soot are produced.

The deposition of soot particles in the chimney is favored by a chimney cross-section that is clearly too large or too small:

  • Too small a cross-section slows down the exhaust gases; they take longer on their way to the exit opening; Soot particles contained in the exhaust gas tend to be deposited on the inner walls of the chimney.
  • If the cross section of the chimney is too large, the inner walls of the chimney will remain cool for a relatively long time after the start of the heating process. They cool the rising exhaust gas; Moisture and soot particles contained in the flue gas tend to condense or deposit on the inner walls of the chimney.

The condensation leads to sooting , and joints can be formed in wet masonry due to frost cracking . Such masonry joints allow hot smoke gases to escape, which, together with flying sparks , can ignite the dry wood of a roof structure, cobwebs hanging there or household items stored in the attic .

In order to avoid this condensation , conventional oil and gas heating systems (i.e. heating systems that do not have condensing technology ) send the exhaust gas relatively hot into the chimney. Wood-burning stoves do this too: at their nozzle, the flue gas has temperatures of around 300 ° C at nominal output.

Modern chimneys are thermally insulated: the pipe that comes into contact with the exhaust gas (for example made of ceramic or stainless steel) is enclosed by an insulating layer of mineral wool . Before 1970, ceramic pipes were also built, which were surrounded by granulate stones. These chimneys heat up quickly; Much less condensation on their inner walls than on non-insulated (e.g. brick) chimney inner walls.

hazards

In the event of a fireplace fire, the surrounding walls are heated to such an extent that wallpaper and adjacent furniture (e.g. cupboards) can catch fire. It can take up to 6 hours for the heat to penetrate the masonry of the fireplace.

Unprofessional attempts to extinguish the fire with water can cause considerable damage. Furthermore, there is a risk of smoke gas poisoning if the chimney is no longer vented and the smoke z. B. penetrates through fireplace doors in the living room.

Trigger of the fire

Completely clogged chimney after a soot fire

Several factors or their interaction can cause an unintended chimney fire:

  • Flames can penetrate connecting pieces (stove pipes) or flues of the fireplace and ignite the soot located there
  • Embers are drawn into the connecting piece or chimney by a strong draft in the chimney and ignite the soot there
  • Burning material with long flames (e.g. coniferous wood, especially its branches) or burning material that makes the combustion chamber extremely hot

In order to save the costs of the chimney sweep, homeowners keep lighting their chimneys on purpose. With the controlled burnout, soot residues can be burned cleanly. Since there is a high risk of an unwanted building fire, deliberate lighting is prohibited in many places for laypersons. The homeowner is often obliged to have the fireplace cleaned by a chimney sweep on a regular basis. On the one hand, this measure prevents unintentional chimney fires, on the other hand, it makes lighting superfluous.

Fire fighting

Heavily swollen soot after a chimney fire

The chimney fire is the only fire that is usually not extinguished.

A chimney fire must not be extinguished with water. 1 liter of water would result in approx. 1700 liters of water vapor at a temperature of 100 ° C. If you were to pour or spray water into the chimney, there would be a sudden increase in pressure in the chimney, which could seriously damage it.

Fire fighting options are:

  • Let the chimney burn out under constant observation (“controlled”). The air supply “from below” should be minimized, ie keep the oven door closed. If several stoves are connected to the burning chimney, this applies to all stoves.
  • With flue cleaning tool the burning soot detach from the walls of the chimney draft and these burn out at the bottom of the stack or taken from the chimney and outside of the chimney (for example, in the boiler room deglaze).
  • Since the soot can swell up due to the high combustion temperatures, the chimney must be prevented from clogging with a suitable device.
  • Powder extinguishers can be used very efficiently. A possible negative side effect is the high pollution of the environment.
  • The chimney can be flooded with carbon dioxide.

It is advisable to notify the fire brigade immediately after discovering the chimney fire ; they will then usually also alert the responsible chimney sweep / chimney sweep.

After the fire has been extinguished, the chimney should be observed for several hours, as it still radiates a lot of heat and this heat could, for example, set fire to roof insulation materials or wooden beams of the roof structure adjacent to the chimney . In the case of three-shell chimneys (consisting of ceramic pipe, mineral insulation and casing stone), this risk is much less than with uninsulated brick chimneys.

history

To prevent a chimney fire , for example, orders from Count Palatine Karl IV. From 1772 in connection with domestic fireplaces were used. According to the simultaneous building regulations, no more wooden chimneys were allowed to be erected, no more wooden hoses were allowed to be installed, which had to lead the smoke from the fireplace to the fireplace, just as it was forbidden to lead stovepipes out of the window.

See also

Web links

Commons : Chimney Fire  - Collection of Images, Videos and Audio Files

Individual evidence

  1. Marburg fire brigade: Measures in the event of chimney fires
  2. Chimney fire on bosy-online.de , accessed on August 28, 2013.
  3. ^ Franz-Josef Sehr : The fire extinguishing system in Obertiefenbach from earlier times . In: Yearbook for the Limburg-Weilburg district 1994 . The district committee of the Limburg-Weilburg district, Limburg-Weilburg 1993, p. 151-153 .