Trainer’s Corner: December 2011
By Ed Brouwer
Chimney fires should never be considered routine. A chimney fire can burn with such explosive intensity that it can be – and often is – detected by neighbours or passersby.
By Ed Brouwer
Chimney fires should never be considered routine. A chimney fire can burn with such explosive intensity that it can be – and often is – detected by neighbours or passersby. Flames may shoot several feet from the top of the chimney. People in the house report being startled by a low, rumbling sound that reminds them of a freight train. Do not respond thinking, “It is only a chimney fire.” Think structure fire and respond accordingly.
Traditionally, chimneys were solid structures that were constructed of heavy stone, block or brick. The chimney either was an integral part of the overall building structure, or was connected to the structure by a series of ties between the chimney and the outside wall of the structure. The flue was constructed of firebrick, clay, slate or tile. Few chimneys are built this way today because they are extremely expensive and there is a shortage of experienced, capable masons.
|The minimum response to a chimney fire should be one engine company, one ladder company and an EMS unit. Smaller departments may have all the necessary equipment on the engine.|
Most modern chimneys are prefabricated from steel tubing or pipe. This double- or triple-walled pipe is extended from the heating device through an insulated thimble in the wall and up the exterior of the structure. The chimney is fastened to the exterior wall by a series of metal brackets. The inner wall of the pipe serves as the actual flue. All chimneys should be equipped with a spark-arrester screen and a cap on the top.
A common cause of chimney fires is the ignition of residue within the flue. This residue is formed when fires are routinely burned at less than free-burning levels. This may be due to an insufficient oxygen flow to the firebox, or when large logs are added to a small fire. Incomplete combustion produces low heat levels and large amounts of fire gases. As these gases travel up the flue, they begin to cool and behave much the same way petroleum does as it is separated at a refinery. When the gases reach their condensation temperature, the liquid clings to the inside surface of the flue. This substance is called creosote. Creosote is black or brown and has a crusty or flaky consistency. It can be tarry, drippy, sticky or shiny. When it is hardened it is highly combustible. If the buildup of the volume of creosote is sufficient, a chimney fire is possible.
Hot, free-burning fires that have plenty of oxygen create very little smoke or residue. These fires develop high levels of heat, ensuring that any residue created makes it out of the top of the chimney. As long as fires are allowed to free-burn, few problems are encountered.
Another cause of chimney fires is the ignition of combustible materials near the chimney or heating device. Proper clearance and insulation between the heating device and other construction materials are crucial in the prevention of a fire that may start between the walls. These fires can burn undetected for a long time and are extremely difficult to fight. Firefighters may be required to completely tear out the walls or ceilings and perform extensive salvage and overhaul to put out the smallest fire.
Creosote buildup is most commonly found at three locations in the chimney: sharp bends in the flue, long horizontal runs in the flue, or the top one-quarter of the flue.
Indicators of a working chimney fire include the following:
- A roaring sound that grows louder as the fire intensifies, reaching temperatures higher than 1,000 C.
- Sparks or flames exiting the top of the chimney.
- A whistling or buzzing sound coming from the chimney.
- A back flow of smoke through the heating device into the structure.
- Discoloration on the walls adjacent to the chimney.
- Smoke emanating from the cracks in the wall or from electrical outlets near the chimney.
|As long as fires are allowed to free-burn, few problems are encountered. |
The minimum response to a chimney fire should be at least one engine company, one ladder company and an EMS unit. The engine company is required for fire extinguishment. The ladder company is required to supply tarps, ventilation fans, overhaul tools and ladders. Smaller volunteer departments may have all of this equipment on the engine. However, due to the fact that there will be firefighters working on the roof, often in freezing or otherwise inclement weather, the potential for injuries at a chimney fire may be greater than first thought.
NFPA 1500 standard on fire department occupational safety and health program requires an EMS unit on fire responses.
Suppression tactics: The following should be considered when establishing an SOG for chimney fires:
- Ensure safety by evacuating the structure. Remember that all fires are unpredictable, so full PPE and SCBA should be worn.
- Perform a size-up of the building to ensure the exact location and size of the seat of the fire is confirmed. Fire will not always be visible from the flue on arrival. Only cancel other responding apparatuses when you have made a good evaluation of the chimney and surrounding areas.
- Check the carbon monoxide readings in the house with a CO detector.
- Check that the fire has not extended into the attic.
Once the fire has been located, and if it is contained within the flue system, move on to chimney fire specific extinguishment methods:
1. Spread a runner or salvage cover en route to the stove or fireplace. Not only does the cover catch any ashes or embers that may fall when and if the wood is removed from the firebox, but it also keeps bunker boots from tracking dirt onto the carpet. Plastic tarps fail quickly when they are exposed to heated embers, so you may want to consider fire-resistant cloth tarps.
2. Stop the flow of oxygen to the flue. Hopefully the occupant will have closed the damper before your arrival. However, if this is not the case, the first fire personnel on the scene should immediately shut off the oxygen supply. Reducing the oxygen flow decreases the intensity of the fire in the flue and, in some cases, will extinguish it completely. This step may not be possible on open fireplaces.
3. Extinguish the fire in the firebox. Before you just put the fire out, consider using the fire in the box to extinguish the fire in the flue. Water may be applied in small quantities (usually one cup of water) from a small bucket, a garden sprinkling can or an air-pressurized water extinguisher. In most cases the steam created from this small amount of water travels up the flue and extinguishes the fire. Multipurpose dry chemical agents will put the fire in the firebox out, but will not usually extinguish anything further up. Only remove fuel from the firebox if it has been extinguished and if absolutely necessary.
4. Establish horizontal ventilation. Some of the extinguishment activities, particularly the removal of wood from the firebox, may create a slight smoke condition in the dwelling. Establishing ventilation before other firefighting activities take place will minimize this. Positive-pressure ventilation is the method of choice in these situations. The ventilation entry point should be at a location remote from the stove or fireplace. The ventilation exit point should be as close to the heating device as possible, thereby minimizing the spread of smoke within the structure.
5. Ladder the roof. With a sufficient number of personnel on the scene, this step should be underway while steps 1 to 4 are being completed. If an aerial device is used, it should be extended to the chimney opening. If ground ladders are being used, a wall or an extension ladder should be placed at a good roof entry point and a roof ladder should be extended to the roofline adjacent to the chimney. If the roof is covered with combustible material, a charged hoseline should be advanced onto the roof as soon as the ladders are in place. All firefighters on the roof should be wearing full PPE, including SCBA – no exceptions. Chimney fires rarely occur when the weather is good so watch your footing in snow or freezing rain conditions. Do not place the ladder near or secure the ladder to the chimney.
6. With all other tasks accomplished, the chimney fire may then be extinguished, assuming it has not already been extinguished during the process. There is some opposition to using water, based on the fear that the water will rapidly cool the flue and cause it to fracture. These fractures may then go undetected, and subsequent use of the chimney may result in heat and products of combustion being released into the walls or attic, which may create a more serious fire situation at a later time. The key is in the amount of water used and how it is applied. There are special nozzles (six litres per minute) designed to apply water inside the chimney.
Some departments place dry chemical extinguisher powder in small Ziploc baggies and drop them down the flue (the weight of the powder causes the bag to drop down to the dampener). The heat melts the plastic bag, releasing the dry chemical agent. The powder is light and will usually be lifted up the flue by the hot air rising from the fire.
Caution must be taken here because not every chimney is safely accessible.
7. Perhaps the most overlooked step is checking the clean-out box. Clean-out boxes are found both inside and outside the house. They are usually covered by an eight-inch by eight-inch metal plate with two handle tabs on it, mounted on the wall in line with the chimney. You should be aware that there may be more than one – I once found three clean-out boxes at one fire. After locating the box, use a small shovel and a metal pail to clean out the burning embers. Once this is done, you can place a small, handled mirror into the box to look up into the flue. You should be able to see if there is still a fire in the flue. Communicate your findings to the roof sector. Looking up one flue, I noticed that the creosote was so thick that the opening in the top quarter of the flue had been reduced by 90 per cent – it was no bigger than a toonie.
8. Check for extension (again). Once the fire has been extinguished, look for obvious signs of fire extension beyond the chimney. All roof, attic and wall areas near the chimney and heating device should be checked for the following signs of fire extension: discoloration or blistering of surface materials; hot-to-touch areas; smoke emitting from cracks and/or from electrical outlets, light fixtures, eaves or roof coverings; and visible glowing embers.
This is a great time to use thermal imaging cameras or heat sensors if your department has them. Should any of these signs be noticed, standard overhaul procedures should be used to expose the area.
Before leaving the scene, inform the resident that a qualified inspector must inspect the chimney and/or heating device before it is used again. Getting the resident to sign a statement to that effect, as well as informing dispatch that the resident has been informed, will help reduce your department’s liability in the matter.
A further note: The fire department is obligated to put out the fire; therefore, any damage caused in the process is a reasonable risk. However, the fire department is not obligated to clean the chimney, so damaging the chimney in this process is not a reasonable risk.
One department I was with encouraged us to use a chimney chain, dropping it down the flue to knock creosote from the walls of the flue onto the bottom of the firebox. It required us to work from the roof and certainly increased the risk factor. Our present SOGs call for us to confirm extinguishment of the fire and lack of fire extension, and then advise the homeowner to have the chimney cleaned and inspected before lighting another fire in the fireplace.
9. Take time during salvage and overhaul operations to use floor runners and fire-retardant salvage covers near the fireplace. Careful cleanup can earn your department valuable praise from the homeowners.
Chimney fires are generally simple to manage if you take the right actions.
Until next time, stay safe out there, and remember to train like their lives depend on it.
Ed Brouwer is the chief instructor for Canwest Fire in Osoyoos, B.C., and Greenwood Fire and Rescue. The 21-year veteran of the fire service is also a fire warden with the B.C. Ministry of Forests, a Wildland Urban Interface fire suppression instructor/evaluator and a fire-service chaplain. Contact Ed at firstname.lastname@example.org