Tactical Approaches for Chimney Fires

Oct 8, 2008

Photo Scott LaPrade
A Lancaster, Mass., firefighter operates at a chimney fire in March.

It's that time of year when the leaves turn, a brisk chill in the air appears and that burned dust smell from freshly fired furnaces shows autumn is upon us — and with it comes a rise in chimney fires. Is your team educated and trained to tackle them? Better start training now before your first chimney fire strikes.

Chimney fires can burn explosively and are generally noisy and dramatic enough to be detected by neighbors or passersby. Victims of them compare the sound of the fire to a low rumbling noise like a freight train or low flying airplane.

Flames have been known to shoot from the top of the chimney accompanied by dense smoke.
The first indication of a chimney fire is usually the noise — a roaring sound that grows louder as the fire intensifies, reaching temperatures of up to 2,000 F.

The volume of fire, smoke and heat from this type of fire can push hot gases out of existing cracks in the chimney mortar or cause internal connectors to fail. When viewed from the exterior, large smoke volume and sparks/fire can extend several feet above the chimney.

Slow burning
However, not all chimney fires are visible from the exterior. Some are slow-burning fires, lacking the levels of air or fuel found in the large, eye-catching visible fires. But even these have high temperatures that can cause as much damage to the chimney structure and nearby combustible parts of the house as the more dynamic fires.
In basic terms, fireplaces and/or wood stoves are designed to allow for fires in a safe controlled fashion with the chimney providing expulsion for the by-products of combustion.

These substances exit the fireplace and/or wood stove, and gradually rise up into the relatively cooler chimney, where condensation occurs. But as the products cool, they can coalesce into a sticky substance — creosote — that adheres to the inner lining of the chimney walls. Creosote is black or brown in appearance with a crusty or flaky consistency. It can be tarry, drippy and sticky or shiny and hardened. Often, all forms will occur in one chimney system.

Regardless of the physical presentation of the creosote, it is highly combustible. If the build-up of the volume of creosote is sufficient, it is possible to start a chimney fire. Although any amount of creosote can burn, professional chimney sweeps are concerned when creosote builds up in sufficient quantities to sustain a long, hot, destructive chimney fire.

All chimneys are essentially manufactured in a similar fashion. The by-products of the fire exit upward by convection through the chimney flue. This is generally known as the fire's “draft." There are several factors that can lead to a creosote buildup which residents in your communities should be aware of, including:

Not maintaining a proper temperature inside the flue
Burning wood that is not dried thoroughly
Failure to clean the chimney on a regular basis.

The size of the fire, the construction style of the fireplace and chimney and its age will add to the possible extension of the fire.

Chimney fire tactics
As with any fire, life safety should be the primary concern. Luckily, the majority of chimney fires allow for occupants to exit under their own power. This vastly reduces the impact for completing an all clear on a primary. Ensure evacuation of the occupancy to ensure safety. Remember that all fires are unpredictable, so full PPE and SCBA should be worn.

Stretch a preconnect hoseline to the front of the structure in case the fire is larger than initially anticipated. Establish command, track your personnel and set up a safety officer when able to do so. Strategy goals should consist of extinguishing the fire, limit extension, ventilation as needed, overhaul to prevent rekindle and finally, salvage.

Chimney fires should be dispatched as a full structural response until the size, location and access impacts are assessed. A good size-up should be performed to ensure the exact location and size of the seat of the fire is confirmed. You will not always have fire visible from the flue on arrival. Only cancel other responding apparatus 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. And remember as the fire burns, it can cause failure of internal support construction features allowing for extension from the flue into walls, ceilings, attics and other hidden construction elements. As soon as the determination for CO is done, send a recon team directly to the attic and make sure that the fire has not extended into this space or the cockloft Remember to inspect the firebox itself and as much of the chimney in the inside of the home as possible. Thermal cameras are significantly helpful during this time.

Once the fire has been located, and if it is contained within the flue system, we can move on to chimney fire specific extinguishment methods:

When it is required to access the roof, remember to utilize the proper ladders.
Access the chimney area and remove the chimney cap, bird screens or spark arrestors. Visually inspect the chimney with a mirror to determine the extent of the fire. Remember, chimney fires rarely occur when the weather is good so watch your footing in snow or freezing rain conditions.
Be cognizant of the dead load you are adding to a roof structure, especially if there has been a significant amount of snow loading the roof support recently.

There are a few different methods of extinguishing a chimney fire though all require an ABC dry chemical extinguishment agent. Regardless of the manner of extinguishment used for a fire in the flue, you will greatly increase your ability to operate near it if the fire in the fire box is extinguished. Unload the wood from the firebox, place it in a metal salvage bucket, and unload outside the residence. Continue to do this until all of the wood and hot ashes have been emptied from the firebox. Unload the bucket outside of the residence, and wet down with a hose, pressurized water can or pre-staged attack line. Make sure the wood and hot ashes are no longer burning -- you don't want the wood or house to catch on fire after you leave. Once the fire has been put out in the firebox (generally with a pressurized water extinguisher), close the draft to reduce the amount of air feeding the fire in the flue.

As for extinguishment methods, here are three:

Utilize a dry chemical powder contained in sealable plastic bags, such as Ziplocks®. This can be dropped from the top of the chimney through the flue top you have already opened. Based on the size of the flue fire, you are presented with, you can drop a few bags through it. As the bags drop, their weight will carry them down toward the draft stop. The bags will then melt, releasing their dry powder into the flue. Once the powder is released, it is light enough to be carried upward and successful extinguishment should occur.
The next method allows for extinguishment of the fire from the base of the flue. This method requires the brief opening of the draft stop, which may temporarily accelerate the size of the fire. Coordinate the opening of the draft stop with the insertion of the nozzle of a dry chemical extinguisher past the draft stop and discharge into the flue in an upward direction. The heat of the fire will carry the extinguishment agent upward to assist with putting the fire out. This method of extinguishment has been known to cause a bit of a mess inside the interior of the house from collateral extinguishment powder travel, so consider placing salvage tarps down before you begin. In addition, a two-story structure may require both of the methods of extinguishment outlined so far to work due to the length of the flue.
The final method is my favorite. It does require some prep time ahead of the call, but it is well worth the work. Cut a piece of plywood about 4 by 4 feet and mount two handles on the same side about a foot in from two parallel sides in the middle. This method requires the use of a positive pressure fan to work well. Prior to utilizing the PPV, ensure your team has located the seat of the fire and is not concerned about fire outside the flue or firebox. Ensure all other openings in the structure have been closed with the exception of the opening the PPV will be using. Place the plywood in front of the firebox and coordinate the start of the PPV fan. Once the PPV fan has been started, slide the plywood to allow for a small opening (about 1 foot wide) on one side or the other. Discharge the extinguisher into the opening and let the PPV fan push the extinguishment agent into the flue area. Keep the plywood open for about a minute, close the draft, stop and reassess the fire with a thermal camera. In all cases, confirm the fire has been extinguished by visual, infra-red or thermal camera methods.

Some departments encourage their personnel to use a "chimney chain" that is dropped from the top of the flue. This device is used to knock creosote from the walls of the flue onto the bottom of the firebox. It requires personnel to work from the roof and increases the risk associated with the completion of the scenario. Consider working from a platform to increase your safety profile if you must perform this maneuver. Our department does not carry this piece of equipment and instead confirms extinguishment of the fire and lack of fire extension, and then advises the homeowners to have a chimney cleaning company respond to clean out their fireplace/flue and have it inspected before setting another fire in their fire place.

The majority of chimney fires will be successfully extinguished utilizing one or more of the methods described above. However, there are other methods of extinguishment that exist out there. Commercially produced chimney nozzles allow for a low volume water extinguishment to occur. Sadly, this also causes an ash / creosote laden water puddle to form on the bottom of the firebox and generally the floor in front of it. Handlines should be utilized only as a last resort as they can permanently damage existing masonry or metal flue liners.
Maximize your customer service skills by remembering to take the 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

Many fire departments run chimney fires on a regular basis when the weather turns cold. Chimney fires are generally simple to manage if you take the right actions. We still need to ensure that our personnel are proficient with the styles of fireplaces that we may have to deal with. Be familiar with how your department prefers to have a chimney fire extinguished. And if you have a different method of extinguishing chimney fires, I would love to hear of them.

About the author

Michael Lee has 25 years experience in pre-hospital paramedic experience and about 20 years experience in the fire service. He started as a FF/Paramedic and worked up through the ranks, including training officer, to his current position as battalion chief. He currently serves as battalion chief at Mountain View Fire Protection District in Colorado. He is currently filling the role of safety officer for FEMA USAR Colorado Task Force One and has military service in the U.S. Navy. To contact Michael, email Michael.Lee@FireRescue1.com.