The most common cause of chimney fires is the ignition of creosote in the flue. Similar to furnaces, wood-burning fireplaces and stoves are designed to safely contain fires. Fireplace chimneys are designed to expel byproducts of combustion (smoke, gases, unburned wood particles, and so on). When these substances rise upward by convection into the relatively cooler chimney flue, condensation occurs and a black/brown residue called creosote sticks to the inner walls. Creosote, which can accumulate in many forms (tar-like, drippy, shiny, hard, crusty, or flaky) is highly combustible; when it builds up, a fire can occur. Creosote accumulates with restricted air supply or cooler-than-normal chimney temperatures, which happens more frequently with chimneys outside the home rather than those that run through the center of the house.
Restrictions of air supply in chimneys are a result of poor ventilation that occurs when glass doors are closed and/or the damper is not open wide enough to let by-products travel rapidly. In wood stoves, restrictions are caused by closing the stove damper or air inlets too soon and too often. There are other factors that can lead to creosote buildup, such as failure to maintain a proper temperature inside the flue, burning wet wood, or failure to clean the chimney on a regular basis. Regardless of how it occurs, the longer the smoke remains in the flue, the more likely it is that creosote will form and eventually catch fire inside the chimney flue, resulting in a chimney fire. Fires in masonry chimneys can burn up to 2,000° F and may result in melting mortar, cracked tiles, or collapsed liners. These fires may damage the outer masonry material, which may in turn provide a pathway for fire to travel to combustible wood frame components, resulting in a house fire that may be confined to the inner walls. Prefabricated metal chimneys are designed and tested to withstand flue temperatures up to 2,100° F without sustaining damage; however, when they are damaged by a chimney fire, they should be replaced.
Chimney fires have distinct characteristic that firefighters should look for on arrival. These include a rumbling or roaring noise that resembles a freight train or low flying airplane; flames, sparks, and dense smoke that extend from the top of the chimney; and products of combustion emanating with velocity from existing cracks in the chimney mortar. If these signs do not exist, you may still have a chimney fire, but a smaller one that is not visible from the exterior.
(1) Firefighters using a chimney chain.
If a fire extends outside of the chimney and ignites combustible materials or makes its way into the walls, it should be treated as a typical structure fire and your department should follow your structure fire standard operating procedures (SOPs). Regardless of whether or not the fire extends outside the chimney, the Universal Structure Fire Tactical Worksheet should be used to accompany this operational guide.
Operational Guide for Chimney Fires
This operational guide outlines the steps to be taken at fires confined within the chimney/flue. We suggest your department places a chimney kit on each apparatus. The kit should consist of a mirror, heat gloves, a weighted chimney chain, and chimney bomb (zipper-seal bags containing dry-chemical powder), all placed inside a metal bucket. In this guide we also offer techniques for departments that do not carry chimney kits.
1. Establish command upon arrival.
2. Conduct an exterior size-up and look for signs of a chimney fire.
Interview occupants about what they witnessed.
Look and listen for signs of a chimney fire, such as:
A rumbling or roaring noise that resembles a freight train or low flying airplane.
Flames, sparks, and dense smoke that extend from the top of the chimney.
Products of combustion emanating with velocity from existing cracks in the chimney mortar.
If you encounter a small and unnoticeable fire from the outside; enter the structure and continue your size-up using a thermal imaging camera (TIC).
Consider the possibility of failed internal connectors, which may result in a house fire.
3. Call for resources to ensure safe operations.
4. Wear full personal protective equipment (PPE) and self-contained breathing apparatus (SCBA).
All fires are unpredictable, even those that seem confined to a chimney.
Personnel operating on the roof and within the structure should be wearing SCBAs and turnout gear.
5. Gain entry; search for and remove victims.
If occupant is not accounted for and the door is locked, force entry.
Account for, evacuate, and temporarily relocate all occupants to a safe location.
6. Monitor oxygen levels and ensure adequate ventilation.
Consistently monitor oxygen levels for carbon monoxide (CO).
Chimney fires can cause the flue to fail and spill CO and other byproducts of combustion into the walls, ceilings, attics and other hidden spaces.
If the interior of the house is filled with smoke, perform horizontal ventilation using a positive pressure fan.
7. Advance a hoseline to the front door as a precaution.
Be prepared if the fire extends from the chimney to the structure itself.
8. Stop or reduce the flow of oxygen to the flue.
This can be as simple as closing the units door(s) and closing any air intakes
9. Spread salvage covers in front of the fireplace (a.k.a. the firebox).
Place floor runners (tarps) from the front door to the firebox to keep the floor clean.
10. Extinguish the fire.
Use a chimney kit (a metal bucket containing a mirror, heat gloves, a weighted chimney chain, and chimney bomb) and take the following actions:
Advance a hoseline to the front door.
Send a company to the attic to make sure the fire has not extended into the attic/cockloft.
Place the wood and ashes from the firebox in a fire safe salvage bucket, bring it outside, unload the contents, and hose it down.
Cautiously remove the chimney cap, bird screens, or spark arrestors with a hand tool.
Inspect the chimney using the mirror.
If there is fire, drop the chimney bombs down. When they reach the firebox, the bag will burst and the normal draft will carry the powder up to extinguish the creosote.
Slowly lower the weighted chimney chain from the top of the flue to the firebox. Spin the chain to knock the creosote from the walls onto the firebox where it can be extinguished with water or a dry-chemical extinguisher.
Tips for firefighters working on the roof include:
Roofs may be pitches and difficult to access. Work off a platform whenever possible.
There may be ice and snow on an already dangerous roof.
Consider the extra weight; limit the number of firefighters on the roof.
Do not look directly into the chimney. Visually inspect the flue with a mirror.
If you do not have a chimney kit, consider the following methods:
Briefly open the draft stop and completely discharge a dry-chemical extinguisher upward. (Beware. This method will add oxygen to the fire and temporarily accelerate it. It will also be messy, so be sure to put salvage covers and tarps down before doing so).
Water extinguishers are an option; however, most professionals don’t advocate using water because of the fear that water will rapidly cool the flue and cause permanent damage to masonry and flue liners. When using a water extinguisher to extinguish the remaining contents in the firebox, close the draft. This will reduce the flow of oxygen into the flue and help with complete extinguishment.
If the fire extends from the chimney, treat as a structure fire.
11. Search for extension.
Use a TIC on each floor.
Look for discoloration or surface materials, smoke coming from cracks, outlets, lighting fixtures, or roof coverings.
Send a recon team to the attic to check for extension.
Inspect the firebox and as much of the chimney in the inside of the home as possible.
12. Perform overhaul.
During overhaul operations, place fire-retardant salvage covers in front of the fireplace and limit the number of personnel walking through that area.
If the owner/occupant has a vacuum or broom, clean around the unit.
13. After the operation is complete:
Advise occupants to have chimney inspected by a certified chimney inspector and cleaned before using it again.
Check the CO levels one more time before terminating the incident.
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