Article by: Michael A. Wieder
One common fall, winter, and spring nemesis that faces firefighters in many parts of the United States and virtually all of Canada, is the chimney or flue fire. The terms "chimney" and "flue" tend to be used interchangeably in many jurisdictions; however, they really do not mean the same thing. The term "chimney" is properly used to describe the entire structure designed to route heat, smoke, and vapors from a heating device to the exterior. The term "flue" is properly used to describe the internal portion of the chimney through which the products of combustion flow to the exterior. For ease of presentation, throughout the rest of this article, we will use the term "chimney fire" to describe these incidents.
Types of Chimneys
Traditionally, chimneys were solid structures that were constructed of heavy stone, block, or brick. The chimney was either an integral part of the overall building structure, or it was connected to the structure by a series of ties between the chimney and outside wall of the structure. The flue itself was constructed of fire brick, clay, slate, or tile. Few chimneys are built this way today as they are extremely expensive and there is a shortage of experienced masons who are capable of building them.
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. It is fastened to the exterior wall by a series of metal brackets. The inner wall of the pipe serves as the actual flue. Both styles of chimneys should be equipped with a spark arrester screen and a cap on the top.
Causes of Fires
There are two common causes of chimney-related fires:
1. Ignition of residue within the flue.
2. Ignition of combustible materials in proximity to the chimney or heating device.
All firefighters receive thorough instruction on fire behavior in any introductory firefighting course. We can use this information to understand how conditions may develop that result in a chimney fire. Hot, free-burning fires that have plenty of oxygen supply will create very little smoke or residues. They also develop high levels of heat that ensure any residues that are created make it out the top of the chimney. As long as fires are allowed to free-burn, few problems will be encountered.
The problems begin when fires are routinely burned at less than free-burning levels. This may occur as a result of insufficient oxygen flow to the fire box, too much fuel in the fire box, or large logs added to a small fire. The resulting incomplete combustion produces low heat levels and large amounts of fire gases. As these gases travel up the flue, they begin to cool much the same way that petroleum is separated at a refinery. When they reach their condensation temperature, the liquid clings to the inside surface of the flue. This substance is called creosote. As the creosote builds up, it develops a black, scaly appearance. Creosote is highly flammable and can ignite when a hotter fire is started in the heating device or when a spark travels up the flue and contacts it.
The second cause, ignition of combustible materials in proximity to the chimney or heating device, is typically a result of improper installation of either of the two. Appropriate manufacturer's instructions, building codes, and fire codes must be followed in regards to stove and chimney installation. Proper clearance and insulation between the heating devices and other construction materials is crucial in the prevention of a fire that may start in between the walls.
These fires often burn for an extensive time before they are detected and are extremely difficult to extinguish. Firefighters are required to completely tear out the walls or ceilings and do extensive salvage and overhaul to put out even the smallest fire. Fire departments in many areas saw extreme increases in these types of fires during the energy crisis period of the early 1980's. Shoddy, hasty installation of supplemental heating devices and chimneys resulted in many chimney-related structural fires. The numbers have decreased somewhat in recent years, but they still remain a common cause of fire.
Many people associate chimney fires with a problem that is limited only to the winter months. This is not necessarily the case. Experienced firefighters realize that these fires are very common during the fall and spring as well. An early autumn freeze may result in people firing up stoves or fireplaces whose chimney has not yet been cleaned from the previous heating season. Fires in the spring result from burning "cooler" fires and a year's worth of creosote in the flue.
Creosote build-up and the resulting fires are most commonly found at three (3) locations within the chimney:
• Sharp bends in the flue
• Long horizontal runs in the flue (such as where it runs through the wall
• The top 1/4 of the flue
Indicators of a working chimney fire include:
• Sparks or flames exiting the top of the chimney
• A whistling or buzzing sound in the chimney (it is often described as though it sounds like a swarm of bees has entered the chimney)
• A backflow of smoke through the heating device into the structure
• Discoloration on the walls adjacent to the chimney
• Smoke emanating from cracks in the wall
Response to Chimney Fires
Different fire departments tend to have different philosophies on alarm assignments to chimney fire responses. Some departments send a full, first-alarm assignment, because of the potential for the incident to turn into a full-blown structure fire. A full assignment would probably consist of at least two engines, a ladder company, maybe a squad or rescue company, an ambulance, and a chief officer. Rural departments may also assign a tanker (tender) or two on the initial response. On the majority of fires that are contained to the flue itself, most of these units would not be required.
Some departments send a reduced assignment to reported chimney fires. The minimum response to a chimney fire should be at least one engine company, and one ladder company (if available). The engine company will be required for fire extinguishment. The ladder company will be required for topside access, tarps, ventilation fans, overhaul tools, and ladders. Some departments choose to send an EMS unit because 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.
NOTE: If a reduced assignment is sent, and anything other than a fire contained to the flue is found when the first units arrive, the balance of the full first-alarm assignment should be requested immediately.
Chimney Fire Tactics
Once on the scene, an established standard operating procedure (SOP) for handling chimney fires can be employed. It is easy to develop a SOP that will handle the vast majority of all chimney fires. The basics of such an SOP are covered in this section. Chimney fires become more difficult when they extend outside the flue itself. That issue will be discussed later in the article.
The following is a blow-by-blow description of the tactics that should be formed into an SOP for routine chimney fires:
1. Stop the flow of oxygen to the flue. Hopefully, the occupant will have shut off the oxygen prior to the fire department's arrival. However, if this is not the case, the first fire personnel on the scene should shut off the oxygen supply immediately while other preparations are being made. Reducing the oxygen flow will decrease the intensity of the fire in the flue and in some cases will extinguish it all together. Shutting the oxygen off on most wood stoves and fireplace inserts is relatively easy. Simply close the unit's door(s) and close any intake air valves. This step may not be possible on open fireplaces.
2. Spread a salvage cover in front of the stove or fireplace. The purpose of the cover is to catch any ashes/embers that may fall when the wood is being removed, or to catch any extinguishing agent that is used in the process of dousing the fire. It is preferable that a fire-resistant cloth tarp be used. Plastic tarps will fail quickly when exposed to a heated ember.
3. Establish horizontal ventilation. Some of the extinguishment activities, in particular the removal of wood from the fire box, may create a slight smoke condition in the dwelling. This can be minimized by establishing ventilation before other firefighting activities take place. While traditional horizontal ventilation using smoke ejectors may be used, positive pressure ventilation is the preferred method 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. This will minimize the spread of smoke within the structure.
4. Extinguish the fire in the fire box. With the aforementioned tactics taken care of, the fire in the heating device should be extinguished as soon as possible. There are two primary agents that are commonly used to accomplish this task: water and multi-purpose dry chemical agents. Water may be applied in small quantities from a small bucket, garden sprinkling can, or an air-pressurized water extinguisher (APW). Apply only enough water to knock down the flames and allow the wood to be removed. In some cases, the steam from this step will travel up the chimney and extinguish the flue fire, thus making the rest of the job even easier.
Some departments use multipurpose dry chemical agents to knock down the fire. In this situation, a supply of agents is carried on the apparatus in a bucket or plastic baggies. When needed the agent is shoveled onto the fire, as opposed to sprayed from an extinguisher. Again, apply only that agent needed to knock down the fire.
Once the fire is knocked down, remove the wood pieces from the heating device and remove them from the structure. Commonly, the occupant will have the fireplace tools and metal bucket to accomplish this. If not, most truck companies have the equipment necessary to do this. Once the wood is in the bucket, remove it through the nearest exit possible. Watch to make sure no embers leave the bucket along the way. Once outside, completely extinguish the wood using a water extinguisher, booster line, or garden hose.
5. Ladder the roof. Assuming enough personnel are on the scene, this step should be underway while steps 1 through 4 are being completed. If an aerial device will be used, extend it to the chimney opening. If ground ladders are being used, place a wall or extension ladder at a good roof entry point, and then extend a roof ladder to the roofline adjacent to the chimney. If the roof has a combustible finish, a charged hoseline should be advanced onto the roof as soon as the ladders are in place. Avoid resting the ladder against the chimney itself. Many older chimneys are unstable and could topple from the weight of a ladder and firefighter being rested against them.
6. Extinguish the chimney fire. With all these other tasks accomplished, the chimney fire may then be extinguished, assuming it has not self-extinguished during the process. There is a myriad of different ways that are employed to extinguish chimney fires. There is no one particular way that is perfect or absolutely the right way to do it. This article covers some of the more common ones. Your department needs to determine which it will use.
Many people are vehemently opposed to the use of water to extinguish chimney fires. This opposition is 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 creating a more serious fire situation down the road.
Other departments routinely use water to extinguish fires successfully. The key is in the amount of water that is used and how it is applied. My hometown department, in Pennsburg, Pennsylvania, has used water very successfully for more than half a century. The water is applied through a specially designed "chimney nozzle." The original nozzle was developed by a volunteer firefighter, who also happened to be a machinist by trade. The nozzle, which is designed to be attached to a booster hose, has fine holes in the end of it. At 100 psi nozzle pressure, the nozzle produces a fine cone of mist to the volume of 6 quarts per minute. When dropped down the length of a chimney, the mist turns into steam and chokes out the fire immediately, without cooling the flue to the point where it will crack. Our department (and several others in the area that were given copies) have used this method for over 70 years without damaging a single chimney. Today, there are a number of commercial companies that offer chimney nozzles that work in the same way as described above.
Some departments routinely use APWs to extinguish flue fires. The stream is directed either from the top down or from the bottom up through the heating device. Again, this amount of water generally will not be sufficient to cause cracking of the flue, but the resulting steam will choke out the fire.
Multipurpose dry chemical extinguishers are used in some jurisdictions. As with APWs, they may be used from either the topside or the bottom. While they will usually be effective in extinguishing the fire, they can be considerably messier than using water. An innovative idea to use dry chemical agents to extinguish flue fires is to carry a small amount of dry chemical agent in a small plastic sandwich “baggie” that can be dropped down the flue. The baggie quickly melts and the agent is released into the flue. These can be stored on the apparatus for deployment when needed.
Some fire departments have found success using commercially-available chimney fire extinguisher cartridges. Commonly referred to as chimney flares or bombs, these devices resemble, and are activated much the same as, typical road flares. They are activated and placed into the heating device fire box. The resulting gas that is given off goes up the flue and extinguishes the fire.
7. Check for extension. Once the fire has been extinguished, look for obvious signs of fire extension beyond the chimney. All wall, attic, and roof areas adjacent to the chimney and heating device should be checked for the following signs of fire extension:
• Discolorations of surface materials
• A hot-to-the-touch feeling
• Smoke emitting from cracks, electrical outlets, light fixtures, eaves, or roof coverings
• Visible glowing embers
Should any of these signs be noticed, standard overhaul procedures should be used to expose the area and further investigate. Any material that is found to be on fire or smoldering should be removed and doused.
Once the above steps have been accomplished and firefighters are certain that all of the fire has been extinguished, the apparatus can be placed back in service and the scene may be cleared.
Some departments will take the chimney fire SOP one step further. Many departments carry chimney brushes and rods, or old metal chains, either of which are dropped down the chimney after the fire is out in an attempt to clean the remaining creosote from the flue. While this may seem like the "neighborly", customer-service-oriented thing to do, there are potential pitfalls that must be considered. The potential for damaging flue liners with any of the cleaning devices is equal to, or greater than, the chance of damaging it while putting out the fire. The fire department is obligated to put out the fire, so the chance of causing damage in the process is a reasonable risk. The fire department is not obligated to clean the chimney, thus the possibility of damaging the chimney in this process may not be a reasonable risk. Fire departments who perform this service need to check with their liability carrier to ascertain whether or not performing such functions is within the scope of their coverage. Otherwise, the department and individuals on the scene could be subjected to liability for damages or problems that occur down the road as a result of these actions.
Most chimney fires are routine operations that take less than 30 minutes to resolve. However, take all of these fires seriously and stick to your SOPs for everyone. Hopefully, this will prevent you from returning to the same location, a few hours later, for a more serious structure fire.
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About the Author: Mike is the Executive Director of IFSTA at Fire Protection Publications at Oklahoma State. University in Stillwater, Oklahoma. He holds undergraduate and graduate degrees in fire protection, occupational health and safety, and adult education. He is a life member of the Pennsburg (Montgomery County) Pennsylvania Fire Company. Mike can be reached at mwieder@osufpp.org.
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