Taking the fight out of a chimney fire

Chimney fire extinguishing aids work by consume available oxygen


The most obvious sign of a chimney fire is when you see flames and sparks shooting out of the chimney like a Roman candle on the 4th of July. Such a visual sign of a chimney fire in action is nothing short of impressive.

When homeowners are present during a chimney fire they have described the experience using phrases such as:

  • "I heard a loud cracking and popping noise."
  • "We saw a lot of dense smoke."
  • "It was an intense, hot smell."

Recognizing a chimney fire

In many cases — because chimney fires can burn explosively — their noise and visual "performance" can attract the attention of neighbors or passers-by even before the homeowner is aware of the situation. When those second parties call 911 to report the chimney fire, they usually describe the scenario as, "flames and heavy smoke shooting out of the chimney." 

If they are at home, homeowners report being startled by a low rumbling sound that reminds them of a freight train or a low-flying airplane. However, don't be misled and think that a chimney fire is not in progress just because the homeowner doesn't describe the situation in those terms. 

A slow-burning chimney fire doesn't get enough air or have fuel to light up the sky, but the temperatures they reach are very high nonetheless. These slow-burners can cause just as much damage to the chimney structure — and nearby combustible parts of the house — as their more spectacular cousins.

What fuels a chimney fire?

Whether is serves a fireplace, wood stove or fireplace insert, the primary function of the chimney is to expel the byproducts of combustion. Those byproducts — as we learned in Firefighter I class — include unburned carbon particles (visible as smoke), water vapor, gases, hydrocarbons, tar fog and assorted minerals. 

As these substances leave their source, they flow up into the relatively cooler chimney and condensation occurs. This condensation creates a residue that sticks to the inner walls of the chimney, a material called creosote.

Creosote is black or brown in appearance. It can be crusty and flaky, tar-like, drippy and sticky, or shiny and hardened. Often, all forms will occur in one chimney system.

Creosote, regardless of its physical form, is highly combustible. So when you get a sufficient amount of creosote build up, then add the right amount of heat to the inside of the chimney's flue — you have a chimney fire.

The danger from a chimney fire is that the typical flue is not designed to withstand such high temperatures, and when severely heated they may crack. Once that happens, the fire within the flue can spread horizontally out of the chimney.

Extinguishing aids for chimney fires

Because putting firefighters on ice- and snow-covered roofs is dangerous, I've looked at products that can all be deployed from the ground.

When looking for chimney fire extinguishment products — either as a homeowner or firefighter — look for those products that have the CSIA Accepted Product Status endorsement from the Chimney Safety Institute of America

Orion Safety Products' Chimfex is similar to a road flare; the user lights it and toss it in to the fire. The manufacturer claims that its studies show that the Chimfex will suppress a fire in an average of 22 seconds by consuming the available oxygen in the flow path, thus extinguishing the fire. The product has a 36-month shelf life and sells for $30 per single unit.

Orion also claims that its chimney fire extinguisher extinguished a test chimney fire in an average of 22 seconds. The manufacturer also states that its product reduces chimney temperatures an average of 53 percent in two minutes; during the same time the oxygen levels within the flue were reduced an average of 43 percent. It sells for $20 per unit.

Kidde's FireEx chimney fire suppressant is not a flare, so no pre-ignition required and can be used in wood stoves and fireplaces. The user throws the entire package onto a burning fire. 

The manufacturer does state that the user should attempt to eliminate any drafts by either closing doors (on the woodstove or insert) or covering the fireplace opening with fire retardant material. The suppressant comes packaged in airtight plastic for indefinite shelf life and zero chance of water damage. It sells for $40 per unit.

Products to prevent chimney fires

The best way to keep a chimney fire from happening is to prevent the build up of creosote and here are a couple of products that can aid you in that effort.

The Creosote Sweeping Log for Fireplaces when used according to the manufacturer's instructions reduces the weight, thickness and flammability of creosote.

Meeco's Red Devil Creosote Destroyer also controls creosote buildup in fireplaces and wood-burning appliances. With regular use according to the manufacturer's recommendations, it acts as a catalyst and destroys the binder that holds the creosote particles together. It sells for $35 for a 5-pound container.

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