There’s nothing like a rekindle to ruin a fire officer’s day. It’s more than the damaged pride or embarrassment. There can be liability implications as well. The officer who makes the final determination that a fire is completely extinguished and allows a family to reoccupy its home bears an enormous responsibility for that family’s safety. Redkindles can cause more damage than the initial fire because walls and ceilings may have been opened, exposing combustible structural members.

Cellulose insulation is essentially ground-up newspaper. Although it is treated with fire-retardant chemicals, it can smolder and rekindle if firefighters fail to recognize it or if they underestimate its tendency to smolder. (Photo by author.)

Additionally, a rekindle in a concealed space, such as an attic, can gain considerable headway before firefighters are called back to the scene. Occupants may have smelled smoke but dismissed it as a residual odor from the previous fire.

Cellulose insulation above old lath-and-plaster ceiling ignited from heat conducted through a ceiling fan fixture. Light fixtures, vents, and ceiling fans break the continuity of the fire resistance inherent in the ceiling material and are, therefore, good places to pull examination holes to check for hidden fire. (Photo by author.)

Often, a rekindle is a result of an officer’s failure to recognize materials that are prone to smoldering; the stuffings in furniture and mattresses are classic examples. Or, it could be that the officer overlooked a defect in construction that can cause fire to spread into the attic and wall spaces.

Dark patches on cellulose insulation indicate that it has been exposed to heat and may be smoldering under the surface. (Photo by Steve Jessup.)

Among the conditions that can lead to a rekindle are the presence of cellulose insulation, fiberboard, and improperly ducted kitchen exhausts.

Cellulose Insulation

Smoke developing in cellulose insulation several hours after firefighters believed that they had extinguished all the hot spots. Fortunately, the company discovered its own “rekindle” by returning to the scene every few hours to check the attic. (Photo by Steve Jessup.)

Cellulose insulation is made primarily from ground or shredded newspapers and is blown into attics and wall spaces. Cellulose was used extensively in the 1970s, when there was a great demand for energy-conserving insulation. Cellulose has excellent insulating properties and is less expensive than fiberglass insulation. Fiberglass and cellulose insulation, however, behave quite differently when they are exposed to an ignition source. Blown-in fiberglass (with no combustible backing paper) is noncombustible. Blown-in cellulose insulation, since it is essentially ground newspaper, is naturally combustible, especially in this finely divided form. Cellulose insulation, therefore, must be treated with chemicals to make it fire retardant. The key words here are fire retardant. Any firefighter who has spent a couple of hours in a hot, smoky attic chasing smoldering pockets of cellulose will tell you that it may be fire retardant, but it is far from being fireproof or noncombustible. In other words, this stuff burns!

Louver vents in gable end used to exhaust smoke from smoldering cellulose insulation. Locate intake and exhaust openings before implementing PPV. Front windows were broken during primary search; therefore, the PPV blower was operated outside the closet, where the scuttle hole to the attic was located. (Photo by Steve Jessup.)

I’ve taken several samples of cellulose insulation from the attics of fire buildings and conducted my own “low-tech” flammability tests. First, I attempted to ignite handful-size samples with a butane lighter. Some of the samples readily ignited and continued flaming combustion after the lighter’s flame was removed. Some samples smoldered, and some self-extinguished after flame contact. Then, I laid a 75-watt lightbulb on the samples and found that every sample eventually began to smolder. It may have taken a few hours, but the end result was the same: smoldering, sustained combustion.

Fiberboard ceiling tiles in an old farmhouse. The pike pole makes an opening at the light fixture. (Photo by Tony Greco.)

I’m not a chemist or fire investigator, so any technical discussion of flammability standards, product quality control, and longevity of fire-retardant chemicals is better left to the experts. But, after working several fires and rekindles involving cellulose insulation, I don’t have to be a scientist to figure out that we have a problem with this material. And, evidently, it’s not just a problem in Florida. I’ve heard firefighters from all over the country relate their own personal “horror stories” about having to return two or more times to fires in attics containing cellulose insulation.

A low-density fiberboard ceiling is an excellent host for flying sparks and embers. Here, a firefighter checks the attic for smoldering. (Photo by author.)

Fire in cellulose insulation is caused in part by improper installation. Installers are instructed to maintain a clearance of at least three inches between the cellulose and any heat source, such as recessed light fixtures, light ballasts, and chimney flues. All too often, however, the installer will cover the entire attic with several inches of insulation, leaving combustible cellulose in intimate contact with heat sources.

To prevent a rekindle in cellulose insulation, you must do the following:

  • First, recognize it. Check with insulation contractors to see if it was used in your area (and it’s a good idea to check your own attic!). The product is fluffy, is gray or brown in color, and may look like newsprint or cotton stuffing from old furniture and mattresses.
  • Do not underestimate the potential for cellulose insulation to smolder, undetected, below its surface with no visible smoke. The smoldering can spread away from the ignition source in tunnels beneath cellulose that had been soaked with water. You must, therefore, examine the full thickness of the insulation blanket at several places in the attic before returning to quarters-or you will be back!
  • Be careful when applying hose streams on burning insulation. A high-velocity stream of water can scatter smoldering particles of insulation and spread the fire to other parts of the attic. Use a gentle spray to carefully wet down the insulation.

The original ceiling in this old school was more than 10 feet high. The ceiling consisted of fiberboard tiles on 1- 2 2-inch wood nailers. Later, a new ceiling was installed to hide ductwork when air-conditioning was installed.

Cellulose insulation tends to turn dark in areas that have been exposed to heat. The darkened surface may feel cool and produce little or no visible smoke. But, dig down. Chances are that you will find smoldering pockets of insulation. Look for dark patches or spots on the surface of the cellulose blanket; they can present a clue of where to start digging.

The smoldering fiberboard ceiling tile the firefighter is holding demonstrates how low density gives the fiberboard a propensity for rapid flame spread and a tendency to smolder. (Photo by Steve Jessup.)

Of course, you can’t see dark particles if the attic is full of smoke. This is where positive-pressure ventilation (PPV) can be a blessing or a curse. A draft channeled up a scuttle hole and across an attic can effectively clear the space of smoke and allow firefighters to enter the attic for overhaul. But, forcing air currents through the attic may be just what it takes for smoldering insulation to burst into flame and spread fire in the attic.

The warning on fiberboard insulation about says it all. A roofer illegally dumped a large pile of roofing debris along the roadside. The engine company had to educt one percent foam to penetrate the stubborn, smoldering material. (Photo by author.)

Before implementing PPV, control any visible fire in the attic. Then identify your inlet and exhaust openings. Typically, your inlet will be a scuttle hole or a hole pulled in the ceiling. Placing a blower at a windward exterior doorway will direct air currents up the hole and into the attic.

Fiberboard insulation stripped from a metal-deck roof. Fire impinging below a metal deck can vaporize and ignite roof tar and cause low-density fiberboard insulation to smolder. (Photo by author.)

Next, identify your exhaust openings. Hopefully, the attic will be vented with natural openings in the gables, vents under the soffits, or turbine ventilators on the roof. Remember to determine where the smoke will vent before you start the blower. One of the dumbest things I have ever done on the fireground was to open an attic scuttle hatch in a duplex that had a fire in the adjacent unit without noticing that a positive-pressure blower was in operation. We were ordered to check the adjacent unit for fire extension. It was perfectly clear of smoke until we pushed up the scuttle hatch, then pressurized smoke from the fire in the adjacent unit blew across the nondraftstopped attic and down into an otherwise uninvolved and smoke-free living unit. The lesson here is this: Determine where your smoke will exhaust before implementing PPV.

A hole cut in a lightweight gypsum roof deck exposes a layer of fiberboard insulation. The hole was cut to install ductwork for a spray booth. Forget about cutting ventilation holes in a lightweight gypsum roof deck. (Photo by author.)

Actually, it seldom is necessary to cut a hole in the roof to rid the attic of smoke from smoldering insulation. When an attic lacks sufficient natural vents, cutting a small opening in a gable end to exhaust PPV can be easier and less expensive to repair. Be prepared in case PPV causes the attic to light up. Make sure personnel are ready with hoselines and pike poles before you start the blower. Watch the smoke as it vents from the attic; hopefully, it will diminish in density until the attic is cleared. Smoke that increases in density or pressure should signal an immediate halt of PPV and the beginning of an aggressive attack on the fire.

Greasy residue on the roof can ignite and burn into the layer of roof insulation. Don’t be afraid to strip the roof covering away from ducts or flues to check for smoldering fiberboard insulation. (Photo by author.)

Heat, smoke, or a lack of access into the attic may necessitate that you look for smoldering insulation from below, by pulling ceilings. Feel the ceiling for hot spots to find areas that must be pulled. Make sure you have plenty of salvage covers to protect furniture from plaster dust and falling insulation. Garbage cans are excellent for hauling the insulation to a safe location outdoors, away from any structures.

A thermal imaging camera can be extremely valuable in detecting subtle differences in heat. Scan the ceilings, and look at the insulation in the attic.

The vent hood above the stove sucked grease fire into the exhaust duct and blew it into the attic. Although most household stove hoods are merely filters, make sure you check for the presence of exhaust ductwork. (Photo by author.)

It can be difficult to pass through an attic scuttle hole with an SCBA tank on your back; it may be tempting to take it off and “eat a little smoke.” Don’t do it! Smoldering insulation produces vast quantities of carbon monoxide, which can linger long after the visible smoke has cleared.

Don’t think that you can completely extinguish smoldering cellulose insulation by applying water only. It may be possible, but the amount of water necessary to do the job will be absorbed by the insulation and cause the ceiling to collapse under its weight. How much water should you apply? How much ceiling should you pull? How much insulation should you remove from the attic? These are tough questions that are best answered after a careful size-up and weighing the damage caused by the fire against damage caused by firefighters.

Remember, however, firefighters who are reluctant to pull ceiling (to overhaul cellulose insulation) because of a fear of criticism of damaging property will probably have to return to the scene and cause even more damage by extinguishing the rekindle. Once the fire has been knocked down and the attic has been cleared of smoke, you now have the time to carefully dig through the insulation, wet down hot spots, and remove smoldering material. Adopt a “wait-and-see” approach. Leave a company on the scene for at least an hour after you think the fire is totally extinguished. Then, have a company return to the scene every couple of hours thereafter. Explain to the homeowner that the only way to be 100 percent sure that the fire in cellulose insulation is completely out is to totally remove every bit of it from the attic. Do not allow a family back into the home at night to go to sleep if you have the slightest suspicion that the cellulose could rekindle. Such a careful, time-consuming approach may seem like overkill to everyone but the officer who has the overall responsibility to safely return a home back to its occupants.


Just as in the case of cellulose, firefighters are likely to return for a rekindle if they fail to recognize fiberboard or are not aware of its tendency to smolder. Fiberboard is made from ground wood pulp or sugarcane fiber. Its light weight and low density give this material a high surface-to-mass ratio for rapid flame spread and a tendency to support stubborn, smoldering combustion.

Years ago, many residential and commercial buildings were built with ceilings consisting of sheets or tiles of fiberboard attached to 1- 2 2-inch wood nailing strips. Today, there’s a good chance that those buildings have been renovated and that the old fiberboard ceiling is now above and hidden by one or more newer ceilings, gypsum board, or acoustical tiles on a suspended grid.

One clue that there may be more than one ceiling is the height of the ceiling. Compare the height with the age of the building. Old homes, schools, and businesses typically had high ceilings; 10-foot heights were not uncommon. The high ceiling allowed warm air to rise and circulate through transom windows above doorways.

Today, if you find an old home or business structure with a seven- to eight-foot ceiling, expect that more than one ceiling is hanging below the original ceiling. New construction also uses fiberboard in exterior sheathing. Here again, the fiberboard will be covered, usually by aluminum siding or brick fa

Fiberboard’s low density makes it excellent for insulation. Sheets of fiberboard are commonly laid on top of a metal deck or lightweight gypsum roof and covered with layers of felt paper, tar, and gravel. Fire impinging on the underside of a metal deck can ignite the layer of fiberboard insulation (in addition to vaporizing the combustible roof weatherproofing).

Fiberboard insulation can also smolder, undetected, in roofs as a result of fires in restaurant ductwork, flues from industrial ovens, and vents from body shop spray booths that terminate on the roof. Fire in fiberboard is difficult to completely extinguish; it is easy to overlook smoldering patches. Additionally, fiberboard ceiling tile can be an excellent host to flying sparks and embers, spreading smoldering fire in the attic. Look for fiberboard in ceilings, roofs, and sheathing. Thoroughly examine it for small, smoldering areas. Don’t be afraid to strip off a little extra siding or peel back roof covering from around a hot duct or flue. My company has had good luck with adding a little detergent or Class A foam to our streams to enhance penetration into fiberboard.

Ductwork from the hood extended fire on the stove through kitchen cabinets and blew it into the attic. This is clearly a building code violation, but contractors occasionally take the easy way out and terminate the kitchen exhaust in the attic instead of running it to the exterior. (Photos by author.)

The keys to preventing a rekindle in fiberboard are to recognize it and to not be in a big hurry to return to quarters-otherwise, you’ll probably be back.


In most homes, the vent hood, mounted below the kitchen cabinets and above the stove, contains only a light blower and a filter element. Cooking vapors are drawn into the hood, filtered, and blown back into the kitchen. This installation is so common that it can be easy for firefighters to overlook the exception: a kitchen hood connected to exhaust ductwork, similar to a restaurant system.

When a hood is connected to ductwork, the exhaust system can draw the flames of even a minor cooking fire into the hood, through the grease-ladened ductwork, and discharge fire wherever the ductwork terminates.

Well, the exhaust ductwork is routed through the roof to discharge cooking vapors outside, you say. That has not been my experience: I’ve found that many household kitchen exhaust ducts terminate in the attic! Kitchen exhaust ductwork that discharges into the attic can fool firefighters who respond to a kitchen fire and find a “pot on the stove” that is out on arrival. Although the minor fire on the stove is out and there is very little damage in the kitchen, there can be a fire in the attic that can rear its ugly head after firefighters have returned to quarters.

No matter how minor the fire, always check for ductwork connected to the stove’s vent hood. It is critical to examine the entire run of the duct to make sure the system hasn’t spread the fire by exhausting into the attic or, by conduction, to combustibles too close to the duct.

Get in the habit of examining the attic before canceling other responding companies. The attic contains a multitude of ignition sources such as electrical wiring, recessed light fixtures, heating, and air-conditioning units. In addition, attics contain a heavy fuel load of storage, roof, and ceiling embers and possibly combustible insulation. Firefighters who fail to routinely examine the attic on minor fire calls will someday have to go back for a rekindle and find fire raging over their heads.

While on the subject of examining attics, most departments I know of (including mine) gain access into residential attics with a 10-foot folding attic ladder. I believe the National Fire Protection Association or some government agency should study how many dollars in damage have been caused over the years by firefighters trying to maneuver a 10-foot folding ladder (11 feet, two inches when collapsed) around corners in the average size home. I’ve seen firefighters smash lamps, windows, vases, and picture tubes. Also, the 10-foot attic ladder sticks up into the attic scuttle hole, partially obstructing the already narrow opening.

The next time you examine an attic, try a stepladder, mini-extension A-frame, or combination ladder. They’re shorter than the attic ladder and a lot easier to carry and climb and reduce the chances of your firefighters becoming bulls in a china shop.

Preventing rekindles can be tedious, time-consuming work. Recognize those materials that tend to smolder, and watch out for defects in construction that can extend hidden fire. Always balance the damage caused by the firefighters against the damage actually caused by the fire. If you’re ever in doubt about how much damage is justified, ask yourself this important question: “What would I do if this were my house?”

BILL GUSTIN is a captain with Miami-Dade (FL) Fire Rescue (formerly Metro-Dade) and lead instructor in his department’s officer training program. He began his 26-year fire service career in the Chicago area and teaches fire training programs in Florida and other states. He is a marine firefighting instructor and has taught fire tactics to ship crews and firefighters in the Caribbean countries. He also teaches forcible entry tactics to fire departments and SWAT teams of local and federal law enforcement agencies. He is an editorial advisory board member of Fire Engineering.

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