Responding to Oil Burner Emergencies

By Frank C. Montagna

The approaching heating season will bring with it increased responses to heating emergencies. These emergencies are often the result of a malfunctioning oil burner. Conditions you usually find on arrival-smoke pouring from a basement or cellar-indicate a malfunctioning heating system.


Puff back/delayed ignition. There are several types of oil burner emergencies to which you may respond. One common type is the puff back or delayed ignition. This occurs when atomized oil is delivered to the combustion chamber but is not immediately ignited. When it finally ignites, an explosion in the firebox takes place ranging from a small thud accompanied by a puff of smoke to a blast that blows the firebox door open and sends a jet of flame across the room. The blast can also knock the flue pipe down. Once the burner door is opened or the flue pipe is down, the burner room and the entire basement rapidly fill up with smoke. If the door is not blown open and the ductwork is not blown down, most of the smoke is channeled up and out the chimney.

A properly functioning oil burner generates little smoke. You will see wispy white smoke exiting the chimney. The color of the smoke resulting from a puff back, however, ranges from dark gray to black, depending on how much soot has been shaken loose from the burner and is entrained in the smoke. Seeing this black smoke exiting the chimney, a neighbor often calls the fire department and reports black smoke coming from the roof.

When you arrive on the scene of the oil burner emergency, you see smoke issuing from either the chimney, if the flue is intact, or the cellar or basement openings. The smoke is relatively cool and deceptively easy to tolerate. However, it does contain carcinogens that require mask use. Basically, all you need to do is shut down the burner, shut the fuel supply, and ventilate the building.

A puff back is usually an emergency-not a fire. It is possible though that, when the puff back occurs, a jet of flame will momentarily leap out from the open door or peephole or that burning oil droplets will be scattered about the basement. The jet of flame or the flaming drops of oil can ignite nearby combustibles. If a great amount of oil is scattered in this way, you may encounter a burning pool of oil on the ground in front of the burner. You may now be faced with a structure fire and, depending on the extent of the fire spread, call for a handline. You can handle small spot fires with a water extinguisher and burning oil with a foam or dry chemical extinguisher. A foam extinguisher should be your extinguisher of choice at an oil burner emergency. It works well on fires in Class A combustibles as well as oil fires. As a precaution, stretch a handline if the fire is out of the firebox.

After fire. Another condition you may encounter is after fire. This occurs when, because of a malfunction, excess oil pools in the firebox and continues to burn after the burner cycles off. When the burner shuts down, the fan shuts down and, as a result, the required quantity of oxygen is not supplied to the flame. The flame becomes oxygen-starved and can produce large quantities of thick, black smoke. The after fire will continue to burn until you extinguish it or until the excess oil is consumed. This is also an emergency-not a structure fire. The fuel burning in the firebox does not necessarily pose a danger, since the firebox is designed to withstand the temperatures associated with an oil fire. It will eventually burn itself out if left alone and if there is not an ongoing fuel leak feeding the fire in the combustion chamber. It is possible, however, for the flame to rise into the ductwork exiting to the chimney. Always check for fire extension around the ducts, especially when they are near joists, studs, or any other flammable material.

When you encounter after fire or puff back, shut down the electric and fuel supply to the burner, check for extension, and ventilate the area and the building if necessary. If the burning oil is escaping the firebox or threatening to extend to the building’s contents or structure, then you must extinguish the fire. Do so with the judicious application of water or dry chemical or foam. If you use water, be wary of a steam explosion that may splatter hot or burning oil. Unless you cool down the hot firebox, the fire may reignite and need to be extinguished again.

Pulsation. A less common emergency, pulsation occurs when the flame repeatedly jumps away from and then back to the nozzle in the combustion chamber, creating a rhythmic pulsation that increases in intensity until it feels like a freight train is speeding past the house. The pulsation can force the combustion chamber open. To prevent the door from opening, a well-meaning homeowner may brace a piece of wood or metal against the door, creating a very dangerous condition. Because the door can’t blow open to relieve the built-up pressure, the burner becomes a time bomb. Severe pulsation coupled with a braced combustion chamber door could cause the burner to rupture explosively. While simply opening the door should stop the pulsation, your initial action should be to kill the power and shut down the fuel supply before approaching the burner.

Another condition you may respond to is the blocked or dislodged flue pipe. This can occur because of a number of reasons. A bird’s nest or other debris in the chimney can block the flue, or a pipe dislodged by a worker or a puff back can result in the flue pipe’s becoming dislodged from the chimney. The result will be a smoke-filled basement or house. Your action would be to shut the electric and fuel supplies and ventilate the area. If smoke has been diverted from the flue and into the structure, also check the building for buildup of deadly carbon monoxide (CO). Because CO, a product of burning fossil fuel, is life-threatening, check all occupants and all parts of the building for CO poisoning. If you find potentially dangerous levels of CO, evacuate the building and ventilate. Only when CO levels are determined safe can occupants return to the building. You may need ventilation fans to clear CO out of cellars and other windowless areas. Fans can also help speed up the ventilation process in other areas of the building.

A myriad of faults can cause an oil burner emergency or fire. Because of the many oil burners in use throughout the country, oil burner emergencies are fairly common.

White ghost. One thankfully rare oil burner-related problem is the white ghost. It is often preceded by hard starting and then by puff back. Eventually, as the condition of the burner deteriorates, the white ghost appears.

The temperature of an oil burner’s combustion chamber can be as high as 2,6007F. If a burner has been operating for some time and ignition fails, and if fuel is still delivered to the hot combustion chamber, it may be vaporized by the existing high heat. The vaporized fuel oil becomes entrained in the smoke, turning it a pearly white and giving it an oily smell. This vaporized fuel fills the combustion chamber, the flue, and the chimney. If the flue is intact and if the combustion chamber door is closed, this flammable vapor vents harmlessly out of the chimney. If the flue piping has been blown down by a puff back or is disconnected, or if the draft in the flue is reversed, the vapor can fill the burner room or the entire basement. Once the fuel oil has been vaporized, all that is needed to trigger a devastating explosion is for the vapor to encounter an ignition source. The ignition source can be provided by the burner cycling into an ignition sequence or the presence of an open flame, sparks, or embers in the basement. This explosion could be accompanied by a large flame front that fills the basement and leaps out of the basement windows and other openings. The pressure from the explosion could cause structural damage to the building. Being in the basement during a white ghost is like being in a gas-filled room when a gas leak ignites and results in a combustion explosion.

A sudden change in smoke color from black to white, accompanied by a strong smell and taste of fuel oil, is a warning sign of the white ghost. Monitoring the color of the smoke escaping from the chimney or building openings on your arrival and noting its change from black or gray to pearly white may give you an advanced warning of the white ghost and alert you to the possibility of an explosion. If smoke suddenly stops coming out of the chimney, suspect a reversal of draft or a damaged flue. The smoke is now exiting somewhere other than from the chimney and can be filling up the basement. If this smoke contains large amounts of vaporized oil, you may be moments away from a devastating white ghost explosion.

Treat the white ghost like a gas leak. Enter the vapor cloud only if absolutely necessary and under the protection of a handline. If you are in the building when the smoke turns white, open your handline for protection and back out. If possible, shut the fuel and electric supply to the burner and stay away from cellar or basement openings. Remember, after the vapor ignites, flames may blow out from these openings. If the building is occupied, consider evacuation, and stretch handlines for protection. If you opt for an interior attack, stretch and have ready a backup line to assist the initial line. Consider the potential for fire spread up though openings in the first floor and via interior stairways as well as from autoexposure to the lower floors via the cellar or basement exterior openings. Stretching interior handlines into the building when a white ghost explosion is imminent will put firefighters in danger of being engulfed in flames and of structural collapse. Only consider this if life is in danger in the building. Instead, be ready to stretch lines to the basement and first floor to control any resultant fire, after you have verified structural stability.

Ventilate the building without exposing yourself to possible injury from the flame that may vent from the basement windows. You can use a fog line from the exterior to help vent the area and to saturate the vapor cloud with water, making it harder to ignite. If you can do so safely, shut the fuel and electrical supply to the burner. Remember, however, that any spark created by throwing the burner’s safety switch may provide an ignition source to trigger the white ghost.


If present, shut off the emergency electrical shutoff to the burner. It is typically found at the top of cellar stairs in private dwellings and is indicated by a red switch plate labeled “Oil Burner Emergency Shutoff Switch” or similar wording. In a commercial building or multiple dwelling, this shutoff may be found outside of the burner room or just inside the door. This, however, is not always a sure method of shutting the electrical supply. The switch may be defective or may not even be connected to the burner’s electrical system. The switch may even be mounted upside down, so that flipping the lever up would actually shut the burner down and flipping it down would turn the burner on.

At all oil burner emergencies, one of your first actions should be to shut off the fuel supply to the burner. This will prevent any additional fuel from being added to an existing fire. Two fuel shutoffs may exist, one at the tank and another at the burner. You must shut both as a precaution if safety permits, because one may not function properly and may continue to allow fuel to flow to the burner. If the shutoffs do not stop the flow of fuel, you may be able to crimp the copper piping supplying fuel oil to the burner, but take care not to rupture the pipe.

Generally, it is a good idea to stay away from the front of an oil burner when operating at oil burner emergencies or fires. This is where you will find the door to the firebox and the peephole, and it can be a dangerous place should the door be blown off or a jet of flame leap out of the firebox. When it is necessary to operate in the front of the burner, stay low, beneath the firebox door and to the side if possible. This should place you out of the way of the door and any flame that is blown out of the burner.

Be alert to the possibility that the oil burner might use natural gas rather than electricity to ignite the oil. This is the case in some larger burners in commercial occupancies as well as in large apartment houses. An oil fire in such a burner might damage the gas line, resulting in a gas leak. Shut down the oil feed and the gas supply.

When you are called to an oil burner-related incident, you are expected to mitigate the hazard, not repair the problem. Repairing the problem leaves you and your department exposed to legal action should the burner malfunction after your repair, so limit yourself to removing the danger.

Issue an order to have the burner serviced by a licensed oil burner repair service. If the occupant turns the burner back on after you leave the scene, it is likely that the problem will recur or worsen. You will be called back to the scene, and this time it might prove dangerous to the occupant or to firefighters. You must make sure that the occupant understands that the burner is not safe to turn back on.

There are many possible causes of oil burner emergencies and fires. Fortunately, despite human error and poor maintenance practices, the millions of oil burners in use today function without a mishap year after year. When they do malfunction, the fire department is called and usually remedies the situation with little effort. But never forget that these seemingly harmless emergencies can and sometimes do turn deadly, whether it be from fire, explosion, or carbon monoxide poisoning, and you must be ever on guard against such instances.

A typical fuel oil system, tank in the cellar. Note the location of the shutoffs.


One of the first actions you should take is to shut the fuel supply to the burner. In addition to the shutoff shown here, another one may be present at the fuel storage tank. Shut both of them. (Photo by author.)


FRANK C. MONTAGNA, a 30-year veteran of the fire service, is a battalion chief with the Fire Department of New York. He has been an instructor at the FDNY Probationary Firefighters School, the officer in command of the FDNY Chauffeur Training School, and an adjunct lecturer at John Jay College in New York City. He is a member of the FDNY Chief’s Association and is the author of Responding to Routine Emergencies (Fire Engineering, 1999). Montagna has a bachelor’s degree in fire science and lectures on firefighting-related topics.

Fuel Oil Explosions

By Vincent Dunn-Fuel oil explosions kill and injure firefighters in several ways. The blast can blow personnel across a street; flying glass and shrapnel can decapitate; flame accompanying the explosion can cause serious burns; and an explosion can collapse walls, partitions, and iron shutters, crushing firefighters beneath them. A fuel oil explosion is one type of blast that occurs at fires. Fuel oil comes in several grades, number 1 to 5 grade oil, and has the following general fire hazard properties: a flashpoint of 1007F to 1507F, a flammable (explosive) range of 0.7 to 5 percent when mixed with air, and an ignition temperature of 4947F.


Fire protection engineers classify explosions into three broad categories: physical explosion, physical/chemical reaction, and chemical reaction. A fuel oil explosion would be classified as a chemical reaction-type blast called a combustion explosion. The same chemical reaction and explosive ingredients are present in a fuel oil explosion as are in any ordinary combustion explosion: fuel, oxygen, and heat. The fuel in a combustion engine explosion driving an automobile is gasoline; the fuel in a fuel oil explosion is diesel oil vapors.

Fire protection engineers define the term explosion as an “effect” produced by a sudden violent expansion of gases. One of the “effects” of an explosion is shock waves, which shatter windows; blow down firefighters; and collapse walls.

There are two important facts to know about any other type of explosion. One is that an explosion can occur even though the gas or vapor does not fill the entire room. If the explosive mixture concentration of fuel oil, air, and heat are in one corner of a large, smoke-filled cellar, the entire area could explode when firefighters enter to search and allow fresh air to enter with them. The other fact is that it does not take much explosive pressure in a confined space for an explosion to cause destruction and death. (For more information on explosion pressures, see the NFPA Fire Protection Handbook, 18th Edition, Section 1/Chapter 6, page 1-69.)


Fortunately, firefighting experience shows us most explosions occurring at fires such as flammable liquid and fuel oil explosions are low-pressure blasts and create peak pressures less than 7 to 8 psi. Glass shatters, firefighters are knocked down, and partition walls collapse.

We must determine ways to manage and control the risk of explosions at fuel oil firefighting operations. We must develop ways to reduce chances of death and injury from such an explosion. There are firefighting tactics that can reduce the destructive effects of a fuel oil explosion. The recognized tactics include venting, quenching, and flanking.

Venting. Opening doors and windows to the cellar areas is one of the most effective methods of protecting firefighters from a fuel oil explosion. Even if the explosion occurs, the blast may be diverted out of the vent opening away from the firefighters advancing the hoseline.

Quenching. Quenching the superheated confined fire area is another safety and survival tactic firefighters can use to prevent fuel oil explosions. Before entering a room that exhibits signs of an explosive atmosphere, position a charged hoseline near the entrance. Firefighters in full protective equipment should immediately discharge a hose stream into a fire area when it is opened up. This water can cool a potentially explosive atmosphere. This action-taken before the searching firefighters and entrained air enter a burning, confined, potentially explosive fire area-might break up the explosive mixture. This is not as effective as roof venting, but sometimes it is the only alternative.

Flanking. When there can be no venting or quenching, firefighters can protect themselves from a fuel oil explosion by flanking a doorway with hoselines. The officer in command can order one or two hoselines into position-each one positioned at the side of a door leading to the room that is suspected of exploding. After the hoselines are charged with water and firefighters are in full protective equipment, the door and windows are vented. Firefighters are then safely out of the path of any potential explosive blast coming out of the opening. Water can be directed into the potentially explosive area.


We must teach the warning signs of fuel oil explosions to rookie firefighters. The signs are reversal of air pulling smoke back into a smoke-filled doorway, black smoke pushing out around a closed door or window frames, and glass windows stained with smoke condensation and pulsating from the pressure of a fire. These warning signs are important to know but, even more important, firefighters must know that explosions happen fast, sometimes even too fast for them to take cover and protect themselves. The only real protection from the blast of exploding fuel oil or any explosion is full protective gear: helmets, hoods, gloves, boots, bunker pants, coat, and face mask. Protective fire gear may be hot, may be cumbersome, and may slow you down; however, the equipment that firefighters caught in an explosion have will determine whether they survive the blast and how serious the burns will be.

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