The flashover simulator is a training unit designed by the Swedish National Survival Board in 1986. It is the first segment of a four-stage firefighting system. This first stage involves trainees as observers only; subsequent stages take firefighters through practical, hands-on suppression methodologies. This article covers only the first stage of the Swedish system.

The flashover simulator consists of two all-metal (14-gauge steel) shipping containers: the burn module and the observation module. They are connected and are open to each other at the connection point. The burn module–elevated three feet higher than the observation module–is 10 feet long, eight feet high, and eight feet wide; the observation module 20 feet long, eight feet high, and eight feet wide. Total weight of the two modules is 6,500 pounds. There are three doors to the unit: the back/side entry door and two rear doors spanning the width of the module for rapid egress should it be necessary.

Fuel for the training exercise is five sheets of one-half-inch particleboard that line the sides and ceiling of the burn module. A small crib fire is ignited in a corner of the burn module with a portable propane torch. Three instructors, trained (by the manufacturer) in the operation of the simulator, control the progress of the fire and rate of burning to achieve desired effects. This is accomplished by coordinating three elements: a manually controlled roof vent located in the observation module approximately 3.5 feet from its connection with the burn module, a European-style handline with high-pressure fog nozzle, and the back/side entry door.

Students observe the controlled fire while seated on low benches in the observation area. All instructors and students are suited in full turnout gear, including hoods, and SCBA.

The primary goals of the flashover simulator are to teach firefighters to recognize the warning signs of flashover and realize the limits of their protective gear. After a two-hour classroom training session (lecture and video) on the science and warning signs of flashover and safe operating procedures, trainees are rotated in groups of six to eight through the trainer. Time in the simulator is about 15 minutes.


At the Rockland County Fire Training Center in Pomona, New York, managers and instructors realized that our concrete live burn building–the state of the art for live burn training–was not a realistic way to demonstrate fire behavior. We were able to illustrate to trainees only a fire that developed from the incipient to free-burning phases–at which point the fire stopped growing. Trainees were left with the impression that interior conditions at actual structure fires reach a point at which the fire remains steady and nonthreatening. There was no way for us to show trainees the full development–growth, free-burning, flash-over, and decay stages–of a fire. The trainees, in our burn building environment, were led to believe that at every fire they could get low enough to get under the intense heat, their turnout gear would protect them under all conditions, and they could push in as fast and as hard as possible. As instructors, we could tell them about flashover dangers, but they couldn`t experience to a significant degree what we were talking about.

Realizing the need for more realistic training that would enhance fireground survivability, the Rockland County Fire Training Center officially placed its flashover training program in service on October 25, 1994. Since that time, at press time, we have conducted more than 100 burns, each with five to six “simulated flashovers.”

The Rockland unit is one of more than 30 units in operation at fire training facilities around the United States.


The “flashovers” created in the trainer are caused by the lighting of the

preheated particleboard into active flame production and ignition of flammable products of combustion. The results are dramatic, since the flame front travels from the burn module toward the trainees and directly over their heads.

Smoke banks down quickly and reduces visibility in both modules. Frequently, fire “snakes” and rollover are seen in the dense smoke just prior to complete “flashover.” [It is important to understand that the term applied to the fire behavior in the unit does not conform to the current, widely accepted definition of flashover; that is, the occurrence within the modules certainly is not a “simultaneous ignition of all ordinary combustibles in the room” caused by “thermal radiation feedback.” It does, however, meet with definitions of flashover as put forth by the Swedish government, Walter M. Haessler, and William E. Clark (see Clark`s article, “Flashover: The Sudden, Silent Killer,” Speaking of Safety, Fire Engineering, June 1994, p. 26).]

Inside the simulator, heat from a crib fire pyrolizes and ignites the wood lining of the burn module. These gases and the products of combustion are trapped inside. The flammable gases light up first in the burn module, then roll out into the observation module. This action is controlled (simulated) by opening the roof vent, allowing oxygen to enter the module and causing rapid ignition of the hot gases.

The nozzleman directs a few short bursts of water into the fire module, and the flashover is subdued. With the roof vent now closed after providing sufficient oxygen to induce the flashover, the vent man reopens the vent to let out the steam created, and instructors allow the fire to rebuild to another gas-layer ignition.

Control of the vent–rather, controlling the rate of oxygen introduced to the module–indicates the speed, size, and duration of the flashovers. If the vent is left closed, or left closed for too long, the fire will not get enough oxygen to burn freely and, therefore, both cannot release enough heat to drive conditions to complete gas-layer ignition and will create an internal atmosphere of superrich fire gases.

On the other hand, if the instructor is liberal with the use of the vent, free-burning is abundant and flashovers occur rapidly. The flashovers, in this case, will occur even with fairly light smoke conditions. Trainees can clearly see the particleboard and ceiling ignite into active combustion. This is immediately followed by the flame front moving down and toward trainees. The flashovers often pass directly over the trainees` heads, extending the full length of the observation module, even through the cracks between the personnel doors at the rear of the unit. We have learned that by opening the rear doors a few inches, more intense and more frequent flashovers can be induced.

In the observation module, preceding flashover, instructors explain to the trainees what is happening and what to look for–the four classic warning signs of flashover: free-burning fire; dense smoke; high heat; and rollover. They describe the flashover event as it unfolds. When the crib fire grows and begins to involve about 25 percent of the particleboard, trainees can see the pyrolysis process and the resultant heavy smoke being driven off the combustible board by the heat. They are reminded of the flammable gases, what they are comprised of, and their role in the upcoming flashover.

As rollover occurs, trainees are asked, What do you do now? The answer, of course, is to get a copious volume of water on the fire immediately or retreat while conditions are still tenable. Just after the flashover occurs and moves out of the fire module and over the firefighters` heads, trainees experience rapid and severe heat penetrating their turnout gear.

The flame front generally travels fairly slowly (three to five seconds) from the burn module, approximately one foot overhead of the seated or kneeling trainees. Instructors continually remind the students that actual flashovers will be much more rapid and may be hidden in dense smoke. Since our fuel load is only five sheets of particleboard, conditions in the simulator may not be as hot as a real flashover. (Temperatures in the observation module five feet above floor level are approximately 600°F.) We also remind the students that in actual fire situations, firefighters do not have the added benefit of the burning room raised three feet for your firefighting comfort–real flash-overs will bring fire down onto and envelope you. The trainees fully understand the seriousness of flashover when we remind them of this fact.


From numerous live burns and flashovers created in the simulator, we have made some important observations:

“Machoism” and turnout gear cannot overcome a high heat environment. This valuable lesson will last a lifetime with firefighters. After the flashover training program, the firefighter knows that his turnout gear and mental and physical toughness have limits when it comes to heat. There will be fire situations when tactical withdrawal (full retreat) is the only option.

“Thermal collapse” occurs after flash-over. Thermal collapse is felt as a sudden rush of heat at the firefighters in the observation module. Up to this point in the fire`s development, heat has been difficult to detect, as their gear has kept the firefighters very comfortable.

This thermal collapse is felt most severely by the trainees seated closest to the burn module. Even the “toughest” firefighters have to retreat after a certain amount of exposure to intense heat. Firefighters have been trained to get low, under the heat and smoke. After thermal collapse, even the floor is untenable. The lesson driven home is that there is no place to hide, and retreat is the only option. If our training has been effective, firefighters will recognize the warning signs of flashover and retreat will be completed before thermal collapse occurs.

Training with the flashover simulator has encouraged us to reevaluate our previous live fire training. It has led us to question if the live burn training given in our concrete burn structure was giving firefighters false confidence. In live burn facilities, the firefighters usually can get low enough to get under the intense heat. In this training environment, rarely do turnouts not provide enough thermal protection. The flashover training takes the firefighter along the time-temperature curve, from incipient to free-burning to flashover to postflashover conditions. We feel that the value of flashover training will manifest itself on the fireground: When extreme heat and dense smoke are pushing firefighters to the floor, they will understand the fire dynamics, even though the flames may be hidden from view, and react accordingly. Learning from real fireground experience is not always survivable; feeling, witnessing, and reacting on the training ground in this type of unit is survivable. In the flashover simulator, firefighters can be placed safely into conditions that approach the design limits of their protective gear.

“Borderline” training: During our training evolutions, we have damaged turnout gear, and a few vent operators and nozzlemen have experienced minor burns. At first, this training seemed too dangerous, bordering on unacceptable risk. However, after more experience and several strategy meetings, we decided to continue the training with some modifications. An SOP was developed to prevent possible injury scenarios. For example, NFPA 1403, Standard for Live Fire Training, is closely followed. Redundant hoselines from separate water sources are required. Flashover training is not conducted when weather conditions are above 85°F and 85 percent humidity. Immediately after the exercise, trainees remain together as a group, with their instructors, and report to the preestablished rehab sector for a 15-minute rest-rehab-discussion period. Instructors monitor trainees for signs of heat exhaustion or other medical problems and review the training session. With the SOPs in place, Training Center management and instructors are confident that the small risk of minor injuries is worth the lifesaving benefits of the training.

The thermal protective performance of our turnout gear has increased to the point that, in the flashover trainer, firefighters cannot easily detect rising heat levels until thermal collapse occurs. The full protective envelope–helmet with ear flaps down, hood, SCBA, coat, bunker pants, and fire boots–protects the firefighter so well that changes in heat conditions cannot be detected until they are severe.

Some firefighters used to scoff at others who said they used their ears as heat detectors. We feel, based on our experience in the flashover simulator, that the position has some merit. Fully protected, how do you monitor the increasing heat? Is this one of the reasons firefighters are getting caught in flashovers with seemingly increasing regularity?

Sacrificing one`s ears is not a recommended practice. However, until the fire service develops some type of reliable, helmet-mounted “thermometer” with alarm device, it may be argued that ear exposure is an option. This is a very personal decision that must be made by individual firefighters. Without some way of judging temperature in the interior fire environment, we are forced to depend on visual indicators of impending flashover–until severe heat overcomes the thermal protective barrier and we are forced to withdraw immediately.

Wearing a cotton sweatshirt improves turnout gear performance. This simple practice was demonstrated when one of the instructors, operating at the nozzle position, did not wear one under his turnout coat; he was driven from his position in the front of the observation module with a first-degree burn on his right shoulder. The turnout gear was compressed by the strap of his breathing apparatus, allowing heat to rapidly conduct to his skin. Repeated evolutions de-monstrated the value of the sweatshirt.

Trainees in the flashover simulator should be encouraged to move a bit as heat begins to penetrate their turnout gear. Most trainees usually feel heat first on their knees as they sit in the observation module. The conducted heat is minimized by advising them to straighten their legs, increasing the insulation properties of the air space inside the gear.

Since in the simulator, fire is passing directly over the nozzleman, he experiences the worst of the radiant heat from the front, top, and rear. He can protect his hands by putting them “in the shade.” When not flowing water, he should place his hands behind him or under his legs, which keeps them significantly cooler. Areas where the gloves are tight, such as at the knuckles, tend to burn first.

Expect reflective trim on the turnout gear to burn under the heat of the flashover container.

We have found that all OSHA-approved and NFPA-compliant helmets perform well in the flashover trainer. Leather helmets do suffer severe paint damage and need to be repainted after only a few burns. Polycarbonate helmets should not be used in the trainer, as severe deformation will occur. Eye and face shields, as well as other firefighter add-ons, such as flashlights, never survive the heat. If a firefighter depends on what he carries on his helmet, he should expect to do without it during extreme heat conditions on the fireground.

After several minutes in the observation module, breathing apparatus air gets very warm. In an actual structure fire situation, hot air from your bottle may indicate a potentially dangerous condition. This will be a very late warning sign.

Instructors at the front of the observation module have noticed that SCBA face pieces have received what appears to be hairline cracks in the lens when subjected to extreme heat, which distort vision to a degree. Lenses have become soft to the point that they can be “molded” with the slightest push of the finger. After the lens cools, permanent thin lines form that distort vision. As face pieces continue to take extreme heat, they bubble and cloud over, becoming impossible to see through.

We have experienced first-degree burns through the face piece. Heat penetrates through the lens to burn the wearer underneath. As with any radiant heat, shading oneself prevents this.

The designers of the training system teach a nozzle technique called “penciling.” They say that if a nozzleman recognizes flashover conditions, he can delay the flashover by directing short bursts of water into the superheated air. This supposedly cools the atmosphere enough to delay flashover while maintaining the thermal balance and visibility enough for the firefighters to escape. It obviously works well in the limited and controlled conditions of the trainer but appears to be questionable on the fireground. If you have a solid line, why not flow significant quantities of water, absorbing the heat that is going to cause the flashover? We all know of firefighters getting trapped and killed by flashover. We don`t know of any firefighters killed by flashover when they had a hoseline operating, flowing copious amounts of water. In Rockland County, we tell firefighters to keep the line with them during their retreat and keep water flowing through a straight-stream or solid-bore nozzle.

* * *

Many firefighters have formed strong opinions about flashover simulator training programs. This training is not perfect and only simulates flashover, flashover conditions, and warning signs for firefighters to witness. However, we feel it is extremely valuable training that increases firefighter safety and survival. n

In the March Editor`s Opinion, I offered a very brief comment on the flashover simulator developed in Europe and currently in use in the United States. It aroused an interesting and heated response (no pun intended). My thanks to all who wrote in.

My comment was based on some sound secondhand testimony and deductive reasoning. Nevertheless, I admit that firsthand experience is antidotal to what could be–in fact, was–construed as premature judgment. So I decided to take my seat in what is affectionately known as “The Can.” Time to put up or shut up.

I asked Jerry Knapp of the Rockland County (New York) Fire Training Center (RCFTC), who has trained numerous firefighters in the flashover simulator and who expressed an interest in making this training technique more widely known through the pages of this journal, to get me in the door. I was graciously welcomed by RCFTC management, Chief Instructor Walter Morris and County Fire Coordinator Gordon Wren.

I was very careful to make clear to Jerry the extent of my experience, or lack of experience, with high-heat environments. He acknowledged this and treated me accordingly (my sincere thanks). I also asked Jack Murphy, fire official of the Leonia (NJ) Fire Department, who had already experienced The Can, to accompany me for his moral support, for which I am most grateful.

I attended the mandatory preburn safety class along with members of the Thiells (NY) Fire Department. Knapp presented a lecture on understanding flashover and recognizing its warning signs. We covered safety procedures and how the evolution and the fire develop. I was sure to remember the signals: thumbs-up for okay and thumbs-down for trouble and a need to exit the simulator.

My survival training as editor has required a continual and intensive study in firefighting and general aspects of fire behavior. In general, I am very careful not to overstep my bounds as student/facilitator/ information broker, but I am comfortable with and conversant in firefighting theory–all you armchair quarterbacks and shortstops know what I mean. But here, the rubber was about to meet the road. I began to get tense. I began to wonder why I hadn`t worn three sweatshirts as insulation under my gear. Would my gear hold up? Could I take the heat? Would I crawl out of The Can prematurely, to my sublime embarrassment? I understood that the purpose of The Can is not to measure how much pain one can endure, but I did wonder about it.


The first trainee team buttons up tight. I am among them. We pass the check at the safety inspection station and go inside.

Knapp will work the vent on this exercise. He`s got a big swatch of proximity suit material covering his helmet. He directs me to sit down on the low bench right next to him, right up front. I do.

Instructor Tom Bierds lights the fire, and we wait a little while for the fire to develop in the open-sided burn chamber. “Watch the fire develop. Notice the crib fire heating and pyrolizing the wood….” Knapp says. A little bit longer. “Let`s go on air,” directs Knapp. We put in our regulators and give the thumbs-up. We`re ready.

The fire starts to cook, fume, spit. The smoke builds in the burn module and rolls out over our heads, lazily at first but getting heavier each second. “Feel any heat yet?” No. A little longer. The smoke is now maybe a foot down from the observation chamber ceiling. I look up front and see the smoke at the lowest levels of the burn compartment move in a side-to-side motion. “You guys all right?” Jerry asks. Thumbs-up. Jerry begins asking me every 20 or 30 seconds how I`m doing. I`m okay. Thumbs-up.

The smoke is now banking down. We`re getting some fire flashes, small ones, overhead. “Any heat yet, do you feel heat?” Jerry asks us. Just a little bit. Knapp and the crew are manipulating the fire. Knapp gives a minimal vent and asks the safety officer to open the rear doors a bit to let the fire get some oxygen. The instructions are short, to-the-point, practical. They have control of this thing. My breathing gets a little less heavy.

More, heavier flashes overhead. Nozzleman Bob Lagrow directs a short burst from the line, then they bring it back up. I think Jerry opens the vent. The gases now are right on top of our helmets. I see the first snakes shooting right over my head. Amazing.

It`s starting to get hot, uncomfortable. I keep fidgeting around to lessen its effect on my shoulders. Flashes and more flashes. They wet the fire a little and let the fire building itself again. Dense black smoke. The gases are pressing down. Stop the stream. Orders to the door man. Vent. Here comes the fire.

The gases ignite in full force, blowing out across our heads. It is getting very hot. That “thermal collapse.” Now my shoulders are really burning, and I am bending under the fire, a big, long stream of it. I think my hands are burning up. I put them in the shade. I drop off the bench on one knee, move around a little, but I can`t get the burning out of my shoulders. The pain goes down to my elbows. Thumbs-up anyway.

I am breathing in very hot air. I don`t like it one bit. Shoulders, hot air. I forget about time, forget about looking up at the pretty fire. I am trying to think about things that will make me forget about this heat. It is no use. I get almost angry that the only comfort in this heat would be my air, if only it wasn`t so very hot. Thumbs-up anyway.

I don`t hear Jerry`s instructional remarks so well now. I know that the firefighters are rotating behind me and on the bench on the other side. My observational power diminishes as my energy is directed to dealing with the heat.

We go through the damping and building routine a few more times. Finally I have had enough. Shoulders and hot air. I tell Jerry. He directs me to crawl out through the back door. “Stay low!” Murphy reminds me.

I get outside. “You okay?” I`m asked. “Okay!” “Look, his helmet`s smoking.” I remove it–gloves on. I don`t feel bad, now. I know I was in there a long time. About 30 seconds later, the rest of the members exit The Can. I am escorted to the rehab unit. I let out a whoop. Adrenaline. No pain.

I check my gear. The reflective material on my helmet and coat arms are burned away. The eagle is black. The eye shield is distorted. Other than that, the gear seems to have held up very well.

After rehab and a discussion of fire behavior, Knapp, now working the back door for the second burn, calls me back to The Can to see the part I missed. I observe from the back. The nozzleman hits the fire with a fog stream. The trainees are engulfed in an instantaneous, seemingly impenetrable “firefighter`s soup.” Nice effect.

Later, Knapp kindly asks me if I want to go in for a second bout with The Can. Once is enough for me, thank you.

That night, my shoulders feel fine. The next morning, walking past the bathroom mirror, I notice a red shoulder. I turn to face the mirror. Two red shoulders, actually. Just a localized sunburn. I`m almost disappointed. I run through the exercise in my mind, remembering I was up close to the burn module the whole time, and wonder how the instructors do it.

* * *

I applaud fire service efforts to improve training techniques. The flashover simulator represents one of these efforts. Live fire training is, of course, a potentially dangerous undertaking any way you look at it. Any live fire training exercise is only as good–that is, is only as effective, with the lowest risk factor–as the instructors who conduct the exercise. My night in Rockland County proved to me that the Swedish flashover simulator can be used effectively and safely with experienced, talented instructors controlling the unit.

Conversely, it is not imprudent to suggest that any live fire exercise in the hands of irresponsible people can lead to disastrous results. Fire instructors must be vigilant in recognizing all potential risks of their live fire training evolutions and take the utmost care to ensure the lowest possible risk to the trainee. The key is to anticipate the worst and develop procedures to eliminate or minimize the potential for disaster.

The flashover simulator presents a controllable fire environment with very few variables, which is probably its strongest asset. However, it is also true, logically, that when a system relies so heavily on just a few basic elements, that system is more prone to catastrophic failure should one of the elements fail. In the case of the flashover simulator, this means, for example, never loading the burn module with combustibles exceeding or differing from the design specifications; supplying the interior handline and redundant handline from separate, continuous water sources; ensuring that only instructors who are trained and certified in the use of the system operate the system; and checking the venting mechanism prior to the start of each evolution. Nevertheless, even with major system checks in place, various human factors–unpredictable student behavior, tight turnout gear, borderline physical conditioning (even though all participants sign a waiver saying they are in good physical condition)–are difficult to address. All users and future users of this system should realize that injuries–thankfully, minor injuries–have occurred, during both its development and subsequent mass use.

Although flashover is a phenomenon that receives much attention in the fire service community and fire service press, it is not well understood by many firefighters. Indeed, there is international debate by fire science scholars over the definition of flashover. It is important for many reasons that the fire service better understands the flashover event; however, even if the flashover simulator is simply an approximation of true flashover, it is clear from this experience that a fully encapsulated firefighter cannot and will not survive the intense levels of heat generated by a flashover for more than a very short period of time. From the visceral assessment of 500°F to 600°F heat at about the midway depth of the observation module, a greater appreciation of almost instantaneous full-room fire involvement is immediate. Your turnout gear cannot save you if you are deeper inside the building than a few seconds and flashover occurs around you.

I believed this fact to be an obvious one, without ever having gone into a flashover simulator. Why, I wondered, with all the knowledgeable local instructors, national lecturers, texts, videos, and other training vehicles readily available and widely disseminated, should we need to place firefighters in a metal box and throw fire at them to reinforce the obvious? Still, I recognize that seeing and feeling for yourself surely has more impact than words ever will. It is beneficial for firefighters not only to appreciate the limits of their protective gear but to experience the free-burning fire, dense smoke, rollover, and high heat–the warning signs of flashover–all of which are present in the simulator. (Remember, though: The only warning sign that always precedes flashover, according to William E. Clark, Firefighting Principles and Practices, is a sudden or rapid increase in heat at lower levels of the fire compartment.) The “misapplication” of the fog stream in the evolution at Rockland–with the instant steam conversion enveloping the simulator trainees–also is an important lesson.

Still, the flashover simulator is but one tool in firefighter survival training. In a broader sense, your “survival training” is your past, present, and future training and actual fire experience. Beyond the props, it`s your sound tactics, coordinated engine-truck SOPs, good knowledge of fire behavior, and firefighting sense that in most cases will keep you out of untenable situations in structure fire situations. n



BILL MANNING is editor of Fire Engineering and survivor of “The Can.”

JERRY KNAPP is a New York State-certified fire instructor working at the Rockland County Fire Training Center in Pomona, New York. He is also a 20-year veteran firefighter/EMT with the West Haverstraw Fire Department. Knapp has a degree in fire protection.

CHRISTIAN DELISIO is a firefighter with the City of New York (NY) Fire Department and a New York State-certified fire instructor, working at the Rockland County Fire Training Center.

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