Flashover Simulators Provide Life-Saving Training

Firefighters can learn the indicators of flashover in a safe, realistic training environment

By Charles L. French Jr
Published Wednesday, December 1, 2010 | From the December 2010 Issue of FireRescue

The first time I heard the words “the Swede,” I was watching a movie called “Heartbreak Ridge” starring Clint Eastwood as a rough and tough Marine Gunnery Sergeant trying to train a group of misfit recon Marines. One of them, a large, muscle-bound guy who’d just got out of the brig, was nicknamed “the Swede.” Eventually, Eastwood’s character faced off with the Swede and knocked him out with one great punch to the chin.

I remembered that scene recently when my department acquired a Swede Survival System flashover trainer. Although these two Swedes are very different, the lesson I learned while watching “Heartbreak Ridge” applies to flashover training as well: Understanding the hazards that you may face and being ready for them is a formula for survivability in almost any situation.

Although my department uses the Swede Survival System, other flashover trainers are available. This article will focus on the broader concepts in flashover training and what a flashover trainer can provide.

Flashover 411
A flashover is a transitional phase that happens between the growth stage and the fully developed stage of a fire (see figure). During a flashover, all the objects within a space are heated to their ignition point due to thermal radiation feedback. Auto ignition of all the contents, including the smoke, occurs in the room almost instantaneously, and the entire space is consumed by fire.

The temperature range in a room when flashover occurs lies somewhere between 900 and 1,200 degrees F. The heat produced by flashover is not survivable for more than a few seconds, even when wearing full PPE and SCBA. If you survive such an event, you’ll likely be severely burned.

We’re faced with the possibility of a flashover at every fire we respond to. With the development of smoke detection systems and traffic-control devices, we’re getting on scene faster than we did years ago, and this means we’re more likely to go into a structure before flashover occurs. Products of incomplete combustion (smoke) are basically fuel; when we enter these structures, we’re “swimming” in that fuel.

Carbon monoxide (CO) is also present at every fire, and it’s a contributing factor to flashover as well. The auto-ignition temperature of CO is 1,128 degrees F, similar to temperatures found during flashover. Therefore, there’s a real possibility that flashover conditions may exist or could rapidly develop during interior operations at any fire. Without an understanding of and ability to recognize flashover conditions, personnel are at great risk of serious injury or death.  

Learning from Oklahoma City
On March 8, 1989, at 0809 hrs, three Oklahoma City firefighters died during a routine house fire that involved a small, single-story, two-bedroom home. The cause of all three deaths was attributed to a flashover that occurred within minutes of an interior fire attack being initiated. The effect on the department was devastating, to say the least. At the time, the Oklahoma City Fire Department had not lost a firefighter in the line of duty in 39 years.

During the incident, flashover indicators were present, with high levels of heat and heavy smoke being reported by first-in companies. However, the fire gave a false indication that it had vented itself through the roof. Unknown at the time to the fire crew operating inside was that the house had two additions. The fire they saw outside the structure was between an existing roof and one of the two added-on roof coverings.

The fire crew gained access through the front door while carrying a preconnected hoseline. Once inside, they crawled through a 30' living room to a doorway toward the rear of the house, where they found what they thought was the seat of the fire in a bedroom. They knocked down the main body of the fire and thought it was extinguished, so they put down their hoseline and made their way toward the exit for reassignment. That’s when the flashover occurred. The additions made to the house held in a tremendous amount of heat, which built up, contributing to the flashover.

One positive outcome of this tragedy: The citizens of Oklahoma City passed a 0.0075 cent sales tax increase, earmarked to help better equip their fire department and to train its members. Needless to say, however, the price that this community paid and the lives that were affected by this event should not be the way to secure fire service funding.

Flashover Indicators
The most effective way for firefighters to minimize their risk of being caught in a flashover is by maintaining an awareness of developing fire conditions and controlling the fire environment with effective water application and ventilation tactics (IFSTA 5th Ed). Flashovers push out of openings, such as doors and windows, faster than a firefighter on their hands and knees can move. When a flashover happens, you may not have enough time to escape, which is why it’s so important to practice your firefighting skills and understand the indicators of a flashover.

A flashover can present itself in a variety of ways during a fire incident. The following are indicators that an impending flashover is about to occur:

  • Buildings: Flashover can happen in any type of structure, but certain building features and contents contribute to how fast a flashover can develop, including fuel load, ventilation profile and thermal properties. The size of the room is also a contributing factor; the smaller the room, the faster flashover conditions can develop. Contents also add to the hazards. The synthetic materials commonly used today have a higher heat release rate than natural products and therefore create flashover conditions much faster than in years past.
  • Smoke: Smoke build-up, density and pressurized movement are typically strong indicators of an impending flashover. Remember: Smoke is a fuel, and smoke conditions indicating a rapidly developing fire should not be ignored. After making entry, the presence of thick black smoke, hot gases and layered smoke are strong indicators that a flashover is about to occur. Heavy smoke banking down with increased heat, keeping firefighters on their hands and knees, is also a strong predictor.
  • Air flow: A strong air current in which air is moving inward and smoke is pushing out should also be a flashover indicator to fire personnel. This is when ventilation can be helpful, if performed correctly, in controlling the heat build-up within the structure. Vertical ventilation can help channel the smoke and the hot gases out of the fire area, reducing the possibility of flashover. However, if ventilation isn’t performed correctly, it can be a contributing factor in a flashover situation.
  • Heat: Rapidly increasing temperature or high heat build-up is also a strong indicator of flashover. However, this is usually a late indicator and means that everything in the room is about to ignite.
  • Flames: The combination of flames traveling out of the hot gas layer and smoke (sometimes referred to as “snaking” or “ghosting”) is another indicator to watch out for. This can be confused with rollover, but it precedes rollover behavior and exhibits a snake-like movement pattern that moves more slowly than rollover flames. The problem for firefighters with this indicator is that it may not be visible due to the smoke conditions in the structure. A thermal imaging camera (TIC) can help firefighters see through the smoke and identify this condition.
  • Rollover: This is an event in which the unburned gases accumulate at the top of a compartment and the smoke ignites, then flames begin to propagate through the hot smoke and gases and roll across the ceiling. Rollover will precede flashover and is a strong indicator that an impending flashover will occur.

Flashover Training
Now that we’re aware of the indicators associated with flashovers, how do we train and gain the necessary experience to be able to recognize them? Flashover simulators like the one my department acquired are an excellent way to train firefighters in safe, yet realistic conditions.

A flashover simulator works like a split-level room, with an upper level for the flashover to occur and a lower level in which firefighters can observe the conditions of the upper level. On the top level, plywood panels used for the fire load are inserted on the walls and ceiling. Then a 55-gallon drum stuffed with wood scraps is set up as a burn barrel to help get the fire started. Once everything is set up, the firefighters and instructor(s) crawl into positions on the floor of the lower level. They watch as the smoke builds and banks down to the level of the floor of the upper container. They can observe the conditions of a flashover begin to develop, as “snaking” of flames begins to stream out into the smoke. Then a small air vent on top of the flashover simulator is opened, and almost instantly, the smoke above the firefighters turns to flames.

To control the flames in our simulator, we use a pre-connect with a fog nozzle and apply three straight bursts from one side to the other, then reverse our pattern with three quick medium-sized fog bursts. At this point, we rotate and watch the whole thing again until each member has taken a turn on the hoseline. This gives everyone a chance to watch a flashover take place several times, become familiar with the indicators of flashover and learn how just a little bit of water, with effective nozzle tactics, can cool the atmosphere.

Firefighters get to see how smoke builds and stratifies, and how it banks down and out when it has no place to go inside a compartment. They get to feel a bit of the heat associated with a flashover and see how untenable conditions are in a room that’s flashed over, making search-and-rescue operations pointless. Finally, they get to learn how, with just a small amount of water from a hoseline, they can change the conditions and cool down the atmosphere without creating a disruption of the thermal balance in the room.

I’m sure some of you reading this article are thinking, “This sounds great, but my department could never afford one of these props.” But grant funding can help, and you may be able to pool resources with regional training centers, community colleges or state training agencies. You can also look into conferences where such classes are offered. Even a few times through a flashover simulator can provide invaluable experience.

Conclusion
Although a flashover simulator does not actually produce a “true” flashover, it can provide an excellent opportunity to teach and recognize the signs of an impending flashover and how to effectively prevent it, thus improving your chances of survival. Training combined with experience allows us to develop the skill sets and knowledge we need when we go to combat, keeping us from becoming another fatality statistic.

If nothing else, I hope you’ll gain more knowledge about flashover and study the warning signs so that you know what to do if you ever find yourself in these dangerous conditions during a fire incident.

Resources

  1. Oklahoma City Flashover [DVD]. American Heat Video. 1989.
  2. Swede Survival System. Drager Safety Inc. 2008. Retrieved Dec. 31, 2009. from www.swedesurvival.com.
  3. Flashover. Firetactics.com/3D Firefighter. 1999–2008. Retrieved Dec. 31, 2009, from www.firetactics.com/FLASHOVER.htm.
  4. Goodson C, Murnane L, eds. IFSTA Essentials of Firefighting and Fire Department Operations, 5th ed. Fire Protection Publications/Oklahoma State University: Stillwater, OK, 2008.
  5. Dunn, V, McGee M (director). Flashover [DVD]. Penwell Corp./Fire Protection Publications/Oklahoma State University: Tulsa, OK, 2006.

    
The Swede Survival System
For the past 4 decades, the Swedish fire service has been developing techniques to help combat flashover. One such technique, the Swede Survival System, is made in Skovde, Sweden. Its main purpose is to teach firefighters how to deal with flashover in a controlled and safe training environment.

The Swedish were some of the first to introduce nozzle tactics utilizing fog patterns and short, controlled spurts to help firefighters cool the hot gases found during a fire. Through these techniques, they discovered they could reduce the heat in the environment without disrupting the thermal balance.

They were also some of the first to develop fire training simulators out of steel shipping containers. Their Swede Survival System is now used to train fire service personnel worldwide about the risks associated with flashover and how to identify the indicators of this powerful and deadly event. 

Comment Now: Post Your Thoughts & Comments on This Story

A flashover simulator, like Tulsa Fire Department's simulator shown here, works like a split-level room, with an upper level where the flashover occurs and a lower level in which firefighters can observe the conditions of the upper level. Photo Charles L. French
Flashover Tool: The Stages of Fire Development



PHOTO GALLERIES

Fire in the Can

Published Monday, April 18, 2011
Firefighters can learn the indicators of flashover in a safe, realistic training environment.