One of the primary killers of firefighters is flashover. Flashover doesn’t care how many years you have on the job or how well trained you are. Countless lectures and videos have been dedicated to flashover survival over the years, and many props and chambers have been constructed to help educate firefighters on the warning signs of impending flashover. Despite all the education, training and knowledge we’ve absorbed, flashover still presents a major hazard, and we must know how to combat it. But first, we must understand what a flashover is and what it isn’t in order to better recognize the signs of flashover and other rapid-fire events.
Flashover: How it happens
Flashover is not a rare phenomenon. In fact, it has the potential to be at every fire to which we respond. When a fire starts, it immediately begins sending out heat and light as energy, and the heat is carried via convection, conduction and radiation. Recalling our firefighter training, we should remember that conducted heat is direct flame contact, and depending on the material being exposed, can yield rapid fire growth. Newer and more modern fuel packages in synthetics, plastics and resins can generate tremendous energy that contributes to rapid fire growth. Simultaneously, these fuels will produce vast amounts of smoke, which we know to be fuel. The smoke becomes super-heated via convection and carried throughout the structure. Radiation, or heat waves, are bounced off surfaces such as the ceiling, walls and floors, and sent back to the flaming fire, which also compounds its growth. This is the growth stage of fire.
As more fuels ignite and the temperature increases, the energy of the fire grows exponentially. Assuming that plenty of oxygen is present, the fire will continue to heat all surfaces to their ignition temperature. Fuels and contents remote of the flame will begin to pyrolysize and off-gas, and then all surfaces rapidly ignite. This is the flashover, and this is why a flashover is not mythical or surprising. It is simply the transition from a growth stage fire to a fully developed fire. In modern terms, the fire has moved from a vent-limited stage to a fuel-limited stage.
It should also be noted that when it comes to structure fires, we sometimes forget or downplay the impact of compartmentation. In buildings, a fire is going to start in a room or some type of compartmented space. For the sake of simplicity, take a private dwelling bedroom fire. The fire starts, grows, builds and flashes the bedroom, then moves to the next space because smoke and fuel will move from areas of high pressure to low pressure. Given that spaces remote from the bedroom have less pressure than the bedroom, the fire will begin to move via conduction, convection and radiation out of the bedroom and down the hallway to the next available box. Each time the fire moves, the fire grows. The cycle repeats itself – growth, flashover, fully-developed. The smaller the compartment, the faster the cycle, as more energy is required to flash a larger compartment like a living room or an open office space in a commercial building.
UL and NIST have conducted numerous tests to show what happens to modern fires once they become vent-limited and receive a steady supply of oxygen from an open front door. Once the door is opened, fire rapidly intensifies, and flashover occurs because the surfaces and fuels inside the building are already sufficiently heated. The door opening could be the result of fire crews or even neighbors or police officers trying to get in to help save trapped occupants. Doors and windows can also fail from the heat and energy of the fire. An opening is an opening, and the fire will rapidly intensify and flashover will occur.
Protection from flashover
How can firefighters combat these challenges? It depends on what you have available. From an engine company standpoint, the answer is water. Flashover is a physics game – the fire is heating up surfaces and fuels to ignite everything rapidly. Therefore, we must cool the fire.
Once attack lines are stretched, begin flowing water into the space and cooling. The “C” in SLICE-RS is to cool from a safe location, meaning that we should no longer be crawling down a superheated hallway to “get close to the fire” but rather should be deliberately targeting our water onto all surfaces as we methodically move down that same hallway. If staffing allows, move interior and begin to reverse the available flowpath by cooling the convective currents of fuel and stopping fire progression. If resources are not available, cool from the exterior and get water on the fire. Our goal is to confine the fire to the area of origin, which is the “C” in RECEO-VS, the strategy of fireground and engine company operations – Rescue, Exposure control, Confine the fire to the area of origin, Extinguish the fire, Overhaul, Ventilate as needed, Salvage as needed.
Flashover temperatures have been measured to be reliably around 1,100 degrees F. If we use the water to cool the fire below those temperatures, the flashover won’t exist. Cool high into the smoke layer, but also cool the walls and floor around you. Move and flow the hoseline, do not conserve water. Even if a water supply isn’t readily available, plan to exhaust the engine’s tank water to cool the fire and knock it out. Subsequent arriving companies can supplement the primary attack engine’s water supply.
What if a hoseline isn’t available? If arriving on an apparatus without the ability of water such as a truck company, then cooling the fire isn’t an option. In this case, limit the availability of oxygen. Always donning turnout gear and SCBA, move interior for search, and isolate the fire from the rest of the building. When conducting searches from a window, ensure that you check the hallway for conditions, and then isolate the room you’ve entered by closing the door. This will allow for smoke to lift and ventilate from the opening you’ve created, which will speed up search operations and bring fresh air to any victims in the space, while simultaneously limiting oxygen to the fire due to the barrier you’ve created. In the absolute best-case scenario, close the door to the room that is fully involved in fire. If the door is gone, consider taking off a door from another room and putting it over the opening so buy some time.
After searching a room, move to the next space and close the door behind you. Again, this will limit the convective currents from targeting other fuels away from the fire compartment and will limit the available oxygen from getting to the fire. Relay pertinent information to the engine company regarding fire and smoke conditions so that proper water flows can be established to combat the fire. Consider using a water can to provide a solid 50 seconds of water application for protection.
Surviving flashover
What happens if you are caught in a flashover? It will be very bright and blinding and quite disorienting, so try to remember this guidance:
Stay low and move out of the space. Some firefighters may remember the FDNY videos from the 1980s explaining how far into a room you can go and survive a flashover – about 6 feet. With our modern turnout gear and enhanced thermal protection, we can move farther into a space, but our facepiece from the SCBA is still highly vulnerable and will delaminate and melt at 500 degrees. Therefore, we should train to recognize the signs of flashover to avoid being caught in one.
Highly pressurized black smoke moving rapidly down a corridor or to an opening is a key indicator of a very hot fire. That smoke is fuel, and the speed signals the tremendous energy it has and is looking for a fresh supply of air. Visibility will be zero, and you will feel heat on your ears, neck and shoulders as you crawl. These are indicative of a rapid-fire event about to occur.
- Back out or attempt to isolate yourself in a room behind a closed door if retreat isn’t possible.
- Know the locations of exits, and prepare to bail out if the fire cannot be cooled.
- Transmit your conditions to incident command and conserve your air supply.
- Work to self-extricate and give your location so that rapid intervention crews and nearby companies can come to your aid.
Kill the flashover
A flashover should not be a game of survival but rather a murderous rampage that we take on as the fire department. Our aim is to kill the flashover and to stop all fire progression from the moment we arrive on scene. We should be quickly and deliberately stretching attack lines and moving into the space under the cover of heavy water application to reverse the flow path and cool the fire below flashover temperatures. We should be transitioning a vent-limited or fuel-limited fire into a decay stage fire with our water application. If fire attack is not a viable option due to a lack of water, then enter searchable spaces and isolate the fire by closing doors and creating barriers between the fire and the rest of the structure. Understand that fire propagation is a time game, and that everything being exposed to fire is weakening. Aggressively move through the space, stay low, and be alert for signs of impending rapid-fire events such as high temperatures and high-velocity smoke. We must continue to train on how to recognize and kill the flashover by being aggressive and prepared firefighters.
This article, originally published on April 07, 2024, has been updated.
