The Four Warning Signs of Flashover

By Joseph Berchtold

There are four warning signs of a flashover that occur before a flashover occurs. However, as we will see, they may or may not be present. As fire development and growth occur and continue being placed in check by a properly placed hoseline, we will eventually reach flashover once we have the right mixture of fuel, temperature, and oxygen. Flashovers have increased in size and intensity and reduced in the time they take to occur (photo 1).

(1) Flashovers have increased in size and intensity. (Photos by Kevin Paul unless otherwise noted.)


Rollover is a reliable sign of a flashover but because of thick, black smoke it may not be visible. You may not be in the room that is on fire; therefore, you might not see it. You may not be looking up for it. Your best means of protection is the use of a thermal imaging camera (TIC). So, for the above-mentioned reasons, you may miss the warning signs of rollover (photo 2).

(2) Rollover.

Free-Burning Fire

A free-burning fire is also a reliable and the most obvious sign. If you have smoke being produced, then you must have a fire. Say you are outside; miss seeing the smoke because you didn’t complete a 360; and are not in the room or unable to see the fire because of the thick, dark smoke. You might not know how intense the fire is or what is burning. Not seeing the fire or knowing what stage the fire is in, you might not realize how close you are to a flashover (photo 3). A TIC is one of the best inventions we have today to not only help to locate victims but also to see the warning signs of a flashover. Never leave it on the front seat of the apparatus.

(3) A free-burning fire.

Thick, Black Smoke

This is another reliable sign of a flashover event, but how may of us are trained in reading smoke? We all should be. Did you see the rear yard where the smoke is pushing from a window on the second floor? Is it too dark at night to see the smoke? Did you not pay attention to it? Are you inside the structure, unable to really determine the intensity? Is it being scrubbed by the building? (The building and material in the building have removed some of the black heavy particles that are in the smoke and give it its color. Therefore, changing its color from dark brown to a lighter color may make you think that the fire is not that bad (photo 4).

(4) Thick, black smoke. (Photo by Chris Saraceno.)

Your location on scene as well as not looking up may keep you from seeing the signs.

Intense Heat

This is the last sign you will see or rather feel. By the time you feel the heat, you are seconds away from being caught in a flashover. However, by crawling thought the thick, dark smoke and placing your gloved hand up for a few short seconds (as high as you can get it) to attempt to measure the heat layer well above your head, you may just be able to determine the heat level and know not to go any farther. You need to measure that heat before it pushes on your back. To do this, it’s as simple as raising that gloved hand up high as you can into the smoke. Leave it there for a second and then pull it down. If the heat penetrates your glove and you can feel it, this might just be telling you that you should not crawl down this hallway or into that room, as you are seconds away from a flashover. This is very hard to determine, especially if you do not have a TIC. Our fire gear does such a great job of encapsulation that we can’t feel the heat. It takes time for that heat to penetrate the layers to the point where you are getting warm (photo 5).

(5) Intense heat.

Heat can also be a funny thing. Firefighters have been misled by high ceilings–i.e., large box stores or family/great rooms with vaulted ceilings–by fire hiding in or above the ceiling, in a cockloft, in a drop ceiling, or in a void space.

Aside from a TIC, having good company officers giving the incident commander detailed and timely progress reports about the fire and the conditions of the smoke might be the only other thing that will help you. These reliable 360 radio reports from an area you can’t see should help you in making the decision whether a flashover will or has occurred (photo 6).

(6) Provide a 360.

There is no simple answer as to when a flashover will occur. There are only these four warning signs, and they may or may not be present. As a firefighter, it will be a constant struggle to work at your skills in reading flashovers. Just know this: When it doesn’t feel right, it probably is not right. Your gut is usually never wrong. Better to be safe and back out than to be a statistic  (photo 7).

(7) The warning signs may or may not be present.

Joseph Berchtold is a 29-year veteran of and a deputy chief in the Teaneck (NJ) Fire Department. He is a New Jersey state-certified level II instructor, arson investigator, fire official, and EMT. He’s an instructor at the Bergen County Fire Academy and has been an FDIC H.O.T. instructor for 19 years. He produced the Training Minutes on “Fire Attack.” He has a B.S. degree in business management.

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