Hostile Fire Events: Flashover
What You Can Do
There is only one thing that will prevent a flashover; cool the room. There are two ways to do that, but you don’t have a lot of time. You can vent the room, or cool the air with water.
VENT: Venting can be done horizontally or vertically. The idea is to get fresh air in the room and cool the atmosphere. You may be thinking, “If venting the fire is all it takes, why didn’t the open wall in the photos above vent the fire enough?” Good question. In fact, that’s an excellent question.
Even with one wall open wide, the remaining walls and ceiling held enough heat in the compartment and facilitated the radiant heat feedback, so that the flashover event still occurred. I would suspect that opening the rear of the compartment, or possibly one of the sides of the compartment in addition to the front of the compartment, would significantly affect the ability of the room to retain enough heat to flashover.
Alternatively, vertical ventilation would prevent the flashover, too. The venting though, must be done early in the burning process. By the time you are thinking of venting because of the pushing heat, or the ceiling-to-floor smoke, or the visible rollover, it is too late to vent. Unless, of course, you have a wrecking ball apparatus on scene.
COOL: Water can possibly cool the room about to flash. A straight stream if you have a fog nozzle, or a solid stream if you run with smooth bore. Aim the stream at the ceiling and give the room several, short blasts.
If you have been trained properly, you have been told to never aim a stream at smoke to extinguish a fire. Instead, you should aim the stream at the seat of the fire. That is the method for extinguishing a fire, and it is damned good advice. However, our immediate goal is to cool this container so it does not give us a preview of Hell-on-Earth.
The hottest part of the room is the cocktail-mix at the ceiling layer of the room; the smoke and gasses up there that are about to burst. Shooting blasts of water up there in “bigger drops” (to use a phrase Andy Fredericks favored) will cool the top layers of the thermally stratified layers in the room enough to delay flashover. If you have a combination fog nozzle, turn it to the right for a straight stream.
In Europe, they use a narrow fog stream with good results, but the droplets will do more good (more cooling) if they reach the higher layers of the room. The further up they go before turning to steam, the more heat the water will absorb at the top.
REMEMBER: Flashover means turbulent smoke, a lot of heat, rollover, then a big fireball. Sometimes, you get a heads-up and time to react. Sometimes you don’t.
To Be Continued in Part 2
Stay Safe and Keep Checking Under the Smoke!
Chief Ed Raposo (Ret.)
Photos taken by author
This series of articles takes on a very informal approach in discussing key aspects of Fire Service issues relevant to today’s firefighters and officers. Similar to a post-incident debriefing back at the firehouse, this series, titled “The Kitchen Table Debrief – (Title)” will hopefully foster discussion, and comments Possibly, if we are not careful, we all may actually learn something along the way! This series is a collection of excerpts from a new book called “SmokeEater 101 – Anatomy of the Fire Incident”, and soon to be completed!