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Recognizing the Warning Signs of Flashover

Issue 8 and Volume 4.

When you ask fire service folks who are in the know about weak areas of training for firefighters, two always seem to rise to the top of the list: building construction and fire behavior. And these two subjects are tied to a lot of firefighter line-of-duty deaths.

No fire department training program can spend too much time on these two important areas. Both have been responsible for firefighter deaths since the beginning of the fire service. The problem: They’re always changing, because technology is always changing.

This month’s Quick Drill focuses on one critical aspect of fire behavior: flashover. To stay safe on the modern fireground, you must understand the conditions that lead to flashover and possess the situational awareness to make changes in the operation to minimize your risk.

What’s Changed
There are a lot of different definitions of flashover; for our purposes, let’s use a common sense definition most of us can agree on: the stage of fire when the contents are heated to their ignition temperatures and flames break out over the entire area almost simultaneously.

We see a lot more flashovers in today’s structure fires than we did 30 years ago, for several reasons. Today, we have a lot more carbon-based interior furnishings, which reach peak temperatures faster and produce up to 500 times the smoke. This can create flashover conditions in just a few minutes, as opposed to the 30 minutes it might have taken in the past.

In addition, buildings now feature thermal pane windows and improved insulation, which trap heat and gas inside. No longer do windows fail easily and rooms vent themselves. Instead, as we make the interior attack, we’re surrounded by a highly flammable and explosive environment.

Our personal protective equipment (PPE) has also been greatly improved, which allows us to make these deep-seated interior attacks. When our gear wasn’t as good and we didn’t have hoods, we simply couldn’t go in as far as we do now. But because we can get in deeper, we experience more flashovers, which has a direct affect on our personnel and our operations. We must make a shift in our tactics so that we’re not relying on staying in until we just can’t take the heat any longer.

Recognize the Conditions
High heat and smoke/gas are the keys to recognizing flashover. Smoke is the fire talking to you. Let’s take a closer look at conditions that warn of flashover:

  • High heat. Flashover is a heat-driven phenomenon. Without heat, the interior contents won’t off-gas and reach their ignition temperatures.
  • Growth-stage fire. A bedroom burning in the back of the house that you can’t get water on provides provides the heat for the flashover event. Remember: Flashover can occur some distance from the area of involvement. If we don’t get water on growth-stage fires, they will continue to feed the fire with two of the three things it needs for flashover: heat and fuel (fire gases).
  • Changing conditions. A rapid increase in the heat level may be a good indicator of impending flashover. Also pay close attention to the smoke conditions. The smoke is loaded with unburned fire gases that ignite under the right conditions. These changes can slow the attack, preventing you from getting that much-needed water on the seat of the fire and allowing the fire cycle to continue.
  • Rollover. The term “flashover” is often misused when interior fire crews see a rollover, which is the ignition of the fire gases in the upper ceiling area. This is the last warning sign before a flashover occurs. It’s very important to be aware that you may or may not see the rollover prior to flashover.

 
Keys to Survival
Following are some keys to surviving a flashover event:

  • Recognize warning signs. Because our PPE now allows us to get in deeper and closer to the fire, we’re more at risk for experiencing flashover, which is why it’s critical to understand and predict the signs leading up to a flashover before it happens. Such recognition may give you time to make changes in the fire attack, such as increasing ventilation or withdrawing from the danger area.
  • Always wear full PPE and wear it correctly. We see folks on the fireground all the time with skin exposed around their hood or with their chinstraps undone or improperly attached. Something as simple as having your helmet knocked off during a flashover—exposing your head to temperatures of 1,500 degrees or higher—could lead to injury or death.
  • Maintain situational awareness. Don’t get so focused on the fire that you miss the big picture. This includes, but is not limited to, your location, your secondary means of escape, fire conditions and where other crews are operating.
  • Stay low. This is old-school, but holds just as true today as it did 50 years ago. In the past, we were taught to stay low because the air near the floor is easier to breathe. Today we have SCBAs, but it still helps to stay low to the ground, where it’s cooler and the visibility is much better so you can read the conditions above you. Today’s PPE has gotten us into some bad habits because it allows us to stand up more than we should.
  • Bring a charged, operating handline. The cooling affect of water is the enemy of the flashover. Using a small amount during the early warning signs of the event will greatly slow the process, allowing time to get out of the area. Note: If you’re searching an area without a line, take extra caution.
  • If caught in a flashover, fight. Get as low as possible and open the nozzle into the overhead to reduce the temperature of the fire gases below their ignition temperature. If operating a fog nozzle, open it to a full-fog above your head and flow water. This will disrupt the thermal balance, creating large amounts of steam. Note: The steam will make interior conditions very uncomfortable and reduce any visibility that was available.

A Final Word
Recognizing the keys to flashover is an essential skill for today’s firefighters. Don’t let fire behavior be a weak area for your crew. Drill regularly on how to recognize, mitigate and survive flashover conditions.
 

 

Drill 1: Flashover in the Classroom

  1. Review the definition of flashover and the conditions that lead to it.
  2. Discuss flashover variables: room size, contents and their combustibility/heat release, insulation qualities of the building, ceiling height and availability of ventilation.
  3. Discuss proper use of PPE at structure fires.
  4. Review warning signs of flashover: high heat, changing conditions, free-burning fire, rollover and heavy smoke.

 

Drill 2: Flashover in the Field

Equipment: Pumping apparatus and the handline that your department most often uses in initial attack.

  1. Let each member of your crew operate the handline so they can practice penciling and aggressive cooling during pre-flashover conditions.
  2. Demonstrate the two nozzle patterns to meet the changing conditions of flashover: full fog (left for life) or straight stream for reach or cooling walls or ceilings.
  3. With two members on the handline, practice opening the nozzle into the overhead while operating at a full fog while members are as low to the ground as possible. The member in the backup position should move as close as possible to the nozzleperson to have protection from the full fog.