Flashover Recognition

  Several weeks ago, I happened to be out at a fire department training center as the department trained with thermal imagers. The only training they planned to conduct was to get the flashover container hot and then go in and see what it looked...


  Several weeks ago, I happened to be out at a fire department training center as the department trained with thermal imagers. The only training they planned to conduct was to get the flashover container hot and then go in and see what it looked like with their thermal imager. The thought...


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Several weeks ago, I happened to be out at a fire department training center as the department trained with thermal imagers. The only training they planned to conduct was to get the flashover container hot and then go in and see what it looked like with their thermal imager. The thought was that full-scale, live-burn training was a waste of time when they could just fast-forward to "the worst imaginable scenario and see what the imager would do."

I asked them if this was something that they commonly ran into in the course of their firefighting, to which their response was, "We are an extremely aggressive department, so yeah, we see them all the time. Almost every fire, one of our crews is involved in a flashover!" Mistaking my hesitation as worry about damaging the imager, the firefighter leading the evaluation asked if I was scared. My answer was, "Yes, but not for the imager."

Flashover: A Threat To Firefighter Safety

You don't have to research very far to find information about firefighters who have lost their lives to a flashover. Plenty of information and training is readily available from multiple sources, but they all seem to come to one really simple conclusion: When a flashover occurs, you do not want to be there!

Being present at the moment of flashover is much akin to throwing yourself on the tracks in front of an oncoming train. Only bad things are going to happen. Your personal protective equipment (PPE) is going to provide only limited protection against this extreme event and the results can be devastating.

The International Society of Fire Service Instructors (ISFSI) produced a training program, "Flashover Recognition and Survival," in which it was demonstrated that an average firefighter, wearing full PPE and without a hoseline, can move at approximately 2½ feet per second. Given only two seconds to exit once a flashover occurs, simple math then establishes the "Point of No Return" as five feet from the entrance. Not very far, is it?

The reason is that flashover happens fast. The fire conditions progress rapidly from what was a hot fire to what becomes an inescapable fire. The images accompanying this column represent a six-second window of a fire conducted by Eastern Kentucky University last spring. We placed a thermal imager in the room and let it run as the room flashed over. You can see in Figure 1 that the fire is in its growth stage, but rapidly progresses through to a complete flashover in less than six seconds (red indicates temperatures in excess of 1,000 degrees Fahrenheit).

It should also be noted that flashover is a momentary phenomenon (see Figure 2). It is a small window of time marking the change from the growth stage to the free-burning stage. At any other point of the fire, the thermal imagery will look more like the image in Figure 3, which was taken just 39 seconds prior to Figures 1 and 2. The sudden release of BTUs and the disruption of the thermal layering that occurs at the moment of flashover is both sudden and dramatic and not the time to be looking at your thermal imager.

Flashover With A Thermal Imager

So how will a thermal imager help if you find yourself caught up in a flashover? Easy — it won't. If you find yourself inside an area at the time of flashover, the thermal imager can't do a thing for you. It's simply too late at that point. According to ISFSI, you have two seconds to react — five feet. If you spend even one second looking at your imager, you had better be closer than 30 inches from the door, since you consumed half of your escape time looking at the imager.

The problem here is two-fold. One is the mistaken belief by some firefighters that a flashover is an extremely common occurrence. The other involves claims that thermal imagers can generate an image during a flashover so that firefighters can find their way out. This then gives the firefighter the impression that being present during a flashover must be a common occurrence; otherwise no one would have developed a product with this scenario in mind. These are dangerous beliefs.

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