Flashovers are extremely dangerous and have claimed the lives of too many firefighters over the years. Many articles and training programs have been produced to help firefighters understand a flashover situation and how to escape safely. In a flashover, fire conditions progress rapidly from a hot fire to what becomes fire that is inescapable.
As an instructor, I have heard firefighters say that a thermal imager (TI) can help you during a flashover. This is not true. A TI is a tool to help detect a flashover, but it cannot help you if you are caught in one. Think about the amount of time, or lack of time, you have in a flashover. You only have a few second to get out of that situation and must move quickly. In this type of scenario, you don’t have time to look at your TI.
A preflashover situation is where a TI can help. The TI can give you a visual indication of warning signs that you would otherwise not see. Without the use of a TI, the thick smoke acts as a visual barrier to what is going on above you. Convective velocity, thermal layering, and even rollovers are often hidden inside the smoke and are difficult or impossible to detect. The TI can help you visualize these events. The TI can help you identify how rapidly the fire gases are moving across the ceiling, indicating that the gases have some place to go other than the room you are in. Thermal layering is also visible to the TI. When any of these two visuals change (convective velocity slows or thermal layers descend), it can serve as an early indicator of potential flashover conditions.
The key part to staying safe when entering a burning building is to always have your TI with you to scan a room prior to entry. This is so important when avoiding a flashover. Scanning with your TI enables you to look for signs of excessive heat buildup, particularly near the ceiling, or levels of high heat closer to the floor where you might not otherwise expect it. The TI will also help you locate potential vertical or horizontal vent points in case you need them and where the secondary means of egress are located. In a flashover situation, these tactics are lifesaving.
The TI is there to help you recognize the danger that you may encounter before it happens so you can avoid the danger and go home safely. Simply put, if you have no other means of control such as ventilation or a hose stream, you must get out quickly. If you wait until the flashover is taking place, it is too late for the TI to help you escape this extremely dangerous occurrence.
1 The importance of conducting flashover training to recognize the signs. (Photos courtesy of Bullard; photos 3, 4 with permission from Max Fire Box.)
2 Recognizing the preflashover signs is important; this is “the calm before the storm.”
3 Understanding fire behavior.
4 A fully developed fire.
It is important to note that the temperature-sensing feature or Relative Heat Indicator (RHI), as it is often called on your TI, is not a reliable indicator of flashover or preflashover conditions. It cannot accurately detect the temperatures of gases, which is where the greatest threat usually lies in the growth stage of a fire. The TI is designed to detect surfaces, not gases. RHI is best used when evaluating the temperature differences in the same or similar materials. For instance, when performing overhaul, you might use the RHI feature to tell you what portion of drywall is hotter than another portion of drywall. When comparing like materials, the actual temperature displayed does not matter as much as the difference between the temperatures.
Fortunately, a flashover is not a routine occurrence but a culmination of successive, prior events that can lead to a potentially catastrophic outcome for firefighters. It is these preflashover events that you must be aware of. In the same way that you use a TI to size up a building prior to entry, you must constantly size up the interior conditions of a fire environment and be observant of change. Once you see the changes coming, you can find a path out of harm’s way.
Many fire departments have training facilities that include flashover or live fire simulators. However, not all departments have that luxury. Training as a firefighter is paramount to understanding fire behavior, stages, and dangerous conditions. If training facilities are not available, there are training props available such as “wooden dollhouses” you can build, or you can use a Max Fire Box, which can enhance your department’s knowledge of these conditions.
Manfred Kihn is a 19-year veteran of the fire service, having served as an ambulance officer, emergency services specialist, firefighter, captain, and fire chief. He has been a member of Bullard’s Emergency Responder team since 2005 and is the company’s fire training specialist for thermal imaging technology. He is certified through the Law Enforcement Thermographers’ Association (LETA) as a thermal imaging instructor and is a recipient of the Ontario Medal for Firefighters Bravery. If you have questions about thermal imaging, you can e-mail him at manfred_kihn@bullard.com.
