Thermal Imaging Carl Nix
Experience coupled with wisdom is often worth sharing. That’s why this column is about the dangers firefighters face when a flashover occurs. I have written about flashovers in other columns because this phenomenon can claim the lives of firefighters. The more knowledge we arm our firefighters with about flashovers, the safer they will be.
A flashover is an extremely dangerous occurrence when a fire rapidly engulfs an area with temperatures reaching more than 1,000˚F. When I explain a flashover to my recruits, I tell them a flashover is when a hot fire becomes an inescapable fire. The fire service gives a great deal of attention to understanding flashovers but in today’s firefighting environment, where firefighters respond less and less often to fire calls, it is even more critical to keep flashover training at the forefront of all discussions. One way to achieve this is to train our firefighters to recognize preflashover signs. What’s important to remember when talking about a flashover is that it builds from a multitude of prior events that lead to what becomes a catastrophic event. The fire service estimates that firefighters have maybe two to three seconds to escape a flashover. Firefighters can train for these events to avoid being in harm’s way when a flashover occurs.
Using a thermal imaging camera (TIC) during preflashover situations can help you determine warning signs that you would not otherwise see without the use of this tool. A TIC will never help you if you are caught in a flashover. I cannot stress this enough. You don’t have enough time to look at your TIC and try to escape a flashover. Remember, the fire service estimates that you have maybe two or three seconds max to get out of the situation. There’s no time to process what’s on your TIC screen and, even if you had a few more seconds, looking at your TIC will only show you what you already know is happening. It’s important to remember that a TIC is a tool to help you detect a flashover.
Firefighters know before entering a structure to use their TIC to size up the exterior, but it’s just as critical to size up the interior of a structure to be aware of constantly changing conditions. Once inside the structure, you can use your TIC for visual readings to help you determine the severity of a situation. Using your TIC to scan inside a structure lets you 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. For example, your TIC can detect how rapidly fire gases are moving across a structure’s ceiling to help you determine if they are moving to other areas or being contained in the room you are in. Use your TIC to help you see through the thick smoke that is happening above you and to also help you detect thermal layering and convective velocity. Thermal layering is very often visible on your TIC in the form of fire gases. If it’s not visible, you can use your TIC to look at the vertical wall surfaces to determine temperature differences. Be aware that early indicators of a potential flashover may be imminent when you see convective velocity and thermal layering changes on your TIC.
Always remember, every time you approach a new room within the structure, use your TIC to scan that room prior to entry. Your TIC 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. This is critical when avoiding a flashover. Some TICs are equipped with a feature that shows high-heat colorization. This is a feature you want to become very familiar with so you can quickly recognize the corresponding temperatures your TIC is giving you to better understand the changing heat conditions in the structure.
Again, it’s important to keep in mind that all the scenarios above are examples of how a TIC can help you recognize and, most importantly, avoid a potential flashover. This is how a TIC can be effective. If you see that the conditions change suddenly, it’s too late for your TIC to help. 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’s too late for your TIC to help you escape. A TIC cannot help you in a flashover but it can help alert you to a pending flashover.
One more word of caution about using your TIC during preflashover conditions: The temperature-sensing feature on your TIC is not a reliable indicator during preflashover conditions. This feature cannot accurately detect the temperatures of gases, which is where the greatest threat usually lies in the growth stage of a fire. Your TIC is designed to detect surfaces, not gases.
Flashovers happen fast. Avoiding a flashover means understanding the events leading up to a flashover. The disruption of the thermal layering that happens at the moment of a flashover is so sudden that looking at your TIC will not help you. You need to get out quickly. Knowing when to use your TIC and when not to use this tool is key to staying safe during any fire conditions, especially flashovers.
Carl Nix is a 32-year veteran of the fire service and a retired battalion chief of the Grapevine (TX) Fire Department. He serves as an adjunct instructor for North Central Texas College and a thermal imaging instructor for Bullard. Nix has a bachelor of science degree in fire administration and is a guest instructor for Texas A&M Engineering Extension Service’s (TEEX) annual fire training in Texas.