N i x Experience coupled with wisdom is often worth sharing. That’s why this column is about the dangers firefight- ers 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 pre-flashover 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,
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.
Keeping You Safe During a Flashover
Using a TIC to avoid a potential flashover