By Carl Nix
News stories about structural fires make great TV coverage for the media. I’m sure you can quickly think of a recent news story that involved a fire of some type. Maybe it was a structural fire, car fire, or chemical fire. Fires are newsworthy, and we in the fire service know that at any time we might be standing in front of a reporter answering questions about a fire we are battling. Recently, I saw a news story involving a structure fire at a local restaurant. The firefighting crew had left the scene thinking the fire was out, only to be called back when the fire reignited.
I’m sure we can all relate to this scenario, and it serves as a great opportunity to discuss the unseen dangers that hide within structures when the fire appears to be out. Keep in mind that fire is deceptive, which is why it’s so difficult to fight. A smoldering fire doesn’t always give firefighters clues to where the fire is hiding within the structure. The obvious visible signs that many firefighters look for when evaluating concealed fires include blistering paint and smoke emitting from a wall. Crackling sounds from combustion coming from the structure are another clue that a fire is hiding somewhere.
One of the most challenging fire conditions to control is the one we don’t see. The most critical tool in your arsenal during situations like this is your thermal imaging camera (TIC). A TIC helps you locate hidden fires. Firefighters need to be using this tool in every situation where hidden fires may exist. I recommend using your TIC to scan from a distance of at least 10 to 15 feet away, so you have a broad perspective of any hidden heat conditions that may cause a fire to reignite. Begin by using your TIC to scan the structure’s interior wall and ceiling surfaces for signs of abnormal heat. What do I mean by abnormal? To distinguish abnormal from normal, firefighters need to consider what an ordinary heat source could be and how it may be impacting thermal signatures. For instance, a fuse box or appliance on the other side of a wall, active heat ducts inside the wall, or outside sunlight affecting the area and warming it can impact what the TIC image shows.
Firefighters should always look for anomalies in the thermal signature of surfaces that cannot be explained by ordinary heat sources that might be creating such a thermal anomaly. Keep in mind, just because your TIC shows you a hot spot doesn’t always mean there’s a hidden fire. Opening up a wall before further investigation could result in unnecessary damage to the structure. Always investigate thoroughly and rely on your firefighter’s experience and knowledge before drawing any conclusions. Your TIC is there to help guide you and should never replace your firefighting experience and training.
It’s also critical to identify the shape of the thermal anomaly. An anomaly with perfectly straight sides suggests a heat source located between studs of some other structural component. A change in the shape, particularly vertical, suggests intensification of the fire. When investigating, firefighters can compare the area being viewed in conjunction with other areas to determine their next steps. Concealed or void space fires frequently involve electrical circuits or equipment. TICs are useful for performing a thermal scan on an electrical distribution panel to see if a circuit is showing a relatively greater heat signature when compared to others. Understanding how your TIC interprets heat sources is critical to your investigation.
Using a TIC to detect exterior hidden fires in a structure is just as critical and challenging. When scanning an exterior, firefighters must always keep in mind the environmental conditions when searching for hot spots. Thermal signatures that seem abnormal or out of place need to be investigated. Always remember when performing an exterior search using the TIC that the time of day will affect what your TIC readings show you. For instance, during daytime hours, solar loading on an exterior wall can often look like a problem area to the TIC when there isn’t one. Always be aware that solar loading can mask or disguise real issues. This also applies when scanning a structure’s roof. Multiple layers of shingles can hide the location of concealed fires underneath. Knowing how to interpret what your TIC is telling you combined with your firefighting experience will help you determine how to move forward.
Without the use of the TIC, you can easily miss hot spots, resulting in the fire reigniting. The advantage to using a TIC is its ability to detect the smallest temperature differences that can indicate a smoldering fire that has not been extinguished. A thorough look with a TIC can pinpoint problematic hot spots, helping to reduce the chance of a rekindle event. By identifying a fire that has the possibility to rekindle, firefighters can help save additional property and eliminate the need to return to a fire scene to fight a reignited fire.
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.