Distinguishing Abnormal from Normal

By Carl Nix

Firefighters are often thrown into situations that require them to make decisions based on what they see or think they see.

I was speaking with a fellow firefighter who shared a story with me about a recent call his crew responded to. It was a call to a local business whose fire alarm had activated. On arrival, the firefighters used the thermal imaging camera (TIC) to scan the interior walls of the business and noticed a hot spot on one wall. The crew decided to open up the wall; instead of finding what they thought would be a smoldering fire, they found a hot water heater on the other side of the wall.

When using a TIC to locate hidden fires, firefighters should look for anomalies in the thermal signature of surfaces that cannot be explained by ordinary heat sources. The shape of the thermal anomaly is important to understand. If the image shows straight sides, it most likely suggests a heat source between studs of some other structural component. A change in the shape, particularly vertical growth, suggests the fire may be intensifying. When using a TIC, it is very helpful to look for thermal comparisons when investigating an area. Firefighters can compare the area being investigated with other areas and make determinations.

1 Thermal imaging cameras can help firefighters detect hidden fires by scanning the exterior of a structure. (Photos courtesy of Bullard
1 Thermal imaging cameras can help firefighters detect hidden fires by scanning the exterior of a structure. (Photos courtesy of Bullard.)

Concealed fires can be obvious, manifesting in such ways as blistering paint, smoke emitting from a wall, or cracking sounds from combustion. A smaller fire, however, may not offer obvious clues to its exact location within the structure. Sometimes the fire is out of plain sight, complicating the process of detection, containment, and suppression. To distinguish abnormal from normal, firefighters should consider what ordinary heat sources could be and how they may be impacting thermal signatures. Some examples include a working appliance on the other side of the wall, active heat ducts inside the wall, and outside sunlight affecting the area and warming it.

The crew who busted through the wall only to find a water heater could have prevented unnecessary damage to the business if members had just looked behind the adjacent door. The use of thermal imaging technology in firefighting is second to none, but firefighters must always use their judgment and experience first before relying solely on thermal imaging technology.

2 Thermal imaging cameras can help firefighters detect hidden fires by scanning the exterior of a structure. (Photos courtesy of Bullard
2 Thermal imaging cameras can help firefighters detect hidden fires by scanning the exterior of a structure. (Photos courtesy of Bullard.)

A TIC, without a doubt, can simplify and expedite the task at hand when searching interiors of a structure looking for hidden fire conditions. A firefighter can scan the interior wall and ceiling surfaces of a structure for signs of abnormal heat from a distance of at least 10 to 15 feet away, providing a broad perspective of possible hidden heat conditions. Concealed or void space fires frequently involve electrical circuits or equipment. Use your TIC to perform a thermal scan on an electrical panel to see if a circuit is showing a relatively greater heat signature when compared to other circuits.

Firefighters can also use a TIC to detect hidden fires from the structure’s exterior. Thermal signatures that seem abnormal or out of place can indicate a hidden problem. Keep in mind, however, that environmental conditions can affect thermal signatures, making it more challenging to accurately locate the hidden fire. For example, in bright daylight, the sun beating on an exterior wall can often look like a problem area to the TIC when it really isn’t. Other times, the sun can mask or disguise a real issue. Similarly, multiple layers of a built-up roof can help hide concealed fires underneath. These examples further point out why firefighters need to thoroughly investigate what the TIC is showing them to confirm the information and make the right tactical decision.

Some of the most challenging fire conditions we respond to are the ones we don’t see. The examples in this column apply not only to locating the initial fire location and controlling it but also to the overhaul stage. Using the TIC to pinpoint problematic hot spots might reduce the chance of a rekindle. The TIC is just one more tool in a fire department’s arsenal to help locate and control fires that firefighters can’t see.

Carl Nix is a 30-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.

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