Thermal Imaging Training: Overhaul

Photo courtesy of Bullard Photo 1 shows two images of the same scene. The fire has been knocked down, and firefighters are overhauling the ceiling. The image on the left shows how the scene appears normally on the TI display. Most of the image is...


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1_thermal1.jpg
Photo courtesy of Bullard
Photo 1 shows two images of the same scene. The fire has been knocked down, and firefighters are overhauling the ceiling. The image on the left shows how the scene appears normally on the TI display. Most of the image is white hot, making it difficult for firefighters to focus their efforts. The image on the right shows how the manual iris control (“Thermal Throttle”) changes the image, making the hottest areas more distinct and guiding the overhaul efforts of firefighters.

Overhaul is one of the most popular uses for a thermal imager (TI). Some fire departments are still learning the potential of TIs, and therefore may limit the use of the technology to overhaul. This series of thermal imaging training columns should have shown you that thermal imaging applications go well beyond overhaul, touching every aspect of firefighting. Leading fire departments are using TIs during every stage of fire suppression, including the overhaul phase.

Essentials

The most important tip to remember during overhaul is that the TI displays scenes on a relative basis. This means that an object that is “hot” on the display (normally shown as white) is hot in comparison to the other items in the scene. This can make image interpretation confusing during overhaul, especially after knockdown and when firefighters are looking for hotspots. To make your TI more effective in overhaul, consider the following:

  • Thermal imagers show temperature differences. After knockdown, if the entire scene is white and light gray on the display, spray some water to create temperature differences. This gives the TI other reference temperatures, and as a result enables it to generate more useful images.

  • If your TI has a manual iris control (sometimes called a “Thermal Throttle”), learn how to use it. This control restricts the amount of heat reaching the TI detector. As a result, only the hottest items remain white on the display, and all others fade to gray.

  • If your TI has a temperature indicator, ensure you understand its uses and limitations. By comparing the temperatures of various surfaces, you may be able to identify sections of wall that deserve additional attention during overhaul.

  • Microbolometer TIs frequently have an “EI Mode,” which indicates that the detector has changed sensitivity levels. Most detectors change sensitivity levels when something that is 300ºF or hotter is in the image. Even TI models without an EI indicator on the display screen will have a momentary freeze of the image (when the shutter “fires”) and change sensitivities. Look for the shutter as a potential indicator that a significant hotspot remains in the scene.

  • A “hotspot” does not always mean “open up.” Thermal imagers are very sensitive. An area may be relatively hot, but not absolutely hot. That means it could show as white on the display, even though the area is not a hotspot that deserves further examination by firefighters.

  • When in doubt, use traditional techniques to determine if a hotspot really needs to be opened up. Feel the area for heat by using your hand. Or, use the TI and compare it to something with a known temperature. Perhaps the easiest comparison point is a partner’s hand. If the spot in question is roughly the same color as the hand, then it is probably not a hotspot that needs attention during overhaul.

Practice Makes Perfect

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Photo courtesy of Bullard
Photo 2 shows a firefighter’s hand next to a suspected hotspot. Notice that the hot electrical box is not significantly hotter than the firefighter’s hand. Since this area is about the same temperature as a human hand, it is probably not worth “opening up.”
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