Firehouse January 2005

Firehouse Magazine, January 2005
Overhaul
By Jonathan Bastian

Overhaul is one of the most popular uses for a thermal imager. 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.

Because overhaul is such a widespread and valuable application, this month’s topic centers on overhaul techniques.

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

The best way to get comfortable using the TI during overhaul is to use it after knockdown at every fire. Yes, every fire…car fires, trash fires and structure fires. While firefighters do not “overhaul” vehicle or trash fires in the traditional sense of the word, using the TI can be a learning experience. These incidents give firefighters the opportunity to see how the effects of fire change the heat signatures of objects and alter their appearance on a TI. These incidents also give firefighters practice in using the various indicators and tools on the TI to help them identify hotspots that require additional overhaul.

Additionally, use these fire incidents to practice using the manual iris control, or watch for a change in sensitivity levels indicated by the shutter fire and EI mode indicator. Look for changes in the display and changes in which areas are portrayed as “hotspots” on the display. Watch with the TI as another firefighter sprays down an area with water, and see how the picture on the TI display improves.

Table Talk

The firehouse kitchen can also be a good place to practice image interpretation during overhaul. While you are brewing coffee, place cups of warm and hot water near the coffee maker. Examine how the different objects appear and, more importantly, how the indicators and tools of your TI help you identify which objects are hotter.

Similar practice scenarios can be set up using the stove or oven, especially while preparing meals. Examine burners or pans to see how they are displayed differently as they heat and cool. Again, practice using the additional tools and indicators on your TI (such as the manual iris control or EI mode) to determine which objects are hottest.

Final Report

As with all thermal imager applications, the ability to use a TI effectively in overhaul requires practice. You cannot expect to use your thermal imager two or three times per month and become proficient at analyzing overhaul scenes. Be sure you are using your TI as frequently as possible to understand how the subtleties of the images can change your course of action. Also, do not forget the traditional overhaul investigative techniques that can help you confirm your image interpretations.

For more ideas on successfully using TIs during overhaul, visit the Technology section of Firehouse.com.

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.

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.”

For Firehouse.com

In January’s Firehouse magazine, the thermal imaging training article discussed overhaul tips. The article emphasized the importance of practice in becoming proficient with using the TI in this application. Because a thermal imager can detect a temperature difference of less than 0.09ºF (0.05ºC), you must become skilled at interpreting images and understanding how a hotspot will appear based on the temperatures of its surroundings.

Depending on the type of TI you have, you can rely on one of three tools that can help gauge how hot an object or area truly is. These were identified in the Firehouse magazine article: the manual iris control (“Thermal Throttle”), the temperature indicator and the EI mode. The more skilled you become with the appropriate tool on your TI, the easier overhaul becomes. Proficient use is critical to avoid a real, but embarrassing, situation.

One fire department responded to a call at a house struck by lightning. The initial investigation revealed an electrical outlet with scorch marks around it. A firefighter examined the wall using a TI, and the TI identified a white hot line running up the wall. Since this white line ran past the outlet, the firefighter took it to be a smoldering electrical line. He and his crew felt they had found a hidden electrical fire and promptly opened the wall from floor to ceiling. They expected to be heroes for preventing a fire; instead, they caused unnecessary property damage. The white hot signature the TI had shown them was nothing more than a hot water pipe feeding a radiator on the second floor.

The electrical line was only damaged in the outlet box; there was no fire running up the wire. If the investigating firefighters had relied on some traditional techniques, they would have saved the homeowner money and spared themselves embarrassment. They could have felt the wall with the back of a hand. They could have removed the outlet cover and inspected the wire in the box to see if there was charring running out of the box. They could have compared the heat signature to a firefighter’s hand to see exactly how hot was “white hot.” They could have even started with a small inspection hole, rather than opening the entire wall.

If you are not comfortable with the indicators and tools on your TI, you will be frustrated when overhauling after a room-and-contents fire. After the fire is knocked down, everything in the room will still be hot. As a result, the room will display in shades of white and light gray on the TI. Many times this frustrates firefighters so much that they stop using the TI to assist during overhaul. However, by using the tools and indicators, firefighters can make the TI work properly in this application. Going back to the basics of how a TI functions can also help.

Remember the TI only sees temperature differences. During overhaul, the TI may generate a better thermal image if firefighters introduce some temperature differences artificially. For example, go ahead and open a small section of wall and spray the area with water. This generates significant temperature differences and helps the thermal imager generate a better picture. If you have a microbolometer-based TI, you will find this tip helps tremendously. Even BST-based imagers without a manual iris control will benefit. The key is to generate temperature differences which adjust the sensitivity settings of the software inside the TI.

The value of a thermal imager in overhaul is threefold. First, the technology helps identify hotspots that firefighters might otherwise miss. This clearly reduces the likelihood of a rekindle and limits additional property loss. Second, by identifying specific areas of concern, firefighters can limit their overhaul efforts (and therefore firefighter-caused damage) to true areas of concern. In certain instances, entire sections of wall may be saved by proper use of a TI. Last, by guiding firefighters promptly and specifically to hotspots, firefighters spend less time on scene and do less work. This reduces the chance of injury and places companies back in service sooner.

So, practice frequently so that your TI can be a true asset in your overhaul efforts. And remember, the TI shouldn’t come out just for overhaul…it should be used for overhaul after it has helped with fire attack and suppression.