Using The Thermal Imager On Size-Ups

Dec. 16, 2003
Firefighters have quickly learned the value of thermal imaging in a smoky environment, so it is a natural jump to use the technology even earlier at the fire.
There is an old saying that, "So goes the size up, so goes the incident." Size up, although a small portion of most incidents, is a critical step that helps set the tone and pace of the operation. Sometimes, action plans are developed after a size up based on incomplete or insufficient information. Rapidly changing conditions, unknown building construction features, blinding smoke and poor nighttime visibility are some obstacles to making well-informed size up decisions. Firefighters may overcome some of these obstacles with the proper use of thermal imagers (TIs).

With more complete information, incident commanders can better determine how and where to deploy resources. When TIs arrive early enough in an incident, the advantages of the technology can also be applied to more than just structure fires.

Structure Fires

Firefighters have quickly learned the value of thermal imaging in a smoky environment, so it is a natural jump to use the technology even earlier at the fire. As the first-in company officer performs his walk-around of the structure, he can combine the information his eyes are showing him with the information that the thermal imager is showing him. At night, this new information can make a dramatic difference; but even in the daytime, an imager can assist.

For example, my former fire department was dispatched to a single-family residential fire, believed by the caller to be electrical in nature. On arrival, we had light smoke drifting from the gable vents. As my company approached the structure, we scanned the outside walls with the thermal imager. Directly above the electric meter, there was a white channel that showed us where a small fire had worked up from the circuit box, into the attic, confined on each side by a wall stud. The fire did not break out of the wall, however. By using the imager early, we were able to identify the exact location and extent of the fire. Furthermore, we already had a good idea that the fire had partially progressed into the attic, and we were able to confirm this before we even went inside the home.

When using your TI for structure fire size ups, keep in mind three key factors. First, realize that building construction will play a huge role in showing or hiding the effects of fire and the transfer of heat. A Type V building, such as a standard wood frame ranch home, has very little mass, with most of the structure made of lightweight truss systems and 5/8" wall material. As a result, this type of building cannot easily hide the effects of fire and heat. Heavier construction, however, is a different matter. Type IV structures, such as a mill with 8" timber framing and 18" brick walls, can absorb huge amounts of heat. These massive buildings can hide the heat from a very large fire for a very long time. During size up, keep in mind the impact of construction on the heat picture you see on your TI.

Second, consider the effects of weather and other factors on the picture your thermal imager generates. Imagine an incident at a single-family residence on a sunny, summer afternoon when the temperature is 97?F (36?C). A company officer should not be surprised to find a black shingle roof displayed as white on his TI screen; after all, black shingle roofs get hot on summer afternoons. However, if the incident is at 02:35 on a winter night when the outside temperature is -10?F (-23?C), then a "white hot" roof could indicate a major problem for firefighters.

Photo Courtesy of Bullard The above photo illustrates how weather can change the interpretation of a heat signature. The "white hot" door is probably not as significant a concern if this image is seen at 03:15 on a cold winter night. We expect buildings to be heated in the winter, and heat can escape through doors. This image is a major concern if it is seen at 17:30 on a hot summer afternoon. Everything else in the image is gray or black, including the firefighters stretching a line. This means that the door is very hot compared to the surroundings. Since the ground and walls should be hot from the effects of the sun, and they appear relatively cool, this image under the second scenario should sound major warning bells in the user's mind.

Third, remember that "white" on your TI display does not always mean a fire. There may be activities inside the building that cause an odd heat signature on the TI. For example, a Type V residence with a sauna in the master bathroom might display a white area on the exterior walls, corresponding with the location of the sauna. In the Type IV mill, the boiler room against an exterior wall may also cause a different thermal signature for that portion of the building, compared to the rest of the wall.

Car Accidents

A number of fire departments respond to more MVAs than they do structure fires. While a TI will not help treat a patient, the proactive fire department may use the technology to help in several ways during scene size-up. First, as you approach the scene, the TI may help you identify any liquid leaks. While it cannot differentiate brake fluid from gasoline, a thermal imager can at least notify you early that you have a potentially hazardous situation. Because the spilled liquid will usually have a different temperature than the ground, it should be visible to your imager.

Second, the imager may help identify skid marks to determine if there are other vehicles involved. For example, at an accident in a rural wooded area, the imager may detect the heat from skid marks going off into the woods or toward a ravine. During size up, this information can prompt firefighters to search for another vehicle off the roadway.

Third, at high-energy collisions, the imager may help identify victims who have been thrown from the vehicle. Because any person ejected from the vehicle should have a different temperature than the surrounding terrain, he or she should be visible on the imager. Because this type of scenario is most likely at night, the victims will normally show as white on the display. Keep in mind, however, that brush may obscure part of the victim's heat signature or block it completely. In winter storm conditions, it might also be possible for a victim to be covered with snow. Snow, being merely frozen water, will block the person's heat signature as well. The thickness of the snow layer, combined with the person's attire, will determine how much of the individual's heat is seen by your imager.

Hazardous Materials

If a fire company is dispatched to investigate a possible hazmat incident, firefighters can use a thermal imager to help assess the risks. The imager can help identify the amount of product in certain containers, as well as identify the presence, location and movement of a leak.

Thermal imagers will show product levels in sealed containers if four specific conditions are in place concurrently. First, the product must be a liquid or a solid. Second, there must be a vapor space. Third, the vapor space in the container must be a different temperature than the product. Fourth, this temperature difference must be translated to the surface of the container. If all four conditions are in place, the imager should detect a product level line. While the likelihood that these four conditions will exist at a hazmat scene is good, it is not guaranteed. As firefighters train with and use the imager, they should be careful not to fool themselves into seeing product levels where none are actually visible.

Photo Courtesy of Bullard This image shows how an imager can identify product levels under the proper conditions. The container on the right may be completely full, completely empty, temperature equalized or too insulated.

The thermal imager can also show the presence and movement of a leak. As long as the material stays on top of nearby surfaces, and it has a different temperature, it will be visible. This will be true as well for liquids that float on water, such as gasoline or fuel oil. Products that mix with the surface, such as alcohol mixing with water, will "disappear" from the imager. Materials that soak into the surface may be visible only if they change the temperature of the surface.

Note that the imager will generally not "see" leaking gases. However, since gases are endothermic when they escape from a pressurized system, the point of a gas leak may be seen as a cold spot on the container or piping. Also, remember that no thermal imager is intrinsically safe. If you or the hazmat team are concerned about LELs and UELs, do not bring an imager into the "hot zone."

Personnel Safety

In this new era of "domestic preparedness," firefighters and their officers need to be vigilant in protecting themselves from criminal activity. A thermal imager, especially at night, can help in that role.

Whether responding to a terrorist act or a suspicious fire, firefighters can use a thermal imager to monitor their surroundings. Firefighters and other first responders are now potential targets for terrorist acts, most likely through secondary devices or events. A thermal imager can be used to scan areas to look for suspicious people lying in wait. At potential arsons, the perpetrator usually likes to stay and watch the incident. In either situation, the company officer can scan the vicinity prior to committing personnel. As long as the suspicious individual has a different temperature than his surroundings, he should be visible on the thermal imager.

One interesting capability of thermal imagers is that they can see through most trash bags. As a result, firefighters searching for explosive devices may be able to "see" inside a trash bag to determine if it is benign or a potential threat. Questionable parcels or containers near an explosion can be scanned with the thermal imager during size up to determine if they are generating heat, possibly indicating a secondary device.


To some extent, the effectiveness of a size up determines the success of an operation. By using thermal imagers early at structure fires, fire officers can gain additional information to help them improve the planning process. At auto accidents, firefighters can ensure all victims are accounted for. During hazmat incidents, additional information can be gathered prior to over-committing the company or prior to notifying the hazmat team. And, proper use of a thermal imager can enhance firefighter safety at certain crime scenes.

Of course, to help in size up, the thermal imager has to arrive early enough to be accessible to the first-in officer. That, however, is an article for another day.

Use your TI often, wisely and safely.

Jonathan Bastian is a Thermal Imaging Specialist for Bullard. He is certified as a thermal imaging instructor by the Law Enforcement Thermographers' Association (LETA). He is also the author of the FD Training Network "FireNotes" book, Thermal Imaging for the Fire Service. Bastian served 12 years on the North Park, IL, Fire Department, including the last three as a captain. He has taught classes on thermal imaging, rapid intervention teams and search and rescue operations. He is currently a police officer in Lexington, Kentucky. If you have questions about thermal imaging, please send them to [email protected].

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