Firehouse, June 2003
The Five Don’ts of Thermal Imaging
By Jonathan Bastian
The thermal imaging camera is coming of age in the fire service. Thousands of fire departments across North America have placed thermal imagers (TI’s) into service. While some departments have only one or two cameras, others have a TI on every fire company. It is clear that TI’s are making the transition from “cool toy” to “critical tool.” The fire service is learning that these tools save firefighter lives and civilian lives, as well as preserve property.
The fact that most fire service TI’s are simple to operate and easy to maintain is also expanding usage. The trend in TI’s has been to smaller, easier-to-operate cameras, with some featuring only an on/off button. Because TI’s are so easy to activate, many firefighters have a misperception that this means imagers are easy to use. A thermal imager is like any other tool on the fireground: properly used, it saves lives and property; improperly used, it can injure firefighters. Firefighters should regularly train with this new tool, carefully avoiding the “Five Don’ts of Thermal Imaging.”
#1: Don’t Lock On To The Image
Structural firefighting is one of the primary uses of thermal imaging. Because infrared wavelengths are longer than visible light wavelengths, they have different properties. The property of greatest interest to firefighters is that infrared’s longer wavelength allows it to penetrate smoke. While visible light is easily scattered by light smoke, infrared waves move through very dense smoke. As a result, a TI gives the firefighter a heat-based image of the objects in an area.
This heat image essentially allows the firefighter to regain his eyesight in a structure fire. As a result, search times are dramatically reduced, while search accuracy and firefighter safety are greatly improved. But regained visibility also brings out the natural human tendency toward succumbing to habits. Because the TI gives back the sense of sight, the firefighter is often tempted to “lock on” to the display, encouraging him to navigate with his eyes. However, this is potentially dangerous.
First, modern TI’s cannot simulate the peripheral view of the human eye. Most firefighting TI’s have a field of view of about 55°, about 1/3 that of a normal human eye. The potential risk is true tunnel vision, with the firefighter diverting all of his attention to the viewing screen while neglecting his immediate surroundings. The firefighter may miss areas in his search, fail to see objects outside the camera’s immediate view or be unaware of dangerous changes in the environment. Second, if a firefighter relies only on his eyesight to enter a structure, he will most likely need to rely on his eyesight to exit a structure. Therefore, if the firefighter loses the use of the TI for any reason, he risks becoming immediately disoriented.
Tactical Advice: A firefighter should use the TI to scan a room slowly and completely, searching for victims, identifying safety issues, and building his “mental map” as he negotiates through a structure. Then, the firefighter should take the TI away from his view prior to moving to the next part of the structure (using the carrying strap available from the manufacturer; or simply crawling with the TI in hand). This not only allows for faster team movement, but it also reinforces the need for “mental mapping” and enables the firefighter to maintain reference points in darkness.
Keeping the TI in hand to avoid “lock in”, a firefighter can crawl. Note that one hand maintains contact with the wall for a reference.
The retractable strap supplied by the manufacturer keeps the TI secured to the SCBA or the firefighter’s coat. The strap permits the firefighter to have both hands free when not using the TI, and allows him to maintain situational orientation.
#2: Don’t Mistake Sight for Safety
Firefighters are trained to crawl (or shuffle on one knee) when they combat a structure fire. Historically, firefighters crawled primarily for the cleaner air, cooler temperatures and better vision found near the floor. While this is true to some extent today, SCBA’s and modern turnout gear have somewhat de-emphasized the original benefits. Now, a major reason firefighters still crawl is to avoid tripping over or falling into hazards. TI’s, however, remove the sense of darkness and the blinding effect of smoke, giving firefighters the ability to see furniture and doors. As a result, they can be tempted to assume it is safe to walk.
When using a TI, firefighters cannot confuse the ability to “see” with the presence of a safe environment. Firefighters should remember that when they “see” with the TI, they are not getting the same perspective as they would get with their eyes. Depth perception and peripheral vision are reduced with a TI. Furniture, stairs or gaps below the view of the TI place a firefighter in unnecessary danger. Despite the fact he can see, the firefighter must remember that the smoke and heat are still present. Of course, to walk with a TI, the firefighter would have to use it constantly, requiring “locking on” to the imager. This violates Don’t #1.
Tactical Advice: In short, if a firefighter would crawl without the TI, he should crawl with the imager as well.
#3: Don’t Think All Victims Are “White” On The Screen
It is an unfortunate truth that few fire departments have regular access to structures in which they can light training fires. Without access to live-fire training, firefighters must resort to drilling in ambient environments. This strategy can be effective for working on skills such as hose line deployment, SCBA drills, entanglement drills and the like. However, with TI’s it can be problematic.
The surface temperature of a human is about 90°F. In most ambient environments (60-80°F), a 90°F item will be the hottest item, and therefore shown as white on the TI display. As a result, when firefighters train in non-fire environments, humans are always displayed as white. The problem is that structure fires are not ambient environments, and a search for a victim may be performed in rooms where surface temperatures are 110°F or more. This means that when firefighters are searching in actual emergencies, humans may not be the hottest items in the room!
Tactical Advice: During TI training, firefighters should be constantly reminded that temperature is relative on a TI. A human may show as white in a cool environment, gray in a warm environment, or black in a heated environment. Therefore, firefighters should be training on shape not on shade when practicing search techniques. When TI training occurs in ambient environments, firefighters should use rescue dummies and heavily clothed humans to help reduce the “hot” profile, and encourage the identification of “victims” by shape.
A “victim” in a warm environment. Potential victims could easily be gray on the TI display.
Normally, humans display as white in ambient environments. Here, the humans show dark gray and black. A very hot day, and a very hot fire across the street have made 90°F skin relatively cool.
#4: Don’t Expect It To Do Everything
No tool can perform every task. Some might argue that the Halligan bar can do anything, but even this multi-purpose tool has limitations. The thermal imager, just like every other tool in the fire service, has limitations.
First and foremost, firefighters should remember that TI’s do not “see through” buildings or people. TI’s receive energy, just like the human eye. The infrared energy the TI receives allows it to display relative differences in surface temperature. One cannot “look” through walls, floors or major obstructions to find victims. (Thin obstructions, such as blankets or single sheets of paneling, may receive enough conducted heat from a victim to show a difference in surface temperature. Do not confuse conducted heat transfer with “seeing through” an object.)
Second, infrared energy does not travel well through glass or water. While glass is transparent to visible light, it is nearly opaque to infrared. The same is true with water. During exterior size up efforts, TI’s cannot be used to see through closed windows to find victims. However, windows that are hotter than other windows will be evident; this may indicate the seat of the fire, the boiler room or the window that has been in the sun all day. TI's assist water rescues only if the victim maintains a heat signature above the water. Inside a structure, an activated sprinkler head may appear as a black cone showering down, masking nearby victims or fire from the TI.
Tactical Advice: Firefighters should use their TI’s as frequently as possible to familiarize themselves with the limitations, as well as explore additional, creative uses.
#5: Don’t Forget The Basics of Firefighting
If there were only “One Don’t”, this would be it. Firefighters absolutely, positively must remain proficient at all the skills they learned before their departments purchased TI’s. Thermal imaging is a valuable technological tool; however, TI’s will not put out the fire. Firefighters need to engage in solid, fundamental firefighting to ensure their own safety and the proper completion of their goals.
Tactical Advice: While the TI will make search efforts easier and faster, the imager should not supplant the standard practice of right- or left-hand search patterns to maintain orientation. Teams should still have a tethered path, such as a hose line or an anchored search rope, leading to safety. While the TI brings back vision, it does not improve air quality and any victim’s ability to breathe. Firefighting companies should still ventilate structures in a timely and effective manner to remove the heated gases and smoke. While the TI helps to monitor structural integrity, it cannot see hidden trusses, nor can it make compromised trusses carry their loads longer. Firefighters still need to be aware of the structural limitations of a building and the dangers therein.
In short, just as a helmet and turnout coat do not make a person invulnerable, neither does a TI.
Conclusion
Fortunately, every day more fire departments understand the benefits
of thermal imaging and add this powerful tool to their departmental
resources. TI manufacturers have responded to fire service demands for
easily operated cameras, but there are still educational hurdles that
fire-training personnel must address. Fire departments would never consider
placing new extrication tools or new SCBA’s in service without
extensive training; thermal imagers should be no different. If firefighters
adhered to the Five Don’ts in every training session and every
incident use of thermal imagers, the risk of injury from misapplication
of infrared technology would be greatly reduced. And, the many stories
of TI success would dramatically increase.