Image interpretation is one of the most critical skills that a firefighter can develop as it relates to successful thermal imaging operations. The ability to glance at the display of the thermal imager (TI) and read the image is an acquired skill that comes through a solid understanding of the technology combined with practice. Nothing will improve your TI operations more than rapid, accurate image interpretation; however, many people fail to consider the impact of Heat Indicating Color (HIC).
Each individual pixel of a microbolometer has the capacity to act as an individual pyrometer measuring temperature across an entire scene at the individual pixel level. This lets manufacturers develop color schemes based on the interpreted temperature of each pixel. This technical ability has led to a plethora of different HIC schemes or palettes available on the market today. These range from the relatively simple, one-color palettes to more complex, seven-color palettes. Some imagers today even have the ability to display multiple, optional color palettes; however, the mere presence of HIC is not valuable. Not all HIC palettes are created equal. A good HIC palette will provide valuable, reliable information that you can react to. A well-designed color palette will tell you something.
Regardless of what make or model of thermal imager your department owns, it is important that you understand if your imager is equipped with HIC and if so, what the color(s) mean so that you can make appropriate decisions in the heat of the battle.
• Tri-color palettes — The most common HIC on the market today is the tri-color palette. This palette generally consists of a yellow-orange-red progression where red indicates the hottest portion of the environment. Nearly every manufacturer offers the tri-color palette; however, they do not all perform or react the same. Some manufacturers activate tri-color HIC as low as 200 degrees Fahrenheit while others do not activate tri-color HIC until as high as 750°F. And other manufacturers activate HIC at lower temperatures, deactivate as temperature climbs and then reactivate when temperatures climb even further. Another manufacturer displays a red-only palette at two different temperature ranges before finally activating tri-color HIC as temperatures climb. All of this variability can lead to confusion and misunderstanding on the fireground. It is critical that you understand what the HIC of your thermal imager means and how it works, and whether the color is constant or will come and go as temperatures climb.
• Multiple-color palettes — Several manufacturers have adopted multiple-color palettes as a selling feature on their thermal imagers. Multiple-color palettes refer to totally different HIC schemes being present on the same imager and are usually user selectable. These palettes range from completely colorized with anywhere from one to seven different colors to single-color palettes that activate only a specific temperature range. Some manufacturers are equipped with as many as 13 different HIC palettes. Generally speaking, these multiple HIC palettes offer little value to the firefighter and serve more as features designed to differentiate the thermal imager during the purchasing process; however, if your imager is equipped with multiple HIC palettes, it is equally important that you understand how each of them works, what they are indicating and, most importantly, how to activate/deactivate/change them.
• Polarity inversion — Polarity inversion has also made its way into fire service TIs. Polarity inversion is changing the imager from a white-hot polarity and inverting it into a black-hot mode. When polarity inverted, a thermal imager will display the hottest areas as black and coldest as white — exactly 180 degrees inverted from a normal view. This feature offers absolutely no benefit to the firefighter whatsoever and should receive careful consideration when considering a new imager purchase. With polarity inversion, it is possible that an imager could display information to the firefighter that is exactly the opposite of what the firefighter might expect to see.
Firefighters often make critical decisions based on what the TI displays and polarity inversion can seriously affect the validity of those decisions. Imagine having a compass that sometimes shows "N" for north, but also is capable of displaying "S" as north. What benefit would that be? Polarity inversion has long existed in the law enforcement and military markets where it does provide a benefit; however, it can only lead to confusion on the fireground without offering any specific benefit.
• Learn your colors — Whatever your position when it comes to HIC, you need to learn what your imager is capable of and what it means. You can start with a quick review of the owner's manual for your TI or contact the manufacturer and ask. You need to know whether your imager is equipped with HIC and what temperature ranges the colors represent. If your imager is equipped with multiple-color palettes, then you need to know the temperature representation of each palette and how to activate/deactivate them.
Once you have this information, grab the imager and head for the kitchen. Of course, live fire is and always will be the best way to train with the HIC feature of your TI, but many firefighters do not have easy access to a burn facility. In this case, a kitchen will suffice. Place a cast-iron skillet on the stove and turn the burner on. Watch the skillet and observe how the imager colorizes. Try the burner at multiple settings from low to high to see how the various temperatures affect the imager's HIC feature.
You should also compare how the color reacts to distance from the skillet. Many HIC palettes will disengage when the heat source occupies too small an area. It is important that you know how big the heat source needs to be to activate the HIC feature of your imager.
HIC should alert the firefighter to dangerous or increasing temperature levels. HIC should be simple to understand and contribute value to the firefighter during suppression operations. A well-designed HIC palette will improve the TI's value as a "tool" without complicating its use. A well-designed color pallet will actually tell you something. What is yours telling you?
BRAD HARVEY is the Thermal Imaging Product Manager at Bullard. He is a veteran of public safety as a firefighter, police officer and paramedic and is certified through the Law Enforcement Thermographers' Association (LETA) as a thermal imaging instructor. Harvey has worked as a high-angle rescue instructor and is a certified rescue technician and fire instructor. If you have questions about thermal imaging, you may e-mail him at firstname.lastname@example.org.