Thermal Imaging and Image Interpretation

Manfred Kihn


As firefighters, we train in all aspects of our job, but we face challenges because we use so many different types of equipment depending on what our duties are. We need to be proficient in using all of them. Why is this month’s topic important? We use thermal imaging cameras (TICs) to help us see where we are going, but what is it that we are really looking at? How are we interpreting the images we are seeing on the TIC?

Carl Nix

Image interpretation is one of the most critical skills a firefighter needs to develop to successfully use a TIC. Firefighters need to be able to glance at the TIC display and understand the image being shown. This is a learned skill that comes with understanding the technology of thermal imaging coupled with practical experience in the field.

Let’s look at a scenario. You are responding to a structure fire call and your crew arrives on the scene to see smoke coming from the building. The crew begins pulling and charging attack lines, and you grab the TIC and do a quick 360° of the structure. The question is, are you interpreting what you are seeing on the TIC’s display correctly? Every structure will demonstrate at least four different but totally normal images on a TIC based on many factors including day vs. night and winter vs. summer conditions. A mobile home, for example, will look different than a masonry structure. A wood-frame-sided home will look different than a steel structure.

Windows will also impact the information your TIC tells you based on single-, double-, or triple-pane designs. Window treatments if covering the window can impact image information as well. Older and poorly designed windows and doors can exhibit thermal images that could easily mislead you as to the real heat value of the structure without a normal image baseline.

When our naked eye sees things, our brain computes it and we understand it, but when we see images through the display lens of a TIC, we now must try to understand what we are looking at. Some heat signatures or anomalies will be obvious, but other images we will not understand. If we detect something and can recognize and understand it, then we move on; but if we detect something, cannot recognize it, and cannot understand it, then we must investigate it.

Photos courtesy of Bullard.

1 Photos courtesy of Bullard.

Photos courtesy of Bullard.
Photos courtesy of Bullard.
Photos courtesy of Bullard.
Photos courtesy of Bullard.

The TIC is giving us a clue. Remember, a TIC is detecting infrared radiation, which comes from anything with molecular activity, whether it be passive, active, or direct emitters. The image in photo 1 is a passive emitter. A passive emitter is an inanimate object, and the image is obviously a chair. The image is showing that someone had been sitting in it. Not all thermal images are going to be that easy to understand.

Testing performed on TICs tells us that these heat signatures or anomalies will last for several minutes to up to a half hour, depending on variables like the weight and size of the person, how long the person was there, the type of material the chair is made from, the room temperature, and much more. In this case, the anomaly in this chair could last upward of 10 to 15 minutes.

In photo 2, the footprints will last only several minutes, especially if they were detected on hardwood flooring as opposed to carpet. If we detect this image through the lens of our TIC, then we know this is very recent and the person could still be inside the structure unless already accounted for.

Again, the obstacles that we must overcome include reflective surfaces that give us reflective images (photo 3), such as glass, glossy surfaces, and stainless steel appliances. If you see someone giving you a wave and that someone is waving back, then I’m pretty sure that is you.

Now, let’s talk about some of the other images you might detect, as structures will emit heat signatures from electronic appliances and heating/cooling systems, which are known as direct emitters or energy sources like in photo 4. Photo 4 is showing a refrigerator and coffee maker in very smoky conditions that display extremely well on a TIC. Other devices that display well on a TIC include cordless phone chargers, TV and DVD players, clock radios, microwaves, and washers and dryers.

When conducting a victim search, sometimes just detecting a part of the body like a hand or foot may be enough or all you can see based on the situation, but that may be enough for a successful search. Again, active emitters also include family pets.

Photo 5 shows five anomalies; two are caused by direct emitters (energy sources), two are passive emitters (two people were on the bed), and the one remaining is an active emitter (cat).

Firefighters need to be proficient in all aspects of their job. The practice of image interpretation through the lens of a TIC is just another example of how critical it is to train daily on the TIC.

Manfred Kihn is a 19-year veteran of the fire service, having served as an ambulance officer, emergency services specialist, firefighter, captain, and fire chief. He has been a member of Bullard’s Emergency Responder team since 2005 and is the company’s fire training specialist for thermal imaging technology. He is certified through the Law Enforcement Thermographers’ Association (LETA) as a thermal imaging instructor and is a recipient of the Ontario Medal for Firefighters Bravery. If you have questions about thermal imaging, you can e-mail him at

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