Temperature measurement devices (called radiometers or pyrometers) are available on almost every thermal imager currently sold to the fire service. You must understand, and communicate to your company, that radiometers and pyrometers do not estimate air temperatures. They only estimate surface temperatures. For details on how temperature measurement works, read the author's article on Myths vs. Realty in the Firehouse.com archives.
While temperature measurement can be accurate when viewing common construction materials, it can be extremely inaccurate when viewing reflective materials, such as metals. To demonstrate why firefighters cannot make critical decisions based on an indicated temperature, fill a shiny aluminum or steel pot with water, place it on the stove and bring it to a boil. Then walk firefighters carefully through the following questions:
- What is the temperature of boiling water? (Answer, 212?F or 100?C)
- If the pot contains boiling water, what is the minimum temperature of the pot? (Answer, 212?F or 100?C?although it is likely much higher)
- Look at the pot with the thermal imager and take a temperature reading from near the bottom of the pot. It will probably read about 100?F or 39?C.
- Can you put your hand in boiling water? (Answer, no -- not if you like your hand)
- Can you put your hand in 100?F (39?C) water? (Answer, yes, it is similar to a hot tub)
This is the easiest way to demonstrate clearly how temperature measurement devices can lead firefighters to make poor decisions. Everyone who uses a thermal imager with temperature measurement must understand that the reading cannot be used to make life-or-death decisions.
Video overlay systems are also an available option and can cause confusion if they are not properly understood. These systems utilize a video camera and mix that image onto a thermal image to create an image that is partially from light and partially from heat. Note that this system does not give special qualities to the thermal imager; it will still not see objects behind glass or under water. If the objects in the scene are all of the same temperature, they will still be difficult to see with the TI.
If you activate the video overlay, the thermal image is reduced (by about 30%) to allow for input of the video image. In dark, stable environments, this can make the TI nearly useless. Take your TI into a windowless area of your firehouse and turn off the lights. Scan first with just the TI and no video overlay. Objects will be difficult to distinguish, but you should still see furniture and structural features. Now activate the video overlay. The TI image should be nearly black. Why? The video overlay sees what your eyes see, light. Therefore, it is laying a black image onto the subtle gray image created by the thermal imager.
Teach your firefighters to recognize the appropriate screen symbol that indicates video overlay is active. Then, if they encounter problems in a particular environment, they can determine if the video overlay is interfering with the thermal imager. Ensure your firefighters understand what the system is actually doing and how it may inhibit or improve their ability to perform.
Temperature measurement and video overlay may make your job easier in certain situations. It is important that you train on the benefits of these options, as well as the limitations. By properly understanding these devices, you will ensure that you do not misapply the technology and that you do not make improper decisions on misinterpreted information.
Use your TI often, wisely and safely.
Related:
- October's Thermal Imaging Article (Firehouse Magazine)
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].
