In this training video we can see the thermal imager camera view from two different positions. Both cameras are FLIR K55 cameras with clean lenses.
The left camera view shows the firefighters and the room next to the fire compartment.
The right camera view shows the same firefighters and room, but shown from yet another room further away from the fire compartment.
Two positions, different temperatures
The colors in the image are the visual representation of the heat registered. But in this example the TIC cameras display very different colors for the smoke over the firefighters head. The same smoke is displayed to have different temperatures simply because of the position of the cameras.
The TIC does not know what you want
The thermal imager camera does not understand if you just want to measure the temperature of the walls and ceiling. To do that it would need to disregard the radiated heat coming from the smoke.
Or if you just want to measure the temperature of the smoke, and disregard the heat coming from the wall och ceiling linings.
The TIC is a compromise
For orientation inside the building the camera should clearly show where the linings, doors, windows and all the furniture are. It should ideally remove all the radiation from the smoke and only show radiation from the surfaces to create a clear picture.
But for fire attack and risk assessment you want to clearly see the smoke temperatures and the smoke movements to assess cooling needs, finding the fire and more.
So a TIC need to show both all the surfaces and also the smoke blocking them. That is a hard problem to solve which will end up in some kind of compromise.
The left camera view
In the left camera you can see the ceiling boards behind the smoke, even showing the knots from the branches. So the surfaces are clearly visible for orientation. It means that some of the radiation hitting the TIC sensor is emitted from those surfaces. The camera is trying to display the correct temperature based on that radiation.
But we also see the smoke moving in front of the surfaces. The rapid changing colors in the display is the radiation coming from flowing smoke particles like soot, and liquids like water.
The camera is receiving the radiation from the surface, and the radiation from the smoke in front of it, and showing that as an average temperature to the firefighter.
The right camera view
The right camera does the same as the left camera. It is receiving surface radiation and smoke radiation, and averages that to the displayed image temperature.
But you can see less details in the ceiling materials above the firefighters, because there is more smoke between the camera and that ceiling. There are more particles and droplets blocking the ceiling radiation reaching the sensor.
It means that the camera is showing mostly smoke temperature, rather then the ceiling temperature.
Smoke cools down really fast
The left camera position probably have hot ceiling temperatures and hot smoke temperatures with radiation hitting the sensor.
The hot smoke then flows towards the right camera position and the smoke is rapidly cooled by the building and cold incoming air being entrained. The smoke closer to the right camera position is thus colder.
The radiation coming from the hot surfaces above the firefighters are being blocked and absorbed by the colder smoke, so the right camera is receiving less radiation from those surfaces. And there is less radiation from the smoke closest to the camera because it is cold.
So the right camera indicates correctly that the average temperature is colder.
Expect hotter then indicated
Always expect that the actual temperature of the surface and/or smoke you are measuring is hotter then the camera is indicating. That is especially true if you are advancing towards the fire, using water and the distance to the target is long.
If you cannot see the surface behind the smoke you are only measuring the smoke temperature. But you might only be measuring the radiation coming from the coldest smoke closest to you, and the smoke behind that might be very hot or even flaming combustion.
A TIC is not a thermometer
The thermal imager camera is not an accurate thermometer while doing interior firefighting. And there are many tripwires to stumble upon when using it.
But the TIC is a phenomenal and vital tool for firefighting. And the measured temperature is most often not that important. We want orientation and that requires differences in temperatures to show that image clearly, not correct temperatures.
And we need rough estimates of smoke temperatures to assess if we need to cool or not, or if we are winning or not. And for those things the modern TIC is a game changer.