In this video from a training burn we can see two normal cameras on the left side.
The bottom camera view is from a camera positioned about 1 meter (3 feet) above the floor.
The top camera view is from a camera positioned directly at the floor.
Both cameras are in the same room directed towards the fire in a compartment further in.
Steam condenses on cold surfaces
The image from the camera positioned higher up starts to get blurry, while the image from the lower camera stays sharp.
The blurry image is due to steam (or water vapor / water gas) in the air that condenses to droplets (liquid) on the cold lens of the camera.
In this case, the steam is created by the combustion process and also vaporized from all the organic materials in the fire compartment.
Air with more steam (wet air) is lighter than air with less steam (dry air). Outside, the steam (commonly called moisture) rises into the sky until it becomes colder and the steam condenses back into tiny droplets (or water mist). And voila, we have clouds.
That is at least partially why the image from the higher camera blurs before the lower one. Steam rises, is a simpler way of describing it.
Steam make the TIC image blurry too
As long as the steam stays in vapor form, the TIC (or Thermal Imager Camera) can see through it.
But if the steam starts to condense into water droplets in air, or directly on the TIC lens, we eventually get a blurry image in the TIC too.
This blog post on cleaning the TIC lens might be interesting to read on that matter.
Breaking hydrogen bonds are hard
To vaporize water to steam requires a lot of energy. You need to break the hydrogen bonds that keep water as a liquid. That is a great feature to use for fire suppression.
But reversely, when steam condenses back into a liquid, that same energy is released.
My basic rule is this. If you are inside smoke from a fire and you cannot see your feet, you should probably be on your knees and staying low.
If steam condensation happens on and inside your PPE, well that is a sucky situation. All that energy will be transferred to you and it will get hot.
Staying low in smoke is important for several reasons, avoiding steam is one of them.
The irony of firefighting
I find it fascinating that one of the big end products from combustion is water. When burning 1 gram of hydrocarbons, the fire creates almost the same amount of water.
It is somewhat ironical as a firefighter 🙂