One important task of the first crew inside is to quickly find the fire and dampen it enough to allow early and massive ventilation of the building.
Early and massive ventilation is our primary tool to achieve rescues, increase safety and save property.
To find the fire quickly, we can often follow the hot convective currents back towards the fire.
Smoke is layered
The smoke from combustion is hot and flows away from the fire under the ceiling. Eventually the smoke will hit a wall and start to flow in a new direction.
During this travel the smoke has cooled down and is now heavier than the latest smoke produced by the fire. This means that the colder smoke will flow under the hot smoke, in some new direction. It might even flow back towards the fire.
The layered smoke has different temperatures, content and movement. And smoke travel inside a building can be very complex.
Smoke blocks vision
Smoke from fires is often visually hard to see through due to all the particles. In the smoke layer, the hottest smoke in the top of the layer is often hidden behind the colder smoke below it.
It means that we most often only see what happens in the bottom smoke layer.
The top smoke layer is hidden
In the left bottom view we can see a normal camera image showing smoke gathering in the ceiling on the second floor up the stairs.
Visually, we can see that there is some movement in the smoke but it is hard to see any clear direction. The smoke is actually coming from a fire on the second floor, to the left up the stairs.
If we only had the vision from our eyes we might not see where the smoke is coming from.
The TIC is bad at showing movement to or from the camera
In the top left view we can see a thermal imager camera (TIC) on the second floor, looking directly against the fire compartment.
In this image we can clearly see that there is lots of movement in the smoke coming from the fire compartment behind the door.
But it is hard to see where the smoke is flowing because it is moving directly against the camera. And the TIC is very bad at showing distance, which make it hard to see movements to and from the camera.
The TIC detects all radiation
In the right video view we can see the image from another TIC looking up the staircase towards second floor.
The TIC is in this situation able to detect the radiation coming from the ceiling surface behind the smoke, the hottest smoke in the top layer and the colder smoke below it.
The resulting image clearly shows the hottest and fastest convective flow of smoke coming from the fire. And because the smoke is not flowing directly against the camera, it is also very easy to see the direction it moves.
Follow the fastest and/or hottest smoke
The fastest current, or the hottest current, of smoke is most often coming from the fire compartment. We can follow that current back against the flow, to its source, to suppress the fire as fast as possible.
The thermal imager camera is an invaluable tool that allow us to see and follow convective currents in the smoke, something that would be hard or impossible with just our eyes.
If you find yourself reverse tracking a hot smoke current which ends up coming from below you, retreat and consider an alternative route to the fire.
Being above the fire could be a dangerous position and should be avoided if possible.