How does watermist interfere with the fires chemical processes?
Fighting the oxidation process
Cooling the fire: The small water droplets are easily evaporated since they have a large surface area per volume water. When water is evaporated it costs energy and this energy is taken away from the fire. If just as much energy can be taken away as the fire produces the fire is under control.
Suffocating the fire: Water steam is created when water is evaporated and steam is an inert gas which does not take part of the oxidation process. It therefore helps reduce the amount of oxygen in the vicinity of the fire, since it replaces the “normal” atmosphere. The more inert gas kept close to the fire, the better the performance is, and if just as much inert gas can be kept as normal atmosphere, the oxygen level will reduce to 11% and the fire cannot exist since it cost more energy to run the oxidation process than it produces.
Fighting the pyrolysis process
Blowing out the fire: Water droplets are distributed from the nozzles with a high velocity and this can be used to blow out the fire. What in fact happens is that the energy source is removed from the fuel surface, so no additional flammable gasses can be created. Doing so enables the fire to suffocate itself.
Wetting the fire: Some of the distributed water will cover the fuel surface and prohibit flammable gasses to be created as the water needs to be evaporated before the fuel surface can be heated up and create the gasses. The more water distributed on the fuel, the more effective it becomes.