The basic principle for this idea is to create a localized change in weather such that a fire will die out, be suppressed or forced to burn away from the area of coverage.
This is accomplished by 3 things: Large volume of high velocity wind, large amount of chilled/cold water, separated into small particulate drops (mist.)
Fire requires 3 things to burn: Fuel, Oxygen and Heat. Reduction and removal of anyone of these will kill the fire.
With a high wind directing the fire in an alternate direction and the cold water dropping the temperature, a forest fire burning toward a neighborhood would be forced to pick a different direction. It would be difficult for the fire to create enough heat to continue moving in the direction toward the firefighting vehicle.
This is accomplished by a large fan specifically designed to move a high volume of air at a high speed. The size should be as large as a truck can handle without tipping over. Water should be fed into the flow of air in such a way that it produces a very thick mist. Preferable the same amount of water used currently in a fire hose should be fed into the fan. Chilled water should be used or the water should be artificially cooled to produce the heat killing effect on the fire.
If the dew point is raised and the air temperature is droped this will significantly reduce the fire or kill it completely. This happens because the energy the fire needs to overcome these weather effects to continue burning, will be too great. It will either turn away and seek easier place to burn, die as it finds itself without fuel left to burn or be suppressed enough firefighters will have a safe enough atmosphere they can get in and safely breakup the fire.
I see this technology being used to protect neighborhoods from forest fires or using this inside a building to quickly change the atmosphere to one in which a fireman can survive.
It can potentially save lots of property and the lives of many fireman.