Water is the first and main known extinguishing agent. It is used in all sprinkler systems.
In contact with the heat, the water vaporizes, and the water vapor thus created heats the air (the steam occupies 1,700 times more space than the volume of water which was used to generate it at 100 ° C., and 4,200 times the volume at 650°C), depriving the fire of oxidizer.
In addition, water participates in cooling (vaporization absorbs heat): the rise in temperature of the water (passage of water at 15 ° C to water at 100 ° C) consumes a lot of energy, but the transition from one state to another (vaporization) consumes even more energy. Thus, water cools the atmosphere, fumes, objects, walls... and thus prevents the fire from spreading. Once the fire has been extinguished, it is possible to continue cooling with water if necessary to prevent the fire from continuing. Fire extinguishing by water is therefore a combination of "choking" by steam and cooling. Water as extinguishing agent is mainly suitable for Class A fires, whose fuel is solid.
For other types of fire, it will be necessary to consider coupling the water to an additive or to change its mode of projection (water mist) to optimize the extinguishing efficiency. Finally, in particularly hostile environments or at risk, the use of an additional foam concentrate will be necessary, it is foam extinguishing systems.