The environmental conditions for using water mist nozzles are very harsh. At first, water mist nozzles were used to cool large flammable and combustible liquid storage tanks placed in the open air to prevent them from exploding, collapsing and causing fires. In addition, a properly designed and installed water spray system can be used to extinguish and control certain flammable liquid fires, certain flammable liquid fires, Class A combustibles fires and transformer fires. Water spray system fire extinguishing is the result of one or several mechanisms of cooling suffocation, emulsification and dilution of flammable liquids. The mechanism of fire control is also exactly the same, except that the fire cannot be extinguished due to the different characteristics of the burning material.

(1) Cooling effect. The water mist particles themselves can absorb heat and have a certain cooling effect, but the process of water becoming steam is what absorbs more heat. For example, 1Ib (pounds) of water with a temperature of 60 F can absorb heat up to 1150 Btu (1 Btu = 252cal). When the surface temperature of the burning material is reduced to such an extent that flammable vapor cannot exist, the fire is extinguished.

(2) Asphyxiating effect. When the water mist turns into steam under the action of the heat generated by the fire, it will produce suffocation. After the water becomes steam, the volume expands nearly 1750 times, so the steam occupies the space where the flame burns, expelling oxygen, and the flame stops burning.

(3) Emulsification. After water and oil or other non-water-soluble liquids are mechanically stirred, the droplets of the two substances will be fully mixed together, which is emulsification. Therefore, the so-called emulsification is the impact of water spray on the surface of flammable liquid, so that the surface of the liquid loses its flammability. For liquids with poor viscosity, the emulsification effect only temporarily exists when the water spray continues to work. For viscous substances, the emulsification effect will last longer.

(4) Dilution effect. For water-soluble liquids, the contribution of dilution to fire extinguishing is small, because dilution requires high temperatures.