This, combined with the fact it is available in large quantities, makes it by far the most widely useful fire extinguishing agent. Water is a good cooling agent because of its high thermal capacity and latent heat of vaporisation. High specific heat capacity (thermal capacity).The properties of a good cooling agent are therefore: To achieve maximum effect, the quantity of heat energy absorbed should be as great as possible. It may react chemically with the burning material.When water is applied, it undergoes changes as it absorbs heat from the fire: Eventually, the rate at which heat is lost from the fire may be greater than the rate of heat production and the fire will die away. This reduces the temperature of the burning mass, reducing the heat release rate. To extinguish a fire by cooling, the rate at which heat energy is lost from the burning material must be increased by removing some of the heat energy. For example, if the rate at which heat is generated by combustion is lower than the rate at which it is lost from the burning material, burning will not continue. This process depends on cooling the fuel to a point where it does not produce sufficient vapour to burn, with the reduction in temperature dependent on the application of an adequate flow of water to establish a negative heat balance. One of the most common methods of extinguishing a fire is by cooling with water.
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