What is the primary function of water when applied to a fire?

The primary function of water when applied to a fire is to cool below combustion temperature. Water is used in firefighting due to its high heat capacity, meaning it can absorb a significant amount of heat without a large increase in temperature. When water is applied to a fire, it absorbs heat from the flames and the surrounding materials, effectively lowering their temperature. This cooling action reduces the temperature of the burning materials below their ignition point, thus interrupting the combustion process and helping to extinguish the fire.

In addition to cooling, water also works by converting to steam when heated, which can further displace oxygen in the vicinity of the fire. However, the primary and most effective action is the cooling effect that water provides, which is crucial in fire suppression tactics.