Water extinguishes fire primarily by cooling the burning material below its ignition temperature and by smothering (displacing oxygen) as it turns into steam. The cooling effect is due to water's high specific heat capacity and high latent heat of vaporization. Cold water, compared to hot or boiling water, needs to absorb more heat to reach its boiling point (100°C) and then vaporize. This means a given mass of cold water can absorb a greater amount of heat from the fire, leading to more efficient cooling and quicker extinguishment. Boiling water is already at its boiling point and only absorbs heat through vaporization, while hot water requires less energy to reach boiling and vaporize compared to cold water. Ice must first absorb heat to melt before it can absorb further heat as liquid water and then vaporize, making its action potentially slower initially compared to liquid water directly applied.
Which one of the following can extinguish fire more quickly?
Asked in UPSC CDS 2 2018 · Topic: Heat and Thermodynamics (Modes of Heat Transfer (Conduction, Convection, Radiation))
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