Why does adding water to a grease fire make it worse?
Pouring water on a grease fire exacerbates the situation due to the fundamental differences in the physical properties of water and oil, and how they interact with heat.
Oil, which is less dense than water, tends to sit above water. When water is poured onto a grease fire, it instantly sinks below the oil due to its higher density. Since the fire is intensely hot, often exceeding the boiling point of water (100°C or 212°F), the water immediately turns into steam. This rapid expansion (water expands by about 1,700 times when it vaporizes) can spray flaming oil droplets into the air, significantly increasing the fire's spread and intensity.
Moreover, the transition from water to steam at such a quick rate creates a violent eruption effect, which can propel burning grease out of the pan. This not only spreads the fire across a larger area but also poses a severe risk of burns to anyone nearby. The explosive reaction is partially due to the sudden release of energy as water molecules transition from a liquid to a gaseous state, dispersing hot oil and flame in the process. This makes controlling or extinguishing the fire much more challenging, as the fire can rapidly spread beyond the initial confines of the cooking vessel.
The heat of the grease fire also plays a critical role in this dangerous interaction. Grease fires occur when cooking oil becomes too hot — typically beyond its smoke point and then to its ignition point. At these extremely high temperatures, adding water causes the water to flash evaporate. Since oil burns at a temperature much higher than water's boiling point, the water at the bottom of the pan is superheated almost instantaneously. This rapid vaporization increases the surface area over which the fire can spread, effectively turning a contained fire into a widespread hazard.
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