Fire whirl

Fire whirl

A fire whirl, colloquially fire devil or fire tornado, is a phenomenon in which a fire, under certain conditions (depending on air temperature and currents), acquires a vertical vorticity and forms a whirl, or a tornado-like effect of a vertically oriented rotating column of air. Fire whirls may be whirlwinds separated from the flames, either within the burn area or outside it, or a vortex of flame, itself.

A fire whirl can make fires more dangerous. An extreme example is the 1923 Great Kantō earthquake in Japan which ignited a large city-sized firestorm and produced a gigantic fire whirl that killed 38,000 in fifteen minutes in the Hifukusho-Ato region of Tokyo. Another example is the numerous large fire whirls (some tornadic) that developed after lightning struck an oil storage facility near San Luis Obispo, California on April 7, 1926, several of which produced significant structural damage well away from the fire, killing two. Thousands of whirlwinds were produced by the four-day-long firestorm coincident with conditions that produced severe thunderstorms, in which the larger fire whirls carried debris 5 kilometers (3 mi) away.

Most of the largest fire whirls are spawned from wildfires. They form when a warm updraft and convergence from the wildfire are present. They are usually 10-50 meters (30-200 ft) tall, a few meters (~10 ft) wide, and last only a few minutes. However, some can be more than a kilometer (0.6 mile) tall, contain winds over 160 km/h (100 mph), and persist for more than 20 minutes.

These can also aid the 'spotting' ability of wildfires to propagate and start new fires.

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