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A fire whirl, colloquially fire devil or fire tornado, is a phenomenon—rarely captured on camera—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 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.
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 away.
Most of the largest fire tornados are spawned from wildfires. They form when a warm updraft and convergence from the wildfire are present. They are usually 10-50 meters tall, a few meters wide, and last only a few minutes. However, some can be more than a kilometer tall, contain winds over 160 km/h, and persist for more than 20 minutes.
Fire whirls can uproot trees up to 15 metres (49 ft) tall. These can also aid the 'spotting' ability of wildfires to propagate and start new fires.
Visually impressive fire whirls may be encountered during dry wind gusts at the annual Burning Man festival in Nevada's Black Rock Desert, late on Saturday or Sunday evening during the burning of The Man or Temple, respectively.