A fire whirl – also commonly known as a fire devil, or, (in many cases) erroneously, as a fire tornado, firenado, or fire twister – is a whirlwind induced by a fire and often made up of flame or ash. They usually start with a whirl of wind or smoke. Fire whirls may occur when intense rising heat and turbulent wind conditions combine to form whirling eddies of air. These eddies can contract into a tornado-like vortex that sucks in burning debris and combustible gases.
Fire whirls are sometimes colloquially called fire tornadoes, but are not usually classifiable as tornadoes as the vortex in most cases does not extend from the surface to cloud base. Also, even in such cases, even those fire whirls are not classic tornadoes, in that their vorticity derives from surface winds and heat-induced lifting, rather than a tornadic mesocyclone aloft. The literal fire tornado is a rare phenomenon, much more powerful and destructive than the a typical fire whirl, in which the wildfire generates a pyrocumulonimbus cloud that then spawns a tornado. When this tornado forms in or enters the fire zone, it fans flames enormously, draws flame and burning debris into itself, and scatters burning debris over a wide area.
A fire whirl consists of a burning core and a rotating pocket of air. A fire whirl can reach up to 2,000 °F (1,090 °C). Often, fire whirls are created when a wildfire or firestorm creates its own wind, which can turn into a vortex of fire. This causes the tall and skinny appearance of a fire whirl's core.
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 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 as they lift burning materials such as tree bark. These burning embers can be blown away from the fireground by the stronger winds aloft.
An extreme example of a fire tornado 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 people 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 7 April 1926, several of which produced significant structural damage well away from the fire, killing two. Many 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.
A fire whirl, of reportedly uncommon size for New Zealand wildfires, formed on day three of the 2017 Port Hills fires in Christchurch. Pilots estimated the fire column to be 100 metres (330 ft) high.
There are currently three known types of fire whirls:
- Type 1: Stable and centered over burning area.
- Type 2: Stable or transient, downwind of burning area.
- Type 3: Steady or transient, centered over an open area adjacent to an asymmetric burning area with wind.
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- van Beynen, Martin (11 March 2017). "Firestorm". The Press. pp. C1–C4. Retrieved 12 March 2017.
- Williams, Forman (22 May 2009). "The Occurrence and Mechanisms of Fire Whirls" (PDF). La Lolla, California; Valladolid, Spain: MAE UCSD; Spanish Section of the Combustion Institute.
- Kuwana, Kazunori; Kozo Sekimoto; Kozo Saito; Forman A. Williams (May 2008). "Scaling fire whirls". Fire Safety Journal. 43 (4): 252–7. doi:10.1016/j.firesaf.2007.10.006.
|Wikimedia Commons has media related to Fire whirls.|
- photo fire whirl outback Australia
- New, Elizabeth (1 November 2012). "Fire tornadoes: a rare weather phenomenon". Australian Geographic. Retrieved 6 March 2017.
- Fire tornado video (whirl) 11 September 2012 Alice Springs Australia
- www.abc.net.au/news Australian researchers document world-first fire tornado.
- Catalyst story: Fire Tornado
- Another photo
- www.youtube.com Video of a Fire whirl (0:30), Brazil.
- "Rare Footage of Fire Tornado". BBC. 25 August 2010.
- Video of a Fire Tornado in San Diego country
- Fire Whirl Simulations