Fire whirl

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A fire whirl with flames in the vortex

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 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.

Most of the largest fire whirls are spawned from wildfires. They form when a warm updraft and convergence from the wildfire are present.[1] 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.[2]

Fire whirls can uproot trees up to 15 metres (49 ft) tall.[3] These can also aid the 'spotting' ability of wildfires to propagate and start new fires as they loft burning materials such as tree bark. These burning embers can be blown away from the fireground by the stronger winds aloft.

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Fire Tornado [edit]

During the 2003 Canberra bushfires, a fire tornado with a diameter of nearly 500 metres with horizontal winds exceeding 250 kph was documented. Further research into the fires confirmed this in 2012.[4]

[5] In this major Canberra fire wind damage consistent with an F3 tornado on the Fujita Scale was observed in addition to the fire damage

Another extreme example of a fire tornado from other than a vegetation fire 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.[6] 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. 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.[7]

Classification [edit]

There are currently three known types of fire whirls:[8]

  • 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.

There is evidence that suggests that the fire whirl in the Hifukusho-ato area, during the Great Kanto Earthquake of 1923, was of type 3. [9]

References [edit]

  1. ^ Umscheid, Michael E.; J.P. Monteverdi, J.M. Davies (2006). "Photographs and Analysis of an Unusually Large and Long-lived Firewhirl". Electronic Journal of Severe Storms Meteorology 1 (2). 
  2. ^ Grazulis, Thomas P. (July 1993). Significant Tornadoes 1680–1991: A Chronology and Analysis of Events. St. Johnsbury, VT: The Tornado Project of Environmental Films. ISBN 1-879362-03-1. 
  3. ^ Otways Fire No. 22 - 1982/83 Aspects of fire behaviour. Research Report No.20 (PDF). Victoria Department of Sustainability and Environment. June 1983. Retrieved 2012-12-19. 
  4. ^ Jessica Nairn (20 November 2012). "Researchers document world-first fire tornado". Australian Broadcasting Corporation. Retrieved 20 November 2012. 
  5. ^ McRae, >McRae, R et al (1 October 2012). "An Australian pyro-tornadogenesis event.". Natural Hazards, Springer Netherlands. Retrieved 20 November 2012. 
  6. ^ Quintiere, James G. (1998). Principles of Fire Behavior. Thomson Delmar Learning. ISBN 0-8273-7732-0. 
  7. ^ Hissong, J. E. (April 1926). "Whirlwinds At Oil-Tank Fire, San Luis Obispo, Calif." (abstract). Monthly Weather Review 54 (4): 161–3. Bibcode:1926MWRv...54..161H. doi:10.1175/1520-0493(1926)54<161:WAOFSL>2.0.CO;2. 
  8. ^ Williams, Forman (22 May, 2009). "The Occurrence and Mechanisms of Fire Whirls". La Lolla, California; Valladolid, Spain: MAE UCSD; Spanish Section of the Combustion Institute. 
  9. ^ Kuwana, Kazunori; Kozo Sekimoto, Kozo Saito, Forman A. Williams (May 2008). "Scaling fire whirls". Fire Safety Journal 43 (4): 252–257. doi:10.1016/j.firesaf.2007.10.006. Retrieved 30 January 2013. 

Sources [edit]

External links [edit]

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