A fire whirl, also colloquially known as a fire devil, fire tornado, or firenado, is a whirlwind induced by a fire and often made up of flame. Fire whirls may occur when intense rising heat and turbulent wind conditions combine to form whirling eddies of air. These eddies can tighten into a tornado-like structure that sucks in burning debris and combustible gases. Rarely, however, do fire whirls grow to become actual tornadoes, which are violently rotating vortices connecting the surface to a cumuliform (such as pyrocumulus or pyrocumulonimbus) cloud base.
A fire whirl consists of a core—the part that is actually on fire—and an invisible pocket of rotating air that feeds fresh oxygen to the core. The core of a typical fire whirl is 1 to 3 feet (0.30 to 0.91 m) wide and 50 to 100 ft (15 to 30 m) tall. Under the right conditions, large fire whirls, several tens of feet wide and more than 1,000 ft (300 m) tall, can form. The temperature inside the core of a fire whirl can reach up to 2,000 °F (1,090 °C)—hot enough to potentially reignite ashes sucked up from the ground. Often, fire whirls are created when a wildfire or firestorm creates its own wind, which can turn into a spinning vortex of flame.
Combustible, carbon-rich gases released by burning vegetation on the ground are fuel for most fire whirls. When sucked up by a whirl of air, this unburned gas travels up the core until it reaches a region where there is enough fresh, heated oxygen to set it ablaze. This causes the tall and skinny appearance of a fire whirl's core.
Real-world fire whirls usually move fairly slowly. Fire whirls can set objects in their paths ablaze and can hurl burning debris out into their surroundings. The winds generated by a fire whirl can also be dangerous. Large fire whirls can create wind speeds of more than 100 mph (160 km/h)—strong enough to knock down trees.
Fire whirls can last for an hour or more, and they cannot be extinguished directly.
During the 2003 Canberra bushfires, a fire whirl with a diameter of nearly 500 metres (1,600 ft) with horizontal winds exceeding 250 km/h (160 mph) was documented. Further research into the fires confirmed this in 2012. In Canberra, wind damage consistent with an F3 tornado on the Fujita Scale was observed, in addition to the fire damage. New research released in 2013 showed that the supercell thunderstorm that caused the tornado originated from the converging winds of firestorm itself, one of the first confirmed observations of an intense thunderstorm forming from a Pyrocumulonimbus cloud.
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.
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.
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.
There is evidence suggesting that the fire whirl in the Hifukusho-ato area, during the Great Kanto Earthquake of 1923, was of type 3.
- Jason Fortofer (20 September 2012) http://news.nationalgeographic.com/news/2012/09/pictures/120920-fire-tornadoes-vortex-firenadoes-devils-science-weather/#/new-fire-tornado-spotted-australia_59442_600x450.jpg
- Jessica Nairn (20 November 2012). "Researchers document world-first fire tornado". Australian Broadcasting Corporation. Retrieved 20 November 2012.
- McRae, >McRae, R et al (1 October 2012). "An Australian pyro-tornadogenesis event.". Natural Hazards, Springer Netherlands. Retrieved 20 November 2012.
- Anja Taylor (6 June 2013). "Fire Tornado". Australian Broadcasting Corporation. Retrieved 6 June 2013.
- Quintiere, James G. (1998). Principles of Fire Behavior. Thomson Delmar Learning. ISBN 0-8273-7732-0.
- Hissong, J. E. (1926). "Whirlwinds At Oil-Tank Fire, San Luis Obispo, Calif.". Mon. Wea. Rev. 54 (4): 161–3. Bibcode:1926MWRv...54..161H. doi:10.1175/1520-0493(1926)54<161:WAOFSL>2.0.CO;2.
- 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.
- 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.
- Church, Christopher R.; John T. Snow; Jean Dessens (1980). "Intense Atmospheric Vortices Associated with a 1000 MW Fire". B. Am. Meteorol. Soc. 61 (7): 682–94. Bibcode:1980BAMS...61..682C. doi:10.1175/1520-0477(1980)061<0682:IAVAWA>2.0.CO;2.
- Fire Whirl Simulations
- 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 Aug 2010.
- Video of a Fire Tornado in San Diego country