A fire whirl or fire devil (sometimes referred to as a fire tornado) is a
whirlwind induced by a
fire and often (at least partially) composed of
flame or
ash. These start with a whirl of
wind, often made visible by
smoke, and may occur when intense rising heat and turbulent wind conditions combine to form whirling
eddies of air. These eddies can contract a
tornado-like
vortex that sucks in debris and combustible gases.
The phenomenon is sometimes labeled a fire tornado, firenado, fire swirl, or fire twister, but these terms usually refer to a separate phenomenon where a fire has such intensity that it generates an actual tornado. Fire whirls 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, those fire whirls very rarely are classic tornadoes, as their
vorticity derives from surface
winds and heat-induced lifting, rather than from a tornadic
mesocyclone aloft.[1]
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).[2] Fire whirls become frequent when a
wildfire, or especially
firestorm, creates its own wind, which can spawn large vortices. Even
bonfires often have whirls on a smaller scale and tiny fire whirls have been generated by very small fires in laboratories.[3]
Most of the largest fire whirls are spawned from wildfires. They form when a warm
updraft and convergence from the wildfire are present.[4] They are usually 10–50 m (33–164 ft) tall, a few meters (several feet) wide, and last only a few minutes. Some, however, can be more than 1 km (0.6 mi) tall, contain
wind speeds over 200 km/h (120 mph), and persist for more than 20 minutes.[5]
Fire whirls can uproot trees that are 15 m (49 ft) tall or more.[6] 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 fire-ground by the stronger winds aloft.
Fire whirls can be common within the vicinity of a
plume during a
volcanic eruption.[7][8] These range from small to large and form from a variety of mechanisms, including those akin to typical fire whirl processes, but can result in
Cumulonimbus flammagenitus (cloud) spawning
landspouts and
waterspouts[9] or even to develop mesocyclone-like updraft rotation of the plume itself and/or of the cumulonimbi, which can spawn tornadoes similar to those in
supercells.[10] Pyrocumulonimbi generated by large fires on rare occasion also develops in a similar way.[11][1][12][13]
Classification
There are currently three widely recognized types of fire whirls:[14]
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
1923 Great Kantō earthquake, was of type 3.[15] Other mechanism and fire whirl dynamics may exist.[16] A broader classification of fire whirls suggested by
Forman A. Williams includes five different categories:[17]
Whirls generated by fuel distribution in wind
Whirls above fuels in pools or on water
Tilted fire whirls
Moving fire whirls
Whirls modified by vortex breakdown
The meteorological community views some fire-induced phenomena as atmospheric phenomena. Using the pyro- prefix, fire-induced clouds are called
pyrocumulus and
pyrocumulonimbus. Larger fire vortices are similarly being viewed. Based on vortex scale, the classification terms of pyronado, "pyrotornado", and "pyromesocyclone" have been proposed.[18]
Notable examples
During the 1871
Peshtigo fire, the community of Williamsonville,
Wisconsin, was burned by a fire whirl; the area where Williamsonville once stood is now Tornado Memorial County Park.[19][20][21]
An extreme example of a fire whirl is the
1923 Great Kantō earthquake in Japan, which ignited a large city-sized firestorm which in turn produced a gigantic fire whirl that killed 38,000 people in fifteen minutes in the
Hifukusho-Ato region of
Tokyo.[22]
Numerous large fire whirls (some tornadic) that developed after
lightning struck an oil storage facility near
San Luis Obispo,
California, on 7 April 1926, 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 km (3.1 mi) away.[23]
Throughout the 1960s and 1970s, particularly in 1978–1979, fire whirls ranging from the transient and very small to intense, long-lived tornado-like vortices capable of causing significant damage were spawned by fires generated from the 1000
MWMétéotron, a series of large oil wells located in the
Lannemezan plain of
France used for testing atmospheric motions and thermodynamics.[25]
During the
2003 Canberra bushfires in
Canberra,
Australia, a violent fire whirl was documented. It was calculated to have horizontal winds of 160 mph (260 km/h) and vertical air speed of 93 mph (150 km/h), causing the
flashover of 300 acres (120 ha) in 0.04 seconds.[26] It was the first known fire whirl in Australia to have EF3 wind speeds on the
Enhanced Fujita scale.[27]
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 m (330 ft) high.[28]
Residents in the city of
Redding, California, while evacuating the area from the massive
Carr Fire in late July 2018, reported seeing
pyrocumulonimbus clouds and tornado-like behaviour from the firestorm, resulting in uprooted trees, cars, structures and other wind related damages in addition to the fire itself. As of August 2, 2018, a preliminary damage survey, led by the
National Weather Service (NWS) in
Sacramento, California, rated the July 26th fire whirl as an
EF3 tornado with winds in excess of 143 mph (230 km/h).[29]
On August 15, 2020, for the first time in its history, the U.S. National Weather Service issued a tornado warning for a
pyrocumulonimbus created by a wildfire near
Loyalton, California, capable of producing a fire tornado.[30][31][32]
Blue whirl
In controlled small-scale experiments, fire whirls are found to transition to a mode of combustion called blue whirls.[33] The name blue whirl was coined because the soot production is negligible, leading to the disappearance of the yellow color typical of a fire whirl. Blue whirls are partially premixed flames that reside elevated in the recirculation region of the vortex-breakdown bubble.[34] The flame length and burning rate of a blue whirl are smaller than those of a fire whirl.[33]
^Chuah, Keng Hoo; K. Kuwana (2009). "Modeling a fire whirl generated over a 5-cm-diameter methanol pool fire". Combust. Flame. 156 (9): 1828–1833.
doi:
10.1016/j.combustflame.2009.06.010.
^Grazulis, Thomas P. (July 1993). Significant Tornadoes 1680–1991: A Chronology and Analysis of Events. St. Johnsbury, VT: The Tornado Project of Environmental Films.
ISBN1-879362-03-1.
^Cunningham, Phillip; M. J. Reeder (2009). "Severe convective storms initiated by intense wildfires: Numerical simulations of pyro-convection and pyro-tornadogenesis". Geophys. Res. Lett. 36 (12): L12812.
Bibcode:
2009GeoRL..3612812C.
doi:
10.1029/2009GL039262.
S2CID128775258.
^Kinniburgh, David C.; M. J. Reeder; T. P. Lane (2016). "The dynamics of pyro-tornadogenesis using a coupled fire-atmosphere model". 11th Symposium on Fire and Forest Meteorology. Minneapolis, MN: American Meteorological Society.
^Kuwana, Kazunori; Sekimoto, Kozo; Saito, Kozo; Williams, Forman A. (May 2008). "Scaling fire whirls". Fire Safety Journal. 43 (4): 252–7.
doi:
10.1016/j.firesaf.2007.10.006.
^Chuah, Keng Hoo; K. Kuwana; K. Saito; F. A. Williams (2011). "Inclined fire whirls". Proc. Combust. Inst. 33 (2): 2417–2424.
doi:
10.1016/j.proci.2010.05.102.
^Williams, Forman A. (2020). "Scaling considerations for fire whirls". Progress in Scale Modeling. 1 (1): 1–4.
doi:
10.13023/psmij.2020.02.
^McCarthy, Patrick; Cormier, Leanne (23 September 2020).
"Proposed Nomenclature for Fire-induced Vortices". CMOS BULLETIN SCMO. Canadian Meteorological and Oceanographic Society.
Archived from the original on 20 October 2020. Retrieved 18 October 2020.
^Coenen, Wilfried; Kolb, Erik J.; Sánchez, Antonio L.; Williams, Forman A. (July 2019). "Observed dependence of characteristics of liquid-pool fires on swirl magnitude". Combustion and Flame. 205: 1–6.
arXiv:2202.06567.
doi:
10.1016/j.combustflame.2019.03.032.
S2CID132260032.