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Fire Whirl Research

Understanding Fire Whirl Genesis and Impacts to Firefighter Safety

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Synthesis of existing knowledge and new research was used to understand fire whirl genesis, behavior, and firefighter safety impacts.

Fire whirls, especially the larger ones, represent a considerable safety hazard to firefighters through increased fire intensity, spotting, erratic spread rate and direction, and wind damage. Fire whirls range in size from less than 1 m in diameter and velocities less than 10 m/s up to possibly 3 km in diameter and winds greater than 50 m/s. They have been observed in wildland, urban, and oil spill fires and volcanic eruptions. Dynamically, they are closely related to other swirling atmospheric phenomena such as dust devils, water spouts, and tornadoes.

Extremely large fire whirls have been reported in urban fires that illustrate their potentially destructive nature. The most devastating on record is probably the 1923 Tokyo fire whirl that was caused by large urban fires following an earthquake. This large whirl was estimated to have killed 38,000 people in less than 15 minutes. Other massive urban fire whirls were reported during the World War II city bombings of Hamburg, Dresden, and Hiroshima. The Hamburg whirl was estimated at 2.4 to 3 km in diameter and 5 km tall.

Small to medium size fire whirls are fairly common on wildland fires, and on rare occasions very large fire whirls may form. These whirls are capable of wind damage similar to weak or moderate tornadoes (probably in the range of EF 0 to EF 2). Uprooting and breaking of large trees, tipping of automobiles, and tearing off roofs of houses have all been documented. Burning rates are significantly increased when fire whirls form, with laboratory studies showing rates up to 7 times the no-whirl case. Profuse spotting typically occurs, along with erratic spread.

Firefighters should use extreme caution when a fire whirl develops in their vicinity. All firefighters in the area should be notified, and moving out of the area should be considered depending on the size, severity, duration, and proximity of the whirl. Fire whirls are normally either stationary or get blown downwind, but recent laboratory evidence suggests that in some cases they could move against the ambient wind. Recent fire whirls that have caused shelter deployments and/or firefighter injuries include the 2001 Fish Fire in Nevada , the 2006 New York Peak Fire in Nevada, and the 2008 Indians Fire in California (lessons learned video). Large fire whirls formed on the 2002 Missionary Ridge Fire in Colorado, as shown on the Firestorm Induced Tornado webpage.

A scientific literature review and synthesis has recently been undertaken to summarize past work. This can be found in the following two publications:

Fire whirl training video

 

 

Modified: Jun 26, 2014

Select Publications & Products

Jason M. Forthofer and Scott L. Goodrick, “Review of Vortices in Wildland Fire,” Journal of Combustion, vol. 2011, Article ID 984363, 14 pages, 2011. doi:10.1155/2011/984363

Werth, Paul A.; Potter, Brian E.; Clements, Craig B.; Finney, Mark A.; Goodrick, Scott L.; Alexander, Martin E.; Cruz, Miguel G.; Forthofer, Jason A.; McAllister, Sara S. 2011. Synthesis of knowledge of extreme fire behavior: volume I for fire managers. Gen. Tech. Rep. PNW-GTR-854. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 144 p.