'If it hadn't been for that damn fire whirl we would have caught it at 5 acres,' yelled the fire boss to his assistant as they watched the fire crews mop up the final smoldering spots in a 250-acre brush fire. The fire had been contained at about 5 acres, and the crew had just started the mop-up work when a fire whirl developed in the heavy fuel near the bottom of a small ravine. Moving out of the fire area, the whirl scattered dozens of spot fires across the fireline. Unable to cope with them all, the fire crew had to abandon most of the fireline and start work anew on the top of the next ridge. The preceding account is fictitious but many such incidents occur every fire season. Fire whirls-whirlwinds of fire-are spectacular and often frustrating phenomenon. In appearance and behavior, they resemble the dust devils that often develop over strongly heated land surfaces. Originally, the term 'fire whirl' was applied only to whirls containing fire. Now it is often used for all whirls that appear in and around a fire, although many of these contain only smoke or other hot gases, ashes, and dust. A frequent even in wildland fires, the whirls vary greatly in size, strength, and duration. Fire whirls usually originate at the ground surface, but sometimes one develops above the surface and then extends to the ground. Most whirls are small, but occasionally a large one of destructive size and force develops. Airspeed in fire whirls has not been accurately measured, but must be high-possibly exceeding 300 miles per hour in large and intense whirls. In the larger whirls, the damage done is similar to that or tornadoes. In the Polo Fire near Santa Barbara, California, in 1964, for example, a large whirl moved out of the fire, demolished two houses, damaged several other buildings, and slammed a piece of quarter-inch plywood 3 inches into an oak tree. Even in moderate-size whirls, limbs may be twisted from trees and shrubs uprooted. The following discussion explores the origins and characteristics of fire whirls.
[This publication is referenced in the "Synthesis of knowledge of extreme fire behavior: volume I for fire managers" (Werth et al 2011).]