Fire Tornado Seen Spinning Over Hungary

The cause of the fire remains unknown, and no casualties were reported, according to the Reuters news service.

Also known as fire whirls, fire devils, or even firenados, fire tornadoes form when high heat and turbulent winds together spur whirling eddies of air, mechanical engineer Jason Forthofer told National Geographic News in September.

These eddies can tighten into a tornado-like structure that sucks in burning debris and flammable gases, said Forthofer, of the U.S. Forest Service's Missoula Fire Sciences Laboratory in Montana.

The fiery core inside the swirling "tube" of winds is usually about 1 to 3 feet (0.3 to 0.9 meter) wide and five to ten stories tall. At the extreme, though, fire tornadoes can stretch dozens of feet wide and more than a hundred stories tall, Forthofer said. (Related: "Giant 'Tornadoes' Seen Erupting From the Sun.")

The firenadoes, he added, aren't so much rare as rarely reported—perhaps because they tend to occur during wildfires, rather than in urban centers.

Relatively persistent, fire tornadoes can last for an hour or more and can be put out only when their sources—the fires below—are extinguished. (Also see "Wildfire Pictures: Russia Burns, Moscow Chokes.")

In addition to studying how fire whirls form and can best be fought, Forthofer hopes to perfect fire tornado prediction.

"If we can identify conditions that are conducive to fire whirls," he said. "That would be a heads-up for firefighters, because there have been some [people] that have been burned by them."

—With reporting by Ker Than

http://news.nationalgeographic.com/news/2011/110304-fire-tornado-picture-firenado-science-whirl-devil-budapest-hungary/