NOVA

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Man

Fire whirls that form on your average fire, you see 'em for a few seconds, and they're gone. -

Narrator

And normally they don't prompt too much concern. But the biggest ones, literally fire tornadoes, cannot be ignored. Scientists used to think they were rare, even unlikely, but as megafires become more common, that is no longer the case. Three months before the camp fire, this is what happens in Redding California. The the Carr Megafire spawns a deadly fire tornado that generates winds approaching 165 miles and hour. But what causes the flames to start spinning? This here, is a fire whirl generator. It's an apparatus that allows us to study how fire whirls form and the structure of the vortex that's produced inside the whirl. -

Narrator

Mark Finney says, "They begin "with turbulent, strong winds "that send a lopsided current of air into the flames." He demonstrates what happens next. You'll notice at the beginning that the flames are very disorganized. But as the inflow begins to come in, in a swirling fashion, the flames themselves become quite organized. -

Narrator

The air streams in faster and faster from the bottom, fanning the flames, strengthening the whirl. The burning rate of the fuel increases by three to eight times as the whirl begins to develop. -

Narrator

The fire tornado in Redding, develops after the wind starts blowing inland, from the Pacific. When it collides with the fire, it creates powerful swirling winds. All the ingredients of an epic fire tornado are now in place. -

Man

This was ranked as a EF-3, Enhanced Fujita Scale. I believe this is the strongest documented fire induced tornado. -

Narrator

Temperatures reach 2700 degrees Fahrenheit. Hot enough to melt steel. It lasts for 30 minutes. We saw things like pipes wrapped around trees. Flipped over cars, power lines that were broken off from 90 foot towers that were taken down. The winds to do that are extreme.