Scientists used to think fire tornadoes were rare, even unlikely, but as megafires become more common, that is no longer the case. Fire tornadoes begin with turbulent, strong winds that send a lopsided current of air into the flames. As the inflow begins to swirl around, the flames themselves become quite organized. Air then streams in faster from the bottom, fanning the flames and strengthening the whirl.
As Megafires Have Become More Common, So Have Fire Tornadoes
Published: May 6, 2019
Craig Clements: Fire whirls that form on your average fire, you see them 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 Carr megafire spawns a deadly fire tornado that generates winds approaching 165 miles an hour.
But what causes the flames to start spinning?
Mark Finney: 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.
Finney: You’ll notice, at the beginning, that the flames are very disorganized. But as the inflow begins to come 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.
Finney: 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.
Clements: This was ranked as an EF3, Enhanced Fujita scale, tornado. I believe this is the strongest documented fire-induced tornado.
Narrator: Temperatures reach 2,700 degrees Fahrenheit, hot enough to melt steel. It lasts for 30 minutes.
Clements: 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 that do that are extreme.
Inside the Megafire
Produced by: Will Toubman
Produced and Edited by: Brian Truglio
Produced and Directed by: Miles O'Brien
Digital Producer: Ana Aceves
© WGBH Educational Foundation 2019