In his four decades of fighting fires, Joe Hessel has rarely seen a fire prove so difficult to control like the Bootleg Fire, the sprawling blaze that over the past two weeks has burned nearly 400,000 acres in southern Oregon.
And what made this the fire different from most, he said on Wednesday, was consecutive days of what firefighters are calling behaviorof extreme fire.
"It is not uncommon to have a few days in a row, or a day here and there, of behavior in 'extreme fire,' said Hessel, an incident commander for the Oregon Department of Forestry team trying to quell the Bootleg fire.
"But on this incident, it was 13 or 14 days in a row," he said. “When you have this type of fiery behavior, it's hard enough to keep up with it, let alone get ahead of it.
So what do firefighters mean by extreme fire behavior? Typically, it includes some or all of the following:
a high spread rate
des flammes that grow through the branches and leaves of trees as well as shrubs, without the aid of ground fire
the existence of fire vortices, which are vortices of hot air and gas rising from a fire on the ground and carrying debris, flames and smoke in the air. They range from less than a foot to over 500 feet in diameter. The bigger ones look like the intensity of a small tornado.
the presence of a convection column, which sends gases, smoke, fly ash, particles and other debris produced by a fire directly into the air, propagating vertically rather than horizontally .
Fires with one or more of these characteristics are difficult to predict because they generate their own weather . Intensity and extreme heat can strain the wind to bypass them, creating clouds and sometimes forming tornadoes of fire.