Fire by Sebastian Junger Read Free Book Online Page B

aluminum layers to delaminate, in turn leading to rips and holes in the shelter. After the Dude fire, investigators found hard hats that had melted, leather gloves that had shrunk down to a couple of inches, and fire shelters that had begun to delaminate. Six men died, all from breathing superheated air. In all six cases they died because they had not deployed their shelters properly or because they had tried to leave them too quickly. Some of the survivors also suffered terrible burns, which suggest another possibility. The men who left the safety of their shelters may have done so because they thought they were dying inside them.
    Mike Rieser and I sat on a rock outcrop eating our lunches and watching the fire. The sun was very hot and trees torched occasionally down in the valley. Every five minutes the Skycrane went by with a tremendous whump of rotors and released another two thousand gallons of Spring Creek Lake. Clouds began to move in above us, and Rieser said that they were called lenticular clouds and that the sculpted tops meant that the upper-level winds were over one hundred miles an hour. If those winds made it down to ground level, they would have a catastrophic effect on the fire. It was his job as branch director to watch out for things like lenticularis formations or castellanus or stage three cumulonimbus or anything else that might make the fire blow up. Two days earlier Rieser had pulled two entire divisions out of a canyon because he hadn’t liked the way the fire was behaving.
    â€œWe might not look like we’re doing much, but if you’re down in the valley digging, you don’t see what’s coming at you,” he said. “Air can rise off a fire, cool in the upper atmosphere, and rush back down. It superheats as it comes down and can overpower the wind field. That’s called a plume-dominated fire. It defies prediction. It’s what killed the people at the Dude fire; the ’shot crews recognized plume-dominated conditions, but the convict crew didn’t. No one could get word to them in time.”
    Stage three cumulonimbus, thunderclouds, are a particular hazard. Not only do they introduce more lightning into the situation, but the air beneath their thirty-thousand-foot heads is extremely unstable. They can generate downward-moving winds of as much as one hundred miles an hour that hit the ground and spread out in a tremendous circle. The effect is to intensify the interaction among all three components of what is known as the fire triangle: fuel, oxygen, and heat. Ground winds spread dry, hot air through as yet unburned fuels, resulting in more fire and more heat, which in turn circulate more air, spreading the fire even faster. The result is a feedback loop that can be brought under control only if the relationships within the fire triangle break down—either by lowering the temperature of the fire or by depriving it of fuel. Water and retardant drops can bring the temperature of a fire down, and fire lines can deprive it of fuel. Otherwise, the fire spreads until the weather changes or there’s nothing left to burn.
    In the Northern Rockies wildfire is usually started by lightning. Any lightning strike that reaches the ground can cause an explosion, but only lightning with a continuous current can start fires. In the Northern Rockies it has been estimated that one lightning stroke in twenty-five is a cloud-to-ground stroke capable of starting a fire. The inital bolt from cloud to ground moves relatively slowly, at one two-thousandths the speed of light, but it returns at one-tenth the speed of light and heats the gases inside it to fifty thousand degrees Fahrenheit. That much energy hitting a tree instantly raises it way past the ignition point, and often the tree just explodes. Flaming chunks of wood are hurled into the forest, and if the conditions are right for fire, the flames take hold.
    Fire is a chemical reaction that releases energy in the form of