Rendering Inferno

Flames leap 200 feet in the air and burn at 2,000 degrees. A rain of fire sets thousands of acres ablaze. The smoke jumpers may get the glory, but the battle is being won by the wildfire simulation brigade.

It was one of the worst years for wildfires in Montana's history: In 2003, more than 2,300 fires torched three-quarters of a million acres - nearly 20 percent of the total burned by wildfires across the US. The western part of the state was hardest hit, especially in late August, when multiple blazes devoured tens of thousands of acres of pristine Rocky Mountain wilderness. Some 2,000 firefighters were deployed throughout the region, as well as nearly every available fire engine, bulldozer, helicopter, and water-tanker plane. Local commanders were flying wildfire specialists in from around the country.

"We had more fire than we could manage and were out of aces, so they started relying on old, beat-up people like me," recalls Dave Bunnell, a retired wildfire expert who spends summers at his cabin near Ronan, Montana.

Shortly after Bunnell arrived at a command center in Kalispell, two more blazes erupted when lightning struck near Beta Lake and Doris Ridge. (Lightning triggers 90 percent of wildfires in the western US. In the east, it's just 10 percent; arsonists take care of the rest.) These fires, dubbed Beta-Doris after they merged, were only 20 miles southwest of Glacier National Park, where on any given summer afternoon about 10,000 people are roaming a million acres, ogling ice-clad peaks, soaring waterfalls, and the occasional grizzly bear.

"The fire making a run to Glacier was well within the realm of possibility," says Bunnell. Worse, Beta- Doris was on a ridge directly above a power station at the north end of the Hungry Horse Reservoir. "If the station went out, we could have had brownouts all the way to Portland." And just beyond the power station lay the town of Martin City. Making the wrong choice about where to deploy the few remaining fire crews could be disastrous. But where would Beta-Doris go? Toward the power station? The town? Or some other direction?

Predicting the path of wildfires has long been a notoriously difficult task because they continually react to an infinite mix of ever-changing conditions. Wind speed, varying terrain, and differing vegetation, for instance, can all influence how fast and furiously a fire burns. Big gusts can drive flames 200 feet into the air and fan fires that wipe out thousands of acres of timber within minutes. Temperatures can reach 2,000 degrees, roughly that of molten lava. The heat creates violent updrafts that loft thousands of golf ball-sized embers, called firebrands, hundreds of feet high, raining a fiery hell onto ground crews and igniting dozens of new fires. The conventional strategy for containing these kinds of big blazes - besides praying for rain - has been brute force. Ground crews, called hotshots, dig trenches and clear vegetation to create "fuel breaks" in the path of approaching flames. Firefighters also rely on tanker planes that drop thousands of gallons of water and chemical retardant. Yet the intense heat and speed of a big blaze can overwhelm almost any attempt to stop it.

Hotshots and tanker planes still play a vital role in battling wildfires, but the overall firefighting strategy - the where, when, and how many - is increasingly being left to computers. Consider a simulation program called Farsite (short for Fire Area Simulator). Created by Mark Finney, a researcher at the US Department of Agriculture's Fire Sciences Lab in Missoula, Montana, Farsite can crunch more than a dozen variables - including wind, air temperature, humidity, altitude, terrain, and vegetation - and in a few minutes spit out 3-D animations that chart the most probable path of a wildfire.

Like the other commanders, Bunnell assumed the Beta-Doris fire would move northwest - away from Martin City. That's because the reservoir placed a big, wet barrier between the fire's northeast perimeter and the town. But he called Finney for a second opinion.

Finney, too, thought the reservoir would stop the flames. Yet when he crunched the data, Farsite predicted a surprisingly different scenario: Beta-Doris would catapult firebrands half a mile across the reservoir and ignite spot fires along the opposite shore. If unchecked, these could overrun Martin City and make a beeline toward Glacier.

There must be an error, thought Finney. Just to be sure, he ran the simulations twice more. The results were the same.

Bunnell was apprehensive about pulling crews from the existing fire and sending them across the reservoir to wait for an unlikely result predicted by a computer program. If he bet wrong, there would be hell to pay - Beta-Doris would likely take out the power station. He took a deep breath, and put his faith in Farsite: "I go to area command and make my play," he says. "I'm old, half bald, people don't remember me very well. And they're wondering, Who is this guy?"

The fire commanders eventually relented and agreed to send four fire trucks and six 20-member crews armed with shovels and Pulaskis to the reservoir's eastern shore. Meanwhile, Finney had uploaded Farsite's Beta-Doris model to a server that wildfire managers could access from the command center. They sent up an aircraft with infrared mapping capabilities that could see through the fire's smoky cloak and track its movement. To everyone's amazement, at 6 pm the next day a sudden wind squall lobbed firebrands across the reservoir. Thanks to Finney and Farsite, crews on the other side were already in position. As spot fires flared up, teams methodically attacked each one, snuffing them out before any torched more than a few acres.

Wildfire experts mark the beginning of fire science with a single event: the Mann Gulch fire. It was spotted at 12:25 pm on August 5, 1949, in the Gates of the Mountains Wilderness about 20 miles north of Helena, Montana. Around 4 pm, 18 smoke jumpers were airdropped just ahead of the flames. By 6 pm, 13 of them were dead. The death toll was unprecedented. Victims' families and the heads of federal and state forestry agencies demanded to know how an elite team could have been overrun so quickly by flames.

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