Rendering Inferno (continued 3/3)

Cohen continued these experiments for the next three summers. He tested whether smoldering pine needles ignited composite shingles; the temperature at which plate-glass windows would shatter; how quickly flames melted vinyl siding. "I lit a small pile of twigs on the vinyl side and another on the cedar side and basically watched the response," he says. He also determined at what distance a wood structure would burst into flames solely from exposure to heat. "I wanted to know how close is close enough for a house to combust without a spark directly igniting the structure." Close enough turned out to be about 60 feet.

Cohen is compiling the results of his work into a modeling program called SIAM (Structure Ignition Assessment Model) that will help builders produce structures less prone to catch fire. The program takes into account home dimensions, number and size of windows and doors, construction materials, location and types of surrounding vegetation, and proximity to other homes, then generates recommendations. These might include redesigning a deck or using specific types of fire-resistant siding. Astronomers at the Mt. Graham International Observatory in southeast Arizona recently consulted Cohen on how to protect their telescope from wildfires. "The observatory is sitting on top of a 10,720-foot-tall mountain in the middle of a spruce forest," he explains. Based on SIAM's calculations, Cohen suggested creating a 200- foot buffer around the complex by clearing away dead vegetation and cutting back overgrown tree branches.

In June, a medium-size blaze breaks out in a remote wilderness about 60 miles north of Grand Junction, Colorado. Forest managers determine this fire isn't a threat to local residents; it will improve habitat by burning off undergrowth without killing the bigger trees. So instead of attacking it, they will let the flames run their natural course. They'll use Farsite models to track and predict its movements, while keeping a few hotshots and aerial tankers on standby, just in case.

Fire ecologist Lathan Johnson takes me to an area near the edge of the blaze. He's here to help supervise a small team of specialists and gather hourly data for input into fire-behavior models. In six days, the fire has razed about 6,900 acres, killing mostly tall grasses and shrubs. As we traverse a blackened ridge, there's a familiar smell in the air - a campfire, only marvelously sweet and earthy. "That's sage, juniper, and pinion pine," says Johnson. The ground is still warm, and wisps of smoke rise from burned-out stumps. The sky is overcast and monochromatic. Aside from our gaudy matching outfits - orange hard hats, plus olive-green pants and bright yellow shirts made from a fireproof fabric called Nomex - the world is utterly black and white.

We pause at a vista about a quarter-mile from the flames. In our day packs we're carrying fire shelters, basically self-pitching pup tents made from a heat-resistant material that resembles aluminum foil. We're supposed to throw these over ourselves if we're unexpectedly trapped by flames. As I ponder the notion of being baked alive in a teepee of Reynolds Wrap, Johnson starts removing gadgets from his pack. With the first one, a digital anemometer, he measures wind speed, force, and direction. Next he takes the air temperature and uses a spinning sling psychrometer to check the dew point and humidity. He notes the scorch height on the tree trunks and the fire's rate of spread, then uses a GPS receiver to pinpoint our location and elevation. He also jots down the shape, color, and opacity of smoke plumes and any obvious thermal inversions (that's when a column of smoke appears to butt up against an invisible glass ceiling). Finally, Johnson takes out a red binder and consults charts to calculate the POI, or probability of ignition - a figure that gives wildfire managers a sense of how quickly and easily the flames will spread under certain conditions. Today, with the cloud cover and high humidity, POI is only 40 percent, well within the safety zone. Johnson repeats this process every hour, collecting real-time data on every conceivable aspect of the fire and surrounding environment, then in the evening delivers the results to the command center in nearby Meeker.

It's dusk when we return to town and join other specialists. Firelab forester Rob Seli enters the data Johnson collected along with the blaze's GPS coordinates into a form on the National Weather Service Web site. In return, he'll get a pinpointed local forecast. Everyone is gathering data as fast as possible because the sooner they can fill in the blanks, the sooner they can run Farsite models.

The next day, as my flight climbs out of Grand Junction, smoke plumes rise in the distance, but they're smaller now. Farsite has done what it's supposed to do - ensure that the forest managers can keep a blaze tame and manageable while it steadily reinvigorates the forest. As Jack Cohen likes to say, Farsite has shown us "how to be compatible with the inevitable."

3