Every child learns that fire is dangerous: that it burns, and if left unchecked, it will spread. But what IS fire, exactly? And how best can it be controlled? These are pressing everyday concerns for the thousands of firefighters who work to protect America's vast forests, national parks and other wild lands every day.
Dan Buckley, a fire expert at the National Parks Service says the scientific definition of fire is pretty simple: It is a chemical reaction of combustible vapors and fuel particles. And always involves fuel, heat oxygen and an ignition source. "That can be lightning strike, or a match, or even a spark from a rolling rock, which then gets picked up by the wind and carried to the forest floor."
Because wind and other weather factors can determine how a fire will behave, meteorologists play an important role in every fire-fighting team. They measure the speed and direction of the winds, which feed oxygen to a fire and steer its movement. Meteorologists also predict the amount of humidity and rain, which help to suppress fires.
"Water also works on the heat side," adds Buckley. "Applying water to the fuel it also cools it, and makes it less available to burn."
For most of the past century, firefighters have tried to extinguish wild fires as quickly as possible. But experts now say this practice interfered with the natural fire cycles of forests, which burn up dead wood and underbrush, and allow for new plant growth. Buckley says suppressing this natural process left forests filled with highly combustible tinder that have helped to fuel larger, more intense forest fires. And that, combined with what seems like the warmer, drier and windier [and] volatile climate we have, has increased fire behavior.
"We are seeing large fires that are driven largely by the fuels. Where, for all of our history, most of our fires were mostly driven by the weather," says Buckley, who reminds us that some forest ecosystems, such as the giant sequoias of the American West, actually depend on fire in order to thrive. "In the case of giant sequoias, they need fire to heat their sequoia cones to the point where they pop open and allow seeds to go on to soil that has been cleaned by fire."
When fire burns under sequoia groves it creates an ash bed, which is an ideal seedbed for young sequoias, and it also helps clean out some of the canopy that shades the soil. Young sequoias need sunlight to grow.
Sometimes a fire can be so hot that it burns the soil on the forest floor beyond its ability to support vegetation. These fires can also wreak havoc on areas untouched by the flames. Merrill Saleen, the Incident Commander at a major forest fire in Idaho's remote Rattlesnake River region says, "If we burn so hot that we remove all vegetation and all stabilization of the soils, we get tremendous runoff and the potential for downstream flooding, and landslide potential."
Deciding whether or not a given fire should be allowed to take its natural course, or be contained or extinguished, is the job of fire managers: hybrid scientific specialists with a grasp of ecology, biology, botany, materials science and other disciplines.
A decision was made to drop chemical retardant in advance of the Rattlesnake Fire in south central Idaho, which consumed over 16,000 hectares of wilderness. The retardant slows the spread of the blaze in the absence of a natural barrier, thus giving fire fighters a chance to battle it from a stationary position.
Jim Turner, who helps to oversee the air operation for the National Inter-Agency Fire Center in Boise, Idaho, says there is minimal environmental danger when dumping the chemicals. "What we do is try to keep it out of the creeks. It's only the direct delivery into the creek that is damaging. There are no indirect effects."
While modern firefighters rely on a wide array of aerial and satellite imagery to track the progress of a fire, it's still important to have human eyes observing a fire directly.
Fire specialist Dale Jablonski peers at a ridge about a half-kilometer away, where a stand of fir and conifers are ablaze, and notes the size and color of the smoke plume. "You've got a hot spot that is heating up, and you've got a couple of trees that torched up [burst into flames]" he observes. "It's changing from white to a different darker shade of grey and the column is starting to expand, burning a little heavier fuels now."
Jablonski signals a hovering helicopter to advance to the flames to drop a load of water on it, thereby "softening it up" for ground. "The pilot is going to move in and make his drop. You don't want to give your enemy a chance!"