Fighting forest fires with shovels, elbow grease . . . and computers

Flint-dry conditions throughout parts of the United States are testing recent advances in the emerging science of fighting forest fires. Bracing for a possible outbreak of blazes this fall, forest rangers are pinning their hopes on tools ranging from chemistry to computers to help limit the damage.

But even as the new weapons are being rolled into place, forces are at work making the job of fighting forest fires a tough task. The urban-to-rural movement, and a growing leisure ethic among Americans, are putting more people into the woods than ever before. Many states, too, have been forced to slash firefighting budgets.

''Firefighting is slowly graduating from the days of the shovel into a sophisticated science,'' observes Kenneth Burton of the Texas Forest Service. ''But there are more risks out there, too.''

Each year forest fires destroy an average of two million acres of land, adding up to more than $400 million in damage. Last year nature granted something of a reprieve: Fewer than 500,000 acres of federal land was charred - the lowest since records were first kept in 1916.

This year's toll has so far been modest: 1.3 million acres burned through mid-August. And while the danger remains low in higher elevations (where valuable timber lies), foresters are worried about blazes across the millions of acres of range and grassland. Heavy spring rains produced a dense growth of grass and brush on flat lands throughout the West, where some 200,000 acres have already been blackened in the first two weeks of August.

These conditions should provide the biggest test so far for a system of computers, lightning detectors, and weather sensors under development by the federal government since the late 1970s. The system will not be completed until 1987. But enough elements have been put in place in 11 Western states to help rangers extinguish some blazes before they rage out of control.

The centerpiece of the system is a series of computer-controlled antennas that can pinpoint lightning strikes (the cause of more than 60 percent of forest fires) up to 225 miles away. Scattered throughout the West, the sensors pick up the radio wave patterns of ground-striking lightning and feed it to a central computer in Boise, Idaho.

Augmenting the sensors is a network of remote weather units located around the region. Looking like lunar landers, they measure such things as wind speed and humidity. They then bounce the information to Boise by satellite. There, federal rangers put it into a computer, along with the lightning data and information about vegetation and terrain (the ''fuel factors'') gleaned from satellite photos.

Within minutes, a ''probability'' profile can be constructed, showing whether there might be a fire and how fast it may spread. Using this profile and computer maps, rangers around the region can decide whether to send in aerial or ground crews.

''You can get people to a site almost instantaneously,'' contends Kenneth Reninger, chief of remote sensing at the Boise-based Interagency Fire Center, a federal group.

The agency is now buying a central computer to back up several smaller units at the Boise headquarters. So far, some 200 weather units are in place. Budgets permitting, rangers expect to have some 400 of the tripod devices in use in the West by 1987.

The US isn't the only country increasingly turning to ''silicon firefighting.'' Several Canadian provinces recently installed lightning-detection systems, the most sophisticated of which is in Alberta. Canadians feel the need acutely, after three years of bad forest fires. Australia, too, has a sensing system.

In addition to these systems, US rangers are also working with:

* New chemicals. Most fire-fighting chemicals dropped from planes contain colored dyes so pilots know exactly where to dump successive loads. The trouble is that the dyes can take weeks or even months to disappear - often angering nearby residents. Recently developed chemical ''retardants,'' however, don't leave the countryside tinted red or pink: Now, says George Roby, fire specialist with the US Forest Service, ''fugitive dyes'' are being used that fade within a few days.

* Foam. Firefighters are being equipped with new tanks and trucks that squirt foam instead of water. By adding a detergent-like chemical to a water tank, rangers can generate 10 times more liquid from the same supply source. Ground crews carrying the special pumps, for instance, can produce 50 gallons of foam from a five-gallon tank.

* Flame throwers. Rangers are also testing long-distance flame throwers - for burning underbrush to prevent fires from breaking out. And they are using chemically laced ''ping-pong-ball'' devices that can be lobbed from helicopters to ignite the forest floor.

None of these ''high-tech'' tools comes cheap. So the key question for firefighters is increasingly becoming how to afford new tools. But since it now costs an estimated $10,000 just to extinguish a 10-acre forest fire, many foresters think the new systems will save plenty of money in the long run by helping put out fires before they get out of control.