A Burning Interest : Research: Forestry scientists study ways to use preventive fires more effectively.

Dozens of firefighters watched calmly Thursday as two men dripped diesel fuel and gasoline on a bone-dry hillside above Santa Clarita, stood back and torched the brush.

Instead of fleeing the choking smoke, Colin Hardy stood in the midst of it, guiding other U.S. Forest Service scientists who were maneuvering into the thickest part of the black cloud a string of large metal pods, designed to capture its essence.

With the cooperation of the Los Angeles County Fire Department, the Forest Service was sampling smoke produced by a controlled burn, part of a program in Los Angeles and Riverside counties to determine burning methods that will cause less air pollution.

Controlled blazes allow fire departments to eliminate shrubbery that otherwise could fuel a wildfire.

Much remains to be learned about smoke, said Jim Carter, vegetation manager for the California Department of Forestry. And with increasing public pressure to reduce air pollution, firefighters fear that they will lose the right to conduct preventive burns unless smoke pollution can be controlled.

A sister sampling program in the Pacific Northwest completed during the past three years led to more effective restrictions on burning in previously logged areas--based on the projected amount of smoke rather than acreage, said Hardy, a research forester.

“An acre of fuel isn’t necessarily an acre of fuel,” Hardy said. “If you burn it one way, you may get much more smoke than another.”

In Oregon and Washington, U.S. Forest Service scientists discovered that emissions were reduced if they burned earlier in the spring when the ground was still moist, cleared out larger pieces of loose wood ahead of time and used a powerful torch dangling from a helicopter to light a faster, hotter fire.

In the Los Angeles experiment, which continues today and Saturday, some areas of greasewood and sagebrush were crushed ahead of time with bulldozers to see if lower flames produced less smoke. In Riverside, near Temecula, burning was done in January on younger plants, soon after the first rains, to test the effect of greener wood, more moisture and cooler temperatures.

“The hypothesis is that there will be a difference in the character of smoke,” Hardy said. “If we succeed, there might be a trade-off: It may be more expensive to burn in one situation, but you’re putting out less smoke, so you get to keep using the tool.”

County and state fire officials who witnessed Thursday’s sampling said they also hope it will help them explain their programs more precisely to regulators such as the South Coast Air Quality Management District.

“Our concern is that people who don’t understand what really goes on out here will set restrictions we can’t follow,” said county Fire Capt. Milan Rupel. “We feel secure that this will help.”

On average, the county Fire Department intentionally burns off vegetation on 7,000 to 10,000 acres a year, said Capt. Scott Franklin, the department’s vegetation management officer. In contrast, a typical wildfire can burn 40,000 acres, he said, and the department has documented at least nine instances since 1982 when wildfires were prevented or reduced by use of preventive burning.

Fires can be set and studied more easily in a laboratory. But the unpredictability of the outdoors--wind, sun, temperature shifts--is harder to orchestrate.

“When you do it inside, you can’t get effects of topography, the arrangement of the fuel and so on,” Franklin said. “Anything you come up with would be suspect.”

Because it is a relatively unprobed area of science, the crew and their predecessors on the project built and refined most of the sampling equipment. They taped together what they call the “umbilical,” a rope of plastic tubes that connect the sampling pods to gas meters as well as clusters of balloonlike sample bags, which will be scrutinized by physical science technician Christine Betchly at a lab in Seattle.

They built the metal collection pods using sensors and filters intended for industrial smokestacks. A red and white cooler jug condenses water out of incoming gases to keep moisture away from the laboratory equipment.