PB: the smoking gun - prescribed burning

American Forests, July-August, 1995 by Neil Sampson

Can we use fire to make forests healthier without running afoul of public attitudes and Clean Air Standards?

ONE OF THE MAJOR CONCERNS ASSOCIATED WITH THE CURRENT FOREST-HEALTH SITUATION IN THE WESTERN UNITED STATES IS THE ALMOST-CERTAIN OCCURRENCE OF LARGE, INTENSE WILDFIRES ACROSS MUCH OF THE REGION. THE MAIN REMEDIES TO REDUCE THIS RISK, AS SUGGESTED BY FOREST ECOLOGISTS, INCLUDE THINNING OVERLY DENSE STANDS TO REMOVE EXCESSIVE FUELS, FOLLOWED WHERE POSSIBLE BY SLASH BURNING TO REDUCE WILDFIRE HAZARD AND RECYCLE NUTRIENTS.

On lands where fuel conditions allow a fire to burn without destructive impact on the forest or surrounding private lands and homes, one of the treatments proposed is a careful "prescribed" fire, intentionally or naturally ignited, that is allowed to burn so long as it stays within the prescribed limits of impact and damage.

Both the untreated situation, with its wildfires, and the treatment, with prescribed fires, will create a significant amount of smoke, and smoke is a public health problem that worries air quality regulators. In 1994 it was estimated that over 1.35 million tons of PM2.5 (particulate matter less than 2.5 microns in diameter) were emitted from 65,700 fires that burned 3.8 million acres of federal lands. Several communities, including Wenatchee, Washington, and Boise, Idaho, experienced smoke pollution well over Air Quality Standards adopted by the Environmental Protection Agency to protect public health.

Currently, the regulations associated with the Clean Air Act classify the smoke from prescribed burning as a "human-induced" pollutant, while the smoke from wildfires is a "natural" pollutant. The first has been regulated by EPA and the states; the second hasn't. That could change in the future, however, as implementation of the 1990 Clean Air Act Amendments proceeds. In this latest version, EPA was instructed by Congress to determine whether "natural" events such as wildfires may now be considered to be "human-caused" if people's actions have contributed significantly to their occurrence. With many wildlands so far outside their normal range of fuel-loading variability because of years of intentional fire-suppression activities, a reasonable case can be made that today's wildfires are at least in part "human-caused" and therefore subject to regulation under the Clean Air Act. Just what EPA would do to regulate them is not clear, but there are suggestions that the agency consider the total smoke pollution from both wild and prescribed fires, and seek to keep that total pollution within acceptable limits.

The result, according to some calculations, may be to limit prescribed fires even more than is the case today. In the face of the current forest-health situation, the Forest Service is proposing to increase prescribed burning by 30 percent a year over the next three years. Such increases clearly pose a conflict with air-quality regulations, which many land managers say already limit the amount of prescribed burning they can accomplish in any one year. Given the amount of forest that currently needs treatment to avoid catastrophic wildfire, many feel that it will be impossible to carry out the necessary prescribed burning and slash disposal under the current Clean Air restrictions.

This raises a major question: Are the current air-quality restrictions going to result in more or less human health impact? Is it possible that if the amount of prescribed burning is restricted, the nation will end up with more smoke and sick people from wildfire effects than would have occurred if the land treatment had been allowed? These questions are increasingly being asked by forest and air-quality managers alike, so AMERICAN FORESTS has posed the question to a wide variety of experts who are studying the situation. As you will see, the answers are far from clear, and the stakes are high.

First, it is important to recognize that the pollution associated with woodburning is a legitimate concern, and that people's health and lives are placed at risk by an increase in airborne soot, smoke, chemicals, and other particles. Major attention is now being paid to the very small particles of soot and chemicals produced by woodburning. These are particles smaller than 2.5 microns in diameter. (In comparison, a human hair is about 75 microns in diameter.) Because they are so very small, such particles can bypass the defenses in the respiratory tract and penetrate deeply into lung tissue. The EPA, which has focused its attention and regulatory limits on particles smaller than 10 microns (PM10 is the term commonly used), is now reviewing its regulations to determine if the present health standards should be revised to focus on the smaller, PM2.5 particles.

There is still controversy over how seriously airborne particles affect human health, because the precise cause-effect relationship still remains largely unknown. Increasingly, however, studies show a direct correlation between increases in airborne particulate matter and rates of school absenteeism, sickness, and death. In a 1993 study of six cities where data were available, and in a 1995 follow-up study tracking the health histories of over a half-million adults, Dr. Douglas Dockery of Harvard University and co-workers found that in cities with the highest PM2.5 pollution levels, people were 15-17 percent more likely to die prematurely than they were in the cleanest cities. This remained true even when such other factors as age, smoking history, other health problems, weather, and similar variables were taken into account.