Dense smoke can pose health hazard

More than once in the last few  years, tree-sheltered subdivisions near Sisters have been evacuated as out-of-control wildfires threatened lives and homes.

The blazes were made worse by the accumulation of vegetation over 100 years of fire suppression. The U.S. Forest Service - on a limited budget - and private landowners now attempt to reduce the "fuel load" in the forest. Tools include "mechanical treatment" such as mowing and burning. 

Fire is especially effective in Central Oregon ecosystems that have adapted to an environment where annual lightning storms blast dry forests.

But where there is fire there is smoke. And smoke, too, can have consequences for health and safety.

The Forest Service hopes to burn up to 1,000 acres this spring,  according to Trevor Miller, Fuels Technician with Sisters Ranger District. They must do so in ways to minimize the impact of smoke to local communities under guidelines provided by the Oregon Department of Forestry (ODF) on what can be burned and when. No controlled burn occurs without the go-ahead from ODF, which takes into account weather and fuel loading.

A burn a couple of weekends ago on private land resulted in smoke in Sisters when the smoke was "trapped" near the ground by an overnight inversion. According to Jim Trost, Meteorology Manager with ODF's  Smoke Management Office in Salem, that fire was limited to units of 1,000 tons or less of fuels to be burned, with units eight miles apart and at least 10 miles from "SSRAs," or "Smoke Sensitive Receptor Areas." 

The local SSRAs are Redmond and Bend. Sisters is not on the SSRA list, according to Trost, and would have to ask to be added. 

The Forest Service does have a computer program for analyzing the production of smoke particles, according to Fuels Technician Miller. Based on ground observation and aerial photographs, the software estimates the amount of particulate matter, both the "10 micron and under" size (PM10) and the "2.5 micron and under" size (PM2.5).  

A grain of salt is about 60 microns, according to a quick Google search; a human hair can be 100 microns wide.

In this case, the larger the better, according to Miller. "It is the 2.5 micron that we are most worried about. That is the stuff that gets down in your lungs and is bad news." (See related story, page 21.)

A controlled burn might produce .08 tons or 160 pounds per acre of particulate matter each in the PM10 and PM2.5 sizes, according to conditions, Miller said. In other words, a 12-acre burn might put out about two tons, or 3,840 pounds, of particulate matter into the air in both the PM10 and PM2.5 and under particle sizes.

"If we burned that unit and (the smoke) just sat there, and didn't disperse, those would be the tons per acre," Miller said. "That is our biggest concern, the smoke and how it will affect communities. The ultimate goal is forest health."

There are few guidelines that equate "tons per acre" to "micrograms per cubic foot" which is what the federal Environmental Protection Agency uses to gauge the impacts of smoke on human health. EPA standards are also calculated over a 24-hour period of exposure. Even thick smoke for a few hours would probably not trigger violations or concern.

However, the 2001 Smoke Management Guide provided by Miller suggests that "the worse the visibility, the worse the smoke. In Montana, the Department of Environmental Quality uses visibility to help you gauge wildfire smoke levels."

The same publication suggests avoiding exercise, and staying indoors if it is smoky outside.

The guide was developed to provide advice during a wildfire, but one could assume that the same suggestions would be valid for fires started intentionally to clear out brush. As for medical direction, the brochure suggests that those adversely affected call their doctor or the county health department.

Even though intentional burns are timed to minimize the impact of smoke on the population, occasionally an inversion will trick fire managers and cause the smoke to linger. "If you don't have wind it will settle in hard," said the Forest Service's Miller. The smoke comes off the ground and mixes with cool air next to the ground, which is more dense than the warmer air above, and a thick haze lies in low spots like water in a basin or creek bed, often over roads or among houses built on lowlands.

The haze in these inversions often "burns off" by midmorning, actually responding to the sun heating the earth and causing the smoke-rich air to warm up, rise and mix with air of warmer temperatures, diluting the smoke.

The Forest Service in Sisters recently acquired a "nephelometer," a suitcase-sized device that will actually allow the agency to measure the quantity of particles that a burn is putting into the air.

The Forest Service has a policy of notifying people who have requested to be put on a list before a burn. These are typically those on oxygen or who have asthma and for whom the burning could cause immediate discomfort. 

"We make notification to everybody who has requested to be notified. I give them a call with as much advance notice as we can," said Miller. To be placed on this list, call 549-7638.

Even with the impact of occasional smoky mornings, there is broad agreement that burning under controlled conditions, when weather and smoke direction can be anticipated, is preferable to out-of-control fires in fuel-loaded forests.

Smoke is generally thought to be particles in the air. There may be invisible vapors and chemicals and other elements with the smoke, but "smoke" that we see to breathe is made up of visible bits and pieces.

Lungs are designed to take molecules of oxygen from the air and get rid of carbon dioxide, according to the  American Lung Association. That makes them fairly effective filters for smoke, which gets left behind when oxygen is taken through cell walls in alveoli, small air sacs of the lungs. Small hair like structures in our airways called "cilia" evolved to trap particles and keep our lungs clean. Cilia are better at getting bugs and pollen than tiny, tiny particles that result from burning. 

A publication provided by the Forest Service titled the 2001 Smoke Management Guide, says particulate matter 2.5 micrometers and smaller (PM2.5), "can build up in the respiratory system, causing a number of health problems, including burning eyes, runny noses and illnesses such as bronchitis. The particles also can aggravate heart and lung diseases, such as congestive heart failure, chronic obstructive pulmonary disease, emphysema and asthma."

The U.S. Environmental Protection Agency has published guidelines for pollution from smoke. In the PM2.5 size, the EPA says that below 40.4 micrograms (mcg) per cubic meter, there is no effect. Above 40.4 mcg, there are increasing symptoms and aggravation, quickly leading to the possibility of premature death for the ill at concentrations of 65.6 mcg per cubic meter of air and above. The general population is also affected.

The Oregon Department of Environmental Quality monitors air pollution in Oregon. Brian Finneran is Senior Air Quality Specialist, Smoke Management and Visibility Coordinator with the Oregon Department of Environmental Quality. Finneran said there are smoke measurement devices in a number of communities. 

Generally these are devices with filters. The weight of the filters is known, air is drawn through, and then the filter is weighed. The difference in weight, before and after, is used to determine the level of particulate matter in the air.

This measuring can take some time, according to Finneran. A different device, called a nephelometer, is used to get estimates that are closer to "real time." A nephelometer shines a light down a tube of known volume. The amount that the light "scatters" is used to estimate the amount of smoke.

The U.S. Forest Service recently acquired a nephelometer, according to Trevor Miller, Fuels Technician with the Sisters Ranger District. This will allow the agency to determine how much smoke a fire has created.

Then there is the good old-fashioned "look outside meter." When reported to the Oregon Department of Forestry, smoke is often characterized as "light," medium" or "heavy." While there is some relationship to readings from a nephelometer, there are no direct equivalents to the EPA's micrograms per cubic meter.

"Light" impact of smoke is visibility of 50 miles, according to Finneran, "medium" smoke is visibility to about 12 miles, and "heavy" smoke limits visibility to about 5 miles, or less than the distance between Sisters and Black Butte.

Finneran emphasized that smoke exposure is regulated by the EPA on the basis of exposure over a 24-hour period. So intense smoke for a half hour might be averaged with other hours of no smoke to determine if the air met standards. This does not mean that short, intense exposure would not be harmful, even if within guidelines.

Finneran said that the EPA looks at their standards for exposure every five years. The EPA has not changed the amount of time that exposure is measured to below 24 hours because of a "lack of qualitative health effects evidence" for shorter exposures.

He did say that the EPA lowered the concentration for exposure from 65 micrograms per cubic meter to 35 micrograms per cubic meter average over that 24-hour period of time, a change he called "significant."