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What’s the Deal with Wildfire Smoke and Human Health?

posted Sep 20, 2016, 1:00 PM by Joe Christy
This July, we’ve all watched the Sobranes fire across the bay, smelled the smoke mornings and evenings, and taken in the depressing prospect of a cap of smoky haze capping our mountain when we visit the lowlands. Unfortunately, this is a subject where studies are few and hard facts are difficult to come by. The exponential growth in the number of wildfires and their severity in this century is forcing scientists to begin examining its many aspects, but settled science lies in the future. The Sobranes fire is now predicted to continue through September, so let’s consider what we do know.
It appears that the greatest health impacts come more from the physics of smoke than the chemistry of its constituents. Chemically, wildfire smoke is much the same soup as we bathe in every day from e.g. cars and trucks, power plants, etc. Wildfire smoke’s signature orange murk contains the clue – it comes from particles, invisible in themselves, but small enough to scatter visible light. Known as PM2.5, for Particulate Matter less than 2.5 microns, about 1/16th the width of a human hair, the particles reach the deepest recess of the lungs, where they lodge and irritate the tissue. Those that do not fetch up in the lungs pass into the blood, to be transported throughout the body.
So what to do? Stay indoors with the windows shut. If your household contains those at greatest risk: children, pregnant women, the elderly, and those with respiratory conditions, consider getting room air cleaners. The acronym to look for here is HEPA, for High-Efficiency Particulate Arresting, filters. Avoid exacerbating the situation by smoking, burning candles or incense. Even vacuuming with non-HEPA bags and filters will relaunch PM2.5 that had finally settled out. While humidifiers don’t directly clean the air, they do make it easier for the lungs to eject particles and, in the case wood smoke, swell the particles, rendering them less invasive. This is particularly useful on days when the poor atmospheric mixing and the temperature inversion associated with a thin marine layer give our mountain that hazy cap, noticeably smokier than lower elevations. If you must go and work outside, consider a face mask; here the acronym is N95, meaning that, according to the National Institute for Occupational Safety and Health, the close-fitting mask will catch at least 95% of PM2.5.
For much more information, I recommend the EPA’s guide to Wildfire Smoke, revised this past May.