The research on wildfires is more recent, reflecting the fact that industrial pollution has been considered more common. But researchers say the differences might not be so pronounced in that the wildfire air carries tiny particulates that threaten lungs from scorched trees, cars, homes and businesses and industrial areas, Dr. MacDonald said. “It could be pretty bad if man-made objects are being burned.”
If the science remains murky, the bottom line seems plain, experts said.
“In the absence of a compelling reason, it’s best to keep the kids at home,” said Dr. David Cornfield, chief of pulmonary, asthma, and science medicine at Stanford Children’s Health. He was involved in cases of two children with severe asthma who died after exposure to smoke from wildfires, one in 2016 and one in 2013.
Air quality is measured by the density of pollutants; when a widely used index of air quality developed by the E.P.A. reads below 50, conditions are considered safe. That index has well exceeded 400 in the areas around Portland, causing them to be labeled “hazardous” and an “emergency situation,” while the levels in the San Francisco Bay Area, hovering between 200 and 300, are “very unhealthy.”
Dr. Cornfield said he didn’t want to be too prescriptive about what precise level should keep children inside but said a decent guideline is to cease outdoor activity at 100. Above 150, he said, “you don’t really want to have people sitting outside.”
That puts a major crimp in school reopening plans, which are predicated on keeping windows open, having ventilation, even holding outdoor classes to stanch the spread of the coronavirus. That, too, preys on the lungs, so administrators are now caught between wildfires that would call for tightly insulated schools and the threat of the virus, which argues for open air.