Health experts advise N95 masks and indoor filtration as Canadian wildfire smoke reaches U.S. regions

Smoke from more than 800 active fires in Canada has drifted into parts of the United States, prompting air quality alerts in states such as Minnesota, Illinois, Pennsylvania and New York. Health officials say that people who work outdoors, are sensitive to smoke, or belong to high-risk groups should use appropriate respiratory protection.

"In order to protect yourself from that, we really need powerful filtration ... wearing an N95 mask is key," said Kai Chen, an associate professor of epidemiology at Yale School of Public Health. He explained that the fine particulate matter (PM2.5) in wildfire smoke is about 30 times smaller than a human hair and can penetrate deep into the lungs and even enter the bloodstream, causing short-term irritation and long-term health risks.

Chen emphasized that only N95 respirators, certified by the National Institute of Occupational Safety and Health and fitted with two head straps for a tight seal, effectively filter PM2.5. He noted that surgical masks, paper dust masks, cloth masks, wet cloths and bandanas do not provide sufficient protection against these fine particles.

He also warned that a proper seal is essential; facial hair or an ill-fitting mask can reduce effectiveness, and some wearers may experience increased breathing effort. Users experiencing severe shortness of breath or dizziness should remove the mask in a cleaner-air environment and seek medical care if symptoms persist.

New York City officials announced the distribution of free KN95 masks at libraries, police precincts, firehouses and transit hubs. Chen added that indoor air quality should be improved by closing windows and using high-efficiency particulate air (HEPA) filters, many of which were installed in public buildings during the COVID-19 pandemic.