Testing material and the whole mask
Cherrie and colleagues tested nine masks marketed for particle pollution in Beijing. They measured filtration of diesel particles through mask material, then tested four mask types on volunteers during sedentary and active tasks. The volunteer tests measured black carbon inside and outside the mask.
Leakage changed the result
Average inward leakage in volunteer tests varied widely: 3–68% while sedentary and 7–66% during active tasks. Only one tested mask type averaged below 10% leakage in both conditions. These figures describe the specific masks, volunteers and tests; they do not rate every respirator currently on sale.
What protection was actually measured
This was a small performance study, not a clinical trial of disease prevention. The material tests and volunteer leakage tests used different measurements and must not be treated as interchangeable. Particle filtration also does not establish protection against gases such as ozone, NO₂ or CO.
Fit belongs in any explanation of masks
Avoid describing a filter rating as a guaranteed reduction in a wearer’s exposure. The study supports explaining both filter performance and facial seal, with suitability considered for the wearer and task. Wearing a mask does not make every pollution level or duration of outdoor activity safe.
Sources
- Cherrie JW, Apsley A, Cowie H, et al.. Effectiveness of face masks used to protect Beijing residents against particulate air pollution. Occupational and Environmental Medicine (2018). DOI: 10.1136/oemed-2017-104765 ↗
- National Institute for Occupational Safety and Health. Filtering Facepiece Respirators. CDC / NIOSH ↗
Educational information; personal health questions belong with your clinician.
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