September 16, 2020

Fit testing, airborne protection of N95, other masks

By: Judy Mathias
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Editor's Note

Masks, such as N95 respirators, are made of material with sufficient high filter capacity to protect against airborne respiratory viruses. However, viral protection can only be provided by masks that properly fit the wearer’s face and provide a tight facial seal, this review article finds.

Among the findings:


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  • The SARS-CoV-2 virus has a diameter of 0.06 to 0.14 µm. N95 masks can filter 94 to 95% of particles sized 0.04-150 µm in diameter, but airborne protection is decreased in the presence of a leak or loose fit because unfiltered air will be drawn inside the mask.
  • Correct mask fit is far more important for airborne protection than the filtration capacity of the material. This is why surgical masks with a leak provide inadequate airborne protection even though they are made of material with a filtration capacity similar to N95 masks.
  • Despite the importance of fit in relation to protection, comfort, price, and availability have frequently guided selection of masks during the COVID-19 pandemic.
  • Though fit checking should be performed every time a mask is donned, it is unreliable in detecting adequate fit or leaks, which is why fit testing is recommended.
  • Fit testing is not performed consistently in all healthcare settings. Efficiently fit testing many healthcare workers in a short period of time is difficult. Passing initial N95 mask fit testing varies between 40% and 90%, and it is especially low in female and Asian healthcare workers.

In conclusion, the authors say transmission risk of SARS-CoV-2 and other respiratory viruses is high for healthcare workers exposed to aerosol-generating procedures. Without adequate fit, the degree of airborne protection provided by N95 and other masks is reduced and fit testing is recommended by international and national agencies to ensure proper fit.

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