If you are afraid to give up wearing your face mask in public, in your car, or even in the privacy of your home, you need to read this post.
-NW

Mask Facts: Association of American Physicians and Surgeons
curated by Marilyn M. Singleton, M.D., J.D.
June 1, 2020
https://aapsonline.org/mask-facts/

Transmission of SARS-CoV-2

Note: A COVID-19 (SARS-CoV-2) particle is 0.125 micrometers (μm); influenza virus size is 0.08 – 0.12 μm; a human hair is about 150 μm.

*1 nm = 0.001 micron; 1000 nm = 1 micron; Micrometer (μm) is the preferred name for micron (an older term)

1 meter is = 1,000,000,000 nm or 1,000,000 microns

Filter Efficiency and Fit

*Data from a University of Illinois at Chicago review

https://www.cidrap.umn.edu/news-perspective/2020/04/commentary-masks-all-covid-19-not-based-sound-data

HEPA (high efficiency particulate air) filters – 99.97 – 100% efficient. HEPA filters are tested with particles that are 0.125 μm.

Masks and respirators work by collecting particles through several physical mechanisms, including diffusion (small particles) and interception and impaction (large particles)

N95 – A properly fitted N95 will block 95% of tiny air particles down to 0.3 μm from reaching the wearer’s face.

https://www.honeywell.com/en-us/newsroom/news/2020/03/n95-masks-explained.

But even these have problems: many have exhalation valve for easier breathing and less moisture inside the mask.

Surgical masks are designed to protect patients from a surgeon’s respiratory droplets, aren’t effective at blocking particles smaller than 100 μm.

https://webcache.googleusercontent.com/search?q=cache:VLXWeZBll7YJ:https://multimedia.3m.com/mws/media/957730O/respirators-and-surgical-masks-contrast-technical-bulletin.pdf+&cd=13&hl=en&ct=clnk&gl=us

Filter efficiency was measured across a wide range of small particle sizes (0.02 to 1 µm) at 33 and 99 L/min.

N95 respirators had efficiencies greater than 95% (as expected).

• T-shirts had 10% efficiency,
• Scarves 10% to 20%,
• Cloth masks 10% to 30%,
• Sweatshirts 20% to 40%, and
• Towels 40%.

All of the cloth masks and materials had near zero efficiency at 0.3 µm, a particle size that easily penetrates into the lungs.

Another study evaluated 44 masks, respirators, and other materials with similar methods and small aerosols (0.08 and 0.22 µm).

• N95 FFR filter efficiency was greater than 95%.
• Medical masks – 55% efficiency
• General masks – 38% and
• Handkerchiefs – 2% (one layer) to 13% (four layers) efficiency.

Conclusion: Wearing masks will not reduce SARS-CoV-2.

N95 masks protect health care workers, but are not recommended for source control transmission.

Surgical masks are better than cloth but not very efficient at preventing emissions from infected patients.

Cloth masks will be ineffective at preventing SARS-CoV-2 transmission, whether worn as source control or as personal protective equipment (PPE).

“Masks may confuse that message and give people a false sense of security. If masks had been the solution in Asia, shouldn’t they have stopped the pandemic before it spread elsewhere?”