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Some Masks Increase Particle Transmission

Not All Masks are Created Equal

    Today, wearing face masks in outdoor settings is a necessity to prevent the transmission of COVID-19. A previous post on this blog went over the three main types of face masks (N-95, surgical and cloth) and identified how effective each mask was at blocking out particles. (See Different Face Masks and their Efficacy). Early this month, a new study performed by a Duke family and published in Science Advances, evaluated face mask efficacy using a homemade tool. The results from this study not only confirms the information published in Different Face Masks and their Efficacy, but also brings new information to light.

Methods

    Martin Fischer, an associate research professor at Duke University, built a simple tool with his daughter Emma to identify visible evidence of airborne particles. The tool they created uses a lens, which expands a laser beam inside a darkened box. When someone speaks into the box, particles are scattered in different directions by the expanded light and recorded by a camera. A computer then calculates the amount of droplets scattered and the rate they pass through the sheet of light.

The Results

   Fourteen different types of masks were tested using the methods above including N-95, surgical, cotton, fleece and more (see figure below). The results were consistent with the findings described in Different Face Masks and their Efficacy; N-95 masks were most effective, with a droplet transmission of 0.1% relative to not wearing a mask. Cloth and surgical face masks were also found to be very effective in preventing droplet transmission. In sharp contrast, bandanas performed poorly in blocking out particles, sometimes allowing even more particles to pass than in comparison to the control (not wearing a mask). Among all 14 types of face masks, fleece masks performed the worst, with an average droplet transmission of 110%. It's believed that these masks allow more particles to pass through than in the control because the porous material of the masks break the larger particles into smaller aerosols. While previously, it was believed that anything is better than nothing when it comes to face masks, this study proves that to be wrong. Masks made with loosely knit material such as bandanas or fleece masks actually increase the droplet transmission. Neck gaiters are a type of commonly worn masks made from fleece. It is better to not wear anything at all than wearing these types of masks.

Conclusion

- N-95 masks are the most effective but should be reserved for essential workers.

- Surgical and cloth masks are also highly effective in reducing particle transmission and should be worn by the general public.

- Masks made from bandanas or fleece (such as neck gaiters) should not be worn to prevent coronavirus as they will increase particle transmission.

Wear a (N-95, surgical or cloth) mask and stay safe!

Sources

1.  Fischer, Emma P., et al. “Low-Cost Measurement of Facemask Efficacy for Filtering Expelled Droplets during Speech.” Science Advances, American Association for the Advancement of Science, 7 Aug. 2020, advances.sciencemag.org/content/early/2020/08/07/sciadv.abd3083/tab-pdf.

2. Heidt, Amanda. “Simple Tool Evaluates Mask Performance at Blocking Droplets.” The Scientist Magazine®, www.the-scientist.com/news-opinion/simple-tool-evaluates-mask-performance-at-blocking-droplets-67814?utm_campaign=TS_OTC_2020.

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