Virus World

Mandates for mask use in public during the recent COVID-19 pandemic, worsened by global shortage of commercial supplies, have led to widespread use of homemade masks and mask alternatives. It is assumed that wearing such masks reduces the likelihood for an infected person to spread the disease, but many of these mask designs have not been tested in practice. We have demonstrated a simple optical measurement method to evaluate the efficacy of masks to reduce the transmission of respiratory droplets during regular speech.

In proof-of-principle studies, we compared a variety of commonly available mask types and observed that some mask types approach the performance of standard surgical masks, while some mask alternatives, such as neck fleece or bandanas, offer very little protection. Our measurement setup is inexpensive and can be built and operated by non-experts, allowing for rapid evaluation of mask performance during speech, sneezing, or coughing.

Original study published in Science Advances (August 7, 2020):

https://doi.org/10.1126/sciadv.abd3083

Dr. Martin Fischer, from Duke University, developed a simple, low-cost technique to visualize the effectiveness of different face coverings on droplet emissions during normal wear. Testing several face coverings, the researchers found that the particles can be blocked by some, but not all recommended face coverings.

N95s without valves, and surgical, and polypropylene masks worked best. Cotton face coverings provided some coverage. Bandanas and neck fleece didn’t block the droplets very much, and indeed the "filter" smaller droplets that remained longer airborne. The experiments clearly shows the importance of wearing masks to prevent spreading of droplets that cary the COVID-19 virus, and also suggest that some face covers don 't do the job at all.

See also original study in Science Advances (August 7, 2020):

https://doi.org/10.1126/sciadv.abd3083