STUDY: measurement of facemask efficacy for filtering expelled droplets during speech

Low-cost measurement of facemask efficacy for filtering expelled droplets during speech 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. Science Advances

The global spread of COVID-19 in early 2020 has significantly increased the demand for face masks around the world, while stimulating research about their efficacy. Here we adapt a recently demonstrated optical imaging approach (1, 2) and highlight stark differences in the effectiveness of different masks and mask alternatives to suppress the spread of respiratory droplets during regular speech.

In general, the term ‘face mask’ governs a wide range of protective equipment with the primary function of reducing the transmission of particles or droplets. The most common application in modern medicine is to provide protection to the wearer (e.g., first responders), but surgical face masks were originally introduced to protect surrounding persons from the wearer, such as protecting patients with open wounds against infectious agents from the surgical team (3), or the persons surrounding a tuberculosis patient from contracting the disease via airborne droplets (4).

This latter role has been embraced by multiple governments and regulatory agencies (5), since COVID-19 patients can be asymptomatic but contagious for many days (6). The premise of protection from infected persons wearing a mask is simple: wearing a face mask will reduce the spread of respiratory droplets containing viruses. In fact, recent studies suggest that wearing face masks reduces the spread of COVID-19 on a population level, and consequently blunts the growth of the epidemic curve (7, 8).

Still, determining mask efficacy is a complex topic that is still an active field of research (see for example (9)), made even more complicated because the infection pathways for COVID-19 are not yet fully understood and are complicated by many factors such as the route of transmission, correct fit and usage of masks, and environmental variables.

From a public policy perspective, shortages in supply for surgical face masks and N95 respirators, as well as concerns about their side effects and the discomfort of prolonged use (10), have led to public use of a variety of solutions which are generally less restrictive (such as homemade cotton masks or bandanas), but usually of unknown efficacy.

While some textiles used for mask fabrication have been characterized (11), the performance of actual masks in a practical setting needs to be considered. The work we report here describes a measurement method that can be used to improve evaluation in order to guide mask selection and purchase decisions.