Visualizing droplet dispersal for face shields and masks with exhalation valves

Abstract

Several places across the world are experiencing a steep surge in COVID-19 infections. Face masks have become increasingly accepted as one of the most effective means for combating the spread of the disease when used in combination with social-distancing and frequent hand-washing. However, there is an increasing trend of people substituting regular cloth or surgical masks with clear plastic face shields and with masks equipped with exhalation valves. One of the factors driving this increased adoption is improved comfort compared to regular masks. However, there is a possibility that widespread public use of these alternatives to regular masks could have an adverse effect on mitigation efforts. To help increase public awareness regarding the effectiveness of these alternative options, we use qualitative visualizations to examine the performance of face shields and exhalation valves in impeding the spread of aerosol-sized droplets. The visualizations indicate that although face shields block the initial forward motion of the jet, the expelled droplets can move around the visor with relative ease and spread out over a large area depending on light ambient disturbances. Visualizations for a mask equipped with an exhalation port indicate that a large number of droplets pass through the exhale valve unfiltered, which significantly reduces its effectiveness as a means of source control. Our observations suggest that to minimize the community spread of COVID-19, it may be preferable to use high quality cloth or surgical masks that are of a plain design, instead of face shields and masks equipped with exhale valves.

Masks and Face Coverings for the Lay Public

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Biosafety during a pandemic: shared resource laboratories rise to the challenge

“…Examples of common PPE used in SRL include masks and other suitable face coverings, face shields, disposable gloves, clean lab coats, and safety goggles. Studies have shown effective reduction in the transmission of particulates through the use of masks (21). Various kinds of face shields and masks are available and reduce droplet spread to different degrees as assessed by physical testing (22).…”

The impact and effectiveness of the general public wearing masks to reduce the spread of pandemics in the UK: a multidisciplinary comparison of single-use masks versus reusable face masks.

“…But since coughing and sneezing expels droplet and aerosols at high pressure, the general consensus is that face masks also protect others by capturing some, if not all, of the droplets and aerosols produced by the wearer. Penetration of droplets through the filter material, exhalation valves and around the face depends on the fit or seal of the mask (3). It is therefore assumed that filtration efficiency is reflective of the mask's efficacy in capturing droplets exerted by the mask wearer.…”