  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.
