  The SARS-CoV-2 virus is primarily transmitted through virus-laden fluid
particles ejected from the mouth of infected people. Face covers can mitigate
the risk of virus transmission but their outward effectiveness is not fully
ascertained. Objective: by using a background oriented schlieren technique, we
aim to investigate the air flow ejected by a person while quietly and heavily
breathing, while coughing, and with different face covers. Results: we found
that all face covers without an outlet valve reduce the front flow through by
at least 63% and perhaps as high as 86% if the unfiltered cough jet distance
was resolved to the anticipated maximum distance of 2-3 m. However, surgical
and handmade masks, and face shields, generate significant leakage jets that
may present major hazards. Conclusions: the effectiveness of the masks should
mostly be considered based on the generation of secondary jets rather than on
the ability to mitigate the front throughflow.
