The SARS-CoV-2 virus is primarily transmitted through virus-laden fluid particles ejected from the mouth of infected people. In some countries, the public has been asked to use face covers to mitigate the risk of virus transmission – yet, their outward effectiveness is not ascertained. We used a Background Oriented Schlieren technique to investigate the air flow ejected by a person while quietly and heavily breathing, while coughing, and with different face covers. For coughing, we found that all face covers without an outlet valve reduce the front flow through jet by at least 63% and perhaps as high as 86% if the unfiltered cough jet distance was resolved to the anticipated maximum distance of 2-3m. For the FFP1 and FFP2 masks without exhalation valve, the front throughflow does not extend beyond one half and one quarter of a metre, respectively. Surgical and hand-made masks, and face shields, generate several leakage jets, including intense backward and downwards jets that may present major hazards. We also simulated an aerosol generating procedure (extubation) and we showed that this is a major hazard for clinicians. These results can aid policy makers to make informed decisions and PPE developers to improve their product effectiveness by design.
Viola, I., Peterson, B., Pisetta, G., Pavar, G., Akhtar, H., Menolascina, F., Mangano, E., Dunn, K., Gabl, R., Nila, A., Molinari, E., Cummins, C., Thompson, G., Lo, M., Denison, F., Digard, P., Malik, O., Dunn, M. & Mehendale, F. 2020, 'Face Coverings, Aerosol Dispersion and Mitigation of Virus Transmission Risk'. To be published in University of Edinburgh [Preprint]. Available at: https://doi.org/10.1109/OJEMB.2021.3053215