Face Coverings, Aerosol Dispersion and Mitigation of Virus Transmission Risk

TL;DR

This study investigates how different face coverings affect aerosol dispersion and virus transmission risk, revealing that while most masks reduce forward airflow, leakage jets may pose hazards, emphasizing the importance of secondary jets over front flow mitigation.

Contribution

The paper introduces a novel use of background oriented schlieren technique to analyze airflow and leakage jets from various face coverings during breathing and coughing.

Findings

All face covers without valves significantly reduce front airflow by 63-86%.

Surgical masks, handmade masks, and face shields generate leakage jets.

Mask effectiveness should be evaluated based on secondary jet generation.

Abstract

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.