Numerical evaluation of face masks for prevention of COVID-19 airborne transmission

Jiaxing Liu,Xin Bian,Ming Hao,Qi Mei,Jian Li,Yang Yang,Kun Liu,Shulei Chen

doi:10.1007/s11356-022-18587-3

Abstract

The COVID-19 pandemic has forced governments around the globe to apply various preventive measures for public health. One of the most effective measures is wearing face masks, which plays a vital role in blocking the transmission of droplets and aerosols. To understand the protective mechanism of face masks, especially in indoor environments, we apply a computational fluid dynamics technique to predict the lifetime of cough droplets. Therefore, we can assess the exposure risk in a ventilated room where an infected individual wears a face mask or not. We focus on the dynamic evaporation and diffusion of droplets in a human-cough process, which is a major cause for the spread of the virus. We find that wearing a face mask can effectively reduce the total mass and Sauter mean diameter of the residual droplets after a single cough. The mass concentration of virus-carrying droplets in the ventilated room decreases by 201, 43,786, and 307,060 times, corresponding to wearing cotton face masks, surgical face masks, and N95 face masks, respectively. However, the maximum travel distance of 80% droplets is insensitive to wearing a face mask or not. Therefore, the residual droplets are widely distributed due to the influence of indoor airflow. Furthermore, we study aerosol exposure risks in different areas of the room and find that high concentrations of aerosols occur in the streamline through an infected individual, especially next to the individual within 1.5 m. This strongly suggests a social distance despite the fact that the majority of droplets are filtered by face masks. This study explains the impact of face masks and airflow on indoor exposure risks and further inspires potential measures for public health, for example, no individuals should sit near the air supply opening.

Highlights

There is a concerning development that coronavirus disease 2019 (COVID-19) cases continue to rebound globally (O’Dowd 2021)
Transient Computational fluid dynamics (CFD) simulations are applied to two cases, namely, no face mask and surgical face mask
The discrepancy in the subsequent stages is relatively large for the case without a face mask, which may be caused by the difference in the initial velocity of the cough airflow between the simulation and the mathematical model

Summary

Introduction

There is a concerning development that coronavirus disease 2019 (COVID-19) cases continue to rebound globally (O’Dowd 2021). One of the reasons is the rapid spread of delta variant, which is declared as a “variant of concern” by the Centers for Disease Control and Prevention (CDC) (Kupferschmidt and Wadman 2021). Various measures have been adopted to alleviate, control, and stop the spread of COVID-19 (Alon et al 2020; Dhama et al 2020; Sabat et al 2020). Vaccination is considered to be the most effective means to control the epidemic (Christie et al 2021). The effectiveness of vaccines against variants may decrease, especially for people who have only received the first dose (Farinholt et al 2021; Lopez Bernal et al 2021). Many countries and international organizations advise people to wear face masks in public even though they have been vaccinated (Liao et al 2021)

Methods

Results

Conclusion