Face Coverings, Aerosol Dispersion and Mitigation of Virus Transmission Risk

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. INDEX TERMS COVID-19 pandemic, face coverings, face masks, aerosol dispersal, aerosol generating procedures. IMPACT STATEMENT These results show the effectiveness of face coverings in mitigating aerosol dispersion and can aid policy makers to make informed decisions and PPE developers to improve their product effectiveness.

COVID-19 false dichotomies and a comprehensive review of the evidence regarding public health, COVID-19 symptomatology, SARS-CoV-2 transmission, mask wearing, and reinfection

“…Mechanistic evidence has demonstrated source control efficacy of medical masks in reducing influenza virus and human seasonal/endemic coronaviruses respiratory emissions from symptomatic individuals [291,496,497], as well as some protection against influenza virus afforded to the wearer [498]. Likewise, fluid dynamics simulation and experimental studies support the role of masks in limiting the spread of respiratory emissions [348,[499][500][501][502].…”

“…In the face of limited data, face shields or visors have been suggested to provide some advantages over face masks in terms of eye protection, frontward airflow protection, no hand-toface contact, breathability, full-face visibility, reuse, and disinfection [261,[517][518][519][520]. However, variable design (shape, materials) of face shields and upward, downward, and sideways leakage jets from the edges, seams, and joints are major issues [482,500,[521][522][523]. Face shields are therefore considered to provide a level of eye protection only [55,424].…”

One size fits all?: A simulation framework for face-mask fit on population-based faces

“…Airborne transmission happens when a susceptible person inhales microscopic bio-aerosols in the air which are generated from a respiratory event such as a cough, sneeze, or even just breathing and talking [2,5]. While larger droplets (�100μm) reach the ground within a second, aerosols can linger in the air for hours, increasing the probability of a susceptible person coming in contact with the virus [6,7]. For this reason, mask fit is important.…”

“…Experimental studies with human subjects and manikins show that mask usage can limit the droplet and airborne transmission of various infections to and from the wearer [8][9][10][11][12][13][14][15][16]. Air leakage has been observed around the perimeter of the mask where it does not make a seal with the face, reducing the effectiveness of the mask [6,17]. Perimeter leakage is caused by loose or improper fitting face masks and can be significantly impacted by facial features [18][19][20][21].…”

Spatiotemporal droplet dispersion measurements demonstrate face masks reduce risks from singing: results from the COvid aNd FacEmaSkS Study (CONFESS)

“…Viola et al did this and demonstrated significant leakage jets that may present major hazards. 31 But their study examined coughing where droplets were 50 μm in diameter and peak velocity was 8 m/s despite wearing masks.…”