Face Coverings, Aerosol Dispersion and Mitigation of Virus Transmission Risk (2005.10720v2)

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.

• The paper demonstrates that non-valved face coverings reduce frontal aerosol dispersion by at least 63%, achieving up to 86% under certain conditions.
• It employs the BOS technique for quantitative visualization of airflow across varied respiratory activities including quiet breathing, heavy breathing, and coughing.
• The study highlights that surgical and homemade masks produce significant secondary leakage jets, indicating a need for improved design to enhance protection.

Assessment of Face Coverings in Aerosol Dispersion and Virus Transmission Mitigation

The paper presented investigates the effectiveness of various face coverings in mitigating aerosol dispersion and the associated risks of virus transmission, specifically in the context of the SARS-CoV-2 virus, utilizing a background oriented schlieren (BOS) technique. The researchers conducted a thorough evaluation of airflow ejected during different respiratory activities such as quiet breathing, heavy breathing, and coughing with and without face coverings.

Key Findings and Methodologies

1. Effectiveness of Face Coverings: The paper found that all tested face coverings without an outlet valve significantly diminished the front throughflow, reducing it by at least 63%, potentially reaching reductions up to 86% if the unfiltered cough jet distance is considered to reach its probable maximum of 2-3 meters. Specifically, FFP2 masks showcased the greatest efficacy in limiting frontal aerosol movement, provided they were properly sealed.
2. Schlieren Technique Utilization: The BOS method was instrumental in visualizing exhaled air's spread and directional properties under various conditions, offering quantitative insights into airflow patterns that were previously derived mainly from qualitative visualizations.
3. Leakage Jets: Notably, while most coverings reduced forward aerosol dispersion effectively, surgical and homemade masks and face shields generated sizable secondary leakage jets that could pose significant transmission risks. This finding suggests that the focus of mask evaluation should shift towards understanding and mitigating these peripheral leakage flows.
4. Respirator Limitations: Masks with valves, such as the respirator tested, were shown ineffective in halting virus dispersion from the wearer. The design allowing unfiltered exhalation highlights their inadequacy as protective barriers for source control.
5. Real-world Implications and Use in Medical Settings: The research yielded quantitative data that highlight risks associated with aerosol-generating procedures (AGPs) in medical settings, such as extubation processes, demonstrating the potential for direct exposure of healthcare workers to aerosols even when face coverings are employed.

Future Implications and Developments

This paper enhances the understanding of face coverings as a control measure in mitigating aerosol spread of SARS-CoV-2, underscoring the importance of comprehensive mask designs addressing both filtration and leakage. The experimental approach provides critical data for PPE design improvements and informs public health policies regarding mask recommendations and requirements.

In future studies, a more diverse set of covering designs and varying environmental conditions, such as humidity and temperature, could be evaluated to provide a broader scope of understanding regarding mask efficacy. Additionally, the development of real-time aerosol detection technologies integrated with the BOS methodology could refine our insight into dynamic airflow environments.

The continuation of research in aerosol dispersion dynamics holds potential both to substantiate face covering recommendations and to pioneer innovative solutions, enhancing prevention strategies against airborne pathogens in both clinical and public domains.