Are face masks effective despite peripheral gaps?
Are face masks effective despite peripheral gaps? lead image
Wearing face masks has emerged as the primary method of reducing COVID-19 spread. Realistically, however, masks do not fit onto faces perfectly. Considering that patients can spread the SARS-CoV-2 virus before symptoms appear, the outward protection of face masks becomes especially important.
Despite multiple recent studies that utilized three-dimensional face-mask models to quantify face-mask effectiveness, many failed to account for peripheral leakage, mask fabric filtration, and particle adherence to airflow. To fill that gap, Ni et al. used a reduced-order model to estimate the outward fitted filtration efficiency (oFFE) of face masks.
“The proposed oFFE is a better metric than the previously used filtration efficiency (FEmin) because it overcomes the underestimation of outward protection by FEmin during normal breathing for the relevant particle sizes.” said author Chuanxin Ni. “In the future, oFFE could also be extended to consider the percentage of filtered aerosol fluid volume as well as the percentage of filtered viral load.”
Ni et al. found that despite significant airflow leakage from the peripheral gaps, all medical masks succeed in providing significant outward protection. The respiratory aerosols generated during normal breathing are relatively large and heavy. Therefore, they do not follow the airflow, but instead impact on the mask and are filtered out by the mask fabric.
In the future, the team hopes to expand their model to include pressure variation inside the mask as well as a rebound and breakup model for aerosols.
“We hope our results on mask effectiveness can benefit the policymaking procedure for reducing the spread of COVID-19 and increase confidence in wearing face masks,” Ni said.
Source: “Face masks provide high outward protection despite peripheral leakage: Insights from a reduced-order model of face mask aerodynamics,” by Chuanxin Ni, Tomas Solano, Kourosh Shoele, Jung-Hee Seo, and Rajat Mittal, Physics of Fluids (2023). The article can be accessed at https://doi.org/10.1063/5.0153513 .
This paper is part of the Flow and the Virus Collection, learn more here .
