Particle leakage through the exhalation valve on a face mask under flow conditions mimicking human breathing: A critical assessment.

Yeeun Kang,Jooyeon Park,Hyungmin Park

doi:10.1063/5.0067174

Abstract

In today's era of active personal protections against airborne respiratory disease, general interest in the multiphase flow physics underlying face masks is greater than ever. The exhalation valves, installed on some masks to mitigate the breathing resistance, have also received more attention. However, the current certification protocol of evaluating airflow leakage only when suction pressure is applied is insufficient to capture practical aspects (particle penetration or leakage). Here, we experimentally measure two-phase flow across valve-type masks under conditions mimicking actual breathing. During exhalation, a high-speed jet through the valve accelerates the transmission of particles from inside while reasonable protection from external pollutants is achieved during inhalation, which supports the warnings from various public health officials. Based on the mechanism of particle penetration found here, we hope a novel design that both achieves high-efficiency shielding and facilitates easy breathing can be developed.

Highlights

Except in some Asian countries with seasonal issue of particulate matters, face masks are generally used as personal protective gear in specialized environments such as medical institutions, hazardous work places, and cleanrooms
The importance of personal shielding against airborne respiratory disease during the global SARS-CoV-2 pandemic increased the public interest in face masks more than ever (Busco et al, 2020; Cheng et al, 2020; Dbouk and Drikakis, 2020a; Mittal et al, 2020a, 2020b; Bourouiba, 2021; Mathai et al, 2021)
A properly functioning exhalation valve permits the minimal inward leakage below 0.01%, but the penetration rate increased as high as 1.1% when the valve operation is hindered at the valve seat, and valves with paint or dust contamination showed a leakage of 0:2–0:6%

Summary

Introduction

Except in some Asian countries with seasonal issue of particulate matters, face masks are generally used as personal protective gear in specialized environments such as medical institutions, hazardous work places, and cleanrooms. The importance of personal shielding against airborne respiratory disease during the global SARS-CoV-2 pandemic increased the public interest in face masks more than ever (Busco et al, 2020; Cheng et al, 2020; Dbouk and Drikakis, 2020a; Mittal et al, 2020a, 2020b; Bourouiba, 2021; Mathai et al, 2021). In addition to the flap, the mask includes a valve seat and cover to hold the flap in place and to protect the device, respectively

Methods

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Discussion

Conclusion