Mechanism of respiratory protective equipment in controlling wearer’s exhaled pollutants

Abstract

Respiratory protective equipment (RPE) filters and blocks exhaled pollutants to prevent their forward movement, protecting the directly exposed individuals and products. Two mechanisms of RPE in controlling wearer's exhaled pollutants, namely filtering and blocking, were examined. Leakage ratio was firstly proposed to evaluate the relative strength of leakage via gaps and leakage via face mask’s surface. Influence of various factors on the two mechanisms was investigated using validated Computational Fluid Dynamics (CFD) technology. The leakage ratio of 0.1–10 μm particles (i.e., 2–36) is generally larger than that of CO2 (i.e., 0.1–10), suggesting that face masks have a stronger blocking effect on the particles compared to the gaseous pollutants. Decreasing the initial velocity of exhaled air and increasing the diameter of exhaled particles, gap’s area, and viscous resistance of face mask’s surface increase the leakage ratio. When the viscous resistance increases from 4.34 × 106 to 4.34 × 1010, the leakage ratios of CO2 and particles increase by 4 and 23, respectively. When the initial velocity increases from 2.7 to 15 m/s, the leakage ratios of CO2 and particles decrease by 2.5 and 19, respectively. Wearing ordinary face masks alone cannot completely prevent the dispersion of exhaled pollutants, it is recommended to combine face masks with well-designed indoor ventilation to jointly control exhaled pollutants. The obtained data establishes a foundation for understanding the mechanism by which face masks control exhaled pollutants, which assists in the improvement of RPE and the formulation of effective measures to protect individuals and products directly exposed.