Face shield intensifies inhaled exposure to self-generated bio-effluents

Abstract

The presence of a face shield may block the forward and upward dilution of bio-effluents, generated from one's own exhalations and skin, through the breathing zone, which might thus intensify the user's inhaled exposure, especially for long-term use. The objective of this study is to quantify this exposure risk. The flow characteristics of the porous region at the top of a typical face shield were tested experimentally. The viscous resistance coefficient and inertial resistance coefficient of the porous region were 4.9 × 107 and −402, respectively. The influence of breathing mode (via mouth and nose), pulmonary ventilation rate (6–8 L/min), and bio-effluents generation location (i.e., exhalation, groin, and armpit) on the exposure risk of bio-effluents were then studied by computational fluid dynamics (CFD) technology in combination with the species transport model. The inhaled fraction (iF) index was used to assess the exposure risk. A face shield can considerably increase the exposure risk, the inhaled fraction index being increased from 0.28% to 2.97% for skin pollutants, and from 2.25% to 6.96% for exhaled pollutants. It means that the fraction of oxygen (O2) in the inhaled air of face shield wearers is 20.58%, being 2% less than that without face shield. For face shield wearers, a higher pulmonary ventilation rate and breathing through nose would further increase the exposure risk. This information would be important boundary conditions for accurate simulation and design of face shield as well as the design of protective clothing.