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Effective Relative Humidity on Textile Mask Filtration Efficiency and Breathability
JOELLE SEGOVIA, Ching-Hsuan Huang, Nanhsun Yuan, Mei-Yu Liao, Jiayang He, Igor Novosselov, University of Washington
Abstract Number: 485
Working Group: Control and Mitigation Technology
Abstract
During the COVID-19 pandemic, a worldwide mask shortage resulted in many having to create reusable masks out of various materials and fabrics. The reusable masks reduce the waste stream associated with disposable masks and can potentially increase the mask use by the population. However, it is unknown how well these masks can protect the wearer or the people in the vicinity over a range of breathing rates and relative humidity. This study evaluates the effectiveness and ease of breathing through a number of readily accessible materials used for masks. Mask effectiveness is described as the measured filtration efficiency with breathability quantified as the pressure drop is recorded across the material. Natural and synthetic materials such as cotton, silk, rayon, and polyester were tested in the aerosol chamber; sodium chloride particles were used as challenge aerosol. Filtration of particle sizes in the range of 0.5-2 micron was evaluated. Filtration efficiency was determined by comparing particle concentration in the filtered flow against reference measurement taken by aerodynamic particle sizer. To mimic variability in the environmental and in the exhaled breath condition, the chamber was set to three different humidity levels (RH= 40%, 60%, and 80%) along with four different face velocities (0.18 m/s, 0.24 m/s, 0.28 m/s, and 0.34 m/s) to simulate different breathing rates. The filtration efficiency and pressure drop were recorded and used to determine the quality factor of the materials; these data are presented as a function of relative humidity and particle size. The quality factor is a figure of merit relating the filtration efficiency to the pressure drop recorded for each material and compared against that of surgical grade masks. Multiple layers of several materials are also analyzed to determine if there is an increase in filtration efficiency and difficulty in breathing.