Abstract

We evaluated the effectiveness of 11 face coverings for material filtration efficiency, inward protection efficiency on a manikin, and outward protection efficiency on a manikin. At the most penetrating particle size, the vacuum bag, microfiber cloth, and single-layer surgical-type mask had material filtration efficiencies >50%, while the other materials had much lower filtration efficiencies. However, these efficiencies increased rapidly with particle size, and many materials had efficiencies >50% at 2 μm and >75% at 5 μm. The vacuum bag performed best, with efficiencies of 54–96% for all three metrics, depending on particle size. The thin acrylic and face shield performed worst. Inward protection efficiency and outward protection efficiency, defined for close-range, face-to-face interactions, were similar for many masks; the two efficiencies diverged for stiffer materials and those worn more loosely (e.g., bandana) or more tightly (e.g., wrapped around the head) compared to an earloop mask. Discrepancies between material filtration efficiency and inward/outward protection efficiency indicated that the fit of the mask was important. We calculated that the particle size most likely to deposit in the respiratory tract when wearing a mask is ∼2 μm. Based on these findings, we recommend a three-layer mask consisting of outer layers of a flexible, tightly woven fabric and an inner layer consisting of a material designed to filter out particles. This combination should produce an overall efficiency of >70% at the most penetrating particle size and >90% for particles 1 μm and larger if the mask fits well.

Copyright © 2021 American Association for Aerosol Research

摘要

我们评估了11种面罩在材料过滤效率，人体模型上的向内防护效率和人体模型上的向外防护效率方面的有效性。在最穿透的粒径下，真空袋，超细纤维布和单层手术型口罩的材料过滤效率> 50％，而其他材料的过滤效率则低得多。但是，这些效率随粒径的增加而迅速增加，许多材料在2μm时的效率> 50％，在5μm时的效率> 75％。真空袋的性能最佳，这三个指标的效率都在54％至96％之间，具体取决于颗粒大小。薄的丙烯酸和面罩表现最差。对于许多面罩而言，为近距离，面对面的互动而定义的向内保护效率和向外保护效率是相似的。与较硬的材料相比，两种效率有所不同，与耳挂式面罩相比，材料的佩戴效率较宽松（例如，头巾）或较紧（例如，包裹在头上）。材料过滤效率与向内/向外防护效率之间的差异表明，口罩的佩戴非常重要。我们计算出，戴口罩时最可能沉积在呼吸道中的粒径约为2μm。基于这些发现，我们建议使用三层口罩，包括柔软的紧密织造织物的外层和内层，该内层由旨在过滤颗粒的材料组成。如果面罩安装得当，这种结合在最穿透的颗粒尺寸下产生的整体效率应> 70％，而对于1μm及更大的颗粒，则应产生> 90％的总体效率。

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