Department of Biomedical Engineering, University of Melbourne, Melbourne, Victoria, Australia.
PLoS One. 2021 Feb 17;16(2):e0246720. doi: 10.1371/journal.pone.0246720. eCollection 2021.
Filtering facepiece respirators (FFRs) and medical masks are widely used to reduce the inhalation exposure of airborne particulates and biohazardous aerosols. Their protective capacity largely depends on the fraction of these that are filtered from the incoming air volume. While the performance and physics of different filter materials have been the topic of intensive study, less well understood are the effects of mask sealing. To address this, we introduce an approach to calculate the influence of face-seal leakage on filtration ratio and fit factor based on an analytical model and a finite element method (FEM) model, both of which take into account time-dependent human respiration velocities. Using these, we calculate the filtration ratio and fit factor for a range of ventilation resistance values relevant to filter materials, 500-2500 Pa∙s∙m-1, where the filtration ratio and fit factor are calculated as a function of the mask gap dimensions, with good agreement between analytical and numerical models. The results show that the filtration ratio and fit factor are decrease markedly with even small increases in gap area. We also calculate particle filtration rates for N95 FFRs with various ventilation resistances and two commercial FFRs exemplars. Taken together, this work underscores the critical importance of forming a tight seal around the face as a factor in mask performance, where our straightforward analytical model can be readily applied to obtain estimates of mask performance.
过滤式面罩（FFR）和医用口罩广泛用于减少空气中颗粒物和生物危害性气溶胶的吸入暴露。它们的防护能力在很大程度上取决于从进入的空气体积中过滤的部分。虽然不同过滤材料的性能和物理性质已经成为密集研究的主题，但口罩密封的影响却了解较少。为了解决这个问题，我们引入了一种基于分析模型和有限元方法（FEM）模型来计算面部密封泄漏对面罩过滤比和适配因子影响的方法，这两种方法都考虑了随时间变化的人体呼吸速度。使用这些方法，我们计算了一系列与过滤材料相关的通风阻力值（500-2500 Pa∙s∙m-1）的过滤比和适配因子，其中过滤比和适配因子作为面罩间隙尺寸的函数进行计算，分析模型和数值模型之间具有良好的一致性。结果表明，即使间隙面积略有增加，过滤比和适配因子也会明显下降。我们还计算了具有不同通风阻力和两种商业 FFR 示例的 N95 FFR 的颗粒过滤率。总的来说，这项工作强调了在口罩性能中形成紧密密封的重要性，我们的简单分析模型可以很容易地应用于口罩性能的估计。
