Abstract
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.
Highlights
Filtering facepiece respirators (FFRs) and medical masks are widely used to reduce inhalation exposure of potentially harmful airborne particles
In this article we quantified the impact of mask seal gaps on filtration ratio and fit factor via analytical and simulation approaches, with application to mask materials with a wide range of ventilation resistances and mask gap areas
Our results show that the face-seal leakage has a significant impact on the fraction of airflow passing around the filter material, where both increased ventilation resistance and mask gap dimensions degrade mask performance
Summary
Filtering facepiece respirators (FFRs) and medical masks are widely used to reduce inhalation exposure of potentially harmful airborne particles. Medical masks and FFRs (collectively referred to here as masks) have been recommended by the World Health Organization (WHO) as infection prevention and control measures by health care workers, including for protection against respiratory diseases such as COVID-19 [1], SARS, seasonal influenza, pandemic influenza and avian influenza [2]. The material and filtration efficiency of masks have been the focus of many studies, including examination of repeatability and comfort of masks made of melt-blown fabric and nanofibers [3, 4] and the study on filtration efficiency for different mask designs and non-.
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