The critical importance of mask seals on respirator performance: An analytical and simulation approach

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.

The effects of face mask specifications on work of breathing and particle filtration efficiency

“…In order to consider the leakage flow through the face mask we assume that there is a small gap between mask and face ( Fig. 1 ) [44] .

Fig.1 Schematic of mask with face-seal leakage [44]

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“…The normal gap area varies between 0 and 5% of the mask area [44] . We can assume that σ=0.05 for SMs with large gap and σ=0.02 for N95 FFRs with small gap.…”

Research on Regularities of Cyclic Air Motion through a Respirator Filter

“…Of course, the filter can be used further, but there is a certain physiological limitation of the pressure drop value, above which it will be rather difficult for a person to breathe and perform production operations. Several works are devoted to the determination of this limit threshold [51][52][53][54][55]. Additionally, one of the results of the research performed is the increase in the weight of the settled dust on the filter fibres before the critical pressure drop occurs (Table 3).…”

What is suitable social distancing for people wearing face masks during the COVID‐19 pandemic?

“…The high‐quality simulations by Tsubokura 50 showed that airflow direction changed to upward, downward, and sideway through the leakages between surgical mask and human face. The analytical model developed by Xu et al 51 showed that the filtration efficiency was only 40%–60% of that without leakages when the ratio between leakage area to mask area was 0.05. At last, cloth mask was soft without any structure to maintain the shape.…”