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Face Mask Performance Related to Potentially Infectious Aerosol Particles, Breathing Mode and Facial Leakage
Abstract
During the COVID 19 pandemic, wearing certified face masks provided important means of protection against direct and indirect infections caused by virus-laden aerosols. Assessing the mask performance associated with infection prevention in standardised certification tests, however, faces drawbacks, such as the representativeness of the test aerosols used, the protection of third parties during exhalation or the effect of facial leaks. To address these drawbacks, we designed a novel test bench to measure the mask performance, namely the number based total efficiency, size-segregated fractional filtration efficiency and net pressure loss, for 11 types of certified surgical masks and Filtering Face Pieces dependent on breathing mode and facial fit. To be representative for the context of potentially infectious particles, we use a test aerosol based on artificial saliva that is in its size distribution similar to exhaled aerosols. In inhalation mode excluding facial leaks, all investigated samples deposit by count more than 85% of artificial saliva particles, which suggests a high efficiency of certified mask filter media related to these particles. In exhalation mode most masks tend to have similar efficiencies but lower pressure losses. This deviation tends to be significant primarily for the masks with thin filter layers like surgical masks or Filtering Face Pieces containing nanofibers and may depend on the masks shape. Both the filtration efficiency and pressure loss are strongly inter-dependent and significantly lower when masks are naturally fitted including facial leaks, leading to a wide efficiency range of approximately 30 – 85%. The results indicate a much greater influence of the facial fit than the filter material itself. Furthermore, masks tend be more effective in self-protection than in third-party protection, which is inversely correlated to pressure loss. Comparing different types of masks, the pressure loss partially differs at similar filtration efficiencies, which points out the influence of the material and the filter area on pressure loss.
SSRN preprint:
https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4238356
... Despite numerous experimental and theoretical works focused on the performance of facemasks with respect to COVID, also including less frequent studies on their role in aerosol elimination during exhalation [29][30][31][32][33], quantitative data on the concentration and size distribution of aerosol emitted at different breathing activities during FMRs use are still lacking. The high filtration efficiency of FMRs obtained in laboratory tests simulating inhalation or aerosol flow through a piece of filter material does not mean they provide equally good performance during various expiratory breathing activities, when the design, leaks, or improper fit of the mask to the face can dominate the overall effectiveness of FMRs. ...
... Thus, it has been demonstrated that wearing FMR of any kind is useful in the partial reduction of emission of exhaled bioaerosols, including viruses. This is consistent with the conclusions on the role of barrier masks in reducing the risk of COVID transmission made by other researchers [29,32,33], but complements them with additional quantitative results. ...
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