Constant vs. cyclic flow when testing face masks and respirators as source control devices for simulated respiratory aerosols

Measuring source control efficacy of different fitted masks for sub-micron aerosols

“…In ( 5) masks installed to soft-skinned head form using standard application procedures were investigated under tidal respiration; however, the employed volumetric ow rate was twice that of the present study and outside of the range for typical quiet breathing (26, 27). Notable gaps near the nose were observed in (5) for some of the masks, confounding the cause of the observed sensitivity of apparent mask ltration e ciencies to particle size at the sub-micron scale, as even minor leakages are expected to signi cantly affect the apparent aerosol ltration for smaller aerosols. Indeed, minor deviations of mask material ltration e ciencies around 90-95% for the submicron range investigated (28, 29) are expectedly insigni cant in comparison to loss of e ciency due to leakages, which are anticipated to be indifferent to submicron particle size, as supported by the present investigation.…”

“…To date, mechanistic studies assessing the e cacy of tted masks in the sub-micron particle size range have been limited. Though signi cant variability in ltration e ciency has been reported across studies (3)(4)(5), they have, in general, observed dependence of ltration on aerosol particle diameter in the submicron size range. While a possible connection of this outcome to the ltration characteristics of the mask material has not been made in these studies, it is unlikely to account for the range of the particles tested based on the standards of the masks investigated.…”