A critical note on filtering-face-piece filtration efficiency determination applying EN 149

During the current COVID-19 pandemic, filtering-face-pieces and their certification get great attention from society. The determination of total filtration efficiency according to DIN EN 149/ DIN EN 13274-7 (European standard for FFP1, FFP2 and FFP3 masks) has several drawbacks, making reliable certification of filtering-face-pieces difficult. This note analyses two of these drawbacks, namely the ambiguous definition of the total filtration efficiency and the broad range of the test aerosol particle size distributions allowed. The range of total filtration efficiency values for individual masks resulting from rather wide or missing specifications in the standard is calculated using size resolved penetration curves of 11 FFP2 masks from literature and 11 FFP2 masks from own measurements. From the 22 FFP2 masks regarded in this analysis, two would either pass or fail certification in dependence of the applied definition of the total filtration ef- ficiency and the test aerosol applied.