Size-specific filtration efficiency and pressure drop of school-aged children's woven and nonwoven masks at varying face velocities

Abstract

Background: Differences in physiology and breathing patterns between children and adults lead to disparate responses to aerosols of varying sizes. No standardized method exists for measuring the filtration efficiency (FE) of children's masks to reflect such differences.

Methods: Using an adult N95 mask as a control and two different face velocities (v_f) (9.3 cm/s representing adults and 4.0 cm/s representing school-aged children), we tested the pressure drop (ΔP) through children's nonwoven masks (surgical and KN95) and children's woven masks (100% cotton and partially-cotton-based masks), as well as their size-specific FE between aerodynamic particle diameters of 0.02 and 2.01 μm.

Results: All three types of mask showed a 1 to 9% absolute increase in minimum FE at the lower v_f and a significant decrease in ΔP. For children's surgical masks the increase in FE was significant for most of the examined particle sizes, but for children's woven masks the increase was limited to particles smaller than 0.04 μm.

Conclusions: Lower v_f for children is likely to lead to a higher FE, lower ΔP, and consequently higher filter qualities in children's masks. For woven masks, the FE for particles larger than 0.04 μm was low (typically <50%) for both v_f's studied.

Keywords: Children; Filtration Efficiency; Masks; Nonwoven; Woven.