Effectiveness of N95 Mask in Preventing COVID-19 Transmission.

Abstract

N95 mask has emerged as a potential measure to mitigate the airborne transmission of respiratory disease such as COVID-19. Herein, we experimentally investigated the impact and interaction of pure water droplets as surrogate to respiratory droplets with the different layers of a commercially available N95 mask to demonstrate the penetration and passage-capability of respiratory fluids through the different layers. The penetration of an impacting droplet through the mask layers was characterized by elucidating the ejection of secondary droplets from the rear-side surface of the target mask material. In addition, the passage of respiratory fluids through the mask layers was characterized by capillary imbibition of the droplet liquid through the pores, as a function of wettability of the mask material. Droplet impact at Weber numbers We = 208 and 416 has been considered in the present study; the chosen We range corresponds to that of cough droplets realized in real respiratory events. Each layer of the N95 mask is hydrophobic that prevents capillary imbibition through the pores: a sessile droplet placed over the surface exhibits classical diffusion-limited evaporation. Droplet impact experiments on N95 mask layer surfaces reveal that a single layer allows liquid penetration at We = 416; while a combination of five layers, as is the case of a commercially available N95 mask, blocks the penetration completely, consistent with the widely known effectiveness of N95 masks. Herein, we devote special attention to compare the so-obtained efficiency of N95 masks to that of a recently designed two-layer cloth mask containing an intermediate High-Efficiency Particulate Air (HEPA) filter layer (Narayan et al. in Phys Fluids 34:061703, 2022). We conclusively show that the performance of the designed cloth mask is identical to that of a commercially available N95 mask. The assessment of mask effectiveness further includes examination of breathability and comfort by means of passage of air through them. A comparative study has been presented herein for a clear demonstration of effectiveness of different masks in preventing air-borne transmission of COVID-19.