An analytical study of facemask performance to mitigate respiratory diseases transmission through coughs and sneezes

Abstract

Upper respiratory infectious diseases are often transmitted through ejected droplets and aerosols at high velocity by coughs or sneezes. In its early stages, the rapid spread of the COVID-19 virus could not be fully controlled without face masks and social distancing, and the measures' effectiveness was in doubt due to the uncertainty of air leakage around the mask edges. This study aims to analytically investigate the effect of wearing face masks on the contamination distance around a coughing infected person in still air. The effect of mask design and the presence of gaps around the mask edges was also investigated in this study. A steady-state analytical model was developed to estimate the contamination distance as a function of mask properties and the gap width around the mask edges. The model was validated against experimental observations, showing good agreement. Results revealed that the effectiveness of a face mask in reducing contamination distances is highly dependent on the tightness of the mask fit around the wearer's face. Masks with high packing density, such as N95, were found to be ineffective with gap widths wider than 0.2 mm around the mask edges due to their high resistance, which diverts most of the flow to leak around the edges. For such wide gaps, more permeable cloth masks with packing densities below 1 % reduce the contamination distance more effectively, despite having a low filtration capacity, by impeding the inertia of the ejected particles.