Inspiratory leakage flow fraction for surgical masks with varying gaps and filter materials

Leakage flows due to a poor fit can greatly reduce the mask protection efficiency. However, accurate quantification of leakages is lacking due to the absence of standardized tests and difficulties in quantifying mask gaps. The objective of this study is to quantify the leakage flows around surgical masks with gaps of varying areas and locations. An integrated ambient-mask-face-airway model was developed with a pleated surgical mask covering an adult's face, nose, and chin. To study the gap effects, the mask edge along the facile interface was divided into different domains, which could be prescribed either as the mask media or air. A low Reynolds number k-omega turbulence model with porous media was used to simulate inspiratory flows. Experimentally measured resistances of two surgical masks were implemented in porous media zones. Results show that even a small gap of 1-cm(2) area could cause a 17% leakage. A gap area of 4.3 cm(2) at the nose bridge, the most frequent misfit when wearing a surgical mask, led to a leakage of 60%. For a given mask, the increase rate of leakage slowed down with the increasing gap area. For a given gap, the leakage fraction is 30-40% lower for a mask with a resistance of 48.5 Pa than a mask of 146.0 Pa. Even though the flow dynamics were very different among gaps at different locations, the leakage intensity appeared relatively insensitive to the gap location. Therefore, correlations for the leakage as a function of the gap area were developed for the two masks.