A study on methods for estimating the mask size required to minimize peripheral leakage

Owing to the spread of COVID-19, masks made from a variety of materials and designs have been used in the absence of guidelines. To inform measures against seasonal influenza and prepare for the next pandemic, this study conducted particle penetration and leakage tests on prototype masks to propose design guidelines for masks used in nonhealthcare settings. In Test 1, the pressure drop and permeability were measured for six types of flat fabric. In Test 2, permeability measurements were performed on 12 prototype masks made from three different materials and categorized into four sizes. The masks were fitted onto facial dummy designed to match the contours of the human face. The peripheral leakage rate was calculated based on the measured leakage. Furthermore, an empirical equation was formulated to estimate the pressure drop Δ P w during wear using the ratio of the flow velocities in each test and the pressure drop of the flat fabric. Subsequently, the peripheral and total leakage rates were plotted against Δ P w ; the transition of leakage from the gaps to the part that covered the nose and mouth occurred at Δ P w = 1 Pa. Next, using the percentage of the peripheral leakage rate to the total leakage rate at 1Pa as an exploratory indicator in the empirical model, the minimum material area required to minimize peripheral leakage was estimated. This estimation method determines the required material area requirements based on the material properties. These findings support the development of standardized methods for mask design and analysis.