Measuring Total Filtration Efficiency of Surgical and Community Face Masks: Impact of Mask Design Features

Surgical and community face masks are used worldwide to reduce the transmission of respiratory infections in indoor environments. Performance parameters for these loose-fitting devices are mainly focused on material filtering efficiency, while, differently from face respirators, there are no standard methods for measuring the fraction of air leaking at the face seal. This study quantifies the total filtration efficiency (TFE), a parameter based both on filter efficiency and air leakage, of 50 face mask models with the aim of understanding the role of several mask design features on TFE performance. An instrumented head form equipped with sensors for measuring volumetric airflow and differential pressure was used to simulate the air exhalation from the mouth of a person wearing a face mask. A response surface method (RSM) was used to model the TFE experimental data. Results showed that TFE values ranged over a wide interval (from 5% to 73%), with better values at higher flow rates. A significant positive correlation was found between TFE and filter breathability. The presence of a nosepiece (NP) showed to increase the TFE on average from 4% to 6%, according to the flow rate. Significant improvements were associated only to nosepieces incorporating a metallic wire. The RSM model evidenced that the increase in the number of the filter layers and the use of a meltblown layer result in higher TFE only when a nosepiece is in place. Differently, the benefit of the nosepiece is less marked for masks made of highly breathable filters. To improve overall mask performance, the design of loose-fitting face masks should carefully compromise between breathability and filtration efficiency of the filter materials. The addition of a metallic nosepiece helps improving the TFE by limiting the air leaking at the face seal.