Effectiveness of respiratory protective equipment on source control of exhaled pollutants

Respiratory protective equipment (RPE) is used either to protect the wearer (protection effect during inhalation) or to protect others from potential transmission of pathogens from the wearer (source control effect during exhalation). Inhalation and exhalation are two processes that generate microenvironments with different characteristics inside the RPE. In order to quantitatively evaluate the source control effectiveness (SCE) of RPE, the gap size between the RPE and the face was measured using volunteers, and the tracer-gas-based method and aerosol-based method were applied to visualize and quantify the dispersion of exhaled pollutants through the face mask and the gap using a manikin. The tracer-gas-based method (using CO2) largely overestimated the concentration of exhaled pollutants in front of the RPE. The SCE of RPE was 76–99% for aerosols and 79–92% for tracer gas. The top gap of the face mask was the dominant leakage route of exhaled pollutants. When the size of the top gap increased from 8 mm to 20 mm, the SCE for aerosols smaller than 1 μm decreased by about 15%. The SCE of the combined RPE with an N95 mask and a face shield was about 7% higher than that for an N95 mask alone. Increasing the pulmonary ventilation rate from 6 to 13 L/min and the respiratory cycle from 3 to 5 s decreased the SCE of RPE by 16% and 9%, respectively, indicating the importance of considering the activity level. The data obtained provides a basis for evaluating and improving the performance of RPE.