INVESTIGATION OF THE EFFECTS OF MASKS ON AIRBORNE AEROSOLISED TRANSMISSION IN AN INDOOR ENVIRONMENT

Abstract

The filtration efficiency of the 3-ply surgical mask and the N95 respirator was investigated under the challenge of aerosolised olive oil and sulfur hexafluoride (SF6) gas in this study. The experiments conducted evolved around the scenario of doctorpatient consultation with patient inflow simulated through cyclical dosing of test agents. Results showed that the upstream and downstream concentrations for both 3-ply surgical mask and N95 respirator will build up over time after the cycles of dosing, displaying an overall uptrend, be it under the challenge of aerosolised olive oil or SF6 gas. Under the challenge of aerosolised olive oil, the filtration efficiency largely follows an overall upwards trend as particle size increases beyond 0.3 μm for both 3-ply surgical mask and N95 respirator. However, there are two anomalies where the 0.900 μm and 1.800 μm particles have negative filtration efficiencies which may be due to effects of particle agglomeration. Other than these, the overall filtration efficiency of the different aerosol sizes for 3-ply surgical mask is calculated to be 33%, while that of the N95 respirator is 43%. This signifies that the N95 respirator does not provide that much of a protective edge over that of the 3-ply surgical mask. Under the challenge of SF6 gas, the overall filtration efficiency of the 3-ply surgical mask has been tabulated to be 2%, while that of the N95 respirator is 6%. The filtration efficiencies are overly low and this implies that the protection offered by the masks is very limited. Although simulations of exhaled droplets using aerosolised olive oil and SF6 gas both supported the conclusion of the N95 respirator being a better respiratory protector, the filtration efficiencies of the masks differed too much under the two test protocols. The overly low filtration efficiencies for SF6 gas suggests that SF6 gas is probably not as suitable as aerosolised olive oil as a surrogate for exhaled particles in the testing of masks.