Experimental efficacy of the face shield and the mask against emitted and potentially received particles
AbstractThe aim of this study was to evaluate the comparative performance of masks and face shields in different experimental configurations. An experimental setup with two mannequin heads positioned at 1.70m high and at 25 cm each other was used. A fogger generated a particle’s airflow with a speed of 5m/sec from the emitter to the receiver head mannequin. Our aerosol generator produced 3 000 times more particles than a physiological cough situation. A particle counter allowed us to evaluate the number of particles received on a mannequin head located at a very short distance of 25 cm. The amount of all particles up to the selected particle sizes were counted with an optical particle counter on channels 0.3 µm, 0.5 µm, 1 µm, 2.5 µm, 5 µm and 10 µm. The reduction factors with a protection worn by the receiver alone, by the emitter alone and then the double protection of emitter and receiver were calculated. When the receiver alone wore a face shield, the amount of total particles was reduced (54.8%), while the reduction was less when the receiver alone wore a mask (21.8%) (p = 0.003). Wearing a protection by the emitter alone reduced much more the level of particles received by 96.8% for both mask and face shield. The double protection allowed for even better results, but close to the protection of the emitter alone: 98% reduction for the face shields and 97.3% for the masks (p=0.022). Even with small particle size emission (≤0.3µm), results were of the same order. Considering our results, protection of the emitter alone or double protection is much more effective than protection of the receiver only. Validated face shield should be included as part of strategies to safely and significantly reduce transmission in the community setting, in addition to masks or for people with disabilities or medical intolerance to masks.
