Experimental efficacy of the face shield and the mask against emitted and potentially received particles

Abstract

The 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.

Experimental Investigation of Aerosol and CO2 Dispersion for Evaluation of COVID-19 Infection Risk in a Concert Hall

“…0.14 µm for SARS-CoV-2) [ 13 , 25 , 26 , 27 ]. Face masks serve to reduce the number of particles, especially heavier ones [ 17 , 28 , 29 ]. Considering this, more attention should be paid to small particle sizes (diameter < 1 µm) when indoor viral aerosol dispersion is discussed.…”

The Effect of Eye Protection on SARS-CoV-2 Transmission: A Systematic Review

“…Several laboratory studies using mannikins have examined the potential effects of face shields but vary greatly in their design and their application to real-world settings. One study tested facing mannikins 25cm apart with the emitter sending an aerosol spray with particles with a range of size from less than 0.3µm to 10 µm; they found a reduction in particles received of 55% with face shields compared to 22% for a mask, and 97% for both 18 . A study with a mannikin 60cm from the spray found greater reductions and face shields providing greater protection than masks 19 .…”

The effect of eye protection on SARS-CoV-2 transmission: a systematic review

“…Several laboratory studies using mannikins have examined the potential effects of face shields but vary greatly in their design and their application to real-world settings. One study tested facing mannikins 25cm apart with the emitter sending an aerosol spray with particles with a range of size from less than 0.3µm to 10 µm; they found a reduction in particles received of 55% with face shields compared to 22% for a mask, and 97% for both 18 .…”