Examining the protection efficacy of face shields against cough aerosol droplets using water sensitive papers

Ronen, A.; Rotter, H.; Elisha, S.; Sevilia, S.; Parizer, B.; Hafif, N.; Manor, A.

Simple plastic face shields have many advantages compared to regular medical masks. They are easily cleaned for reuse and comfortable to wear. In light of the spreading COVID-19 pandemic, the potential of face shields as a substitution for medical masks, as a recommendation to the general population, was tested. Testing the efficacy of the protective equipment utilized a cough simulator that was carefully tuned to replicate human cough in terms of droplet size distribution and outlet velocity. The tested protective equipment was worn on a manikin head simulating human breathing. An Aerodynamic Particle Sizer (APS) was used to analyze the concentration and size distribution of small particles that reach the manikin head respiration pathways. Additionally, Water sensitive papers were taped over and under the tested protective equipment, and were subsequently photographed and analyzed. For droplets larger than 3m by diameter, the efficiency of shields to block cough droplets was found to be comparable to that of regular medical masks, with enhanced protection on face parts the mask does not cover. Additionally, for finer particles, of the order 0.3 to few microns, a shield was found to perform even better, blocking about 10 times more fine particles than the medical mask. This implies that for the general population that is not intendedly exposed to confirmed infected individuals, recommending the use of face shields as an alternative to medical masks should be considered.