LOS ANGELES (KABC) -- Face shields alone provide only minimal protection from coronavirus particles, UCLA researchers found, but combining shields with a mask can be fairly effective at blocking droplets.
If you are standing close to a coughing person, a face shield would only reduce airborne particles by about 4%, according to the study.
"This is likely because the face shield does not fit the face snugly, and thus, cough droplets can escape from the open gaps around the shield," the study said, noting that the airflow of a room can also play a role.
A cloth mask would provide a 77% reduction and the combination of face shield and mask would reduce particles by 89% - which is just slightly below the protection offered by professional surgical masks.
The study also noted that without any mask or face covering, six feet of social distancing may not be enough.
"We found that a simple cough could send particles more than six feet away, without face coverings," said Yifang Zhu, a professor in the Department of Environmental Health Sciences and associate dean for academic programs at the UCLA Fielding School of Public Health.
Zhu's team, which includes UCLA scholars Liqiao Li and Muchuan Niu, set up a test space in a lab and measured the particle number concentration (PNC) and particle size distribution under seven different conditions: (1) no face covering; (2) face shield only; (3) cloth mask; (4) face shield + cloth mask; (5) surgical mask; (6) face shield + surgical mask; (7) N95 respirator or equivalent (i.e., KN95 mask).
The use of a surgical mask or the N95 respirator/KN95 mask provided more than 94% reduction.
"To minimize the infection risk of aerosol transmission, stricter mitigation measures should be adopted for indoor environments, which are more likely to be enclosed and crowded,'' Li said. One of the simplest is a mask.''
Their article was published in the peer-reviewed journal Aerosol Science and Technology and can be viewed here.
City News Service contributed to this report.