‘One way to think about plastic barriers is that they are good for blocking things like spitballs but ineffective for things like cigarette smoke…’
Clarification: The Virginia Tech study referenced in the article below involved plastic barriers used in many public buildings. However, the science is the same for plastic face-shields, as the video above from Florida Atlantic University shows airborne toxins escaping from around the mask.
New research could not demonstrate that plastic shields prevent COVID-19‘s transmission, but studies did show that they cause air to stagnate and virus particles to linger, Breitbart reported.
One such study found that plastic barriers provide the same limited protection as facemasks, capturing some large droplets from coughs and sneezes, although they cannot combat the small particles that cause most infections.
In reporting on the study, the New York Times admitted that the barriers “don’t help” and “may make things worse.”
Linsey Marr, professor of civil and environmental engineering at Virginia Tech, said plastic barriers restrict normal air circulation.
“If you have a forest of barriers in a classroom, it’s going to interfere with proper ventilation of that room,” she said. “Everybody’s aerosols are going to be trapped and stuck there and building up, and they will end up spreading beyond your own desk.”
Rooms normally circulate fresh air in 15 or 30 minutes.
“One way to think about plastic barriers is that they are good for blocking things like spitballs but ineffective for things like cigarette smoke,” Marr said.
Plastic barriers immediately worsen the air quality for people on the same side as someone who has a respiratory illness. Over a longer period, plastic barriers increase exposure to viral particles for people on both sides of the barriers.
“The smoke simply drifts around them, so they will give the person on the other side a little more time before being exposed to the smoke,” she said. “Meanwhile, people on the same side with the smoker will be exposed to more smoke since the barriers trap it on that side until it has a chance to mix throughout the space.”
The Virginia Tech research confirms a John Hopkins University study from June, a 2014 Australian study and a 2013 British study.
Richard Corsi, dean of engineering at the University of California-Davis, likewise warned against plastic barriers.
“If there are aerosol particles in the classroom air, those shields around students won’t protect them,” he said. “Depending on the airflow conditions in the room, you can get a downdraft into those little spaces that you’re now confined in and cause particles to concentrate in your space.”