In-Depth: Plastic barriers likely don't block COVID and may increase the risk

COVID plastic barrier
Posted at 4:40 PM, Aug 27, 2021

SAN DIEGO (KGTV) -- A growing body of research suggests it’s time to rethink those anti-COVID plastic barriers used as fortifications in retail stores, restaurants and countless other indoor settings.

Studies on aerosols and airflow reveal these screens are “unlikely to provide any direct benefit,” according to a group of scientists who advise the U.K. government. And there is some evidence the barriers can actually increase the risk of infection.

Unless a plastic barrier is carefully installed by an airflow engineer, “it is potentially harmful rather than being helpful,” said UC San Francisco infectious disease expert Dr. Peter Chin-Hong.

The air in a typical room gets replaced with fresh air every 15 to 30 minutes. Experts say rows of plastic barriers can trap air and impede ventilation.

“It’s very clear that indoors without much ventilation turns out to be the worst thing for the virus to spread,” said Dr. Davey Smith, chief of infectious diseases at the UC San Diego School of Medicine.

In May, researchers in New Mexico published particle simulations showing plastic barriers were good at blocking big droplets from coughs or sneezes. However, they showed the tiniest particles drifted over the screen after about 30 seconds.

Those tiny particles, called aerosols, are also emitted while talking.

“We’ve learned that aerosols are a much more significant factor in transmission, particularly in indoor settings,” said Dr. Chin-Hong.

Without proper ventilation, these infectious aerosols can linger in the air for hours. Plastic barriers can create pockets of “dead air” where these particles can gather.

“What the plexiglass does is it basically may redirect airflow and concentrate aerosols in a particular way that may be more dangerous,” he said.

Several studies have examined the impact of barriers at schools. A study in a Massachusetts school found plexiglass dividers with side walls impeded airflow. A large study from Johns Hopkins found desk screens in classrooms were associated with an increased risk of coronavirus infection.

Researchers say there are specific circumstances where barriers can help, particularly floor-to-ceiling barriers that separate one person from others. A modeling study on buses showed a screen completely separating the driver can shield that person from particles emitted by passengers.

In any case, experts said barriers should be designed and installed by engineers who can measure the airflow unique to each environment.

Instead of barriers, aerosol scientists say people should work to improve ventilation, add HEPA air filtering machines, and require masks.