In an effort to help curb the spread of COVID-19, many stores and public-facing businesses have opted to install plastic barriers separating employees from customers. By one estimate, more than $750 million has been spent on these Plexiglas-type products. The premise is that the physical separation may help reduce viral particles from being communicated from one party to another.

According to a recent report in The New York Times, that may not be the case.

In speaking with experts, the Times asserts that instead of blocking particles, the barriers may simply be redirecting them to other work colleagues on one side of the barrier—or, worse, reducing ventilation in the space, which is a key component of helping mitigate viral spread indoors.

In the case of a school classroom, which may have barriers for each seat, the problem can be amplified. “If you have a forest of barriers in a classroom, it’s going to interfere with proper ventilation of that room,” Linsey Marr, professor of civil and environmental engineering at Virginia Tech, told the Times. “Everybody’s aerosols are going to be trapped and stuck there and building up, and they will end up spreading beyond your own desk.”

What limited research exists on barrier effectiveness generally indicates only limited benefit. A plastic shield will almost certainly stop a larger particle from a cough or sneeze from ending up on a person’s face, but smaller aerosols expelled during a conversation may instead drift, moving over the barrier (which rarely extends to ceiling height) where it can hang in the air and remain a potential source of infection.

Benefits are noticeable when the barrier is more substantial—think a doctor’s office reception partition, a bank, or a bus driver enclosed in a space. But partial barriers installed without regard to the effects of airflow or ventilation may not be doing the job.

Should you be concerned about plastic barriers increasing your risk of illness? Not necessarily. Vaccination, masking, and social distancing remain the most effective ways to manage possible exposures. A limited time spent near a barrier is not likely to significantly impact those odds, though employees who spend hours in that situation and without proper airflow in the building might not find themselves in ideal circumstances.

[h/t The New York Times]