RESTRICTIONS: Those anti-Covid screens that shops and bars use? They may make things worse

Erected as coronavirus precautions, the barriers may redirect germs to others, research suggests

Intuition tells us a plastic shield would be protective against germs. But scientists who study aerosols, airflow and ventilation say that, much of the time, the barriers do not help and probably give people a false sense of security. And sometimes the barriers can make things worse.

Research suggests that, in some instances, a barrier protecting an assistant behind a checkout counter may redirect the germs to another worker or customer. Rows of clear plastic shields, like those you might find in a nail salon or classroom, can also impede normal airflow and ventilation.

Erecting plastic barriers can change airflow in a room, disrupt normal ventilation and create dead zones where viral aerosol particles can build up and become highly concentrated

Under normal conditions in stores, classrooms and offices, exhaled breath particles disperse, carried by air currents and, depending on the ventilation system, are replaced by fresh air roughly every 15-30 minutes. But erecting plastic barriers can change airflow in a room, disrupt normal ventilation and create “dead zones” where viral aerosol particles can build up and become highly concentrated.

“If you have a forest of barriers in a classroom, it’s going to interfere with proper ventilation of that room,” says Linsey Marr, professor of civil and environmental engineering at Virginia Tech and one of the world’s leading experts on viral transmission. “Everybody’s aerosols are going to be trapped and stuck there and building up, and they will end up spreading beyond your own desk.”

There are some situations in which the clear shields might be protective, but it depends on a number of variables. The barriers can stop big droplets ejected during coughs and sneezes from splattering on others, which is why buffets and salad bars are often equipped with transparent sneeze guards above the food.

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