The New York Times: “Covid precautions have turned many parts of our world into a giant salad bar, with plastic barriers separating sales clerks from shoppers, dividing customers at nail salons and shielding students from their classmates. Intuition tells us a plastic shield would be protective against germs. But scientists who study aerosols, air flow and ventilation say that much of the time, the barriers don’t 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 a clerk 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 air flow and ventilation. 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 to 30 minutes. But erecting plastic barriers can change air flow in a room, disrupt normal ventilation and create “dead zones,” where viral aerosol particles can build up and become highly concentrated…”

A study published in June and led by researchers from Johns Hopkins, for example, showed that desk screens in classrooms were associated with an increased risk of coronavirus infection. In a Massachusetts school district, researchers found that plexiglass dividers with side walls in the main office were impeding air flow. A study looking at schools in Georgia found that desk barriers had little effect on the spread of the coronavirus compared with ventilation improvements and masking.