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Those Anti-Covid Plastic Barriers Probably Don’t Help and May Make Things Worse

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.

“If you have a forest of barriers in a classroom, it’s going to interfere with proper ventilation of that room,” said 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 often are equipped with transparent sneeze guard above the food.

But Covid-19 spreads largely through unseen aerosol particles. While there isn’t much real-world research on the impact of transparent barriers and the risk of disease, scientists in the United States and Britain have begun to study the issue, and the findings are not reassuring.

Three Types of Acrylic Sheet

There are three main ways plexiglass is manufactured. Each style of plexiglass acrylic has its own advantages and disadvantages. This article will outline the differences.

 

Cell Cast Acrylic Sheet

This style is produced by melted liquid PMMA resin poured between two plates of glass

Least amount of expansion and contraction

Highest margin of error on thickness tolerance

Standard thickness tolerance from .118” - .500” is +/- 8%

This is the best material to use when cutting or routing

Highest molecular weight

Widest range of colors available

Standard material for signs, aquariums, and high-end fabrication

Continuous Cast Acrylic Sheets

This style is produced by pouring melted liquid PMMA resin between two belts of polished stainless steel

Best material consistency

Least amount of expansion and contraction

2nd best thickness tolerance

Widest ranges of sizes available up to 9’ wide and 16’ long

Standard material for forming, fabrication, and skylights

Extruded Acrylic Sheets

Semi-soft melted resin is pushed between rollers and cut to size

Highest internal stress within the sheet

Most expansion and contraction

Generally, the best thickness consistency

Thickness tolerance +/- 10%

Softest sheet

Gums up routers more when cutting

Easy to glue

Standard material for displays, and replacement windows. Some signage acrylic sheet uses.

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