These Anti-Covid Plastic Barriers Probably Won’t Help and Could

Covid measures have turned many parts of our world into a giant salad bar, with plastic barriers separating clerks from shoppers, separating customers in nail salons, and protecting students from their classmates.

Intuition tells us that a plastic shield will protect against germs. But scientists who study aerosols, airflow and ventilation say that most of the time, obstacles don’t help and likely give people a false sense of security. And sometimes obstacles can make things worse.

Research shows that in some cases, a barrier protecting an officer behind a cash register can direct germs to another employee or customer. Rows of clear plastic shields, as you might find in a nail salon or classroom, can also block normal airflow and ventilation.

Under normal conditions, breath particles exhaled in shops, classrooms and offices are dispersed by air currents and are replaced with fresh air roughly every 15 to 30 minutes, depending on the ventilation system. But erecting plastic barriers can alter the airflow in a room, disrupt normal ventilation and create “dead zones” where viral aerosol particles can accumulate and become highly concentrated.

“If you have a barrier forest in your classroom, it will impede 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. “Everyone’s aerosols will get trapped, get trapped there, and eventually spread beyond your own desk.”

There are some situations where transparent shields can be protective, but that depends on a number of variables. Barriers can prevent large droplets from coughing and sneezing from splashing onto others, so buffets and salad bars are often equipped with clear sneeze guards over food.

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

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

before the pandemic, a study An article published in 2014 found that office dividers were among the factors that could contribute to disease transmission during a tuberculosis epidemic in Australia.

British researchers did modeling work It simulates what happens when a person on one side of a barrier (such as a customer in a store) inhales particles while talking or coughing under various ventilation conditions. The screen is more effective when the person coughs because larger particles have more momentum and hit the barrier. But when a person speaks, the screen does not trap the exhaled particles – they just float around it. While the shop attendant can avoid a sudden and direct blow, the particles are still in the room, posing a risk to the clerk and others who might breathe the polluted air.

“We’ve shown this effect of blocking larger particles, as well as smaller aerosols that pass over the screen and mix into room air in about five minutes,” said Catherine Noakes, professor of environmental engineering for buildings at the University of Leeds. Britain. “This means that if people interact for more than a few minutes, they will likely be exposed to the virus regardless of the screen.”

Dr. Noakes said that installing barriers may seem like a good idea, but can have unintended consequences. He conducted a study It was published in 2013 examining the effect of partitions between beds in hospitals. The study showed that while some people were protected from germs, the partitions directed the air in the room towards others.

Therefore, an employee behind a transparent barrier may be protected from some of the germs of the customer, while a nearby employee or customers on the line may still be exposed. Dr. Noakes said most of the screens he saw were “badly positioned and unlikely to offer much benefit.”

Dr. “I think this can be a particular issue in places like classrooms where people are staying longer,” Noakes said. “Too many individual screens block airflow and create pockets of higher and lower risk that are difficult to identify.”

Dr. To understand why screens often have little effect in protecting people from aerosol particles, it’s helpful to think of exhaled breath like the smoke of a cigarette, Marr said.

Dr. “One way to think about plastic barriers is that they’re good for blocking things like saliva balls, but ineffective for things like cigarette smoke,” Marr said. “Smoke drifts around them, so it gives the person on the other side a little more time before being exposed to the smoke. Meanwhile, people on the same side as the smoker will be exposed to more smoke because the barriers trap him on that side, until they have a chance to mix throughout the area.”

Most researchers say screens are most likely helpful in very specific situations. For example, a bus driver who is protected from the public by a floor-to-ceiling barrier is likely protected from breathing in much of what passengers breathe. A bank cashier behind a glass wall or an officer checking patients in a doctor’s office may be at least partially protected by a barrier.

A study by researchers He tested different sizes of clear barriers in an isolation room using a cough simulator with the National Institute of Occupational Safety and Health in Cincinnati. The study, which has not yet been peer-reviewed, found that under the right conditions, taller shields above “cough height” prevented about 70 percent of particles from reaching the particle counter on the other side. store or salon employee sitting or standing.

But the study’s authors noted the limitations of the research, particularly that the experiment was conducted under highly controlled conditions. The experiment took place in an isolation room with consistent ventilation rates that “do not accurately reflect all real-world situations,” the report said.

The study didn’t take into account that employees and customers were walking around, that other people could inhale re-directed particles in the room, and that many stores and classrooms have several stations with acrylic barriers, not just one, that block normal airflow.

While more research is needed to determine the effect of adding clear shields around school or office desks, all aerosol experts interviewed agreed that desk shields are unlikely to help and may interfere with normal room ventilation. Depending on the conditions, plastic shields can cause viral particles to accumulate in the room.

“If there are aerosol particles in the classroom air, these shields around students will not protect them,” said Richard Corsi, the new dean of engineering at the University of California, Davis. “Depending on the airflow conditions in the room, you could get a downdraft into those small spaces you’re currently closed to and cause particles to condense in your space.”

Aerosol scientists say schools and workplaces should focus on encouraging workers and eligible students to get vaccinated, improve ventilation, add HEPA air filtration machines as needed, and impose mask requirements – all proven ways to reduce virus transmission.

The problem, according to experts, is that most of the people responsible for installing barriers in offices, restaurants, nail salons and schools do not do so with the help of engineering professionals who can evaluate the airflow and ventilation for each room.

People shouldn’t panic when they see transparent barriers, but they shouldn’t see them as purely protective either. Dr. Corsi said that workers and students with transparent shields around them should continue to wear masks to reduce the risk.

Dr. “Airflow in rooms is pretty complex,” Corsi said. “Each room is different in the arrangement of the furniture, the height of the walls and ceilings, the vents, the places where the bookshelves are. All of this has a huge impact on the actual flow and air distribution in a room because every classroom or office space is different.”

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