According to some studies on Covid infections, partitions in shops, offices and schools could have a counterproductive effect because they hinder the exchange of air in the rooms
I dividers now they are part of our lives: they separate shop assistants, public office employees, teachers from customers, users, students. But do they represent an effective weapon against the risk of contagion? Intuitively yes, since they act with the same logic of the mask, that is, blocking what comes out of the nose and mouth of those in front of us. According to some studies, however, the plastic barriers would give a false sense of security, as the virus travels mainly via aerosols (the light droplets that remain suspended). Not only that: they could even make things worse, since they hinder proper air exchange in closed environments. it has been shown that open windows frequently for a few minutes it allows to limit the risk of contagion even in crowded places such as school classes: it is clear that a forest of barriers makes cleaning of what you breathe extremely slower.
The particles are deflected by the barriers
An article published on New York Times
takes stock of the pros and cons of this extremely widespread preventive measure. The point is that the Plexiglas sheets modify the normal air flow in the premises and the result can be unpredictable: for example, a salesman can be protected but if there is a positive with high viral load the infectious particles could be deflected by the barrier and infect another employee, or a customer. Furthermore, in a room with many partitions, dead zones could be created where air exchange does not occur and the virus can concentrate at high levels. A forest of barriers in a classroom interferes with proper ventilation – explains Linsey Marr, professor of engineering at Virginia Tech in Blacksburg -. The aerosols of everyone present will be trapped and accumulate, eventually spreading out of the individual space. A study published in June by researchers from Johns Hopkins University in Baltimore shows that screens placed between desks in classrooms are associated with an increased risk of infection. In a Massachusetts school district, scholars have found that i plexiglas dividers prevent airflow, and a study of schools in Georgia showed that the plates between the desks have a limited effect on the spread of the virus, as opposed to frequent air exchange and the use of masks.
The aerosol mixes in the air
In Britain, investigations have been made to simulate what happens when a person behind a barrier exhales particles while talking or coughing, under various ventilation conditions. Result: the screen is most effective when the person coughs, because the large particles go fast and hit him. But when a person speaks, the exhaled particles float in the air and are not blocked. We have shown that the aerosol smaller ones travel over the screen and mingle in the room air within about 5 minutes – explains Catherine Noakes, Professor of Environmental Engineering at the University of Leeds -. If people interact for more than a few minutes, they are likely to be exposed to the virus regardless of the screen.
Like cigarette smoke
Before the pandemic in 2013, Noakes had conducted a study to examine the effect of dividers between beds in hospitals: some people were found to be protected from germs, but the barriers channeled the air to the direction of other patients. Airflow is obstructed and pockets of higher or lower risk are created, which are difficult to identify, says the expert. To understand why screens do not protect against aerosol, Professor Linsey Marr uses the comparison with cigarette smoke, which is able to overcome any obstacle by walking around it. Not to mention the fact – adds Marr – that people who are on the same side of the barrier as the smoker are exposed to passive smoke for a longer time, because dispersion occurs more slowly. The same mechanisms occur with the light particles of the coronavirus, those exhaled by simply speaking or breathing.
Screens in schools and offices
Experts agree that screens can only be useful in specific situations. A bus driver completely separated from the public by a barrier certainly less at risk of contagion. The same goes for a bank teller or employee who welcomes patients to a doctor’s office. What instead to avoid the forest of dividers in places like restaurants or classrooms. A study by the National Institute for Occupational Safety and Health in Cincinnati tested transparent barriers of different sizes in a closed room, using a cough simulator. The work, not yet published, shows that, under the right conditions, the tallest screens have stopped about 70 percent of the particles. But the same authors point out that the experiment was conducted in artificially created conditions, with adequate ventilation levels that are not always possible to find in real situations.
The solution: mask vaccines
Further research is needed to determine the effect of transparent screens around school desks or offices, but many experts agree that desk barriers do not protect and indeed interfere with proper ventilation of the rooms, causing an accumulation of viral particles. There solution for schools and offices – say the experts – vaccinate teachers, students and workers and impose the use of the mask, as well as improve ventilation, for example by adding Hepa-type air filtering machines. The problem is that very often the barriers are placed without the assistance of experts who can evaluate the air flow and ventilation. Therefore, those who have screens around their desk should still protect themselves with the mask to reduce the risk of contagion, since it is not safe. Each room is different in terms of furniture arrangement, height of walls and ceilings, air vents – says Richard Corsi, Professor of Engineering at the University of California -. All of these things have a huge impact on the actual flow and distribution of the air.
August 21, 2021 (change August 21, 2021 | 14:55)
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