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Why plexiglass alone can’t prevent Covid-19

Trump says plexiglass “is not the answer” to prevent Covid-19. Experts weigh in.

A restaurant in Belgium erects clear plastic barriers between tables in preparation for its reopening.
A restaurant in Genval, Belgium, erects clear plastic barriers between tables in preparation for its reopening.
Philippe Crochet/Getty Images

During Thursday night’s presidential debate, President Donald Trump countered his Democratic rival Joe Biden’s call for businesses to erect plexiglass barriers and other safety precautions to reduce the spread of Covid-19.

“These are restaurants that are dying,” the president said. “These are businesses without money. Putting up plexiglass is unbelievably expensive and is not the answer.”

He added, “Are you going to sit there in a cubicle wrapped around in plastic? These are businesses that are dying Joe, you can’t do that to people.”

Trump’s comments, however, neglect the separate guidelines issued by the Centers for Disease Control and Prevention and the US Department of Labor, which encourage the use of plastic partitions in schools, businesses, and workplaces. Grocery stores, salons, restaurants, nursing homes, and even offices across the country have newfound use for plexiglass, erecting transparent barriers between groups of people as a preventative measure against the coronavirus.

Most businesses — some of which are struggling to stay afloat — have opted for more basic, makeshift shields. My neighborhood bánh mì joint, for example, has set up a vinyl curtain to separate the cashier from the customer. So has my local grocery store, which installed a thin divider in front of the employee’s checkout monitor.

At nail salons, patrons are sticking their hands through a hole cut in a sneeze guard as masked technicians work on their manicures. Restaurants have constructed table barriers between parties — sometimes for both indoor and outdoor operations — that can create a bleak illusion of closed-off safety, in spite of the virus’s potential for airborne transmission.

However, Trump may be right in suggesting that plexiglass shields and similar plastic barriers are not the answer for a different reason — not cost, but efficacy. At least, they’re not the answer alone, explained Shelly Miller, a University of Colorado Boulder professor of environmental engineering.

“These barriers are designed to prevent large spray-born droplets, which are released when someone talks loudly or coughs at close range,” she told me. “But you also have to account for the smaller particles that can go around the plexiglass barrier and stay airborne for longer periods of time, which someone can still inhale.”

These clear dividers can be useful, though, in places like grocery stores, shopping malls, or banks, where customers interact closely with workers but are still masked and distanced from others.

Public health experts have advocated for a layered approach to protecting oneself from the virus, Miller said. There is no silver bullet in combating the coronavirus’s spread. That means in addition to plastic shields, businesses should still ask customers to social distance and wear masks, while ensuring that there’s proper ventilation so that even if airborne particles are released, they won’t linger for very long. Even face shields, which are popular among wait staff, need an extra layer of protection.

“I would never wear a face shield without a mask. It won’t protect you in any way from inhaling an airborne virus,” Miller added. “I would recommend wearing eye protection if you’re sharing air with an infectious person, since we have receptors that can pick up Covid in our eyes, mouth, and nose.” (The president, having had Covid-19, also referred to wearing goggles during Thursday’s presidential debate, to some surprise.)

In July, the Atlantic’s Derek Thompson coined the phrase “hygiene theater” to describe the ritualistic devotion to temperature checks and surface sanitizing that, in some instances, complicates this layered approach: “Covid-19 has reawakened America’s spirit of misdirected anxiety, inspiring businesses and families to obsess over risk-reduction rituals that make us feel safer but don’t actually do much to reduce risk — even as more dangerous activities are still allowed.”

In recent months, people have become more attuned to these performative protections (which include plastic) that don’t really do a good job at protecting us in high-risk situations.

Aerosol scientists and epidemiologists pointed out how the two transparent barriers between Sen. Kamala Harris and Vice President Mike Pence — which Pence initially made a fuss over — at the vice presidential debate in early October, won’t effectively block any microscopic aerosols that are released in the air by an infectious person.

Yet the prevalence of plastic and plexiglass has skyrocketed since the reopening of most businesses across the country. Some establishments are even getting creative in the endeavor to mixed results: A French interior designer is selling ceiling-strung dining pods for $173 a pop. A handful of New York City’s most Instagrammable restaurants are offering dine-in bubble tents as the winter approaches. One of the most dystopian images I’ve seen is that of an older couple locked in a passionate embrace, their masked faces pressed tightly against a plastic “hugging curtain” used in some European nursing homes.

Some Americans are dining or working out indoors again, assured by the many hygiene precautions advertised by places like restaurants and gyms. People’s willingness to engage in these higher-risk activities highlight the lack of cohesive public health messaging surrounding the virus, which has confused many Americans since March.

Without comprehensive guidance from the federal government, things like mask compliance and dining capacity can vary from state by state, or even city by city. As a result, some have found comfort — and a false sense of security — in the sanitation craze championed by businesses eager to welcome back customers.

This can be especially dangerous inside restaurants or bars, where patrons have to take their masks off to dine and drink. Booth partitions create an oddly claustrophobic sense of enclosure, which could make customers feel separated from nearby parties, even if they aren’t spaced 6 feet apart.

“It’s possible that these shields can create a micro-environment for one group of diners willing to take the risk with each other or if they’re in the same Covid cluster,” said William Bahnfleth, a Pennsylvania State University professor of architectural engineering. “But if there isn’t good air flow in the space, the plastic barriers might not have much effect at all.”

New York City residents sit in clear plastic bubble tents while dining outside.
A cafe in New York City’s Upper West Side offers socially-distanced bubble tents for patrons eating outdoors.
Noam Galai/Getty Images

Bahnfleth said restaurants should consider adding air purifiers or other ways to increase the indoor air change rate — the frequency at which air in a space is recycled, which would reduce the likelihood of customers inhaling viral particles. The height and density of these partitions could also impede the natural air flow of an indoor space, Miller said, which could lead to certain areas having a higher concentration of lingering aerosol particles than others.

But as winter approaches, some establishments have become inventive with their outdoor set-ups to keep patrons warm, even if it isn’t epidemiologically sound.

The plastic bubble tents seen around the streets of New York, for example, appear to reduce air flow, even if it’s technically part of a restaurant’s outdoor dining operation. While these bubbles are keeping diners inside warm, there doesn’t appear to be any ventilation.

“If these spaces had a small opening, that would be better,” Miller said. “I think it’s a cool idea, but I can only see eating in one with my family or people I socialize with on a daily basis.” Her biggest concern with the bubbles is if they’re inhabited by an asymptomatic person, the virus particles they exhale can build up in very high concentrations with nowhere to go.

The market for these products is booming, although some acrylic suppliers are hesitant to say whether this demand will last beyond the pandemic, Forbes reported. Lucite International, one of the top international suppliers of acrylic-based products, braced for “a very large downturn” when the coronavirus first hit, since the company supplies to a variety of customers in the automotive, construction, retail, and signage industries. (Acrylic is the formal name of the type of polymer used to manufacture plexiglass.)

The sudden interest in acrylic barriers for essential workers and businesses helped, although Lucite doesn’t anticipate the demand for them to last beyond 2021. Alan Ledger, Lucite’s US-based national sales manager, said in an email to Vox that while “there will be ongoing demand for replacement [acrylic] panels, the largest surge has already occurred.”

Plus, some of the industry’s long-time customers, such as construction and retail, are hurting from the pandemic, reported the business news publication Marker.

But if we take hints from the security theater that resulted from the 9/11 attacks, it’s possible that sanitation habits and plastic displays could be here to stay in a post-Covid-19 world. Urbanists are predicting that the pandemic could influence people to socialize and eat outdoors more, which would impact restaurant set-ups. Experts are also anticipating a shift in social behavior: People could possibly become hyper-vigilant about hygiene and share space with strangers, since it’s likely that another pandemic could be in our future.

If masks become a normalized post-pandemic accessory, it’s not a stretch of the imagination to predict that plastic sneeze guards and barriers will be, too.

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