Government entities like the US Centers for Disease Control and Prevention, the US Occupational Safety and Health Administration, and the World Health Organization (pdf) have gotten behind using barriers made of plastic or glass to protect against Covid-19 transmission. But their recommendations focus on spaces where people who may have Covid-19 interact closely with people who may not: patient intake at hospitals, the service window at a pharmacy, an office setting.  These precautions are aimed at protecting the cashiers, nurses, and pharmacists who work in high-exposure occupations.

Other settings in which these groups recommend the use of plexiglass or other impermeable barriers include manufacturing facilities, taxis/rideshares (pdf), retail environments, and restaurants. Accordingly, the barriers have been in high demand for months.

So are they likely to help in a debate format? On Oct. 7, vice president Mike Pence and Democratic vice presidential nominee Kamala Harris will be standing at least 12 feet apart on a stage in a large auditorium at the University of Utah that seats nearly 2,000 people. When people are that far apart, does a physical barrier actually offer additional protection? (Debate organizers did not respond to Quartz’s email confirming the use of these barriers and asking about their dimensions.)

The most intuitive way these partitions work is to intercept the droplets emitted from someone’s mouth that might contain the virus. But that’s not all they do. They’re also effective at “re-enforcing physical distancing requirements, even when users are unwilling or forgetful” according to a blog post on the web site for Canada’s National Collaborating Centre for Environmental Health.

But physical barriers also have their limitations. The biggest is that they could limit ventilation, reducing the air change rate in a given space. Preliminary results (pdf) from a study about Covid-19 prevention in a performing arts space notes that, “Plexiglass partitions or barriers between musicians are not recommended because the room HVAC system cannot properly change the air as designed. ‘Dead zones’ or areas where aerosol can build-up are a concern.”

Bill Bahnfleth, a professor of architectural engineering at Penn State University, isn’t worried that the barriers will change the air flow patterns too much in a space as large as an auditorium. But he’s not sure they’ll do much good, either. “The barriers are mainly to impede short-range transmission,” he says—namely, larger droplets that could contain viral particles. “When you distance people by a good amount already, and you put in a physical barrier, it perhaps seems a bit redundant.”

The biggest issue with barriers in situations outside the debate, Bahnfleth says, is that they give a false sense of security. “If you put them in offices or restaurants, people think they can be side-by-side without masks and not worry. That’s the issue here—that it’s sending a message that if we just put in plexiglass barriers, we don’t have to worry so much,” he says. Depending on the air flow in the space, air containing the tiniest aerosolized particles can flow around barriers and be inhaled by others.

“Those barriers are useless. They are ignoring science doing the debate indoors like that,” says Jose-Luis Jimenez, a chemistry professor and aerosol expert at the University of Colorado at Boulder. He’s concerned that the candidates are setting a bad example. “We know that talking indoors without masks is not safe. Perhaps the ventilation is good in that debate hall, but many people will assume that talking indoors without masks is ok if one keeps sufficient distance, and will do that in less ventilated spaces.”

Like many other tools in the Covid-reducing toolbox, plexiglass partitions appear to work best in conjunction with other strategies, like social distancing and mask compliance. They don’t eliminate the need for physical distancing, hand-washing, or any other coronavirus prevention strategies. For maskless people talking loudly but presumably far apart during the debate, they shouldn’t be considered a silver bullet.

This piece has been updated to include comments from Jose-Luis Jimenez.

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