One day in March, the kids were there. The next day, there was no one. Then on a Saturday in August, a man came into an empty public school in suburban Boston carrying a container of dry ice, trying to figure out how to bring the students back to their desks.
Since January, that man, Joseph Allen, a professor at Harvard’s School of Public Health, has been saying to anyone who will listen that air—the stuff that everybody breathes and nobody thinks about—has got to move. Before the lockdown, his lab’s whiteboard was dense with notes about how the SARS-CoV-2 coronavirus might spread indoors. Trapped at home, he wrote scads of op-eds, talked to journalists, and was one of the scientists who reviewed an open letter to the World Health Organization demanding that it acknowledge that the virus can be spread through tiny particulates in the air.
With the billowing plumes of dry ice, Allen, his team, and the school’s maintenance employees conducted experiments, measuring the flow of air in various buildings. If Allen has anything to say about it, in some classrooms this fall you might see a fan with a crinkly white HEPA filter strapped to it. In the walls, ventilation systems may be fitted with filters too. As long as the weather permits it, windows will be flung open and wedding tents will be pitched on fields, as school administrations focus on what seems like a simultaneously simple and overwhelming task: Move the air around. Filter it. Dilute it.
While physical distancing and mask wearing help cut down transmission via larger droplets, when it comes to airborne transmission, ventilation and filtration, which reduce the concentration of virus floating in the air, will also be key to making indoor spaces safer.
Allen, who worked as a safe-buildings consultant before entering academia, has been helping schools, universities, and daycare centers work on plans for reopening. “Very often I get the comment, ‘Oh! You’re the first person we’ve heard talk about ventilation!’” Allen says. “That’s deeply concerning.”
The pandemic spotlights a problem that Allen and his colleagues have known about for years, but that most other people have no clue about: Schools are chronically under-ventilated. A commonly used standard for air movement says that, at minimum, 15 cubic feet per minute (cfm) per person should flow into a classroom; Allen says that for Covid prevention, he recommends 30 cfm. But studies show many American classrooms have an average ventilation rate of only 6 to 11 cfm per person.
Even when there isn’t a pandemic going on, that’s not good, because a substantial body of research suggests that better air flow is correlated with increased test scores and reduced absences. At least one study using air filters in classrooms also found increases in student achievement.
The care and feeding of air fell out of public consciousness a long time ago, though. So as fall approached, Allen and his colleagues released a detailed report on how to open schools more safely and provided guidance to those who’ve reached out to them. “The problem is, we’ve lost our way over the years,” Allen says.
It’s taken a worldwide pandemic to get us to pay attention to the air children breathe.
When it came to designing buildings, airflow used to be way up there on the priority list. After much of Britain’s parliament building, the Palace of Westminster, burned in 1834, David Boswell Reid, a doctor, chemist, and inventor, was asked to handle the ventilation of the new building. Members of Parliament had found the old building stuffy, and serious air pollution in London made cracking open a window a risky and extremely unpleasant move. Reid had developed an elaborate ventilation system for his private lab in Edinburgh, and he spent the next few years testing and perfecting his design for Parliament. His plan relied on the natural buoyancy of gases to pull air out of debating chambers and draw fresh air in, and even used wet canvas to filter out pollution. In the temporary House of Commons, he put in an entire ecosystem of ducts that vented air up through flues on the roof. In Reid’s design for the permanent structure, towers that look like Gothic whimsies are, in fact, functional tools for ventilation.
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Keeping the air at a comfortable temperature was Reid’s overriding concern, but he also strove to keep fresh air circulating. For much of the 19th century, the prevailing theory was that diseases like malaria or cholera were caused by miasmas, or “bad air.” The theory was invoked to explain why people living near swamps got sick (today we’d probably say mosquitoes) and why slums were festering pits of disease (we’d now put it down to poor sanitation). And yet they were on to something when it came to air movement.
Medical professionals of the time noted that sunshine and fresh air seemed to have salutary effects. One of the strongest proponents of ventilation was Florence Nightingale, who trained nurses during the Crimean War. Increasing the flow of air reduced the spread of disease among soldiers, she found. “Keep the air he breathes as pure as the external air,” she famously wrote. In Nightingale’s writings, there’s more than a whiff of miasma theory, but while she may have been wrong about the cause, the solution was apt. It wasn’t until the very end of the 19th century that germ theory—how we currently explain illness—caught on. It’s true that ventilation can reduce disease, but it probably does so by reducing the concentration of pathogens in the air.
With the understanding that germs cause disease, rather than some mystical quality of the atmosphere, previous eras’ emphasis on ventilation started to look a bit silly. Then, in the 1970s, a worldwide energy crisis put ventilation even further out of favor. In the name of energy efficiency, schools and office buildings were increasingly designed with windows that didn’t open. This lowered heating and cooling bills, but it meant less air was moving in and out. In his 1986 book Home, architect Witold Rybczynski writes somewhat condescendingly: “No nineteenth-century book on houseplanning was complete unless it included at least one chapter on the subject of ventilation and ‘the evils of bad air.’”
Many of us might think of a stuffy office building or classroom as a temporary inconvenience. But stagnant air may affect us in ways we don’t always realize. Inadequate ventilation is linked to worse performance on cognitive tasks in office workers, Joe Allen’s group has found. At Lawrence Berkeley National Labs, scientists have been studying indoor air quality in schools for decades. Using surveys that ask students if they have any respiratory symptoms and correlating the responses with how much fresh air classrooms get, they’ve found that, after controlling for factors like socioeconomic status, more fresh air is linked to fewer symptoms, says Rengie Chan, a research scientist at LBL. What’s not clear is whether this connection is related to long-term health benefits of breathing fresher air or to lower pathogen concentrations in the air, or some other factor.
Other research has found an association between ventilation and learning, as well. In one study, the scientists had students take tests in rooms whose ventilation they controlled. They found that students in better ventilated spaces had better scores. “There’s pretty strong evidence that improved ventilation will get you improved student performance,” Chan says. There is also evidence, albeit more mixed, that better ventilation reduces absences.
The science has yet to penetrate into practice, though. In one study, coauthored by Chan, 85 percent of the California classrooms included failed to meet the minimum standard of 15 CFM per person. Across the country, many classrooms have unit ventilators, big metal boxes that sit against exterior walls and push air out and suck fresh air in. (Allen often sees them covered with books or potted plants.) Some schools have centralized systems with vents in the ceiling. But even in schools with upgraded systems, Chan and colleagues at LBL and UC Davis found that about half of classrooms still didn’t get enough fresh air, because controls were not set to adequate ventilation, or the systems weren’t maintained or installed correctly.
People are starting to realize this is an issue, even on the level of the federal government, Chan says. A Government Accountability Office report from before the pandemic found that 40 percent of schools needed to upgrade their HVAC systems. But, when the novel coronavirus pandemic hit, not much had been done.
Outside that Boston-area school this summer, Allen and his team found an unobtrusive vent in the white-painted brick wall and wrapped it in blue fabric. In this way, the air coming out of the classroom on the other side of the wall was funneled into a small black box called a balometer. On the device’s screen, a number popped up, revealing just how much air was moving out of the classroom.
This was the first step in what Allen says is a pretty simple way to reduce the likelihood that SARS-CoV-2 will spread in schools.
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Allen estimates that for reducing Covid-19 risk, the air in the room should be completely replaced at least five times an hour. In that Boston school, the balometer registered about 400 cfm of fresh air coming in through the unit ventilator in one classroom. The room measured 1,010 square feet and had 9.5 foot ceilings: It had 9,595 cubic feet of air. Multiply 400 cubic feet per minute by 60 minutes, divide it by the volume, and you find that the air only gets turned over 2.5 times an hour. That’s subpar by Allen’s standards.
Opening the windows and doors could boost that number past five, sometimes far higher. Allen and his team confirmed that finding this summer, when they placed dry ice, which produces carbon dioxide, in classrooms to mimic a room full of people. With a cheap carbon dioxide sensor, they could see how quickly the CO2 dissipated. “In one, when the windows and doors were open, we were at 17 to 20 air changes per hour,” Allen says.
When windows and doors can’t be opened—which will become more of an issue as cold weather arrives—installing a filter in the unit ventilator or the central ventilation system can help. While the air itself isn’t always coming from out of doors, it’s been pushed through a filter. Viruses travel in tiny specks of fluid, and these specks are large enough that they can be captured by filters of a certain grade. MERV13, which pulls out particles as small at 0.3 microns, is the rating that Allen suggests for this situation. When that’s not an option, the next best choice is to add in a portable air cleaner, which, again, is just a HEPA filter and a fan.
In a spreadsheet tool that Allen’s team and their collaborators at the University of Colorado created, you can calculate how big an air cleaner you need. You put in the room’s volume and a guess at how well ventilated it is already, and you get an estimate for how hefty a cleaner you need to bring it up to at least five room changes per hour, along with examples of products that meet that description. Thomas Talhelm, the founder of SmartAir, a social enterprise that makes simple, inexpensive air cleaners, says that interest has definitely increased this summer.
But in the long term, beyond this pandemic, a better awareness of ventilation could benefit both students and teachers.
“I hope beyond hope we have an effective vaccine. But we may not. And we probably won’t this school year, and we may not in the next three years,” says Westyn Branch-Elliman, an infectious disease doctor at Beth Israel Deaconess in Boston and a former hospital epidemiologist who has written about school openings. “We need to come up with a multiyear plan, as opposed to a week- or month-to-month plan.”
Developing the infrastructure for better ventilation could be a long-term boon, and not just for preventing Covid-19. “There are all these benefits we’ll continue to reap for years to come, in terms of better health outcomes and better academic performance, better attendance,” notes Emily Jones, one of Allen’s graduate students. “It’s a no-lose scenario to invest in ventilation in schools.”
So far, the Harvard report has been downloaded more than 7,000 times, and the report’s site has logged more than 112,000 visits in a couple of months.
“This is a time for the basics of healthy buildings,” Allen says. “And that’s bringing more fresh outdoor air in.”
Those big plumes of CO2, drifting through empty classrooms, almost recall the vapors of miasma theory. But this time, there’s modern science behind it.