Tens of thousands of schools have dangerously poor ventilation, raising the risk that the coronavirus could spread through the air

• As schools reopen, teachers and parents worry that weak ventilation will put students at greater risk of catching the coronavirus.
• Poor air quality can impact test scores and learning; it's been a problem in US schools for decades.
• A June report estimated that 41% of school districts — 36,000 schools — need major upgrades to their ventilation systems.
• Experts suggest schools with poor air quality install portable ventilation systems.

Three years ago, teacher Kerri Landry found a hole in the wall of her middle-school classroom in Coventry, Rhode Island. It looked strange, so Landry took a flash photo of the inside of the hole — and captured a troubling image.

"The entire inside of that wall was all black mold, the entire thing," she told Business Insider.

Landry showed her husband Tom the picture. A specialist in heating, ventilation and air conditioning (HVAC) at a local company called Environmental Systems, Tom knew the mold was an indicator of the building's poor air quality.

School custodians patched up the hole and treated the mold, but Landry said she's seen mold in other classrooms, too. She thinks it may be a sign that her school — the Alan Shawn Feinstein Middle School — shouldn't bring students back at all.

"This has been an ongoing issue for years," Landry said, adding that she's recently been telling anyone who will listen that the school district must fix its ventilation systems before students return. She feels strongly about that for her own safety as well as that of her students and two youngest sons, who attend a high school in the district.

However, Landry's school district decided on Monday to do a phased reopening, with all grades slated to be back by October 13.

Landry's school isn't exceptional: Research shows that air quality is a major issue in tens of thousands of schools across the US. A June report from the Government Accountability Office estimated that 41% of districts nationwide, or 36,000 schools, need major upgrades to their HVAC systems.

Before the pandemic, poor air quality in schools was problematic because it impeded kids' learning and lowered their test scores. But now, faulty HVAC systems are even more concerning since they could facilitate the spread of the coronavirus.

The link between coronavirus transmission and HVAC systems

The coronavirus most commonly spreads via respiratory droplets emitted when an infected person coughs, sneezes, speaks, or breathes heavily. But research suggests it can also be airborne, meaning the virus gets transmitted via aerosols: tiny particles or droplets that can hang in the air, potentially for hours at a time.

Either way, most instances of documented coronavirus transmission have occurred in tight, poorly ventilated indoor spaces; one study (though not yet peer-reviewed) suggested that a person might be nearly 20 times more likely to spread the coronavirus inside than outside.

Studies have also shown that poor HVAC systems can spread the coronavirus around, sparking outbreaks. In one case study, a single person infected nine others at a restaurant in Guangzhou, China. Epidemiologists found that the strong airflow in the restaurant's air conditioning — and lack of effective filtration and ventilation — likely carried droplets from one table to several others.

"The biggest risk comes from poorly ventilated, crowded environments where people spend a lot of time. Unfortunately, that kind of perfectly describes a lot of schools," Jeffrey Siegel, a professor of civil engineering at the University of Toronto, told Business Insider.

To ensure an HVAC system removes coronavirus particles from the air — at a school or elsewhere — it needs have adequate ventilation and filtration, not just circulation. One crucial factor, then, is airflow: the amount of new air that flows through a building. Most buildings should have at least 15 cubic feet per person per minute.

Filtration is also key: On commercial HVAC units, filters are rated according to their minimum efficiency reporting value (MERV). Both HEPA and MERV-13 or -14 filters can block most coronavirus particles.

Most schools don't have safe indoor air

Most US schools don't meet the standards necessary to prevent coronavirus transmission indoors, according to Corey Metzger, who leads the school-reopening task force for The American Society of Heating, Refrigerating and Air-Conditioning Engineers, or ASHRAE. The group offers a list of HVAC guidelines for schools.

"A large percentage of facilities, if not the majority, don't meet our recommended minimums for ventilation or other operating capabilities," Metzger said.

These standards include proper filter installation, ensuring circulation of outdoor air, and balanced humidity levels.

Landry's husband, Tom, said these problems certainly persist in the schools where his wife teaches and sons study: Most don't have systems that can support MERV-13 and 14 filters.

"Our schools are very old and [have] antiquated HVAC systems," he said. "The majority of schools in our town don't have any fresh air coming into them at all."

Craig Levis, the Coventry district's superintendent, told Business Insider that the middle school where Landry teaches is his "primary focus" in terms of addressing air quality. He said he's hired HVAC specialists to inspect the district's other buildings and help with quick fixes, like placing fans near windows to increase ventilation.

"If there are simple things I can do to mitigate the virus, I put a stake in the ground, and that's what we're doing," he said.

Siegel said he's concerned that fall and winter could make air-quality problems in schools even worse, since cold weather will likely lead teachers to close windows, and holding classes outside will be difficult. Plus, Siegel said, indoor heating could dry out the air, enabling viral particles to travel farther and drying out people's mucous membranes, which can weaken immune systems.

What parents can look out for, and what teachers can do

Even before the coronavirus hit, poor ventilation in schools created problems for students, primarily due to the buildup of carbon dioxide. Previous studies have shown that high levels of CO2 in classrooms can contribute to poor focus and lower test scores.

But upgrading a school's HVAC system can cost millions of dollars and take months to years.

Siegel said a few other measures can mitigate the risks of low-quality ventilation systems in the meantime, though. For instance, portable ventilation systems can help filter air in individual classrooms. The filters are loud, but they work.

"I don't want anyone to think that I'm saying this is a simple problem, but it is a solvable problem," Siegel said.

Additionally, although there's no simple, easy, or cheap way to measure coronavirus particles in the air, carbon dioxide can be a "canary in the coal mine," according to Roger Silveira, an air-quality specialist and the facilities director at San Jose's East Side Union High School District. Carbon-dioxide monitors sell for about $100.

In a building with good ventilation, CO2 levels should generally stay under 1,100 parts per million, Silveira said.

Opening windows is another obvious way to mitigate the problem, as is holding classes in larger spaces, like gymnasiums and auditoriums, according to Dr. Tina Tan, an infectious-disease specialist at Northwestern University's Feinberg School of Medicine.

"I think right now we have to think outside the box," Tan said.

She also recommends that teachers limit activities involving shouting or singing, since those create more potentially virus-laden droplets than ordinary talking.

Of course, remote learning is likely the safest option for many districts, though it comes with plenty of its own challenges.

Some districts that are reopening still offer a remote option for that reason; Landry's is one of them. At the moment, she's not sure what to do. Her sons want to go back to school, but both have preexisting respiratory issues. She doesn't want them to have a subpar, remote education, but she's also afraid for their lives.

"It's so difficult as a parent to make this decision — no parent should have to make it," Landry said, adding, "it's like playing Russian roulette."