A KIPP DC charter school in Washington. There are seven KIPP campuses around the District that serve a total of 7,000 students. (Astrid Riecken for The Washington Post)

As chief operating officer of the District of Columbia’s largest charter school network, Dane Anderson is racing to clean the air in time for late August, when some students are expected to come back to a starkly different environment.

“We want the interior of our buildings to be essentially on lockdown related to virus,” Anderson said of KIPP DC, a publicly funded and privately operated network of seven campuses with 1,200 employees and 7,000 students.

A majority of those students live in neighborhoods that have high concentrations of black, low-income residents — swaths of the city with the greatest number of coronavirus deaths as well as the highest asthma rates, according to the nonprofit DC Asthma Coalition. Nationally, African Americans have suffered disproportionately from the virus.

As Americans contemplate returning to schools, offices and other indoor spaces they fled under threat of the deadly virus this spring, building managers like Anderson are figuring out how to reopen safely and prevent infection. They are focused on spaces where the virus can spread, from workspaces to bathrooms to elevators and heating, ventilation and cooling systems — and balancing the cost and practicality of changes.

“Building owners and operators are looking at what they can do to make their buildings safer. It’s not just a real risk, it’s a psychological risk,” said William Bahnfleth, an expert on indoor air at Pennsylvania State University and chair of the epidemic task force at ASHRAE, a global expert body on the management of building systems. “People aren’t going to be inclined to go back into buildings if they’re concerned about how safe they are.”

When it comes to schools and office buildings, wearing face masks and cleaning surfaces are not enough, experts say. They are recommending a menu of additional measures, many of which call for different ways of circulating and filtering the air.

But these steps are often expensive, rarely mandatory and generally require help from professional engineers. And they can run counter to modern building design, which aims to seal the so-called building envelope to reduce heating and cooling costs. In the time of coronavirus, the new goal is to bring in more fresh air.

“Across the nation, I’m really concerned about K-through-12 schools and universities not being prepared for the fall, when students and staff and teachers come back,” said Richard Corsi, dean of the Maseeh College of Engineering and Computer Science at Portland State University, and an air-quality expert.

Corsi says the steps being taken by schools like KIPP DC will lower risks, but he worries not everyone will be able to do the same. “It sounds like this school has the resources to do it right, and a lot of school districts don’t have the resources,” he said.

Elimination of all risk isn’t possible, but keeping schools closed has its own costs, argues Joseph Allen, who runs the Healthy Buildings program at Harvard’s T.H. Chan School of Public Health and co-wrote a report released Wednesday about reopening schools during the pandemic.

“There will be cases in schools,” Allen said. “That’s unavoidable at this point because of the choice our national government has taken in terms of this absolutely failed response to controlling cases. … We’re stuck in this situation. But we still have to march forward. And I know that if we follow the science, we can significantly reduce risk in schools.”

Viruses in the air

The KIPP DC schools have an advantage when it comes to the coronavirus and building upgrades — they have modern infrastructure to begin with. Since the charter network opened its first D.C. school in 2001, it has poured hundreds of millions of dollars into new buildings and modernized older buildings it rents from the city. KIPP DC has heavy philanthropic support and financial resources that other charters and traditional public school systems lack. D.C. Public Schools, which educates just over 50 percent of the city’s 100,000 public school students, said it is still considering what it needs to do before reopening buildings, a spokesman said.

As early as February, the KIPP DC schools were considering what to do should the virus hit hard in the United States. In April, Anderson and board chairman Terry Golden, who has a real estate background and previously headed Host Marriott, discussed making sure the buildings were able to control air quality to prevent infection. Now KIPP DC is investing in a range of changes to increase safety, particularly when it comes to how air travels through these buildings.

Ventilation systems for buildings can vary but most rely on the same basic principles. Here is what an ideal system optimized to filter the coronavirus could look like.

Stale indoor air is pulled from the room as fresh air from outside is pumped in.

Classroom

MERV-13

filter bank

UV-C light

Filter

With outside ventilation increased to maximum, prefilters catch large particles from outside air while MERV-13 filters further clean the air and capture virus particles.

UV-C lights may also be installed in air-handling units or ducts to kill airborne viruses. Clean air is vented back into the room while the stale air is vented outside.

The goal would be to have the air filtered and pass UV-C lights every 10 minutes.

Ventilation systems for buildings can vary but most rely on the same basic principles. Here is what an ideal system optimized to filter the coronavirus could look like.

Stale indoor air is pulled from the room as fresh air from outside is pumped in.

Classroom

MERV-13

filter bank

UV-C light

Filter

With outside ventilation increased to maximum, prefilters catch large particles from outside air while MERV-13 filters further clean the air and capture virus particles.

UV-C lights may also be installed in air-handling units or ducts to kill airborne viruses. Clean air is vented back into the room while the stale air is vented outside.

The goal would be to have the air filtered and pass UV-C lights every 10 minutes.

Ventilation systems for buildings can vary but most rely on the same basic principles. Here is what an ideal system optimized to filter the coronavirus could look like.

Stale indoor air is pulled from the room as fresh air from outside is pumped in.

Classroom

MERV-13

filter bank

Filter

UV-C light

With outside ventilation increased to maximum, prefilters catch large particles from outside air while MERV-13 filters further clean the air and capture virus particles.

UV-C lights may also be installed in air-handling units or ducts to kill airborne viruses. Clean air is vented back into the room while the stale air is vented outside.

The goal would be to have the air filtered and pass UV-C lights every 10 minutes.

Ventilation systems for buildings can vary but most rely on the same basic principles. Here is what an ideal system optimized to filter the coronavirus could look like.

Classroom

Stale indoor air is pulled from the room as fresh air from outside is pumped in.

MERV-13

filter bank

Filter

UV-C light

With outside ventilation increased to maximum, prefilters catch large particles from outside air while MERV-13 filters further clean the air and capture virus particles.

UV-C lights may also be installed in air-handling units or ducts to kill airborne viruses. Clean air is vented back into the room while the stale air is vented outside.

The goal would be to have the air filtered and pass UV-C lights every 10 minutes.

Ventilation systems for buildings can vary but most rely on the same basic principles. Here is what an ideal system optimized to filter the coronavirus could look like.

Classroom

Stale indoor air is pulled from the room as fresh air from outside is pumped in.

MERV-13

filter bank

Filter

UV-C light

With outside ventilation increased to maximum, prefilters catch large particles from outside air while MERV-13 filters further clean the air and capture virus particles.

UV-C lights may also be installed in air-handling units or ducts to kill airborne viruses. Clean air is vented back into the room while the stale air is vented outside.

The goal would be to have the air filtered and pass UV-C lights every 10 minutes.

At the KIPP DC Webb campus in the Trinidad neighborhood, for instance, roughly $50,000 has been committed so far to reprogram systems to bring in more fresh air and to install UV-C lights inside large building air handlers to kill viruses, among other measures.

KIPP DC has so far committed $350,000 for engineering upgrades at its seven campuses in the city, just one of many planned changes.

Experts say the greatest danger of coronavirus transmission is when one is in close proximity — usually within six feet — to someone who’s already sick and coughing. While much remains unknown about transmission, mounting evidence suggests the virus can also travel in aerosolized droplets that are lighter and smaller than the large droplets produced in coughs, allowing them to float and linger in air.

This can happen when a person who is infected, but not necessarily showing symptoms, is talking or even just breathing. That’s one key reason that public health experts say wearing a mask is one of the most effective ways to reduce the spread of the disease.

“Aerosols can accumulate, remain infectious in indoor air for hours, and be easily inhaled deep into the lungs,” a recent study in Science magazine noted.

ASHRAE, which writes standards for indoor air systems, has already determined that the risk of airborne coronavirus transmission indoors is serious enough that building systems should be modified to try to stop it.

Building engineers say the most important practice is to make sure that air turns over frequently, mixing in lots of fresh air, and that it passes through filters that remove viruses.

“It’s the combination of ventilation and filtration that results in the indoor air quality,” Bahnfleth said. “So if you’ve got a good level of filtration and a good level of ventilation, that could be sufficient in a lot of environments.

Some experts also recommend electronic devices, such as UV-C lights, that kill viruses and other microorganisms that may get past the filters.

“Every 10 minutes … we’d like the air to touch a filter, or get diluted, or start to hit an electronic,” said Raj Setty, an engineer who is president and principal at Setty and Associates and is advising KIPP DC on the reopening. “Something to kill things in the air.”

MERVs and HEPAs

Setty recommends that KIPP DC do everything from using sanitizing mats for students to walk across at entryways, to installing special closets for personal protective equipment in classrooms, to making water fountains touchless.

He is not a big fan of indoor barriers or partitions. Air vents tend to push air down from the ceiling and “pick up viruses and spread them around the room,” moving around barriers, Setty said.

The goal should be to make sure the air is clean, rather than trying to prevent its circulation, he said.

To that end, the systems in the KIPP DC schools will be reprogrammed to admit more outside air. When it comes to filtering, meanwhile, KIPP’s new and renovated schools have an advantage over many outdated buildings.

For instance, the large air-handling units at KIPP DC schools already use an air filtration system, rated at a level known as MERV-13, that matches what is being recommended for the novel coronavirus. So much of the battle will simply involve properly maintaining these filters. That level of filtration should capture about 80 percent of the air particles that can convey the coronavirus, said Corsi, the air-quality expert at Portland State.

The coronavirus is about 500 times smaller than the width of a human hair, which measures around 50 microns or more, Corsi said. That’s exceedingly tiny, but the virus would be traveling in somewhat larger aerosol particles, making it easier to be caught by filters. And when air passes through filters repeatedly, it is more likely virus will be captured, Setty said.

“If the MERV-13 filters are properly seated, and everything is done right, then a MERV-13 filter will remove a lot of the small, the tiny particles, down to about 1 micron, that can convey the virus,” added Corsi.

Human red blood cell

7.5 micrometer diameter

E. coli bacteria

Coronavirus

0.1 micrometer

average diameter

2 micrometers long

Though individual coronavirus particles are very small, evidence suggests they may travel in larger groups of aerosolized droplets, which can be trapped by filters

HEPA filter

MERV-13 filter

As small as

0.3 micrometers

As small as

1 micrometer

Human red blood cell

7.5 micrometer diameter

E. coli bacteria

Coronavirus

0.1 micrometer

average diameter

2 micrometers long

Though individual coronavirus particles are very small, evidence suggests they may travel in larger groups of aerosolized droplets, which can be trapped by filters

HEPA filter

HEPA filter

MERV-13 filter

As small as

0.3 micrometers

As small as

1 micrometer

Human red blood cell

Coronavirus

E. coli bacteria

0.1 micrometer

average diameter

2 micrometers long

7.5 micrometer diameter

Though individual coronavirus particles are very small, evidence suggests they may travel in larger groups of aerosolized droplets, which can be trapped by filters

HEPA filter

HEPA filter

MERV-13 filter

As small as

0.3 micrometers

As small as

1 micrometer

Human red blood cell

Coronavirus

E. coli bacteria

0.1 micrometer

average diameter

2 micrometers long

7.5 micrometer diameter

Though individual coronavirus particles are very small, evidence suggests they may travel in larger groups of aerosolized droplets, which can be trapped by filters

HEPA filter

HEPA filter

MERV-13 filter

As small as

0.3 micrometers

As small as

1 micrometer

An even more exacting air filtration system is called HEPA, or high-efficiency particulate air. But experts say HEPA is not easily adapted to large buildings because its filters are very thick and require large amounts of energy to clean the air, and because most large buildings weren’t designed for this type of equipment. Stand-alone HEPA units can be installed in individual rooms.

“What we’re trying to do is recommend things that can be implemented in the short term,” said Bahnfleth, of Penn State. “If every building had to have its HVAC system overhauled, that just wouldn’t be feasible.

Across the spectrum

Theoretically, ultraviolet light might sound like the ideal fix.

“With ultraviolet, for a long enough contact time, you’ll deactivate or destroy pretty much any virus,” Corsi said.

But there’s a drawback — direct exposure to UV rays, and especially the shorter-wavelength UV-C rays traditionally used for disinfection — can be dangerous to people. Therefore, the devices have to be put in empty locations, such as the dark interiors of air systems. The New York Metropolitan Transportation Authority has been experimenting with using UV light at night on empty trains, said David Brenner, a physicist and radiation expert at Columbia University.

But it’s unclear how long it takes ultraviolet light to kill coronavirus particles as they are flying through a building’s air system, Corsi said.

That’s being taken into account, Setty said.

“With each pass, we will get disinfection occurring, and that is also why we are running the units two hours before and after occupancy,” said Setty, who is recommending that KIPP place UV-C light inside central building air handlers. “We also have the ability to specify more intensity of the UV-C, which we will do if the air is moving too fast.”

The ultimate solution may lie in research conducted by Brenner that shows that there is a less-used wavelength of UV radiation, which he calls “far UV-C” light, that will kill viruses but will not penetrate the outer layer of human skin. That would theoretically allow the light to disinfect populated spaces.

“If you have a nice clean room at 5 in the morning, people will come into it and start coughing and sneezing,” Brenner said. “So the idea is to be able to use that to decontaminate continuously over the course of the day.” However, this idea remains under study for now, although Brenner says he thinks the safety data at this point is encouraging.


Students at a KIPP DC school in Washington in 2019. (Astrid Riecken for The Washington Post)

No policy

Demand for solutions that clean indoor air and protect against the coronavirus is largely being driven by the market, not government regulation.

“There’s nothing legislated. There’s nothing mandated. That’s going to take years,” Setty said.

The result, in the near term, is likely to be a patchwork — some commercial buildings, schools, colleges and other facilities will make investments while others don’t.

Brenner and others think changes prompted by the coronavirus will at some point become standard.

“These approaches are nice because they’re not only going to be helpful for covid-19 but for next year’s flu season. And come the next pandemic, they’re going to be helpful there, too,” he said. “Developing a vaccine is going to be very specific to the covid-19 pandemic. So you can think of them as more long-term solutions.”