Joseph G. Allen is an associate professor and director of the Healthy Buildings program at Harvard University’s T.H. Chan School of Public Health. He co-wrote “Healthy Buildings: How Indoor Spaces Can Make You Sick — Or Keep You Well.”

We might be on the verge of an indoor air quality revolution, and it could be among the most important public health victories of the 21st century.

Two events in the past few days have contributed to this moment: First, the Centers for Disease Control and Prevention on Friday released a new health-based ventilation target that can dramatically improve indoor air. Shortly after, a less well-known but powerful standard-setting organization called the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) boosted the CDC’s recommendations by releasing its own enhanced ventilation standard, open now for public comment.

You might be thinking, “Is this really news?” Haven’t we been discussing the importance of ventilation since it became clear that the coronavirus was primarily transmitted through the air?

Yes, the CDC and other groups did call for higher ventilation rates. But they failed to put out a target number. Without a specific ventilation standard, that resulted in confusion and a lack of accountability. “Did you improve ventilation?” is very different from “Did you improve it by a specific amount?”

The CDC’s new goal is at least five air changes per hour (ACH), meaning the equivalent of all the air in a room is replaced five or more times within an hour. For context, a typical home has less than 0.5 ACH. This represents the first time in history that the agency has set a ventilation target to address respiratory infectious diseases.

This is not an arbitrary number; it is right in-line with the guidance of four to six ACH that I laid out with a group a researchers in June 2020 to help get schools open, later published in JAMA. It also follows the recommendations of a task force I chair for the Lancet Covid-19 Commission, made up of experts from around the world.

The inadequacy of our previous approach was made clear to a devastating degree during the pandemic. The virus slammed into a population that spends the vast majority its time indoors – in offices, senior-care facilities, meatpacking plants, prisons – with bare-minimum ventilation standards since the 1970s. Is it any wonder the pandemic was as disastrous as it was?

It’s not just the coronavirus that spreads indoors. Influenza, respiratory syncytial virus (RSV) and other respiratory pathogens do, too. And the problems of inadequate ventilation go beyond infectious disease. Poor ventilation has been linked to “sick building syndrome,” which includes headaches, inability to concentrate, worse performance on cognitive function tests, more missed workdays for adults, and worse performance on math and reading tests for children of all ages in schools.

The CDC also made other important recommendations, such as raising minimum filtration rates with higher-grade MERV-13 filters, which capture not only particles from lungs but also those from outdoor air pollution. This is a no-brainer. The agency also recommends regular tuneups for buildings, which can improve energy efficiency and save money.

Kudos are due. When Rochelle Walensky took over the CDC in early 2021, ventilation started to appear on the agency’s website as key to addressing the coronavirus. She ultimately approved the latest targets. The White House team, in particular the Coronavirus Task Force led by Ashish Jha and the Office of Science and Technology Policy, also elevated the issue and held a summit on indoor air quality last fall, signaling that it was a top priority.

That signal was heard, as ASHRAE’s response shows. The industry group had previously recommended low ventilation rates for schools, offices, homes and other places you spend most of your time.

Its course correction is necessary and in line or higher than what the Lancet Covid-19 Commission recommended. The specifics will likely change after the public comment period is up, and there are important questions it will need to address. For one, ASHRAE now has three guidance documents that are not fully aligned. Its previous standard for health-care settings recommended four to six ACH, and its guidance for schools released this winter recommended three to six. Its most recent recommendations call for roughly the equivalent of 24 ACH for hospitals and eight ACH for schools. (It used a different but related metric that I converted to ACH for comparison purposes.)

In one important aspect, ASHRAE’s proposed standard doesn’t go far enough. It differentiated between “risk mitigation mode” and “normal mode,” meaning that its standard to improve indoor air would apply only during undefined “high-risk” periods. Because the proposal is framed that way, it’s unlikely it will get into building codes as standard practice going forward; it will be reactionary. This isn’t ideal. Don’t we want cleaner indoor air at all times? Why not apply higher standards to every new building and every new renovation?

Nevertheless, this represents a monumental shift. The floor for minimum clean indoor air standards is being raised, beginning to correct a mistake from several decades ago that has had disastrous consequences. For public health advocates who have been pushing for this change for years, it’s a moment to exhale.


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