“Do your little bit of good where you are; it’s those little bits of good put together that overwhelm the world.” ~Desmond Tutu

It’s heartening to see people pulling together, even if many recognize they have few other choices right now. Parents, students, healthcare workers, and community groups are building DIY portable air filtering units to help prevent transmission of the devastating airborne pathogen Covid-19 as well as the colds and flu that spread so easily in indoor spaces.

These units also filter particulate matter, particularly relevant in a time when wildfire smoke and other sources of particulate pollution are so dangerous. These often unavoidable exposures are linked to asthma, bronchitis, heart failure, stroke, lung disease, and premature birth. Indoor air pollution has been found to affect the developing fetus and young child, altering brain structure in ways that damage motor function, learning processes, and mental health into adolescence and beyond.  

Plus, filtration helps to mitigate the damaging health effects of volatile organic compounds (VOCs) present in common products such as carpet/furniture/flooring, cleaners, room deodorizers, disinfectants, personal care products, solvents, paints, pesticides, dry-cleaned clothing, copiers, aerosol sprays, and other materials present in the home, school, stores, and elsewhere. VOCs can cause eye, nose, and throat problems; headaches; impaired coordination; nausea; damage to liver, kidneys, and central nervous system; and many are suspected carcinogens.

One way of assessing indoor ventilation is by ‘air changes per hour’ (ACH) — the number of times that all the air in the room has been replaced (ideally, by outdoor air). CDC and ASHRAE guidelines note typical ACH rates.

• Hospital operating rooms are expected to stay at 20 or better ACH. 
• Hospital airborne isolation rooms are kept at 12 ACH or greater.
• Hospital patient rooms are often around 6 ACH.
• Classrooms are typically well under 2 ACH.
• Home ventilation is often less than 1 ACH.

A recent study found indoor space with air exchanged five times per hour can cut the risk of Covid transmission by 50 percent. Another study compared classrooms without ventilation to those with controlled mechanical ventilation. It found better ventilation could reduce the risk of Covid infection in schools by 40 percent with two to four air changes per hour, and nearly 83 percent with six air changes per hour. And this study shows that 12 air changes per hour from air filtration may approximate N95 protection.

In active response to this data, people are putting together inexpensive filters to better equip their communities to ward off infection and other effects of trapped indoor air. Many are building inexpensive Corsi-Rosenthal box fan filters (C-R Box) which arose from an online collaboration between Richard Corsi, dean of engineering at University of California, Davis and Jim Rosenthal, owner of an air filtration company in Texas.

Fortune interviewed Joseph Fox, chair of the indoor air quality advisory group with the Ontario Society of Professional Engineers. Dr. Fox said, “These Corsi-Rosenthal units use MERV-13 filters, which can only remove 60% to 80% of those particles, (but) the fan on the C-R box is much bigger and can clean more air. All you care about in the end is the total rate at which the air is cleaned. So, what the C-R box lacks in efficiency, it makes up for in airflow.” A peer-reviewed study found the C-R Box performed better than standard HEPA air cleaning units.

These models are about ten times cheaper than commercial air purifiers. There are many resources online, including what air filter brands to avoid and how to use a round fan when square models aren’t an option. Here’s more science plus additional how-to’s from the collaborative Edge Collective.

Better air filtration shouldn’t be left to community members. It should be a priority in new builds and renovations, guided by more stringent building codes to protect public health. It should be part of a robustly-funded countrywide initiative for schools, daycare centers, public buildings, senior facilities, libraries, shelters for unhoused people, and other gathering places. But right now, the DIY filtration movement is led by students, teachers, parents, and other concerned community members.

A group in Philadelphia is building units for classrooms and speaking up at school board meetings to spread awareness.

Arizona State University students are building boxes to donate to area K through 12 schools. They’re also teaching younger students how to build the boxes themselves.

These box fan filters are a project elementary school-age students can do together. In Kansas, the Wyandotte County Health Equity Task Force offers guidance for doing this with groups of children (school classes, scout groups, 4H, and others) including how to incorporate it into STEM curricula.

Alex LeVine designs similar filtration boxes using inexpensive illuminated computer fans lively enough to feature in many businesses.

And we’re beginning to see them in public spaces.

The Harvard T.H. Chan School of Public Health offer more guidance on measuring outdoor air ventilation rates and strategies to improve air quality in these detailed links: How To Assess Classroom Ventilation and ASHRAE Reopening Schools and Universities Guidance. Here’s how you can use a carbon-dioxide monitor to assess Covid risk from indoor spaces

Andrew Noymer, an associate professor of population health and disease prevention at UC Irvine, said in an interview with the LA Times, “When cholera ravaged Europe and North America in the 19th century, people ‘revolutionized sewage’ by creating the modern sewage system. They could have just said, ‘Boil your water.’ But they didn’t do that. They gave people clean drinking water.” He went on to say, “Ensuring clean air indoors is the 21st century equivalent.”

“Breathe deep today, and continue walking toward that which will enlighten, no matter what burdens you are carrying of shame, grief, or fear. No one can buy their way or push their way ahead of everyone else. We are all in this together.”     ~Joy Harjo