This fall, teachers and parents have been sharing photos on social media of DIY air purifiers they have made for classrooms to help protect children from the spread of COVID-19.
But do these inexpensive purifiers really work?
According to the researchers, they do.
They’re called the Corsi-Rosenthal Boxes, a do-it-yourself air purifier that was first conceived in the summer of 2020 by two air filtration experts, Richard Corsi and Jim Rosenthal.
Since then, its effectiveness has been backed up by scientists, studies, and a company that makes air filters.
Studies have shown that poor ventilation is associated with a much higher spread of COVID-19. But many buildings in Canada, including schools and workplaces, are still not equipped with proper ventilation systems or HEPA purifiers.
Unlike HEPA purifiers, which can cost anywhere from $200 to more than $500, a Corsi-Rosenthal box can be made for around $100 with materials that can be purchased at any hardware store.
A York University engineering professor who has been hauling his Corsi-Rosenthal box with him around campus for the past week says he heard about them on social media in mid-2021.
“Some ventilation engineers were talking about them and they seemed like a practical and easy way to get more clean air into schools and into my home,” James Andrew Smith told CTVNews.ca in an email.
“I don’t think we’re doing enough for clean air,” she added, saying she feels better about the level of risk in her classroom when using the home air purifier along with other measures.
The boxes also seem to have longevity.
“This guy behind me just turned eight months a couple of days ago,” Corsi said. in a Twitter video on Monday, referring to his own Corsi-Rosenthal Box humming past his shoulder. “He’s still doing his job, he’s still reducing inhalation-dosed aerosol particles, including virus-laden respiratory aerosol particles. It’s not rocket science, folks.”
WHAT ARE CORSI-ROSENTHAL BOXES?
There are variations, but the basic Corsi-Rosenthal box is made from four air filters, a box fan, and some cardboard, all taped together to form a cube. A Tutorial from University of California, Davis specifies the use of MERV-13 filters.
The case fan should have the airflow pointing outwards and all edges should be sealed with tape. The sixth end side of the cube must be closed with cardboard or even a fifth air filter.
To make the filter more efficient, you can also cut a circle out of a piece of cardboard and tape it to the outside of the box fan to reduce backflow.
The idea behind the Corsi-Rosenthal setup is that the air entering the box will pass through multiple filters for purification, and the sealed hub means the fan will only exhaust filtered air into the room.
Studies indicate that while it won’t be able to filter as many particles as a HEPA filter, a Corsi-Rosenthal box can recycle the air in a room at a rate sometimes faster than HEPA purifiers, removing viral particles from the air . At a fraction of the cost.
A study published in march in the journal Aerosol Science and Technology, which listed Corsi as one of its authors, found that the boxes could quickly filter an entire room at a much faster rate than HEPA purifiers.
Looking at the “cost per unit of air cleaned,” the study said that “the DIY air filter is about a tenth of the initial cost of a commercially available HEPA-based air filter.”
3M, a company that makes air filters, said in a february press release that their scientists had studied the Corsi-Rosenthal Boxes and that the DIY idea works.
“Indoor air is shared air,” Kelsey Hei, a 3M Filtrete brand engineer, said in the statement. “Many viruses like COVID-19 are airborne and can be highly concentrated in poorly ventilated spaces. I am heartened to see so many people advocating for the importance of clean air, especially in schools.”
another study published in September in the journal Science of the Total Environment looked at nine different configurations of DIY air purifiers and compared them to three HEPA purifiers.
The study found that DIY options, including a single filter with a box fan, Corsi-Rosenthal boxes, and a variation of them that uses three filters and two box fans in a bucket, were comparable to or better than HEPA purifiers in terms of the speed with which they filtered the air.
CLEAN AIR KEY TO LESS COVID TRANSMISSION
As it became clear that COVID-19 was airborne, scientists began to emphasize the importance of good ventilation as a tool to slow transmission.
An Italian study published last March that analyzed more than 10,000 classrooms found that efficient ventilation systems were able to reduce the transmission of COVID-19 in schools by more than 80 percent.
Infections were much lower in the 316 classrooms that were equipped with a mechanical ventilation system, compared to those that did not. When ventilation systems changed to completely replace classroom air with fresh air 2.4 times per hour, infections were reduced by 40 percent. If they replaced the air six times an hour, infections dropped by 82 percent, the study found.
With few back-to-school public health measures still in place, teachers have increasingly turned to tools like the Corsi-Rosenthal box to make their classrooms safer.
THE CLASSROOM TAKE
As students returned to classrooms this fall, teachers and parents took to social media to share photos of their Corsi-Rosenthal Boxes. On Twitter, the #CorsiRosenthalBox hashtag includes numerous creative designs meant to be kid-friendly.
A Manitoba user posted a photo of a Corsi-Rosenthal Box for his son’s classroom that had been enhanced to look like a robot, complete with googly eyes, antennae and arms.
Other designs used large eyes, brightly colored paint, and a variety of animal ears to transform boxes into friendly creatures.
In Quebec, parents and teachers have posted a petition asking Jean-Francois Roberge, Minister of Education, to allow them to provide Corsi-Rosenthal Boxes to their children’s schools, saying that the citizens’ initiatives have “met with strong administrative resistance”.
“Installing home air purifiers, known as Corsi-Rosenthal cubes, is an effective and inexpensive way to improve indoor air quality,” the description reads.
The petition, started last month, has more than 1,600 signatures.
At York’s Lassonde School of Engineering, Smith says wearing a Corsi Rosenthal Box has sparked questions and curiosity among students.
“How much do I care about my students? Enough to build them a #CorsiRosenthalBox on wheels to take to class.” he tweeted on Monday.
Smith and other faculty members have asked the Dean’s Office at York’s Lassonde School of Engineering to fund and distribute portable air purifiers to faculty members, but so far, these motions have been denied.
“Personally, I think they’re a no-brainer,” Smith told CTVNews.ca. “They are easy to install, easy to operate, they are nowhere near the controversial issues that are vaccines or masks. They make the air filter for smog, smoke, dust… generally a great idea.”
These boxes are being used in classrooms all over the world.
In November 2021, the Brown University School of Public Health in Rhode Island launched a project to build Corsi-Rosenthal Boxes for classrooms and study them, and have since installed boxes in numerous classrooms and student lounges.
Oliver Patrick, a county councilor in the UK, started a GoFundMe last month to provide Corsi-Rosenthal Boxes to schools in his district. stating that he was worried about the lack of public health measures in their region.
“I want to make sure we do everything we can to make sure the school is as safe as possible for the kids,” Patrick wrote.
The California Department of Public Health listed the Corsi-Rosenthal boxes as a recommended option for classrooms in a February newsletter to improve air quality in schools to combat COVID-19.