A Medify MA-112 HEPA filter at Franklin not long after being cleaned, with a note written in dry erase marker indicating its cleaning date. Franklin used its Temporary Distance Learning week during January to clean the school’s portable filtration system. Photo by Luke Ramsey.

PPS will be replacing its High-Efficiency Particulate Air (HEPA) filters in the coming months, some in March and others as late as the summer, depending on need.

HEPA filters are portable filtration devices designed to remove small particles from the air. During the COVID-19 pandemic, they have become a critical component of all indoor public spaces due to their ability to filter viruses. Some capture more than 99 percent of particles in the air that measure at least 0.1 microns, or one-ten-thousandth of a millimeter.

There were some existing filtration systems in the district, particularly at Harriet Tubman Middle School and Faubion PK-8, according to Jon Athey, Project Manager for Facilities and Asset Management at PPS. “Tubman has an insane HVAC system,” he said. “Really, we put air purifiers in those classrooms as well. But that system that’s almost cleanroom-like, like an Intel cleanroom [an almost-completely-sterilized factory] type air purification system. That is an absolutely phenomenal air system.” Tubman already had an extensive HVAC filter system due to an earlier and ongoing controversy involving its proximity to Interstate 5.

The district uses two types of HEPA filters, according to Athey: Medify-112 and Intellipure Ultrafine 468. Because they are more functional in large rooms, the Medify filters are used in most of Franklin’s rooms to accommodate larger classes, according to Franklin Business Manager Sonya Harvey.

HEPA filters become less effective over time, and it typically takes about a year before they need replacement. PPS first acquired the filters toward the end of 2020, according to Athey, and installed them in early 2021. Because schools are not in operation 24 hours per day, the filters have not been on the entire time since installation in most schools, which saves some of their function.

While the HEPA filters have not been replaced, “We are in the process of soliciting/hiring a contractor to help replace all 5,500 filters across PPS buildings,” wrote a PPS media contact in an email. The replacements will be installed when the filters indicate that they need to be replaced. The pre-filters, which can handle larger particles, demand frequent cleaning.

The use of the filters has not been perfect in every school. Some have had more to clean than others. “I’ve seen schools where even [on] the pre filter … there’s hardly any dirt on it at all, and they run it all day long,” said Athey. “Then I went to some schools that … [have] to clean it once a week because it’s so dirty.”

Others have had trouble due to older, less efficient filtration systems. “They’re doing a really good job about getting the schools up to speed,” said Athey. “But just in general […] some of them with the older systems, it’s tough […] to move a lot of air that they’re […] asking us to do.” He adds that some schools have had to clean pre-filters once a week, as they have become too dirty at high speed.

At Franklin, however, pre-filter cleanup has been consistent and effective, according to Athey. “They clean pretty regularly,” he said. The pre-filter cleaning procedure is relatively simple for Franklin’s Medify filters, and “according to our Head Custodian, Rob Carron, each unit takes about 5 minutes to clean,” wrote Harvey in an email.

Filtration has long been one of the most effective measures to take against the spread of COVID-19. Filters can remove most viruses from the air even if windows are closed, which drastically limits the ability of viruses to spread. The HEPA units being used by the school are able to clean rooms twice per hour, said Athey.

The Centers for Disease Control (CDC) created a list of ventilation recommendations during the pandemic, last updated in early June 2021. It is recommended that buildings, whenever possible, increase the flow of outdoor air into the building. According to the CDC website, “even a slightly open window can introduce beneficial outdoor air.” They also recommend the use of fans when windows are open. However, these only apply when the weather allows windows to be safely open. Cold, humid, and hot weather make these measures more difficult. Opening windows can lead to the pre-filters becoming dirty and in need of cleaning earlier than they otherwise would be.

Medify and Intellipure filters are both more effective than the CDC’s minimum acceptable guideline, said Athey.

In addition to the pre-filter and filter, Medify HEPA units contain a carbon filter capable of removing many toxic substances, like odors and formaldehyde, according to information from a Medify spokesperson.

HEPA filters may become a permanent part of schools after the pandemic. PPS, said Athey, will likely maintain the filters for a few more years, maybe a couple after the end of the dangerous pandemic, but after that teachers and schools will still have the option to keep the filters going. “It’ll probably be the schools’ individual responsibility after that,” he said. Even in a world without COVID-19, many viruses may transmit through the air in schools, and COVID-19 may become a permanent fixture of life on Earth, like the influenza virus. Keeping the filters may help prevent the spread between teachers and students, especially those in rooms that lack sufficient access to windows or want to keep windows closed.

The CDC recommends that building users “run the HVAC system at maximum outside airflow for 2 hours before and after the building is occupied.” While this means never being able to turn off filters at all in certain environments, like hospitals, that are open 24 hours a day, schools are able to conserve energy by keeping filters off for significant periods of each day. Some have not been doing this consistently, though. “ Some of the schools, some of the purifiers … don’t get turned off at night,” said Athey. “And so they are running 24 hours a day, seven days a week.”

Along with ventilation, wearing masks and getting vaccinated can help protect oneself and others from COVID-19.

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