Given that aerosolized particles with SARS-CoV-2, the virus that causes COVID-19, can remain suspended in the air for long stretches of time, ventilation and air purification represent key preventative strategies. In its guide to opening schools, the Centers for Disease Control and Prevention (CDC) recommends schools consider adding portable air purifier units with high efficiency particulate air (HEPA) filters to “enhance air cleaning wherever possible.” The CDC’s FAQ on ventilation notes, “Portable HEPA filtration units that combine a HEPA filter with a powered fan system are a preferred option for auxiliary air cleaning.” 

An investigation by The Classic has found that, though it has told the public that two “HEPA Purifiers” will be in each classroom this fall, the New York City Department of Education (DOE) will be providing devices (Intellipure compact air purifiers) that do not match that description. The DOE has repeatedly referred to the Intellipure units as “HEPA purifiers” on its website, in a “DOE Homecoming Health and Safety Guide,” and in statements to The Classic. Multiple experts have told The Classic that to be a “HEPA Purifier” the units should have within them an actual HEPA filter, but they do not.

When asked by The Classic to comment on the accuracy of the DOE’s decision to describe the Intellipure units as “HEPA purifiers,” DOE spokesperson Nathaniel Styer said, “We never said that the units had HEPA filters. We said that they met the standard for HEPA filtration. That they are HEPA purifiers.”

On Twitter, Mr. Styer claimed that HEPA refers to a rating that could be applied to “different types of machines” that filter particles at the level of HEPA filters. According to the Environmental Protection Agency, the designation HEPA is specifically applied to “a type of pleated mechanical air filter” tested to a standard level of efficiency. Citing the CDC, Mr. Styer said that because Intellipure’s process as a whole can filter at HEPA filter levels, it is a HEPA purifier. The Classic contacted the CDC, however, and a representative said the two technologies are distinct. 

“The distinction between an air cleaner using a true high-efficiency particulate air (HEPA) filter and one that does not should be clear,” said Dr. Steve Martin, an engineer and expert on ventilation at the National Institute of Occupational Safety and Health, a branch of the CDC, in an email to The Classic. 

Dr. Martin said that while “it is certainly possible for other air cleaners to use a combination of filtration technologies that can perform at ‘HEPA-equivalent’ levels (and maybe even higher),” the Intellipure air purifiers are not true HEPA devices. “The distinction should be clear between true HEPA air cleaners and others,” he said. 

The difference between a true HEPA filter and a HEPA-equivalent device can be significant, according to Dr. Martin. “The biggest concern with air cleaners claiming ‘HEPA-equivalent’ performance is how they perform over time. As a true HEPA filter loads with particles over time, the overall filtration efficiency will only increase.  The same can not necessarily be said for other technologies,” he said. 

Other experts spoke to The Classic about whether it was accurate for the DOE to describe the Intellipure units as HEPA purifiers to the public.

“HEPA refers to having a specific type of filter… so a product should have one of those filters in it to be a HEPA purifier,” said Dr. Delphine Farmer, an atmospheric chemist with a research focus in air pollution from Colorado State University, in an email to The Classic. 

According to an email from Dr. Donna Green, an associate professor at the University of New South Wales, Australia and a founding member of the Climate Change Research Centre, “[Intellipure] uses a different process, which may meet or exceed the filtration standards of a HEPA, but that only makes it HEPA like, not true HEPA.”

The HEPA filter level of efficiency is set by the United States Department of Energy, but manufacturers do not receive certification for their filters from the government. Dr. Martin said, “HEPA filters are tested and certified by their manufacturers according to consensus standards.” The consensus testing standards he referenced come from the Institute of Environmental Sciences and Technology, a nonprofit membership organization.

Intellipure does not refer to its devices as HEPA purifiers. The Classic spoke to Isaac Mulvihill, the senior vice president of Delos, the company that procured the Intellipure units on contract for the city. “As it relates to claims being made by school systems that have purchased the Intellipure Compact devices, we stand by any statement or representation made that these devices meet or exceed the HEPA efficiency standard,” he said in an email.

The name the DOE uses to describe the devices to the public matters for a number of reasons. First, the department’s declaration that a non-HEPA product is in fact a HEPA product obscures the fact that the devices now in schools are not what the CDC recommends for schools (“portable air cleaners that use high-efficiency particulate air (HEPA) filters”).

Second, according to reporting by Chalkbeat New York, purifiers containing actual HEPA filters can be less expensive than the Intellipure devices and other units had better clean air delivery rates, a metric that experts say is essential in keeping rooms supplied with fresh air and less likely to be carrying the COVID virus. 

Third, while the Intellipure devices use a total filtration system to reach or exceed the standards of the HEPA filter, the level of peer-reviewed, independent testing of the Intellipure system pales in comparison to the mountain of testing done on the industry-standard HEPA filters since the 1940s, when the filters were created for the Manhattan Project to filter out radioactive toxins.

In an interview about air purifiers with the MedCram YouTube channel, Dr. Joseph Allen, an associate professor at Harvard’s T.H. Chan School of Public Health, said, “If you’re looking for a portable air cleaner, look for a HEPA filter and nothing else. You don’t want any of these bells and whistles.”

It is, however, the ‘bells and whistles’ that bring the Intellipure devices up to HEPA-level standards. 

Different features might make non-HEPA devices vulnerable to further problems, Dr. Allen told MedCram. “So you want to be careful that we’re not solving one problem and creating others, and importantly, there’s something else that’s actually less expensive that will do the job the same or even better,” he said.

The Intellipure process

Delos maintains that the efficiency of a filter in an overall unit is less important than how the unit functions as a whole. Mr. Mulvihill said it’s essential to validate a system’s overall performance “instead of relying solely on a HEPA rating for the filters inside. Every Intellipure Compact device produced from the factory line is individually tested for efficiency at the total device level to meet or exceed the HEPA efficiency standard.” 

Citing a Delos fact sheet on Intellipure in NYC schools, Mr. Styer of the DOE told The Classic that “These devices were purchased for the entire unit’s ability to provide HEPA-level filtration. It would be misleading to report otherwise.”

The Intellipure compact air purifier units use a technology called a Disinfection Filtration System (DFS), which relies on a process of electrostatic precipitation to effectively capture particles. The airstream passes through a prefilter and into an ionization field. The particles are charged, which “forces those remaining particles to agglomerate to one another, thus enhancing the filtration capabilities of the downstream mechanical filter (the main filter),” according to Mr. Mulvihill.

In other words, the unit enhances the main filter through ionization to combine smaller particles so they can get captured by the filter. According to Mr. Mulvihill, the units use a series of filters. The main filter makes it difficult for ions to escape, and an additional grounding grid captures ions that are not sequestered by the media filter, “ensuring ions do not disseminate outside the device.”

Explaining the purchase

The New York City Department of Citywide Administrative Services acquired the Intellipure compact filter units for NYC public schools, including Townsend Harris, in a two-contract $43.3 million dollar deal. Two air purifier units will be placed in each classroom all across the NYC school system for the new school year. 

According to a representative from the DOE, “The most important consideration in our choice of a purifier was the level of filtration it provides. The units we chose use a technology that filters to .007 microns, which is beyond the HEPA standard of 0.3 microns.”

In a Twitter thread responding to Chalkbeat’s report, DOE Press Secretary Danielle Filson linked to Intellipure’s website and wrote, “We are providing MORE protection than a HEPA filter.” 

The Intellipure web page that Filson linked to reads, “HEPA is theoretically supposed to capture particles down to 0.3 (µm). As air passes through the filter, large particles get trapped, but anything smaller than 0.3 (µm) can get through and [be] released back out into the air. Many harmful pollutants like certain chemicals, bacteria, allergens, and airborne viruses are much smaller than 0.3(µm).” 

However, Dr. Martin of the CDC said that claims that HEPA filters are only efficient “down to” 0.3 microns “show a fundamental misunderstanding of how HEPA filters truly work, and they simply are not true.” 

In fact, HEPA filters are highly efficient at trapping particles smaller than 0.3 microns. This happens because at such small scales the particles move erratically in a phenomenon called Brownian motion, which allows them to be trapped in the mesh of the filter. 

In a statement to The Classic, Mr. Styer said, “New York City Schools are the gold standard for health and safety. Our HEPA purifiers clean air particles at .007 microns – far beyond traditional HEPA filters.”

Dr. Martin, on the other hand, said HEPA filters can “filter down to 0.007 micrometer particles… To control diseases spread through the air, there is no practical reason to be ‘beyond HEPA.’”

In an email to The Classic, Mr. Mulvihill of Delos reiterated his claim that Intellipure’s efficiency standard is more reliable because the company tests how its overall unit functions. He said that many devices which use HEPA filters can and do perform below HEPA efficiency levels when the overall device containing the HEPA filter is tested. 

“Intellipure’s products evidently ‘surpass HEPA filter standards,’ but, how much does that matter if the difference is between 99.97% efficient and 99.99%? … So, as long as the efficiency is high, I recommend not getting hung up on exactly how high,” said Dr. William Bahnfleth, an affiliate researcher and professor of architectural engineering at Penn State, as well as a presidential member of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). “What I wonder about is whether New York could have acquired actual HEPA/activated carbon filter units that would provide the same uncontaminated air delivery rate for a significantly lower cost.”

Functionality and safety after long-term usage

A general consensus among the experts The Classic spoke to is that maintenance is an important factor when selecting an air purifier, particularly with electrostatic precipitation, which can be effective but requires attention.

Dr. Martin said that electrostatic precipitators become covered in layers of dust as they capture particles, and their efficiency can diminish over time. 

“It is unclear how efficient the overall air cleaner will be when this happens,” he said. “This decreased efficiency can be limited with careful, routine cleaning and maintenance of the air cleaner, but it will likely require more frequent maintenance and a more time-consuming process [than] that [of] a true HEPA air cleaner.”

Mr. Mulvihill said that Intellipure does use electrostatic precipitation but not in the same way as traditional electrostatic precipitators, which use collection plates to gather particles. Such plates, Mr. Mulvihill said, need to be managed regularly, but Intellipure instead uses “a synthetic filtration media” to capture ions along with a “grounding mechanism” opposite the main filter designed to capture ions that may pass through. He says that this distinction ensures “the purification efficiency over the lifetime of the installed filter is significantly enhanced.”

Delos maintains that the Intellipure unit is safe and has been tested to ensure that it does not release harmful byproducts into the air, noting the device is California Air Resources Board (CARB) and UL2998 (Zero Ozone Emissions from Air Cleaners) certified. 

“It sounds like the manufacturer has done testing to determine that no reactive byproducts are produced – while the information is short on details, this is important to know,” said Dr. Charles Haas, a professor of environmental engineering and the head of the environmental engineering program at Drexel University.

Mr. Mulvihill said that Intellipure units require maintenance, a process shown in this video tutorial, but are not different from other units requiring filter replacements and the removal of dust buildup. He added that Intellipure units also require “the simple removal of any dust present on the metal grid ahead of the main filter – taking only a few more seconds of cleaning.”

Some experts, however, said that the school environment might make maintenance difficult.

“Electrostatic precipitators, such as this system, properly designed and maintained can be an excellent solution… The big challenge in public schools is facilities maintenance,” said Dr. Donald Milton, a professor of Environmental Health at the University of Maryland School of Public Health. “So, while I’m confident that at the start of the school year, these devices will work very well, it will require vigilance to ensure that they continue to work and don’t emit hazardous chemicals (ozone and its reaction products) into the classrooms.”

Dr. Green, from the Climate Change Research Centre, said “Given that [the Intellipure units] are not likely to be as carefully maintained (two in each classroom with already overworked staff), my preference would be to use true HEPA to reduce the likelihood of accidental release of products that can be harmful to health.”

As made evident by the multiple perspectives garnered by The Classic, purifiers operating at HEPA-equivalent levels of efficiency and units using true HEPA filters are different technologies. Delos provided timely, detailed answers to every inquiry The Classic sent, and these responses demonstrated there are many distinctions between their units and units containing HEPA filters. Parents, students, school administrators, and teachers deserve full and clear information about the Intellipure devices so they can ask legitimate questions surrounding the safety of schools as the upcoming academic year approaches. 

Additional reporting done by Elsa Oreen and Jocelyn Wang, Science and Technology Editors

Photo by Matthew Merino, Accuracy Editor