The sprawling cafeteria at Manhattan’s Murry Bergtraum High School will soon be filled with students taking off their masks to eat each day. The school has undergone several ventilation upgrades in preparation—to reduce the risk that the coronavirus will linger in the air if anyone is infected.
Fresh air pumps into the cafeteria via the school’s central HVAC system, which is now retrofitted with MERV-13 filters that can trap virus particles. At the front of the cafeteria, a super-sized version of the air purifiers the city is installing in classrooms provides additional filtration.
On Wednesday morning, officials from the city’s Department of Education walked journalists through the lunchroom and classrooms, while school facilities staff took measurements of the air flow.
One classroom was getting an impressive 19 air changes per hour—a measurement used to assess the ventilation in a building. A minimum hourly rate of 3 air changes is in line with the standards from the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) for an elementary school room that's 1,000 square feet with an 8-foot ceiling.
The society has created a formula for determining the appropriate air change rate based on the size and occupancy of a room, which guides back-to-school COVID recommendations from the Centers for Disease Control and Prevention and Harvard T.H. Chan School of Public Health. According to the staff's handheld meters, the cafeteria was being replaced with fresh air 22 times per hour.
But Murry Bergtraum High School occupies a newer building (built in 1975) with a functioning HVAC system. The city has been reluctant to publicly disclose whether all of the classrooms that have been cleared for use in the coming school year meet established air quality standards. Whether the ventilation will be adequate and consistent in the 4,000 or so classrooms across the city that rely only on natural ventilation—that is, functioning windows—remains a point of contention. The city has also added air purifiers to supplement ventilation and is defending the brand they purchased despite criticism that it doesn’t meet the top filtration standards.
Read More: NYC Approves 4,000 Classrooms For In-Person Schooling Despite Unreliable Ventilation
While engineers who have spoken to WNYC/Gothamist have called windows a less reliable source of ventilation because they depend on fickle weather conditions, city officials argue they are not only adequate but sometimes more effective than an HVAC system.
The cafeteria at Murry Bergtraum High School has a larger version of the Intellipure air purifiers being placed in city classrooms.
“Windows are the mainstay of infection control throughout the entire world,” Dr. Jay Varma, the mayor's advisor and consultant for public health, said in an interview with WNYC/Gothamist at the DOE's behest. “Anybody who tells you that windows aren't a good form of ventilation has some form of bias built into them.”
But Varma says he has not looked at the data on how well ventilation is working in different classrooms, although the DOE says it is tracking this information. All city public schools are being supplied with devices called anemometers to measure air change rates as well as handheld monitors for carbon dioxide, which builds up in the air as we exhale. Aerosol scientists say carbon dioxide levels can be used as a proxy for determining whether virus particles might also linger in a room.
During Wednesday’s school tour, City Councilman Mark Levine questioned whether older buildings without central air would achieve the same ventilation levels as Murry Bergtraum High School. “It must be harder to get big numbers of airflow without a system like this,” said Levine, the chair of the city council’s health committee.
Councilman Mark Levine and NYC Schools Chancellor Meisha Porter got a tour of the safety measures at Murry Bergtraum High School from school facilities officials.
John Shea, head of the Division of School Facilities at the DOE, disagreed. “Not necessarily,” he countered, pointing out that some of the city’s school buildings were designed in the wake of the 1918 flu pandemic with ventilation in mind. “If you open those windows just a little bit, they’re so large, and there’s so many of them that you can get more [ventilation] than a typical central system.”
Who’s right? There’s no absolute answer as to whether natural ventilation or mechanical ventilation is better in every situation, said Faye McNeill, a professor at Columbia University and aerosol scientist. A lot can depend on the setting and building design. In other words, windows cannot achieve suitable ventilation in all scenarios, 100% of the time.
McNeill recently worked with researchers across the country to measure the effectiveness of ventilation in different school and university buildings. The resulting paper, which has not yet been published, concluded that “naturally ventilated buildings on the West Coast studied here were designed for cross-ventilation and had relatively high [air changes per hour],” but that “older buildings in the Northeast U.S. without mechanical ventilation, designed to keep heat in during cold winters, often have insufficient air exchange.” The study did not specifically look at New York City public schools, however.
McNeill said that adding portable air purifiers to classrooms that can filter out particles showed the DOE was being proactive—and said the devices could theoretically help improve indoor air quality. However, she and several other scientists and engineers who spoke to WNYC/Gothamist rejected the city’s claim that the Intellipure-brand purifiers the city purchased for classrooms are essentially the same as purifiers that have HEPA filters, the industry standard.
HEPA filtration has been widely proven for many decades.
“HEPA filtration has been widely proven for many decades,” said Alex Huffman, an aerosol scientist who teaches at the University of Denver. “The distinction in that specific Intellipure case is that it does take some particles out of the room, but the main issue there is that it does it really inefficiently.”
As reported by The Classic, HEPA filters also get better at cleaning the more they pull gunk out of the air. A ventilation expert from the CDC told the Townsend Harris High School newspaper that “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.”
In his interview with WNYC/Gothamist, Dr. Varma questioned the importance of the distinction between HEPA and non-HEPA filtration, arguing that there has never been a randomized control trial—the gold standard of evidence-based medicine—showing that HEPA filters can reduce the incidence of respiratory infections in humans.
He claimed HEPA filters had only been validated in laboratories; however, field studies have shown that the devices can reduce infectious disease rates in hospitals and operating rooms. Varma also said he and the DOE had based their decision to pick the Intellipure air purifiers on laboratory data.
School custodian engineers will use handheld devices called anemometers to measure air flow in classrooms.
“What I rely on and what the DOE engineers have relied on is the laboratory data from manufacturers,” Varma said of the Intellipure air purifiers. “Based on that data, they appear to filter virus particles of the size that we would expect in a classroom of people.”
Both Varma and air quality experts agree in any case that air purifiers should only be used to supplement natural or mechanical forms of ventilation and that they cannot replace large amounts of air on their own.
“There is ample evidence that there are many adverse effects of underventilating a building, including less effective learning," said Dr. William Bahnfleth, chair of ASHRAE’s Epidemic Task Force and a professor of architectural engineering at Pennsylvania State University. "So, there is a developmental risk as well as a health risk in those buildings.”
Shea said that custodian engineers would regularly measure airflow and carbon dioxide levels in classrooms and strive to achieve four to six air changes per hour. But the DOE won’t report that data to the public. Rather, he said, if there’s a problem, the custodian engineer will note it in a complaint log and, if necessary, alert their deputy director of facilities.
“If a principal or a teacher has a concern,” Shea said, “we’ll go in there, we’ll check that room, and if we find it is outside of our guidelines, we’re going to close that room. And we’re going to find another place for those kids until we can fix the ventilation.”
This story was updated to include more details on ASHRAE’s ventilation guidance.
