COVID-19 is an airborne disease, and epidemiologists agree that containing the pandemic depends in part on limiting the coronavirus that causes the disease from spreading when infected people cough, sneeze, or talk. But as schools work to bring students back to full-time, in-person learning safely, staff members are finding it difficult to literally clear the air.
In a study released this month, researchers from the American Society of Heating, Refrigerating, and Air-Conditioning Engineers surveyed more than 4,000 public and private schools in 47 districts across 24 states on their efforts to improve indoor air quality during the pandemic. The Centers for Disease Control and Prevention considers improved ventilation and indoor air quality to be one of the core virus-mitigation strategies needed to reopen schools in person safely, along with masking, social distancing, and contact tracing.
Participants reported air-quality improvements have generally proved to be a lower priority compared with other prevention strategies, both because of cost and pressure from the outside community.
“Because air quality is intangible, not touchable, [the public] can’t see how that could change,” one district survey participant told the researchers. “Unfortunately, that’s probably why maybe it wasn’t top on our list. But a lot of our decisions were made with the more tangible things of the six-feet spacing … changing our classroom setups … changing our cleaning routines … things you could see and put into practice.”
The researchers looked at six air-quality approaches that have been found to reduce viral particles and are recommended by groups like the CDC, the Environmental Protection Agency, and the World Health Organization:
- Use the building’s heating, ventilation, and air conditioning, or HVAC, system to increase the amount of outdoor air drawn through the building.
- “Flush” the indoor air for a certain period of time or for a number of air exchanges whenever the building is unoccupied.
- Open windows to increase airflow.
- Place fans in windows and doors to move room air outside.
- Upgrade HVAC filters to a “minimum efficiency reporting value,” or MERV, of at least 13 out of 16 units on a filtering scale, in order to better filter out viral particles.
- Install high-efficiency particulate air, or HEPA, cleaners, which filter out at least 99.97 percent of human viral particles.
Nearly all districts have started to implement at least some of these improvements in the 2020-21 school year, with districts prioritizing using their existing HVAC systems to bring additional outside air into buildings and flush the indoor air when buildings are not occupied.
While the CDC recommends districts make use of existing windows and doors for fresh air as much as possible, the least expensive option, far fewer than half of surveyed districts did so, primarily because their buildings weren’t designed to let the windows open properly or otherwise be used. In fact, school staff frequently reported their buildings weren’t designed to allow many of the recommended air-quality interventions.
Before the pandemic started, only 6 percent of schools surveyed had HVAC filters of 13 MERV units or higher, that were considered efficient enough to prevent the viral spread; most had filters half that efficient, with HVAC systems that were too old to cope with higher-grade—and more expensive—filters. Researchers found wealthier school districts were more likely to have installed new filters or HEPA air cleaners.
Unsurprisingly, for districts that were able to upgrade their systems, 88 percent reported that along with better air quality, they had lower energy costs, particularly when the school buildings were not occupied.
A 2020 study by the U.S. Government Accountability Office found more than 40 percent of U.S. districts would need to update or replace heating, air conditioning, and ventilation systems in at least half their schools to have systems capable of preventing the spread of the coronavirus, which studies have found is up to 20 times more likely to cause infections indoors than outside.
