There’s an ongoing push to revamp indoor air systems to slow the transmission of the coronavirus.
"The indoor environment has a massive impact on our health," said Dr. Joseph Allen, Professor in the Department of Environmental Health at Harvard Chan School of Public Health and Director of the Healthy Buildings Program.
Dr. Allen told KCBS Radio's "Ask An Expert" that while people have a good understanding of the hazards of pollution and poor outdoor air, far less attention has been paid to indoor air, until now.
"Healthy buildings have a role to play in keeping us healthy, or facilitating the spread of disease," he said. "The common underlying thread in all these outbreaks linked to time spent indoors is underperforming indoor environments, meaning low ventilation, low outdoor air coming in and low filtration."
His team at Harvard has developed thorough risk reduction and reopening strategies for schools and other types of buildings, but he explained that the various engineering strategies boil down to a few key principles: ventilation and filtration.
Luckily, improving indoor air quality can be quite simple as even portable air purifiers can be highly effective at filtering air.
"Four air changes per hour is good, five is excellent, six is ideal," said Dr. Allen. Six air changes per hour would mean that the air in a room is filtered entirely every 10 minutes. The general metric to look for when shopping for an air purifier is a clean air delivery rate, or CADR, or 300 for every 500 square feet of space in the room.
Place them as close to the center of the room as possible, and if you are using multiple air purifiers in one space, place them apart from each other and any open windows to optimize their efficiency.
Dr. Allen said while there are many additional features available on the market today such as ionizing filters or automatic sensors, they often add little value.
"You just want a good fan, a HEPA filter and a high clean air delivery rate, that’s really what you’re looking for," he said. "HEPA filters capture 99.97% of particles. That’s a lot. That’s the best filter you’re going to get."
Ventilation and filtration can significantly reduce risk, but there is one even lower tech solution that is more effective: universal masking.
"Universal masking is absolutely critical," said Dr. Allen. "If you look at any of the risk models that exist for airborne spread, including my own team’s, the engineering controls - ventilation and filtration - are really effective at reducing risk, but the most effective strategy is universal masking. Anytime you put this in the models it drives risk way down."