Bigger is not always better
It is tempting to see the solution as increased ventilation, said Ehsan Mousavi, PhD, assistant professor of construction science and management at Clemson (S.C.) University, who studies indoor air quality and ventilation in hospitals.
“We are ventilating the heck out of hospitals,” he said in an interview. But there is much debate about how much ventilation is the right amount. Too much and “you can blow pathogens into an open wound,” he explained. “Bigger is not always better.”
And there is still debate about the best mix of outside and recirculated air. An increase in the intake of outdoor air can refresh indoor air if it is clean, but that depends on where you live, he pointed out.
The mix used in most standard office buildings is 15% outside air and 85% recirculated air, Dr. Mousavi said. Boosting the percentage of outside air increases costs and energy use.
In fact, it can take five times more energy to ventilate hospital spaces than office spaces, he reported.
Engineers searching for clean-air solutions need to know what particulates are in the air and whether they are harmful to humans, but the sensors currently available can’t identify whether a virus is present in real time.
Samples have to be taken to a lab and, “by the time you know a virus was in the space, the moment is gone,” Dr. Mousavi explained.
More research is needed. “We need a reasonable answer that looks at the problem holistically, not just from the infectious disease perspective,” he said.
Hydrating indoor air
Research is making it clear that health care environments can play a significant role in patient recovery, according to Stephanie Taylor, MD. Dr. Taylor is president of Building4Health, which she founded to help businesses assess the quality of air in their buildings and find solutions. The company uses an algorithm to arrive at a health assessment score.
Air hydration is the most important aspect to target, she said.
Since the 1980s, research has shown that a relative humidity of 40%-60% is healthy for humans, she said. Currently, in an office building in a winter climate, the humidity level is more like 20%.
Canada is the first country to officially recommend the 40%-60% range for senior citizen centers and residential homes.
“Properly hydrated air supports our immune system and prevents skin problems and respiratory problems. It also inactivates many bacteria and viruses,” Dr. Taylor explained. Inhaling dry air compromises the ability of the body to restrict influenza virus infection, researchers showed in a 2019 study.
In the case of COVID-19, as virus particles attach to water molecules, they get bigger and heavier and eventually drop out of the breathing zone and onto surfaces where they can be wiped away, she explained.
But when the particles “are very small – like 5 microns in diameter – and you inhale them, they can lodge deep in the lungs,” she said.
In properly hydrated air, particles will be larger – about 10-20 microns when they attach to the water vapor – so they will get stuck in the nose or the back of the throat, where they can be washed away by mucous and not travel to the lungs.
“Indoor air metrics” can support our health or contribute to disease, “not just over time, but quickly, within minutes or hours,” she said.
No one expects the world’s building stock to suddenly upgrade to the ideal air quality. “But that doesn’t mean we shouldn’t move in that direction,” Dr. Taylor said. Changes can start small and gradually increase.