Ventilation: A powerful Covid-19 mitigation measure
“The challenge for organizations that improve air quality is that it’s invisible,” said Joseph Allen, director of the Healthy Buildings Program at the Harvard T.H. Chan School of Public Health.
It’s true: Other Covid tools are more tangible. But visualizing how the virus might behave in poorly ventilated spaces can help people better understand this mitigation measure.
Allen likens it to cigarette smoke. “If I’m smoking in the corner of a classroom and you have low ventilation/filtration, that room is going to fill up with smoke, and everyone is breathing that same air.”
Then apply that to the outdoors.
“I could be smoking a cigarette, you could be a couple of feet from me, depending which way the wind was blowing, you may not even know I’m smoking.”
If you’re indoors, you could be breathing in less fresh air than you think.
“Everybody in a room together is constantly breathing air that just came out of the lungs of other people in that room. And depending on the ventilation rate, it could be as much as 3% or 4% of the air you’re breathing just came out of the lungs of other people in that room,” Allen said.
He describes this as respiratory backwash.
“Normally, that’s not a problem, right? We do this all the time. We’re always exchanging our respiratory microbiomes with each other. But if someone’s sick and infectious … those aerosols can carry the virus. That’s a problem.”
It’s airborne
“We’ve known for decades how to keep people safe in buildings from infection, from airborne infectious diseases like this one,” Allen said.
From the beginning of the pandemic, Allen and other experts have waved red flags, saying that the way we were thinking about transmission of Covid-19 — surfaces, large respiratory droplets — was missing the point.
The coronavirus itself is very small — about 0.1 microns — but that doesn’t affect how far it can travel.
“The size of the virus itself doesn’t matter because, as we say, the virus is never naked in air. In other words, the virus is always traveling in respiratory particles that develop in our lungs. And those are all different sizes,” Allen said.
Singing or coughing can emit particles as large as 100 microns (almost the width of a human hair), he said, but the virus tends to travel in smaller particles — between 1 and 5 microns.
The size of these particles affects not only how far it can travel but how deeply we can breathe it into our lungs, and how we should approach protecting ourselves from this virus.
“When you’re talking about an airborne disease, there’s the what’s right around…
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