If going back to school in person is to be safe, community transmission of coronavirus must be under control. That’s according to a leading expert on how this virus spreads through the air.
It could be an accident waiting to happen. School opens in a district where the virus is not under control and by day one or two, we see cases of coronavirus popping up. That’s already happened already at some schools.
“Those are not cases that kids picked up in the school,” says Virginia Tech Engineering professor Linsey Marr. Marr is considered a world expert on viral transmission. “Those were cases that kids brought to the school, and that could then be transmitted to other students and staff members in the school.”
Exactly the scenario no one wants to see.
Marr’s expertise is in aerosols – tiny droplets that move through the air on breezes and drafts indoors and out. If you inhale enough virus containing droplets, it could cause infection. Marr says in addition to wearing masks at all times inside buildings, it also means “paying attention to ventilation and opening windows and doors whenever possible.”
Another fix she recommends making sure that HVAC systems are working properly and adjusting dampers and settings to bring in more outdoor air and use less recirculated air.
“They should all be upgrading the filters that are used in their HVAC systems and where those things are not possible. They could a put portable air purifiers into classrooms.”
She says it’s important to pay attention to how the air systems work and how well they operate but also to open windows whenever possible. “Even when all the windows and doors are closed, it gets replaced within a couple of few hours usually. And if you have the windows open, that happens much faster. If you're running a fan or an HVAC system that can happen faster. But the caveat with the HVAC system is that it often recirculates air through a filter, which may or may not remove much of the virus droplets in the air.”
Marr says depending on the size of the droplet, they can hang in the air anywhere from seconds to hours, dissipating more quickly outdoors, more slowly indoors.
If class can be held outdoors, that’s a good option. But when it gets to cold, Marr suggests opening the windows and bundling up. “I would certainly prefer that kids go to school with extra clothing, jackets, hats, and gloves, and keep the doors and windows open.” That way, you get better airflow than you would running the heater which could allow virus to accumulate in the air, leading to a higher risk of transmission, says Dr. Marr.
“I think that's a worthwhile trade off. Let’s be a little more, a little uncomfortable, maybe a little hotter than usual or a little colder than usual; dress appropriately for those conditions. And let's, continue our education.”
Which Masks Are Effective?
Marr’s team is in the process of testing different masks to determine how effective they are.
“We've looked at the CDC’s designs, where one is where you take two layers of pillowcase and sew them together with your loops. And another is just taking a tee shirt and cutting it. And all of those perform decently removing at least half of droplets that are two microns and larger.”
She says, “The performance for the smaller droplets is variable. What we found to be most important, there is a, is a good fit because if there's gaps in the mask, then those smaller droplets can easily flow into your mouth or back out, through those gaps.”
One surprising result so far is that even a relatively loose bandana, the kind made of heavier material actually works pretty well. “The bandana is tied around the back of your head and it hangs down well over your neck. And if you're breathing in it, it (the cloths) gets sucked up against your mouth and nose, and that helps provide a better seal than we would expect.”
And if an infected person is wearing a bandana, she says, “It actually traps a lot more virus from getting out, than I would have expected. The cloth hanging down there, slows everything down and there's time for it to kind of end up sticking to the bandana material.”
Because virus particles are larger than air molecules, masks do a decent job of keeping them out, while allowing you to breathe normally. And what to watch for is the amount of virus you may be breathing in. Anything you can do to reduce the amount of virus you breathe in, will help reduce the chance of getting sick.
