Life in the Box: Breath and Covid-19: Part One
“A lot of people, when they hear that you can’t completely get rid of your risk, they think, ‘Well, that means that it’s inevitable… “But there are lots of things you can do in between nothing and everything.”
Risk assessment during the 2020 Covid outbreak has been difficult; it seems we don’t have quite enough information or that the info is contradictory. Some people just give up. Not me. I want some facts to help keep the odds in my favor. I really want to avoid this disease.
Much of the early literature about staying safe from Covid was about transmission of the disease by surface contact. I think we all know about this now: washing our hands often and keeping our fingers away from eyes, mouth and noses. I have to admit that just writing about that makes my eyes itch. Keep… fingers… on… keyboard!
Since I’m already doing what I can in regards to avoiding the disease on surfaces, I am more curious about how the virus spreads through the air, so I’ve spent some time researching the following questions.
We hear recommendations to stay at least 6 feet away from others. I’ve also heard 10 feet, 1.5 meters, and other measures. Why the differences? Is it the same indoors and outdoors? What about wind currents? What about other factors like air pressure and humidity? And what do we need to know about the size of both the virus particles and the droplets that spread them? And if the Covid particles are tiny, why do we need to wear masks? Can’t those particles get through? What kinds of masks work best?
Droplet Size Matters
…transmission actually depends on a large range of factors, including the number of droplets, their size, and their velocity during expiratory events like coughing, sneezing, and breathing. Phys article on fluid dynamics of Covid
When we exhale, the particles in our breath enter the atmosphere carried on the humidity from our lungs, and spray in front of us in a shape that depends on the environment’s air currents and humidity. The distance our exhaled particles and spittle travel depends on the velocity of our exhale. And the number of particles that come out depends on how large a breath we’ve taken.
Droplet behavior also depends on the size of the droplets we exhale, which is a mix of all different sizes. Big droplets don’t go as far before they fall and stay on surfaces; small ones (called aerosols) can travel farther and stay suspended in air longer… up to three hours. Both can transmit Covid.
I found out that sneezing expels way more droplets than coughing does (up 100 times more), and sends those droplets up to 20 feet away. That’s probably why we are told to wear our masks up over our noses, not just our mouths. And that’s why standing 6 feet away doesn’t cover all circumstances.
The Nasal Gateway
Another good reason to make sure your mask covers your nose is presented in a new North Carolina study. It shows that the nasal passage is the area most easily infected area by Covid.
Study authors speculate that the virus gets a foothold in the nose, then sneaks down the respiratory tract when breathed into the airways.
How big are the Covid particles?
The Covid particles are tiny: .1 micron. So, they can travel farther on an exhale, and float around in the air longer than bigger particles. Some people wonder why N95 masks, which have openings a bit larger than Covid particles (.3 microns), are effective. It turns out that the tiniest Covid particles move in a zig-zag, making them more likely to get caught in the N95. Also, there is an electrostatic charge to the N95 that absorbs particles.
By the way, did you know that the N95 is named that way because it is 95% effective? Did you know that Covid-19 is called that because it was discovered in 2019?
How does droplet size matter for mask selection?
When we sneeze and cough into a mask, the larger droplets we expel will be absorbed by our masks. Some of the smaller droplets will still make it through, just not as many and not as far. Almost any mask will keep the air around us a lot freer of germs of all kinds. But many droplets we exhale will go up (into our eyes and above the head) and out to the sides (assuming our mask doesn’t fit tightly). So, if you are facing someone while wearing a mask, at least you won’t be expelling (many) droplets into their face.
Here’s a laser visualization of particles exhaled without a mask and then with a mask.
A mask of any sort may help capture some virus-laden droplets before they can enter the air. They also will reduce the forward force of the exhaled cloud of droplets, diverting flow and cutting turbulence. That should limit how far the particles can travel. But a mask “does not replace social distancing,” says Lydia Bourouiba of the Massachusetts Institute of Technology in Cambridge. Link to entire Science article
NPR article looking at many studies says “yes, wear masks”
If the person across from you is wearing a mask, too, it isn’t very likely that the germs they expel towards you will get around or through your mask. The largest droplets will get stuck on the outer surface of your mask. That eliminates the majority of germ-carrying particles. So, it makes sense that you both wear masks.
When you take your mask off, don’t touch the front of it because it’s probably contaminated with other people’s germs. And, the inside is contaminated with your own germs. Put it aside, wash it daily if it’s washable. Then wash your hands.
It looks like the practice of wearing masks, washing hands, and social distancing has cut back the regular flu season this year by about 6 weeks.
What fabric should I use to make a mask?
Even though the holes in woven fabrics used in mask-making are much larger than the Covid particles, fabric masks still work to hold back most of the larger droplets. Different fabrics are being tested and the general consensus, so far, is to use a tightly woven fabric. In fact, if you use two layers of fabric, you should be fine.
Here is an unpublished study from the University of Illinois comparing cotton, mixed cotton and polyester, and fabric from used clothing vs. new fabric. Strangely, used fabrics worked better than some of the new fabrics.
An April 2020 Chicago study reports a combination of cotton and silk is almost as good as N95. But it has to fit very well.
Another article from NBC health news likes cotton fabric with 180 thread count the best. Unlike the U of I study, this one doesn’t like the use of t-shirts. The main source of this article is Dr. Scott Segal, chair of anesthesiology at Wake Forest Baptist Health in Winston-Salem, North Carolina.
How do I stop my glasses from steaming up when I wear a mask?
There is a lot of advice about how to keep your glasses from steaming while wearing a mask. Most of it doesn’t work. A nurse in the video link, below, decided that leaving a little gap at the sides of your mask to let air in and out works best. However, leaving those gaps will lower the effectiveness of your mask at filtering out all the germs and virus particles you breathe in and exhale. One article said masks, including those blue surgical masks made with a plastic coating, only keep out about 75% of particles, but that even that much can saves thousands of people from getting infected.
One other hint I like in this video is: to make your mask fit better, twist the side elastics to make a figure 8 before putting them over your ears. (My photo at the end of this article shows an example.) It does seem to reduce the steaming.
Longish video video (15 min) that basically shows a lot of ways that don’t work… the solution comes at about 9:45 min. into it.
What about those plastic face shields?
The University of Iowa Hospitals recommend face shields to the public, and require them in their hospitals. They say these face shields work better than homemade face masks for the general public. And that they are more available than N95 masks in hospitals. Here is their additional reasoning:
- Durability, in that they can be “reused indefinitely” and easily cleaned.
- Comfort, reducing the chance the wearer will touch his or her face.
- Broad protection, in that they block portals of viral entry.
- Clarity, as people wearing masks often have to remove them to communicate.
My investigation continues in Part Two… with questions about how to evaluate and maybe improve some indoor environments.
Nancy Heather Brown is a retired, Emmy Award-winning television producer whose career has included interviewing, writing, narrating and editing for a span of four decades. Today, she enjoys learning new things and reflecting upon the creative process and life issues, both inside and outside the box. Her opinions are her own, and are not necessarily those of this web site.
Note: This research was performed the week of June 22,2020. Hopefully, there will be new science and our understanding will expand and change.
Fact Check: The research was fact-checked on Media Bias/Fact Check