My name is Dr. Kimberly Henthorn, and I’ve been an Associate Professor of Chemical Engineering
at Rose-Hulman since 2010.
My expertise lies in the field of particle technology, which includes a range of topics
from particle synthesis and transport to fluidization and filtration.
As COVID-19 began to spread across the United States earlier this year, people were encouraged
to start wearing masks to help slow the spread of the virus.
This has been met with some resistance, and much of it has been due to the large amount
of misinformation being passed around social media.
I hope this video helps to educate our campus on why wearing masks is so important.
Experts say that COVID-19 particles range from 60-140 nanometers in size with an average
diameter of 125 nanometers, or 0.125 microns.
To give that some perspective, the average diameter of a human hair is typically between
75 and 100 microns.
These viruses are tiny!
So how can a homemade mask possibly capture particles this small?
In the case of COVID-19, our masks are trying to capture respiratory droplets that may contain
the virus, not the individual virus particles themselves.
The size of these droplets can vary greatly depending on how they were formed.
According to a study published in the Journal of the Royal Society Interface, respiratory
droplets can range from 1 to 1000 microns in size.
Sneezing can generate around 100 microns, and shouting or singing can produce much larger
droplets.
Even the simple act of breathing generates droplets; think about being able to see your
condensed breath outside on a cold winter day.
The droplets you emit stick to the fibers of the mask because of surface tension.
Think about how much harder it is to pour wet sand out of the holes of a colander than
dry sand.
Do some particles get through the mask?
Sure!
But the goal is to reduce the spread of the virus, not eliminate it completely.
Plus, you need a critical number of virus particles to overwhelm your immune system
to get sick...so if other people around you are also wearing masks, then the likelihood
that enough viruses will wind their way through the fibers of the second mask to make them
sick are greatly reduced.
So that brings me to a second point.
There's a higher risk if a healthy person is wearing a mask and an infected person isn’t,
but a much lower risk if the mask is put on the infected person instead.
Although, it's MUCH lower if both people are wearing a mask.
So, why does it matter *who* is wearing the mask?
The difference is where the droplets end up.
If the infected person is wearing a mask and sneezes, talks, or coughs, then most of their
droplets end up stuck in the fibers of their mask from surface tension.
The few that get through likely don't have enough viral load or velocity to make it to
someone else to get them sick (unless they’re really close or have prolonged exposure).
On the other hand, if the non-infected person is wearing the mask and the infected person
isn't, the droplets literally go all over the place.
That means the non-infected person can get them in their eyes, on their hands, in their
hair, on their clothes, and all over their face.
So at that point, even if the mask kept them from straight-up inhaling most of the droplets,
they can get infected through their eyes, when they take off their dirty mask or brush
their hair or whatever.
It's kind of like walking through one of those misting machines at a theme park that keep
you cool.
If you cover the misting heads, you don't get very wet when you walk by them.
If you uncover the misting heads but cover your face, you're very damp on most of your
body (except the part you protected).
There has been no confirmed evidence that correctly wearing a mask causes hypoxia or
lung infections.
Oxygen and carbon dioxide molecules are less than one nanometer in diameter and are not
trapped in respiratory droplets, so they can easily pass through the fibers of your mask.
If your mask is clean, there is no evidence of an increased risk of developing pneumonia
or bacterial, viral, or fungal lung infections.
Very young children and people with certain medical conditions should not wear a mask.
If you struggle to breathe well in a mask because of anxiety or asthma, try breathing
through your nose instead of your mouth.
When we perceive danger, we tend to breathe through our mouths to to rapidly oxygenate
the body.
Mouth-breathing when wearing a face mask can backfire, because the body isn’t able to
get enough additional oxygen, which can cause your body to spin further into panic or terror.
N95 masks filter out more than 95% of all particles greater than 0.3 microns and surgical
masks may block 70-90% of particles, but we should reserve those for medical personnel.
Typical homemade masks with 2-3 layers of fabric filter about 40-50% of particles.
According to a recent paper published in the journal Infectious Disease Modeling, if half
of the population wore masks that are 50% effective, transmission rates would be halved.
Even if 80% of people wore masks that only filter 20% of particles, transmission rates
can be cut by 1/3.
What about those cool masks with vents?
Vented masks contain one-way valves that protect the wearer from breathing in contaminants.
But if you’re infected, you’re basically exhaling the virus all over the place.
One study says that these types of masks can actually accelerate the virus so that it travels
farther than if you had no mask at all.
Vented masks work great if you’re working around dust or chemicals, but they won’t
keep everyone around you safe.
Okay, what about face shields?
Face shields are fine to use in combination with masks, but should not be used alone.
Some larger respiratory droplets will be captured by face shields upon impaction, but a majority
of the droplets will be able to follow air currents and travel around the shield.
Basically, treat it like you would your underwear.
If you wear your mask for a good portion of the day or if it gets wet or dirty, wash it
or throw it away.
If you only wear it for a very short period of time, you can spray it down with a concentrated
alcohol solution and reuse it.
Be sure your mask fits well around the sides of your face so that you’re not breathing
out the edges of your mask.
Also, make sure your mask isn’t too restrictive; if you can’t breathe through the fabric,
then you are going to force unfiltered air out the sides.
A nose clip at the top can help make your mask fit better and reduce foggy glasses.
Having a mask with two distinct patterns can help you to remember which side is potentially
contaminated before you have a chance to wash it.
And be sure to cover your nose too!
The nose is often the first place the virus attaches and is a replication hotspot.
Finally, remember that wearing a mask does not make you invincible.
Masks are only one part of a cocktail of defenses we have against COVID-19.
Masking, social distancing, good hygiene, and good ventilation must be used together
in order to be effective.