I haven’t been an “anti-masker” but also haven’t been totally convinced of the efficacy of masks. I guess I’ve been indifferent and have worn them when required.
This is largely due to the bombardment of conflicting information, with each piece of information having some truth but nobody really putting the pieces together for us. Or maybe it was due to my freedom-loving nature, preventing me from really diving into the subject.
But then enters Noah, my son-in-law who is a student and senior in the mechanical engineering program at the U of M.
He was wearing a mask when we were all out together. We joked that he didn’t need to wear one when in an area that didn’t require it. He told us he felt it was important, based on information he had learned from a presentation that one of his professors made in a class. This piqued my curiosity.
The professor he referred to is Chris Hogan, a University of Minnesota Department of Mechanical Engineering professor. He is also the Editor-in-Chief of the Journal of Aerosol Science and has been educated at Cornell, Yale and Washington University. He explained the physics behind mask-wearing to his senior engineering class.
So I asked Noah to send me the presentation, and after watching it several times to gain a better understanding, it changed my view on mask wearing.
Hogan explained that the first message from the Center for Disease Control (CDC) was that people don’t need to wear masks. That resonated and stuck with a lot of us I think. But he went on to explain why this was just the first message.
The CDC was initially focused on masks as PPE (personal protective equipment). The group was worried that if they gave N95 masks to everyone weekly, they would be giving out 300 million masks per week and would run out, leaving inadequate supply for healthcare workers. The CDC wasn’t initially thinking of masks where they should be, he explained, and that the focus wasn’t on preventing the spread of the virus by focusing on exhalation. He said that it was a harder, more nuanced thing to explain to the public.
So as to the physics of why wearing a mask is important, that would come out in a series of terms like aerosol and diffusion and charts and diagrams (which is why I had to watch it five times to break it down).
Hogan first said what we all know: that masks, whether they’re cloth or surgical masks, aren’t very good at filtering out small particles such as the coronavirus.
But they are good at collecting larger particles. He explained that we are continually expelling particles when we speak, breathe, cough, or sneeze, and those particles are initially larger with the virus attached to those larger particles as they come from our mouths.
Viruses aren’t isolated by themselves at this initial point of exhaling, he explained. When particles go out from someone, they start to evaporate and get smaller, with the virus itself now more isolated.
He said that masks, even poorly fitted cloth masks, are really good at collecting almost 100% of large particles. “Even if the mask is leaky and if the flow leaks around the mask, particles have inertia which makes them cling to the mask,” he said.
He explained that particles are in the air until they are deposited onto something or are cleared out by ventilation.
He then explained how masks act as diffusers. They slow down the velocity of particles. “Even if it’s leaky, it slows down the velocity and reduces the penetration depth. This makes social distancing that much more effective and gives ventilation a chance to do its job,” said Hogan.
He reiterated, “Mask quality isn’t as important; they don’t provide protection during inhalation. But during exhalation, they do a decent job. They act as a diffuser and collect the largest particles.”
He presented a summary of his physics-based argument for the effectiveness of masks in the following bullet points.
What masks do:
• They will efficiently collect larger particles and droplets from talking, breathing, coughing, and sneezing.
• They will slow down the speed of coughs, sneezes, breathing, and speech emissions.
• They make social distancing more effective to give ventilation a chance to do its work.
What masks don’t do:
• Provide 100% protection to the wearer.
• Replace social distancing measures.
• Eliminate the need for good ventilation.
So, to mask or not to mask, that is something we all have to decide for ourselves, though it is now required in most establishments. But for me personally, looking into the physics-based evidence of why we are doing all this helped me make more sense of it.
I’ll leave on a lighter, non-masking note on something I saw in a meme recently … which might be true!
“So I just figured out 2020, and it’s pretty obvious what happened … ‘Baby Shark’ is an ancient chant that opens a portal to Hell.”
Traci LeBrun is the editor of the Messenger.