Slow-Motion Video Contrasts Mask Effectiveness Against Spread of COVID-19

A recent slow-motion video demonstrates the ways masks prevent the spread of COVID-19 illness.
Brad Bergan

Knowing which mask is best to prevent person-to-person transmission of the COVID-19 coronavirus is still an open question for most, but slow-motion video shared on YouTube early in July provides a visual basis to judge how best to keep safe amid the global pandemic.


Slow-motion video contrasts mask effectiveness amid COVID-19

Professor Joe Hanson of the YouTube channel "It's Okay To Be Smart" released a video earlier in July, reviewing the basics of why people should wear masks — in a visual review and primer and recent studies on the effectiveness of masks to prevent the spread of the COVID-19 coronavirus.

It's rare for sneezes and even coughs to be visible to the naked eye — which happens when oral expulsions move through a ray of light. Hanson and his team decided to demonstrate how breath leaves the body using the Schlieren imaging technique combined with slow-motion cameras set to roughly 250 frames per second.

This method detects the flow of air at different temperatures and densities — not unlike the way distorted wavering light can appear above a hot road on sunny summer days.

This is why Fluid Dynamicist and Mechanical Engineer of the National Institute of Standards and Technology (NIST) Matthew Staymates used this technique to analyze the flow of air when we speak, breathe, and cough.

The visualizations show how without a mask — while coughing, speaking, and breathing — we expel air directly forward at various speeds and distances. When a virus is present in one's breath, it might move up to 2 meters (6.5 feet), depending on which type of air-expulsion someone performs.

PBS It's Okay To Be Smart Talking
While talking without a mask, the virus can move several meters ahead of us. Source: PBS / It's Okay To Be Smart

Masks reduce air's momentum, redirects COVID-19

While one wears a mask, the air is expelled at a different trajectory and pace, with numerous nuances working against the possibility of viral transmission, Bored Panda reports.

Firstly, the mask significantly reduces the air's momentum, which reduces the distance a virus might travel to roughly 30 centimeters (about one foot). Additionally, airflow is redirected upward and downward to the top and bottom of the mask — and, according to the visual demonstration, there is a significant reduction in the air's momentum.

PBS It's Okay To Be Smart Mask
Masks reduce the velocity of transmission, and redirect breathing up and down. Source: PBS / It's Okay To Be Smart

Already-exhaled COVID-19 sneaks through masks

Additionally, airborne viruses like the coronavirus are capable of sneaking through conventional masks. But since they move via tiny droplets of moisture big enough to stick to fabric, they are effectively stopped from spreading.

Without a mask, the virus — inside a moisture bubble — will move farther, and when the bubble evaporates the virus might take flight on a gust of wind. This allows it easy access to our internal systems, once we breathe it in.

So it seems that while wearing a mask won't prevent the wearer from catching the COVID-19 coronavirus, the only way for carriers to prevent transmission — asymptomatic or not — is to wear a mask, which disrupts and localizes the flow of air that typically travels at speeds and directions too close to comfort.

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