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Why you should always wear a mask in a public restroom

Researchers at Yangzhou University have reported that flushing a toilet or urinal sends a cloud of tiny aerosol particles  into the air.

Researchers found that 57 percent of the tiny aerosol particles ejected by flushing a urinal leave the urinal.
Researchers found that 57 percent of the tiny aerosol particles ejected by flushing a urinal leave the urinal.
Photo by HelpStay.com on Unsplash

If you find yourself having to use a public restroom, be sure to wear a mask.

Last June, Chinese researchers at Yangzhou University reported that the strong turbulence caused by flushing a toilet sends a cloud of tiny aerosol particles from the waste and water in the toilet spewing into the air. Using mathematical modeling, the researchers determined that up to 60 percent of those ejected particles travel above the toilet seat. Within 35 seconds, some reach a height of almost 3 feet and may linger in the air for up to 70 seconds.

But toilets aren’t the only concern. Last week, the same group of researchers reported similarly “alarming results” regarding urinals. Using the same type of mathematical modeling, they found that 57 percent of the tiny aerosol particles ejected by flushing a urinal leave the urinal. The particles then quickly reach a height of 2.75 feet, or, as the authors put it, the height of a man’s thigh.

How quickly? Within 5.5 seconds, which is seven times faster than occurs after a toilet is flushed.

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Both studies were published in the journal Physics of Fluids, which is published by the American Institute of Physics.

‘A challenge to public health’

There’s more than just an “eew” factor involved here. Previous research has detected the COVID-19 virus (SARS-CoV-2) in stool and urine samples. And although you are much less likely to become infected with COVID-19 by this form of transmission (inhaling a cloud of infected particles from a flushed toilet or urinal) than you are by inhaling the respiratory droplets generated by an infected person’s breathing, coughing and sneezing, the authors of the new study urge people to take precautions. They claim that China has documented a handful of cases in which people became infected from a public toilet.

“Wearing a mask should be mandatory within public restrooms during the pandemic, and anti-diffusion improvements are urgently needed to prevent the spread of COVID-19,” says study co-author Xiang-Dong Liu of Yangzhou University, in a released statement.

“It can be predicted that in public restrooms, especially those in densely populated areas, urinals are used more frequently and particles will travel faster and fly farther, which poses a great challenge to the public health,” add Liu and his colleagues in their latest paper.

Dynamic virus movement during and after a 2.6 s urinal flushing with a total duration of 5.5 s.
American Institute of Physics/Physics of Fluids
Dynamic virus movement during and after a 2.6 s urinal flushing with a total duration of 5.5 s.

Keep hands clean, too

Of course, you should also avoid touching surfaces as much as possible in a public restroom, as infected aerosol droplets, whether from a flushed toilet or a person’s cough, may have contaminated some of the room’s surfaces. A study published last spring in the New England Journal of Medicine found that SARS-CoV-2 can live in a laboratory on stainless steel and plastic surfaces for several days, although it’s not entirely clear that the amounts that survive on such surfaces in a “real world” environment would be enough to get someone sick.

Good hand hygiene — washing your hands with soap and water for at least 20 seconds or using a hand sanitizer comprised of at least 60 percent alcohol — is strongly recommended in public restrooms, as it is everywhere else. Such practices can easily destroy the COVID-19 virus, as well as other unwanted pathogens.

Practice social distancing in restrooms, too.

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FMI: You can read both the “toilet” and the “urinal” studies in full on the Physics of Fluids website.