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video of germ-filled toilet spray shows why we should all wear masks in a public bathroom

there is health risk just walking into a restroom where many toilets have been flushing, according to study author john crimaldi, who says he is now more likely to mask up when using public toilets.

by karen hawthorne

dec 14 2022

4 minute read

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no matter what your thoughts are on public restrooms, a new study published in scientific reports is adding serious ick factor around sharing space with others to do our business.

researchers at the university of colorado boulder’s ecological fluid dynamic lab have shown for the first time just how airborne particles shoot out of a lidless public toilet, spreading potential germs far and wide. in fact, the video of the study results could change the way you think about using public toilets.

everyone should put the lid down

if there’s a lid on the toilet, put it down before you flush to help limit the risk of infection, says the study’s lead author john crimaldi, professor of civil, environmental and architectural engineering.

“our role in doing this study was to understand how the contents of a toilet bowl are spread and where those contents move,” he says. “what is certainly known is that aerosol droplets, which are just tiny little droplets of water like the ones that come out of a toilet when you flush it, can be vectors for exposing people to diseases because those little droplets of water can harbour pathogens.”

crimaldi and his team straddle the line between engineering and physics, and use bright green lasers and camera equipment to measure particles in the air and fluid flows that are invisible to human eyes.

in this case, they looked at the trajectories and velocities of the particles in the aerosol “plume” ejected into the air when a lidless commercial toilet is flushed.

previous research has used scientific instruments to show that when a toilet is flushed, solids and liquids go down as designed, but invisible particles are also released into the air above flushed toilets and larger ones can land on surrounding surfaces. now crimaldi’s work allows us to see exactly what these plumes look like and how the particles release and land.

“i am more inclined to wear a mask in a public restroom”

airborne particles shoot out fast at speeds of two metres per second, reaching 1.5 metres above the toilet within eight seconds. the largest droplets usually settle onto surfaces within seconds, while the smaller particles can remain in the air for minutes or longer. so with many people going in and out of public bathrooms, people are not just at risk of breathing in their own waste particles, but those of other patrons.

“i think it’s especially a wakeup call for the public because these images drive home the point on the scientist side of things,” says crimaldi, explaining that other studies have shown that pathogens can stay in the toilet bowl for dozens of flushes, increasing the risk for exposure.

“this work will change people’s perspective and change behaviours,” he says, revealing his own plan to protect himself from getting sick from public washrooms. “i certainly am far more inclined to wear a mask in a public restroom, even more so than i would have before i saw these images.”

and while the study would be compelling enough in normal times, crimaldi says the heightened awareness and fear of pathogens since the beginning of covid have catapulted his team’s study into the headlines.

“people have known that covid is present in feces,” he says. “people have known that toilets can emit aerosols. so there was kind of this perfect storm when we were able to show just how dramatic these aerosol plumes are that really got people’s attention.”

plumes “squirt out the side under the lid”

whether you flush the toilet or it flushes by itself doesn’t matter, the health risk happens just by walking into the restroom where many toilets have been flushing, according to crimaldi. and while closing the lid on public toilets — and your toilet at home — reduces the formation of these aerosol plumes, it doesn’t eliminate it.

“there’s always a pretty sizeable gap there, at least in the way a conventional lid is designed,” he says. “our work shows that there’s so much energy in the plume that’s pushing the fluid upwards out of the toilet, that it just squirts out the side under the lid.”

the great part about using laser technology in his lab is that it not only drives the point home for public health messaging, but it helps other scientists look at the results in a visual way.

“doing stuff in the laboratory with lasers almost always produces something that has a really strong visual component to it that helps us as visual creatures to really understand that phenomena,” he says. “and in many cases, and ironically, even in the case of this toilet that’s spewing up these contents, which in many ways are not appealing, the physics and the images that we took of that are extraordinarily beautiful in their own way.”

crimaldi, who is also the lead investigator for the odor to action network , a group of 80 scientists around the world working to understand how animal brains use smells to make behavioural decisions, says his team’s technology can help improve ventilation and disinfection strategies and promote healthy and sustainable buildings.

karen hawthorne is a toronto-based writer.

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karen hawthorne

karen hawthorne worked for six years as a digital editor for the national post, contributing articles on health, business, culture and travel for affiliated newspapers across canada. she now writes from her home office in toronto as a freelancer, and takes breaks to bounce with her son on the backyard trampoline and walk bingo, her bull terrier.

video of germ-filled toilet spray shows why we should all wear masks in a public bathroom

there is health risk just walking into a restroom where many toilets have been flushing, according to study author john crimaldi, who says he is now more likely to mask up when using public toilets.

everyone should put the lid down

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“i am more inclined to wear a mask in a public restroom”

plumes “squirt out the side under the lid”

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video of germ-filled toilet spray shows why we should all wear masks in a public bathroom

there is health risk just walking into a restroom where many toilets have been flushing, according to study author john crimaldi, who says he is now more likely to mask up when using public toilets.

everyone should put the lid down

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