Scientists have used a combination of green lasers and cameras to shed light on the effect a toilet flushes on its surroundings – and we doubt you’ll be lucky enough to leave the lid open while flushing after you’ve seen the results.
The video clip made by a team of researchers from the University of Colorado at Boulder, in the United States, shows a burst of small water droplets, invisible to the naked eye, flying out of the toilet bowl after the flush. It’s kind of super gross, if you think about what might be hanging in those tiny drops.
“People knew the toilets were emitting aerosols, but they couldn’t see them,” says civil and environmental engineer John Crimeldifrom the University of Colorado at Boulder.
“We’re showing this thing to be a much more energetic, fast-spreading plume than even people who were aware of it realized.”
As the researchers themselves admit, there’s an “ick factor” here – heightened by the eerie green glow of the laser light – but there’s also an important message about bathroom hygiene, to both in private homes and public toilets which are often uncovered.
Crimeldi and his fellow researchers are keen to point out that they are not epidemiologists, so there are no precise calculations here in terms of the potential for the disease to spread. However, their display provides a graphical element to other studies that attempt to estimate the qualities of bacteria-laden aerosols.
Whereas previous studies have clearly established the possibility of particles escaping from the toilet bowl during flushing, there is still a lot of uncertainty as to how these particles move and where they might go.
Two lasers were used: one shining continuously on the toilet from above illuminating the scene, and one sending rapid pulses of light onto the top of the toilet bowl to highlight the movement of the particles. High resolution images were captured with cameras at the same time.
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The researchers showed droplets reaching heights of up to 1.5 meters (4.9 feet) after a flush, moving at speeds exceeding two meters (6.6 feet) per second in some places. Larger droplets settle faster on services, while smaller ones can linger in the air for several minutes, the researchers showed.
“We expected these aerosol particles to float somehow, but they came out like a rocket,” Crimeldi said.
“The purpose of the toilet is to effectively remove waste from the bowl, but it’s also the opposite, which sprays a lot of the contents upwards.”
There was nothing in the toilet bowl except water during the experiment. There was also no cubicle surrounding the restroom, nor were there people moving around like there might be in a public restroom. In real life, all of these variables would affect droplet travel.
However, even in this rather artificial setting, there’s clearly plenty of room for water – and whatever it carries – to get out of the toilet bowl, where it could get stuck to surfaces and clothing.
Researchers believe more should be done to reduce the risk of pathogens like Escherichia coli, Clostridium difficilenoroviruses and adenoviruses are spreading in public restrooms, with improved design, ventilation and disinfection approaches all options.
For these improvements to work effectively, it’s crucial to know where the water is moving, which this study shows more dramatically than ever – and in ways we’ll never forget.
“If it’s something you can’t see, it’s easy to pretend it doesn’t exist,” says Crimaldi. “But once you see these videos, you’ll never think of a toilet flush the same way again.”
“By creating dramatic visual images of this process, our study can play an important role in public health messaging.”
The research has been published in Scientific reports.
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