“It’s Like A Volcano Erupting”: New Research Illuminated The Clouds Of Germy Microparticles That Spew Up After You Flush Commercial Toilets

After you use the restroom and reach for the handle to flush, do you stop and make sure to close the toilet lid first?
Well, after learning about this new research conducted by engineers from the University of Colorado Boulder, you might never be able to flush the same way again.
The team of engineers, led by professor of hydrology John Crimaldi, launched a study surrounding the “spray” of commercial toilets and what they found would send most germaphobes into a panic.
Every time a commercial toilet is flushed, a Vesuvius-like cloud of aerosol particles and tiny droplets are released from the bowl– reaching over five feet above the toilet seat.
Now, this plume of microparticles is invisible to the human eye. However, when the engineers illuminated a flushing toilet using green lasers, what spewed out basically resembled a puff of microscopic confetti.
And even though the team only flushed toilets that contained clean water, we know that is not the case in virtually all commercial restrooms.
“We all were astonished. I said, ‘Oh my god, that’s what happens?'” Crimaldi recalled his reaction to the discovery.
As a professor of hydrology, he is an expert on fluid mechanics. In other words, how water and air transport other materials that flow along with them.
In the past, Crimaldi has studied how animals interpret odor particles traveling through the air to gather information and analyzed the various ways ocean currents distribute reproductive agents to fertilize corals.

Drobot Dean – stock.adobe.com – illustrative purposes only, not the actual person
Although one of Crimaldi’s colleagues, Karl Linden, is an environmental engineer who specifically studies ultraviolet light’s disinfectant properties.
So, after Linden pushed Crimaldi to turn his focus to toilet bowls, the two Boulder scientists teamed up to conduct this study together.
Linden first got the idea of studying toilet bowls after brainstorming to find the ideal germy test case for a surface disinfectant based on UV technology.
Then, after thinking about the most common places people are exposed to viruses and pathogens, he settled on restrooms.
More specifically, though, Linden envisioned the toilets located in commercial restrooms– which are typically tankless, lidless, and have a lever most people press with their foot as opposed to a handle.
And in North America, most of these commercial toilets actually have a flushometer-style valve. This means that pressure is relied upon to force water back into the bowl instead of gravity– ultimately causing a high-powered flush that can leave a microscopic cloud of vapors behind.
Of course, past research has confirmed that public restroom stalls are breeding grounds for fecal bacteria.
So, Linden had a hunch that UV light could be an effective answer for disinfection.
Before this technology could be deployed, though, he realized that he needed a more concrete understanding of how these tiny pathogens travel throughout space. Thus, Linden went to Crimaldi for help, and the toilet study was born.
At Crimaldi’s fluid mechanics lab, he holds a yearly summer tradition in which one week is dedicated to tackling a small scientific challenge of sorts.
This challenge is not provided with any funding, and there is actually no pressure to publish any official findings. So, he believed this toilet mystery was a great fit.
First, the engineers actually installed a working commercial toilet on top of a metal frame inside the fluid mechanics lab. This process was easier than lugging all of their equipment to the nearest bathroom since the installed porcelain throne could be perfectly aligned with their lasers.
Then, after calibrating their green lasers and finally flushing the toilet, the results defied their expectations.
“It’s like a volcano erupting. Some of us were stunned into silence. Some of us were just laughing out of disbelief, and also kind of like, ‘Oh my God, we are really on to something here,” Crimaldi explained.
Afterward, the team decided to train a pulsed laser and a few scientific cameras onto the spray in order to calculate the speed of each water particle.
And ultimately, they found that aerosols from this toilet plume can reach a max velocity of nearly 4.5 miles per hour.
Yes, once airborne, these microparticles do eventually settle down. However, even almost eight seconds after flushing the toilet, the researchers found that airborne particles still hover over five feet above the toilet bowl’s rim. For reference, this is well above nose level for most adults.
So now, with these gross findings, the engineers are starting to rethink their bathroom safety precautions.
“I certainly am much more inclined after seeing these videos to wear a mask in a public restroom than I might have been before,” Crimaldi admitted.
It is also crucial to reiterate that the study was conducted using toilets filled with clean water. But, once human fecal matter, urine, and toilet paper are added into the mix, Crimaldi suspects the microscopic flume might be even more chaotic.
“I have an intuitive sense that the presence of solids might exacerbate the problem because there are just additional things for the water to impinge on and to create more opportunities for this energetic mixing of fluids,” he explained.
So now, the researchers are hopeful that their study’s findings will serve as a launchpad for future research in the travel of pathogens and bacteria in aerosol clouds.
Plus, depending on those results, new questions regarding how to increase public restrooms’ safety–whether via new disinfectant strategies or even toilet bowl redesigns– will have to be answered.
To read the study’s complete findings, which have since been published in Scientific Reports, visit the link here.
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