Visualization of "toilet plumes" may lead to cleaner, safer bathrooms

Visualization of "toilet plumes" may lead to cleaner, safer bathrooms
The toilet used in the study just contained clean tap water ... but such wouldn't be the case in a real-word flushing scenario
The toilet used in the study just contained clean tap water ... but such wouldn't be the case in a real-word flushing scenario
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The toilet used in the study just contained clean tap water ... but such wouldn't be the case in a real-word flushing scenario
The toilet used in the study just contained clean tap water ... but such wouldn't be the case in a real-word flushing scenario
The lab setup utilized in the study
The lab setup utilized in the study

You've probably heard it before – if you don't put the lid down on the toilet, droplets of filth will fly out when you flush it. Scientists have now visualized that process for the first time, in hopes of reducing it with better toilet designs.

For at least 60 years now, it has been known that if you flush a toilet with its lid up, a plume of aerosolized toilet-water droplets will rise up out of the bowl. Those airborne droplets can then drift onto other surfaces in the bathroom, potentially spreading pathogens such as E. coli bacteria.

So far, we've only known about this phenomenon via studies in which scientific instruments detected the presence of those droplets. Now, however, researchers at the University of Colorado-Boulder have gotten some rather unsettling pictures of it.

Led by Prof. John Crimaldi, the scientists started out by setting up a brand new lidless toilet, of the type commonly used in North American public restrooms. It was connected to a conventional flushing mechanism, and filled with clean tap water.

The lab setup utilized in the study
The lab setup utilized in the study

Two green lasers were then aimed on and above the toilet. One shone continuously, in order to show where in three-dimensional space the droplets were located, while the other laser rapidly pulsated, to measure the speed and direction of their movements. Two cameras recorded HD stills and video while the toilet was flushed – and the result was much more dramatic than anticipated.

"We had expected these aerosol particles would just sort of float up, but they came out like a rocket," said Crimaldi.

For the most part, the droplet plume moved upward and back towards the lab's rear wall. That said, much of it also rose straight up until it was blocked by the ceiling, at which point it spread forward into the room. And importantly, when the size of the droplets was measured using a device known as an optical particle counter, it was found that the smallest – which remain airborne for the longest – were small enough to evade a person's nose hairs and make their way into the lungs.

It's also worth noting that the experiment was conducted in an open, relatively empty space, free of bathroom stall walls and people moving around. Crimaldi believes that the presence of both could make the problem worse, facilitating dispersal of the droplets.

It is now hoped that by being able to visualize the plume in this fashion, the problem can be better addressed moving forward ... and hopefully also, people who see the images will be more motivated to put the lid down when flushing at home.

"Our methodology could be used to evaluate new toilet bowl and flush valve designs that reduced the upward ejection of aerosol particles while still remaining effective at flushing waste downwards," Crimaldi told us. "The methods could also be used to evaluate new ventilation and UV disinfection systems that could reduce exposure risk to plumes that are ejected."

There's more information in the following video.

Shining a light on what comes up when you flush

Source: University of Colorado-Boulder

Jim Powell
From the picture, it seems that the water supply comes from a least 2 metres. The experiment should be repeated with a low head of water as per a normal cistern
Most modern toilets in Japan have a deodorising system that sucks out odours from the bowl. A fan turns on when you sit down and remains on for a period after you get up off the seat.
Jim, are you suggesting cheating?
The word 'aerosals' seems appropriate to the subject (LOL)
Captain Danger
Reminds me of the Fecal glasses skit I saw on SNL many years back.
even showed all the fecal matter as glowing green.
So our already under-challenged immune systems must be subjected to even fewer opportunities to increase their capability?
I doesn't matter if the lid is up or down. Toilet seats have a 1/2" gap between the seat and the bowl. Putting the lid down would just make the aerosol come out horizontally.
Bob Flint
Putting it into perspective, the effluence came out of your body, so little harm to yourself, it's the next person in the stall beside you. Worst yet are the hand dryers, that blast partially washed hands germs for many meters in all directions. We had paper towels, during the last 2 years, now switched back to those noisy, harmful, inefficient, as far as time to actually properly dry your hands, standing there takes 30 to 45 seconds. I'm back at my desk working as I used to dry with paper while walking on my way back, way before that saving several minutes every day times 500 people. 25 hours of non productive work daily, that's if people even bother to stay and dry them, much worse, don't even wash....always wipe the seat!
A solution in search of a problem. "Potentially spreading pathogens"--it doesn't happen via toilet flushing. You may think it's gross, but we live in a germ-filled world generally safely. What a joke and waste of resources. University people needed to find justification for grant money.
Brian M
Perhaps we need to take a cue from cats - and use a litter tray!
Given that humanity seems to have survived since the 1850's after the rise of the flushing loo's, suspect this is more of a yuck factor than a real danger to most of humankind.

Perhaps the matter of lid up or down is more determined by gender and one's risk appetite to mobile phones!
What kind of jet assist are they using on that toilet? It was at least 90dB! Was it an air or water jet? All toilets I've bought use gravity flush systems.