Newest coronavirus threat: "Toilet plumes"

The virus has forced us to rethink so many assumptions of modern life already. Now we have another: “If it’s yellow, let it mellow. If it’s brown, flush it down.”


What if flushing down the brown might kill you?

Personally, I’d rather die than use an unflushed public toilet. But here’s a PSA from scientists to feed our collective anxiety until the vaccine arrives: If the person who used the toilet before you happened to “shed” a little coronavirus in their waste, then — theoretically — particles of the virus may be floating around in the stall when you step in, suspended in aerosolized water droplets as high as three feet in the air after being ejected from the bowl by the act of flushing.

You’re walking into a potentially lethal dookie mist when you step in there, in other words, generated by what scientists politely call a “toilet plume.”

Researchers say the virus’s presence in excrement and the gastrointestinal tract raises the prospect of transmission via toilets, because many covid-19 patients experience diarrhea or vomiting. A study of air samples in two hospitals in Wuhan, China, found that although coronavirus aerosols in isolation wards and ventilated patient rooms was very low, “it was higher in the toilet areas used by the patients.”

Wang decided to use computer models to simulate toilet plumes while isolating at home, per Chinese government orders, and thinking about how a fluids researcher “could contribute to the global fight against the virus.”

The resulting study was published Tuesday in the journal Physics of Fluids. It found that flushing of both single-inlet toilets, which push water into the bowl from one port, and annular-inlet toilets, which pour water into the bowl from the rim’s surrounding edge with even greater energy, result in “massive upward transport of virus.” Particles can reach heights of more than three feet and float in the air for more than a minute, it found.


More details from the Times, which deserves congratulations for working the phrase “fecal-oral route” into its story about the findings:

A computer simulation of the toilet flushing mechanism showed that when water pours into the toilet and generates a vortex, it displaces air in the bowl. These vortices move upward and the centrifugal force pushes out about 6,000 tiny droplets and even tinier aerosol particles.

Depending on the number of inlets in the toilet, flushing can force anywhere from 40 to 60 percent of the produced aerosols high above the seat.

“It’s very alarming,” said Ji-Xiang Wang, who studies fluid dynamics at Yangzhou University and was a co-author of the study.

Bathrooms typically aren’t well-ventilated either. What ends up in the air in a small enclosed space is apt to hang around there.

How do we solve this dilemma? I’ll give you five possibilities, in order of increasing personal preference.

1. Lids. We could just, you know, put lids on all public toilets and close them before we flush. That’s what the study authors suggest.

2. “Flush and run,” as one expert described it to WaPo. I’m not entirely clear on that, though. What you’re worried about here is being infected by virus that was left in the toilet by the last person to use it before you. When you flush, you’re only aerosolizing your own, uh, droppings, from which you have no reason to run. Right? Or are we facing a scenario where particles from multiple previous users are still in the bowl after several flushes and could be kicked up into your face by your own flush?


I don’t want to think about it anymore. Moving on.

3. Just wait 90 seconds or so to give the aerosolized particles time to “settle” before you step in. The first excerpt quoted above says they can hang around in the air for “more than a minute”; let’s study that further and figure out how long it takes for them to descend so that we can wait them out. It’s not like you’re in a rush normally to enter a stall in which someone’s just finished “dropping the kids off at the pool.” Give the air a minute to clear before stepping in. Problem solved.

4. Depends. There’s no reason why masks should be the only supplemental attire we don in the age of coronavirus.

5. Outdoor latrines. No flushing, perfectly ventilated. Plus, it’d build esprit de corps to cop a squat in the open air next to perfect strangers. If we’re going to go all-out to defeat the virus, let’s really do it.

Alternately, we could just keep doing what we’re doing, pretending that there is no virus and returning to normal with predictably stupid consequences. Here’s quickie video from the LA Times of a nightclub in Arizona, where attendees do not give an F about whether they get infected or which older people in their social orbit might die when they pass the virus along. Exit quotation from a young hedge-fund manager named Austin, perfectly in character: “If you’re at risk or you’re old or you’re sick, you need to stay home… If you’re healthy and young, you need to be out here spending money to help the economy.”


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John Stossel 1:00 PM | June 15, 2024