A powerful green laser helps visualize the aerosol plumes from a toilet when it’s being flushed. Photos by Patrick Campbell/CU Boulder.
HQ team
December 10, 2022: Time and again, you have been told to flush the toilet with the lid closed as water droplets tend to escape in the air and contaminate the nearby surfaces. Scientists have now visualized that process in hopes of better-designed toilets that reduce the risk of contamination from flying filth.
Researchers at the University of Colorado-Boulder led by Prof. John Crimaldi have visually recorded the phenomenon. The team used a brand-new lidless toilet, commonly used in public restrooms and connected it to a conventional flushing mechanism.
They then aimed two green lasers at the toilet. One shed constant light, while the other laser rapidly pulsated to measure the speed and direction of the droplet movements. Two cameras were used to record the flushing in high resolution. The result was dramatic.
“We had expected these aerosol particles would just sort of float up, but they came out like a rocket,” said Crimaldi.
The airborne water particles mostly projected upwards and curved back towards the rear wall. Some went straight up to the ceiling and spread out into the room.
The experiment was straight-up done without the normal scenario in a restroom. These real-life variables could all exacerbate the problem, said Crimaldi.
An optical particle counter, a device that sucks a sample of air in through a small tube and shines a light on it, was used to study the droplets. Smaller particles not only float in the air for longer but can escape nose hairs and reach deeper into one’s lungs—making them more hazardous to human health—so knowing how many particles and what size they are was also important.
The research team hopes that the results will force public health and plumbing designers to improve the design and find better disinfection and ventilation strategies to reduce exposure risk to pathogens in public restrooms.
“None of those improvements can be done effectively without knowing how the aerosol plume develops and how it’s moving,” said Crimaldi. “Being able to see this invisible plume is a game-changer.”
Is the SARS-CoV-2 virus found in toilet flush?
Previous epidemiologic studies have found evidence implicating toilet plumes in disease outbreaks on cruise ships, in restaurants, on airplanes, and within apartment complexes. Some pathogens that reside and thrive in faeces can survive for long on surfaces, such as the norovirus. It is also resistant to some common cleaning agents.
Studies are still ongoing to determine if the SARS-CoV-2 virus is found in toilet flush droplets.
This query merits further investigation, but we have to acknowledge that live virus may sometimes be present in faeces, though it’s possible this occurs only rarely or only in the case of very severe illness, say experts.
Bottom line? “flush and rush” is probably the best strategy in any public restroom at any time, pandemic or not. Do not forget to wash your hands on your way out!