Scientists have long known that flushing a toilet spews an aerosol mist of particles (including pathogens from feces) into the bathroom air. In new research from the University of Colorado, Boulder, engineers used a laser to illuminate the aerosol plume emerging from a commercial toilet in a public restroom. See the video above. According to the research, the airborne particles spray as high as 5 feet into the air at a very high rate of speed. Closing the lid before flushing would certainly help but unfortunately most public toilets lack lids. From CU Bolder Today:
"If it's something you can't see, it's easy to pretend it doesn't exist. But once you see these videos, you're never going to think about a toilet flush the same way again," said John Crimaldi, lead author on the study and professor of civil, environmental, and architectural engineering. "By making dramatic visual images of this process, our study can play an important role in public health messaging."
Researchers have known for over 60 years that when a toilet is flushed, solids and liquids go down as designed, but tiny, invisible particles are also released into the air. Previous studies have used scientific instruments to detect the presence of these airborne particles above flushed toilets and shown that larger ones can land on surrounding surfaces, but until now, no one understood what these plumes looked like or how the particles got there.
Understanding the trajectories and velocities of these particles—which can transport pathogens such as E. coli, C. difficile, noroviruses and adenoviruses—is important for mitigating exposure risk through disinfection and ventilation strategies, or improved toilet and flush design. While the virus that causes COVID-19 (SARS-CoV-2) is present in human waste, there is not currently conclusive evidence that it spreads efficiently through toilet aerosols.
"People have known that toilets emit aerosols, but they haven't been able to see them," said Crimaldi. "We show that this thing is a much more energetic and rapidly spreading plume than even the people who knew about this understood."