‘Aerosolized Droplets’ Hang in the Air After Toilet Flush

By Cara Murez
HealthDay reporter

THURSDAY, April 22, 2021 (HealthDay News) – If you are in a public washroom you may not want to stay too long as there are plenty of airborne pathogens lying around as well.

Researchers at Florida Atlantic University’s College of Engineering and Computer Science performed flush tests in public restrooms with both a toilet and a urinal.

“After about three hours of testing involving over 100 rinses, we saw a substantial increase in the aerosol levels measured… with the total number of droplets generated in each rinse test going up to tens of thousands,” said study co-author Siddhartha Verma. He is an assistant professor of oceanic and mechanical engineering at the university.

Pathogens that can cause Ebola virus, norovirus, and even COVID-19 can be found in standing water, as well as in urine, stool and vomit. According to the research team, the flushing can generate large amounts of airborne germs, depending on the flushing power, toilet design and water pressure.


For the study, the researchers placed a particle counter at different heights of the toilet and urinal to capture the size and number of droplets generated by the flush. They did the same with a covered toilet. (Few public toilets in the United States have lids and the urinals are not covered.)

Droplets were detected at heights of up to 1.50 meters for 20 seconds or more after starting a rinse, the results showed.

Investigators detected fewer droplets when the lid was closed before rinsing, but the number was not much less. This suggests that aerosol droplets escaped through small spaces between the lid and the seat.

Verma noted that the toilet and urinal generated large amounts of droplets smaller than 3 microns, posing a significant risk of transmission if they contained infectious microorganisms.

“Due to their small size, these droplets can stay in suspension for a long time,” Verma explained in a college press release.

The researchers reported a 69.5% increase in measured levels of particles between 0.3 and 0.5 micrometers in size; an increase of 209% for particles of 0.5 to 1 micrometer; and a 50% increase for particles between 1 and 3 micrometers.


According to study co-author Masoud Jahandar Lashaki, “The significant build-up of aerosol droplets generated by flushing over time suggests that the ventilation system was not effective in removing them from the confined space, even. if there was no noticeable lack of air circulation in the toilet. “Lashaki is an assistant professor of civil, environmental and geomatics engineering.

“In the long term, these aerosols could increase with the updrafts created by the ventilation system or by people moving in the toilet,” he explained.

Even larger aerosols can add risks, the study authors noted.

Co-author Manhar Dhanak, president of Oceanic and Mechanical Engineering, pointed out that the study suggests that “incorporating adequate ventilation into the design and operation of public spaces would help prevent the build-up of aerosols in high traffic areas such as public toilets. “

The toilets were thoroughly cleaned and closed 24 hours before the experiments were conducted, and the ventilation system was functioning normally.

The report was recently published in the journal Fluid physics.

Stella Batalama is the Dean of Engineering and Computer Science at the college. She concluded that “aerosol droplets play a central role in the transmission of various infectious diseases, including COVID-19, and this latest research from our team of scientists provides additional evidence to support the risk of transmission of infection. in confined and poorly ventilated spaces. ”


More information

The US Centers for Disease Control and Prevention has more on COVID-19.

SOURCE: Florida Atlantic University, press release, April 20, 2021

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