Flushing a public toilet? Do not delay, as aerosol drops do

Depending on the design, water pressure or flushing power of the toilet can generate large amounts of microbial-containing aerosols. A variety of pathogens are commonly found in stagnant water, as well as in urine, feces and vomit. When spread widely by aerosolization, it can cause Ebola, norovirus, which causes violent food poisoning, as well as COVID-19 caused by SARS-CoV-2.

Respiratory droplets are the major source of transmission for COVID-19, but alternative routes may exist, given the discovery of a small number of viable viruses in urine and fecal samples. Public toilets are of particular concern for the transmission of COVID-19 because they are relatively restricted, experience heavy foot traffic and may not have adequate ventilation.

A team of scientists from Florida Atlantic University College of Engineering and Computer Science once again tested the physics of liquids to investigate droplets generated by flushing a toilet and a urinal in a public toilet under normal ventilation. conditions. To measure the droplets, they use a particle counter placed at different heights of the toilet and urinal to capture the size and number of droplets generated during flushing.

Results of the study, published in the journal Physics of liquids, demonstrates how public toilets can serve as hotspots for the transmission of airborne diseases, especially if they do not have adequate ventilation or if toilets do not have a lid or cover. Most public restrooms in the United States are often not equipped with toilet seat covers and are urinally covered.

For the study, researchers obtained data from three different scenarios: toilet flush; covered toilet flush and urinal flush. They examined the data to determine the increase in aerosol concentration, the behavior of droplets of different sizes, how high the droplets rose and the impact of covering the toilet. Environmental aerosol levels were measured before and after the experiments.

“After about three hours of testing with more than 100 rinses, we found a significant increase in the measured aerosol levels in the ambient environment, with the total number of droplets generated in each rinse test up to tens of thousands,” said Siddhartha Verma. , Ph.D., co-author and an assistant professor in FAU’s Department of Ocean and Mechanical Engineering. “Both the toilet and urinal have generated large amounts of droplets that are smaller than 3 micrometers in size. This poses a significant transmission risk if they contain infectious microorganisms. Due to their small size, these droplets can hang for a long time.”

The droplets were detected for 20 seconds or longer at altitudes of up to 5 feet after flushing was started. Researchers detected a smaller number of droplets in the air when the toilet was flushed with a closed lid, though not much, suggesting that aerosolized droplets escaped through small gaps between the lid and the seat.

“The significant accumulation of flush-generated droplets over time indicates that the ventilation system was not effective in removing it from the enclosed space, although there was no noticeable lack of airflow in the toilet,” said Masoud Jahandar Lashaki, Ph.D. D. , co-author and an assistant professor in the FAU’s Department of Civil, Environmental and Geomatic Engineering. “In the long run, these aerosols can get up with work done by the ventilation system or by people moving around in the toilet.”

There was a 69.5 percent increase in measured levels for particles from 0.3 to 0.5 micrometers, an increase of 209 percent for particles from 0.5 to 1 micrometer, and a 50 percent increase for particles. from 1 to 3 micrometers. Apart from the smallest aerosols, relatively larger aerosols also pose a risk in poorly ventilated areas, even though they experience heavy gravity. They often undergo rapid evaporation in the environmental environment and the consequent decrease in size and mass, or the eventual formation of droplet nuclei, can leave microbes hanging for several hours.

“The study suggests that the use of adequate ventilation in the design and operation of public spaces would help prevent aerosol accumulation in high-occupancy areas such as public toilets,” said Manhar Dhanak, Ph.D., co-author, chair of the FAU ‘s Department of Ocean and Mechanical Engineering, and Professor and Director of SeaTech. “The good news is that it is not always necessary to overhaul the entire system, as most buildings are designed according to certain codes. It can only be to redirect the airflow based on the toilet’s layout.”

During the 300-second sampling, the toilet and urinal were rinsed by hand five different times at the 30, 90, 150, 210, and 270-second point, with the rinsing handle for five consecutive seconds. The toilet was deeply cleaned and closed 24 hours before the experiments, while the ventilation system was operating normally. The temperature and relative humidity in the toilet were 21 degrees Celsius (69.8 degrees Fahrenheit) and 52 percent, respectively.

“Aerosolized droplets play a key role in the transmission of various infectious diseases, including COVID-19, and this latest research by our team of scientists provides additional evidence to support the risk of transmission of infections in confined and poorly ventilated areas,” he said. Stella Batalama said. Ph.D., dean of the College of Engineering and Computer Science.