Flushing a toilet can generate large amounts of aerosol containing microbes depending on the design, water pressure or flushing power of the toilet. A variety of pathogens are commonly found in standing water as well as in urine, feces, and vomit. When widely dispersed by aerosolization, these pathogens can cause Ebola virus, the norovirus that causes severe food poisoning, as well as COVID-19 caused by SARS-CoV-2.
Respiratory droplets are the main source of transmission of COVID-19, however, alternative routes may exist given the discovery of a small number of viable viruses in urine and stool samples. Public toilets are of particular concern for the transmission of COVID-19 because they are relatively confined, experience heavy foot traffic and may not have adequate ventilation.
A team of scientists from Florida Atlantic University’s College of Engineering and Computer Science once again put fluid physics to the test to study droplets generated by flushing toilets and a urinal in public restrooms under normal ventilation conditions. To measure the droplets, they used a particle counter placed at different heights of the toilet and urinal to capture the size and number of droplets generated during the flush.
The results of the study, published in the journal Physics of Fluids, demonstrate how public toilets could serve as hotbeds for the transmission of airborne diseases, especially if they do not have adequate ventilation or if the toilets do not have cover or cover. Most public toilets in the United States often do not have toilet seat covers, and urinals are not covered.
For the study, the researchers obtained data from three different scenarios: toilet flushing; covered flush and urinal flush. They looked at the data to determine the increase in aerosol concentration, the behavior of droplets of different sizes, the height of droplet rise and the impact of the toilet cover. The ambient aerosol levels were measured before and after the performance of the experiments.
“After about three hours of testing involving more than 100 rinses, we saw a substantial increase in the aerosol levels measured in the ambient environment, with the total number of droplets generated in each rinse test going up to tens of thousands. Said Siddhartha Verma, Ph.D., co-author and assistant professor in the Department of Oceanic and Mechanical Engineering at FAU. “The toilet and urinal generated large amounts of droplets smaller than 3 micrometers, posing a significant risk of transmission if they contain infectious microorganisms. Due to their small size, these droplets can stay in suspension for a long time. “
Droplets were detected at heights of up to 1.50 meters for 20 seconds or more after the start of flushing. Researchers detected a smaller number of droplets in the air when the toilet was flushed with a closed lid, but not by many, suggesting that aerosol droplets escaped through small spaces between the lid and the seat. .
“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 though there was no noticeable lack of circulation. air in the toilet, ”said Masoud Jahandar Lashaki, Ph.D., co-author and assistant professor in the Department of Civil, Environmental and Geomatics Engineering at FAU. “In the long term, these aerosols could increase with updrafts created by the ventilation system or by people moving in the toilet.”
There was a 69.5% increase in measured levels for 0.3 to 0.5 micron size particles, a 209% increase for 0.5 to 1 micron size particles, and a 50% increase for particles of size 1 to 3 micrometers. In addition to the smaller aerosols, the comparatively larger aerosols also pose a risk in poorly ventilated areas, even if they experience stronger gravitational settling. They often undergo rapid evaporation into the surrounding environment and the resulting decreases in size and mass, or the eventual formation of droplet nuclei, can allow microbes to remain in suspension for several hours.
“The study suggests that incorporating adequate ventilation into the design and operation of public spaces would help prevent aerosol buildup in high traffic areas such as public toilets,” said Manhar Dhanak, Ph.D., co-author, chairman of the FAU Ocean and Mechanical Engineering Department, and Professor and Director of SeaTech. “The good news is that it may not always be necessary to overhaul the entire system, as most buildings are designed according to certain codes. It may simply be a matter of redirecting the airflow into depending on the arrangement of the toilets. “
During the 300 second sampling, the toilet and urinal were manually flushed five times at 30, 90, 150, 210, and 270 seconds with the flush handle held down for five consecutive seconds. The toilets were thoroughly cleaned and closed 24 hours before the experiments were carried out, with the ventilation system functioning normally. The temperature and relative humidity in the toilet were 21 degrees Celsius (69.8 degrees Fahrenheit) and 52%, respectively.
“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 spaces and poorly ventilated, ”said Stella Batalama, Ph.D., dean of the College of Engineering and Computer Science.
Co-authors of the study are Jesse H. Schreck, lead author and graduate student in the Department of Oceanic and Mechanical Engineering; and Javad Hashemi, Ph.D., associate dean for research and professor in the Department of Oceanic and Mechanical Engineering.