FLORIDA ATLANTIC UNIVERSITY
Summary Aerosolized droplets play a central role in the transmission of various infectious diseases, including Legionnaires’ disease, the gastroenteritis-causing norovirus, and, more recently, COVID-19. Respiratory droplets are known to be the most important source of COVID-19 transmission; however, alternative routes may exist given the discovery of a small number of viable viruses in urine and fecal samples. The washing of biomaterial can lead to the aerosolization of microorganisms; Therefore, there is a possibility that bioaerosols generated in public restrooms may pose a concern for COVID-19 transmission, especially as these areas are relatively confined, experience heavy traffic, and may suffer from inadequate ventilation. To quantify the extent of aerosolization, we measured the size and quantity of droplets generated by flushing toilets and urinals in a public restroom. The results indicate that the particular designs tested in the study generate a large number of droplets in the size range of 0.3 μm to 3 μm, which can reach heights of at least 1.52 m. Covering the toilet reduced aerosol levels, but did not eliminate them completely, suggesting that aerosol droplets escaped through small gaps between the cover and the seat. In addition to consistent increases in aerosol levels immediately after flushing, there was a notable increase in ambient aerosol levels due to droplet accumulation from multiple discharges performed during testing. This highlights the need to incorporate adequate ventilation into the design and operation of public spaces, which can help prevent aerosol accumulation in high occupancy areas and mitigate the risk of transmission of airborne diseases. |
Flushing a toilet can generate large amounts of aerosols containing microbes, depending on the design, water pressure, or flushing capacity of the toilet. A variety of pathogens are usually found in stagnant water, as well as in urine, feces, and vomit. When widely dispersed through aerosolization, these pathogens can cause Ebola, norovirus resulting in violent food poisoning, as well as COVID-19 caused by SARS-CoV-2.
Respiratory droplets are the most important source of COVID-19 transmission; however, alternative routes may exist given the discovery of a small amount of viable virus in urine and fecal samples.
| Public restrooms are of particular concern for COVID-19 transmission 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 put fluid physics to the test again to investigate droplets generated when flushing a toilet and urinal in a public restroom under normal ventilation conditions. . To measure droplets, they used a particle counter placed at various heights of the toilet and urinal to capture the size and number of droplets generated when flushing.
The results of the study, published in the journal Physics of Fluids , demonstrate how public bathrooms 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 a lid or lid. Most public restrooms in the United States are often not equipped with toilet seat covers and urinals are not covered.
For the study, researchers obtained data from three different scenarios: toilet flushing; covered toilet and urinal flush. They examined the data to determine the increase in aerosol concentration, the behavior of droplets of different sizes, the height of the droplets, and the impact of covering the toilet. Ambient aerosol levels were measured before and after experiments were performed.
"After approximately three hours of testing involving more than 100 discharges, we found a substantial increase in aerosol levels measured in the ambient environment with the total number of droplets generated in each discharge test up to tens of thousands," said Siddhartha Verma. . , Ph.D., co-author and assistant professor in the Department of Mechanical and Ocean Engineering at FAU. "Both the toilet and urinal generated large quantities of droplets less than 3 micrometers in size, posing a significant transmission risk if they contain infectious microorganisms. Due to their small size, these droplets can remain suspended for a long time ."
Droplets were detected at heights up to 5 feet for 20 seconds or more after initiating the discharge. The researchers detected fewer airborne droplets when the toilet was flushed with the lid closed , although not by much, suggesting that the aerosolized droplets escaped through small gaps between the lid and the seat.
"The significant accumulation of aerosol droplets generated by the discharge over time suggests that the ventilation system was not effective in removing them from the enclosed space even though there was no discernible lack of airflow within the bathroom," he said. Masoud Jahandar Lashaki, Ph.D. , co-author and assistant professor in the Department of Civil, Environmental and Geomatic Engineering at FAU. "In the long term, these aerosols could rise with updrafts created by the ventilation system or by people moving around in the bathroom."
There was a 69.5 percent increase in measured levels for 0.3 to 0.5 micrometer particles, a 209 percent increase for 0.5 to 1 micrometer particles, and a 50 percent increase for 1 to 3 micrometers. Apart from smaller aerosols, comparatively larger aerosols also pose a risk in poorly ventilated areas even though they experience stronger gravitational settling. They often undergo rapid evaporation into the environment and the resulting decreases in size and mass, or the eventual formation of droplet nuclei, can allow microbes to remain suspended 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-occupancy areas such as public restrooms," said Manhar Dhanak, Ph.D., co-author, chair. from the Department of Oceanic and Mechanical Engineering, 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 to certain codes. It could simply be a matter of redirecting airflow based on the layout of the bathrooms."
During the 300-second sampling, the toilet and urinal were manually flushed five different times at the 30, 90, 150, 210, and 270-second marks, with the flush handle depressed for five consecutive seconds. The bath was thoroughly cleaned and closed 24 hours before conducting the experiments, with the ventilation system operating normally. The temperature and relative humidity inside the bathroom were 21 degrees Celsius (69.8 degrees Fahrenheit) and 52 percent, 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 infection transmission in confined, poorly ventilated spaces." said Stella Batalama. Ph.D., dean of the Faculty of Engineering and Informatics.
