Study showed how toilets can become a breeding ground for the spread of airborne diseases, especially if the toilet does not have a lid or adequate ventilation
After knowing the conclusions of this study, you probably won’t forget anymore. Urine and feces can contain remains of a wide variety of pathogens, including SARS-CoV-2. And flushing from a toilet, depending on the design, water pressure, or flush capacity of the appliance, can generate large amounts of aerosols containing microbes.
A team of scientists from Florida Atlantic University’s College of Engineering and Computer Science has put fluid physics to the test to investigate the droplets generated by flushing a toilet and urinal into a public bathroom under normal ventilation conditions. They used a particle counter placed at various heights of the toilet to capture the size and number of drops caused by flushing.
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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 bath were 21 and 52%, respectively.
The results of the study, published in the journal “Physics of Fluids“, demonstrated how public toilets may serve as a breeding ground for the spread of airborne diseases, especially if they do not have adequate ventilation or if the toilets do not have lids.
Most public toilets in the United States are often not equipped with this system and it is not usual for urinals to be covered.
For the study, the researchers obtained data from three different scenarios: toilet flushing; toilet flush with lid, and urinal flush. They examined the data to determine the increase in aerosol concentration, the behavior of different-sized droplets, the height of the droplets, and the impact of covering the volcano. The ambient levels of aerosols were measured before and after conducting the experiments.
“After approximately three hours of tests involving more than 100 shocks, we found a substantial increase in aerosol levels measured in the environment with a total number of droplets generated in each shock test of up to tens of thousands,” explains Dr. Siddhartha Verma, co-author of the study and assistant professor in the Department of Mechanical and Ocean Engineering at FAU.
“Both the toilet and urinary generated great amounts of droplets less than 3 microns in size, representing a significant risk of containing infectious organisms if transmission. Due to their small size, these droplets can remain suspended for a long time,” he continues.
Droplets were detected at heights of up to one and a half meters for 20 seconds or more after initiating the discharge. The researchers found fewer airborne droplets when the toilet was flushed with the lid closed, but not much, suggesting that the aerosol 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 confined space despite the fact that there was no perceptible lack of airflow within the bath. In the long term, these aerosols could be raised by updrafts created by the ventilation system or by people moving into the bathroom
warns Dr. Masoud Jahandar Lashaki, also a co-author of the research and an assistant professor in the Department of Civil Engineering at Environmental and Geomatics of the FAU.
There was a 69.5% increase in measured levels for particles from 0.3 to 0.5 microns, a 209% increase for particles from 0.5 to 1 micron, and a 50% increase for particles from 1 to 3 micrometers. Aside from the smaller aerosols, the comparatively larger ones also pose a risk in poorly ventilated areas even though they experience stronger gravitational settling.
They are often subjected to 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.
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The study suggests that incorporating adequate ventilation into the design and operation of public spaces would help prevent the accumulation of aerosols in high-occupancy areas such as public restrooms
says Dr. Manhar Dhanak, co-author and chair of 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 review the entire system as most buildings are designed to certain codes. It could simply be a matter of redirecting the airflow according to the distribution of the bathrooms
For her part, Dr. Stella Batalama, dean of the Faculty of Engineering and Informatics, points out that “aerosol drops play a central role in the transmission of various infectious diseases, including Covid-19, and this latest research by our team of Scientists provide additional evidence to support the risk of infection transmission in confined and poorly ventilated spaces.