1, when the flush button is pressed, the water jets exit through many small ports and a main flushing port on one side of the toilet bowl. It is therefore crucial for the general public to understand the infectious transmission risk when accessing public lavatories and using toilets.įor a typical squat toilet with a cistern as shown in Fig. The microorganisms may also form a biofilm on the inner wall of the toilet bowl 1, and thus they may still be detected days or weeks later 11. Even multiple flushes may not completely eliminate microorganisms from the toilet bowl surfaces 1, 9, 10. Early studies also reported the presence of SARS-CoV-1 6, MERS-CoV 7, norovirus and rotavirus 8 in urine and feces. The detected SARS-CoV-2 in the urine and stool of infectors 2, 3, 4, 5 highlights the risk of transmission through the fecal–oral route. The droplets and droplet nuclei may contain infectious microorganisms after an infector uses the toilet 1. The flushing may cause particles to deposit on the flushing button and lavatory door handle as well as inhalation exposure even remaining in the lavatory for half a minute after flushing, especially for those lavatory users whose respiratory zones are below 1.0 m.įlushing a toilet can entrain airflow and produce droplets and droplet nuclei. A single flushing process can produce 0.29 million particles with diameters greater than 0.3 μm, among which 90% of the particles are submicron-sized. The results revealed that flushing a squat toilet can drive toilet plume to rise up to 0.9 m above the toilet bowl. The risks from skin contact of the deposited particles on the flushing button and the door handle and the possible inhalation of the released aerosols were evaluated. For inference of the particle emission rate, the toilet bowl was covered by an enclosed box for particle concentration measurement. The maximum height of the impacted airflow was identified by an ultrasonic anemometer. The flushing-induced airflow was both visualized and quantitatively measured by particle image velocimetry. This investigation constructed a lavatory mock-up with a squat toilet. The flushing of a squat toilet can entrain strong airflow and produce aerosols. Squat toilets are widely used in developing countries due to local customs and low costs.
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