A recent study conducted by a team of researchers aimed to address the question of whether it is more sanitary to close the toilet lid before flushing, a practice that gained attention during the COVID-19 pandemic. Signs advocating for lid closure in public restrooms became more common during the pandemic, with enhanced awareness around hygiene practices, though some recommendations lacked scientific backing.
The research team, led by experts from the National Institute of Advanced Industrial Science and Technology (AIST), carried out an experiment to scientifically assess the impact of lid closure on hygiene practices during toilet flushing. Their experiment involved installing a toilet bowl in a sealed booth that mimicked a private bathroom setting, where they analyzed the behavior of droplets and viruses during the flushing process.
During the experiment, researchers utilized the siphon type flushing method commonly found in toilets, which employs strong suction to effectively wash away water and waste. The study indicated that when the toilet lid was open during flushing, droplets were observed to reach a height of 40-50 centimeters and eventually fall, while smaller aerosols remained airborne for extended periods inside the enclosed space. Furthermore, aerosols were found to disperse widely, including 40 cm above the toilet bowl and 15 cm in front of it, when the lid was left open.
Interestingly, the researchers discovered that closing the toilet lid before flushing led to a notable reduction in the spread of aerosols, as particles did not escape upward towards the top part of the toilet, but rather leaked out towards the front of the bowl due to air pressure from the water flow. The findings suggested that closing the lid could potentially mitigate the aerosol effect, especially if the toilet was at a sufficient distance from the lid. Subsequent analysis using simulated viruses revealed that approximately one-third of the viruses deposited on the walls and underside of the toilet seat when the lid was closed, emphasizing the importance of comprehensive cleaning practices.