Study on the air gap effect when closing toilet lid on droplet and pathogen escaping from flushing

Closing the toilet lid before flushing is widely recommended to minimize the dispersal of pathogen-laden aerosols. However, an often-overlooked issue is that aerosols can still escape through the air gap between the bowl and seat even when the lid is closed.

We conducted a pilot investigation on how the gap height and lid influence droplet and bioaerosol escape in a seated toilet. Three microbes were studied, including one bacterium Escherichia coli, and two viruses (MS2 and P22). Bioaerosol escape ratios were calculated as the normalized concentration with the lid closed relative to the open-lid condition.

92% of droplets generated during flushing were smaller than 1.0 µm. Additionally, bioaerosol escaping from the toilet seat increased with gap height-when the gap height increased to 6 mm, the escape ratios rose to 24% for E coli, 49% for P22, and 57% for MS2.

The air gap between the toilet seat and bowl allows bioaerosols to escape during flushing. Viruses MS2 and P22 escaped more readily through the gap compared to the E coli. This study offers critical insights into how toilet lid closure and air gap height impact the release of bioaerosols generated by flushing.