From time-to-time, needs must: you have to resort to a public restroom.
You are right to be concerned. Toilet bowls harbor persistent pathogens: reported examples are the SARS coronavirus, and species of Staphylococcus and Legionella. These disease agents are poised for the next flush, whereupon they will launch their airborne assault within an invisible plume of aerosol particles. The risk is elevated in healthcare settings.
So, you might take solace from this being a topic for academic study. There are scientists who aim to reduce this infection risk by testing the value to plume reduction of novel flush valve cycles, bowl geometries, and disinfection strategies. To do this, they are improving the methods used to quantify particle paths and flight times of toilet plumes.
In 2021, one such research team at the University Colorado Boulder described their new experimental design in the journal Scientific Reports. Here, Professor John Crimaldi and his colleagues, from within the Department of Environmental and Architectural Engineering, described their laboratory setup in which a pulsed laser is fired at a flushing toilet. The particles within the blast of aerosol disrupted the path of the laser, causing light scatter, which was itself monitored by high resolution cameras.
The human eye’s version of the resulting green plume – up to five feet high – is depicted both in in their paper and arguably more dramatically through Professor Crimaldi’s article in The Conversation. In that on-line post, Prof. Crimaldi explains that their new method illuminates the aerosol spread, but more accurately and quantitatively than prior methods, which involved the placement of air samplers, or computational models.
Professor Crimaldi’s team notes that as bad as their plumes seem, they are likely diluted by their well-ventilated laboratory, which lacked partitions. More concentrated plumes can be expected in real-life. The scientists also acknowledge they did not test the influence of either toilet paper or fecal matter (good luck adding poop to the experimental protocol!).
Of course, as they also note, the target-range of plumes could be minimized with the assistance of a closed lid – a precautionary option that is typically absent from public toilets. So instead, after I have finished 'visiting the facilities', I utilize the positive pressure of my airways to reduce the chance of infection; I exhale while flushing. Then I exit the area like it’s an emergency situation. “But wait”, I hear you ask. “Without lingering to wash your hands?”
That’s a separate topic I will return to in a subsequent post.
By Lydia Goode, August 2023