Toilets spew invisible aerosol plumes with every flush – and scientists used high-powered lasers to illuminate and photograph them

John Crimaldi is Professor of Civil, Environmental and Architectural Engineering at the University of Colorado, Boulder.

Every time you flush a toilet, it releases tiny water droplets into the air around you. These droplets, called aerosol plumes, can spread pathogens from human waste and expose people to infectious diseases in public toilets.

Scientific understanding of the spread of aerosol plumes – and public awareness of their existence – has been hampered by the fact that they are normally invisible. My colleagues Aaron True, Karl Linden, Mark Hernandez, Lars Larsen and Anna Pauls and I were able to use high-powered lasers to illuminate these plumes, allowing us to spot aerosol plumes from flushing commercial toilets. and made capable of depicting and measuring motion. Vivid details.

Aerosol plumes from commercial toilets can rise up to 5 feet above the bowl.

John Crimaldi / Scientific Reports, CC BY-NC-ND

going up instead of down

Toilets are designed to efficiently empty the contents inside the bowl through a downward motion in the drain pipe. In the flush cycle, the water comes into forceful contact with the contents inside the bowl and creates a fine spray of suspended particles in the air.

We found that a typical commercial toilet generates a strong upward jet of air with a velocity greater than 6.6 feet per second (2 meters per second), rapidly carrying these particles up to 5 feet (1.5 meters) above the bowl. Flush within eight seconds of starting to go.

To visualize these plumes, we set up in our laboratory a typical lidless commercial toilet with a flushometer-style valve similar to those found throughout North America. Flushometer valves use pressure rather than gravity to direct water into the bowl. We used specialized optics to create a thin vertical sheet of laser light that illuminated the area from the top of the bowl to the ceiling. After flushing the toilet with a remote electrical trigger, the aerosol particles scatter enough laser light to be visible, allowing us to use cameras to image the particles’ plumes.

Even though we expected to see these particles, we were surprised by the strength of the jet that ejected the particles from the bowl.

A related study used a computational model of an ideal toilet to predict the formation of an aerosol plume, with speeds above the bowl leading to upward transport of particles up to 3.3 feet per second (1 meter per second). , which is about half of what we saw. With real toilet.

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Why laser?

Scientists have known for decades that flushing toilets can release aerosol particles into the air. However, experimental studies have largely relied on instruments that sample the air at fixed locations to determine the number and size of particulate matter.

During the flush cycle, water is forced into the toilet bowl.

South Hamsian / Wikimedia Commons, CC BY-NC-SA

While these earlier approaches can confirm the presence of aerosols, they provide little information about the physics of plumes: what they look like, how they spread and how fast they move. This information is important for developing strategies to reduce the formation of aerosol plumes and their ability to transmit disease.

As an engineering professor whose research focuses on the interactions between fluid physics and ecological or biological processes, my lab specializes in using lasers to determine how different things are transported by complex fluid flows. In many cases, these things are invisible until we illuminate them with lasers.

One advantage of using laser light to measure fluid flow is that, unlike physical probes, the light does not alter or disrupt what you are trying to measure. Furthermore, the use of lasers to make invisible things visible helps people better understand the complexities in liquid environments as visible organisms.

aerosols and disease

Aerosol particles containing pathogens are important human disease vectors. Small particles that remain suspended in the air for some time can expose people to respiratory diseases such as influenza and COVID-19 through inhalation. Large particles that settle quickly on surfaces can spread enteric diseases such as norovirus through contact with hands and mouth.

Toilet bowl water contaminated with feces can contain pathogen concentrations that persist after dozens of flushes. But it is still an open question whether toilet aerosol plumes present a transmission risk.

While we were able to visually and quantitatively describe how aerosol plumes move and spread, our work does not directly address how toilet plumes spread disease, and this remains an ongoing aspect of research. Is.

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Limiting Toilet Plum

Our experimental methodology provides a basis for future work to test multiple strategies for reducing the risk of diseases from flushing toilets. This may include assessing changes in the aerosol plume emitted from new toilet bowl designs or flush valves that change the duration or intensity of the flush cycle.

In the meantime, there are ways to reduce human exposure to toilet plume. An obvious strategy is to close the lid before flushing. However, this does not completely eliminate aerosol plumes, and many toilets in public, commercial and healthcare settings do not have lids. Ventilation or UV disinfection systems can also reduce exposure to aerosol plumes in bathrooms.


This article is republished from Conversation Under Creative Commons Licence.

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