travelling in a pandemic: study looks at the safest place to sit on public transit
research highlights the importance of air ventilation and filtration in protecting people from covid-19 infection.
3 minute read
air in public transit vehicles is regularly circulated by intakes at the top of the cars and vents at the bottom near the window seats. getty
public transit is a necessity for many, but since covid-19 made distancing a top priority, it’s left many of us wondering how to stay safe on a crowded rush hour bus.
researchers from ibm research europe suggest that where you choose to sit on a bus or train could have an impact on your level of exposure to exhaled droplets from others.
in the study, published in physics of fluids by aip publishing, researchers studied the effects of heat, evaporation, humidity, and ventilation systems on public transport using a multi-physics model — a type of program that simulates multiple objects with different sorts of physics simultaneously,
“by visualizing the droplets and the flow, you realize the number of physical phenomena taking place around us that go unnoticed, such as the complex interactions between natural body plumes, exhalation, and ventilation,” the study’s author carlos peña-monferrer said. “when it comes to preventing risk of infection, this is precisely what makes it difficult to contain.”
the simulation consisted of three women sitting together and observing the droplets from their breath. none of them were wearing masks, and the researchers did not look into different types of exhales such as sneezing or coughing. instead, they chose to focus on standard breathing that produced a standard amount of droplets. droplets from both the nose and mouth were examined.
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air in public transit vehicles is regularly circulated by intakes at the top of the cars and vents at the bottom near the window seats. droplets exhaled from people sitting in the window seats were found to rise farther and enter other people’s space quickly. passengers in the middle seat were found to have droplets end up around the aisle row, which indicates the downward flow of ventilation could direct droplets down and increase risk of infection.
droplets from passengers in the aisle seats fell almost immediately thanks to the ventilation system.
between 19.5 and 27.4 per cent of droplets were removed through the ventilation system within 40 seconds, and none of the droplets actually hit another person in the mouth. the majority of droplets passed by other passengers without issues, though some came as close as less than one centimetre to another person.
however, droplets can stick around and linger in the air for hours, depending on their size, according to the u.s. centers for disease control. inhaling these droplets can cause covid-19, though the amount required to get sick seems to vary from person to person.
there is potential growth for the simulation as well, since a similar system could be used for further research in more settings.
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“these high-resolution simulations were focused on public transportation vehicles, but they could be extended to commercial or residential buildings, health care facilities, offices, or schools,” peña-monferrer said.
the study’s conclusion reads that more attention should be put on proper outdoor air ventilation and improving air filtration, citing the cdc as saying that directional airflow could play a major role in protecting people from droplets. the authors add that special consideration is required when looking into ventilation systems on public transport, since the majority of the research has been done on aircrafts, and little has been done on buses or trains.
though it does add that the supply of air in a train car can be replaced every five to nine minutes, depending on the type of train.
in september 2021, there were nearly 63 million public transport rides taken in canada, according to a release from the federal government.
chris arnold is a toronto-based freelance writer . he can be reached here.
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