Researchers have shown that airborne diseases such as COVID-19 spread along a train car and have found that there is no “safer place” for passengers to minimize the risk of transmission. .
We hope that this research will give people an idea of the types of risk of an airborne disease in public transport. “
Rick de Kreij
Researchers at Cambridge University and Imperial College London developed a mathematical model to help predict the risk of disease transmission in a train car and found that in the absence of effective ventilation systems, the risk is the same throughout. of the carriage.
The model, which was validated with a controlled experiment on a real train car, also shows that masks are more effective than social distancing to reduce transmission, especially on trains that are not ventilated with fresh air.
The results, published in Indoor Air magazine, show how difficult it is for people to calculate absolute risk and how important it is for train operators to improve their ventilation systems to help keep passengers safe.
Because COVID-19 is transmitted through the air, ventilation is vital to reduce transmission. And while COVID-19 restrictions have been lifted in the UK, the government continues to stress the importance of good ventilation to reduce the risk of COVID-19 transmission, as well as other respiratory infections such as the flu. .
“To improve ventilation systems, it’s important to understand how airborne diseases spread in certain scenarios, but most models are very basic and can’t make good predictions,” said first author Rick de Kreij. who completed the investigation while in Cambridge. Department of Applied Mathematics and Theoretical Physics. “Most simple models assume that the air is completely mixed, but that’s not how it works in real life.
“There are many different factors that can affect the risk of transmission on a train: if people on the train are vaccinated, if they wear masks, if there are people, etc. Any of these factors can change the risk. “We look at relative risk, not absolute risk, it’s a toolbox that we hope will give people an idea of the types of risk of airborne illness on public transportation.”
The researchers developed a one-dimensional (1D) mathematical model that illustrates how an airborne disease, such as COVID-19, can spread along a train car. The model is based on a single train car with doors that close at each end, although it can be adapted to different types of trains, or to different types of transport, such as planes or buses.
Model 1D considers physics essential for the transport of pollutants in the air, although it is still economically economical, especially compared to 3D models.
The model was validated by measurements of controlled carbon dioxide experiments performed on a large-scale train wagon, where participants ’CO2 levels were measured at various points. The evolution of CO2 showed a high degree of overlap with the modeled concentrations.
The researchers found that the movement of air is slower in the middle of a train car. “If an infected person is in the middle of the carriage, they are more likely to infect people than if they were at the end of the carriage,” de Kreij said. “However, in a real scenario, people don’t know where an infectious person is, so the risk of infection is constant no matter where you are in the carriage.”
Many commuter trains in the UK have been manufactured to be as cheap as possible in terms of passenger comfort, with the maximum number of seats per wagon. In addition, most commuter trains recirculate air instead of attracting fresh air from outside, as fresh air has to be heated or cooled, which is more expensive.
So if passengers don’t know if they’re sharing a train car with an infected person, what should they do to stay safe? “Space as much as you can reasonably: physical distancing is not the most effective method, but it works when capacity levels are below 50 percent,” de Kreij said. “And wear a high-quality mask, which will not only protect you from COVID-19, but from other common respiratory illnesses.”
Researchers are now looking to expand their 1D model to a slightly more complex, yet still energy-efficient zonal model, where cross-flow is characterized in different areas. The model could also be expanded to include thermal stratification, which would provide a better understanding of the spread of a pollutant in the air.
The research was funded in part by the Research Council in Engineering and Physical Sciences.
de Kreij, RJB, et al. (2022) Modeling disease transmission in a train car using a simple 1D model. Indoor air. doi.org/10.1111/ina.13066.