How Does Public Transportation Transmit Virus Droplets?

Researchers developed a new multiphysics model involving air and droplet dynamics, heat transfer, evaporation, humidity, and effects of ventilation systems.

A new multiphysics model is developed by researchers at IBM Research Europe with an unprecedented level of detail and focused on conditions that are more characteristic of asymptomatic transmission. The model findings are published in the journal Physics of Fluids.

The COVID-19 pandemic has revealed the urgency of understanding how public transportation ventilation systems transmit viruses and how exhaled droplets evolve in ventilated spaces. Researchers have wondered if those ventilation systems can be improved to mitigate virus transmission.

Coronavirus
Coronaviruses infect animals, humans, and birds. Human coronaviruses, such as SARS, MERS, and 2019-nCoV cause respiratory distress and even death. The S protein is the infectious agent of the virus.

‘Understanding asymptomatic transmission of droplets in public transportation can mitigate virus transmission.’

"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," said author Carlos Peña-Monferrer.

Researchers analyzed what happens when speech droplets are exhaled from a row of sitting passengers in a ventilated space, like those in public vehicles. In some of these systems, the air is injected at the top and extracted at the bottom through the vents near the window seats.

This generates an internal recirculation to enhance thermal comfort and remove contaminants, but the researchers were interested in whether certain seat positions affect the circulation adversely.

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They found droplets from the window seat rose more and invaded the space of other passengers to a lesser extent shortly after exhalation.

Moreover, droplets released from the middle seat contaminated the aisle passengers more, indicating the downward flow of personal ventilation in aisle seats could move droplets down and increase the risk of infection.

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Researchers modeled various scenarios in close detail, such as a situation where passengers in different seats were pronouncing a vowel for a few seconds. By creating a detailed representation of the flow field and tracking every single droplet, they were able to reconstruct their ventilation paths.

In the future, they will reproduce conditions that more closely represent the diverse human activity on public transport vehicles to help inform actions, design, and operation of future ventilation systems for safer environments.

Test your Knowledge on Coronavirus (COVID-19)
Coronavirus is a large positive-strand RNA virus that is surrounded by a protein envelope. The virus obtains its name from the S protein spikes on its surface, which resemble a crown. The overall pattern of increasing coronavirus cases is shown to spike up with the “second wave” of COVID-19.

With spiking effects of the second wave of coronavirus, the best way to keep it at bay is to follow COVID-appropriate safety practices like wearing a mask, regularly cleaning your hands, and coughing into a bent elbow or tissue along with physical distancing (6 feet about 2 arm's length), that may help evade the severity of COVID-19 infection.

These high-resolution simulations were focused on public vehicles, but they could be extended to commercial or residential buildings, health care facilities, offices, or schools.

Source-Medindia