COVID-19: What to do to reduce the risk of transmission in cars

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As the car represents a closed space, the risk of contamination is present during the COVID-19 pandemic if it contains several people, either its own or transport by applications. To limit it, researchers in a recent study evoke the advice to follow: everything is a matter of configuring open or closed windows.

The transmission of infectious respiratory diseases, including SARS-CoV-2, is facilitated by the transport of expired droplets and aerosols that can remain in the air for long periods of time. After studies on the risks of transmission of the virus in closed transports such as trains and airplanes, researchers from the University of Massachusetts Amherst (or UMass Amherst) became interested in the risk related to the automobile. In fact, it is the mode of transport where social distancing is very difficult to respect: should it be completely avoided? Their study published in the journal "Science Advances" provides part of the answer.

For maximum social isolation, driving alone is ideal, but this habit is not environmentally sustainable and there are many situations where two or more people must travel together. Wearing a mask and disinfecting the cabin is an effective first step in reducing the risk of infection in the car, but even with such protective measures, the release of microscopic aerosols is almost inevitable. Therefore, the researchers wanted to know what air circulation patterns within a car could increase or limit the risk of airborne infections during daily trips.

Closed windows and air conditioning: risky combination

"We imagine that people instinctively open the windows that are next to them when traveling with a companion during the pandemic. This may not be optimal, although it is better than not opening any windows," explains the studys lead author, the professor. Varghese Mathai, member of UMass Amherst. "We designed this investigation from a shared ride, a traditional taxi or an Uber or for non-commercial trips, with a driver and a passenger sitting in the back, so that the space between occupants is optimal. Therefore, their study suggests that opening the windows farthest from the driver and passenger may offer the best protection. "

Various airborne pathogen transmission scenarios in a car have been taken into account: opening all windows, as well as supplying fresh air through the vents, are supposed to create the best environment to reduce air risk of transmission due to increased ventilation. On the contrary, keeping all windows closed and using only recirculation mode would be the riskiest option. But, aware of the impossibility of keeping all windows open in winter or rainy weather, the researchers also looked at what happens to aerosols exhaled by occupants inside the car under various open and closed window configurations.

Always open windows away from passengers

"These small potentially pathogenic particles remain in the air for long periods of time without settling, so if they are not vented outside the cabin, they can accumulate over time, increasing the risk of infection." The scientific team recommends opening the rear and front windows but on opposite sides of the car occupants to create a stream of air that goes from the rear to the front of the cabin to pass through it. Specifically, opening the front window on the right side and the rear window on the left side could better protect the driver and passenger from the hundreds of aerosol particles that are released with each breath.

"The simulations showed an air stream that acts as a barrier between the driver and the passenger," adds Professor Varghese Mathai, who compared this phenomenon to the air curtain created by a vertically blown airflow at certain supermarket entrances, which prevents air from mixing with indoor air even if the entrance door is open. "While these measures are not a substitute for wearing a mask inside a car, they can help reduce the burden of pathogens within the very confined space of a cabin," he concludes. The scientific team specifies, however, that the implications of the study are limited to the airborne mode of transmission.

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