Over the past year, as health authorities have sought to prevent Covid-19 pandemic, researchers have trained their scientific attention on a number of potentially dangerous environments. : places where large groups of people congregate and the coronavirus novel has ample opportunity to spread. They have surfaced cruise ships, tracked case numbers in gyms, sampled ventilation units in hospitals, mapped restaurant seating arrangements in restaurants and modeled procedures in airplanes.
They paid less attention to another everyday environment: the car. A typical car, of course, doesn’t carry nearly enough people to host a traditional superspreader event. But cars come with risks for themselves; they are tiny, tightly sealed spaces that make social distance impossible and capture the tiny particles, or aerosolas, that the coronavirus can transmit.
“Even if you have a face mask, you can still get tiny aerosols that are emitted every time you breathe,” said Varghese Mathai, a physicist at the University of Massachusetts, Amherst. “And if it’s a confined cabin, you keep releasing these tiny bits, and they would naturally build up over time. ”
Read: Coding how airflow inside a car could affect Covid-19 transmission risk
In a new study, Mathai and three colleagues at Brown University – Asimanshu Das, Jeffrey Bailey and Kenneth Breuer – used computer simulations to map how virus-filled air particles could flow through the interior of a car. Their findings, published in early January in Science Advances, suggest that the opening of some windows can create air currents that can help keep both cyclists and drivers safe from disease. infectious as Covid-19.
To conduct the study, the research team hired what are called computer dynamic dynamic simulations. Engineers typically use these types of computer simulations, which model how gases or elevators move, to create race cars with lower drag, for example, or planes with better construction.
The team imagined a loose Toyota Prius-based car driving at 50 mph with two occupants: a driver in the front seat on the left and one passenger on the right rear, seating arrangements. is common in taxis and cycling sections and is a social booster. astar. In their first study, the researchers found that the way the air flows around the outside of the moving car creates a pressure gradient inside the car, with the pressure of the air in front of it slightly lower than the air pressure in the rear. As a result, air circulating inside the cabin tends to flow from the rear of the car to the front.
Next, they modeled indoor airflow – and symbolic aerosol movement – when a combination of windows was open or closed. (The air conditioning was on in all cases.) Not surprisingly, they found that the level of ventilation was lowest when all four windows were closed. In this scenario, about 8% to 10% of aerosols emitted by one of the occupants of the car could reach the other, the simulation suggested. When the windows were fully open, on the other hand, ventilation levels went up, and the fresh air flowed many of the air grains out of the car; only 0.2% to 2% of the typical aerosols traveled between driver and passenger.
The results are in line with public health guidelines that recommend opening windows to reduce the spread of the novel coronavirus in confined spaces. “It basically takes the outdoors, and we know the risk to the outdoors is very low,” said Joseph Allen, a ventilation expert at Harvard TH Chan School of Public Health. In an op-ed last year, he highlighted the risk that cars could stand up to the spread of coronavirus, and the potential benefits of opening the windows. “When you have so much air turnover, the residence time, or the length of time the aerosols stay inside the cabin, is very short,” said Allen.
Since it is not always practical to have all the windows open, especially in the depths of winter, Mathai and his colleagues modeled several other options. They found that while the most likely solution – with the driver and passenger rolling all the windows down – was better than keeping all the windows closed, it was too early. an even better device is to open the windows facing each occupant. This arrangement allows fresh air to flow in and out of the left rear window and out through the right front window and helps to create a barrier between the driver and the passenger. .
“It’s like an air curtain,” said Mathai. “It flows out the air released by the passenger, and it also creates a strong wind area between the driver and the passenger. ”
Richard Corsi, an air quality expert at Portland State University, praised the new study. “It’s very solemn, what they did,” he said, although he warned that changing the number of passengers in the car or the driving speed could affect the results.
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Corsi, who co-authored the op-ed with Allen last year, has developed his own model for coronavirus aerosol inhalation in different conditions. His results, as yet unpublished, suggest that a 20-minute car trip with someone who releases infectious coronavirus grains can be much more dangerous than sharing a classroom or restaurant. with that person for over an hour.
“The focus has been on superstitious events” because they involve a lot of people, he said. “But I think what people sometimes miss is that superstitious events are started by someone with the disease who come to that event, and we don’t talk about it often enough. where that person was caught. ”
In a follow-up study, which has not yet been published, Mathai found that opening the window halfway appeared to provide about the same benefit as opening them fully, while slicing them straight. a quarter of the open route was less efficient.
Mathai said the general decisions might hold for many four-door, five-seater cars, not just the Prius. “For minivans and pickups, I would still say that opening every window or opening at least two windows can be beneficial,” he said. “Beyond that, I would put too much away. ”
Travel sharing companies should encourage this research, Mathai said. He sent a copy of his study to Uber and Lyft, he said, but received no response.