With winter fast approaching in the Northern Hemisphere and people returning to school, college, or their workplace, many of us will start spending more time indoors with more people. Just in time for these changes, a bunch of new research is showing how important ventilation and airflow is in the spread of Covid-19, whether that’s in an office, classroom, a gym, commuter train, or an airplane. Some of the findings are a bit fiddly, but the key takeaways are simple: some ventilation systems are better than others, wear a face mask, and cracking open a window is always a good idea. Most evidence now says that Covid-19 is primarily spread through airborne mucus droplets and smaller aerosols, pumped out into the surroundings by coughs, sneezes, breathing, and talking. These tiny airborne particles are then able to disperse through the air and likely linger for a certain span of time. As such, airflow is an important factor when understanding how Covid-19 might spread between people, especially in the context of an office, restaurant, or airplane. First up, new research from the University of Cambridge has shown that ventilation systems in many modern office buildings may increase the risk of exposure to the coronavirus. It’s a complex problem, however. Reported in the Journal of Fluid Mechanics, the risk of transmission through ventilation systems involves a number of factors, from the placement of vents, windows, and doors to the flows generated by heat emitted by people and other equipment in a building. The risk of transmission also varies between different types of ventilation systems. Mixing ventilation, the most common in contemporary buildings, uses inlet and outlet vents to keep conditions uniform in all parts of the room, which may potentially disperse airborne contaminants throughout the space. On the other hand, displacement ventilation – a less common system that uses vents placed at the bottom and the top of a room to create a cooler lower zone and a warmer upper zone – appears to be the most effective at reducing exposure risk. However, one aspect of the research was clear: use a face mask. The new research highlighted the effectiveness of masks at reducing the spread of exhaled breath and the spread of aerosols through a confined indoor space, such as an office. “One thing we could clearly see is that one of the ways that masks work is by stopping the breath’s momentum,” Professor Paul Linden, lead study author from Cambridge’s Department of Applied Mathematics and Theoretical Physics, said in a statement. “Masks stop larger droplets, and a three-layered mask decreases the amount of those contaminants that are recirculated through the room by ventilation.” While it might not make for a very fun office environment, laughing was also found to be the riskiest means of spreading the virus through expelling droplets. Equally, simply opening windows was shown to dramatically reduce the risk of transmission. “Keep windows open and wear a mask appears to be the best advice,” added Linden. “Clearly that’s less of a problem in the summer months, but it’s a cause for concern in the winter months.” Another study looked at an environment that’s raised concern in recent months: airplanes. Obviously, airplanes are cramped environments where it’s impossible to simply crack a window. However, there are some simple strategies you can use to reduce your risk of exposure. A recent article published by JAMA Patient Page shows that air in a commercial plane enters and leaves the cabin at the same seat row or nearby rows. There is relatively little airflow forward and backward between rows, making it less likely to spread respiratory particles between rows. On top of that, the researchers note that airflow on planes is actually faster than a typical indoor building. Rather reassuring, this means that the risk appears to be lower than you might first assume, just as previous case studies have suggested. The best way to reduce the risk of spread on an airplane is by simply following the common-sense advice: Don’t travel if you feel unwell, stay seated as much as possible, maintain as much distance as possible in the airport, and – yep, once again – wear a mask.
