In the beginning of March 2020 COVID19 was the name on everyone's lips. It was found quite quickly that this virus seems to be spreading to fast to not be airborne. This means that it was very likely that the virus can spread from person to person without any physical contact. Now comes the problem of how should the government act to restrict the spreading and not overload the hospitals? No one really knew. Then, better be safe than sorry, restrict a lot, limit where possible. However, can you restrict too much? What will happen then. Well in hindsight, poverty has increased as a direct cause of restrictions. The reason, people that are economically vulnerable, working in services such as taxi and restaurants, were more or less shut down during the peak of the pandemic. In addition, global education has taken a hit for the students that had to study from home. There are even more examples of negative consequences of restrictions which all remind us to not impose them lightly.
So restrictions are important but also has down sides. So the problem remains, how much restrictions are the right amount. This is where we in the spray-imaging group thought that we could contribute. The spreading mentioned above is through small droplets that essentially is a spray and we have a long experience of studying sprays. Then, to help understand the spreading, it is interesting to understand where the droplets end up after a person has launched them. This then of course also give information of where the viruses end up. Two factors that largely affect where the droplets go are their speed and size so we applied our experimental skills to try and image these droplets and measure speed and size.
Our results consist of 14 Terabytes of movies where 4 different persons have been coughing, speaking and screaming. These movies were recorded using two high speed cameras recording at 15 000 frames per second. In addition, high power lasers where used to make the droplets shine and then we can see smaller droplets. Since we have been coughing, speaking and screaming we can try to find differences between how the droplets are produced in addition to differences between different people. In the movie attached to this article you can see one person coughing together with speeds and sizes found for this individual cough. Here, it was generally found that coughing produce many droplets that are fast but during a much shorter time compared to speaking and yelling. So even though the coughed droplets are fast and will go far, a person might be speaking for a long time and launch enough droplets to get a comparable risk of spreading disease.
The next step is to use these results in simulations to estimate how far the droplets go before touching the ground or evaporating enough to become aerosols. These results take us one step forward in our understanding of the spreading of viruses and how we should prioritize restrictions in a pandemic.