Models, simulations and experiments have been put in place in recent weeks to understand how the novel coronavirus is transmitted. Today we know that when we speak, sneeze, cough or even breathe, we emit droplets of different sizes. If we are sick these infected droplets can become the cause of contagion reaching the faces of other people or surfaces that would become infected. Just to limit the possibility of infection as much as possible, governments have imposed very stringent measures such as social distancing, the use of a mask and hygiene rules such as washing your hands often with soap and water and using disinfectant gels with at least 60% alcohol. Social distancing has been indicated, in most cases, at 2 meters, or six feet, since, as has been observed, saliva droplets fall to the ground at distances almost never higher than 1 meter. However, a study recently published in the journal Physics of fluid by a team from Cyprus (Dbouk et al, May 2020) adds a consideration that could revise this distance considered safe. Let's try to understand.
How the experiment took place
More than a real experiment it is a computer simulation that has allowed, through the choice of physical models, to simulate how the saliva drops emitted by a person move in particular conditions of temperature, humidity and wind. Scientists analyzed the situation by setting a 20° C temperature and 50% relative humidity. A first simulation took place in the absence of wind. In this case, the droplets actually fell almost all within a meter. A small part managed to travel beyond one meter but at a height less than half a meter. The only risk, in this case, can be given by a small child but he/she has to be within two meters from the person. Then, the scientists also included the wind in the simulation and saw that, with a wind of up to 15 km/h, the droplets could reach the distance of 6 meters. Not only that, as the wind speed increases, the reduction in particle mass also increases and the droplets evaporate faster. Instead, in presence of a light wind, this allows longer evaporation times and therefore a longer survival time in air. This could consequently increase the risk of infection.
Consequences of the experiment
The experiment did not analyze the viral load of the droplets nor their real ability to infect a person. However, it must be taken into consideration, especially now that, with the arrival of the summer season, we try to stay more outdoors and not always observe the distances or the protection rules. The article therefore makes it clear how important it is to protect yourself with a mask and observe the social distance that, in presence of wind, could exceed the recommended two meters or six feet.
