That’s why masks and distances are not enough: new study

Published on: 10/20/2020 8:16 PM

Wear a mask, keep your distance, avoid the crowd – these are the ‘pillar’ anti-Covid recommendations of anti-virus strategies. However, the scientific basis on which these recommendations are based is decades old. Thus, several research groups in the field of fluid dynamics have come together and developed a new model relating to the spread of the dreaded infectious droplets. Wearing masks and keeping your distance have been shown to make sense, but this shouldn’t give you a false sense of security. Even with a mask, infectious droplets can travel for several meters and stay in the air longer than you think.

A particle with a diameter of 10 micrometers (the average size of the emitted droplets of saliva), for example, takes almost 15 minutes to fall to the ground., the researchers explain. The research project involved TU Wien (Vienna University of Technology), the University of Florida, the Sorbonne in Paris, Clarkson University (USA) and MIT in Boston, described in the International Journal of Multiphase Flow ‘ . The study is signed by the Italian Alfredo Soldati from TU Wien. “Our globally accepted understanding of droplet propagation is based on measurements from the 1930s and 1940s, explains Soldiers of the Institute for Fluid Mechanics and Heat Transfer at TU Wien. At the time, the measurement methods were not as good as the ones. Today, we suspect that particularly small droplets could not be reliably measured. “

In previous models, a clear distinction was made between large and small droplets: large droplets are pulled down by gravity, small droplets move almost in a straight line, but evaporate very quickly. “This image is extremely simplified,” says Alfredo Soldati. Therefore, it is time to adapt the models to the latest research to better understand the spread of Covid-19 ”.

“Even when the drop of water has evaporated, an aerosol particle remains, which can contain the virus. This allows viruses to spread over distances of several meters and remain in the air for a long time,” says Soldati. In typical everyday situations, a particle with a diameter of 10 microns (the average size of the emitted droplets of saliva) takes almost 15 minutes to fall to the ground. So it is possible to come into contact with the virus even observing the rules of distancing., for example, in an elevator that has been used by infected people shortly before.

Especially problematic are environments with high relative humidity, such as poorly ventilated meeting rooms. And special attention is required in winter, because the relative humidity is higher than in summer. “Masks are helpful because they block large drops. And it’s okay to keep a safe distance, too.” “But our results show that none of these measures can provide guaranteed protection.“says Soldati.