COVID-19: Distancing and masks -- good but not enough

Date:
October 20, 2020
Source:
Vienna University of Technology
Summary:
Decades-old data is being used to describe the propagation of
tiny droplets. Now a fluid dynamics team has developed new models:
Masks and distancing are good, but not enough. Even with a mask,
infectious droplets can be transmitted over several meters and
remain in the air longer than previously thought.



FULL STORY ==========================================================================
Wear a mask, keep your distance, avoid crowds -- these are the common recommendations to contain the COVID-19 epidemic. However, the scientific foundations on which these recommendations are based are decades old and
no longer reflect the current state of knowledge. To change this, several research groups from the field of fluid dynamics have now joined forces
and developed a new, improved model of the propagation of infectious
droplets. It has been shown that it makes sense to wear masks and
maintain distances, but that this should not lull you into a false sense
of security. Even with a mask, infectious droplets can be transmitted
over several meters and remain in the air longer than previously thought.


==========================================================================
TU Wien (Vienna), the University of Florida, the Sorbonne in Paris,
Clarkson University (USA) and the MIT in Boston were involved in the
research project.

The new fluid dynamics model for infectious droplets was published in the "International Journal of Multiphase Flow." A new look on old data "Our understanding of droplet propagation that has been accepted worldwide
is based on measurements from the 1930s and 1940s," says Prof. Alfredo
Soldati from the Institute of Fluid Mechanics and Heat Transfer at
TU Wien. "At that time, the measuring methods were not as good as
today, we suspect that especially small droplets could not be measured
reliably at that time." In previous models, a strict distinction was
made between large and small droplets: The large droplets are pulled
downwards by gravity, the small ones move forward almost in a straight
line, but evaporate very quickly. "This picture is oversimplified,"
says Alfredo Soldati. "Therefore, it is time to adapt the models to
the latest research in order to better understand the propagation
of COVID-19." From a fluid mechanics point of view, the situation is complicated -- after all, we are dealing with a so-called multiphase
flow: The particles themselves are liquid, but they move in a gas. It
is precisely such multiphase phenomena that are Soldati's specialty:
"Small droplets were previously considered harmless, but this is clearly wrong," explains Soldati. "Even when the water droplet has evaporated,
an aerosol particle remains, which can contain the virus. This allows
viruses to spread over distances of several meters and remain airborne for
long time." In typical everyday situations, a particle with a diameter of
10 micrometers (the average size of emitted saliva droplets) takes almost
15 minutes to fall to the ground. So it is possible to come into contact
with virus even when distancing rules are observed -- for example in an elevator that was used by infected people shortly before. Particularly problematic are environments with high relative humidity, such as poorly ventilated meeting rooms. Special care is required in winter because
the relative humidity is higher than in summer.

Protection rules: Useful, but not enough "Masks are useful because they
stop large droplets. And keeping a distance is useful as well. But our
results show that neither of these measures can provide guaranteed
protection," says Soldati. With the mathematical model that has now
been presented, and the current simulations under way it is possible to calculate the concentration of virus-carrying droplets at different
distances at different times. "Until now, political decisions on COVID-protection measures have mainly been based on studies from the
fields of virology and epidemiology. We hope that in the future, findings
from fluid mechanics will also be included," says Alfredo Soldati.


========================================================================== Story Source: Materials provided by Vienna_University_of_Technology. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. S. Balachandar, S. Zaleski, A. Soldati, G. Ahmadi,
L. Bourouiba. Host-to-
host airborne transmission as a multiphase flow problem for
science-based social distance guidelines. International
Journal of Multiphase Flow, 2020; 132: 103439 DOI:
10.1016/j.ijmultiphaseflow.2020.103439 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201020111329.htm

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