Do you need to wash your hands for 20 seconds to be effective? Scientists use mathematical models to show you: it's true
The answer to stopping the spread of COVID-19 lies in fluid mechanics?
Scientists used mathematical models of fluid mechanics to determine the speed and time required to remove germ particles from two rough surfaces. The study pointed out that the flow of liquid alone cannot wash away germ particles, including the new coronavirus, and it is necessary to rub your hands in the water for about 20 seconds to remove the germ particles. This is about the same time as experts previously pointed out that you should sing “Happy Birthday” twice when washing your hands.
“Journal of Fluid Mechanics” once published a study on the transmission mode of COVID-19 virus, summarizing its main three transmission routes. The first is droplet infection, the second is atomization infection, and the third is airborne infection. Droplets and Contact infection is most common. The infection process of virus particles is related to the flow phenomenon of objects. From a fluid mechanics perspective, blocking particles from standing still and allowing them to flow can effectively reduce the risk of infection, including washing hands, wearing masks, maintaining ventilation, and maintaining social distance between people. It is an effective and simple method.
It takes 20 seconds to wash your hands to have enough fluid power to remove the virus
The latest study on how the fluid dynamics of hand washing can remove COVID-19 virus particles has been calculated through mathematical models. Particles attached to rough surfaces must use a certain amount of energy (kinetic energy) to transfer the particles to the flowing surface. In liquids, rapid hand friction will produce stronger fluid dynamics, helping to remove particles from rough surfaces.
Study author Paul Hammond, PhD in Applied Mathematics at the University of Cambridge, said that if the friction action when washing hands is too light and too slow, the force generated by the fluid may not be enough to cause enough pressure on the surface particles. He also used the metaphor of removing stains on a shirt to remove stains faster. The wiping action can better remove surface dirt.
Wash your hands and sing happy birthday twice. There is evidence that soap can destroy the bacterial film.
By comparing the variable estimates with the speed of the friction action, it was found that it takes about 20 seconds for the particles to escape from the surface, which is consistent with the length of hand washing recommended by the US CDC. In instructions issued by the CDC, it is recommended that people wash their hands with soap and water for 20 seconds, which is about the same length as singing Happy Birthday twice. However, the CDC’s recommendations are not based on mathematical models, but on past research data on microorganisms remaining on human surfaces.
Hammond pointed out that this study did not take into account the effect of soap (saponification), and soap can not only remove dirt and bacteria, but more importantly, it can destroy the outer membrane of virus and bacterial particles, thereby destroying the integrity of the bacterial particles, making It cannot survive.
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