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Physicists have found the perfect method to hand washing to remove particles of bacteria and viruses, including the novel coronavirus. They found that it takes about 20 seconds to dislodge viral or bacterial particles from our hands. This should sound familiar to you – it’s in line with what most public health experts recommend.
For the study, published Tuesday (August 16) in the journal Fluid physics, the researchers created a simple mathematical model to simulate the movement of particles (such as viral or bacterial particles) when washing hands. In the model, the hands are represented by two rough surfaces that intersect (to mimic hands rubbing together), separated by a thin film of liquid.
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The model showed that particles are attracted to rough surfaces and that a certain amount of energy is required to allow the particles to escape into the fluid. Faster movement of the hands creates a stronger flow of fluid and removes particles more easily, the authors said.
“If you move your hands too gently, too slowly, relative to each other, the forces created by the flowing fluid are not great enough to overcome the force that holds the particle down,” study author Paul Hammond, scientific consultant at Hammond Consulting Limited. United Kingdom, said in a press release. Hammond likened the situation to removing a stain from a shirt; faster scrubbing action removes stain more easily.
Using reasonable estimates for the variables, including the speed of hand movement, the model found that it takes about 20 seconds for the particles to escape. This is in line with the recommendations of the Centers for Disease Control and Prevention (CDC), which advises people to wash their hands with soap and water for 20 seconds, about the time it takes to sing “Happy Birthday” twice.
The CDC’s recommendation is not based on physical modeling, but rather on studies of the levels of microbes that remain on hands after washing during certain periods of time.
Hammond noted that the new study did not take into account the biological action of soap. Soap not only helps remove dirt and germs from hands, but it also disrupts the membrane surrounding viral or bacterial particles, thereby destroying them.
Future research should take this soap “chemical attack” into account, but the current study is laying the groundwork, Hammond said.
Originally posted on Live Science.
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