Aug 19, 2021 06:00:00

Physically elucidate the effect of '20 seconds of hand washing'

A study simulating the behavior of particles with a mathematical model reiterated that 20 seconds of hand washing effectively removes the virus from the skin. This physically supports the claim of

19th-century doctor Semmelweis Ignats , who discovered the importance of hand washing before the presence of viruses and pathogens was known.

Will we ever wash our hands of lubrication theory ?: Physics of Fluids: Vol 33, No 8
https://aip.scitation.org/doi/10.1063/5.0060307

Wash your hands for 20 seconds: Physics shows why
https://phys.org/news/2021-08-seconds-physics.html

Here's why you need to wash your hands for 20 seconds, according to physics | Live Science
https://www.livescience.com/hand-washing-physics-to-remove-viruses.html

Since the effects of hand washing were discovered in the mid-19th century , hand washing has been practiced in the medical field for over 170 years. However, surprisingly, no 'paper that hydrodynamically verified the effect of hand washing' has been published so far.

Therefore, Paul Hammond, a scientist at Hammond Consulting Limited, a British consulting firm, conducted a study using a mathematical model to simulate the movement of virus and bacterial particles during hand washing. In Mr. Hammond's model, the skin is defined as an object with a rough surface, and by assuming that it rubs against each other across a thin film of fluid, the appearance of hand washing is reproduced.

As a result of the simulation, it was found that a certain amount of energy is required to transfer the particles adsorbed on the surface of the hand into the liquid. This means that in order to effectively remove the particles adhering to the hands, it is necessary to speed up the movement of rubbing the hands and increase the speed of flushing water.

Hammond commented on this result: 'If the hand moves too slowly, the force generated by the flow of liquid loses the force that holds the particles on the surface of the hand, but conversely, if the hand moves fast. You can get rid of the particles, which is the same as the faster you rub the stains on your shirt, the easier it will be to remove the stains. '

The study also found that when variables such as the speed of hand movement were set to reasonable numbers, it took 20 seconds to clear the particles from the surface of the hand. .. This is about the same as the hand-washing time recommended by the World Health Organization (WHO) in the hand hygiene guidelines.

'This study doesn't take into account chemical or biological effects, such as the effect of soap on destroying viral particles, so not all of the effects of hand washing have been elucidated,' Hammond said. It will be an important basis for various future researches. '