Wash Your Hands for 20 Seconds: Physics Shows Why
Despite hand-washing being confirmed effective in combating the spread of illness and infection, its physics has rarely been studied. However, in Physics of Fluids, by AIP Publishing scientists from Hammond Consulting Limited describe a straightforward model that catches the essential mechanics of hand-washing.
They estimated the time scales on which particles, like viruses and bacteria, were removed from hands by imitating hand-washing.
The mathematical model acts in two dimensions, with one wavy surface area passing one more bumpy surface and a thin film of liquid between both. Wavy surface areas stand for hands because they are rough on tiny spatial scales.
Particles are stuck on the harsh surface areas of the hand in prospective wells. To put it simply, they are at the base of a valley, and also, for them to run away, the power from the water circulation needs to be high enough to obtain them up and out of the valley.
The strength of the streaming fluid relies on the speed of the moving hands. A more powerful flow eliminates fragments more easily.
“Generally, the flow informs you the forces on the fragments,” claimed writer Paul Hammond. “After that, you can figure out how the fragments relocate and also identify if they obtain removed.”
He likens the procedure to rubbing a discolor on a tee shirt: the quicker the motion, the more probable it is to disappear.
“If you move your hands too delicately, too slowly, about one another, the forces generated by the flowing liquid are not large enough to conquer the pressure holding the particle down,” said Hammond.
Even when fragments are extracted, that procedure is not fast. Like those from the Centers for Illness Control and Prevention, common hand-washing standards suggest a minimum of 20 seconds under the faucet. Results from Hammond’s version agree.
It takes around 20 seconds of strenuous movement to dislodge potential viruses as well as bacteria.
The design does not consider chemical or organic processes that occur when using soap. However, recognizing the mechanisms that physically get rid of fragments from hands may offer clues to creating more reliable, eco-friendly soaps.
“Nowadays, we are required to be a little bit more thoughtful regarding what takes place to the wash chemicals when they go down the plughole as well as go into the environment,” claimed Hammond.
Hammond claimed this is not the whole tale of hand-washing, but it does respond to vital questions and lay the foundation for the future research study.
Originally published on Smart Water Magazine. Read the original article.
Reference: “Will we ever wash our hands of lubrication theory?” by Paul S. Hammond, 17 August 2021, Physics of Fluids.
DOI: 10.1063/5.0060307
