Explains: Why wearing a weak mask is more risky than no mask at all

Written by Kabir Firaque, edited by Explained Desk | New Delhi |

December 16, 2020, 7:28:36 pm





Why an old mask is worse than no mask, how masks protect us, why should I wear a mask, mask advantages, are masks necessary, indian express, express explainsThe efficiency of a mask for filtering particles varies greatly between new and old masks. The simulations showed that a new surgical mask has a filtration efficiency of up to 65%, which can drop to 25% after multiple uses. (Photo for illustration: Reuters)

The primary purpose of wearing a mask is to protect other people around you. From the point of view of your own protection, how does your mask affect the flow of air around your face, the particles you breathe, and the way those particles settle in your upper airways or lungs? A new study in physics of fluids, a journal from the American Institute of Physics, studies the effects of wearing a three-layer surgical mask on such air currents and particle build-up.

Main results

* Wearing a used mask with low particle filtering efficiency may be riskier than wearing no mask at all.

* A mask is the best way to protect the upper airway from particles larger than 10 micrometers (a micrometer, also called a micrometer, is one millionth of a meter).

* A mask is the best way to protect the face and lungs from particles smaller than 10 microns (such particles are PM10 by definition).

These results were derived from simulations using a computational model of a person wearing a three-layer surgical mask with pleats and then using numerical methods to track the particles through the mask.

Used mask against no mask

The efficiency of a mask for filtering particles varies greatly between new and old masks. The simulations showed that a new surgical mask has a filtration efficiency of up to 65%, which can drop to 25% after multiple uses.

Study author Jinxiang Xi, a biomedical engineer at the University of Massachusetts at Lowell, explained how the airflow around the face differs with and without a mask. “Without a mask, air enters a narrow region in the mouth and nose. With a mask, the airflow comes close to the mouth / nose over the entire face of the mask, ”said Xi The Indian Express, by email.

Also, the airflow around the face is slower when you wear a mask. “The mask can slow down the inspiratory airflow considerably and spread (droplets) over the entire surface of the mask. The slower flow of air makes it easier to breathe droplets into the nose, ”said Xi.

The amount of droplets you breathe in depends, of course, on how many of them pass through the mask – which is what makes filtration efficiency critical.

“The main finding from this study is that an old mask with poor filtration efficiency may not look good. If the mask filtration efficiency drops below 30% (after 2-3 uses), the airflow is more favorable than without a mask, and therefore “an old mask” offers relatively poor protection for the upper airways from smaller particles, “said Xi.

The nose and the lungs

An efficient mask can reduce the buildup in the lungs by three times for particles ranging in size from 1 to 10 microns. In the upper airways, a 65% efficiency mask will also reduce the deposition of all particle sizes except those 1 to 3 microns in size.

“Our noses also act as filters,” Xi explained. “Without a mask, the nose filters out all the large particles and only allows smaller particles to get into the lungs. When you wear a mask, the mask blocks almost all large particles, thus protecting the nose from large particles. Due to the slower flow rate, more small particles are now deposited in the nose and thus protect the lungs from small particles. “

Wrinkles & Particles

Once particles have passed through the mask, they are deposited in high concentrations in the folds (or folds). The study found a high rate of flow in the folds.

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“More droplets crossed the folds (or folds) and have a slightly higher speed (ie 10 cm / s). In addition, the air currents through the folds are more focused on the nose, resulting in more inhalation of the nose to move a little faster, ”Xi said.

The general takeaway is that thinking twice about the results, wearing a mask is always better than wearing no mask. “It is true that one wearer protects others. This also applies to self-protection against large aerosols, ”said Xi. “However, this does not always apply to self-protection against small droplets (PM2.5). Wearing a used mask with poor filtration efficiency may pose a higher risk to the wearer. “

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