"Surgical masks are usually worn by medical staff and have received numerous tests in clinical environments. However, there was no quick, simple and inexpensive way to demonstrate the effectiveness of a variety of other mask types such as loose fabric masks or facial coverings," said Fischer.
How was the experiment carried out with masks?
For the study, the researchers developed an easy -to -carry, inexpensive laser experiment in order to measure the amount of drops of breath that leak out from different covers when the carrier speaks. The setup consisted of a black box (dark housing), a laser, lens and a cell phone camera-everything costs about $ 200. The laser rays were used to create a light layer within the box.
For the test, a person was asked to wear every mask and to stand in the dark enclosure. Then the person was asked to say the sentence "stay healthy, humans" five times in the direction of the laser beam, who scattered the light of the droplets released during the speech. Using a mobile camera, the droplets were recorded and a simple computer algorithm counted them.
"Companies and manufacturers can set up this and test their mask designs before they are manufactured, which would also be very useful," said the researchers.
The masks were classified based on the relative number of droplets on a scale of 1.0, which represents the number of droplets that met the leaf when the person had no facial cover until 0.0, if minimal or no droplets were distributed.
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The different types of face masks used by researchers from Duke University for the study (source:
Science Advances)
What did the study result?
The experiment showed that N95 masks without exhaling valves, droplets best blocked and had a relative number of droplets of zero. N95 masks with valves took seventh place and registered a relative number of droplets in the range from 0.1 to 0.2.
"Adapted N95 masks without valve are far superior to the N95 masks with valve, since the exhalation valve is opened outwards for a strong air flow. This can reduce the protection of the people around the wearer," says the study.
The three -layer surgical mask finished second and had a more variable relative number of droplets in the range from zero to 0.1. At the third and fourth place, those with polypropylene were: the cotton polypropylene cotton mask and the 2-layer polypropylene apron mask.
Four different two -layered cotton masks and a single -layer cotton mask occupied from fifth to the eleventh with a relative number of droplets from zero to 0.4. At the ninth place there was a single-layer Maxima AT-Mask, while knitted masks were at the twelfth position and had a large relative number of droplets from about 0.1 to almost 0.6
The study shows that the last two masks could actually be worse than to wear no mask at all. At number 13, the headscarf had an area of 0.2 to 1.1, while the fleece mask ended at number 14, with an average relative drop of droplets of 1.1. To put it, this means that a person who carries a fleece mask has produced more droplets than if the nose and mouth were not covered at all. The researchers said this was likely because these types of masks disassemble large droplets into smaller particles so that they can slip out of the cover sides more easily.
Drop transmission by face masks. (A) Relative droplet transmission through the corresponding mask. (B) The time development of the number of droplets (left axis) is shown for representative examples that are marked in (a) with the corresponding color: no mask (green), bandana (red), cotton mask (orange) and surgically (blue - not visible on this scale). The cumulative number of droplets for these cases is also displayed (right axis). (Source: Science Advances)
borders of the study
However, the study has its own limits. Not all possible versions of the different masks have been tested and you cannot judge how much virus spreads in the droplets. Each droplet may not contain enough SARS-COV2 to infect others. In addition, only the droplets that emerge from the front of the spokesman's mouth were measured in the study, and the droplets released by the sides of the mask were not taken into account. "This was just a demonstration - further work is necessary to examine differences in masks, speakers and their wearing comfort," said Fischer.
What kind of masks does the Ministry of Health, the WHO and the CDC recommend?
The Ministry of Health encouraged the public to use homemade facial masks or coats of fabric, preferably cotton, that can be bound or fastened via nose and mouth. The World Health Organization proposed in its revised guidelines in June that everyone in public should wear fabric masks (not medically). Fabric masks should contain at least three layers of different materials. The US centers for the control and prevention of diseases have stated in their latest guidelines that masks made of densely woven fabric should be used, but should not have valves or ventilation slots.
Source: IndianExpress
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