Masks put to the test: New study examines the effects of masks with frightening and positive results (video)

„Chirurgische Masken werden üblicherweise von medizinischem Personal getragen und haben in klinischen Umgebungen zahlreiche Tests erhalten. Es gab jedoch keine schnelle, einfache und kostengünstige Möglichkeit, die Wirksamkeit einer Vielzahl anderer Maskentypen wie loser Stoffmasken oder Gesichtsbedeckungen zu demonstrieren “, sagte Fischer.

How was the experiment with masks carried out?

For the study, researchers developed an easy-to-perform, low-cost laser experiment to measure the amount of respiratory droplets that emerge from various coverings when the wearer speaks. The setup consisted of a black box (dark housing), a laser, a lens and a cell phone camera - all costing about $200. The laser beams were used to create a layer of light within the box.
For the test, one person was asked to wear each mask and stand in the dark enclosure. Then the person was asked to say the phrase “Stay healthy, people” five times in the direction of the laser beam, which 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 this up and test their mask designs before they are manufactured, which would also be very useful,” the researchers said.
The masks were ranked based on relative droplet count on a scale from 1.0, representing the number of droplets that hit the sheet when the person did not have a face covering, to 0.0, when minimal or no droplets were spread.

Die verschiedenen Arten von Gesichtsmasken, die von Forschern der Duke University für die Studie verwendet wurden (Quelle: Science Advances)

What did the study show?

The experiment found that N95 masks without exhalation valves blocked droplets best and had a relative droplet count of zero. N95 masks with valves ranked seventh, registering a relative droplet count in the range of 0.1 to 0.2.
"Fitted N95 masks without a valve are far superior to N95 masks with a valve because the exhalation valve is opened to allow a strong flow of air to the outside. This can reduce the protection of those surrounding the wearer," the study says.
The three-layer surgical mask came in second and had a more variable relative droplet count, ranging from zero to 0.1. In third and fourth place were the ones with polypropylene: the cotton-polypropylene cotton mask and the 2-layer polypropylene apron mask.

Four different two-layer cotton pleat masks and one single-layer cotton pleat mask occupied sites from the fifth to the eleventh with a relative droplet number range of zero to 0.4. In the ninth position was a single-layer Maxima AT mask, while knitted masks were in the twelfth position and had a wide relative droplet count range from about 0.1 to just under 0.6.

The study shows that the latter two masks could actually be worse than not wearing a mask at all. At number 13, the bandana had a range of 0.2 to 1.1, while the non-woven mask ended at number 14, with an average relative droplet count of 1.1. Simply put, this means that a person wearing a non-woven mask generated more droplets than if their nose and mouth were not covered at all. The researchers said this is likely because these types of masks break down large droplets into smaller particles, making it easier for them to slip out of the sides of the covering.

Tröpfchenübertragung durch Gesichtsmasken. (A) Relative Tröpfchenübertragung durch die entsprechende Maske. (B) Die zeitliche Entwicklung der Tröpfchenzahl (linke Achse) ist für repräsentative Beispiele gezeigt, die in (A) mit der entsprechenden Farbe gekennzeichnet sind: Keine Maske (grün), Bandana (rot), Baumwollmaske (orange) und chirurgisch ( blau – auf dieser Skala nicht sichtbar). Die kumulative Tröpfchenzahl für diese Fälle wird ebenfalls angezeigt (rechte Achse). (Quelle: Science Advances)

Limitations of the study

However, the study has its own limitations. Not all possible versions of the different masks have been tested and there is no way to judge how much virus is spreading in the droplets. Each droplet may not contain enough SARS-CoV2 to infect others. Additionally, the study only measured droplets emanating from the front of the speaker's mouth and did not take droplets released from the sides of the mask into account. “This was just a demonstration – more work is needed to examine differences in masks, speakers and their comfort,” Fischer said.

What type of masks has the Department of Health, WHO and CDC recommended?

The Health Ministry has encouraged the public to use homemade face masks or coverings made of cloth, preferably cotton, that can be tied or secured over the nose and mouth. The World Health Organization suggested that everyone wear cloth (non-medical) masks in public in its revised guidelines in June. Cloth masks should contain at least three layers of different materials. The U.S. Centers for Disease Control and Prevention has said in its latest guidelines that masks made of tightly woven fabric should be used but should not have valves or vents.

Source: Indian Express

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