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Wstarted in spring as a small experiment for a clinic’s own needs, it has now resulted in a scientific study. At the Gießen and Marburg University Hospital, protective equipment was in short supply at the start of the corona pandemic in March and April. If masks were available, they were those without certification, supplied at exorbitant prices by previously unknown manufacturers. In Marburg, a team led by Professor Frank Günther, the hospital’s chief of hygiene, began a series of tests. “At that time we couldn’t even assess whether these masks from China were adequate to protect us and our patients,” says Günther. “We quickly discovered that there are significant differences.” Meanwhile, medical professionals have also tried everyday masks, such as those offered by clothing manufacturers, and have come up with some surprising findings. You are preparing a publication in a specialized magazine.
The scientists screwed on a plexiglass box, a sealed cube with an edge length of half a meter. On the one hand, the smallest particles are introduced through a hose: aerosols with a diameter of less than five micrometers, that is, five thousandths of a millimeter, and droplets that are a little larger but still small. These particles simulate what happens when a person exhales. A fan spins the air in the chamber to distribute all the particles evenly.
The doctors put a head model there. It is based on data from American researchers who have measured thousands of heads and calculated average values from them. The Marburg doctors sent these values to a 3D printer. The measuring head with this shape can be fitted with any face mask. Its mouth sucks in air and a laser spectrometer measures how many particles of what size get there. The reverse experiment setup can determine how many particles still pass through the mask when you exhale. A range of 0.3 to 10 microns is tested.
Mask fit does not influence standard test
The test setup in Marburg has a great advantage over standardized test methods: it is much more practical. “In the oral and nasal medical protection tests required for approval, only the material is tested,” says Christian Sterr, potential specialist in hygiene and environmental medicine. “It doesn’t matter how the mask fits and if there is a leak through which air can pass over the edge.”
Christian Sterr (front) and Frank Günther equip the head in the measuring chamber with medical protection for the mouth and nose, which is often used in operating rooms.
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Image: Lucas Bäuml
The first finding was that simple medical protection for the mouth and nose, such as that used in operations, works surprisingly well in comparison. It conforms quite well to the shape of the head, which means there is little leakage. Aerosols were significantly reduced by more than 50 percent, droplets by more than 70. Many other masks were stiff and did not fit properly, some of them only had 20 percent filtering performance, although they supposedly met the Chinese standard KN95, which is supposed to correspond to the European standard FFP2. Such masks, including those that the federal government and the state of Hesse had acquired in the crown pandemic, could not be worn in hospitals. “We noticed that there was just standard information printed there that had nothing to do with reality,” says Günther.
The second finding was the confirmation of a long-standing assumption: that masks, even simple mouth and nose protection, protect the wearer very well and not just the opposite person. “For us hospital hygienists, this has been common for years,” says Günther, “and I was surprised that the public initially gave a different impression. There is one thing to say: we do not have enough skins to equip the entire population with them. But you can’t say they are only there for external protection anyway, and months later you can say that now it does something for me. I was surprised that this was also featured in professional circles. Credibility is lost. “
