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Face shields and valve masks protect other people from coronavirus infection less reliably than cloth masks, American researchers report after video analyzes. Consequently, potentially infectious breath droplets can easily move around the plastic visors.
For the study, the scientists sprayed distilled water and glycerin in tiny droplets through the mouth of a doll, as if someone were coughing or sneezing. They then used lasers to study how the droplets spread in a dark room.
Others are hardly protected
Initially, a visor was able to block the ejection of the droplets, Florida Atlantic University scientists report in the journal “Physics of Fluids.” But: “The ejected droplets can move around the visor relatively easily and spread over a larger area.”
The effect is similar for valve masks. With them, the breathable air passes unfiltered through the valve opening and is distributed. Therefore, such a mask is not suitable for preventing the spread of the coronavirus by an infected person, the researchers report. According to the researchers, special respiratory masks (standard N95) and frequently used simple cloth masks allow significantly fewer drops to pass through.
The study did not focus on whether visors or protective masks with valves can protect a person from infection by the virus. Rather, it was about the question of whether an infected person can be prevented from spreading the virus, that is, whether wearing the mask can protect other people from infection.
It was already known that such third-party protection is not available for mask with valves. They only filter the air that is inhaled. In Germany, the Federal Institute for Medicines and Health Products (BfArM) and the Robert Koch Institute (RKI) have emphasized this.
Many people would wear protective visors and masks with a valve because they are more comfortable than non-valve masks, US researchers report. But that could undermine efforts to contain the virus.
