New SARS-CoV-2 variants not only change the infectiousness of the virus, the spread of the mask types in everyday public life is also affected. The Omikron variant is replacing the diversified, light surgical mask in favor of the more protective but also more expensive FFP2 mask. Like the surgical mask, this is clearly designed as a disposable product. But very often the mask is worn several times, sometimes even for several days. Therefore, Hamid Azizi and Christian Schwarzbauer from the Munich University of Applied Sciences are now investigating the reusability of FFP2 masks. Central aspects were filter performance and breathing resistance.
For their series of studies, the two researchers chose 15 FFP2 mask models available in Germany – purchased from discounters, drugstores or online (see table below for list). The researchers did not select any subjects for the practical tests, but constructed a special ventilation simulator to make the tests easier to compare. This simulator simulated regular breathing during light physical work. Both the flow of the breathing air and the humidification of the breath were imitated as realistically as possible. Each mask type was “worn” by the simulator’s head model for 22 hours. In addition, the researchers placed the masks in a dry oven at 80 degrees Celsius for “decontamination” after twelve hours and for one hour at the end of the simulation.
Before and after the usage simulation, the researchers determined the filter performance and breathing resistance of all mask types in cooperation with the ift Rosenheim testing laboratory. With the exception of one outlier (brand “Mea Vita”), new masks met the standard of six percent transmittance for FFP2 masks (DIN EN 149:2009-08). Twelve types even showed a transmittance of less than one percent, which meets the requirements of FFP3 masks. 14 out of 15 masks also complied with the maximum permissible breathing resistance at 30, 95 or 160 liters of breathing air per minute.
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Mask tests for permeability and breathing resistance
Even after the almost one-day stress test, most mask types were able to convince. Eight models had a slightly worse filter performance, but all of them were well below the limit value of 6 percent. Only the outlier model continued to break the limit, this time even with a transmittance of more than twelve percent (see figure below). The breathing resistance decreased only slightly with most masks, so they still met the norm. Only one mask type (“Altapharma” brand) was slightly above the allowable limit for breathing resistance before and after the simulation.
For everyday mask wearing, good filter performance with a low degree of permeability combined with low breathing resistance is desirable. This criterion was best met by a mask (brand “3M Aura 9320”). But the other 13 models also served their purpose very well. This small series of studies shows that most types of masks can provide good protection even after 22 hours of use – assuming regular decontamination in hot, dry oven air and the correct wearing of the mask.
Now everyone decides for themselves whether they use a new FFP2 mask at least once a day or decontaminate a worn mask in the oven in the evening. The aspects of waste avoidance and energy consumption must be weighed up. However, according to current data, it is not advisable to wear the disposable FFP2 mask for longer than 22 hours.