Experimental evaluation of the bidirectional filtration efficiency of respirators and face masks against airborne particles during cyclic breathing

In this work we investigate the bidirectional filtration efficiencies of respirators, such as FFP2 masks and medical masks, under cyclic breathing and different fits. We developed a test bench, which consists of a test chamber with an artificial head, and which is connected to a specially developed artificial breathing function. The exhalation filtration performance of masks can be evaluated by exhaling particle-laden air into the test chamber. Similarly, the inhalation filtration performance can be evaluated by inhalation of particle-laden air from the test chamber. We compare four different types of masks (medical mask and three types of FFP2 masks). In addition, we investigate the influence of different mask fits (e.g., nose clip fitting) on the filtration efficiency of the masks, as a perfect mask fit cannot always be guaranteed in realistic scenarios and filtration efficiency may therefore be reduced. The results show that different maximum filtration efficiencies are achieved depending on the mask type. Only one of the three FFP2 masks can achieve filtration efficiencies above 89% while one only achieves a maximum of 59%. Depending on the fit, the medical mask can achieve up to 55% for self-protection. The fit of the mask has a major influence on the filtration efficiencies. If the mask is used without putting on the nose clip, a value of only 10 to 45% can be achieved, depending on the mask type and direction of protection. With two of the FFP2 masks, simply putting on the nose clip is enough to achieve filtration efficiencies of at least 75%. It was also shown that a medical mask with the best fit protects at least as well in both directions as the three FFP2 masks with the worst fit level. In addition, the fit of the mask and the filtration efficiency correlate very well with the measured pressure difference across the mask.