For medical face masks, we often see these characters such as PFE, BFE and VFE. What is the meaning of these indicators? There is a certain correlation between PFE and BFE. For medical face masks, with NaCl aerosol, flow rate 30L/min, when the PFE is higher than 90.0%, the BFE can be higher than 99.0%. Compared with VFE, PFE, when the PFE reach 91.83%, the VFE can reach more than 98%, even higher than 99%. Test aerosol of BFE and VFE are bacteria and bacteriophage respectively, and biological experiment is a very troublesome and complicated process. For mask manufacturers, these indicators are too complex as routine tests. Therefore, some indirect experiences are often used in practice.
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