Effect of Particle Size on the Performance of an N95 Filtering Facepiece Respirator and a Surgical Mask at Various Breathing Conditions

The effect of aerosol particle size on the performance of an N95 filtering facepiece respirator (FFR) and a surgical mask (SM) was evaluated under different breathing conditions, including breathing frequency and mean inspiratory flow (MIF) rate. The FFR and SM were sealed on a manikin headform and challenged with charge-equilibrated NaCl aerosol. Filter penetration (P-filter) was determined as the ratio of aerosol concentrations inside and outside the FFR/SM size-selectively (28 channels) within a range of 20 to 500nm. In addition, the same models of the FFR and SM were donned, but not sealed, on an advanced manikin headform covered with skin-like material. Total inward leakage (TIL), which represents the total particle penetration, was measured under conditions identical to the filter penetration experiment. Testing was conducted at four mean MIFs (15, 30, 55, and 85 L/min) combined with five breathing frequencies (10, 15, 20, 25, and 30 breaths/min). The results show that SM produced much higher P-filter and TIL values, and thus provide little protection against aerosols in the size range tested. P-filter was significantly affected by particle size and breathing flow rate (p < 0.05) for the tested FFR and SM. Surprisingly, for both devices, P-filter as a function of the particle size exhibited more than one peak under all tested breathing conditions. The effect of breathing frequency on P-filter was generally less pronounced, especially for lower MIFs. For the FFR and SM, TIL increased with increasing particle size up to about 50nm; for particles above 50nm, the total penetration was not significantly affected by particle size and breathing frequency; however, the effect of MIF remained significant.