Total Inward Leakage of Nanoparticles Through Filtering Facepiece Respirators

Abstract

Nanoparticle (<100 nm size) exposure in workplaces is a major concern because of the potential impact on human health. National Institute for Occupational Safety and Health (NIOSH)-approved particulate respirators are recommended for protection against nanoparticles based on their filtration efficiency at sealed conditions. Concerns have been raised on the lack of information for face seal leakage of nanoparticles, compromising respiratory protection in workplaces. To address this issue, filter penetration and total inward leakage (TIL) through artificial leaks were measured for NIOSH-approved N95 and P100 and European certified Conformit'e Europe'en-marked FFP2 and FFP3 filtering facepiece respirator models sealed to a breathing manikin kept inside a closed chamber. Monodisperse sucrose aerosols (8-80 nm size) generated by electrospray or polydisperse NaCl aerosols (20-1000 nm size) produced by atomization were passed into the chamber. Filter penetration and TIL were measured at 20, 30, and 40 l min(-1) breathing flow rates. The most penetrating particle size (MPPS) was ∼50 nm and filter penetrations for 50 and 100 nm size particles were markedly higher than the penetrations for 8 and 400 nm size particles. Filter penetrations increased with increasing flow rates. With artificially introduced leaks, the TIL values for all size particles increased with increasing leak sizes. With relatively smaller size leaks, the TIL measured for 50 nm size particles was ∼2-fold higher than the values for 8 and 400 nm size particles indicating that the TIL for the most penetrating particles was higher than for smaller and larger size particles. The data indicate that higher concentration of nanoparticles could occur inside the breathing zone of respirators in workplaces where nanoparticles in the MPPS range are present, when leakage is minimal compared to filter penetration. The TIL/penetration ratios obtained for 400 nm size particles were larger than the ratios obtained for 50 nm size particles at the three different flow rates and leak sizes indicating that face seal leakage, not filter penetration, contributing to the TIL for larger size particles. Further studies on face seal leakage of nanoparticles for respirator users in workplaces are needed to better understand the respiratory protection against nanoparticle exposure.

Effects of Breathing Frequency and Flow Rate on the Total Inward Leakage of an Elastomeric Half-Mask Donned on an Advanced Manikin Headform

“…The cited study did not detect an MPPS for wood and paper aerosols due to multiple peaks in the ${\mathrm{TIL}}_{d_{\mathrm{normalp}}}$ curves. Previous TIL studies have focused on N95 FFRs or surgical masks, for which the particle size effect was found significant and the TIL values were close to the penetration levels observed for the filters only (Myers et al , 1991; Cho et al , 2010a; Rengasamy and Eimer, 2011). At the same time, little information has been generated with respect to the MPPS for face seal leakage.…”

“…At the same time, little information has been generated with respect to the MPPS for face seal leakage. When testing N95 FFRs with artificially created cylindered leaks, Rengasamy and Eimer (2011) found that for leak diameters ≤1.65 mm, the MPPS was ~50 nm; we believe that this value likely represents the N95 filter penetration, whereas the TIL of the respirator used in this study (equipped with P100 filters) is primarily governed by the face seal leakage penetration. This likely explains the suppressed peaks or the plateaus seen in the curves presented in Fig.…”

“…Several published FFR studies also reported that face seal penetration decreased with increase in breathing flow when challenged with particles >500 nm (Chen et al , 1990; Cho et al , 2010b). On the other hand, another FFR study observed no significant increase or decrease in face seal penetration by 8–400 nm particles associated with increasing breathing flow (Rengasamy and Eimer, 2011). …”

“…To account for these two penetration pathways (filter and face seal leakage), NIOSH has proposed the total inward leakage (TIL) method for testing respirators (NIOSH/CDC, 2009). Several studies addressed this issue by creating artificial slit-like or circular leaks to assess the face seal leakage (Hinds and Bellin, 1987; Myers et al , 1991; Chen and Willeke, 1992; Rengasamy and Eimer, 2011). However, artificial fixed leaks are not representative of actual conditions when a respirator is worn by humans.…”

Comparison of Simulated Workplace Protection Factors Offered by N95 and P100 Filtering Facepiece and Elastomeric Half-Mask Respirators against Particles of 10 to 400 nm

“…It is acknowledged that the filtration efficiency of P100 rated filters is higher than that of N95 rated filters for nanoparticles. However, contribution from the faceseal leakage could be higher for P100 respirators (both FFR and EHR) due to higher breathing resistance (pressure drop) versus N95 respirators [ 19 ] , although there is some debate [ 20 ] . As a result, the performance for P100 respirators (i.e., any FFR or EHR with aP100 filter) may be similar to the N95 respirators 1 if the respirator does not seal well.…”