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

Abstract

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 500 nm. 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 50 nm; for particles above 50 nm, the total penetration was not significantly affected by particle size and breathing frequency; however, the effect of MIF remained significant.

Performance of Composite Filters Assembled from Multiple Layers of Basic Filtration Media

“…The filtration performance of FFRs has been widely investigated (e.g., Brosseau et al, 1997;Balazy et al, 2006a, b;Eninger et al, 2008;Rengasamy et al, 2008;Eshbaugh et al, 2009;Rengasamy et al, 2009;Cho et al, 2010;He et al, 2013;Zuo et al, 2013). For example, Balazy et al (2006b) evaluated the filtration performance of N95 FFRs using NaCl particles ranging from 10 to 600 nm in diameter.…”

A comparison of total inward leakage measured using sodium chloride (NaCl) and corn oil aerosol methods for air-purifying respirators

“…Recent studies also showed TIL was particle size-dependent for different types of aerosols. [ 10 , 16 ] …”

Respiratory Flow Characterization of Workers in Healthcare Environment

“…when exposed to a range of known and unknown occupational infectious agents (CDC, 2014). Traditionally, surgical masks and N95 filtering facepiece respirators (FFRs) are widely used to reduce exposure to airborne hazards in healthcare settings, even though various studies have demonstrated that surgical masks offer minimal protection and N95 FFRs are not comfortable to use due to the high air resistance of the filter (Davidson et al, 2013;He et al, 2013b;He et al, 2014;Rengasamy et al, 2014). Following the 2003 severe acute respiratory syndrome (SARS), 2009 H1N1 influenza, and the recent Ebola outbreak, significant attention has been directed towards using powered air-purifying respirators (PAPR) for HCWs (IOM, 2015).…”

“…However, the users have to increase their breathing effort to overcome the resistance of the N95 respirator filter, difficulty breathing was therefore identified, leading to hypoventilation and elevated CO2 level inside the respirator, which maybe the reason for one-third of HCWs' headaches for long-term use of N95 FFRs (Lim et al, 2006). Since improperly fitted N95 FFR would lead to significant leakage and noteworthy decrements in protection level (He et al, 2013b;Rengasamy and Eimer, 2011), annual fit-testing is required for N95 FFRs. An assigned protection factor (APF) of N95 FFR is 10, indicating properly fitted wearers could expect to inhale no more than one-tenth of the concentration of aerosols in the workplace (OSHA, 2006).…”

“…Surgical masks and N95 filtering facepiece respirators (FFRs) are traditional respiratory protection equipment (RPE) used by HCWs in hospital environment (Carias et al, 2015;Wizner et al, 2016). However, various studies have shown that surgical masks are not designed to protect against bioaerosols <1 µm, and N95 FFRs are not comfortable to use due to high breathing resistance (Davidson et al, 2013;He et al, 2013b;2014;Rengasamy et al, 2014). Frequently outbreaks of highly contagious pathogens (e.g., 2003SARS, 2009H1N1, and 2014 have emphasized the need of powered air-purifying respirators (PAPRs) for HCWs (Khoo et al, 2005;IOM, 2015;Wizner et al, 2016).…”