Penetration of Fiber Versus Spherical Particles Through Filter Media and Faceseal Leakage of N95 Filtering Facepiece Respirators with Cyclic Flow

Abstract

This study investigated differences in penetration between fibers and spherical particles through faceseal leakage of an N95 filtering facepiece respirator. Three cyclic breathing flows were generated corresponding to mean inspiratory flow rates (MIF) of 15, 30, and 85 L/min. Fibers had a mean diameter of 1 μm and a median length of 4.9 μm (calculated aerodynamic diameter, d ae = 1.73 μm). Monodisperse polystyrene spheres with a mean physical diameter of 1.01 μm (PSI) and 1.54 μm (PSII) were used for comparison (calculated d ae = 1.05 and 1.58 μm, respectively). Two optical particle counters simultaneously determined concentrations inside and outside the respirator. Geometric means (GMs) for filter penetration of the fibers were 0.06, 0.09, and 0.08% at MIF of 15, 30, and 85 L/min, respectively. Corresponding values for PSI were 0.07, 0.12, and 0.12%. GMs for faceseal penetration of fibers were 0.40, 0.14, and 0.09% at MIF of 15, 30, and 85 L/min, respectively. Corresponding values for PSI were 0.96, 0.41, and 0.17%. Faceseal penetration decreased with increased breathing rate for both types of particles (p ≤ 0.001). GMs of filter and faceseal penetration of PSII at an MIF of 30 L/min were 0.14% and 0.36%, respectively. Filter penetration and faceseal penetration of fibers were significantly lower than those of PSI (p < 0.001) and PSII (p < 0.003). This confirmed that higher penetration of PSI was not due to slightly smaller aerodynamic diameter, indicating that the shape of fibers rather than their calculated mean aerodynamic diameter is a prevailing factor on deposition mechanisms through the tested respirator. In conclusion, faceseal penetration of fibers and spherical particles decreased with increasing breathing rate, which can be explained by increased capture by impaction. Spherical particles had 2.0-2.8 times higher penetration through faceseal leaks and 1.1-1.5 higher penetration through filter media than fibers, which can be attributed to differences in interception losses.

Evaluation of N95 Filtering Facepiece Respirators Challenged with Engineered Nanoparticles

“…Penetration of welding fume particles was lower than that of sodium chloride test particles, suggesting that the sodium chloride is a conservative surrogate for weld fume. Cho et al (2013) found for an N95 FFR that penetration of a glass fiber aerosol with an aerodynamic diameter of 1.73 µm was less than polystyrene latex spheres of 1.05 and 1.58 µm in a N95 filter, although all aerosols showed penetration below 5%.…”

Quantitative analysis of the role of fiber length on phagocytosis and inflammatory response by alveolar macrophages

“…Short fibers were obtained by crushing at 10 tons and re-crushed at 15 tons, while long fibers were crushed at 2 tons. Each batch yields ~ 1.3 g of fiber [26]. …”

Evaluation of particle penetration and breathing resistance of N95 filtering face-piece respirators and uncertified dust masks

“…However, when FFR users breathe, air moves in two directions, inhalation and exhalation flows that are similar to a cyclic flow (Johnson, 1993). Despite a large amount of research associated with evaluating FFRs, few studies have been conducted to determine FFR performance under cyclic flow (Cho et. al.…”

“…NIOSH certifies FFRs when the inhalation BR is less than 35 mm of H2O and the exhalation BR is less than 25 mm of H2O measured at constant one-direction airflow of 85 L min -1 (NIOSH, 2005). However, FFR efficiency and BR can be affected by numerous conditions such as air velocity, particle size diameter, fiber diameter, and humidity (Johnson, 1993;Cho et al 2010;Cho et al 2013).…”

“…Despite a large amount of research associated with evaluating FFRs, few studies have been conducted to determine FFRs efficiency under cyclic flow (Cho et. al.…”