Xinjian He

Manikin-based performance evaluation of elastomeric respirators against combustion particles.

This study investigated the effects of faceseal leakage, breathing flow, and combustion material on the overall (non-size-selective) penetration of combustion particles into P-100 half and full facepiece elastomeric respirators used by firefighters. Respirators were tested on a breathing manikin exposed to aerosols produced by combustion of three materials (wood, paper, and plastic) in a room-size exposure chamber. Testing was performed using a single constant flow (inspiratory flow rate = 30 L/min) and three cyclic flows (mean inspiratory flow rates = 30, 85, and 135 L/min). Four sealing conditions (unsealed, nose-only sealed, nose and chin sealed, and fully sealed) were examined to evaluate the respirator faceseal leakage. Total aerosol concentration was measured inside (Cin) and outside (Cout) the respirator using a condensation particle counter. The total penetration through the respirator was determined as a ratio of the two (P = Cin / Cout). Faceseal leakage, breathing flow type and rate, and combustion material were all significant factors affecting the performance of the half mask and full facepiece respirators. The efficiency of P-100 respirator filters met the NIOSH certification criteria (penetration ≤0.03%); it was not significantly influenced by the challenge aerosol and flow type, which supports the current NIOSH testing procedure using a single challenge aerosol and a constant airflow. However, contrary to the NIOSH total inward leakage (TIL) test protocol assuming that the result is independent on the type of the tested aerosol, this study revealed that the challenge aerosol significantly affects the particle penetration through unsealed and partially sealed half mask respirators. Increasing leak size increased total particle penetration. The findings point to some limitations of the existing TIL test in predicting protection levels offered by half mask elastomeric respirators.

Laboratory Evaluation of the Particle Size Effect on the Performance of an Elastomeric Half-mask Respirator against Ultrafine Combustion Particles

OBJECTIVES This study quantified the particle size effect on the performance of elastomeric half-mask respirators, which are widely used by firefighters and first responders exposed to combustion aerosols. METHODS One type of elastomeric half-mask respirator equipped with two P-100 filters was donned on a breathing manikin while challenged with three combustion aerosols (originated by burning wood, paper, and plastic). Testing was conducted with respirators that were fully sealed, partially sealed (nose area only), or unsealed to the face of a breathing manikin to simulate different faceseal leakages. Three cyclic flows with mean inspiratory flow (MIF) rates of 30, 85, and 135 L/min were tested for each combination of sealing condition and combustion material. Additional testing was performed with plastic combustion particles at other cyclic and constant flows. Particle penetration was determined by measuring particle number concentrations inside and outside the respirator with size ranges from 20 to 200 nm. RESULTS Breathing flow rate, particle size, and combustion material all had significant effects on the performance of the respirator. For the partially sealed and unsealed respirators, the penetration through the faceseal leakage reached maximum at particle sizes >100 nm when challenged with plastic aerosol, whereas no clear peaks were observed for wood and paper aerosols. The particles aerosolized by burning plastic penetrated more readily into the unsealed half-mask than those aerosolized by the combustion of wood and paper. The difference may be attributed to the fact that plastic combustion particles differ from wood and paper particles by physical characteristics such as charge, shape, and density. For the partially sealed respirator, the highest penetration values were obtained at MIF = 85 L/min. The unsealed respirator had approximately 10-fold greater penetration than the one partially sealed around the bridge of the nose, which indicates that the nose area was the primary leak site.

How Does Breathing Frequency Affect the Performance of an N95 Filtering Facepiece Respirator and a Surgical Mask Against Surrogates of Viral Particles

Breathing frequency (breaths/min) differs among individuals and levels of physical activity. Particles enter respirators through two principle penetration pathways: faceseal leakage and filter penetration. However, it is unknown how breathing frequency affects the overall performance of N95 filtering facepiece respirators (FFRs) and surgical masks (SMs) against viral particles, as well as other health-relevant submicrometer particles. A FFR and SM were tested on a breathing manikin at four mean inspiratory flows (MIFs) (15, 30, 55, and 85 L/min) and five breathing frequencies (10, 15, 20, 25, and 30 breaths/min). Filter penetration (Pfilter) and total inward leakage (TIL) were determined for the tested respiratory protection devices against sodium chloride (NaCl) aerosol particles in the size range of 20 to 500 nm. “Faceseal leakage-to-filter” (FLTF) penetration ratios were calculated. Both MIF and breathing frequency showed significant effects (p < 0.05) on Pfilter and TIL. Increasing breathing frequency increased TIL for the N95 FFR whereas no clear trends were observed for the SM. Increasing MIF increased Pfilter and decreased TIL resulting in decreasing FLTF ratio. Most of FLTF ratios were >1, suggesting that the faceseal leakage was the primary particle penetration pathway at various breathing frequencies. Breathing frequency is another factor (besides MIF) that can significantly affect the performance of N95 FFRs, with higher breathing frequencies increasing TIL. No consistent trend of increase or decrease of TIL with either MIF or breathing frequency was observed for the tested SM. To potentially extend these findings beyond the manikin/breathing system used, future studies are needed to fully understand the mechanism causing the breathing frequency effect on the performance of respiratory protection devices on human subjects.

Penetration of Combustion Aerosol Particles Through Filters of NIOSH-Certified Filtering Facepiece Respirators (FFRs)

Filtering facepiece respirators (FFRs) are commonly worn by first responders, first receivers, and other exposed groups to protect against exposure to airborne particles, including those originated by combustion. Most of these FFRs are NIOSH-certified (e.g., N95-type) based on the performance testing of their filters against charge-equilibrated aerosol challenges, e.g., NaCl. However, it has not been examined if the filtration data obtained with the NaCl-challenged FFR filters adequately represent the protection against real aerosol hazards such as combustion particles. A filter sample of N95 FFR mounted on a specially designed holder was challenged with NaCl particles and three combustion aerosols generated in a test chamber by burning wood, paper, and plastic. The concentrations upstream (Cup) and downstream (Cdown) of the filter were measured with a TSI P-Trak condensation particle counter and a Grimm Nanocheck particle spectrometer. Penetration was determined as (Cdown/Cup) ×100%. Four test conditions were chosen to represent inhalation flows of 15, 30, 55, and 85 L/min. Results showed that the penetration values of combustion particles were significantly higher than those of the “model” NaCl particles (p < 0.05), raising a concern about applicability of the N95 filters performance obtained with the NaCl aerosol challenge to protection against combustion particles. Aerosol type, inhalation flow rate and particle size were significant (p < 0.05) factors affecting the performance of the N95 FFR filter. In contrast to N95 filters, the penetration of combustion particles through R95 and P95 FFR filters (were tested in addition to N95) were not significantly higher than that obtained with NaCl particles. The findings were attributed to several effects, including the degradation of an N95 filter due to hydrophobic organic components generated into the air by combustion. Their interaction with fibers is anticipated to be similar to those involving “oily” particles. The findings of this study suggest that the efficiency of N95 respirator filters obtained with the NaCl aerosol challenge may not accurately predict (and rather overestimate) the filter efficiency against combustion particles.

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

OBJECTIVES The objective of this study was to investigate the effects of breathing frequency and flow rate on the total inward leakage (TIL) of an elastomeric half-mask donned on an advanced manikin headform and challenged with combustion aerosols. METHODS An elastomeric half-mask respirator equipped with P100 filters was donned on an advanced manikin headform covered with life-like soft skin and challenged with aerosols originated by burning three materials: wood, paper, and plastic (polyethylene). TIL was determined as the ratio of aerosol concentrations inside (C in) and outside (C out) of the respirator (C in/C out) measured with a nanoparticle spectrometer operating in the particle size range of 20-200nm. The testing was performed under three cyclic breathing flows [mean inspiratory flow (MIF) of 30, 55, and 85 l/min] and five breathing frequencies (10, 15, 20, 25, and 30 breaths/min). A completely randomized factorial study design was chosen with four replicates for each combination of breathing flow rate and frequency. RESULTS Particle size, MIF, and combustion material had significant (P < 0.001) effects on TIL regardless of breathing frequency. Increasing breathing flow decreased TIL. Testing with plastic aerosol produced higher mean TIL values than wood and paper aerosols. The effect of the breathing frequency was complex. When analyzed using all combustion aerosols and MIFs (pooled data), breathing frequency did not significantly (P = 0.08) affect TIL. However, once the data were stratified according to combustion aerosol and MIF, the effect of breathing frequency became significant (P < 0.05) for all MIFs challenged with wood and paper combustion aerosols, and for MIF = 30 l/min only when challenged with plastic combustion aerosol. CONCLUSIONS The effect of breathing frequency on TIL is less significant than the effects of combustion aerosol and breathing flow rate for the tested elastomeric half-mask respirator. The greatest TIL occurred when challenged with plastic aerosol at 30 l/min and at a breathing frequency of 30 breaths/min.

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 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. Copyright 2013 American Association for Aerosol Research

Analytical Performance Issues: Exploring a Novel Ultrafine Particle Counter for Utilization in Respiratory Protection Studies

Correspondence to: Sergey Grinshpun, University of Cincinnati, Environmental Health, 3223 Eden Ave., P.O. 670056, Cincinnati, OH 45267; e-mail: sergey. grinshpun@uc.edu. Exposure to ultrafine (≤0.1 μm) particles is widespread at various workplaces. Several studies have revealed associations between ultrafine particle exposures and adverse health effects, including respiratory problems, impairment of cardiovascular function, and others.(1–3) Condensation particle counters (CPCs) are conventionally deployed to measure the ultrafine particle concentrations in real time. For example, the P-Trak (Model 3007, TSI Inc., Shoreview, Minn.) is the most commonly used CPC in occupational environments. However, commercially available CPCs are typically too bulky to serve as workers’ personal exposure monitors; furthermore, their performance is generally affected by their orientation. Several attempts have been made recently to design a better instrument for real-time personal exposure assessment, including a novel ultrafine particle counter (prototype) developed at the University of Cincinnati (UC UFP counter, Figure 1).(4,5) The operation principle of this device, like any CPC, involves condensation on nuclei; however, the novelty of this instrument is that the condensation takes place on nano-materials entering through the input channel. After passing a PM filter (cyclone), the particles enter a non-wetting, porous evaporationcondensation tube. Enlarged due to condensation growth, they are detected with an optical laser counter. Capillary force spontaneously generated on the surface of the non-wetting tube prevents flooding regardless of orientation and movement. This makes the instrument particularly advantageous for field applications. In addition, its time of response to a change in aerosol concentration is as low as approximately 0.3 sec. The detection particle size range is 4.5 nm to >1.0 μm that, in contrast to conventional CPCs, includes a low nano-scale. The present prototype of the UC UFP counter is portable; however, it is undergoing additional miniaturization to make the device wearable. In this study, we examined the feasibility of using the UC UFP counter for measuring the aerosol particle penetration through an elastomeric half-mask respirator donned on a breathing manikin.(6,7) Elastomeric respirators are commonly used by firefighters and first responders. The UC UFP counter was tested against the TSI Model 3007 CPC operating side by side. Combustion particles (generated by burning wood, paper, or plastic) were used as challenge aerosols. Exposures to combustion aerosols at various workplace environments have been associated with adverse health outcomes.(2,3) More than 70% (by number) of particles in a firegenerated smoke are ultrafine.(8) The penetration values were obtained by measuring the aerosol concentrations inside and outside the respirator. The sampled airflow was split with 0.3 L/min directed to the UC UFP counter and 0.7 L/min to the TSI CPC. Measurements were conducted for four respirator sealing conditions (unsealed, sealed at the nose area, sealed at chin and nose, fully sealed) and for three cyclic breathing flow rates (mean inspiratory flow = 30, 85, and 135 L/min) and one constant flow rate (30 L/min).

Performance of an improperly sized and stretched-out loose-fitting powered air-purifying respirator: Manikin-based study

ABSTRACT The objective of this study was to investigate the protection level offered by a Powered Air-Purifying Respirator (PAPR) equipped with an improperly sized or stretched-out loose-fitting facepiece using constant and cyclic flow conditions. Improperly sized PAPR facepieces of two models as well as a stretched-out facepiece were tested. These facepieces were examined in two versions: with and without exhaust holes. Loose-fitting facepieces (size “large”) were donned on a small manikin headform and challenged with sodium chloride (NaCl) aerosol particles in an exposure chamber. Four cyclic flows with mean inspiratory flows (MIFs) of 30, 55, 85, and 135 L/min were applied using an electromechanical Breathing Recording and Simulation System (BRSS). The manikin Fit Factor (mFF) was determined as the ratio of aerosol concentrations outside (Cout) to inside (Cin) of the facepiece, measured with a P-Trak condensation particle counter (CPC). Results showed that the mFF decreased exponentially with increasing MIF. The mFF values of the stretched-out facepiece were significantly lower than those obtained for the undamaged ones. Facepiece type and MIF were found to significantly affect the performance of the loose-fitting PAPR. The effect of the exhaust holes was less pronounced and depended on the facepiece type. It was concluded that an improperly sized facepiece might potentially offer relatively low protection (mFF < 250) at high to strenuous workloads. The testing was also performed at a constant inhalation flow to explore the mechanism of the particle-facepiece interaction. Results obtained with cyclic flow pattern were consistent with the data generated when testing the loose-fitting PAPR under constant flow conditions. The time-weighted average values of mFF calculated from the measurements conducted under the constant flow regime were capable of predicting the protection under cyclic flow regime. The findings suggest that program administrators need to equip employees with properly sized facepieces and remove stretched-out ones from workplace. Manufacturers should emphasize the importance of proper sizing with their user instructions.

Performance of N95 FFRs Against Combustion and NaCl Aerosols in Dry and Moderately Humid Air: Manikin-based Study

OBJECTIVES The first objective of this study was to evaluate the penetration of particles generated from combustion of plastic through National Institute for Occupational Safety and Health (NIOSH)-certified N95 filtering facepiece respirators (FFRs) using a manikin-based protocol and compare the data to the penetration of NaCl particles. The second objective was to investigate the effect of relative humidity (RH) on the filtration performance of N95 FFRs. METHODS Two NIOSH-certified N95 FFRs (A and B) were fully sealed on a manikin headform and challenged with particles generated by combustion of plastic and NaCl particles. The tests were performed using two cyclic flows [with mean inspiratory flow (MIF) rates = 30 and 85 l min(-1), representing human breathing under low and moderate workload conditions] and two RH levels (≈20 and ≈80%, representing dry and moderately humid air). The total and size-specific particle concentrations inside (C in) and outside (C out) of the respirators were measured with a condensation particle counter and an aerosol size spectrometer. The penetration values (C in/C out) were calculated after each test. RESULTS The challenge aerosol, RH, MIF rate, and respirator type had significant (P < 0.05) effects on the performance of the manikin-sealed FFR. Its efficiency significantly decreased when the FFR was tested with plastic combustion particles compared to NaCl aerosols. For example, at RH ≈80% and MIF = 85 l min(-1), as much as 7.03 and 8.61% of combustion particles penetrated N95 respirators A and B, respectively. The plastic combustion particles and gaseous compounds generated by combustion likely degraded the electric charges on fibers, which increased the particle penetration. Increasing breathing flow rate or humidity increased the penetration (reduced the respirator efficiency) for all tested aerosols. The effect of particle size on the penetration varied depending on the challenge aerosol and respirator type. It was observed that the peak of the size distribution of combustion particles almost coincided with their most penetrating particle size, which was not the case for NaCl particles. This finding was utilized for the data interpretation. CONCLUSIONS N95 FFRs have lower filter efficiency when challenged with contaminant particles generated by combustion, particularly when used under high humidity conditions compared to NaCl particles.

Experimental study on centerline velocities of a rectangular capture hood under realistic conditions

ABSTRACT Capture hoods are an important component of a local ventilation system designed to reduce exposures to airborne contaminants. The velocity at any point along the centerline of the hood (Vx) is currently estimated using one of many predictive equations developed since the 1930s. It is unproven that those predictive equations for Vx are accurate, despite the prodigious number of studies concerning them. Among other issues, almost all experimental verifications were conducted for conditions that were either unrealistically ideal without competing air currents (e.g., zero cross draft) or were not described. This study measured values of Vx along the midline using Particle Image Velocimetry (PIV) at distances of 1–14 inches in front of a rectangular capture hood. The experiments were conducted in a large wind tunnel (9′ × 12′ × 40′, H × W × L) using a heated, breathing, anthropomorphically sized manikin. Three 0 degree draft velocities (Vdraft = 4, 14, and 50 ft/min) were tested, all directed toward the hood face and the back of the manikin (if present). For each value of Vdraft, the velocity fields were measured in a factorial design with and without the manikin, and with and without a worktable underneath the hood. An ideal condition was represented by a freestanding hood at the 4 fpm draft. Nonideal conditions included the presence of a worktable or manikin, and the combination of table and manikin. Each condition was tested at the three levels of Vdraft. The experimental results found significant effects (p < 0.001) for Vdraft, the presence of the manikin, the presence of the worktable, and all combinations of those factors. The effects of the independent variables were most pronounced at distances greater than 10 in (25.4 cm) from the hood face. It is concluded that none of the previously published models accurately predicted Vx under the realistic conditions tested in this study. A satisfactory model will have to include terms for Vdraft and the presence of a worktable and a worker.