Respiratory Protection II

Respiratory Protection II

Tuesday, June 2, 2015, 10:30 AM - 12:30 PM

SR-116-01 Simulation of N95 FFR Efficiency to Determine a Potential Protection Factor

P. O’Shaughne​ssy, University of Iowa, Iowa City, IA

Objective: The “95” in the designation “N95” of a filtering facepiece respirator (FFR) refers to the lowest efficiency provided by the respirator occurring at any one of all airborne particle sizes. It therefore does not indicate the percent reduction in aerosol concentration; a quality of a respirator that is referred to as a protection factor. The OSHA “assigned protection factor” is a function of the filtering qualities of the FFR and potential leaks through the faceseal. The objective of this study was to use numerical simulations to determine the ideal, or “potential”, protection factor (PPF) that occurs without leaks for an N95 subjected to aerosols derived from a range of lognormal distributions.

Methods: Using the best available equations that model the performance of an N95 FFR, including fiber charging effects, an overall model of N95 efficiency across a wide range of particle sizes (1 nm to 100 micrometers) was developed. This effort resulted in an efficiency curve relative to particle size for a typical N95 FFR with a minimum efficiency of exactly 95%. With that curve, the mass of all particles collected by the filter could be computed to determine a PPF of the FFR. The PPF was determined for 42 spherical, unit-density aerosols with mass median aerodynamic diameters (MMAD) ranging from a 2–14 (by every 2) and geometric standard deviations (GSD) from 1.6–3.6 (by every 0.4). The PPF was computed in terms of both total mass and respirable mass.

Results: The worst-case aerosol occurs when then the MMAD is low and the GSD is high. This results in a wide distribution of small particles that overlap the N95 efficiency curve in the region where it dips to 95%, which occurs between 0.01 - 0.3 micrometers. Regardless, this FFR has a PPF of 99.86% for all mass and 99.79% for respirable mass for the lowest MMAD (2) and highest GSD (14) analyzed. Dusts with MMAD’s > 4 micrometers had PPF values above 99.96% regardless of GSD.

Conclusions: Results of this analysis indicate that N95 FFR are highly protective if leakage is not considered. The OSHA assigned protection factor (APF) for this respirator is 10 which translates to an overall efficiency of 90%. Given that the APF includes faceseal leakage, the large discrepancy between the PPF and the APF indicates that the N95 FFR is either underutilized or overdesigned because of leaks. Future efforts should involve the development of FFRs that can be worn without developing leaks.

SR-116-02 Comparing Real-Time Fit Factors to Traditional Fit Factors by OSHA Exercise for N95 Respirators

M. Sietsema, L. Brosseau, University of Illinois at Chicago, Chicago, IL

Objective: This project compares respirator fit using two methods: 1) the traditional OSHA fit test using a single Portacount and alternating measurements of particle concentration inside and outside the respirator and 2) a newly-developed “real-time” method that uses two Portacounts simultaneously measuring inside and outside particle concentrations. Validation will allow the latter method to be used to examine the concentration between specific healthcare tasks and traditional fit test exercises.

Methods: Sixteen human subjects of varying face size (width and length) were recruited to participate in this study. After donning an N95 FFR subjects randomly performed a traditional or a real-time fit test, followed immediately by the opposite test without removing the respirator. For each test, subjects completed the 8 exercises as prescribed by the OSHA protocol. Fit factors for each exercise and for all exercises combined were compared between the two fit test methods using a correlation analysis.

Results: The real-time fit factors ranged from 1 to 1,226. Traditional fit factors ranged from 2 to 2,020; Pearson’s correlation coefficients (r) of the fit factors for individual exercises ranged from ­0.03 for the grimace exercise to 0.76 for the deep breathing exercise. The overall fit factor (all exercises combined) had a correlation coefficient of 0.47 (p = 0.07). No exercise had a significant difference in real-time mean versus traditional mean when compared using a student’s t-test (0.19 < p-value < 0.93).

Conclusions: The significantly high correlation between overall fit factors for the traditional and real-time fit test suggest that the new method can be used in future experiments to further examine the effect of specific workplace tasks on respirator fit. The low correlation for the bending over exercise suggests that respirator fit may be dependent on the re-seating of the respirator on the face immediately after significant facial movement (i.e. the grimace exercise).

SR-116-03 Filter Performance of N95 FFRs in Dry and Moderately Humid Air: Manikin-based Study with NaCl and Combustion Aerosols

S. Gao, S. Grinshpun, J. Kim, M. Yermakov, Y. Elmashae, T. Reponen, University of Cincinnati, Cincinnati, OH; X. He, West Virginia University, Morgantown, WV

Objective: To evaluate the filter performance offered by two N95 filtering facepiece respirators (FFRs) sealed on a manikin against combustion aerosol particles and conventional NaCl aerosol in dry and moderately humid air.

Methods: Two N95 FFRs (A and B) obtained from different manufacturers were sealed on a manikin head form and challenged with combustion particles (generated by burning plastic) and NaCl particles in a large exposure chamber (24.3 m3). A cyclic breathing pattern was simulated using an electromechanical Breathing Recording and Simulation System (BRSS; Koken Ltd., Tokyo, Japan) providing two mean inspiratory flows (MIFs) of 30 and 85 L/min. Two relative humidity conditions (RH≈20% and 80%) were applied to represent dry and moderately humid workplace environments. The total and size-selective particle concentrations inside (Cin) and outside (Cout) of the respirator were measured with a P-Trak condensation particle counter (8525, TSI, Inc., MN, USA) as well as a Nanocheck (1320, Grimm Technologies, Inc., Ainring, Germany). The particle penetration was determined as (Cin/Cout)×100%.

Results: For Respirator A, the average total penetration of combustion particles was significantly higher than that of NaCl particles regardless of the MIF and the relative humidity. The penetration levels of combustion particles and NaCl particles ranged from 1.4% to 7.0%, and from 0.3% to 4.8%, respectively. Penetration increased with increasing MIF. The penetration at RH≈80% was significantly higher than that at RH≈20% for both aerosols and both MIFs, which can be attributed to the effect of high RH on electric charges on the filter fibers. The most penetrating particle size (MPPS) was identified below 100 nm for both aerosol challenges. No consistent change in the MPPS was observed with the increase of RH. Respirator B provided lower protection levels: the total penetration was 2.1% to 8.6% for combustion particles and 1.4% to 5.7% for NaCl particles. The effects of challenge aerosol and RH followed the same trend as obtained for Respirator A. The MPPS was also observed in the particle size range below 100 nm.

Conclusions: The manikin-based testing with cyclic breathing showed that the filtration level of an N95 FFR obtained with NaCl particles may significantly underestimate its filtration efficiency against combustion aerosols. Higher relative humidity may reduce the filter performance.

SR-116-04 Evaluation of the Effect of Head Strap Length on Facial Fit of N95 Filtering Facepiece Respirators

M. Bergman, Z. Zhuang, A. Palmiero, D. Niezgoda, NIOSH/NPPTL, Pittsburgh, PA

Objective: A three-year study was performed to validate the scientific basis for the periodicity of fit testing by investigating changes in NIOSH-approved N95 filtering facepiece respirator (FFR) fit on a group of test subjects as a function of time. In this presentation, data from the periodicity of fit testing study is used to explore the relationship between head strap length and N95 FFR fit. The relationship of head strap length to N95 FFR fit has not been previously reported.

Methods: A group of 229 subjects was initially enrolled and tested every six months. During each visit, subjects performed a total of nine fit tests using three samples of the same FFR model. The facial dimensions of all subjects were also measured during each visit to determine changes over time that may affect respirator fit. Seven FFR models were included in the study. Inward leakage and filter penetration were measured for each donned respirator to determine face seal leakage (FSL). Unstretched head strap length was measured beginning on the second or third visit. For each respirator model, a linear regression was performed on geometric mean (GM) FSL of individual respirator samples using data from all visits (dependent variable) to the unstretched top and bottom strap lengths of those samples (independent variables).

Results: A total of 195 subjects completed the second visit and 134 subjects completed all seven visits. The data collected from all participating test subjects at each visit was used for this study. Among the seven FFR models, the mean top strap length ranged from 194.8 to 321.8 mm with relative percent standard deviation (%RSD) ranging from 0.31to 5.18. The mean bottom strap length ranged from 194.6 to 299.5 mm with %RSD ranging from 0.42 to 5.11. For four of the seven respirator models, top and or bottom strap length was found to have a significant (P < 0.05) correlation with GM FSL.

Conclusions: Head strap lengths were found to be quite variable within some FFR models. Unstretched head strap length had some association with FFR fit. Further analysis of the data will be performed to explore the interaction of strap length with other factors such as weight changes and changes in facial dimensions to determine the effect on respirator fit. Future studies should be performed with respirators of controlled strap lengths to better understand the effect of length on respirator fit.

SR-116-05 Particle Size Penetration of Diesel Particulate Matter through Respirator Filter Media

K. Burton, J. Whitelaw, A. Jones, University of Wollongong, Wollongong, NSW, Australia

Objective: Diesel engine emissions are known to cause adverse health impacts including lung cancer, cardiovascular and irritant effects. The diesel particulate component of the emissions is in the nanoparticle size range. Respiratory protection is commonly used to mitigate worker exposure. Current test methods to evaluate penetration through respirator filter media may not consider smaller size particles due to the diameter of the challenge aerosol and the detection limit for the instrument. The objective of this study was to determine the Most Penetrating Particle Size (MPPS) through a range of commonly used respirator filters in Australia, to evaluate whether MPPS is included in standard testing criteria for respirator filtering efficiency. Additionally the project evaluated penetration through the filter media using diesel particulate, rather than NaCl, as the challenge aerosol. 

Methods: Emissions from a Perkins 4.4L diesel engine were fed into an experimental chamber. Penetration of these emissions was determined by sampling elemental carbon, using NIOSH Method 5040, before and after the respirator filter. A Scanning Mobility Particle Sizer with attached Condensation Particle Counter was used to measure penetration as a function of particle size. 

Results: Initial results indicate that when challenged with DPM, the MPPS varied for each of the respirator models. The filtering efficiency at the MPPS appeared to meet the requirements for P2 certification in Australia or N/P/R95 NIOSH certification requirements.

Conclusions: Filtering efficiency in Australia is determined by challenging filter media with aerosolized sodium chloride and calculating penetration at designated flow rates. Current standard test requirements do not account for the differences in structure and chemical characteristics of DPM and sodium chloride nor do they include particle sizes below the instrument detection limit and diameter of the challenge aerosol. This study showed that the Most Penetrating Particle Size of diesel emissions through 3 commonly used respirator filters varies dependent on the filter and hence may not be included in filtering efficiency calculations. These findings will inform development of Australian and International Standards on the selection and evaluation of respiratory protection to ensure workers are protected against this common workplace carcinogen.

SR-116-06 Development of a New Data Acquisition System for Recording and Analyzing In-Facepiece Pressures during NIOSH Breathing Machine Tests

J. Parker, NIOSH, Pittsburgh, PA

Objective: This paper describes the development and testing of a new data acquisition system for recording and analyzing the in-facepiece pressure tracings when respirators are tested for various performance criteria with the NIOSH breathing machine. These tests are used for evaluating the performance of self-contained breathing apparatus (SCBA). The current system utilizes a combination strip-chart recorder and signal conditioning unit. Historical data has shown that when respirators are tested on breathing machines, it is often found that in-facepiece pressure sample tracings will include very short duration spikes below zero. The problem is how to determine if the negative spike(s) truly represent(s) a negative facepiece pressure, or not. This decision determines if a test passed or failed. NIOSH has always required that the spike must contain a certain minimum area that represents the combined duration and intensity of the spike in order to constitute a failure. This evaluation is currently performed qualitatively by examining the strip chart recording. Other researchers and scientists have accepted or rejected negative excursions based on duration only.

Methods: The new system uses a ±10 VDC, 16-Bit simultaneous sampling analog input device to capture the transducer outputs and to send these outputs to a custom LabVIEW® program. The LabVIEW® program performs a continuous integration of the area below zero and is designed to automatically log and display a failure if the calculated area within a time window of 0.05 seconds exceeds -0.002 inches of water-seconds at a sampling rate of 70 Hz. These failure criteria were based on calculations of the area within the negative spikes that are considered failures on the strip charts. Eight different makes and models of NIOSH-approved SCBA were tested on both systems. Three runs were performed consecutively on each respirator. 

Results: Results are presented of comparison testing that was performed between the LabVIEW® and chart recorder systems. The results indicate that the LabVIEW® and chart recorder systems are logging data within 0.05 inches of water for the lowest in-facepiece pressure levels measured.

Conclusions: The conclusions of this study are that the new LabVIEW® system is capable of replacing the strip chart recorder with the additional benefits of complete data logging and a reduction of the subjectivity associated with determining pass / fail results. ​