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Thursday, May 26, 2016, 8:00 AM - 11:00 AM


Respirator Probe Bias Evaluation Using the Advanced Headform Respirator Test System

M. Bergman, A. Rizor, E. Brochu, Z. Lei, and Z. Zhuang, CDC/NIOSH/NPPTL, Pittsburgh, PA

Objective: Our lab has successfully used advanced manikin headforms in several studies to simulate respirator fit on humans. However, sampling probes may yield biased measurements due to imperfect mixing of test agents or streamlining within a respirator. This study used advanced headforms under different test conditions to evaluate factors that affect respirator probe bias in filtering facepiece respirators (FFR) and elastomeric half-mask respirators (EHR).

Methods: Three N95 FFR models, one P100 FFR model, and one P100 EHR model were tested on two sizes of static headforms (medium and large) connected to a breathing simulator. Respirators were probed with a flush probe. Three samples of each model were tested. Sodium chloride aerosol was used as the challenge agent. Two PortaCount® units (model: 8038+; TSI, Inc.) were used to measure manikin fit factor (FFman) of the respirator (mask location) and FFman at a location directly downstream of the headform (reference location). Three test conditions were evaluated: 1) cyclic breathing only (CB); 2) cyclic breathing with heated/humidified exhaled air (100% RH, 34.5 ± 2 C) (H1); and 3) cyclic breathing with heated/humidified exhaled air and heated PortaCount sample lines to reduced humidity condensation (H2). Each test condition was conducted at two different minute ventilations (25 and 40 L/min), each for one minute. Analysis of variance (ANOVA) was used to test independent variables (HF (i.e., headform size), CONDITION, FLOWRATE, CLASS (i.e., N95 or P100), and STYLE (i.e., FFR or EHR) and their interactions for significant effects on probe bias. Duncan’s Multiple Range Test was used to test significant differences in mean probe bias for each independent variable.

Results: Significant (P < 0.05) variables and interactions were: CLASS, STYLE, CONDITION, HF*STYLE, CONDITION*STYLE, and CONDITION*CLASS. The mean bias for the condition CB (1.2%) was significantly different than H2 and H1 which were 3.2% and 3.6%, respectively. The significantly different mean biases for CLASS were -2.1% and 5.8% for P100 and N95 classes, respectively. The significantly different mean biases for STYLE were -0.1% and 3.5% for EHR and FFR styles, respectively.

Conclusions: The test procedures evaluated show small probe bias (< 4%) and may be considered as candidates for developing standardized test methods using advanced headforms.



Field of View Respirator Certification Standards Comparison

K. Coyne, US Army, Aberdeen Proving Ground, MD

Objective: Visual field may be decreased while wearing an air-purifying respirator (APR). The United States’ National Institute for Occupational Safety and Health (NIOSH), the European Standard (EN136), and a committee draft (CD) International Standards Organization (ISO) method use the same equipment to assess visual field, but each analyzes the results differently. NIOSH uses a Visual Field Score grid with 110 points along 10 meridians. NIOSH requires a minimum Visual Field Score (VFS) of 90 to pass certification for commercial chemical, biological, radiological, and nuclear (CBRN) APRs. The CD ISO standard adds 8 additional points to the NIOSH VFS grid and requires that 96 of those points be within the peripheral isopter. Additionally, this draft standard identifies the four points on the 85° meridian as critical points and requires that a minimum of two critical points be included in the visual field. For EN 136, the effective field of vision and effective overlapped field of vision are expressed as a percentage of the natural field of vision and overlapped field of vision, respectively. A passing score requires an effective field of vision greater than or equal to 70% and an overlapped field of vision of 80%. The goal of this effort was to assess and compare the visual field of eleven NIOSH certified CBRN APRs using the NIOSH, EN 136, and CD ISO standards.

Methods: Each respirator was mounted on the headform that accompanies the apertometer and the headform placed in position. The eye lights were illuminated and the shadow on the apertometer was checked to ensure that it was symmetric about the origin. The outline of the shadow on the apertometer was recorded and the field of view was determined according to each method. The overall score for a respirator was determined by averaging the scores for three separate fittings of each respirator.

Results: As expected, all respirators exceeded the NIOSH minimum. Three respirators failed the CD ISO standard due to the fact that less than two of the critical points were within the peripheral limits. Two of these respirators had dual eye lenses. These three respirators also failed the EN136 standard as did one additional respirator. The additional respirator had a single lens.

Conclusions: A respirator that passes the NIOSH standardized test may not pass the CD ISO or EN 136 standards. The EN 136 standard was the most stringent of the three certification standards.



Comparison of Methods Suggested in 29CFR1910.134 for Determining Change Schedules for Air Purifying Respirators

G. Wood, Consultant, Los Alamos, NM; C. Manning, Assay Technology, Livermore, CA

Situation/Problem: An employer desires to use an air-purifying respirator (APR) to protect workers against organic vapors, (e.g. hexane, chloroform, etc.) in a workplace. A specific respirator and applicable cartridge (manufacturer & model) were selected. The use environment was characterized for primary vapor concentration, co-vapors, temperature, atmospheric pressure, relative humidity, and average breathing rate (APR) or total flow (PAPR). The maximum acceptable breakthrough concentrations (MACs) for setting cartridge change schedules have been decided. Now, how does one get the corresponding breakthrough times to set change schedules?

Resolution: Several methods were suggested in 29CFR1910.134 to get breakthrough times for setting change schedules: 1) Review manufacturer’s recommendations; 2) Use the manufacturer’s Service Life Calculator; 3) Review recommendations and Service Life Calculator art OSHA web-site; 4) Use the NIOSH MultiVapor service life estimation program; 5) Search the literature for measured breakthrough times; and 6) Measure cartridge breakthrough times in a laboratory.

Results: An MSA Safety Works half-mask, with pairs of Multi-Purpose cartridges, was selected and purchased from an online supplier for use against 1000 ppm hexane (MAC = 50 ppm) or 500 ppm chloroform (MAC = 10 ppm). Each of the methods suggested in 29CFR1910.134 produced breakthrough times that are compared with those measured in the laboratory.

Lessons learned: Certain of the suggested methods require more effort and expense to gain greater accuracy. For common chemicals, all six methods are available, while for rare chemicals, some methods (manufacturer’s recommendations and/or service life calculators) may not be available. Ultimately, one must decide how accurate a result is required based on the safety factor that is selected. The accuracy required in the service life will suggest how much effort one should expend to obtain it.



Can the SWPF Study be the New WPF Study?

C. Colton, 3M PSD, St. Paul, MN

Situation/Problem: To determine respirator assigned protection factors (APF), workplace protection factors (WPF) have been used to measure respirator workplace performance. For many reasons (cost, workplace logistics and reproducibility between worksites, among other things), the simulated workplace protection factor (SWPF) has been considered a good substitute for the WPF. To use an APF of 1000 for a respirator with a loose-fitting hood, OSHA states the employer must have evidence that testing of these respirators demonstrates performance at a level of protection of 1000. This can be demonstrated by performing a WPF, SWPF or equivalent testing. These types of testing can be very different; one is done in the workplace and the other in the laboratory. However, no one has determined with precision the correlation of the results between the two types of tests.

Resolution: WPF and SWPF studies performed on various respirator types were reviewed. Six WPF studies indicate the performance of one respirator type was always different from laboratory results. Review of recent SWPF studies indicates they can also be different from each other, perhaps in part due to the fact that SWPF protocols can use different exercises, testing equipment and aerosol challenges, among other things. A search of the literature for definitions of WPF, SWPF and equivalent testing was conducted.

Results: A thorough understanding of the differences between these studies needs to be understood. To date these differences have not been identified in the published definitions. Some studies had different steps for simulating work than others. Some studies used a “safety factor.” No guidance or standards exist for establishing a safety factor for all respirator types or the type of testing. The review of laboratory testing protocols identified several factors that may contribute to differences including: aerosol particle size, work rate, environmental conditions, work activities and test duration.

Lessons learned: WPF studies appear to be the most direct measurement of respirator performance in the workplace. SWPF studies have used a wide range of exercises and test conditions which may account for differences between laboratory and workplace results. Some SWPF studies use test protocols that more closely resemble certain workplaces than others. Stricter definitions or use of SWPF may help define more relevant SWPF studies. The use of a safety factor, its level, or other statistical approaches could then be dependent on the protocol.



Efficacy for Using Facepiece Embedded Fans for PAPR Like Protection

D. Caretti, D. Barker, and D. Wilke, U.S. Army Edgewood Chemical Biological Center, Aberdeen Proving Ground, MD

Objective: For reasons related to size, weight, logistics and blower operating restrictions, commercially available powered air-purifying respirators (PAPR) are not conducive for use by tactical first responders. A recent attempt was made to circumvent these issues by mounting two small fans within the facepiece of an air-purifying respirator (APR) to independently supply air to the eye and nose cup regions. This investigation compared respiratory protection levels afforded by this design to those obtained with a traditional PAPR blower system.

Methods: Simulated workplace protection factors (SWPFs) were obtained from 7 volunteers aged 33 ± 5 yr. (mean ± SD) who completed 14 min wear trials with an Avon Protection C50 facepiece modified with embedded fans (EF-APR) and a commercially available C420 PAPR (CA-PAPR). The EF-APR modifications also segmented the eye and nose cup regions of the facepiece so breathing air exchange only occurred in the nose cup cavity. Flow rates for the EF-APR nose cup and eye fans were 32 L/min and 11 L/min, respectively; the CA-PAPR system also used a C50 facepiece and supplied air at 105 L/min. In addition to quantifying SWPFs in the nose and eye regions of the facepiece, eye cavity pressure data and subjective feedback on comfort and facial thermal sensation were obtained.

Results: Although the CA-PAPR produced the highest average nose and eye cavity SWPFs within each task, no significant differences were observed between EF-APR and CA-PAPR conditions at any time. Pressure data showed that the eye cavity went negative relative to atmosphere more frequently with the CA-PAPR compared to the EF-APR during the Crawl (13.5% vs. 9.4%), Shovel (15.4% vs. 4.9%) and Stair Climb (10.8% vs. 0.7%) tasks. No differences in comfort or thermal sensation responses were observed between conditions.

Conclusions: These findings suggest that the EF-APR concept provided respiratory protection levels comparable to a commercial PAPR system without compromising comfort and thermal sensation advantages associated with PAPRs. Additionally, the EF-APR design was better at maintaining positive pressures within the respirator facepiece at all times despite the substantially lower air flow rates compared to the CA-PAPR. The primary advantage of the facepiece-embedded fan design is a significant reduction in size, weight, required fan power and bulkiness compared to traditional PAPR motor-blowers and hoses.



Respiratory Protection for Firefighters—Evaluation of CBRN Canisters for Use During Overhaul II: In Mask Analyte Sampling with Integrated Dynamic Breathing Machine

L. Jones, E. Lutz, and J. Burgess, University of Arizona, Tucson, AZ

Objective: This study expands on previous work by introducing the use of a dynamic breathing machine that accurately simulates the rate, volume, and oscillation of normal breathing patterns. It is hypothesized that the introduction of the breathing machine combined with in-mask analyte sampling will better demonstrate the protectiveness of CBRN canisters and their potential use as an alternative to SCBAs to protect firefighters during post fire operations.

Methods: To determine analyte reduction effectiveness of CBRN canisters/cartridges a series of 12 burns with associated sampling durations was conducted at the Northwest Fire Districts training center. Measured quantities of common household items were used during burns to simulate actual overhaul environments. Three commercially available NIOSH approved CBRN canisters and one non-CBRN cartridge were used during testing. Each head form was drilled to allow insertion of five Tygon tubes around the nose and mouth area to allow for in-mask sampling, as well as a large stainless steel pipe for attachment to the breathing machine. The sampling system was placed inside the burn room via a wheeled cart approximately one meter from the smoldering materials in a position that approximated a firefighters working breathing zone. Sampling durations were randomized for each test iteration (15 minutes or 60 minutes).

Results: Sampling indicated the presence of 10 of the 55 analytes were detected above the level of quantification. Of the 10 analytes detected above the LOQ in the post-fire overhaul ambient environment, acetaldehyde and formaldehyde were the only analytes to be detected downstream of any filters on a fairly consistent basis. Benzene was detected downstream of one filter on the last burn cycle. All filters appreciably reduced concentrations of acetaldehyde and formaldehyde during all test iterations.

Conclusions: At the ambient analyte concentrations generated during this study, the CBRN filters evaluated effectively reduced levels of hazardous chemicals and respirable particulates to below occupational exposure limits during simulated overhaul. Although reduced to below occupational exposure limits at the currently tested ambient levels, the carcinogenicity of formaldehyde combined with breakthrough observed at higher concentrations, warrants the recommendation that firefighters continue to use SCBAs during post-fire activities.



Inter-Laboratory Comparison of the Performance of Firefighting Self-Contained Breathing Apparatus

J. Parker, CDC/NIOSH, Pittsburgh, PA

Objective: The objective of this study is to compare the performance of all available NIOSH and NFPA approved firefighting SCBAs in two NIOSH laboratories when tested against the major NIOSH certification tests and the NFPA air flow performance test.

Methods: Testing was performed on eight NIOSH approved SCBAs that also meet the requirements of NFPA 1981 Standard on Open-Circuit Self-Contained Breathing Apparatus (SCBA) for Emergency Services, 2007 edition. NIOSH certification tests for positive pressure, rated service time (duration), exhalation resistance, static pressure, remaining service-life indicator, and gas flow at zero facepiece pressure were conducted. The NFPA air flow performance test at maximum work rate was also performed. For comparing the Morgantown Laboratory measurements to the Pittsburgh Laboratory measurements, the difference measured within each “Run” was used for statistical analysis. Because of the small sample sizes (n=3) for each system, the Wilcoxon Signed Rank (WSR) test was used to test if the difference is zero, and p-values were calculated. The Kruskal-Wallis test and the sign test were also used to test if the results are different.

Results:  For the rated service time test, no statistically significant differences comparing Morgantown to Pittsburgh results were found. For the positive pressure test, the results indicated that Morgantown results are higher than the Pittsburgh results. For the remaining service-life indicator test, the static pressure test and the exhalation resistance test, the results indicated no statistically significant differences between the Morgantown results and the Pittsburgh results. For the positive pressure, gas flow and NFPA tests, the results indicated a statistically significant difference between the Morgantown results and the Pittsburgh results.

Conclusions: There is good agreement between the test labs for all tests except for positive pressure, gas flow and NFPA tests. The differences in the positive pressure test were attributed to differences in the equipment, which have been eliminated, and further testing has shown no significant differences. New equipment has been ordered for the gas flow and NFPA tests. Agreement in test results between the laboratories contributes to the validation of the test methods.



Do P100 FFRs Perform Better than N95 FFRs When Faceseal Leakage Presents?

X. He, J. Zhu, R. Dodrill, and S. Guffey, West Virginia University, Morgantown, WV

Objective: The NIOSH approved P100 Filtering Facepiece Respirators (FFRs) have a higher filter efficiency than that of N95 FFRs. However, P100 filters are typically associated with higher flow resistance than N95 filters. Consequently, when a leak occurs, the proportion of total air flow through the faceseal leakage of P100 FFRs may exceeds that of N95 FFRs, which may result in a higher particle penetration through the P100 FFRs. The objective is to compare the particle penetration between an N95 FFR and a P100 FFR when faceseal leakage is present.

Methods: The tested N95 and P100 FFRs were mounted on a manikin headform placed inside an exposure chamber (1.2m×1.2m×1.2m). The filters’ efficiency and flow resistance were measured when the two FFRs were sealed. Tw​​o artificially fixed faceseal leaks were created: 1) a needle with a diameter of 0.8mm inserted in-between the respirator and the lower cheek of the head form, and 2) two needles with a diameter of 0.8mm inserted at the lower cheek of the headform. Three constant (15, 50, and 85 L/min) and three cyclic breathing flows (mean inspiratory flow, MIF = 15, 50, and 85 L/min) were tested. Sodium chloride (NaCl) was used as the challenge aerosol. The concentrations inside (Cin) and outside the respirator (Cout) were measured with a NanoScan SMPS Nanoparticle Sizer (Model 3910, TSI Inc.). The total particle penetration was determined as Cin/Cout.

Results: When fully sealed, the filter efficiency of the P100 FFR was much higher than that of the N95 FFR, but a significantly higher flow resistance was also observed for the P100 respirator. In most conditions the P100 FFR was associated with a significantly (p < 0.05) lower total particle penetration than the N95 FFR. One exception was when the lowest flow rate (15 L/min) and the larger artificial leak (two needles) were introduced. In that case the N95 FFR produced lower penetration values (0.42±0.06% under constant flow, 1.73±0.02% under cyclic flow) than the P100 FFR (3.42±0.19% under constant flow, 1.93±0.03% under cyclic flow).

Conclusions: Overall, the findings suggest that when significant faceseal leakage occurs and these two respirators are used by workers performing low work activities, the P100 FFR with higher flow resistance may not be as protective as the low-flow-resistance N95 FFR. This study will have an impact on manufacturers to design P100 FFRs with low flow resistance.



Searching for the Optimal Challenge Aerosol Size Distribution for QLFT

K. Yang, S. Huang, and C. Chen, National Taiwan University, Taipei, Taiwan; W. Kuo, Chung Hwa University of Medical Technology, Tainan, Taiwan; C. Chen, Institute of Labor, Occupational Safety and Health, Ministry of Labor, New Taipei City, Taiwan

Objective: Several QLFT aerosol generators have been commercially available, but the generated aerosol size distributions have not been well defined and justified. In addition, the data on aerosol penetration through face seal leaks is still quite limited. Therefore, this study aimed to characterize the aerosol penetration through small diameter tubing, and to derive the appropriate range of size distribution of challenge aerosol particles for QLFT.

Methods: Microtubes with different length and diameter were employed to simulate faceseal leaks. An ultrasonic nebulizer was used to generate polydisperse NaCl particles with various size distributions as the challenging aerosol. Aerosol number concentrations and size distributions upstream and downstream of the microtubes were measured by an Aerodynamic Particle Sizer. Aerosol penetration data were taken at different flow rate through microtubes and under tube orientation (horizontal and perpendicular). Empirical models taking into account the aerosol aspiration efficiency and gravitational deposition were used to calculate the faceseal leakage, and to compare with experimental results. The filter penetration was predicted based on the single fiber efficiency theory. Accordingly, fit factors, obtained by combining the filter penetration and faceseal leakage, were shown as a function of mass medium diameter and geometric standard deviation.

Results: Experimental results agreed well with the modelled data, showing that aerosol penetration was significantly affected by aspiration efficiency which was a strong function of particle size. Aspiration effect increased with increasing leak flow through microtubes, given in the calm air environment. Gravitational deposition loss in the microtubes was apparent, especially when the tube was placed horizontally and leak flow was low. Experimental data and modelled results all showed that leak size, leak length, leak orientation, breathing flow, filter properties all affected and contributed to the total inward leakage, and therefore, the fit factor.

Conclusions: The upper limit of the size distribution of challenge aerosols was mainly determined by the aerosol deposition in the faceseal leaks, while the lower limit was governed by the filter penetration. The optimal challenge aerosol size distribution for QLFT was found to be 0.4< MMD< 2.0 μm and GSD< 2, with 25% error. When a more accurate (10% error) fit factor was desired, the aerosol size distribution should be 0.5< MMD < 1.3 μm and GSD around 1.5.​