Elastomeric Half-mask Respirators Research Articles

Elastomeric half-mask respirator disinfection practices among healthcare personnel.

Disposable N95 respirator shortages during the COVID-19 and 2009 H1N1 influenza pandemics highlighted the need for reusable alternatives, such as elastomeric half-mask respirators (EHMRs). Two US medical organizations deployed reusable EHMRs during the COVID-19 response. In addition to wipe-based disinfection following patient care episodes expected per local policies at both organizations, postshift centralized cleaning and disinfection (C&D) was expected at one site (A), permitting shared-pool EHMR use, and optional at the other (Site B), where EHMRs were issued to individuals. Using a survey, we evaluated disinfection practices reported by EHMR users and predictors of disinfection behaviors and perceptions. Surveys assessed EHMR disinfection practices, occupational characteristics, EHMR use frequency, training, and individual-issue versus shared-pool EHMR use. Of 1080 EHMR users completing the survey, 76% reported that they disinfect the EHMR after each patient encounter, which was the expected practice at both sites. Increasing EHMR use, recall of disinfection training, and work in intensive care or emergency settings significantly influenced higher reporting of this practice. 36% of respondents reported using centralized C&D, although reporting was higher at the site (A) where this was expected (53%). Confidence in cleanliness of the EHMR following centralized C&D was not influenced by individual versus shared-pool EHMR issue. Most EHMR users reported adherence with expected post-care individual-based disinfection of EHMRs but did not necessarily use standardized, centralized C&D. Future efforts to limit reliance on behavior related to respirator disinfection may improve EHMR implementation in healthcare to avert dependence on single-use, disposable N95 respirators.

Examining the Roles of Training, Fit Testing, and Safety Climate on User Confidence in Respiratory Protection: A Case Example with Reusable Respirators in Health Delivery Settings

A lack of confidence in the efficacy of respiratory protection can contribute to uncertainty among workers and cast doubt on workplace safety. To date, no research has been conducted to study and understand the introduction of elastomeric half-mask respirators (EHMRs)—without exhalation valves (EVs) or with exhalation valve filters (EVFs), both representing new designs that address source control—in the workplace. To study this issue, researchers collaborated with partners at 32 health delivery settings that received EHMRs from the Strategic National Stockpile during the COVID-19 pandemic. EHMR users (n = 882) completed an online survey between October 2021 and September 2022. Analyses demonstrated that employees were statistically significantly more confident in the efficacy of EHMRs with no EV/with an EVF (including the efficacy in protecting the user from COVID-19) if they had been fit tested and received training. Respondents were also statistically significantly more confident in the efficacy of their EHMR if they had a more positive perception of their organization’s safety climate. The results provide insights for tailored fit testing and training procedures as manufacturers continue to improve respirator models to enhance worker comfort and use. Results also show that, even during a public health emergency, the role of safety climate cannot be ignored as an organizational factor to support worker knowledge, attitudes, and participation in health and safety behaviors specific to respirator use.

Evaluation of the effects of wiping decontamination for filter cartridges of elastomeric half-mask respirators (EHMRs)

A major concern among healthcare experts is a shortage of N95 filtering facepiece respirators during a pandemic. If the supply of N95 filtering facepiece respirators becomes limited, reusable elastomeric half-mask respirators (EHMRs) may be used to protect healthcare workers. The focus of this study was to evaluate the effects on the filter performance of wiping decontamination for EHMR P100 filter cartridges. The filter cartridge exterior of EHMR Honeywell, Moldex, and Mine Safety Appliance (MSA) models was wiped using quaternary ammonium and sodium hypochlorite wipes. These filter cartridge properties were assessed including observational analysis and filter performance tests. These wiping and assessing procedures were repeated after each set of wiping cycles (50, 100, 150, 200, and 400 cycles) to determine the effects of wiping decontamination. For sodium hypochlorite wipes, Honeywell, Moldex, and MSA models passed the National Institute for Occupational Safety and Health (NIOSH) liquid particulate penetration criteria for all wiping cycles from 50 to 400 (penetrations<0.014%). For quaternary ammonium wipes, filter penetrations of Moldex failed (penetrations>0.03%) after 150 cycles, while the filter penetrations of Honeywell and MSA passed for all wiping cycles (penetrations ≤0.013%). Wiping decontamination methods using sodium hypochlorite and quaternary ammonium wipes could be considered promising decontamination candidates for Honeywell, Moldex, and MSA reuse, except for the wiping number selection for Moldex (<150 cycles) when using the quaternary ammonium wipe.

Use of Elastomeric Half-Mask Respirator in the Clinical Care Environment: Health Care Worker Perceptions.

Elastomeric half-mask respirators (EHMR) reduce health care workers' exposure to airborne hazards including bioaerosols but have primarily been used in the industrial setting. To assess health care workers' perceptions, attitudes, and experiences wearing EHMRs in a clinical environment. Employees within a single health care system who wore the EHMR continuously during their shift completed an investigator developed survey. Descriptive statistics and thematic analysis were used. Of the 8273 EHMR "fit-tested" eligible employees, 1478 met inclusion criteria and participated. Respondents reported that they felt well protected with the EHMR and confident in their care and maintenance of the EHMR. Although skin changes developed, they were primarily managed by adjusting the straps. Clarity of communication was a concern across all respondents and disciplines. The EHMR was preferred over reusing the N95 although clarity in communication was challenging.

Innovate and Stockpile: Respiratory Protection for Essential Workers in a Catastrophic Pandemic.

Innovate and Stockpile: Respiratory Protection for Essential Workers in a Catastrophic Pandemic.

Filtration performance and breathing resistance of elastomeric half mask respirator P100 filter cartridges after repeated and extended use in healthcare settings

In 2020, the Centers for Disease Control and Prevention recommended the use of the National Institute for Occupational Safety and Health-certified Elastomeric Half Mask Respirators equipped with N95 or P100 respirator filter cartridges for protection against the SARS-CoV-2 viral agent, as a viable alternative to N95 filtering facepiece respirators. Additionally, the Centers for Disease Control and Prevention recommendations stated that based on current practice, it was acceptable to repeatedly use these filter cartridges for up to 12 months as a contingency capacity strategy during anticipated respirator shortages. To validate this recommendation, an investigation was undertaken in which Elastomeric Half Mask Respirators equipped with P100 respirator filter cartridges were deployed and used by healthcare professionals in clinical settings (i.e., inpatient nursing units, operating rooms) for extended periods. These filter cartridges were subsequently tested to accurately quantify their filtration efficiency and breathing resistance to determine if they continued to meet National Institute for Occupational Safety and Health’s performance requirements. Findings from this investigation confirmed that an Elastomeric Half Mask Respirator when equipped with a P100 filter cartridge continues to provide a high level of aerosol filtration performance (≥99.97%) and exhibits little change in breathing resistance even after 12 months of repeated use (i.e., wear, cleaning, and disinfection between patient use and at the end of work shift) in healthcare settings.

Evaluation of total inward leakage for NIOSH-approved elastomeric half-facepiece, full-facepiece, and powered air-purifying respirators using sodium chloride and corn oil aerosols

Recently, total inward leakage (TIL) for filtering facepiece and elastomeric half-mask respirators (EHRs) was measured according to the International Organization for Standardization (ISO) test method standard 16900-1:2014 that showed larger TIL for corn oil aerosol than for NaCl aerosol. Comparison of TIL measured for different aerosols for higher protection level respirators is lacking. The objective of this study was to determine TIL for EHRs, full-facepiece respirators, and loose-fitting and tight-fitting powered air-purifying respirators (PAPRs) using NaCl and corn oil aerosols to compare. TIL was measured for two models each of EHRs, full-facepiece respirators, and loose-fitting and tight-fitting PAPRs. After fit testing with a PortaCount (TSI, St. Paul, MN) using the Occupational Safety and Health Administration (OSHA) protocol, eight subjects were tested in the NaCl aerosol chamber first and then in the corn oil aerosol chamber, while another eight subjects tested in the reverse order. Subjects were randomly assigned to one of the two groups. TIL was measured as a ratio of mass-based aerosol concentrations inside the mask to the test chamber while the subjects performed ISO 16900-1-defined exercises using continuous sampling methods. The concentration of corn oil aerosol was measured with one light scattering photometer, alternately, and NaCl aerosol was measured using two flame photometers. Results showed the geometric mean TIL for EHR was significantly (p < 0.05) larger for corn oil aerosol than for NaCl aerosol. EHR models equipped with P100 filters showed relatively smaller TIL values than the same models with N95 filters showing that TIL was inversely related to filter efficiency. Interestingly, TIL was significantly (p < 0.05) larger for NaCl aerosol than for corn oil aerosol for PAPRs, but not for full-facepiece respirators. TIL was inversely related to fit factors of respirator types. Overall, filter efficiency and faceseal leakage determine TIL. The relative trends in TIL for the two aerosols’ test methods differ between respirator types indicating that generalization of TIL for respirator types may not be appropriate when using different test agents.

Effectiveness of Elastomeric Half-Mask Respirators vs N95 Filtering Facepiece Respirators During Simulated Resuscitation

Effectiveness of Elastomeric Half-Mask Respirators vs N95 Filtering Facepiece Respirators During Simulated Resuscitation

Elastomeric Respirator Contamination of Sterile Fields Compared to Surgical Masks

Background: Elastomeric half mask respirators (EHMRs) are a reusable, reliable option for protection from infectious aerosol particles such as SARS-CoV2. There is a lack of safety data for their use in sterile fields. We hypothesized an equivalent reduction in aerosol/droplet contamination of the sterile field for an EHMR covered with a surgical mask (EHMRwM) as achieved by a standard surgical mask.Methods: In an operating room setting, participants performed droplet and aerosol generating procedures while wearing: (Group 1) EHMRwM, (Group 2) EHMR only, (Group 3) N95, and (Group 4) surgical mask. A positive control was established with the participant unmasked (Group 5). Contamination of the sterile, anesthesia, and nursing field was measured by microbial growth on settling plates and optical particle counters (0.2+ and 2 um+ particles). 16 experiments were performed by 4 participants with 4 iterations with randomized testing order.Findings: There was a reduction in microbial contamination at the sterile field (pInterpretation: An EHMR covered by a surgical mask is as effective as a standard surgical mask for reducing contamination at the sterile field in an operating room. Consideration should be given to expanding the use of EHMRs to operating rooms with sterile fields.Funding Statement: No funding sources were used in this research.Declaration of Interests: Brittany E. Howard MD: This author has no personal or financial disclosures. Ryan M. Thorwarth MD: This author has no personal or financial disclosures. Karam Abi Karam BS: This author has no personal or financial disclosures. Sam L. Snider BS: This author has no personal or financial disclosures. Erica Forzani PhD: This author has no personal or financial disclosures related to this research. She does have a pending patent application “SYSTEM AND METHOD FOR MITIGATING AIRBORNE CONTAMINATION IN CONDITIONED INDOOR ENVIRONMENTS” E. Forzani, B. Patel, K. McKay, G. Pyznar, Provisional Patent, August, 2020. Joseph G. Hentz MS: This author has no personal or financial disclosures related to this research. He has previously received grant funding from the Patient-Centered Outcomes Research Institute. Erin H. Graf PhD: This author has no personal or financial disclosures. Bhavesh Patel MD: This author has no personal or financial disclosures. Kelly J. McKay EMT-P: This author has no personal or financial disclosures. Michael L. Hinni MD: This author has no personal or financial disclosures related to this research. He is the inventor of a laryngoscope manufactured and sold by Karl Storz. He receives an honorarium from this. Devyani Lal MD: This author has no personal or financial disclosuresEthics Approval Statement: This study was approved by the Mayo Clinic Institutional Review Board.

Training and Fit Testing of Health Care Personnel for Reusable Elastomeric Half-Mask Respirators Compared With Disposable N95 Respirators

This study examines the feasibility of rapidly training and fit testing health care workers to use elastomeric half-mask respirators (EHMRs), widely used in construction and manufacturing, as an alternative to N95 respirators during periods of shortage.

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

The International Organization for Standardization (ISO) standard 16900-1:2014 specifies the use of sodium chloride (NaCl) and corn oil aerosols, and sulfur hexafluoride gas for measuring total inward leakage (TIL). However, a comparison of TIL between different agents is lacking. The objective of this study was to measure and compare TIL for respirators using corn oil and NaCl aerosols. TIL was measured with 10 subjects donning two models of filtering facepiece respirators (FFRs) including FFP1, N95, P100, and elastomeric half-mask respirators (ERs) in NaCl and corn oil aerosol test chambers, using continuous sampling methods. After fit testing with a PortaCount (TSI, Inc., St. Paul, MN) using the Occupational Safety and Health Administration (OSHA) protocol, five subjects were tested in the NaCl chamber first and then in the corn oil chamber, while other subjects tested in the reverse order. TIL was measured as a ratio of mass-based aerosol concentrations in-mask to the test chamber, while the subjects performed ISO 16900-1-defined exercises. The concentration of NaCl aerosol was measured using two flame photometers, and corn oil aerosol was measured with one light scattering photometer. The same instruments were used to measure filter penetration in both chambers using a Plexiglas setup. The size distribution of aerosols was determined using a scanning mobility particle sizer and charge was measured with an electrometer. Filter efficiency was measured using an 8130 Automated Filter Tester (TSI). Results showed the geometric mean TIL for corn oil aerosol for one model each of all respirator categories, except P100, were significantly (p < 0.05) greater than for NaCl aerosol. Filter penetration in the two test chambers showed a trend similar to TIL. The count median diameter was ∼82 nm for NaCl and ∼200 nm for corn oil aerosols. The net positive charge for NaCl aerosol was relatively larger. Both fit factor and filter efficiency influence TIL measurement. Overall, TIL determination with aerosols of different size distributions and charges using different methodologies may produce dissimilar results.

Respiratory Protection Provided by Negative Pressure Half Mask Filtering Respirators in Coal Mines

Two studies were conducted in the coal mines to evaluate worker exposures to a dust, and the effectiveness of air-purifying negative-pressure half mask respirators and was found that miners’ protection were insufficient. An elastomeric and filtering half-mask negative pressure respirators with (mid-efficiency) filters P2 (FFP2) were studied. Measurements of total dust concentrations in the in-mask and outer air were conducted simultaneously. Not identical sampling system led to an underestimation of the actual total inside dust concentration in the first study. The results have been corrected to reduce the systematic error. The inside total dust concentrations Ci exceeded national Permissible Exposure Limit (PEL) in most cases in both studies; in first GM Ci=24.7 mg/m3; in second 8.6 mg/m3. Protection factors were: from 2.9 to 6.9 in first study; and from 5.6 to 34 in second. Low efficiency of respirators can be caused by its non-continuous usage. High risk of miners’ occupational diseases should be reduced by decreasing the dust concentration in the breathing zone. It is advisable to check the possibility of improving respiratory protection of miners by powered air-purifying respirators.

Application of direct-reading and elemental carbon analysis methods to measure mass-based penetration of carbon nanotubes through elastomeric half-face and filtering facepiece respirators.

The aim of this study was to apply a direct-reading aerosol instrument method and an elemental carbon (EC) analysis method to measure the mass-based penetration of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) through elastomeric half-mask respirators (EHRs) and filtering facepiece respirators (FFRs). For the direct-reading aerosol instrument method, two scanning mobility particle sizer/aerodynamic particle sizer systems were used to simultaneously determine the upstream (outside respirator) and downstream (inside respirator) test aerosols. For the EC analysis method, upstream and downstream CNTs were collected on filter cassettes and then analyzed using a thermal-optical technique. CNT mass penetrations were found in both methods to be within the associated efficiency requirements for each type and class of the respirator models that were tested. Generally, the penetrations of SWCNTs and MWCNTs had a similar trend with penetration being the highest for the N95 EHRs, followed by N95 FFRs, P100 EHRs, and P100 FFRs. This trend held true for both methods; however, the CNT penetration determined by the direct-reading aerosol instrument method (0.009-1.09% for SWCNTs and 0.005-0.21% for MWCNTs) was greater relative to the penetration values found through EC analysis method (0.007-0.69% for SWCNTs and 0.004-0.13% for MWCNTs). The results of this study illustrate considerations for how the methods can be used to evaluate penetration of morphologically complex materials through FFRs and EHRs.

Inward leakage variability between respirator fit test panels – Part II. Probabilistic approach

ABSTRACTThis study aimed to quantify the variability between different anthropometric panels in determining the inward leakage (IL) of N95 filtering facepiece respirators (FFRs) and elastomeric half-mask respirators (EHRs).We enrolled 144 experienced and non-experienced users as subjects in this study. Each subject was assigned five randomly selected FFRs and five EHRs, and performed quantitative fit tests to measure IL. Based on the NIOSH bivariate fit test panel, we randomly sampled 10,000 pairs of anthropometric 35 and 25 member panels without replacement from the 144 study subjects. For each pair of the sampled panels, a Chi-Square test was used to test the hypothesis that the passing rates for the two panels were not different. The probability of passing the IL test for each respirator was also determined from the 20,000 panels and by using binomial calculation. We also randomly sampled 500,000 panels with replacement to estimate the coefficient of variation (CV) for inter-panel variability.For both 35 and 25 member panels, the probability that passing rates were not significantly different between two randomly sampled pairs of panels was higher than 95% for all respirators. All efficient (passing rate ≥80%) and inefficient (passing rate ≤60%) respirators yielded consistent results (probability >90%) for two randomly sampled panels. Somewhat efficient respirators (passing rate between 60% and 80%) yielded inconsistent results. The passing probabilities and error rates were found to be significantly different between the simulation and binomial calculation. The CV for the 35-member panel was 16.7%, which was slightly lower than that for the 25-member panel (19.8%).Our results suggested that IL inter-panel variability exists, but is relatively small. The variability may be affected by passing level and passing rate. Facial dimension-based fit test panel stratification was also found to have significant impact on inter-panel variability, i.e., it can reduce alpha and beta errors, and inter-panel variability.

Inward Leakage Variability between Respirator Fit Test Panels – Part I. Deterministic Approach

Inter-panel variability has never been investigated. The objective of this study was to determine the variability between different anthropometric panels used to determine the inward leakage (IL) of N95 filtering facepiece respirators (FFRs) and elastomeric half-mask respirators (EHRs). A total of 144 subjects, who were both experienced and non-experienced N95 FFR users, were recruited. Five N95 FFRs and five N95 EHRs were randomly selected from among those models tested previously in our laboratory. The PortaCount Pro+ (without N95-Companion) was used to measure IL of the ambient particles with a detectable size range of 0.02 to 1 μm. The Occupational Safety and Health Administration standard fit test exercises were used for this study. IL test were performed for each subject using each of the 10 respirators. Each respirator/subject combination was tested in duplicate, resulting in a total 20 IL tests for each subject. Three 35-member panels were randomly selected without replacement from the 144 study subjects stratified by the National Institute for Occupational Safety and Health bivariate panel cell for conducting statistical analyses. The geometric mean (GM) IL values for all 10 studied respirators were not significantly different among the three randomly selected 35-member panels. Passing rate was not significantly different among the three panels for all respirators combined or by each model. This was true for all IL pass/fail levels of 1%, 2%, and 5%. Using 26 or more subjects to pass the IL test, all three panels had consistent passing/failing results for pass/fail levels of 1% and 5%. Some disagreement was observed for the 2% pass/fail level. Inter-panel variability exists, but it is small relative to the other sources of variation in fit testing data. The concern about inter-panel variability and other types of variability can be alleviated by properly selecting: pass/fail level (IL 1–5%); panel size (e.g., 25 or 35); and minimum number of subjects required to pass (e.g., 26 of 35 or 23 of 35).

Protection of Firefighters Against Combustion Aerosol Particles: Simulated Workplace Protection Factor of a Half-Mask Respirator (Pilot Study)

The present pilot study investigated the penetration of ultrafine particles originated by combustion of different materials into elastomeric half-mask respirators equipped with two P100 filters. We determined the Simulated Workplace Protection Factor (SWPF) for 11 firefighters wearing elastomeric half-mask respirators and performing activities simulating those conducted during fire overhaul operations. The tests were performed in a controlled laboratory setting. A newly-developed battery-operated Portable Aerosol Mobility Spectrometer (PAMS) was used to measure size-resolved aerosol particle concentrations outside (Cout) and inside (Cin) of an air-purifying respirator donned on a firefighter, and the SWPF was calculated as Cout/Cin. Based on the total aerosol concentration, the “total” SWPF ranged from 4,222 (minimum) to 35,534 (maximum) with values falling primarily in a range from 11,171 (25 percentile) to 26,604 (75 percentile) and a median value being ≈15,000. This is consistent with the recently reported fit factor (FF) data base.(1) The size-resolved SWPF data revealed a dependency on the particle size. It was concluded that a portable device such as PAMS can be used on firefighters during overhaul operations (as well as on other workers wearing elastomeric half-mask respirators) to monitor the aerosol concentrations in real time and ultimately help prevent overexposure.

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

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. 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. 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.

Development of a new test system to determine penetration of multi-walled carbon nanotubes through filtering facepiece respirators

Carbon nanotubes (CNTs) are currently used in numerous industrial and biomedical applications. Recent studies suggest that workers may be at risk of adverse health effects if they are exposed to CNTs. A National Institute for Occupational Safety and Health (NIOSH) survey of the carbonaceous nanomaterial industry found that 77% of the companies used respiratory protection. Elastomeric half-mask respirators and filtering facepiece respirators (FFRs) are commonly used. Although numerous respirator filtration studies have been done with surrogate engineered nanoparticles, such as sodium chloride, penetration data from engineered nanoparticles such as CNTs are lacking. The aims of this study were to develop a new CNT aerosol respirator testing system and to determine multi-walled CNT (MWCNT) penetration through FFRs.A custom-designed CNT aerosol respirator testing system (CNT-ARTS) was developed which was capable of producing a sufficient amount of airborne MWCNTs for testing of high efficiency FFRs. The size distribution of airborne MWCNTs was 20–10,000nm, with 99% of the particles between 25 and 2840nm. The count median diameter (CMD) was 209nm with a geometric standard deviation (GSD) of 1.98. This particle size range is similar to those found in some work environments (particles ≤6000nm). The penetration of MWCNTs through six tested FFR models at two constant flow rates of 30 and 85 LPM was determined. Penetration at 85 LPM (0.58–2.04% for N95, 0.15–0.32% for N99, and 0.007–0.009% for P100 FFRs) was greater compared with the values at 30 LPM (0.28–1.79% for N95, 0.10–0.24% for N99, and 0.005–0.006% for P100 FFRs). The most penetrating particle size through all six tested FFR models was found to be in the range of 25–130nm and 35–200nm for the 30-LPM and 85-LPM flow rates, respectively.

Particle Release from Respirators, Part I: Determination of the Effect of Particle Size, Drop Height, and Load

In late 2001, some U.S. Postal Service workers and a few members of Congress were exposed to anthrax spores. This led to an increased effort to develop employable methods to protect workers from exposure to anthrax. Some investigations focused on selection and use of respirators to protect workers against airborne anthrax. The present study evaluated the potential for several types of half-mask respirators to release deposited particles. Four brands of the most commonly used filtering facepiece respirators (hereafter termed masks) were loaded with 0.59-μm, 1.0-μm, and 1.9-μm polystyrene latex (PSL) microspheres (nominally 0.6, 1.0, and 2.0 μm) and then dropped onto a rigid surface. The load conditions were 10, 20, or 40 million particles, and drop heights were 0.15, 0.76, and 1.37 m. For the average conditions of 0.76 m, 1.15 μm size and 22 million particles loaded, the average particle release was 0.604 particles per 10,000 (95% CI: .552, .662) particles loaded for all of the filtering facepieces tested. The averaging of conditions is a useful tool to provide generalized information and is also useful when making risk estimates. For most filtering facepiece respirators, particle release tended to increase with drop height and particle size, and there appeared to be a slight inverse relationship with particle load. Two brands of reusable elastomeric half-mask respirators with P100 high-efficiency particulate air (HEPA) filter cartridges were also evaluated. Results of these tests were inconclusive. Part II in this issue addresses the release of particles when simulating removal of a filtering facepiece from a wearer's head.

Statistical Issues with Respect to Workplace Protection Factors for Respirators

A workplace protection factor (WPF) for a respirator wearer is the measured concentration of a contaminant outside the respirator divided by the simultaneous concentration of that contaminant inside the respirator. The Occupational Safety and Health Administration (OSHA) proposed an assigned protection factor (APF) of 10 to negative-pressure, half-facepiece, air-purifying respirators (HFAPR), based on the criterion that the 5th percentile of WPF for HFAPR be larger than the APF. This class of half-facepiece respirators includes both filtering facepiece and elastomeric half-mask respirators. Nicas and Neuhaus developed a statistical model for log-normally distributed WPF that separated between-wearer and within-wearer variation. Using results from applying this model to seven studies of HFAPR, they proposed an APF of 5 for this class of respirator, based on the criterion that the 5th percentile of the 5th percentile of individual worker WPF distributions be larger than the APF. In this article, two reasons are suggested for these differing proposals: (1) the Nicas and Neuhaus criterion is inherently more conservative than that of OSHA, and (2) substantially different databases were used to evaluate the two criteria. The Nicas and Neuhaus model is expanded to allow for differences in WPF distributions for different types of HFAPR and different contaminants and for separately estimating within-wearer variation and variation due to measurement error. Appropriate statistical methods are illustrated for implementing these models when some of inside-the-respirator measurements are nondetects. Results from applying this expanded model to two new WPF studies suggest that an APF of 10 would be sufficiently protective in these studies using the OSHA criterion but more marginally so using the Nicas and Neuhaus criterion.