Evaluation of a quantitative fit testing method for N95 filtering facepiece respirators

A method for performing quantitative fit tests (QNFT) with N95 filtering facepiece respirators was developed by earlier investigators. The method employs a simple clamping device to allow the penetration of submicron aerosols through N95 filter media to be measured. The measured value is subtracted from total penetration, with the assumption that the remaining penetration represents faceseal leakage. The developers have used the clamp to assess respirator performance. This study evaluated the clamp's ability to measure filter penetration and determine fit factors. In Phase 1, subjects were quantitatively fit-tested with elastomeric half-facepiece respirators using both generated and ambient aerosols. QNFT were done with each aerosol with both P100 and N95 filters without disturbing the facepiece. In Phase 2 of the study elastomeric half facepieces were sealed to subjects' faces to eliminate faceseal leakage. Ambient aerosol QNFT were performed with P100 and N95 filters without disturbing the facepiece. In both phases the clamp was used to measure N95 filter penetration, which was then subtracted from total penetration for the N95 QNFT. It was hypothesized that N95 fit factors corrected for filter penetration would equal the P100 fit factors. Mean corrected N95 fit factors were significantly different from the P100 fit factors in each phase of the study. In addition, there was essentially no correlation between corrected N95 fit factors and P100 fit factors. It was concluded that the clamp method should not be used to fit-test N95 filtering facepieces or otherwise assess respirator performance.     

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.     

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

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 (C_out) to inside (C_in) 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.     

Errors associated with three methods of assessing respirator fit

Three fit test methods (Bitrex, saccharin, and TSI PortaCount Plus with the N95-Companion) were evaluated for their ability to identify wearers of respirators that do not provide adequate protection during a simulated workplace test. Thirty models of NIOSH-certified N95 half-facepiece respirators (15 filtering-facepiece models and 15 elastomeric models) were tested by a panel of 25 subjects using each of the three fit testing methods. Fit testing results were compared to 5th percentiles of simulated workplace protection factors. Alpha errors (the chance of failing a fit test in error) for all 30 respirators were 71% for the Bitrex method, 68% for the saccharin method, and 40% for the Companion method. Beta errors (the chance of passing a fit test in error) for all 30 respirator models combined were 8% for the Bitrex method, 8% for the saccharin method, and 9% for the Companion method. The three fit test methods had different error rates when assessed with filtering facepieces and when assessed with elastomeric respirators. For example, beta errors for the three fit test methods assessed with the 15 filtering facepiece respirators were < or = 5% but ranged from 14% to 21% when assessed with the 15 elastomeric respirators. To predict what happens in a realistic fit testing program, the data were also used to estimate the alpha and beta errors for a simulated respiratory protection program in which a wearer is given up to three trials with one respirator model to pass a fit test before moving onto another model. A subject passing with any of the three methods was considered to have passed the fit test program. The alpha and beta errors for the fit testing in this simulated respiratory protection program were 29% and 19%, respectively. Thus, it is estimated, under the conditions of the simulation, that roughly one in three respirator wearers receiving the expected reduction in exposure (with a particular model) will fail to pass (with that particular model), and that roughly one in five wearers receiving less reduction in exposure than expected will pass the fit testing program in error.     

Particle release from respirators, part II: determination of the effect of tension applied in simulation of removal

This study evaluated the potential for disposable filtering facepiece respirators (hereafter termed masks) contaminated with 1-μ m particles to release particles as a result of lateral tension applied to the mask. The lateral tension was designed to simulate the removal of a contaminated mask from a user's head. Four brands of filtering facepieces were loaded with approximately 20 million 1.0-μ m polystyrene latex (PSL) microspheres. The respirators were then placed in a test chamber and subjected to lateral tension between 17.8-26.7 N (4-6 lbs) for 1 to 2 sec. The findings suggest that neither mask type nor loading condition affects particle release. This supports our hypothesis that when filtering facepiece respirators are properly removed from the head they will not release a significant number of particles.     

Evaluation of particulate filtering respirators using inward leakage (IL) or total inward leakage (TIL) testing--Korean experience

Korean certification regulation for particulate filtering respirators requires inward leakage (IL) or total inward leakage (TIL) testing according to European Standard EN 13274-1, and the standard levels of compliance are similar to those of the European Standard. This study was conducted to evaluate particulate filtering respirators being commercially used in the Korean market using an IL or TIL test and the validity of standard level in Korea. Three half masks and 10 filtering facepieces (two top class, four 1st class and four 2nd class)-a total of 13 brand name respirators-were selected for the test with panels of 10 subjects. Each subject was classified with nine facial dimension grid squares in accordance with face length and lip length. IL or TIL testing was conducted at the laboratory of the 3M Innovation Center in which the experimental instruments and systems were established in compliance with European standards. The testing procedure followed EN 13274-1 (2001). As expected, leakages of half masks were less than those of filtering facepieces and the latter were significantly different among brands. TILs of the 1st class filtering facepieces were found to be much more than those of the 2nd class and the result may cause a wearer to get confused when selecting a mask. The main route leakage for filtering facepieces may not be the filter medium but the face seal. Therefore, it is necessary to develop well-fitting filtering facepieces for Koreans. Because leakages were significantly different for different facial dimensions, a defined test panel for IL or TIL testing according to country or race should be developed. A more precise method to demonstrate fit, for example, fit testing such as in the US regulations, will be needed before IL or TIL testing or when selecting a respirator. Another finding implies that geometric mean of five exercises for IL or TIL may be better than arithmetic mean to establish a standard individual subject mean.     

Correlation between respirator fit and respirator fit test panel cells by respirator size

The National Institute for Occupational Safety and Health (NIOSH), recognizing the difficulties inherent in using old military data to define modern industrial respirator fit test panels, recently completed a study to develop an anthropometric database of the measurements of heads and faces of civilian respirator users. Based on the data collected, NIOSH researchers developed two new panels for fit testing half-facepiece and full-facepiece respirators. One of the new panels (NIOSH bivariate panel) uses face length and face width. The other panel is based on principal component analysis (PCA) to identify the linear combination of facial dimensions that best explains facial variations. The objective of this study was to investigate the correlation between respirator fit and the new NIOSH respirator fit test panel cells for various respirator sizes. This study was carried out on 30 subjects that were selected in part using the new NIOSH bivariate panel. Fit tests were conducted on the test subjects using a PORTACOUNT device and three exercises. Each subject was tested with three replications of four models of P-100 half-facepiece respirators in three sizes. This study found that respirator size significantly influenced fit within a given panel cell. Face size categories also matched the respirator sizing reasonably well, in that the small, medium, and large face size categories achieved the highest geometric mean fit factors in the small, medium, and large respirator sizes, respectively. The same pattern holds for fit test passing rate. Therefore, a correlation was found between respirator fit and the new NIOSH bivariate fit test panel cells for various respirator sizes. Face sizes classified by the PCA panel also followed a similar pattern with respirator fit although not quite as consistently. For the LANL panel, however, both small and medium faces achieved best fit in small size respirators, and large faces achieved best fit in medium respirators. These findings support the selection of the facial dimensions for developing the new NIOSH bivariate respirator fit test panel.     

Variation in penetration of submicrometric particles through electrostatic filtering facepieces during exposure to paraffin oil aerosol

Several studies show the increase of penetration through electrostatic filters during exposure to an aerosol flow, because of particle deposition on filter fibers. We studied the effect of increasing loads of paraffin oil aerosol on the penetration of selected particle sizes through an electrostatic filtering facepiece. FFP2 facepieces were exposed for 8 hr to a flow rate of 95.0 ± 0.5 L/min of polydisperse paraffin aerosol at 20.0?± 0.5?mg/m(3). The penetration of bis(2-ethylhexyl)sebacate (DEHS) monodisperse neutralized aerosols, with selected particle size in the 0.03-0.40?μm range, was measured immediately prior to the start of the paraffin aerosol loading and at 1, 4, and 8 hr after the start of paraffin aerosol loading. Penetration through isopropanol-treated facepieces not oil paraffin loaded was also measured to evaluate facepiece behavior when electrostatic capture mechanisms are practically absent. During exposure to paraffin aerosol, DEHS penetration gradually increased for all aerosol sizes, and the most penetrating particle size (0.05?μm at the beginning of exposure) shifted slightly to larger diameters. After the isopropanol treatment, the higher penetration value was 0.30?μm. In addition to an increased penetration during paraffin loading at a given particle size, the relative degree of increase was greater as the particle size increased. Penetration value measured after 8 hr for 0.03-μm particles was on average 1.6?times the initial value, whereas it was about 8?times for 0.40-μm particles. This behavior, as well evidenced in the measurements of isopropanol-treated facepieces, can be attributed to the increasing action in particle capture of the electrostatic forces (Coulomb and polarization), which depend strictly on the diameter and electrical charge of neutralized aerosol particles. With reference to electrostatic filtering facepieces as personal protective equipment, results suggest the importance of complying with the manufacturer instructions when it is specified that their use has to be restricted to a single shift.     

Comparison of N95 disposable filtering facepiece fits using bitrex qualitative and TSI Portacount quantitative fit testing

As a means of evaluating the use of denatonium benzoate (bitrex) as a qualitative fit test agent with filtering facepiece respirators, the bitrex qualitative and TSI Protacount(R) quantitative fit-test methods were compared using N95 filtering facepieces. Seventy-nine paired tests (trial) were performed. Detection of bitrex during a qualitative fit test or measurement of a fit factor of <100 during a quantitative fit test constituted a failure. Qualitative and quantitative methods were performed using identical test protocols. Data were analyzed using pass/fail criteria, and matched-pair analysis methods were applied. The results of this study indicate that the use of bitrex during qualitative fit testing of N95 disposable filtering facepieces results in an increase in failure and/or rejection in cases where a TSI Portacount (plus N95 companion accessory) quantitatively establishes an acceptable fit.     

Evaluation of the filtration performance of NIOSH-approved N95 filtering facepiece respirators by photometric and number-based test methods

N95 particulate filtering facepiece respirators are certified by measuring penetration levels photometrically with a presumed severe case test method using charge neutralized NaCl aerosols at 85 L/min. However, penetration values obtained by photometric methods have not been compared with count-based methods using contemporary respirators composed of electrostatic filter media and challenged with both generated and ambient aerosols. To better understand the effects of key test parameters (e.g., particle charge, detection method), initial penetration levels for five N95 model filtering facepiece respirators were measured using NaCl aerosols with the aerosol challenge and test equipment employed in the NIOSH respirator certification method (photometric) and compared with an ultrafine condensation particle counter method (count based) for the same NaCl aerosols as well as for ambient room air particles. Penetrations using the NIOSH test method were several-fold less than the penetrations obtained by the ultrafine condensation particle counter for NaCl aerosols as well as for room particles indicating that penetration measurement based on particle counting offers a more difficult challenge than the photometric method, which lacks sensitivity for particles < 100 nm. All five N95 models showed the most penetrating particle size around 50 nm for room air particles with or without charge neutralization, and at 200 nm for singly charged NaCl monodisperse particles. Room air with fewer charged particles and an overwhelming number of neutral particles contributed to the most penetrating particle size in the 50 nm range, indicating that the charge state for the majority of test particles determines the MPPS. Data suggest that the NIOSH respirator certification protocol employing the photometric method may not be a more challenging aerosol test method. Filter penetrations can vary among workplaces with different particle size distributions, which suggests the need for the development of new or revised "more challenging" aerosol test methods for NIOSH certification of respirators.     

Respiratory protection and the risk of Mycobacterium tuberculosis infection

Tuberculosis (TB) can be transmitted to susceptible healthcare workers via inhalation of droplet nuclei carrying viable Mycobacterium tuberculosis bacilli. Several types of respiratory protective devices are compared with respect to efficacy against droplet nuclei penetration: surgical masks, disposable dust/mist particulate respirators (PRs), elastomeric halfmask respirators with high-efficiency (HEPA) filters, and powered airpurifying respirators (PAPRs) with elastomeric halfmask facepieces and HEPA filters. It is estimated that these devices permit, respectively, 42%, 5.7%, 2%, and 0.39% penetration of droplet nuclei into the facepiece. More limited data for the disposable HEPA filtering-facepiece respirator suggest that it would allow droplet nuclei penetration of 3% or less, similar to the value estimated for the elastomeric halfmask HEPA filter respirator. Because a respirator wearer's cumulative infection risk depends on the extent of droplet nuclei penetration, the cumulative risk will differ, given use of these different respirators. Hypothetical but realistic “low-exposure” and “high-exposure” scenarios are posed that involve, respectively, a 1.6% and a 6.4% annual risk of infection for healthcare workers. For the low-exposure scenario, the 10-year cumulative risks given no respirators versus surgical masks versus disposable dust/mist PRs versus elastomeric halfmask HEPA filter respirators versus HEPA filter PAPRs are, respectively, 15%, 6.7%, 0.94%, 0.33%, and .064%. For the high-exposure scenario, the 10-year cumulative risks for no respirator use versus use of the same four types of respirators are, respectively, 48%, 24%, 3.7%, 1.3%, and 0.26%. The use of disposable HEPA filtering-facepiece respirator should permit cumulative risks close to those estimated for the elastomeric halfmask HEPA filter respirator. It is concluded that when an infectious TB patient undergoes a procedure that generates respiratory aerosols, and when droplet nuclei source control is inadequate, healthcare workers attending the patient may need to wear highly protective respirators, such as HEPA filter PAPRs.     

Respiratory source control using a surgical mask: An in vitro study

Cough etiquette and respiratory hygiene are forms of source control encouraged to prevent the spread of respiratory infection. The use of surgical masks as a means of source control has not been quantified in terms of reducing exposure to others. We designed an in vitro model using various facepieces to assess their contribution to exposure reduction when worn at the infectious source (Source) relative to facepieces worn for primary (Receiver) protection, and the factors that contribute to each. In a chamber with various airflows, radiolabeled aerosols were exhaled via a ventilated soft-face manikin head using tidal breathing and cough (Source). Another manikin, containing a filter, quantified recipient exposure (Receiver). The natural fit surgical mask, fitted (SecureFit) surgical mask and an N95-class filtering facepiece respirator (commonly known as an “N95 respirator”) with and without a Vaseline-seal were tested. With cough, source control (mask or respirator on Source) was statistically superior to mask or unsealed respirator protection on the Receiver (Receiver protection) in all environments. To equal source control during coughing, the N95 respirator must be Vaseline-sealed. During tidal breathing, source control was comparable or superior to mask or respirator protection on the Receiver. Source control via surgical masks may be an important adjunct defense against the spread of respiratory infections. The fit of the mask or respirator, in combination with the airflow patterns in a given setting, are significant contributors to source control efficacy. Future clinical trials should include a surgical mask source control arm to assess the contribution of source control in overall protection against airborne infection.     

Development of Medium-size Half-mask Facepiece for Male Workers at a Shipyard and Its Fit Performance in Korea

Ten years ago, three differently sized half-mask facepiece prototypes were constructed from silicon using computer graphics and statistical analysis to fit them according to Korean facial dimensions. The purpose of this study was to complete the medium-size half-mask respirator based on the prototype, which would provide an adequate fit performance for male workers at a shipyard, Hyundai Samho Heavy Industry Co., in Korea. The complete respirator—the hardness 55—was manufactured with existing accessories such as a filter, exhalation valve, and strap attached. The fit performance test was conducted by performing a quantitative fit-test on 48 male subjects: workers who usually wear half-mask respirators (Dobulife Tech Co., Model DM-911, Gwangju, Gyeonggi-do, Korea). The results showed that the hardness 55 provided male subject workers with much better fit performance than the existing mask constructed by the same company. Because softness of the material of the facepiece, in particular the inner part, influenced faceseal leakage, further research on developing better-fit respirator facepieces should consider carefully the fine control of material softness.     

Development of an Advanced Respirator Fit-Test Headform

Improved respirator test headforms are needed to measure the fit of N95 filtering facepiece respirators (FFRs) for protection studies against viable airborne particles. A Static (i.e., non-moving, non-speaking) Advanced Headform (StAH) was developed for evaluating the fit of N95 FFRs. The StAH was developed based on the anthropometric dimensions of a digital headform reported by the National Institute for Occupational Safety and Health (NIOSH) and has a silicone polymer skin with defined local tissue thicknesses. Quantitative fit factor evaluations were performed on seven N95 FFR models of various sizes and designs. Donnings were performed with and without a pre-test leak checking method. For each method, four replicate FFR samples of each of the seven models were tested with two donnings per replicate, resulting in a total of 56 tests per donning method. Each fit factor evaluation was comprised of three 86-sec exercises: “Normal Breathing” (NB, 11.2 liters per min (lpm)), “Deep Breathing” (DB, 20.4 lpm), then NB again. A fit factor for each exercise and an overall test fit factor were obtained. Analysis of variance methods were used to identify statistical differences among fit factors (analyzed as logarithms) for different FFR models, exercises, and testing methods. For each FFR model and for each testing method, the NB and DB fit factor data were not significantly different (P > 0.05). Significant differences were seen in the overall exercise fit factor data for the two donning methods among all FFR models (pooled data) and in the overall exercise fit factor data for the two testing methods within certain models. Utilization of the leak checking method improved the rate of obtaining overall exercise fit factors ≥100. The FFR models, which are expected to achieve overall fit factors ≥ 100 on human subjects, achieved overall exercise fit factors ≥ 100 on the StAH. Further research is needed to evaluate the correlation of FFRs fitted on the StAH to FFRs fitted on people.

[Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following free supplemental resource: a file providing detailed information on the advanced head form design and fabrication process.]     

Manikin-based size-resolved penetrations of CE-marked filtering facepiece respirators

The purpose of this manikin-based study was to determine the percentage penetrations of nine CE-marked filtering facepiece respirator models (two samples from each) from filtering classes FFP1, FFP2, and FFP3 and to demonstrate by an independent measurement method the disadvantages and shortcomings of the currently valid European Norm (EN 149:2001) for filtering facepieces. All of the filtering facepieces were evaluated size-selectively in an experimental chamber using charge-neutralized monodisperse ammonium sulfate in 9 sizes ranging from 20–400 nm of count median diameter (CMD) under flowrate of 95 L/min. The results were then compared to the previous study concerning penetrations of 47-mm diameter filters cut from the filtering material of identical filtering facepieces. Although these two experimental methods for measuring penetrations of filtering materials from filtering facepieces are in good agreement (R² = 0.91), the results show within-respirator variations in all three filtering classes (5.5–19.3% for all FFRs in FFP1, 2.8–8.5% in FFP2, and 0.1–2.8% in FFP3). The most penetrating particle size (MPPS) in this study was found to be in the range of 25–65 nm (CMD), which is in agreement with the range of 30–60 nm found in the previous study. Moreover, 7 out of 9 FFR models reached higher penetrations from manikin-based respirator measurements than during measurements of filters from the respective respirators. Furthermore, penetration levels increased up to ～50% when the respirator was not sealed around the face of the manikin, indicating that the real protection level provided by these filtering facepieces may be even lower if the respirator does not fit perfectly. Considering that poor filtration efficiency and poor fit may increase under real work conditions, the particle penetration is even higher than was found in this study. Therefore, the CE-marked respirators examined in this study may not be efficient in providing the expected level of protection for workers exposed to nanoparticles.     

Powered air-purifying respirator use in healthcare: Effects on thermal sensations and comfort

Twelve subjects wore an N95 filtering facepiece respirator (N95 FFR), one tight-fitting full facepiece powered air-purifying respirator (PAPR), two loose-fitting PAPRs, and one elastomeric/PAPR hybrid for 1 hr each during treadmill walking at 5.6 km/hr while undergoing physiological and subjective response monitoring. No significant interaction (p ≥ .05) was noted between the five respirators in heart rate, respiratory rate, oxygen saturation, transcutaneous carbon dioxide, and perceptions of breathing effort or discomfort, exertion, facial heat, and overall body heat. Respirator deadspace heat/humidity were significantly greater for the N95 FFR, whereas tympanic forehead skin temperatures were significantly greater for the hybrid PAPR. Temperature of the facial skin covered by the respirator was equivalent for the N95 FFR and hybrid PAPR, and both were significantly higher than for the other three PAPRs. Perception of eye dryness was significantly greater for a tight-fitting full facepiece PAPR than the N95 FFR and hybrid PAPR. At a low-moderate work rate over 1 hr, effects on cardiopulmonary variables, breathing perceptions, and facial and overall body heat perceptions did not differ significantly between the four PAPRs and a N95 FFR, but the tight-fitting, full facepiece PAPR increased perceptions of eye dryness. The two loose-fitting PAPRs and the full facepiece tight-fitting PAPR ameliorated exercise-induced increases in facial temperature, but this did not translate to improved perception of facial heat and overall body heat.     

Development of a National Occupational Exposure Survey and Database associated with NIOSH hazard surveillance initiatives

NIOSH pioneered hazard surveillance in the workplace by designing and conducting the 1972 to 1974 National Occupational Hazard Survey (NOHS), the 1981 to 1983 National Occupational Exposure Survey (NOES), and the 1984 to 1989 National Occupational Health Survey of Mining (NOHSM). The databases developed from these three on-site surveys represent unique resources for associating potential chemical, physical and biological agents with industries and occupational groups. The data have been a primary source of information for NIOSH, regulatory agencies, health professionals, researchers, and labor organizations in establishing priorities for prevention strategies that include medical and engineering interventions, development of occupational standards, and the identification of research needs. Recognizing that the data from these surveys are becoming dated, a multidisciplinary team comprising members from various NIOSH research divisions was established to develop a hazard surveillance strategy for the Institute, including options for a national hazard surveillance survey and database. The proposed new hazard survey builds on lessons learned from the previous surveys, seeks opportunities to incorporate existing data from other sources, expands the scope of industries and hazards, and takes advantage of advances in data gathering, processing and dissemination technology. This article presents current considerations and recommendations for a new hazard survey and database.     

A comparison of facemask and respirator filtration test methods

NIOSH published a Federal Register Notice to explore the possibility of incorporating FDA required filtration tests for surgical masks (SMs) in the 42 CFR Part 84 respirator certification process. There have been no published studies comparing the filtration efficiency test methods used for NIOSH certification of N95 filtering facepiece respirators (N95 FFRs) with those used by the FDA for clearance of SMs. To address this issue, filtration efficiencies of “N95 FFRs” including six N95 FFR models and three surgical N95 FFR models, and three SM models were measured using the NIOSH NaCl aerosol test method, and FDA required particulate filtration efficiency (PFE) and bacterial filtration efficiency (BFE) methods, and viral filtration efficiency (VFE) method. Five samples of each model were tested using each method. Both PFE and BFE tests were done using unneutralized particles as per FDA guidance document. PFE was measured using 0.1 µm size polystyrene latex particles and BFE with ～3.0 µm size particles containing Staphylococcus aureus bacteria. VFE was obtained using ～3.0 µm size particles containing phiX 174 as the challenge virus and Escherichia coli as the host. Results showed that the efficiencies measured by the NIOSH NaCl method for “N95 FFRs” were from 98.15–99.68% compared to 99.74–99.99% for PFE, 99.62–99.9% for BFE, and 99.8–99.9% for VFE methods. Efficiencies by the NIOSH NaCl method were significantly (p = <0.05) lower than the other methods. SMs showed lower efficiencies (54.72–88.40%) than “N95 FFRs” measured by the NIOSH NaCl method, while PFE, BFE, and VFE methods produced no significant difference. The above results show that the NIOSH NaCl method is relatively conservative and is able to identify poorly performing filtration devices. The higher efficiencies obtained using PFE, BFE and VFE methods show that adding these supplemental particle penetration methods will not improve respirator certification.     

Aerosol penetration through filtering facepieces and respirator cartridges.

Air-purifying respirators must be certified following the National Institute for Occupational Safety and Health (NIOSH) filter test criteria (30 CFR 11). The criteria specify a range for the mean particle size and the measure of spread permissible for the test aerosol. The authors' experiments have shown that aerosol penetration as a function of particle size differs considerably among certified respirators of the same type. Filtering facepieces (disposable respirators) and cartridges of the dust-mist, dust-mist-fume, and high-efficiency particulate air type were tested. The respirators were sealed to mannequins in a test chamber. The aerosol concentrations inside and outside the respirator were measured by an aerodynamic particle sizer and a laser aerosol spectrometer over a particle size range of 0.1 to 15 microns. Five flow rates ranging from 5 to 100 L/min were used to study flow dependency. The aerosol penetration through the filters is presented as a function of particle size. Aerosol penetration and pressure drop are combined to express the performance of each filter in terms of "quality factor." Under the same test conditions, the quality factor of one respirator may be as much as 6.6 times more than that of another respirator of the same type. The filter quality factor has a greater aerosol size dependency as airflow and aerosol size increase. In general, cartridges have a larger surface area than filtering facepieces but not necessarily lower filter penetration or higher filter quality.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterizing inward leakage in a pressure-demand, self-contained breathing apparatus

An analytical model of the flow across a resistive flow path such as an orifice or pipe was applied to predict the inward leakage in the facepiece of a self-contained breathing apparatus (SCBA) during a steady below-ambient facepiece pressure. The model was used to estimate leakage rates with respect to the size of the leak and for below-ambient (negative) pressure conditions reflective of measured occurrences. Results of the model were also used to make quantitative estimates of the protection level of the respirator. Experiments were designed to induce a continuous below-ambient pressure inside the facepiece of a pressure-demand SCBA mounted on a headform. Negative facepiece pressure measured in the presence of a leak correlated with the measured particle concentration ratio. Results show that the analytical model generated reasonable estimates of leakage rates during conditions of negative pressure inside the facepiece. Thus, the analytical model performed well for constant flow conditions, demonstrating the capability to predict a momentary compromise in respirator protection during momentary negative facepiece pressure conditions.