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.     

Comparison of pressure drop and filtration efficiency of particulate respirators using welding fumes and sodium chloride

Respirators are used to help reduce exposure to a variety of contaminants in workplaces. Test aerosols used for certification of particulate respirators (PRs) include sodium chloride (NaCl), dioctyl phthalate, and paraffin oil. These aerosols are generally assumed to be worst case surrogates for aerosols found in the workplace. No data have been published to date on the performance of PRs with welding fumes, a hazardous aerosol that exists in real workplace settings. The aim of this study was to compare the performance of respirators and filters against a NaCl aerosol and a welding fume aerosol and determine whether or not a correlation between the two could be made. Fifteen commercial PRs and filters (seven filtering facepiece, two replaceable single-type filters, and six replaceable dual-type filters) were chosen for investigation. Four of the filtering facepiece respirators, one of the single-type filters, and all of the dual-type filters contained carbon to help reduce exposure to ozone and other vapors generated during the welding process. For the NaCl test, a modified National Institute for Occupational Safety and Health protocol was adopted for use with the TSI Model 8130 automated filter tester. For the welding fume test, welding fumes from mild steel flux-cored arcs were generated and measured with a SIBATA filter tester (AP-634A, Japan) and a manometer in the upstream and downstream sections of the test chamber. Size distributions of the two aerosols were measured using a scanning mobility particle sizer. Penetration and pressure drop were measured over a period of aerosol loading onto the respirator or filter. Photos and scanning electron microscope images of clean and exposed respirators were taken. The count median diameter (CMD) and mass median diameter (MMD) for the NaCl aerosol were smaller than the welding fumes (CMD: 74 versus 216 nm; MMD: 198 versus 528 nm, respectively). Initial penetration and peak penetration were higher with the NaCl aerosol. However, pressure drop increased much more rapidly in the welding fume test than the NaCl aerosol test. The data and images clearly show differences in performance trends between respirator models. Therefore, general correlations between NaCl and weld fume data could not be made. These findings suggest that respirators certified with a surrogate test aerosol such as NaCl are appropriate for filtering welding fume (based on penetration). However, some respirators may have a more rapid increase in pressure drop from the welding fume accumulating on the filter. Therefore, welders will need to choose which models are easier to breathe through for the duration of their use and replace respirators or filters according to the user instructions and local regulations.     

Nanoparticle penetration through filter media and leakage through face seal interface of N95 filtering facepiece respirators

National Institute for Occupational Safety and Health recommends the use of particulate respirators for protection against nanoparticles (<100 nm size). Protection afforded by a filtering facepiece particulate respirator is a function of the filter efficiency and the leakage through the face-to-facepiece seal. The combination of particle penetration through filter media and particle leakage through face seal and any component interfaces is considered as total inward leakage (TIL). Although the mechanisms and extent of nanoparticle penetration through filter media have been well documented, information concerning nanoparticle leakage through face seal is lacking. A previous study in our laboratory measured filter penetration and TIL for specific size particles. The results showed higher filter penetration and TIL for 50 nm size particles, i.e. the most penetrating particle size (MPPS) than for 8 and 400 nm size particles. To better understand the significance of particle penetration through filter media and through face seal leakage, this study was expanded to measure filter penetration at sealed condition and TIL with artificially introduced leaks for 20-800 nm particles at 8-40 l minute volumes for four N95 models of filtering facepiece respirators (FFRs) using a breathing manikin. Results showed that the MPPS was ~45 nm for all four respirator models. Filter penetration for 45 nm size particles was significantly (P < 0.05) higher than the values for 400 nm size particles. A consistent increase in filter penetrations for 45 and 400 nm size particles was obtained with increasing breathing minute volumes. Artificial leakage of test aerosols (mode size ~75 nm) through increasing size holes near the sealing area of FFRs showed higher TIL values for 45 nm size particles at different minute volumes, indicating that the induced leakage allows the test aerosols, regardless of particle size, inside the FFR, while filter penetration determines the TIL for different size particles. TIL values obtained for 45 nm size particles were significantly (P < 0.05) higher than the values obtained for 400 nm size particles for all four models. Models with relatively small filter penetration values showed lower TIL values than the models with higher filter penetrations at smaller leak sizes indicating the dependence of TIL values on filter penetration. When the electrostatic charge was removed, the FFRs showed a shift in the MPPS to ~150 nm with the same test aerosols (mode size ~75 nm) at different hole sizes and breathing minute volumes, confirming the interaction between filter penetration and face seal leakage processes. The shift in the MPPS from 45 to 150 nm for the charge removed filters indicates that mechanical filters may perform better against nanoparticles than electrostatic filters rated for the same filter efficiency. The results suggest that among the different size particles that enter inside the N95 respirators, relatively high concentration of the MPPS particles in the breathing zone of respirators can be expected in workplaces with high concentration of nanoparticles. Overall, the data obtained in the study suggest that good fitting respirators with lower filter penetration values would provide better protection against nanoparticles.     

Nanoparticle filtration performance of NIOSH-certified particulate air-purifying filtering facepiece respirators: evaluation by light scattering photometric and particle number-based test methods

National Institute for Occupational Safety and Health (NIOSH) certification test methods employ charge neutralized NaCl or dioctyl phthalate (DOP) aerosols to measure filter penetration levels of air-purifying particulate respirators photometrically using a TSI 8130 automated filter tester at 85 L/min. A previous study in our laboratory found that widely different filter penetration levels were measured for nanoparticles depending on whether a particle number (count)-based detector or a photometric detector was used. The purpose of this study was to better understand the influence of key test parameters, including filter media type, challenge aerosol size range, and detector system. Initial penetration levels for 17 models of NIOSH-approved N-, R-, and P-series filtering facepiece respirators were measured using the TSI 8130 photometric method and compared with the particle number-based penetration (obtained using two ultrafine condensation particle counters) for the same challenge aerosols generated by the TSI 8130. In general, the penetration obtained by the photometric method was less than the penetration obtained with the number-based method. Filter penetration was also measured for ambient room aerosols. Penetration measured by the TSI 8130 photometric method was lower than the number-based ambient aerosol penetration values. Number-based monodisperse NaCl aerosol penetration measurements showed that the most penetrating particle size was in the 50 nm range for all respirator models tested, with the exception of one model at ~200 nm size. Respirator models containing electrostatic filter media also showed lower penetration values with the TSI 8130 photometric method than the number-based penetration obtained for the most penetrating monodisperse particles. Results suggest that to provide a more challenging respirator filter test method than what is currently used for respirators containing electrostatic media, the test method should utilize a sufficient number of particles <100 nm and a count (particle number)-based detector.     

Filtration performance of NIOSH-approved N95 and P100 filtering facepiece respirators against 4 to 30 nanometer-size nanoparticles

This study investigated the filtration performance of NIOSH-approved N95 and P100 filtering facepiece respirators (FFR) against six different monodisperse silver aerosol particles in the range of 4-30 nm diameter. A particle test system was developed and standardized for measuring the penetration of monodisperse silver particles. For respirator testing, five models of N95 and two models of P100 filtering facepiece respirators were challenged with monodisperse silver aerosol particles of 4, 8, 12, 16, 20, and 30 nm at 85 L/min flow rate and percentage penetrations were measured. Consistent with single-fiber filtration theory, N95 and P100 respirators challenged with silver monodisperse particles showed a decrease in percentage penetration with a decrease in particle diameter down to 4 nm. Penetrations less than 1 particle/30 min for 4-8 nm particles for one P100 respirator model, and 4-12 nm particles for the other P100 model, were observed. Experiments were also carried out with larger than 20 nm monodisperse NaCl particles using a TSI 3160 Fractional Efficiency Tester. NaCl aerosol penetration levels of 20 nm and 30 nm (overlapping sizes) particles were compared with silver aerosols of the same sizes by a three-way ANOVA analysis. A significant (p < 0.001) difference between NaCl and silver aerosol penetration levels was obtained after adjusting for particle sizes and manufacturers. A significant (p = 0.001) interaction with manufacturers indicated the difference in NaCl, and silver aerosol penetrations were not the same across manufacturers. The two aerosols had the same effect across 20 nm and 30 nm sizes as shown by the absence of any significant (p = 0.163) interaction with particle sizes. In the case of P100 FFRs, a significant (p < 0.001) difference between NaCl and silver aerosol (20 nm and 30 nm) penetrations was observed for both respirator models tested. The filtration data for 4-30 nm monodisperse particles supports previous studies that indicate NIOSH-approved air-purifying respirators provide expected levels of filtration protection against nanoparticles.     

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)     

Electrostatic respirator filter media: filter efficiency and most penetrating particle size effects

New electrostatic filter media has been developed for use in 42 CFR 84 negative pressure particulate respirator filters. This respirator filter media was not available for evaluation prior to the change from 30 CFR 11 to 42 CFR 84. Thus, characterization of this filter media is warranted. In this study, the new 42 CFR 84 electrostatic respirator filters were investigated with respect to filter penetration and most penetrating particle size. Three different models of N95 filters, along with one model each of the N99, R95, and P100 class filters were used in this study. First, three of each filter were loaded with a sodium chloride (NaCl) aerosol, and three of each filter were loaded with a dioctyl phthalate (DOP) aerosol to obtain normal background penetration results for each filter. Then, two new filters of each type were dipped in isopropanol for 15 seconds and allowed to dry. This isopropanol dip should reduce or eliminate any electrostatic charge on the fibers of each filter, as reported in the technical literature. These dipped filters, along with controls of each filter type, were tested on a TSI 8160 filter tester to determine the most penetrating particle size. These same filters were then tested against a NaCl aerosol to get final penetration values. Electret filters rely heavily on their electrostatic charge to provide adequate filter efficiencies, and correlations between penetration and a filter's electrostatic characteristics are found in the technical literature. In all six of the filter models tested, filter penetration values increased considerably and the most penetrating particle size noticeably shifted toward larger particles. These results are important in better understanding how these new filter materials perform under various conditions, and they indicate the need for additional research to define environmental conditions that may affect electrostatic filter efficiency.     

Advanced testing method to evaluate the performance of respirator filter media

Filter media for respirator applications are typically exposed to the cyclic flow condition, which is different from the constant flow condition adopted in filter testing standards. To understand the real performance of respirator filter media in the field it is required to investigate the penetration of particles through respirator filters under cyclic flow conditions representing breathing flow patterns of human beings. This article reports a new testing method for studying the individual effect of breathing frequency (BF) and peak inhalation flow rate (PIFR) on the particle penetration through respirator filter media. The new method includes the use of DMA (Differential Mobility Analyzer)-classified particles having the most penetrating particle size, MPPS (at the constant flowrate of equivalent mean inhalation flow rate, MIFR) as test aerosol. Two condensation particle counters (CPCs) are applied to measure the particle concentrations at the upstream and downstream of test filter media at the same time. Given the 10 Hz sampling time of CPCs, close-to-instantaneous particle penetration could be measured. A pilot study was performed to demonstrate the new testing method. It is found that the effect of BF on the particle penetration of test respirator filter media is of importance at all the tested peak inhalation flow rates (PIFRs), which is different from those reported in the previous work.     

Performance of respirator filters using quality factor in Korea

A respirator filter of good quality has not only high aerosol collection efficiency but also low air resistance. "Quality factor", which is expressed with aerosol penetration and pressure drop, can be used to rank the performance of respirator filters within the same category. This study focuses on evaluating several respirator filters which are widely used in Korea using quality factor. Two mechanical filters and three filtering facepieces made by different manufacturers were measured aerosol penetrations and pressure drops by an automatic filter tester (CertiTest Model 8110, TSI Inc., St. Paul, USA) at four flow rates of 10, 32, 64 and 85 L/min. NaCl aerosols used were reported to be mean size of 0.1 microm and geometric standard deviation of <1.9. The penetrations and pressure drops of all filters have strong flow rate dependency. The filter quality factors decrease sharply as flow rates are increased. The mechanical filter S and filtering facepiece M are shown better filter quality than others in the same category. Since some certified filters are found to be inappropriate in the workplace exposed to fume, this result suggests that the current certified filter test protocol for respirators should be changed for the new protocol using smaller aerosols.     

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?相似文献   

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.     

Evaluation of respirator filters for asbestos fibers

Fiber aerosols are known to have different aerodynamic behaviors than spherical particles and usually carry higher electrostatic charges. We investigated the effects of flow rate and charge status of filter cartridges on the penetration of spherical and fiber aerosols. Four types of test respirator filters were selected: two for passive respirators, one for a powered respirator, and one disposable respirator. Surface charges on respirator filters were determined using a noncontact field electrostatic field meter. Penetration tests were performed for filter cartridges before and after charge neutralization. The surface charge measurements on the respirator filters showed that some filters, including those used in disposable face masks, are charged to enhance the collection efficiency. Only high-efficiency particulate air filters performed consistently for both spherical test aerosols and the three types of asbestos fibers. The surface charge potential of filter cartridges and flow rate did not appear to affect the performance of these filters. In contrast to the high-efficiency filters, the aerosol penetration performance of low-efficiency filters and face masks deteriorated when the charge potential on the filter was removed. Our data also showed that the surface charges decreased in a high-temperature, high-humidity environment and disappeared after 1 week. Deposition of spherical particles and fibers in the charged disposable facemask filter was enhanced. For charged-neutralized, low-efficiency filter cartridges, asbestos fibers may penetrate more than spherical particles with a mean particle size of 0.3 microm diameter.     

Performance of dust respirators with facial seal leaks: I. Experimental

The ability of representative half-mask and single-use respirators with facial seal leaks to provide protection against aerosols was evaluated by experimental measurement. Respirators were mounted on a manikin in a test chamber and operated at seven steady flow rates over the range of 2 to 150 L/min. Samples of polydisperse and monodisperse aerosols were taken from inside and outside the respirator and analyzed by a calibrated optical particle counter over the particle-size range 0.1 to 11.3 microns. Measurements were made separately for filter performance as a function of particle size and flow rate, and simulated leak performance (penetration) as a function of particle size, pressure drop, and leak size. Flow rate vs. pressure drop measurements were made for all filters and leaks tested. For a given leak condition the percentage of the total flow traversing the leak varied several fold over the usual range of airflow rates through a respirator. Aerosol penetration was found to depend strongly on particle size and flow rate for filters, and to depend strongly on particle size and less strongly on pressure drop for leaks. One can conclude from these measurements that the aerosol-size distribution inside a respirator will nearly always be significantly different from that outside the respirator.     

Manikin-based performance evaluation of N95 filtering-facepiece respirators challenged with nanoparticles

Protection of the human respiratory system from exposure to nanoparticles is becoming an emerging issue in occupational hygiene. The potential adverse health effects associated with particles of approximately 1-100 nm are probably greater than submicron or micron-sized particles. The performance of two models of N95 half-facepiece-filtering respirators against nano-sized particles was evaluated at two inhalation flow rates, 30 and 85 l min(-1), following a manikin-based protocol. The aerosol concentration was measured outside and inside the facepiece using the Wide-Range Particle Spectrometer. Sodium chloride particles, conventionally used to certify N-series respirators under NIOSH 42 CFR 84 regulations, were utilized as the challenge aerosol. The targeted particle sizes ranged from 10 to 600 nm, although the standard certification tests are performed with particles of approximately 300 nm, which is assumed to be the most penetrating size. The results indicate that the nanoparticle penetration through a face-sealed N95 respirator may be in excess of the 5% threshold, particularly at high respiratory flow rates. Thus, N95 respirators may not always provide the expected respiratory protection for workers. The highest penetration values representing the poorest respirator protection conditions were observed in the particle diameter range of approximately 30-70 nm. Based on the theoretical simulation, we have concluded that for respirators utilizing mechanical filters, the peak penetration indeed occurs at the particle diameter of approximately 300 nm; however, for pre-charged fiber filters, which are commonly used for N95 respirators, the peak shifts toward nano-sizes. This study has confirmed that the neutralization of particles is a crucial element in evaluating the efficiency of a respirator. The variability of the respirator's performance was determined for both models and both flow rates. The analysis revealed that the coefficient of variation of the penetration ranged from 0.10 to 0.54 for particles of 20-100 nm in diameter. The fraction of N95 respirators for which the performance test at 85 l min(-1) demonstrated excessive (>5%) penetration of nanoparticles was as high as 9/10. The test results obtained in a relatively small (0.096 m(3)) test chamber and in a large (24.3 m(3)) walk-in chamber were found essentially the same, thus, suggesting that laboratory-based evaluations have a good potential to adequately represent the respirator field performance.     

Measurements of the efficiency of respirator filters and filtering facepieces against radon daughter aerosols.

The filtration efficiencies of respirator filters and filtering facepieces have been tested against radon daughters in a fluorspar mine. The test method involved the use of sampling filters exposed to natural radon daughters in air filtered by the test respirators. Respirators with a filtration efficiency high enough for them to be considered suitable for use against toxic dusts generally reduced radon daughter levels by 90% or more, though nuisance dust masks were ineffective. The measured penetration of radon daughters through the former types of filter correlated reasonably well with the penetration of 0.1 microns neutralized monodisperse aerosols, and with that of the BS 4400 sodium chloride aerosol, measured in the laboratory. To simulate exposure in working conditions mine air containing radon daughters was drawn through the test filters for 8 h, but their performance was not affected and they were not measurably radioactive as a result.     

A Quantitative Assessment of the Total Inward Leakage of NaCl Aerosol Representing Submicron-Size Bioaerosol Through N95 Filtering Facepiece Respirators and Surgical Masks

Respiratory protection provided by a particulate respirator is a function of particle penetration through filter media and through faceseal leakage. Faceseal leakage largely contributes to the penetration of particles through a respirator and compromises protection. When faceseal leaks arise, filter penetration is assumed to be negligible. The contribution of filter penetration and faceseal leakage to total inward leakage (TIL) of submicron-size bioaerosols is not well studied. To address this issue, TIL values for two N95 filtering facepiece respirator (FFR) models and two surgical mask (SM) models sealed to a manikin were measured at 8 L and 40 L breathing minute volumes with different artificial leak sizes. TIL values for different size (20–800 nm, electrical mobility diameter) NaCl particles representing submicron-size bioaerosols were measured using a scanning mobility particle sizer. Efficiency of filtering devices was assessed by measuring the penetration against NaCl aerosol similar to the method used for NIOSH particulate filter certification. Results showed that the most penetrating particle size (MPPS) was ～45 nm for both N95 FFR models and one of the two SM models, and ～350 nm for the other SM model at sealed condition with no leaks as well as with different leak sizes. TIL values increased with increasing leak sizes and breathing minute volumes. Relatively, higher efficiency N95 and SM models showed lower TIL values. Filter efficiency of FFRs and SMs influenced the TIL at different flow rates and leak sizes. Overall, the data indicate that good fitting higher-efficiency FFRs may offer higher protection against submicron-size bioaerosols.     

Total inward leakage of nanoparticles through filtering facepiece respirators

Nanoparticle (<100 nm size) exposure in workplaces is a major concern because of the potential impact on human health. National Institute for Occupational Safety and Health (NIOSH)-approved particulate respirators are recommended for protection against nanoparticles based on their filtration efficiency at sealed conditions. Concerns have been raised on the lack of information for face seal leakage of nanoparticles, compromising respiratory protection in workplaces. To address this issue, filter penetration and total inward leakage (TIL) through artificial leaks were measured for NIOSH-approved N95 and P100 and European certified Conformit'e Europe'en-marked FFP2 and FFP3 filtering facepiece respirator models sealed to a breathing manikin kept inside a closed chamber. Monodisperse sucrose aerosols (8-80 nm size) generated by electrospray or polydisperse NaCl aerosols (20-1000 nm size) produced by atomization were passed into the chamber. Filter penetration and TIL were measured at 20, 30, and 40 l min(-1) breathing flow rates. The most penetrating particle size (MPPS) was ～50 nm and filter penetrations for 50 and 100 nm size particles were markedly higher than the penetrations for 8 and 400 nm size particles. Filter penetrations increased with increasing flow rates. With artificially introduced leaks, the TIL values for all size particles increased with increasing leak sizes. With relatively smaller size leaks, the TIL measured for 50 nm size particles was ～2-fold higher than the values for 8 and 400 nm size particles indicating that the TIL for the most penetrating particles was higher than for smaller and larger size particles. The data indicate that higher concentration of nanoparticles could occur inside the breathing zone of respirators in workplaces where nanoparticles in the MPPS range are present, when leakage is minimal compared to filter penetration. The TIL/penetration ratios obtained for 400 nm size particles were larger than the ratios obtained for 50 nm size particles at the three different flow rates and leak sizes indicating that face seal leakage, not filter penetration, contributing to the TIL for larger size particles. Further studies on face seal leakage of nanoparticles for respirator users in workplaces are needed to better understand the respiratory protection against nanoparticle exposure.     

What does respirator certification tell us about filtration of ultrafine particles?

Recent interest in exposures to ultrafine particles (less than 100 nm) in both environmental and occupational settings led the authors to question whether the protocols used to certify respirator filters provide adequate attention to ultrafine aerosols. The authors reviewed the particle size distribution of challenge aerosols and evaluated the aerosol measurement method currently employed in the National Institute for Occupational Safety and Health (NIOSH) particulate respirator certification protocol for its ability to measure the contribution of ultrafine particles to filter penetration. Also considered were the differences between mechanical and electrically charged (electret) filters in light of the most penetrating particle size. It was found that the sodium chloride (NaCl) and dioctylphthalate (DOP) aerosols currently used in respirator certification tests contain a significant fraction of particles in the ultrafine region. However, the photometric method deployed in the certification test is not capable of adequately measuring light scatter of particles below approximately 100 nm in diameter. Specifically, 68% (by count) and 8% (by mass) of the challenge NaCl aerosol particles and 10% (by count) and 0.3% (by mass) of the DOP particles below 100 nm do not significantly contribute to the filter penetration measurement. In addition, the most penetrating particle size for electret filters likely occurs at 100 nm or less under test conditions similar to those used in filter certification. The authors conclude, therefore, that the existing NIOSH certification protocol may not represent a worst-case assessment for electret filters because it has limited ability to determine the contribution of ultrafine aerosols, which include the most penetrating particle size for electret filters. Possible strategies to assess ultrafine particle penetration in the certification protocol are discussed.     

Powered, air-purifying particulate respirator filter penetration by a DOP aerosol

In 1995, new certification requirements for all nonpowered, air-purifying particulate filter respirators were put in place when 42 CFR 84 replaced 30 CFR 11. However, the certification requirements for all other classes of respirators, including powered air-purifying respirators (PAPRs), were transferred to 42 CFR 84 from 30 CFR 11 without major changes. Since the inception of 42 CFR 84, researchers have learned that the efficiency of electrostatic filter media, in contrast with mechanical filter media, can be rapidly degraded by oil aerosols. Further, confusion may exist among respirator users, since electrostatic PAPR filters have the same magenta color assigned to high-efficiency filters for nonpowered particulate respirators that have been tested and certified for use against oil aerosols (i.e., P100 filters). Users may expect that the magenta color of certified PAPR filters indicates suitability for use against oil aerosols. This may not be the case. To illustrate the potential degradation of electrostatic PAPR filters, new filters certified under 42 CFR 84 were tested using a TSI model 8122 Automated Respirator Tester against charged and neutralized DOP aerosols with intermittent loading schedules. The performance of a magenta-colored electrostatic PAPR filter--one for which the manufacturer's user instructions appropriately indicates is not suitable for use in oily environments--was compared with the performance of several mechanical PAPR filters. In tests against both DOP aerosols, the electrostatic PAPR filter showed a significant decrease in performance at DOP loadings exceeding 400 mg, whereas mechanical filters showed no significant change in the performance except at extremely high loadings. The decreased performance of the electrostatic PAPR filter was found to be significantly greater when tested against a neutralized DOP aerosol when compared with a charged DOP aerosol. While laboratory tests show that the filtration efficiency of this electrostatic PAPR filter degrades with exposure to DOP aerosol, the observed laboratory degradation may or may not affect workplace performance, as similar degradation has not been verified in workplace studies. Based on these laboratory results, a proposed method for evaluating high-efficiency PAPR filters is presented. This proposed method would ensure that high-efficiency PAPR filters (> or = 99.97% efficient and magenta in color) meet critical performance criteria when loaded.     

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.