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.     

Size distribution of mist generated during metal machining

Mist generated by machining processes is formed by three mechanisms: impaction, centrifugal force, and evaporation/condensation. This study characterized the size distribution of soluble and mineral oil mists that resulted from these formation mechanisms. Salient parameters influencing the particle size distributions also were identified. Variables investigated included metalworking fluid and machining characteristics. The size distribution of the mist generated on a small lathe by each mechanism was measured using an Aerosizer LD. For impaction, only the mineral oil viscosity influenced the mass median diameter of the mist. No parameter affected the geometric standard deviation. High-viscosity mineral oil mist had a mass median diameter of 6.1 microns and a geometric standard deviation of 2.0. Low-viscosity mineral oil mist had a mass median diameter of 21.9 microns and a geometric standard deviation of 2.2. The mass median diameter of the mist generated by centrifugal force depended on the type of metalworking fluid, fluid flow, and rotational speed of the lathe. Mass median diameters for low-viscosity mineral oil mist ranged from 5 to 110 microns. Mass median diameters for soluble oil mist varied between 40 and 80 microns. The average geometric standard deviation was 2.4, and was not affected by any parameter. The mass median diameter and geometric standard deviation of the mist generated by evaporation/condensation varied with the type of metalworking fluid. The mineral oil mist and soluble oil mist mass median diameters were 2.1 microns and 3.2 microns, respectively. No machining or fluid parameter was important because the mist size distribution depended on the rate of condensation, coagulation processes, and the dynamics of the apparatus. Using the size distribution data from all three mechanisms, the estimated inhalable, thoracic, and respirable fractions of the total mass generated for each metalworking fluid were 60 percent, 12 percent, and 8 percent, respectively. To minimize exposure to the inhalable mass fraction, the amount of mist generated by centrifugal force must be reduced or the size of the drops generated must be increased. Altering the machining or fluid parameters did not change the mist size distribution and reduce exposure to the respirable mass fraction.     

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.     

Experiments supporting the use of ambient aerosols for quantitative respirator fit testing

Most methods for testing facial seal leakage on subjects undergoing respirator fit tests involve comparing the generated aerosol particulate concentration inside the subject's respirator to the concentration in a test chamber. These aerosols are produced by fogging substances such as corn oil, dioctyl sebacate, or dioctyl phthalate (DOP) into the test chamber. The health effects of these substances and of their aerosols on respiratory systems are uncertain. The proposed alternate method uses as a test medium ambient particles which exist in most room atmospheres. The proposed method eliminates the need for a test chamber and for an intentionally produced aerosol. The subject is tested for respirator inleakage by comparing the particulate count concentration inside the subject's respirator to that of the room atmosphere outside the respirator. This method is less expensive and simpler to administer than the use of oil or other deliberately produced aerosols because it uses an existing ambient test medium. Statistical analysis of the test data indicates favorable comparison with the conventional chamber-aerosol method.     

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.     

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.     

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 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.     

Evaluation of filter media for particle number, surface area and mass penetrations

The National Institute for Occupational Safety and Health (NIOSH) developed a standard for respirator certification under 42 CFR Part 84, using a TSI 8130 automated filter tester with photometers. A recent study showed that photometric detection methods may not be sensitive for measuring engineered nanoparticles. Present NIOSH standards for penetration measurement are mass-based; however, the threshold limit value/permissible exposure limit for an engineered nanoparticle worker exposure is not yet clear. There is lack of standardized filter test development for engineered nanoparticles, and development of a simple nanoparticle filter test is indicated. To better understand the filter performance against engineered nanoparticles and correlations among different tests, initial penetration levels of one fiberglass and two electret filter media were measured using a series of polydisperse and monodisperse aerosol test methods at two different laboratories (University of Minnesota Particle Technology Laboratory and 3M Company). Monodisperse aerosol penetrations were measured by a TSI 8160 using NaCl particles from 20 to 300 nm. Particle penetration curves and overall penetrations were measured by scanning mobility particle sizer (SMPS), condensation particle counter (CPC), nanoparticle surface area monitor (NSAM), and TSI 8130 at two face velocities and three layer thicknesses. Results showed that reproducible, comparable filtration data were achieved between two laboratories, with proper control of test conditions and calibration procedures. For particle penetration curves, the experimental results of monodisperse testing agreed well with polydisperse SMPS measurements. The most penetrating particle sizes (MPPSs) of electret and fiberglass filter media were ~50 and 160 nm, respectively. For overall penetrations, the CPC and NSAM results of polydisperse aerosols were close to the penetration at the corresponding median particle sizes. For each filter type, power-law correlations between the penetrations measured by different instruments show that the NIOSH TSI 8130 test may be used to predict penetrations at the MPPS as well as the CPC and NSAM results with polydisperse aerosols. It is recommended to use dry air (<20% RH) as makeup air in the test system to prevent sodium chloride particle deliquescing and minimizing the challenge particle dielectric constant and to use an adequate neutralizer to fully neutralize the polydisperse challenge aerosol. For a simple nanoparticle penetration test, it is recommended to use a polydisperse aerosol challenge with a geometric mean of ~50 nm with the CPC or the NSAM as detectors.     

Uncertainties in aerosol deposition within the respiratory tract using the icrp 66 model: a study in workers

This study estimates uncertainties in aerosol deposition within the main regions of the human respiratory tract calculated using the ICRP 66 model. Uniform, triangular, normal, or lognormal distributions were assigned to the model parameters, which involve physical properties of aerosols, their inhalability, their thermo- and aerodynamic deposition efficiencies, and the anatomy, physiology, and exertion level of the individuals. Calculations were performed over a range of aerosol sizes from 0.01 to 50 mum. Monodispersed aerosols were characterized by their aerodynamic diameter (dae). Polydispersed aerosols were characterized by their activity median aerodynamic diameters (AMADs) and the geometric standard deviation (GSD) in diameter. Lognormal distributions of particle deposition were generally observed with low GSD (< 2). The highest uncertainties were observed within the deep lung for the smallest and the largest aerosol sizes, which were mainly due either to particle density or to aerodynamic deposition efficiencies and anatomical and physiological variability, respectively. In the case of diameters larger than 5 mum, uncertainties in the deep lung deposition were much more important for monodispersed than for polydispersed aerosols. This was explained both by the size distribution of the deposited aerosol, the median of which corresponded to a maximal dae value of about 7 and 5 in bronchioles and alveoli, respectively, and by the absence of deposition, which occurs for dae equal to or larger than 50 mum, depending on the exertion level. Thus, in the range of AMADs considered, for the four default workers proposed by ICRP 66, uncertainties in aerosol deposition remain low, with GSD smaller than 3.     

Analysis of sampling line bias on respirable mass measurement

This study investigated the bias introduced by an inlet sampling line on a respirable mass monitor. The 1.5-m electrically conductive, flexible sampling line conducts aerosol at a flow rate of 2.2 Lpm from a helmet-mounted inlet to a waist-mounted sensor for mass concentration measurement. Particulate transport was modeled for each section of the sampling line and considered the effects of diffusion, gravitational settling, and inertial impaction. An estimate of respirable mass concentration measured with the sampling line was determined by integrating assumed workplace aerosols with the transport curves. The bias introduced by the sampling line was then calculated by dividing the difference between the respirable mass concentration with and without the sampling line by that without the sampling line. For the current sampling line, in which the inner diameter is 4.83 mm, bias was calculated as -0.3 percent, -2.4 percent, -4.6 percent, and -6.7 percent for four test aerosols with mass median aerodynamic diameters of 0.6 microm, 4 microm, 12 microm, and 30 microm, respectively. Optimization studies suggest that increasing the sampling line with a larger inner diameter by a factor of 1.25 to 1.75 will minimize bias to below -3.0 percent. An experimental study confirmed that bias due to the presence of the sampling line is small.     

Aerosol penetration through respirator exhalation valves

Exhalation valves are a critical component of industrial respirators. They are designed to permit minimal inward leakage of air contaminants during inhalation and provide low resistance during exhalation. Under normal conditions, penetration of aerosol through exhalation valves is minimal. The exhalation valve is, however, a vulnerable component of a respirator and under actual working conditions may become dirty or damaged to the point of causing significant leakage. Aerosol penetration was measured for normal exhalation valves and valves compromised by paint or fine copper wires on the valve seat. Penetration increased with increasing wire diameter. A wire 250 microns in diameter allowed greater than 1% penetration into the mask cavity. Dirt or paint accumulated on the exhalation valve allowed a similar level of penetration. Work rate had little effect on observed penetration. Penetration decreased significantly with increasing aerosol particle size. The amount of material on the valve or valve seat necessary for significant (greater than 0.5%) inward leakage in a half-mask respirator could be readily observed by careful inspection of the exhalation valve and its seat in good lighting conditions.     

Aerodynamic size associations of 212Pb and 214Pb in ambient aerosols

The aerodynamic size distributions of short-lived Rn daughters (reported as 214Pb and 212Pb) in ambient aerosol particles were measured using low-pressure as well as conventional low-volume and high-volume impactors. The activity distribution of 214Pb and 212Pb, measured by alpha spectroscopy, was largely associated with submicron aerosols in the accumulation mode (0.08 to 2 microns). The activity median aerodynamic diameter ranged from 0.09 to 0.37 micron (mean 0.16 micron) for 214Pb and from 0.07 to 0.25 micron (mean 0.13 micron) for 212Pb. The mean values of the geometric standard deviation (sigma g) were 2.97 and 2.86, respectively. By comparison, the median diameters of cosmogenic 7Be and ambient SO4(2-) were about 0.24 micron higher. In almost 70% of the low-pressure impactor measurements, the activity distribution of 214Pb showed a small shift to larger particle sizes relative to 212Pb. This shift probably results from alpha-recoil detachment of parent 218Po, which preferentially depletes 214Pb from smaller particles. The subsequent recondensation of 214Pb causes an enrichment of larger aerosols. Early morning and afternoon measurements indicated that similar size associations of 214Pb occur, despite humidity differences and the potential for fresh particle production in the afternoon. Health physics implications of the results are also discussed.     

Characterization of particulate matter in carbon-graphite/epoxy advanced composite material smoke

The physical and chemical properties of the particulate fraction of carbon-graphite/epoxy advanced composite material (cgeACM) smoke were measured to address concerns regarding potential health hazards posed by the release of fibers during pyrolysis of this material. Filter, low-pressure cascade impactor, and electrostatic precipitator samples were collected from cgeACM smoke in which the aerosol concentration ranged from 0.20 to 5.39 g/m3. Fibers were found in the smoke among individual, spherical, or nearly spherical particles and chain aggregates. The fibers had a mean count diameter of 0.54 micron and an average length of 2.84 microns. However, fibers accounted for approximately 0.3% of the particles counted. The smoke aerosols (including fibers) had mass median aerodynamic diameters (MMAD) ranging from 1.4 to 1.9 microns with standard geometric deviations ranging from 1.6 to 1.8, and hence more than 88% of the particles were in the thoracic size range (MMAD < or = 4.0 microns). All particles were composed primarily of carbon, silicon, sulfur, and oxygen with traces of other metals. By comparison fibers were composed almost exclusively of silicon.     

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.     

Filter performance of n99 and n95 facepiece respirators against viruses and ultrafine particles

The performance of three filtering facepiece respirators (two models of N99 and one N95) challenged with an inert aerosol (NaCl) and three virus aerosols (enterobacteriophages MS2 and T4 and Bacillus subtilis phage)-all with significant ultrafine components-was examined using a manikin-based protocol with respirators sealed on manikins. Three inhalation flow rates, 30, 85, and 150 l min(-1), were tested. The filter penetration and the quality factor were determined. Between-respirator and within-respirator comparisons of penetration values were performed. At the most penetrating particle size (MPPS), >3% of MS2 virions penetrated through filters of both N99 models at an inhalation flow rate of 85 l min(-1). Inhalation airflow had a significant effect upon particle penetration through the tested respirator filters. The filter quality factor was found suitable for making relative performance comparisons. The MPPS for challenge aerosols was <0.1 mum in electrical mobility diameter for all tested respirators. Mean particle penetration (by count) was significantly increased when the size fraction of <0.1 mum was included as compared to particles >0.1 mum. The filtration performance of the N95 respirator approached that of the two models of N99 over the range of particle sizes tested ( approximately 0.02 to 0.5 mum). Filter penetration of the tested biological aerosols did not exceed that of inert NaCl aerosol. The results suggest that inert NaCl aerosols may generally be appropriate for modeling filter penetration of similarly sized virions.     

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.     

Nose-only exposure system for inhalation exposures of rodents to large particles

A large-particle exposure system for small animals was designed, constructed and evaluated. The system was designed by incorporating a fluidized bed aerosol generator (FBG) and a nose-only exposure device to accommodate 40 small animals into a single unit. The system has four levels of exposure ports, each level having ten exposure ports radially positioned around the aerosol delivery components of the system. The aerosol generator produces aerosols that travel to the top of the system then downwards in order to be drawn past each animal's nose via vacuum ports immediately above the exposure ports. Nearly monodisperse polystyrene latex aerosols with nominal sizes of 3.0, 9.0 and 15.0 micron were generated as dry powders in an FBG with an inside diameter of 5 cm. During 60-min test runs, average aerosol mass concentrations up to 37 mg/m3 were achieved with less than 10% variation in mass concentration distribution throughout the unit.     

Comparison of five methods for fit-testing N95 filtering-facepiece respirators

Five fit-testing methods (Bitrex, ambient aerosol condensation nuclei counter using the TSI PortaCount Plus, saccharin, modified ambient aerosol condensation nuclei counter using the TSI PortaCount Plus with the N95-Companion, and generated aerosol using corn oil) were evaluated for their ability to identify poorly fitting N95 filtering-facepiece respirators. Eighteen models of NIOSH-certified, N95 filtering-facepiece respirators were tested by a panel of 25 subjects using each fit-testing method. The penetration of the corn oil and the ambient aerosols through the filter media of each respirator was measured in order to adjust the corresponding generated and ambient aerosol overall fit factors, reflecting only face-seal leakage. Fit-testing results were compared to 5th percentiles of simulated workplace protection factors. Beta errors (the chance of passing a fit-test in error) ranged from 3 percent to 11 percent. Alpha errors (the chance of failing a fit-test in error) ranged from 51 percent to 84 percent. The ambient aerosol using the TSI PortaCount Plus and the generated aerosol methods identified poorly fitting respirators better than the saccharin, the Companion, and Bitrex methods. These errors rates should be considered when selecting a fit-testing method for fitting N95 filtering-facepieces. When both types of errors were combined as an assignment error, the ambient aerosol method using the TSI PortaCount Plus had the lowest percentage of wearers being assigned a poor-fitting respirator.     

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.