Documentation of a dustiness drum test

A rotating drum dustiness test is described and the results with this device run at standardized conditions from 1989 to 1994 are presented. The measured dustiness indices covered a range of about a factor 2000. The test was good at ranking different materials. Influences of the test conditions on the drum method were studied in a 2⁴ factorial design using super ground alumina with small particles and a narrow size distribution. The variables mass, flow, rotation speed and sampling time were run at base and high level and the air humidity was kept fixed at 50% RH. An analysis of variance showed a correlation between these different variables with a particularly strong interaction between the mass and the rotation speed. Time resolved dust measurements showed the importance of being able to monitor the dust release during time. For some test conditions a continuous dust release was found, while most tests showed primarily an initial dust release.     

A novel device for measuring respirable dustiness using low-mass powder samples

Respirable dustiness represents the tendency of a powder to generate respirable airborne dust during handling and therefore indicates the propensity for a powder to become an inhalation hazard. The dustiness of 14 powders, including 10 different nanopowders, was evaluated with the use of a novel low-mass dustiness tester designed to minimize the use of the test powder. The aerosol created from 15-mg powder samples falling down a tube were measured with an aerodynamic particle sizer (APS). Particle counts integrated throughout the pulse of aerosol created by the falling powder were used to calculate a respirable dustiness mass fraction (D, mg/kg). An amorphous silicon dioxide nanopowder produced a respirable D of 121.4 mg/kg, which was significantly higher than all other powders (p < 0.001). Many nanopowders produced D values that were not significantly different from large-particle powders, such as Arizona Road Dust and bentonite clay. In general, fibrous nanopowders and powders with primary particles >100 nm are not as dusty as those containing granular, nano-sized primary particles. The method used here, incorporating an APS, represents a deviation from a standard method but resulted in dustiness values comparable to other standard methods.     

Evaluation of nano- and submicron particle penetration through ten nonwoven fabrics using a wind-driven approach

Existing face mask and respirator test methods draw particles through materials under vacuum to measure particle penetration. However, these filtration-based methods may not simulate conditions under which protective clothing operates in the workplace, where airborne particles are primarily driven by wind and other factors instead of being limited to a downstream vacuum. This study was focused on the design and characterization of a method simulating typical wind-driven conditions for evaluating the performance of materials used in the construction of protective clothing. Ten nonwoven fabrics were selected, and physical properties including fiber diameter, fabric thickness, air permeability, porosity, pore volume, and pore size were determined. Each fabric was sealed flat across the wide opening of a cone-shaped penetration cell that was then housed in a recirculation aerosol wind tunnel. The flow rate naturally driven by wind through the fabric was measured, and the sampling flow rate of the Scanning Mobility Particle Sizer used to measure the downstream particle size distribution and concentrations was then adjusted to minimize filtration effects. Particle penetration levels were measured under different face velocities by the wind-driven method and compared with a filtration-based method using the TSI 3160 automated filter tester. The experimental results show that particle penetration increased with increasing face velocity, and penetration also increased with increasing particle size up to about 300 to 500 nm. Penetrations measured by the wind-driven method were lower than those obtained with the filtration method for most of the fabrics selected, and the relative penetration performances of the fabrics were very different due to the vastly different pore structures.     

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.     

Biodistribution of ultrafine particles of titanium dioxide by intratracheal administration to mice

TiO2 ultrafine particles are used as photo-catalysis. When ultrafine particles are exposed to hosts, they are invaded in alveolar, transferred to organs through blood vessels and may express biological effects. We administered TiO2 ultra-fine particles (5 nm, 100 nm) intratracheally to mice, and collected whole blood and removed organs (liver, lung, kidney, spleen and brain) after 1, 4 and 24 hours. The quantity of Ti in the blood and these organs was analyzed by PIXE (Particle Induced X-Ray Emission) or ICP/MS (Inductively Coupled Plasma-Mass Spectrometry). Compared to control mice, the quantity of Ti in the exposed mice was not different. Consequently, we observed the solution of dissolved TiO2 ultrafine particles by Scanning Electron Microscope, and observed the particles which aggregated. That diameter was about 1 microm. We concluded that the particles had aggregated before administration to mice, so they didn't invade the blood vessels or organs from the pulmonary alveolus in the lung.     

Physical properties and lung deposition of particles emitted from five major indoor sources

The physical properties of indoor particles were measured with an Scanning Mobility Particle Sizer (SMPS) system (14.6–850 nm), an Aerodynamic Particle Sizer (APS, 0.54–18 μm) and an Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) in an apartment located in an urban background site in Prague (Czech Republic) from 15 August to 8 September, 2014. The total particle maximum number concentration was 9.38?×?10⁴, 1.46?×?10⁵, 2.89?×?10⁴, 2.25?×?10⁵ and 1.57?×?10⁶ particles cm^?3 for particles released from vacuum cleaning, soap/W5 cleaning spray, smoking, incense burning and cooking (frying) activities, respectively. Particles emitted from cleaning activities showed unimodal number size distributions, with the majority of particles (>98.2 %) in the ultrafine size range (Dp <100 nm) and modes at a diameter of 19.8 nm for vacuum cleaning and 30.6 nm for soap/W5 cleaning. Smoking and incense burning predominantly generated particles in the accumulation mode with a count median diameter around 90–150 nm while cooking emissions showed a bimodal structure with a main mode at 47.8 nm. Particles from vacuum cleaning, incense burning, smoking and cooking emissions were found to be “nearly hydrophobic” with an average growth factor (G_f) around 1.01–1.10, while particles emitted from desk cleaning using organic compounds were found to be “less-hygroscopic” (G_f ～1.12–1.16). Based on an adjusted MPPD model with a consideration of the hygroscopic properties of particles, the total lung deposition fractions of these particles by number when they penetrate into the human lung were 0.73?±?0.02, 0.62?±?0.03, 0.37?±?0.03, 0.32?±?0.03 and 0.49?±?0.02 for vacuum cleaning, desk cleaning, smoking, incense burning and cooking, respectively.     

Factors affecting the Heubach and MRI dustiness tests

The effect of test parameters upon material dustiness measured by the Heubach dust measurement appliance and the MRI dustiness tester was studied. The users of these tests can alter test parameters such as flow rate, sampling time, mass of material tested, bulk density, and vibrator setting. The effect of these parameters upon the aerosol produced in the dustiness tester was experimentally studied. All of the parameters affected in a complicated manner, the amount of dust and the size distribution of the dust generated during these tests. Therefore, dustiness test results should not be adjusted for variations in test parameters. The users of dustiness tests need to carefully control dustiness test parameters in order to have reproducible dustiness tests.     

Determining the dustiness of powders--a comparison of three measuring devices

The dustiness of 12 test powders was determined using three different measuring methods. One of the methods, the continuous drop method, is a reference test method according to the EN 15051 'Workplace atmospheres--Measurement of the dustiness of bulk materials--Requirements and reference test methods'. A test of equivalence between the reference test method and the other two methods, the modified Heubach Dustmeter, a rotating drum method and the Palas Dustview, a single-drop method, has been carried out as provided in Annex D of the European standard. No equivalence was found between any of the test methods. An applied best-case scenario yielded a slightly better outcome, but the results lead to the conclusion that it is impossible to generate viable values using the test of equivalence provided in the standard. This outcome was expected and is due to the different handling procedures applied-which, however, relates to the reality of the variety of material-handling procedures in the workplace.     

Daily mortality and particulate matter in different size classes in Erfurt, Germany

The link between elevated concentrations of ambient particulate matter (PM) and increased mortality has been investigated in numerous studies. Here we analyzed the role of different particle size fractions with respect to total and cardio-respiratory mortality in Erfurt, Germany, between 1995 and 2001. Number concentrations (NC) of PM were measured using an aerosol spectrometer consisting of a Differential Mobility Particle Sizer and a Laser Aerosol Spectrometer to characterize particles between 0.01 and 0.5 and between 0.1 and 2.5 microm, respectively. We derived daily means of particle NC for ultrafine (0.01-0.1 microm) and for fine particles (0.01-2.5 microm). Assuming spherical particles of a constant density, we estimated the mass concentrations (MC) of particles in these size ranges. Concurrently, data on daily total and cardio-respiratory death counts were obtained from local health authorities. The data were analyzed using Poisson Generalized Additive Models adjusting for trend, seasonality, influenza epidemics, day of the week, and meteorology using smooth functions or indicator variables. We found statistically significant associations between elevated ultrafine particle (UFP; diameter: 0.01-0.1 microm) NC and total as well as cardio-respiratory mortality, each with a 4 days lag. The relative mortality risk (RR) for a 9748 cm(-3) increase in UFP NC was RR=1.029 and its 95% confidence interval (CI)=1.003-1.055 for total mortality. For cardio-respiratory mortality we found: RR=1.031, 95% CI: 1.003-1.060. No association between fine particle MC and mortality was found. This study shows that UFP, representing fresh combustion particles, may be an important component of urban air pollution associated with health effects.     

Real-time monitoring of particles, PAH, and CO in an occupied townhouse

Beginning in October 1996, indoor and sometimes outdoor air at an occupied house in a suburban area of Virginia has been monitored continuously for particles, PAH, and CO. Two Climet monitors have been used to count particles in six size ranges between 0.3 and > 10 microns, with 1-minute averages being collected every 5 minutes. Two Ecochem PAH monitors have been used to sample for particle-bound PAHs once every minute. Also, two Langan CO monitor-data loggers have measured CO once each minute while logging the PAH data. Two Aethalometers measure black carbon. A single Scanning Mobility Particle Sizer (SMPS) measures ultrafine particles. The pairs of monitors are set up either to provide an indoor/outdoor or an upstairs office/downstairs kitchen comparison. Air exchange is occasionally measured using a Bruel & Kjaer 1302 SF6 monitor, as a parameter necessary for estimating deposition rates for particles and PAH. Results from the first 16 months of monitoring (approximately 10 M observations) include: neighborhood woodburning and morning rush hour traffic are the most important sources of PAH and black carbon outdoors; candles, matches, incense, and frying, sauteeing, broiling, deep-frying, and stir-frying are additional important indoor sources of PM. One citronella candle was an extremely powerful PAH source. Neither woodburning nor vehicles appears to be an important source of particles indoors, but frying, grilling, and sauteeing are extremely strong indoor sources, together with combustion events such as use of matches and candles. Physical movement was an important source of coarse but not fine particles. Use of the gas stove for extended periods of time led to increased CO concentrations--vehicles and woodburning were relatively minor sources in comparison. The gas oven, gas burners, and electric toaster oven were important sources of ultrafine particles (< 0.1 micron). A source-proximity effect was noted with the kitchen monitor reading two to five times higher than the upstairs monitor for particles from kitchen events, while the upstairs monitor often read higher than the kitchen monitor for events caused by physical activity alone.     

Characterization of particle exposure in ferrochromium and stainless steel production

This study describes workers’ exposure to fine and ultrafine particles in the production chain of ferrochromium and stainless steel during sintering, ferrochromium smelting, stainless steel melting, and hot and cold rolling operations. Workers’ personal exposure to inhalable dust was assessed using IOM sampler with a cellulose acetate filter (AAWP, diameter 25 mm; Millipore, Bedford, MA). Filter sampling methods were used to measure particle mass concentrations in fixed locations. Particle number concentrations and size distributions were examined using an SMPS+C sequential mobile particle sizer and counter (series 5.400, Grimm Aerosol Technik, Ainring, Germany), and a hand-held condensation particle counter (CPC, model 3007, TSI Incorporated, MN). The structure and elemental composition of particles were analyzed using TEM-EDXA (TEM: JEM-1220, JEOL, Tokyo, Japan; EDXA: Noran System Six, Thermo Fisher Scientific Inc., Madison,WI).

Workers’ personal exposure to inhalable dust averaged 1.87, 1.40, 2.34, 0.30, and 0.17 mg m^?3 in sintering plant, ferrochromium smelter, stainless steel melting shop, hot rolling mill, and the cold rolling mill, respectively. Particle number concentrations measured using SMPS+C varied from 58 × 10³ to 662 × 10³ cm^?3 in the production areas, whereas concentrations measured using SMPS+C and CPC3007 in control rooms ranged from 24 × 10³ to 243 × 10³ cm^?3 and 5.1 × 10³ to 97 × 10³ cm^?3, respectively. The elemental composition and the structure of particles in different production phases varied. In the cold-rolling mill non-process particles were abundant. In other sites, chromium and iron originating from ore and recycled steel scrap were the most common elements in the particles studied.

Particle mass concentrations were at the same level as that reported earlier. However, particle number measurements showed a high amount of ultrafine particles, especially in sintering, alloy smelting and melting, and tapping operations. Particle number concentration and size distribution measurements provide important information regarding exposure to ultrafine particles, which cannot be seen in particle mass measurements.     

The surface area rather than the surface coating determines the acute inflammatory response after instillation of fine and ultrafine TiO2 in the rat

Alterations in the hydrophobic status of particle surfaces have been suggested to modify the toxic properties of ultrafine TiO2. We investigated the acute inflammatory responses and cell damage after intratracheal instillation of surface modified (hydrophilic and hydrophobic) fine (180 nm) and ultrafine (20-30 nm) TiO2 particles 16 h at equivalent mass (1 or 6 mg) and surface doses (100, 500, 600 and 3000 cm2) in rats. Inflammatory response and most enzyme levels were significantly related to the administered surface dose. The hydrophobic surface of the TiO2 particles, achieved by methylation, induced a lower total cell number and influx of neutrophils (PMN) compared to rats instilled with the 1 mg of the untreated, fine or ultrafine TiO2 but the outcomes were not statistically significant. No differences were observed between fine/ultrafine and hydophilic/hydrophobic TiO2 at the high dose (6 mg) or surface dose over 600 cm2. The differences in BAL cellularity at the low dose were reflected in changes in the chemokine MIP-2, but no differences were seen in levels of macrophage cytokines. Considering the large influx of PMN little cell damage was seen when studying enzyme leakage in lavage fluid, although PMNs appeared to be activated as suggested by increased myeloperoxidase (MPO) activity in the lavage fluid. We conclude that the surface area rather than the hydrophobic surface determines the acute, pulmonary inflammation induced by both fine and ultrafine TiO2.     

Assessing potential nanoparticle release during nanocomposite shredding using direct-reading instruments

This study was conducted to determine if engineered nanoparticles are released into the air when nanocomposite parts are shredded for recycling. Test plaques made from polypropylene resin reinforced with either montmorillonite nanoclay or talc and from the same resin with no reinforcing material were shredded by a granulator inside a test apparatus. As the plaques were shredded, an ultrafine condensation particle counter; a diffusion charger; a photometer; an electrical mobility analyzer; and an optical particle counter measured number, lung-deposited surface area, and mass concentrations and size distributions by number in real-time. Overall, the particle levels produced were both stable and lower than found in some occupational environments. Although the lowest particle concentrations were observed when the talc-filled plaques were shredded, fewer nanoparticles were generated from the nanocomposite plaques than when the plain resin plaques were shredded. For example, the average particle number concentrations measured using the ultrafine condensation particle counter were 1300 particles/cm(3) for the talc-reinforced resin, 4280 particles/cm(3) for the nanoclay-reinforced resin, and 12,600 particles/cm(3) for the plain resin. Similarly, the average alveolar-deposited particle surface area concentrations measured using the diffusion charger were 4.0 μm(2)/cm(3) for the talc-reinforced resin, 8.5 μm(2)/cm(3) for the nanoclay-reinforced resin, and 26 μm(2)/cm(3) for the plain resin. For all three materials, count median diameters were near 10 nm during tests, which is smaller than should be found from the reinforcing materials. These findings suggest that recycling of nanoclay-reinforced plastics does not have a strong potential to generate more airborne nanoparticles than recycling of conventional plastics.     

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.     

Experimental examination of factors that affect dust generation by using Heubach and MRI testers.

Four factors that affect dust generation were investigated--type of test material, particle size distribution of the test material, moisture content of the test material, and apparatus used to generate dust. Dust generated from silicon carbide and aluminum oxide was measured by using MRI and Heubach dustiness testers modified to allow the measurement of dust particle size distribution with an Andersen impactor. The two materials investigated generated similar dusts. The size distribution of the test material slightly influenced the amount but strongly influenced the size distribution of the dust generated. Increased moisture content decreased the amount of dust generated; moisture content had little influence on dust size distribution. The two testers generated different amounts of dust; however, the dust particle size distributions generated were similar. These results help explain factors that affect dust generation and the relative importance of alternative methods for dust control.     

Biological effects and toxicity assessment of titanium dioxides: anatase and rutile

Anatase and rutile are titanium dioxides (TiO2) with different crystal lattices. The particles of TiO2 are considered a "nuisance" dust. It has been reported that rutile can be considered "inert". However, anatase, because of its hemolytic activity in vitro and slow lung clearance, should warrant further research regarding its toxicity. We exposed rats to an aerosol of either anatase or rutile and determined the TiO2 retention in the lung up to 132 days post exposure. Particle clearance from the lung, calculated from the retention data, was similar in both the anatase and the rutile groups with T1/2 of 51 or 53 days, respectively. In addition a pulmonary cell response test was performed on other rats. After intratracheal instillation of anatase and rutile in doses of 0.5 or 5.0 mg/rat, lung lavage was performed and the harvested cells counted. The counts of all cells, alveolar macrophages (AM), peroxidase positive AM, and polymorphonuclear leukocytes were compared. The pulmonary cell response test also yielded similar results for both types of TiO2. Thus there was no indication that the crystal lattices of TiO2 altered the biological effects of TiO2 particles. The evidence suggests that both anatase and rutile are "nuisance" dusts.     

Dust inhalation exposures from the handling of small volumes of powders

Worker exposure to airborne particulates was stimulated in a laboratory under controlled conditions. Small volumes, 3.8 L (1 gal.), of finely divided powders were transferred at 1-min intervals to 23-L (6-gal.) containers over 30-min time intervals. A high-volume filter array in the exit vent of the specially designed exposure laboratory was used both to control the ventilation rate and to determine the emission factor of the pouring operation. The room ventilation rate, method of transfer, and drop height were varied, and the resulting particulate concentrations were monitored by personal and area samplers. The four powders studied were talc, sodium chloride, Portland cement, and Direct Yellow 4 dye. Based on this study, a model was developed to predict potential worker exposure from the pouring of small volumes of powders. The model is based on the following major conclusions. First, the space- and time-averaged concentration of suspended particulate matter at breathing height agrees well with the mean concentration of suspended particulate matter in the room air effluent. Second, material-specific suspended particulate emission factors vary approximately in direct proportion to the drop height. Third, emission factors for scooping/dumping operations agree well with factors for pouring operations for a given drop height. Fourth, emission factors compare well with dustiness indexes that were determined using a bench-scale dustiness test chamber described in a companion paper. Parameters of the exposure model include dustiness index, drop height of the pouring operation, total quantity of material poured, averaging time, and the fraction of respirable material. For the validation of the model, additional data would be necessary.     

An investigation of dust generation by free falling powders.

To identify the dust generation processes, aluminum oxide powder was dropped as a free falling slug in a test chamber. The effect of the slug's mass, diameter, and drop height upon the aerosol concentration and size distribution was measured with an aerodynamic particle sizer. To differentiate between aerosol generated during the free fall and at the end of the fall, the slug was dropped either onto a flat surface or into a container of water that suppressed dust generation associated with the impact at the end of the fall. Aerosol generation occurred during the slug's free fall as well as at the end of the fall. The falling solid induced an airflow that followed the falling solid to the end of the fall. This induced airflow contained the aerosol generated during the free fall. At the end of the free fall, the induced airflow, combined with air jets created on impact, dispersed the aerosol throughout the test chamber. Additional measurements were made by using "neutral buoyancy" helium-filled bubbles to visualize the airflow in the test chamber. The airflow and ensuing turbulence were sufficient to keep large, inspirable particles suspended throughout the test chamber for periods greater than 10 min. During experimental work, the effect of drop height, mass, and slug diameter upon aerosol generation by a single slug of powder was studied. The results indicated that the manner in which a powder is handled may be as important as material dustiness as measured by a dustiness tester. Aerosol generation can be reduced by minimizing the contact between the falling powder and the air.     

Does lung surfactant promote disaggregation of nanostructured titanium dioxide?

OBJECTIVE: Nanostructured titanium dioxide (TiO2) is highly aggregated and agglomerated when inhaled. There are discussions regarding whether lung surfactant may promote the disaggregation of TiO2 particles. We investigated whether dipalmitoyl phosphatidyl-choline (DPPC), the main component of lung surfactant, can split the bonds between TiO2 aggregates and agglomerates. METHODS: We calculated the energy required to split aggregates into primary particles and agglomerates into aggregates as well the energy of the interaction of a TiO2 surface with a DPPC bilayer. To test the calculations, we measured the particle size distribution of TiO2 suspensions in a pulmonary liquid model. RESULTS: Calculated splitting energy between TiO2 aggregates was 1 J/m2 and 10 J/m2 between primary particles. The calculated interaction between DPPC and TiO2 was significantly weaker (0.05 J/m2). Calculations were shown to be in accordance with the measured particle size distribution of TiO2 suspensions in the pulmonary liquid model. CONCLUSION: We conclude that lung surfactant does not promote the disaggregation of TiO2 agglomerates and aggregates.     

Evaluation of the performance of the N95-companion: effects of filter penetration and comparison with other aerosol instruments

Fit factor is the ratio of the particle concentration outside (C(out)) to the inside (C(in)) of the respirator and assumes that filter penetration is negligible. For Class-95 respirators, concerns were raised that filter penetration could bias fit test measurements. The TSI N95-Companion was designed to overcome this limitation by measuring only 40-60 nm size particles. Recent research has shown that particles in this size range are the most penetrating for respirators containing electrostic filter media. The goal of this study was to better understand the performance of the N95-Companion by assessing the impact of filter penetration and by comparing C(out)/C(in) ratios measured by other aerosol instruments (nano-Differential Mobility Analyzer/Ultrafine Condensation Particle Counter (nano-DMA/UCPC) and the TSI PortaCount Plus) using N95 filtering facepiece respirators sealed to a manikin and with intentionally created leaks. Results confirmed that 40-60 nm-diameter size room air particles were most penetrating for the respirators tested. A nonlinear relationship was found between the N95-Companion-measured C(out)/C(in) ratios and the other instruments at the sealed condition and at the small leak sizes because the N95-Companion measures only charged particles that are preferentially captured by the electrostic filter media, while the other instrument configurations also measure uncharged particles, which are captured less efficiently. The C(out)/C(in) ratios from the N95-Companion for experiments conducted under sealed condition suggest that filter penetration of negatively charged 40-60 nm size particles was less than 0.05%. Thus, the N95-Companion measured C(out)/C(in) ratios are due primarily to particle penetration through leakage, not through filter media, while the C(out)/C(in) ratios for the PortaCount, nano-DMA/UCPC, and UCPC result from a combination of face seal leakage and filter penetration.