Fit evaluation of NIOSH approved N95 filtering facepiece respirators with various skin protectants: A pilot study.

Widespread disease outbreaks can result in prolonged wear times of National Institute for Occupational Safety and Health Approved N95 filtering facepiece respirators by healthcare personnel. Prolonged wear times of these devices can cause the development of various adverse facial skin conditions. Healthcare personnel have been reported to apply "skin protectants" to the face to reduce the pressure and friction of respirators. Because tight-fitting respirators rely on a good face seal to protect the wearer, it is important to understand if the fit is affected when skin protectants are used. This laboratory pilot study included 10 volunteers who performed quantitative fit tests to evaluate respirator fit while wearing skin protectants. Three N95 filtering facepiece respirator models and three skin protectants were evaluated. Three replicate fit tests were performed for each combination of subject, skin protectant (including a control condition of no protectant), and respirator model. Fit Factor (FF) was affected differently by the combination of the protectant type and respirator model. The main effects of the protectant type and respirator model were both significant (p < 0.001); additionally, their interaction was significant (p = 0.02), indicating FF is affected by the combined effects of the protectant type and respirator model. Compared to the control condition, using a bandage-type or surgical tape skin protectant decreased the odds of passing the fit test. Using a barrier cream skin protectant also decreased the odds of passing the fit test across all models compared to the control condition; however, the probability of passing a fit test was not statistically significantly different from the control condition (p = 0.174). These results imply that all three skin protectants reduced mean fit factors for all N95 filtering facepiece respirator models tested. The bandage-type and surgical tape skin protectants both reduced fit factors and passing rates to a greater degree than the barrier cream. Respirator users should follow respirator manufacturers' guidance on the use of skin protectants. If a skin protectant is to be worn with a tight-fitting respirator, the fit of the respirator should be evaluated with the skin protectant applied before use in the workplace.

Assessing the Fit of N95 Filtering Facepiece Respirators Fitted with an Ear Loop Strap System: A Pilot Study.

Throughout the COVID-19 pandemic, hundreds of millions of people worldwide have become new users of respiratory protective devices. Facemasks and KN95 respirators utilizing an ear loop straps system (ELSS) have recently become popular among occupational and non-occupational populations. Part of this popularity is due to the ease of wearability as compared with traditional devices utilizing two headbands, one worn over the head and the other behind the neck-a universal strap system used in NIOSH-certified N95 filtering facepiece respirators (FFRs). Some users convert the two-strap configuration to an adjustable ELSS. The first objective of this pilot study was to quantitatively characterize how such a conversion impacts the respirator fit. Additionally, a novel faceseal (NFS) technology, which has been previously demonstrated to enhance the fit of N95 FFRs, was deployed to modify the ELSS-converted N95 FFRs. The second objective of this study was to quantify the fit improvement that results from adding the NFS to the ELSS. The study was conducted by performing the Occupational Safety and Health Administration (OSHA)-approved quantitative fit testing (QNFT) on 16 human subjects featuring different facial shapes and dimensions. Three models of cup-shaped N95 FFRs were tested in three versions: the standard version with manufacturer's strap system, the ELSS-converted, and the ELSS-converted version modified by adding the NFS. QNFT demonstrated that the fit of an N95 FFR featuring the traditional/standard headbands strap system is negatively impacted when this system is converted to an ELSS. The fit of an ELSS-converted respirator can be significantly improved by the addition of the NFS. We found that the FFR model and the strap system version are significant factors affecting the QNFT-determined respirator fit factor (FF), as well as the OSHA QNFT pass rate (FF ≥100). The findings suggest that the current NFS, if further improved, has a potential for developing a 'universally fitting' ELSS-equipped N95 FFR that can be used by the general public, the vast majority of whom do not have access to OSHA fit requirements.

Technical note: Impact of face covering on aerosol transport patterns during coughing and sneezing.

COVID-19 is spread via different routes, including virus-laden airborne particles generated by human respiratory activities. In addition to large droplets, coughing and sneezing produce a lot of small aerosol particles. While face coverings are believed to reduce the aerosol transmission, information about their outward effectiveness is limited. Here, we determined the aerosol concentration patterns around a coughing and sneezing manikin and established spatial zones representing specific elevations of the aerosol concentration relative to the background. Real-time measurements of sub-micrometer aerosol particles were performed in the vicinity of the manikin. The tests were carried out without any face covering and with three different types of face covers: a safety faceshield, low-efficiency facemask and high-efficiency surgical mask. With no face covering, the simulated coughing and sneezing created a powerful forward-propagating fine aerosol flow. At 6 ft forward from the manikin head, the aerosol concentration was still 20-fold above the background. Adding a face covering reconfigured the forward-directed aerosol transmission pattern. The tested face coverings were found capable of mitigating the risk of coronavirus transmission; their effectiveness is dependent on the protective device. The outward leakage associated with a specific face covering was shown to be a major determinant of the exposure level for a person standing or seating next to or behind the coughing or sneezing "spreader" in a bus/train/aircraft/auditorium setting. Along with reports recently published in the literature, the study findings help assess the infectious dose and ultimately health risk for persons located within a 6-ft radius around the "spreader."

Homemade facemasks: particle filtration, breathability, fit, and other performance characteristics.

Homemade cloth masks and other improvised face coverings have become widespread during the COVID-19 pandemic driven by severe shortages of personal protective equipment. In this study, various alternative (mostly common household) materials, which have not traditionally been used in respiratory protective devices, were tested for particle filtration performance and breathability. Most of these materials were found of some-but rather limited-utility in facemasks. At a breathing flow rate of 30 L min-1, 17 out of 19 tested materials demonstrated collection efficiency below 50%; at 85 L min-1, only one material featured particle collection efficiency above 50%. Pressure drop values were mostly below 4 mm w.g. (observed in 89% of cases for the two flow rates), which provides comfortable breathing. Only for one fabric material (silk) tested at 85 L min-1 did the pressure drop reach 11 mm w.g. Based on these results, a three-layer facemask prototype was designed and fabricated comprised of the best performing materials. Additional tests were conducted to examine possible particle detachment/shedding from the materials used in the newly developed facemask, but no such phenomenon was observed. The prototype was evaluated on 10 human subjects using the standard OSHA-approved quantitative fit testing protocol. The mask protection level, determined as an adopted fit factor, was found to lie between that of the two commercial surgical/medical masks tested for comparison. A 10-cycle washing of the mask prototype lowered its collection efficiency across the particle size range; however, washing did not substantially affect mask breathability. The study revealed that although homemade masks offer a certain level of protection to a wearer, one should not expect them to provide the same respiratory protection as high-end commercial surgical/medical masks or-by any means-NIOSH-certified N95 filtering facepieces.

Eficacia de la mascarilla facial con filtro de partículas N95 y de la mascarilla quirúrgica durante la respiración humana: dos vías para la penetración de partículas.

RESUMENEl nivel de protección ofrecido por las mascarillas con filtro de partículas y las mascarillas se establece considerando el porcentaje de partículas ambientales que penetran dentro del dispositivo de protección. Existen dos vías de penetración: (1) la infiltración a través del sellado facial de la mascarilla y (2) a través del medio filtrante. El objetivo principal de este estudio fue diferenciar el aporte proveniente de cada una de estas dos vías para partículas cuyo tamaño oscila entre 0.03-1 µm en condiciones de respiración reales. Así, mientras se realizaban pruebas de ajuste convencionales, se evaluaron una mascarilla respiratoria autofiltrante N95 y una mascarilla quirúrgica usada comúnmente en entornos de atención médica en 25 sujetos (número coincidente con el último panel de pruebas de ajuste del Instituto Nacional de Seguridad y Salud Laborales). Asimismo, ambas mascarillas fueron evaluadas empleando maniquíes de respiración que imitaban de forma precisa los patrones de respiración registrados previamente en los sujetos evaluados. Posteriormente, se compararon los datos de penetración obtenidos en las evaluaciones realizadas con sujetos humanos y con maniquíes para determinar los diferentes tamaños de partículas, así como los patrones de respiración. Así se determinaron 5,250 valores de penetración específicos correspondientes al ejercicio y el tamaño de las partículas. Para cada valor se calcularon la tasa de infiltración a través del sellado facial de la mascarilla y la tasa de infiltración a través del filtro, con la finalidad de cuantificar los aportes relativos realizados por cada vía de penetración. El número de partículas que penetra mediante infiltración del sellado facial de la mascarilla autofiltrante/mascarilla quirúrgica probadas excedió ampliamente el número de aquellas que lo hacen a través del filtro. Para la mascarilla autofiltrante N95, el exceso fue (en promedio) de un orden de magnitud y se incrementó notablemente al aumentar el tamaño de las partículas (p < 0.001): ∼7 veces mayor para 0,04 µm, ∼10 veces para 0.1 µm y ∼20 veces para 1 µm. En el caso de la mascarilla quirúrgica, la tasa de infiltración a través del sellado facial de la misma con respecto al filtro osciló entre 4.8 y 5.8 y no se vio significativamente afectada por el tamaño de las partículas para la fracción del submicrómetro evaluado. El movimiento facial/corporal tuvo un efecto pronunciado en el aporte relativo de las dos vías de penetración. La intensidad de la respiración y las dimensiones faciales mostraron alguna influencia (aunque limitada). Considerando que la mayoría de las partículas que penetraron ingresaron a través del sellado facial, al desarrollar la mascarilla autofiltrante/mascarilla quirúrgica la prioridad debería ser realizar una adecuación que permitiera eliminar o minimizar la infiltración a través del sellado facial y no mejorar la eficiencia del medio de filtro.

¿Cómo afecta la frecuencia respiratoria el desempeño de una mascarilla respiratoria autofiltrante N95 y de una mascarilla quirúrgica contra sustitutos de partículas virales?

ResumenLa frecuencia respiratoria (respiraciones/min) difiere entre los individuos y dependiendo de los niveles de actividad física. Las partículas ingresan a las mascarillas respiratorias mediante dos vías principales de penetración: infiltración a través del sellado facial y penetración a través de filtros. Sin embargo, se desconoce la forma en que la frecuencia respiratoria afecta el desempeño general de las mascarillas autofiltrantes N95 (filtering facepiece respirators, FFR) y las mascarillas quirúrgicas (MQ) contra partículas virales y otras partículas submicrómicas de importancia para la salud. En un maniquí de respiración a cuatro flujos inspiratorios medios (FIM) (15, 30, 55 y 85 L/min) y cinco frecuencias respiratorias (10, 15, 20, 25 y 30 respiraciones/min) se probaron una FFR y una MQ. En los dispositivos de protección respiratoria probados se determinaron la penetración a través del filtro (Pfiltro) y la infiltración total hacia el interior (ITI) de partículas de aerosol de cloruro de sodio (NaCl) en tamaños que oscilaban entre 20 y 500 nm. Asimismo, se calcularon las proporciones de penetración de la "infiltración a través del sellado facial con respecto al filtro" (ISFF). Tanto el FIM como la frecuencia respiratoria mostraron efectos significativos (p < 0.05) en el Pfiltro y la ITI. El aumento de la frecuencia respiratoria incrementó la ITI para las FFR N95 mientras que en las MQ no se observaron tendencias claras. El aumento del FIM incrementó la Pfiltro y disminuyó la ITI, lo que dio lugar a una disminución de la proporción de la ISFF. La mayoría de las proporciones de la ISFF fueron >1, lo que sugiere que la infiltración a través del sellado facial fue la vía primaria de penetración de partículas a diversas frecuencias respiratorias. La frecuencia respiratoria es otro factor (además del FIM) que puede afectar significativamente el desempeño de las FFR N95: las frecuencias respiratorias más altas aumentan la ITI. En el caso de las MQ probadas no se observó ninguna tendencia consistente de aumento o disminución de la ITI relacionada con el FIM o la frecuencia respiratoria. Para ampliar potencialmente estos hallazgos más allá del maniquí/sistema respiratorio utilizado, se necesitan estudios futuros orientados a comprender plenamente el mecanismo que hace que la frecuencia respiratoria afecte el desempeño de los dispositivos de protección respiratoria en los sujetos humanos.

Evaluation of AccuFIT 9000: A Novel Apparatus for Quantitative Fit Testing of Particulate Respirators.

Various strategies developed for protecting frontline workers and the general public from the novel coronavirus, SARS-CoV-2, largely rely on respiratory protective devices (RPDs), especially considering recent evidence about the aerosol transmission route of COVID-19. Performance of an RPD primarily depends on how well the protective device fits the wearer. Therefore, quantitative fit testing of particulate respirators is crucial for achieving the intended protection level. Millions of fit tests are conducted every year using a US OSHA-accepted standard protocol involving a PortaCount® (TSI Inc., Shoreview, MN, USA) which measures a respirator fit factor. Recently, several alternative fit testing instruments have been developed and introduced to the market. Among them is an AccuFIT 9000 (Kanomax-Japan Inc., Suita-city, Osaka, Japan), which, like the PortaCount®, utilizes the condensation particle counting principle, but features an advanced saturation chamber design allowing for a longer residence time and greater flow stability. It is also claimed to have a more cost-efficient assembly than its predecessors. In this study, the novel AccuFIT apparatus was extensively evaluated against the PortaCount® (the reference instrument) using the traditional standard fit testing protocol and following the American National Standards Institute (ANSI) standard (Z88.10-2010 Annex A2). The evaluation was performed with three types of respirators, N95 filtering facepiece respirator (FFR), P100 FFR, and half-mask elastomeric facepiece, of different models and manufacturers donned on 25 subjects. The comparative testing and analysis showed that the AccuFIT 9000 is capable of identifying an inadequate fit of the tested respirators with a sensitivity 0.95 and specificity of 0.97, which meets the ANSI requirement of ≥0.95. The other ANSI requirements/recommendations were also met. It was concluded that the novel fit testing apparatus demonstrated an acceptable performance and, thus, can be successfully deployed for the quantitative respirator fit testing.

Coronavirus Disease 2019 Patients in Earlier Stages Exhaled Millions of Severe Acute Respiratory Syndrome Coronavirus 2 Per Hour.

Coronavirus disease 2019 (COVID-19) patients exhaled millions of severe acute respiratory syndrome coronavirus 2 RNA copies per hour, which plays an important role in COVID-19 transmission. Exhaled breath had a higher positive rate (26.9%, n = 52) than surface (5.4%, n = 242) and air (3.8%, n = 26) samples.

Breath-, air- and surface-borne SARS-CoV-2 in hospitals.

The COVID-19 pandemic has brought an unprecedented crisis to the global health sector. When discharging COVID-19 patients in accordance with throat or nasal swab protocols using RT-PCR, the potential risk of reintroducing the infection source to humans and the environment must be resolved. Here, 14 patients including 10 COVID-19 subjects were recruited; exhaled breath condensate (EBC), air samples and surface swabs were collected and analyzed for SARS-CoV-2 using reverse transcription-polymerase chain reaction (RT-PCR) in four hospitals with applied natural ventilation and disinfection practices in Wuhan. Here we discovered that 22.2% of COVID-19 patients (n = 9), who were ready for hospital discharge based on current guidelines, had SARS-CoV-2 in their exhaled breath (~105 RNA copies/m3). Although fewer surface swabs (3.1%, n = 318) tested positive, medical equipment such as face shield frequently contacted/used by healthcare workers and the work shift floor were contaminated by SARS-CoV-2 (3-8 viruses/cm2). Three of the air samples (n = 44) including those collected using a robot-assisted sampler were detected positive by a digital PCR with a concentration level of 9-219 viruses/m3. RT-PCR diagnosis using throat swab specimens had a failure rate of more than 22% in safely discharging COVID-19 patients who were otherwise still exhaling the SARS-CoV-2 by a rate of estimated ~1400 RNA copies per minute into the air. Direct surface contact might not represent a major transmission route, and lower positive rate of air sample (6.8%) was likely due to natural ventilation (1.6-3.3 m/s) and regular disinfection practices. While there is a critical need for strengthening hospital discharge standards in preventing re-emergence of COVID-19 spread, use of breath sample as a supplement specimen could further guard the hospital discharge to ensure the safety of the public and minimize the pandemic re-emergence risk.

New respirator performance monitor (RePM) for powered air-purifying respirators.

Powered air-purifying respirators (PAPRs) that offer protection from particulates are deployed in different workplace environments. Usage of PAPRs by healthcare workers is rapidly increasing; these respirators are often considered the best option in healthcare settings, particularly during public health emergency situations, such as outbreaks of pandemic diseases. At the same time, lack of user training and certain vigorous work activities may lead to a decrease in a respirator's performance. There is a critical need for real-time performance monitoring of respiratory protective devices, including PAPRs. In this effort, a new robust and low-cost real-time performance monitor (RePM) capable of evaluating the protection offered by a PAPR against aerosol particles at a workplace was developed. The new device was evaluated on a manikin and on human subjects against a pair of condensation nuclei counters (P-Trak) used as the reference protection measurement system. The outcome was expressed as a manikin-based protection factor (mPF) and a Simulated Workplace Protection Factor (SWPF) determined while testing on subjects. For the manikin-based testing, the data points collected by the two methods were plotted against each other; a near-perfect correlation was observed with a correlation coefficient of 0.997. This high correlation is particularly remarkable since RePM and condensation particle counter (CPC) measure in different particle size ranges. The data variability increased with increasing mPF. The evaluation on human subjects demonstrated that RePM prototype provided an excellent Sensitivity (96.3% measured on human subjects at a response time of 60 sec) and a Specificity of 100%. The device is believed to be the first of its kind to quantitatively monitor PAPR performance while the wearer is working; it is small, lightweight, and does not interfere with job functions.

Estimated dermal exposure to nebulized pharmaceuticals for a simulated home healthcare worker scenario.

The duties of home healthcare workers are extensive. One important task that is frequently performed by home healthcare workers is administration of nebulized medications, which may lead to significant dermal exposure. In this simulation study conducted in an aerosol exposure chamber, we administered a surrogate of nebulizer-delivered medications (dispersed sodium chloride, NaCl) to a patient mannequin. We measured the amount of NaCl deposited on the exposed surface of the home healthcare worker mannequin, which represented the exposed skin of a home healthcare worker. Factors such as distance and position of the home healthcare worker, room airflow rate and patient's inspiratory rate were varied to determine their effects on dermal exposure. There was a 2.78% reduction in dermal deposition for every centimeter the home healthcare worker moved away from the patient. Increasing the room's air exchange rate by one air change per hour increased dermal deposition by about 2.93%, possibly due to a decrease in near field particle settling. For every 10-degrees of arc the home healthcare worker is positioned from the left side of the patient toward the right and thus moving into the ventilation airflow direction, dermal deposition increased by about 4.61%. An increase in the patient's inspiratory rate from 15-30 L/min resulted in an average of 14.06% reduction in dermal deposition for the home healthcare worker, reflecting a relative increase in the aerosol fraction inhaled by the patient. The findings of this study elucidate the interactions among factors that contribute to dermal exposure to aerosolized pharmaceuticals administered by home healthcare workers. The results presented in this paper will help develop recommendations on mitigating the health risks related to dermal exposure of home healthcare workers.

Predicting Indoor Concentrations of Black Carbon in Residential Environments.

Black carbon (BC) is a descriptive term that refers to light-absorbing particulate matter (PM) produced by incomplete combustion and is often used as a surrogate for traffic-related air pollution. Exposure to BC has been linked to adverse health effects. Penetration of ambient BC is typically the primary source of indoor BC in the developed world. Other sources of indoor BC include biomass and kerosene stoves, lit candles, and charring food during cooking. Home characteristics can influence the levels of indoor BC. As people spend most of their time indoors, human exposure to BC can be associated to a large extent with indoor environments. At the same time, due to the cost of environmental monitoring, it is often not feasible to directly measure BC inside multiple individual homes in large-scale population-based studies. Thus, a predictive model for indoor BC is needed to support risk assessment in public health. In this study, home characteristics and occupant activities that potentially modify indoor levels of BC were documented in 23 homes, and indoor and outdoor BC concentrations were measured twice. The homes were located in the Cincinnati-Kentucky-Indiana tristate region and measurements occurred from September 2015 through August 2017. A linear mixed-effect model was developed to predict BC concentration in residential environments. The measured outdoor BC concentrations and the documented home characteristics were utilized as predictors of indoor BC concentrations. After the model was developed, a leave-one-out cross-validation algorithm was deployed to assess the predictive accuracy of the output. The following home characteristics and occupant activities significantly modified the concentration of indoor BC: outdoor BC, lit candles and electrostatic or high efficiency particulate air (HEPA) filters in heating, ventilation and air conditioning (HVAC) systems. Predicted indoor BC concentrations explained 78% of the variability in the measured indoor BC concentrations. The data show that outdoor BC combined with home characteristics can be used to predict indoor BC levels with reasonable accuracy.

Inactivation of bacterial and fungal spores by UV irradiation and gaseous iodine treatment applied to air handling filters.

Exposure to viable bacterial and fungal spores re-aerosolized from air handling filters may create a major health risk. Assessing and controlling this exposure have been of interest to the bio-defense and indoor air quality communities. Methods are being developed for inactivating stress-resistant viable microorganisms collected on ventilation filters. Here we investigated the inactivation of spores of Bacillus thuringiensis var. kurstaki (Btk), a recognized simulant for B. antracis, and Aspergillus fumigatus, a common opportunistic pathogen used as an indicator for indoor air quality. The viability change was measured on filters treated with ultraviolet (UV) irradiation and gaseous iodine. The spores were collected on high-efficiency particulate air (HEPA) and non-HEPA filters, both flattened for testing purposes to represent "surface" filters. A mixed cellulose ester (MCE) membrane filter was also tested as a reference. Additionally, a commercial HEPA unit with a deep-bed (non-flattened) filter was tested. Combined treatments of Btk spores with UV and iodine on MCE filter produced a synergistic inactivation effect. No similar synergy was observed for A. fumigatus. For spores collected on an MCE filter, the inactivation effect was about an order of magnitude greater for Btk compared to A. fumigatus. The filter type was found to be an important factor affecting the inactivation of Btk spores while it was not as influential for A. fumigatus. Overall, the combined effect of UV irradiation and gaseous iodine on viable bacterial and fungal spores collected on flat filters was found to be potent. The benefit of either simultaneous or sequential treatment was much lower for Btk spores embedded inside the deep-bed (non-flattened) HEPA filter, but for A. fumigatus the inactivation on flattened and non-flattened HEPA filters was comparable. For both species, applying UV first and gaseous iodine second produced significantly higher inactivation than when applying them simultaneously or in an opposite sequence.

Indoor particulate matter and lung function in children.

People generally spend more time indoors than outdoors resulting in a higher proportion of exposure to particulate matter (PM) occurring indoors. Consequently, indoor PM levels, in contrast to outdoor PM levels, may have a stronger relationship with lung function. To test this hypothesis, indoor and outdoor PM2.5 and fungal spore data were simultaneously collected from the homes of forty-four asthmatic children aged 10-16 years. An optical absorption technique was utilized on the collected PM2.5 mass to obtain concentrations of black carbon (BC) and ultraviolet light absorbing particulate matter, (UVPM; a marker of light absorbing PM2.5 emitted from smoldering organics). Enrolled children completed spirometry after environmental measurements were made. Given the high correlation between PM2.5, BC, and UVPM, principal component analysis was used to obtain uncorrelated summaries of the measured PM. Separate linear mixed-effect models were developed to estimate the association between principal components of the PM variables and spirometry values, as well as the uncorrelated original PM variables and spirometry values. A one-unit increase in the first principal component variable representing indoor PM (predominantly composed of UVPM and PM2.5) was associated with 4.1% decrease (99% CI = -6.9, -1.4) in FEV1/FVC ratio. 11.3 µg/m3 increase in indoor UVPM was associated with 6.4% and 14.7% decrease (99% CI = -10.4, -2.4 and 99% CI = -26.3, -2.9, respectively) in percent predicted FEV1/FVC ratio and FEF25-75 respectively. Additionally, 17.7 µg/m3 increase in indoor PM2.5 was associated with 6.1% and 12.9% decrease (99% CI = -10.2, -1.9 and 99% CI = -24.9, -1.0, respectively) in percent predicted FEV1/FVC ratio and FEF25-75, respectively. Outdoor PM, indoor BC, and indoor fungal spores were not significantly associated with lung function. The results indicate that indoor PM is more strongly associated with lung function in children with asthma as compared with outdoor PM.

Combining sensor-based measurement and modeling of PM2.5 and black carbon in assessing exposure to indoor aerosols.

Accurate, cost-effective methods are needed for rapid assessment of traffic-related air pollution (TRAP). Typically, real-time data of particulate matter (PM) from portable sensors have been adjusted using data from reference methods such as gravimetric measurement to improve accuracy. The objective of this study was to create a correction factor or linear regression model for the real-time measurements of the RTI's Micro Personal Exposure Monitor (MicroPEM™) and AethLab's microAeth® black carbon (AE51) sensor to generate accurate real-time data for PM2.5 (PM2.5RT) and black carbon (BCRT) in Cincinnati metropolitan homes. The two sensors and an SKC PM2.5 Personal Modular impactor were collocated in 44 indoor sampling events for 2 days in residences near major roadways. The reference filter-based analyses conducted by a laboratory included particle mass (SKC PM2.5 and MicroPEM™ PM2.5) and black carbon (SKC BC); these methods are more accurate than real-time sensors but are also more cumbersome and costly. For PM2.5, the average correction factor, a ratio of gravimetric to real-time, for the MicroPEM™ PM2.5 and SKC PM2.5 utilizing the PM2.5RT and was 0.94 and 0.83, respectively, with a coefficient of variation (CV) of 84% and 52%, respectively; the corresponding linear regression model had a CV of 54% and 25%. For BC, the average correction factor utilizing the BCRT and SKC BC was 0.74 with a CV of 36% with the associated linear regression model producing a CV of 56%. The results from this study will help ensure that the real-time exposure monitors are capable of detecting an estimated PM2.5 after an appropriate statistical model is applied.

Evaluation of total and inhalable samplers for the collection of carbon nanotube and carbon nanofiber aerosols.

A growing number of carbon nanotubes and nanofibers (CNT/F) exposure and epidemiologic studies have utilized 25-mm and 37-mm open-faced cassettes (OFC) to assess the inhalable aerosol fraction. It has been previously established that the 37-mm OFC under-samples particles greater than 20 µm in diameter, but the size-selective characteristics of the 25-mm OFC have not yet been fully evaluated. This article describes an experimental study conducted to determine if the 25- and 37-mm OFCs performed with relative equivalence to a reference inhalable aerosol sampler when challenged with CNT/F particles. Side-by-side paired samples were collected within a small Venturi chamber using a 25-mm styrene OFC, 37-mm styrene OFC, 25-mm aluminum OFC, and Button Inhalable Aerosol Sampler. Three types of CNT/F materials and an Arizona road dust were used as challenge aerosols for the various sampler configurations. Repeated experiments were conducted for each sampler configuration and material. The OFC samplers operated at flow rates of 2 and 5 liters per minute. Results showed that the 25-mm OFC performed comparably to the Button Sampler when challenged with CNT/F aerosols, which was demonstrated in five of the six experimental scenarios with an average error of 20%. Overall, the results of this study indicate that the sampling efficiency of the 25- and 37-mm OFCs adequately followed the ISO/ACGIH/CEN inhalable sampling convention when challenged with CNT/F aerosols. Past exposure and epidemiologic studies that used these OFC samplers can directly compare their results to studies that have used other validated inhalable aerosol samplers.

Effectiveness of a portable air cleaner in removing aerosol particles in homes close to highways.

Outdoor traffic-related airborne particles can infiltrate a building and adversely affect the indoor air quality. Limited information is available on the effectiveness of high efficiency particulate air (HEPA) filtration of traffic-related particles. Here, we investigated the effectiveness of portable HEPA air cleaners in reducing indoor concentrations of traffic-related and other aerosols, including black carbon (BC), PM2.5 , ultraviolet absorbing particulate matter (UVPM) (a marker of tobacco smoke), and fungal spores. This intervention study consisted of a placebo-controlled cross-over design, in which a HEPA cleaner and a placebo "dummy" were placed in homes for 4-weeks each, with 48-hour air sampling conducted prior to and during the end of each treatment period. The concentrations measured for BC, PM2.5 , UVPM, and fungal spores were significantly reduced following HEPA filtration, but not following the dummy period. The indoor fraction of BC/PM2.5 was significantly reduced due to the HEPA cleaner, indicating that black carbon was particularly impacted by HEPA filtration. This study demonstrates that HEPA air purification can result in a significant reduction of traffic-related and other aerosols in diverse residential settings.

Assessing the accuracy of commercially available gas sensors for the measurement of ambient ozone and nitrogen dioxide.

The objective of the National Institute for Occupational Safety and Health (NIOSH) accuracy criterion is to ensure that measurements from monitoring devices are within ±25% of the true concentration of the analyte with 95% certainty. To determine whether NO2 and O3 sensors meet this criterion, three commercially available units (Cairclip O3/NO2, Aeroqual NO2, and Aeroqual O3 sensors) were co-located three times with validated instruments (NOx chemiluminescence [NO2mon] and photometric O3 analyzers [O3mon]) at an outdoor monitoring station. As cofactors of sensor performance such as temperature (T) and relative humidity (RH) potentially influence the response of NO2 and O3 sensors, corrections for cofactors were made by using T, RH, and the sensor measurements to predict measurements made by NO2mon and O3mon during the first co-location period (training dataset). The developed models were tested in the merged data obtained from the second and third co-location periods (testing dataset). In the training and testing datasets, the mean NO2 as measured by NO2mon was 4.6 ppb (range = 0.4-35 ppb) and 9.4 ppb (range = 1-37 ppb), respectively. The mean O3 in the training and testing datasets as measured by O3mon was 38.8 ppb (range = 1-65 ppb) and 35.7 ppb (range = 1-61 ppb), respectively. None of the sensor measurements in the training dataset were within the NIOSH accuracy criterion (mean error ≥25%). After correcting for cofactors of sensor performance, the accuracy of the Cairclip O3/NO2 and the Aeroqual O3 sensors considerably improved when tested with the testing dataset (mean error = -1% and 14%, respectively). However, the Aeroqual NO2 sensor had an error that was not within ±25%. Raw measurements from the tested sensors may be unsuitable for assessing workers' exposure to NO2 and O3. Corrections for cofactors of Cairclip O3/NO2 and Aeroqual O3 sensor performance are required for more accurate occupational exposure assessment.

Performance of a novel real-time respirator seal integrity monitor on firefighters: Simulated workplace pilot study.

Millions of workers, including firefighters, use respiratory protective device. The key aspect in assuring the intended protection level of a respirator is its fit. However, even if the respirator originally fits well, the faceseal may be breached during its use. Until now, there have been no practically viable, inexpensive means to monitor the performance of a respirator during actual use. A novel Respirator Seal Integrity Monitor (ReSIM) was developed and recently evaluated on manikins by our team. The objective of this study was to evaluate the ReSIM effectiveness on respirator-wearing firefighters exposed to aerosols while performing simulated routine operational activities. Initially, 15 subjects were recruited for the study. Following a preliminary investigation that resulted in modifications in the ReSIM prototype and testing protocol, a subset of nine firefighters was chosen for a full-scale evaluation. The testing was conducted in a 24.3-m3 exposure chamber using NaCl as the challenge aerosol. Controlled faceseal leaks were established by opening a solenoid valve for 10, 15, or 20 sec. Leaks were also established as the tested firefighter slightly repositioned the respirator on his/her face. During the testing, the ReSIM measured particles inside a full-face elastomeric respirator with a 72.7% leak detection sensitivity (probability of correct leak identification) and an 84.2% specificity (probability of correct identification of the intervals which are absent of any leak). After adjusting for false negatives and persistent false positives, sensitivity and specificity increased to 83.6% and 92.2%, respectively. The factors causing minor limitations in leak detection sensitivity and specificity can be attributed to variability among subjects, moisture's effect on the particle sensor, and some in-mask sampling bias. In conclusion, the ReSIM can promptly detect the breach in a respirator faceseal with high sensitivity and specificity. Due to its capability to alert the wearer of possible overexposure to hazardous aerosols, the ReSIM concept has a remarkable potential to be applied in various working environments, where respirators are used.

Laboratory Evaluation of a Novel Real-Time Respirator Seal Integrity Monitor.

Background: A low-cost real-time Respirator Seal Integrity Monitor (ReSIM) was recently developed to monitor a respirator's actual performance at a workplace. The objective of this study was to evaluate the capability of the new ReSIM prototype in manikin-based laboratory experiments to rapidly detect induced leakage of a half-mask elastomeric respirator. Methods: Two phases of testing were conducted in this study. First, the accuracy of ReSIM measuring an aerosol concentration was assessed by comparing the outputs of ReSIM against a reference optical aerosol spectrometer (OAS) in a flow-through set-up. Second, the capability to detect a leak was tested using a manikin-based set-up to simulate leaks into a functional respirator. Results: The regression curve of ReSIM versus OAS had an R2 of 0.936, indicating its high accuracy within the targeted particle size range of 0.5-2 µm. The ReSIM provided a leak detection sensitivity (probability of correctly identifying intervals with the true leak) of 98.4% when challenged with a combustion aerosol, compared to 71.8% when challenged with a NaCl aerosol. Its specificity (probability of identifying intervals without a leak) was 99.8% after adjusting for persistent false positives for both types of challenge aerosol. Conclusion: The ReSIM prototype not only can estimate the particle concentration with high accuracy but also can rapidly detect respirator faceseal leakage in real time with sufficient sensitivity and specificity. In addition, it can trigger an alarm when the faceseal integrity is compromised.