Last data update: Apr 29, 2024. (Total: 46658 publications since 2009)
Records 1-19 (of 19 Records) |
Query Trace: Dunn KH[original query] |
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Transmission of SARS-CoV-2 in the workplace: Key findings from a rapid review of the literature
Cox J , Christensen B , Burton N , Dunn KH , Finnegan M , Ruess A , Estill C . Aerosol Sci Technol 2023 57 (3) 233-254 At the beginning of the COVID-19 pandemic, the primary route of transmission of the SARS-CoV-2 virus was not well understood. Research gathered from other respiratory infectious diseases, including other coronaviruses, was the basis for the initial perceptions for transmission of SARS-CoV-2. To better understand transmission of SARS-CoV-2, a rapid literature review was conducted from literature generated 19 March 2020, through 23 September 2021. 18,616 unique results were identified from literature databases and screened. Of these, 279 key articles were reviewed and abstracted covering critical topics such as environmental/workplace monitoring, sampling and analytical method evaluation, and the ability of the virus to remain intact and infectious during sampling. This paper describes the results of the rapid literature review, which evaluated pathways that contribute to transmission as well as the strengths and limitations of current sampling approaches. This review also evaluates how different factors, including environmental conditions and surface characteristics, could impact the transmission potential of SARS-CoV-2. A continual rapid review in the midst of a pandemic proved particularly useful for quickly understanding the transmission parameters of the virus and enabled us to comprehensively assess literature, respond to workplace questions, and evaluate our understanding as the science evolved. Air and surface sampling with the accompanying analytical methods were not generally effective in recovering SARS-CoV-2 viable virus or RNA in many likely contaminated environments. In light of these findings, the development of validated sampling and analysis methods is critical for determining worker exposure to SARS-CoV-2 and to assess the impact of mitigation efforts. © This work was authored as part of the Contributor’s official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law. |
The effect of the body wake and operator motion on the containment of nanometer-scale airborne substances using a conventional fume hood and specially designed enclosing hood: a comparison using computational fluid dynamics
Shen C , Dunn KH , Woskie SR , Bennett JS , Ellenbecker MJ , Dandy DS , Tsai CSJ . J Nanopart Res 2022 24 (4) Airborne substances in the nanoparticle size range would mostly follow the primary airflow patterns, which emphasizes the importance of understanding the airflow dynamics to effectively control exposures to toxic airborne substances such as nanometer-sized particles. Chemical fume hoods are being utilized as primary controls for worker exposure to airborne substances including nanometer-scale materials due to their overall availability and history of effective contaminant. This study evaluates the impact of the body wake on the containment performance of a conventional constant air volume (CAV) and a new “nano” ventilated enclosing hood using numerical methods. Numerical studies have been performed to predict leaks of nanomaterials handled inside the hood. We further performed experiments in this study to validate the velocity fields predicted by the computational fluid dynamic (CFD) models and to provide a basis for evaluating the impact of the human body on fume hood containment performance. Using these validated models, the effects of the motion of the arms moving out of the hood were simulated using CFD to assess how one of the common actions of an operator/user may affect containment. Results of our simulations show that areas near the hood side airfoils and directly behind the sash are more likely to concentrate contaminants released inside the hood and potentially result in leakage based on internal airflow patterns. These areas are key to monitor when assessing fume hood containment along with the operator/mannequin breathing zone to get an understanding of potential leak areas which might contribute to operator exposure as well as exposure to others inside the laboratory. © 2022, The Author(s), under exclusive licence to Springer Nature B.V. |
Toxicity evaluation following pulmonary exposure to an as-manufactured dispersed boron nitride nanotube (BNNT) material in vivo
Xin X , Barger M , Roach KA , Bowers L , Stefaniak AB , Kodali V , Glassford E , Dunn KL , Dunn KH , Wolfarth M , Friend S , Leonard SS , Kashon M , Porter DW , Erdely A , Roberts JR . NanoImpact 2020 19 Boron nitride nanotubes (BNNT) are multi-walled nanotubes composed of hexagonal B[sbnd]N bonds and possess many unique physical and chemical properties, creating a rapidly expanding market for this newly emerging nanomaterial which is still primarily in the research and development stage. The shape and high aspect ratio give rise to concern for the potential toxicity that may be associated with pulmonary exposure, especially in an occupational setting. The goal of this study was to assess lung toxicity using an in vivo time course model. The sample was manufactured to be 5 nm wide and up to 200 μm long, with ~50% purity covalently bound with hexagonal boron nitride (hBN) in the sample. Following preparation for in vivo studies, sonication of the material disrupted the longer tubes in the complex and the size distribution in dispersion medium (DM) of the structures was 13–23 nm in diameter and 0.6–1.6 μm in length. Male C57BL/6 J mice were exposed to 4 or 40 μg of BNNT or DM (vehicle control) by a single oropharyngeal aspiration. Pulmonary and systemic toxicity were investigated at 4 h, 1 d, 7 d, 1 mo and 2 mo post-exposure. Bronchoalveolar lavage (BAL) studies determined pulmonary inflammation (neutrophil influx) and cytotoxicity (lactate dehydrogenase activity) occurred at early time points and peaked at 7 d post-exposure in the high dose group. Histopathological analysis showed a minimal level of inflammatory cell infiltration in the high dose group with resolution over time and no fibrosis, and lung clearance analysis showed ~50% of the material cleared over the time course. The expression of inflammatory- and acute phase response-associated genes in the lung and liver were significantly increased by the high dose at 4 h and 1 d post-exposure. The increases in lung gene expression of Cxcl2, Ccl2, Il6, Ccl22, Ccl11, and Spp1 were significant up to 2 mo but decreased with time. The low dose exposure did not result in significant changes in any toxicological parameters measured. In summary, the BNNT-hBN sample used in this study caused acute pulmonary inflammation and injury at the higher dose, which peaked by 7 d post-exposure and showed resolution over time. Further studies are needed to determine if physicochemical properties and purity will impact the toxicity profile of BNNT and to investigate the underlying mechanisms of BNNT toxicity. |
Reducing ultrafine particulate emission from multiple 3D printers in an office environment using a prototype engineering control
Dunn KL , Hammond D , Menchaca K , Roth G , Dunn KH . J Nanopart Res 2020 22 (5) Recent studies have shown that high concentrations of ultrafine particles can be emitted during the 3D printing process. This study characterized the emissions from different filaments using common fused deposition modeling printers. It also assessed the effectiveness of a novel engineering control designed to capture emissions directly at the extruder head. Airborne particle and volatile organic compound concentrations were measured, and particle emission rates were calculated for several different 3D printer and filament combinations. Each printer and filament combination was tested inside a test chamber to measure overall emissions using the same print design for approximately 2 h. Emission rates ranged from 0.71 × 107 to 1400 × 107 particles/min, with particle geometric mean diameters ranging from 45.6 to 62.3 nm. To assess the effectiveness of a custom-designed engineering control, a 1-h print program using a MakerBot Replicator+ with Slate Gray Tough polylactic acid filament was employed. Emission rates and particle counts were evaluated both with and without the extruder head emission control installed. Use of the control showed a 98% reduction in ultrafine particle concentrations from an individual 3D printer evaluated in a test chamber. An assessment of the control in a simulated makerspace with 20 printers operating showed particle counts approached or exceeded 20,000 particles/cm3 without the engineering controls but remained at or below background levels (< 1000 particles/cm3) with the engineering controls in place. This study showed that a low-cost control could be added to existing 3D printers to significantly reduce emissions to the work environment. |
Exposures during wet production and use processes of nanomaterials: a summary of 11 worksite evaluations
Glassford E , Neu-Baker NM , Dunn KL , Dunn KH . Ind Health 2020 58 (5) 467-478 From 2011-2015, the National Institute for Occupational Safety and Health Nanotechnology Field Studies Team conducted 11 evaluations at worksites that either produced engineered nanomaterials (ENMs) via a wet process or used ENMs in a wetted, suspended, or slurry form. Wet handling or processing of ENMs reduces potential exposure compared to dry handling or processing; however, air sampling data indicated exposures may still occur. Information was gathered about each company, production processes, ENMs of interest, and control measures. Exposure assessments included air sampling using filter media, surface wipe sampling, and real-time particle counting by direct-reading instruments. Electron microscopy analysis of air filters confirmed the presence of ENMs of interest (10 of 11 sites). When a method was available, chemical analysis of filters was also used to detect the presence of ENMs (nine of 11 sites). Wipe samples were collected at four of the 11 sites, and, in each case, confirmed the presence of ENMs on surfaces. Direct-reading data showed potential nanomaterial emissions (nine of 11 sites). Engineering controls included fume hoods, cleanrooms, and enclosed processes. Personal protective equipment was required during all 11 evaluations. Recommendations to address potential exposures were provided to each company following the hierarchy of controls. |
Three-dimensional printer emissions and employee exposures to ultrafine particles during the printing of thermoplastic filaments containing carbon nanotubes or carbon nanofibers
Dunn KL , Dunn KH , Hammond D , Lo S . J Nanopart Res 2020 22 (2) Recent studies have reported emission rates of up to 1012 ultrafine particles/min from fused filament fabrication three-dimensional printers when operated in unventilated or minimally ventilated test chambers. However, in these studies, there are no data to relate this rate to airborne concentrations in a manufacturing environment. An assessment of particle exposures of workers was conducted at a three-dimensional printing shop using multiple fused filament printers with unfilled and carbon nanotube and/or carbon nanofiber-infused polyetheletherketone filaments. The study simultaneously evaluated emissions in two environments: (1) in a field portable test chamber with one three-dimensional printer and (2) in the manufacturing area with multiple printers in use. Emission rates were calculated for a variety of filaments and ranged from 1.21 to 33.5 x 1011 particles/min, with geometric mean diameters ranging from 11.4 to 33.3 nm. The emission rates estimated by a scanning mobility particle sizer were much lower than from the fast mobility particle sizer due to differences in the lower size resolution. Samples collected in the chamber and manufacturing area by thermophoretic sampling included free (no polymer) carbon nanotubes and nanofibers and their bundles. The company reportedly never handled free carbon nanotubes or nanofibers, and prior research has indicated that the release of free nanomaterials through three-dimensional printing or mechanical action is highly unlikely. This presents the possibility that these materials are being released from the matrix during use or that these materials were brought into the facility through the supply chain, or by other means. |
Characterization and workplace exposure assessment of nanomaterial released from a carbon nanotube-enabled anti-corrosive coating
Brame JA , Alberts EM , Schubauer-Berigan MK , Dunn KH , Babik KR , Barnes E , Moser R , Poda AR , Kennedy AJ . NanoImpact 2018 12 58-68 Improvement of methods to quantify the release and characterization of engineered nanomaterials (ENMs) from nano-enabled products is essential to enhance the accuracy and usability of environmental health and safety evaluations. An anticorrosive coating containing multi-wall carbon nanotubes (MWCNTs) was analyzed for nano-scale material and workplace exposure potential. Worker breathing zone measurements for elemental carbon (EC) and electron-microscopy-based structure counts showed negligible MWCNT exposure to workers during laboratory and spray-painting operations over the course of two 8-hour shifts (arithmetic mean inhalable EC and electron microscopy structure count concentrations were 6.47 g/m3 and 0.084 structures/cm3 respectively). UV weathering prior to abrasion testing increased the nano-size fraction of released material as measured by a fast mobility particle sizer (FMPS) and visual inspection by SEM indicated increased presence of exposed MWCNTs embedded in the polymer matrix. However, no free MWCNTs were identified, despite evidence of MWCNTs embedded in airborne particles. TiO2, used as a pigment in the coating and not anticipated as a candidate for nano-specific scrutiny, contained a small fraction (3.5% in number) of nano-sized constituents (100 nm). This work emphasizes need for rigorous characterization of additive materials to properly assess potential health hazards and to better our understanding of what qualifies as nano. |
Control banding tools for engineered nanoparticles: What the practitioner needs to know
Dunn KH , Eastlake AC , Story M , Kuempel ED . Ann Work Expo Health 2018 wxy002-wxy002 Control banding (CB) has been widely recommended for the selection of exposure controls for engineered nanomaterials (ENMs) in the absence of ENM-specific occupational exposure limits (OELs). Several ENM-specific CB strategies have been developed but have not been systematically evaluated. In this article, we identify the data inputs and compare the guidance provided by eight CB tools, evaluated on six ENMs, and assuming a constant handling/use scenario. The ENMs evaluated include nanoscale silica, titanium dioxide, silver, carbon nanotubes, graphene, and cellulose. Several of the tools recommended the highest level of exposure control for each of the ENMs in the evaluation, which was driven largely by the hazard banding. Dustiness was a factor in determining the exposure band in many tools, although most tools did not provide explicit guidance on how to classify the dustiness (high, medium, low), and published data are limited on this topic. The CB tools that recommended more diverse control options based on ENM hazard and dustiness data appear to be better equipped to utilize the available information, although further validation is needed by comparison to exposure measurements and OELs for a variety of ENMs. In all CB tools, local exhaust ventilation was recommended at a minimum to control exposures to ENMs in the workplace. Generally, the same or more stringent control levels were recommended by these tools compared with the OELs proposed for these ENMs, suggesting that these CB tools would generally provide prudent exposure control guidance, including when data are limited. |
Characterizing workforces exposed to current and emerging non-carbonaceous nanomaterials in the U.S
Babik KR , Dahm MM , Dunn KH , Dunn KL , Schubauer-Berigan MK . J Occup Environ Hyg 2017 15 (1) 0 OBJECTIVE: Toxicology studies suggest that exposure to certain types of engineered nanomaterials (ENMs) may cause adverse health effects, but little is known about the workforce in the United States that produces or uses these materials. In addition, occupational exposure control strategies in this industry are not well characterized. This study identified US ENM manufacturers and users (other than carbon nanotubes and nanofibers, which have been characterized elsewhere), determined workforce size, characterized types and quantities of materials used, occupational exposure control strategies, and the feasibility of occupational ENM exposure studies. METHODS: Eligible companies were identified and information was collected through phone surveys on nanomaterials produced or used, workforce size, location, work practices, and exposure control strategies. The companies were classified into groups for additional examinations. RESULTS: Forty-nine companies producing or using ENMs in the US were identified. These companies employed at least 1500 workers. Most companies produced or used some form of nanoscale metal. More than half of the eligible companies were suppliers for the coatings, composite materials, or general industries. Each company provided information about worker exposure reduction strategies through engineering controls, administrative controls, or personal protective equipment. Production-scale companies reported greater use of specific exposure control strategies for ENMs than laboratory-scale companies. CONCLUSIONS: Workplaces producing or using ENMs report using engineering and administrative controls as well as personal protective equipment to control worker exposure. Industrywide exposure assessment studies appear feasible due to workforce size. However, more effort must be taken to target industries using specific ENMs based on known toxicological effects and health risks. |
Respiratory and ocular symptoms among employees of an indoor waterpark resort - Ohio, 2016
Chiu SK , Burton NC , Dunn KH , de Perio MA . MMWR Morb Mortal Wkly Rep 2017 66 (37) 986-989 In July 2015, a municipal health department in Ohio received complaints of respiratory and ocular symptoms from patrons of an indoor waterpark resort. In response, the health department conducted an online survey in August 2015 through which 19 (68%) patron and employee respondents reported eye burning, nose irritation, difficulty breathing, and vomiting. On August 11, 2015, the health department requested a health hazard evaluation by CDC's National Institute for Occupational Safety and Health to characterize the prevalence of symptoms among employees and determine the etiology of work-related symptoms. In January 2016, CDC investigators performed a cross-sectional epidemiologic study, environmental sampling, and ventilation system assessment (1). Findings suggested that chlorine disinfection byproducts and environmental conditions contributed to a higher prevalence of work-related respiratory and ocular symptoms among employees in the waterpark compared with employees in other resort areas. Recommendations included servicing the ventilation system, changing work practices to decrease the amount of disinfection byproduct precursors, and responding promptly to employee reports of symptoms. |
Particle emissions from laboratory activities involving carbon nanotubes
Lo LM , Tsai CSJ , Heitbrink WA , Dunn KH , Topmiller J , Ellenbecker M . J Nanopart Res 2017 18 (293) This site study was conducted in a chemical laboratory to evaluate nanomaterial emissions from 20–30-nm-diameter bundles of single-walled carbon nanotubes (CNTs) during product development activities. Direct-reading instruments were used to monitor the tasks in real time, and airborne particles were collected using various methods to characterize released nanomaterials using electron microscopy and elemental carbon (EC) analyses. CNT clusters and a few high-aspect-ratio particles were identified as being released from some activities. The EC concentration (0.87 μg/m3) at the source of probe sonication was found to be higher than other activities including weighing, mixing, centrifugation, coating, and cutting. Various sampling methods all indicated different levels of CNTs from the activities; however, the sonication process was found to release the highest amounts of CNTs. It can be cautiously concluded that the task of probe sonication possibly released nanomaterials into the laboratory and posed a risk of surface contamination. Based on these results, the sonication of CNT suspension should be covered or conducted inside a ventilated enclosure with proper filtration or a glovebox to minimize the potential of exposure. |
Performance of particulate containment at nanotechnology workplaces
Lo LM , Tsai CSJ , Dunn KH , Hammond D , Marlow D , Topmiller J , Ellenbecker M . J Nanopart Res 2015 17 435 The evaluation of engineering controls for the production or use of carbon nanotubes (CNTs) was investigated at two facilities. These control assessments are necessary to evaluate the current status of control performance and to develop proper control strategies for these workplaces. The control systems evaluated in these studies included ventilated enclosures, exterior hoods, and exhaust filtration systems. Activity-based monitoring with direct-reading instruments and filter sampling for microscopy analysis were used to evaluate the effectiveness of control measures at study sites. Our study results showed that weighing CNTs inside the biological safety cabinet can have a 37 % reduction on the particle concentration in the worker's breathing zone, and produce a 42 % lower area concentration outside the enclosure. The ventilated enclosures used to reduce fugitive emissions from the production furnaces exhibited good containment characteristics when closed, but they failed to contain emissions effectively when opened during product removal/harvesting. The exhaust filtration systems employed for exhausting these ventilated enclosures did not provide promised collection efficiencies for removing engineered nanomaterials from furnace exhaust. The exterior hoods were found to be a challenge for controlling emissions from machining nanocomposites: the downdraft hood effectively contained and removed particles released from the manual cutting process, but using the canopy hood for powered cutting of nanocomposites created 15-20 % higher ultrafine (<500 nm) particle concentrations at the source and at the worker's breathing zone. The microscopy analysis showed that CNTs can only be found at production sources but not at the worker breathing zones during the tasks monitored. |
Evaluation of leakage from fume hoods using tracer gas, tracer nanoparticles and nanopowder handling test methodologies
Dunn KH , Tsai CS , Woskie SR , Bennett JS , Garcia A , Ellenbecker MJ . J Occup Environ Hyg 2014 11 (10) D164-73 The most commonly reported control used to minimize workplace exposures to nanomaterials is the chemical fume hood. Studies have shown, however, that significant releases of nanoparticles can occur when materials are handled inside fume hoods. This study evaluated the performance of a new commercially available nano fume hood using three different test protocols. Tracer gas, tracer nanoparticle, and nanopowder handling protocols were used to evaluate the hood. A static test procedure using tracer gas (sulfur hexafluoride) and nanoparticles as well as an active test using an operator handling nanoalumina were conducted. A commercially available particle generator was used to produce sodium chloride tracer nanoparticles. Containment effectiveness was evaluated by sampling both in the breathing zone (BZ) of a mannequin and operator as well as across the hood opening. These containment tests were conducted across a range of hood face velocities (60, 80, and 100 ft/min) and with the room ventilation system turned off and on. For the tracer gas and tracer nanoparticle tests, leakage was much more prominent on the left side of the hood (closest to the room supply air diffuser) although some leakage was noted on the right side and in the BZ sample locations. During the tracer gas and tracer nanoparticle tests, leakage was primarily noted when the room air conditioner was on for both the low and medium hood exhaust airflows. When the room air conditioner was turned off, the static tracer gas tests showed good containment across most test conditions. The tracer gas and nanoparticle test results were well correlated showing hood leakage under the same conditions and at the same sample locations. The impact of a room air conditioner was demonstrated with containment being adversely impacted during the use of room air ventilation. The tracer nanoparticle approach is a simple method requiring minimal setup and instrumentation. However, the method requires the reduction in background concentrations to allow for increased sensitivity. |
Exposure controls for nanomaterials at three manufacturing sites
Heitbrink WA , Lo LM , Dunn KH . J Occup Environ Hyg 2014 12 (1) 16-28 Because nanomaterials are thought to be more biologically active than their larger parent compounds, careful control of exposures to nanomaterials is recommended. Field studies were conducted at three sites to develop information about the effectiveness of control measures including process changes, a downflow room, a ventilated enclosure, and an enclosed reactor. Aerosol mass and number concentrations were measured during specific operations with a photometer and an electrical mobility particle sizer to provide concentration measurements across a broad range of sizes (from 5.6 nm to 30 mum). At site A, the dust exposure and during product harvesting was eliminated by implementing a wait time of 30 minutes following process completion. And, the dust exposure attributed to process tank cleaning was reduced from 0.7 to 0.2 mg/m3 by operating the available process ventilation during this task. At site B, a ventilated enclosure was used to control dust generated by the manual weigh-out and manipulation of powdered nanomaterials inside of a downflow room. Dust exposures were at room background (under 0.04 mg/m3 and 500 particles/cm3) during these tasks however, manipulations conducted outside of the enclosure were correlated with a transient increase in concentration measured at the source. At site C, a digitally controlled reactor was used to produce aligned carbon nanotubes. This reactor was a closed system and the ventilation functioned as a redundant control measure. Process emissions were well controlled by this system with the exception of increased concentrations measured during the unloading the product. However, this emission source could be easily controlled through increasing cabinet ventilation. The identification and adoption of effective control technologies is an important first step in reducing the risk associated with worker exposure to engineered nanoparticles. Properly designing and evaluating the effectiveness of these controls is a key component in a comprehensive health and safety program. |
Evaluation of engineering controls for the mixing of flavorings containing diacetyl and other volatile ingredients
Hirst DV , Dunn KH , Shulman SA , Hammond DR , Sestito N . J Occup Environ Hyg 2014 11 (10) 680-7 Exposures to diacetyl, a primary ingredient of butter flavoring, have been shown to cause respiratory disease among workers who mix flavorings. This study focused on evaluating ventilation controls designed to reduce emissions from the flavor mixing tanks, the major source of diacetyl in the plants. Five exhaust hood configurations were evaluated in the laboratory: standard hinged lid-opened, standard hinged lid-closed, hinged lid-slotted, dome with 38-mm gap, and dome with 114-mm gap. Tracer gas tests were performed to evaluate quantitative capture efficiency for each hood. A perforated copper coil was used to simulate an area source within the 1.2-meter diameter mixing tank. Capture efficiencies were measured at four hood exhaust flow rates (2.83, 5.66, 11.3, and 17.0 cubic meters per minute) and three cross draft velocities (0, 30, and 60 meters per minute). All hoods evaluated performed well with capture efficiencies above 90% for most combinations of exhaust volume and cross drafts. The standard hinged lid was the least expensive to manufacture and had the best average capture efficiency (over 99%) in the closed configuration for all exhaust flow rates and cross drafts. The hinged lid-slotted hood had some of the lowest capture efficiencies at the low exhaust flow rates compared to the other hood designs. The standard hinged lid performed well, even in the open position, and it provided a flexible approach to controlling emissions from mixing tanks. The dome hood gave results comparable to the standard hinged lid but it is more expensive to manufacture. The results of the study indicate that emissions from mixing tanks used in the production of flavorings can be controlled using simple inexpensive exhaust hoods. |
A summary of research and progress on carbon monoxide exposure control solutions on houseboats
Hall RM , Earnest GS , Hammond DR , Dunn KH , Garcia A . J Occup Environ Hyg 2014 11 (7) D92-100; quiz D101-3 BACKGROUND: Investigations of carbon monoxide (CO) related poisonings and deaths on houseboats were conducted by the Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. These investigations measured hazardous CO concentrations on and around houseboats that utilize gasoline powered generators. Engineering control devices were developed and tested to mitigate this deadly hazard. METHODS: CO emissions were measured using various sampling techniques which included exhaust emission analyzers, detector tubes, evacuated containers (grab air samples analyzed by a gas chromatograph), and direct reading CO monitors. RESULTS: CO results on houseboats equipped with gasoline powered generators without emission controls indicated hazardous CO concentrations exceeding immediately dangerous to life and health (IDLH) levels in potentially occupied areas of the houseboat. Air sample results on houseboats that were equipped with engineering controls to remove the hazard were highly effective and reduced CO levels by over 98% in potentially occupied areas. CONCLUSION: The engineering control devices used to reduce the hazardous CO emissions from gasoline powered generators on houseboats were extremely effective at reducing CO concentrations to safe levels in potentially occupied areas on the houseboats and are now beginning to be widely used. |
Personal carbon monoxide exposures among firefighters at prescribed forest burns in the southeastern United States
Dunn KH , Shulman S , Stock AL , Naeher LP . Arch Environ Occup Health 2013 68 (1) 55-9 Exposure to combustion products from wildland fires causes respiratory irritation and decreased lung function among firefighters. The authors evaluated carbon monoxide (CO) exposures of a group of wildland firefighters who conducted prescribed burns in the southeastern United States of America. A total of 149 person-days of samples were collected using data logging CO monitors. A questionnaire was administered to collect data on job tasks and self-reported smoke exposure. Overall, the highest exposures were seen amongst firefighters assigned to holding and mop-up tasks (geometric mean [GM]: 2.6 ppm), whereas the lowest were associated with lighting and jobs such as burn boss (GM: 1.6 and 0.3 ppm, respectively). The self-reported smoke exposure showed a significant linear trend with increasing CO exposure. The numbers of acres burned or burn duration, however, were not good predictors of exposure. |
Aerosol monitoring during carbon nanofiber production: mobile direct-reading sampling
Evans DE , Ku BK , Birch ME , Dunn KH . Ann Occup Hyg 2010 54 (5) 514-31 Detailed investigations were conducted at a facility that manufactures and processes carbon nanofibers (CNFs). Presented research summarizes the direct-reading monitoring aspects of the study. A mobile aerosol sampling platform, equipped with an aerosol instrument array, was used to characterize emissions at different locations within the facility. Particle number, respirable mass, active surface area, and photoelectric response were monitored with a condensation particle counter (CPC), a photometer, a diffusion charger, and a photoelectric aerosol sensor, respectively. CO and CO(2) were additionally monitored. Combined simultaneous monitoring of these metrics can be utilized to determine source and relative contribution of airborne particles (CNFs and others) within a workplace. Elevated particle number concentrations, up to 1.15 x 10(6) cm(-3), were found within the facility but were not due to CNFs. Ultrafine particle emissions, released during thermal treatment of CNFs, were primarily responsible. In contrast, transient increases in respirable particle mass concentration, with a maximum of 1.1 mg m(-3), were due to CNF release through uncontrolled transfer and bagging. Of the applied metrics, our findings suggest that particle mass was probably the most useful and practical metric for monitoring CNF emissions in this facility. Through chemical means, CNFs may be selectively distinguished from other workplace contaminants (Birch et al., in preparation), and for direct-reading monitoring applications, the photometer was found to provide a reasonable estimate of respirable CNF mass concentration. Particle size distribution measurements were conducted with an electrical low-pressure impactor and a fast particle size spectrometer. Results suggest that the dominant CNF mode by particle number lies between 200 and 250 nm for both aerodynamic and mobility equivalent diameters. Significant emissions of CO were also evident in this facility. Exposure control recommendations were described for processes as required. |
Ocular and respiratory symptoms among lifeguards at a hotel indoor waterpark resort
Dang B , Chen L , Mueller C , Dunn KH , Almaguer D , Roberts JL , Otto CS . J Occup Environ Med 2010 52 (2) 207-13 OBJECTIVES: To determine the cause of eye and respiratory irritation symptoms among lifeguards at an indoor waterpark. METHODS: Investigators 1) performed environmental sampling for chloramine, endotoxin, and microbials; 2) administered symptom questionnaires; 3) reviewed ventilation system designs; and 4) reviewed water chemistry. RESULTS: Airborne trichloramine concentrations were found at levels reported to cause irritation symptoms in other studies. Some endotoxin concentrations were found at levels associated with cough and fever in previous studies. Exposed lifeguards were significantly more likely to report work-related irritation symptoms than unexposed individuals. The ventilation system may not have provided sufficient air movement and distribution to adequately capture and remove air contaminants at deck level. No water microbes were detected, and water chemistry met state standards. CONCLUSIONS: Indoor waterparks need to control water chemistry and ensure adequate air movement and distribution to control air contaminants and reduce health symptoms. |
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