Last data update: May 13, 2024. (Total: 46773 publications since 2009)
Records 1-5 (of 5 Records) |
Query Trace: Ellenbecker M[original query] |
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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. |
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. |
Focused actions to protect carbon nanotube workers
Schulte PA , Kuempel ED , Zumwalde RD , Geraci CL , Schubauer-Berigan MK , Castranova V , Hodson L , Murashov V , Dahm MM , Ellenbecker M . Am J Ind Med 2012 55 (5) 395-411 There is still uncertainty about the potential health hazards of carbon nanotubes (CNTs) particularly involving carcinogenicity. However, the evidence is growing that some types of CNTs and nanofibers may have carcinogenic properties. The critical question is that while the carcinogenic potential of CNTs is being further investigated, what steps should be taken to protect workers who face exposure to CNTs, current and future, if CNTs are ultimately found to be carcinogenic? This paper addresses five areas to help focus action to protect workers: (i) review of the current evidence on the carcinogenic potential of CNTs; (ii) role of physical and chemical properties related to cancer development; (iii) CNT doses associated with genotoxicity in vitro and in vivo; (iv) workplace exposures to CNT; and (v) specific risk management actions needed to protect workers. (Am. J. Ind. Med. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.) |
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