Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, EPHB-356-18a, 2013 Oct; :1-29
The National Institute for Occupational Safety and Health (NIOSH) Engineering and Physical Hazards Branch (EPHB) and the University of Massachusetts Lowell (UMass Lowell) Environmental Health and Safety Team assessed nanoparticle emissions in a chemical laboratory at UMass Lowell. The laboratory conducted bench-top scale product development using 20-30 nm diameter bundles of single-walled carbon nanotubes (CNTs). The tasks evaluated in this study included weighing, mixing, sonicating, coating, drying, and cutting, which are common activities in most research and commercial production facilities. Weigh-out, mixing, and sonication were conducted on the bench-top without engineering controls, while coating, drying, and cutting were conducted inside a fume hood or a ventilated enclosure. The study results provide information on exposure potential and control for common nanomanufacturing processes. The research teams used direct-reading instruments to monitor the tasks in real time and collected filter samples to characterize released nanomaterials by microscopy and chemical analysis. Particle emissions can be identified by comparing the aerosol concentrations at source and in the personal breathing zone (PBZ) with background data. Most of the elemental carbon (EC) concentrations obtained from filter samples in this study were estimated values due to low mass (between the lower limit of detection and the limit of quantification) collected from short sampling times. All samples were within the range of EC concentrations observed in urban environments (0.6+/-0.72 microg/m3), and below the NIOSH proposed recommended exposure limit (REL). At the time of publication of this report, the NIOSH proposed REL for CNTs is 7 microg/m3. No meaningful particle releases were identified by the direct-reading instruments or filter sampling during CNT weigh-out without control measures. However, handling nanomaterials in dry powder form has been identified as a task that commonly results in worker exposure [Brouwer 2010; Dahm et al. 2012; Methner et al. 2010]. A ducted enclosure equipped with high efficiency particulate air (HEPA) filters is recommended to protect the operator during nanomaterial handling. Following the weigh-out, CNTs were mixed with a solution and dispersed by bath and probe sonication in an open beaker. The task of probe sonication increased EC concentrations at the source to nearly twice as high as background (0.46-0.79 microg/m3). Transmission electron microscopy (TEM) analysis identified CNT clusters in micro size from the sample collected by the ESPnano electrostatic precipitator after probe sonication. However, only one CNT was observed by TEM on the filter sample collected in the PBZ and none were found on the filter sample taken at the source. The inconsistent findings between the EC and TEM results could be interpreted as low mass collected on filters. 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 CNTs should be conducted inside a ventilated enclosure, such as a fume hood, to minimize the potential for worker exposure. The tasks of spin coating and substrate cutting were performed in a conventional fume hood and a ventilated enclosure, respectively. According to the EC and TEM data, the fume hood running at a high face velocity, around 171 cm/sec (337 ft/min), prevented particle emissions from the spin coating process. The ventilated enclosure was operated at a lower face velocity, around 100 cm/sec (51 ft/min), during the cutting of the CNT-coated substrates. TEM data confirmed that carbon fibers could be generated from cutting the substrate. However, EC results for the cutting task were confusing: a high EC concentration (2.63 microg/m3) was found in the PBZ but was not detectable near the source or at the background sampling locations.
Region-1; Control-technology; Engineering-controls; Nanotechnology; Exposure-assessment; Laboratory-techniques; Laboratory-testing; Emission-sources; Chemical-structure; Industrial-emission-sources; Industrial-processes; Chemical-analysis; Analytical-instruments; Analytical-processes; Microscopy; Breathing-zone; Sampling; Exposure-limits; Materials-handling; Electrostatic-precipitators; Filters; Exhaust-hoods