In-depth survey report: engineering controls for nano-scale graphene platelets during manufacturing and handling processes.
Lo L-M; Hammond D; Bartholomew I; Almaguer D; Heitbrink W; Topmiller J
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 356-12a, 2011 Dec; :1-54
This report summarizes the study results of an evaluation of engineering controls for manufacturing and handling graphene nanoplatelets in the workplace. Direct-reading instruments, the Fast Mobility Particle Sizer (FMPS) spectrometer, the Aerodynamic Particle Sizer (APS) spectrometer, a gravimetric aerosol monitor (DustTrak), and a black carbon monitor were used to provide real-time characterization of the airborne particle concentrations released from the processes in the production areas. For the refining process, measurement results indicated that larger size particles (or agglomerated nanomaterials) at 2.3 micrometers (um) were released into the workplace. These critical tasks included raw material preparation, product harvesting, and product transfer. There was no control measure for material preparation and product harvesting. Product transfer was performed inside a ventilated enclosure operated at an average face velocity of 78 feet per minute (fpm). Fume hoods and glove boxes were used in the laboratory areas. No noticeable particle emissions were measured by the direct-reading instruments when these control measures were used for research and development (R&D) activities. In the post-treatment process, the tasks of tube cooling and insulator removal from tubes generated high concentrations with peak number concentrations higher than 2x106 particles per cubic centimeter (#/cm3); most of the particles were less than 15 nanometers (nm) in diameter. The test results also demonstrated that extending tube cooling time can lower nanoparticle concentrations released from this process. The existing local exhaust ventilation located on top of a reactor did not effectively reduce particle emissions, because of the low operating flow rate (96 cubic feet per minute, cfm) and no appropriate receiving hood to capture airborne contaminants. Special attention should be paid to the high particle concentrations found in the non-production areas. The nanoparticle concentrations with peaks at 10 and 70 nm in the R&D laboratories were 19%-64% higher than the background concentrations found in the production areas (1X104 #/cm3). The results of particle size analysis for the office areas showed that the fine particles less than 560 nm were lognormally distributed at 25-40 nm in different locations. Flexible enclosures are recommended to prevent releases during material preparation and product harvesting in the refining process. Higher air velocities are preferred to provide good containment during product transfer, though the average face velocity of the enclosure meets the recommended criteria from the Occupational Safety and Health Administration (OSHA) (60-100 fpm) and the American Conference of Industrial Hygienists (ACGIH) (75-100 fpm). Modifying the existing canopy hood or using an isolated work area (e.g., downflow booth) for the post-treatment process are also suggested to mitigate particle emissions. Because the particle concentrations in both the production areas and the non-production areas are on the same order of magnitude, using separate ventilation systems and maintaining a positive pressure for the non-production areas are recommended. A preferred pressure scheme of 0.04 +/- 0.02 inches of H2O [ACGIH, 2010] can improve air quality. No specific regulatory occupational exposure limit (OEL) for nanographene platelets exists, but improved containment is recommended to lower potential risks associated with these nanomaterials. Installation of appropriate engineering controls in the workplace can protect workers during manufacturing and handling of the engineered nanomaterials.
Control-technology; Engineering-controls; Nanotechnology; Industrial-equipment; Industrial-exposures; Analytical-instruments; Analytical-processes; Particle-aerodynamics; Particulate-sampling-methods; Spectrographic-analysis; Airborne-particles; Aerosol-particles; Monitors; Refineries; Industrial-dusts; Industrial-factory-workers; Emission-sources; Workplace-studies; Air-contamination; Ventilation-systems; Air-pressure; Air-quality; Air-quality-control
Field Studies; Control Technology
NTIS Accession No.
National Institute for Occupational Safety and Health