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In-depth survey report: case study: modifying processes to control exposure to engineered nanographene particles.
Lo L-M; Heitbrink W; Devine E
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 356-15a, 2013 Jan; :1-32
This report summarizes the results of reducing exposure by adopting process changes at a nanomanufacturing site producing graphene platelets. Although the length and width of these platelets are on the order of micrometers, the platelet thickness is under 100 nanometers (nm). Aerosol instruments - including an aerosol photometer, a fast mobility particle sizer, and an aerodynamic particle sizer - were used to measure concentrations during routine product refining and post-processing operations. In some cases, worker activities were recorded on video concurrently with the concentration measurements. The purpose of these measurements was to understand the relationship between concentration and worker activity. Surface temperature measurements were made for two reasons: (1) temperature affects ventilation system performance and (2) surface temperatures in excess of 44 degrees C pose a risk of a contact burn. During product refining, dust exposures occurred during removal of collection containers from the processing equipment for product harvesting and during transfer of powder from the collection containers to storage containers in a ventilated booth. The emissions from product harvesting can be avoided by allowing the process to rest longer (at least 15-30 minutes in this case). This process change can effectively mitigate dust emissions up to 97.5% (reducing dust concentrations from 2.4 to 0.06 mg/m3 after a 30-minute delay). During routine operations, the collection equipment surface temperatures can exceed 70 degrees C. A 20-minute cooling time would allow surface temperatures on the sidewall of the collection containers to fall below 44 degrees C and thus reduce the risk of a contact burn during product harvesting. The ventilated booth, operated at a face velocity of 120 feet per minute (fpm), generally contained the aerosol generated during the transfer process, but dust exposures were elevated from about 0.03 to as much as 0.13 milligrams per cubic meter (mg/m3) when the worker poured the remaining powder into the storage container. This slight exposure peak could be caused by the fall of the powder or by the obstruction of the booth's inlet. Air from this booth is discharged back into the workplace, and this was probably a source of dust emissions. The efficiency rating of the booth's filters was Minimum Efficiency Reporting Value (MERV) 11, too low to efficiently collect the dust generated by handling the product. Manual cleaning of process equipment and material handling inevitably cause dust exposures. High particle concentrations generated from process tank maintenance can be largely reduced with process ventilation. The case study has shown that ventilation exhaust can result in 83% reduction of dust. In the post-processing treatments, cleaning the fiberglass plugs caused concentration spikes of nearly 2 mg/m3, as compared to a background concentration of 0.05 mg/m3. At times, the workers would break up clumps of powder in the product collection containers, causing concentration spikes of 1-7 mg/m3. Good work practices are required to prevent dust emissions, but a down-flow ventilated booth is recommended to minimize exposure and contain particulate emission during the post-treatment process.
Control-technology; Engineering-controls; Nanotechnology; Industrial-processes; Industrial-exposures; Analytical-instruments; Analytical-processes; Particle-aerodynamics; Particulate-sampling-methods; 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; Case-studies; Exposure-assessment; Employee-exposure; Platelets; Photometry; Measurement-equipment; Industrial-equipment; Temperature-measurement; Dust-exposure; Work-operations; Work-practices; Storage-containers; Ventilation-equipment; Materials-handling
Field Studies; Control Technology
NTIS Accession No.
National Institute for Occupational Safety and Health
Page last reviewed: April 12, 2019
Content source: National Institute for Occupational Safety and Health Education and Information Division