In-depth survey report: evaluation of engineering controls for manufacturing nanofiber sheets and yarns.
Lo L-M; Dunn KH; Hammond D; Almaguer D; Bartholomew I; Topmiller J; Tsai CS-J; Ellenbecker M; Huang C-C
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 356-11a, 2012 Jan; :1-33
This field study addresses the evaluation of exposures and control measures used in a nanomanufacturing facility. The purpose of this study was to investigate the ability of engineering controls to mitigate exposure to engineered nanomaterials during nanomanufacturing. Direct-reading instruments were used to measure the baseline levels of airborne particles and monitor activities in this facility. Integrating all instruments on a mobile sampling cart allowed for the monitoring of spatial and time variation of nanoparticles from processes or tasks. At this study site, carbon nanotube products were synthesized in furnaces contained within ventilated enclosures. During normal operation, enclosure doors were often kept open to allow access and reduce heat built up by these hot processes. In addition, the low enclosure exhaust flow rates resulted in release of fugitive nanoparticles into the workplace. High concentrations of nanoparticles released during furnace maintenance and product harvesting were observed because both tasks required partially and fully opening furnace chambers. Compared to background (approximately 1.0x105 #/cm3), the task of furnace maintenance caused a twofold increase in nanoparticle concentration. Product harvesting also resulted in the release of nanoparticle concentrations at least one order of magnitude (approximately 3.0x105 #/cm3) higher than background (approximately 2.0x104 #/cm3). Two ventilation systems referred to as exhaust ventilation systems (EVSs) were installed in the furnace room. The EVSs, with integral filters connected to the furnace enclosures, were used in the production area to remove fugitive nanoparticles. Two identical Fast Mobility Particle Sizers were used to assess the filtration performance of the EVSs. One EVS serving two furnaces had higher filtration efficiency (95.80% on average) than the other EVS serving seven furnaces (92.73% on average). The filter inefficiency could be the result of bypass from damaged filter media, faulty seals, and/or sheet metal leaks. Measurements from the office and laboratory areas also suggested that most nanoparticles below 100 nanometers found in non-production areas likely migrated from the production area. According to the TEM analysis and report done by the University of Massachusetts Lowell (UMass Lowell) researchers, most nanoparticles released from the production processes were not engineered nanomaterials, but soot particles. A second visit by the UMass Lowell team showed that nanoparticle concentrations in the non-production areas decreased after improvement of facility ventilation. Those test results are also summarized in a separate report. This in-depth field survey provides important observations and measurements regarding ventilated enclosures used during nanomanufacturing. Nanoparticle emissions can be reduced by optimizing the design and operation parameters of the engineering controls and by maintaining a preferred pressurization scheme inside the facility. Maintaining the CNT production area under negative pressure relative to the rest of the plant can be done by setting a flow differential of 5%, but no less than 1,416 liter per minute (i.e., 50 cubic feet per minute), between supply and exhaust flow rates. Using higher exhaust flow rates and keeping enclosures closed should reduce particle emissions. Better containment design to accommodate heat and access for workers can also improve the control efficiency of enclosures. Because hazards and risks related to health effects from exposure to engineered nanomaterials are still unclear, effective control of nanoparticle emissions in the workplace is highly recommended.
Control-technology; Engineering-controls; Nanotechnology; Industrial-equipment; Industrial-exposures; Analytical-instruments; Analytical-processes; Particle-aerodynamics; Particulate-sampling-methods; Airborne-particles; Aerosol-particles; Monitors; Industrial-dusts; Emission-sources; Workplace-studies; Air-contamination; Ventilation-systems; Air-pressure; Air-quality; Air-quality-control; Monitoring-systems; Ventilation; Exposure-levels;
Author Keywords: Engineering Controls; Engineered Nanomaterials; Control Evaluation
Field Studies; Control Technology
NTIS Accession No.
National Institute for Occupational Safety and Health