Air Sampling Approaches for Engineered Nanoparticles used in
Air Sampling Approaches for Engineered Nanoparticles used in the Semiconductor Industry Michele N. Shepard, PhD, MS, CIH QEEN II: 2nd Quantifying Exposure to Engineered Nanomaterials from Manufactured Products Workshop, Washington, D.C. October 9, 2018 Occupational Health, Safety & Environmental Consultants ALBANY, NY n ATLANTA, GA n BOSTON, MA n ERIE, PA n NEW YORK, NY n PHILADELPHIA, PA n SYRACUSE, NY 1 Workplace Exposure Assessment Consider risks from engineered nanomaterials (ENMs) across the product lifecycle, applying a management system framework: Hazard Characterization Exposure Assessment Risk Characterization
Risk Management Evaluate data on physiochemical properties and toxicity. Apply the most practical method to identify and evaluate data on exposure scenarios. Air sampling to quantify exposures Follow banding models, screening methods, other recommended approaches. Consider uncertainty. Apply the hierarchy of controls and confirm protection. Communicate risks and controls. Periodically re-evaluate and improve. 2 Air Sampling Approaches Screening level to more comprehensive approaches, depending on objectives. Common metrics include: Number Mass Size *Particle surface area is a key factor in toxicity but not as commonly measured in workplace exposure assessments. Screening with
direct-reading instruments Filter-based samples: mass and composition Electron microscopy (TEM/EDX): size, shape, number, composition See the AIHA Fact Sheet: Nanoparticle Sampling and Analysis (2016) 3 Air Sampling Challenges Measurement Commonly involves multiple methods/instruments
Electron microscopy methods resource-intensive Validated methods limited Time-resolved devices non-specific Background characterization for number metric Differentiation from incidental ultrafine particles Results Interpretation Metrics and correlation to biological activity Consensus lacking on size ranges to include and data analysis methods Comparative values limited Images: TSI CPC; TSI SMPS 4 Workplace Exposure Scenario: Semiconductor Fabrication Chemical Mechanical Planarization (CMP) ENMs are used as abrasives in wafer polishing processes in semiconductor fabrication Product formulations: typically include amorphous
silica, aluminum oxide, or cerium oxide nanoparticles Physical forms at semiconductor fabs: slurry, powder depending on site *or embedded on pad Activity Duration Frequency 1.Operate bulk slurry delivery system 0.25-1 hr Daily/ weekly 2.Operate CMP Tool 2-8 hrs
Daily 3.Set up CMP Tool < 0.5 hr Daily 4.Conduct PM on CMP Tool 5.Change pre-filter on CMP WWT system 2-8 hrs Monthly ~ 0.5 hr Monthly < 1 hr As needed
6.Clean up slurry overflow or spill 5 Exposure Assessment Approach used for an academic research project Sampling approach applied in a semiconductor workplace. Air sampling approach used in Shepard and Brenner, Ann Occ Hyg, 2014 and surface sampling in Shepard and Brenner, Int J Occup Environ Health, 2014. Direct-Reading Instruments Air Sampling Qualitative Assessments Optical Particle Counter Optical Particle Scanning Mobility
Counter Particle Sizer Filter-Based Samples Surface Sampling Condensation Particle Counter Microvacuum Wipe ICP-AES and Gravimetric TEM/EDX ICP-AES: inductively coupled plasma - atomic emission spectroscopy. TEM/EDX: transmission electron microscopy/energy dispersive x-ray spectroscopy. Figure: Shepard M. 2014 6 Applicable Reference Values: Number
Benchmark levels above background exposures for biopersistent particles 1-100 nm (IFA, 2009, 2011) 20,000 p/cc for granular ENMs with density > 6,000 kg/m3 40,000 p/cc for granular ENMs with density < 6,000 kg/m3 20,000 p/cc above background (BSI, 2007) 7 Applicable Reference Values: Mass 0.3 mg/m3 TWA for nanoscale titanium dioxide, for up to 10 hours (NIOSH CIB 63, 2011) 0.3 mg/m3 TWA as an upper bound categorical guideline adjusted for other poorly soluble low toxicity (PSLT) nanoparticles (Schulte et al., J Nanopart Res 2010; NIOSH CIB 63, 2011) 0.06 x Bulk OEL for insoluble, non-fibrous ENMs (BSI, Nanotechnologies-Part 2, 2007) 8 Screening Approach
used by EHS practitioners Sampling approach currently being applied at three semiconductor manufacturing sites in the U.S. Considerations in selecting initial assessment approach: Materials of interest: ubiquitous (silica, alumina) Clean environments with high degree of process control Short duration tasks with potential for inhalation exposure Limited budget/resources (for TEM or multiple DRI sets) Limits of detection and instrument specifications Instruments available for rental No site-specific baseline data 9 Screening Approach used by EHS practitioners Screening Methods and Action Limits:
Number: task measurements with condensation particle counter; probe positioned in worker breathing zone 20,000 p/cc above background Safety factors: measuring particles 20 to~1000 nm and comparing to reference value for particles <100 nm; non-specific Mass: personal breathing zone task measurements with laser photometer with cyclone 0.03 mg/m3 TWA Instrument lower size range: 0.1 m Safety factors: set at 10% of NIOSH REL for nanoscale TiO2; measuring respirable particle mass; non-specific 10 Progress and Future Directions General increase in amount and quality of data from toxicology studies Improved capability to collect, evaluate and interpret air sampling data with advances in:
Occupational exposure limits (OELs) or banding approaches Method for setting OELs Instrumentation/sampling devices Guidelines for air sampling and analysis Image credit: NIOSH. Agglomerates/aggregates of amorphous silica nanoparticles. [NIOSH Nanotechnology Field Team report to CNSE, 10.25.11] 11 Acknowledgements and Disclaimers For previous research in this area: Funding provided by the US EPA STAR Fellowship FP-91730701 (2011-2014). The views expressed in this presentation are my own and have not been reviewed or endorsed by the EPA. Exposure assessments of semiconductor applications conducted at SUNY Albany CNSE (2010-2014), with acknowledgements to Dr. Sara Brenner and group members. Funding for air and surface sampling equipment and laboratory analysis provided by the NanoHealth and Safety Center and SEMATECH. No information presented is intended to provide consulting advice on specific scenarios or applications; any use or adaptation of this information is at the risk of the user. This presentation is intended to share experiences and observations on air sampling methods used to assess and quantify airborne concentrations and potential workplace exposures to engineered nanoparticles, and references current guidelines and standards.
12 Questions or comments: Michele N. Shepard, PhD, MS, CIH [email protected] 518-490-2261 Occupational Health, Safety & Environmental Consultants ALBANY, NY n ATLANTA, GA n BOSTON, MA n ERIE, PA n NEW YORK, NY n PHILADELPHIA, PA n SYRACUSE, NY 13
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