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Introduction

Welding Processes and Exposure Assessment Stephanie R. Carter, CIH University of Washington/Central Washington University CIHC 16 th Annual Conference December 4, 2006 San Diego, CA. Introduction. Need for welders “Where have All the Welders Gone, As Manufacturing and Repair Boom?”

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Introduction

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  1. Welding Processes and Exposure AssessmentStephanie R. Carter, CIHUniversity of Washington/Central Washington UniversityCIHC 16th Annual ConferenceDecember 4, 2006San Diego, CA

  2. Introduction • Need for welders • “Where have All the Welders Gone, As Manufacturing and Repair Boom?” • Average age of welders = 54 • 10% decline in number of welders since 2004 • By 2010, demand for welders may outweigh supply by 200,000 • Need more trained welders Wall Street Journal 8/15/2006

  3. In 2020, welding will continue to be the preferred method of joining…. Increases in Plastics, composites, new alloys Aluminum Robotic welding FCAW, GMAW R&D challenges (heavy industry) Make the workplace more attractive by eliminating fumes, noise, and radiation Materials to replace Cr and Ni (Mn?) Introduction Welding Technology Roadmap: Vision, AWS/EWI (2000)

  4. Consumable electrodes purchased in 1991: SMAW – 45% GMAW – 34% FCAW – 17% SAW – 4% One California shipyard SMAW – 50% GMAW/GTAW – 5% FCAW – 20% SAW – 25% Introduction Development of Particulate and Hazardous Emission Factors for Electric Arc Welding (AP-42,Section 12.19), 1994

  5. Introduction • Emerging Issues • Health Effects • Sampling/Analysis • Process Determinants of Exposure • Controls

  6. Pulmonary Decreased lung function Asthma Lung cancer Increase in infections Other Metal fume fever Conjunctivitis Nervous system Ocular Melanoma/skin cancer Fatality Health Effects

  7. Health Effects • Exposure fatality • 2003 fatality in WA/Oregon • Oregon sales rep • Applied chromium and nickel based thermal sprays for 2 days in WA

  8. Health Effects • UV and welding • Case-control studies link ocular malignancy with welding • Arc welding produces full spectrum of UVR • Short distances from source • Controls • Clothing and sunscreen • Aluminum welders need highest protection Dixon, A., B. Dixon. MJA 2004; 181:155-157

  9. Health Effects • UV and welding • Welding helmet allows UV in from sides and top, problem for • Highly reflective areas, multiple welders • Exposure assessment (compared to ACGIH MPE) Tenkata,T. Collins, M. AIHAJ 58(1)33-38

  10. Tenkata,T. Collins, M. AIHAJ 58(1)33-38

  11. Questions of old Placement of sampler Grinding influence Analysis Gravimetric Elemental As Pb Co Etc… Newer questions Hexavalent chromium Particle size Analysis Radiation Sampling and Analysis

  12. Sampling and Analysis • Evaluation of the allowed samplers and procedures (ISO 10882-1:2001) • Different samplers UK, German, HSE • French, Danish (similar to U.S.) • Left or right side positioning • Lapel vs helmet sampling • Grinding effects • Surrogate measures of fume composition Chung, et al., Applied Occupational and Environmental Hygiene, 14((107-118), 1999.

  13. Sampling and Analysis

  14. Sampling and Analysis • Results (Chung, et al) • Little difference between samplers • Variable effect from right vs. left • All collected grinding dust • Percent of individual contaminants in fume different than MSDS • Lapel sampling • Larger ratios than in helmet sampling • Collected more grinding dust • Except for HSE

  15. Comparison of Air Samplers to Dummy

  16. Sampling and Analysis • Hexavalent Chromium • OSHA-215 Revision 2 • Cr(VI) samples collected on PVC filters from welding operations must be analyzed within 8 days of sampling • NIOSH Methods (7605 and 7703) • Higher recoveries of CrVI compared to OSHA-215 although not statistically significant • NIOSH 7703 Chromium, Hexavalent, by Field-Portable Spectrophotometry • No evidence of CrVI reduction to CrIII perhaps related to ultrasonic extraction • QA/QC

  17. Nanoparticles or ultrafine particles <100 nm Arise in workplace through Nucleation Combustion Saturated vapors Mechanical processes Nanophase technology Deposition and alveolar clearance differences Negligible in terms of mass concentration Better to look at surface area or number No personal monitoring devices available Estimation of SSA by respirable sampling Sampling and Analysis

  18. Sampling and Analysis • Particle size • Number or surface area of particles vs. mass • Ultrafine particles may have greater biological effect than an equivalent mass of larger particles • Count median diameter of SMAW = 120 nm • Mass median diameter of SMAW = 590 nm • Clusters behavior determined by AED, but • Primary particles more surface area Hewitt,P. AIHAJ,56(2)128-143

  19. Sampling and Analysis • Total lung deposition of GMAW estimated to be 60% greater than for SMAW • GMAW deliver 3 times the particle surface area to lungs • Particle surface chemistry and lung clearance rates vary as well Hewitt,P. AIHAJ,56(2)128-143

  20. Analysis questions On-site analysis Portable micro-balances (0.1 mg possible) Portable XRF Non-destructive, filters, wipes, bulks Acceptable LOD except for Cobalt and Arsenic with TWA samples (400 L) No speciation Analysis questions Laboratory analysis PIXE analysis ICP-AES/MS Digestion protocol Sampling and Analysis Nygren,O. JEM,2002, 4,623-627

  21. Sampling and Analysis • Thorium and GTAW • Tungsten electrodes can contain 1-4% Thorium • 2% most common (WT-20) • 232Th, 228Th, 230Th • Alpha emitter • Exposure potential • “Vapors” during welding • Grinding to shape tip Gafvert,T. et.al, RPD,103(4),349-257(2003)

  22. Welding DC < 3mBq/m3 AC < 10 mBq/m3 Up to 141 mBq/m3 for inexperienced Total dust, outside helmet Grinding 5 mBq/m3 Respirable dust Dose estimates Welding 0.3 to 1 mSv Grinding 10 µSv to 63 µSv Sampling and Analysis Gafvert, et al. Radiation Protection Dosimeter, 103(4)pp.349-357 (2003)

  23. Sampling and Analysis • TIG welding and Thorium • Controls • LEV • No contact with open cuts or wounds • Clean-up • No eating, drinking, smoking • Thorium-free tungsten electrode • CeO2 (2%) or La2O3 (1-2%), Zr (1%), Pure Tungsten The Proper Selection and Preparation of Tungsten Electrodes for Arc Welding, www.diamondground.com

  24. Welding process itself plus other variables Flux Gas Composition Operating conditions Travel speed Voltage Current Arc length Polarity Welding position Electrode angle Deposition rate Quantity and particle size of emissions depends

  25. By Electrode/Process Development of Particulate and Hazardous Emission Factors for Electric Arc Welding (AP-42,Section 12.19), 1994

  26. Emissions by Current Development of Particulate and Hazardous Emission Factors for Electric Arc Welding (AP-42,Section 12.19), 1994

  27. Emissions by Shielding Gas 2001 Ship Production Symposium, EWI

  28. Effects on Particle Size Zimmer,A. JEM, 2002(4),628-632

  29. Process Selection from SMAW to GMAW Fume extraction welding gun Engineering controls Local exhaust Dilution Process modification Power variation (GMAW) Low-fume electrodes Composition changes to minimize spatter or to shift metals to slag Welding Emissions Control

  30. Controls – Process Selection Fume Generation Rate (g/min) Fiore,S. Welding Journal, 2006, August, 38-42.

  31. Controls – Fume Extractions Guns Wallace, M., et al Applied OEH (2001), 16(8),771-779

  32. Effects of Ventilation • Elemental with ventilation • Arsenic – 2 of 16 exceeded OSHA PEL • Hexavalent chromium – Reduced exposures, but still above 50 µg/m3 Wallace, M., et al(2002), Applied OHE 17(3),145-151

  33. Effect of Ventilation – Confined Spaces • Success of either ventilation depends on • Work practices • backing out • backing in • Equipment maintenance Wurzelbacher,S. Applied OEH, 17(11):735-740(2002)

  34. Welding Processes and Exposure • Effect of pulsed power Wallace, et. Al Applied OEH,16(2), 93-97, 2001

  35. Hex chromium formation (in MIG welding) Courtesty John Dennis

  36. Controls • Process modification • Various strategies explored over 10 years • 1. Adding some substance to: • a) the consumable to react with O3 before it reacts with Cr • b) increase the O3 destroying wavelengths of UV • c) reduce the O3 forming wavelengths of UV • 2.Using a first or second shield gas or a gas in the macro environment of the arc to • a) absorb O3 forming wavelengths • b) react rapidly with O3. • 3. Use a suitable ‘shroud’ to block UV transmission • 4. Engineering modification of welding equipment and welding parameters to produce weld conditions which emit little Cr (VI). Courtesty John Dennis

  37. Courtesty John Dennis

  38. Courtesty John Dennis

  39. Dennis JH et al. Control of Exposure to Hexavalent Chromium and Ozone in Gas Metal Arc Welding of Stainless Steels by use of a Secondary Shield Gas. Annals of Occupational Hygiene 46:1, 43-48. 2002.

  40. Dennis JH et al. Control of Occupational Exposure to Hexavalent Chromium and Ozone in Tubular Wire Arc-welding Processes by Replacement of Potassium by Lithium or by Addition of Zinc. Annals of Occupational Hygiene 46:1, 33-42. 2002

  41. Controls • Practical Issues • Creativity/ownership • Skills • To modify • Persistence • “not sufficiently applicable to moving work” • The future • Thinking outside the box

  42. Light Sensing Self-Adjusting Hood Ojima, J. JOH,45(2):125-126 (2003)

  43. Turkem et. al, AWS, 2005

  44. Turkem et. al, AWS, 2005

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