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


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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


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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)


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Consumable electrodes purchased in 1991: joining….

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


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Introduction joining….

  • Emerging Issues

    • Health Effects

    • Sampling/Analysis

    • Process Determinants of Exposure

    • Controls


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Pulmonary joining….

Decreased lung function

Asthma

Lung cancer

Increase in infections

Other

Metal fume fever

Conjunctivitis

Nervous system

Ocular Melanoma/skin cancer

Fatality

Health Effects


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Health Effects joining….

  • Exposure fatality

    • 2003 fatality in WA/Oregon

    • Oregon sales rep

    • Applied chromium and nickel based thermal sprays for 2 days in WA


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Health Effects joining….

  • 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


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Health Effects joining….

  • 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


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


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Questions of old joining….

Placement of sampler

Grinding influence

Analysis

Gravimetric

Elemental

As

Pb

Co

Etc…

Newer questions

Hexavalent chromium

Particle size

Analysis

Radiation

Sampling and Analysis


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Sampling and Analysis joining….

  • 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.



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Sampling and Analysis joining….

  • 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



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Sampling and Analysis joining….

  • 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


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Nanoparticles or ultrafine particles joining….

<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


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Sampling and Analysis joining….

  • 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


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Sampling and Analysis joining….

  • 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


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Analysis questions joining….

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


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Sampling and Analysis joining….

  • 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)


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Welding joining….

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)


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Sampling and Analysis joining….

  • 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


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Welding process itself plus other variables joining….

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


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By Electrode/Process joining….

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


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Emissions by Current joining….

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


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Emissions by Shielding Gas joining….

2001 Ship Production Symposium, EWI


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Effects on Particle Size joining….

Zimmer,A. JEM, 2002(4),628-632


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Process Selection joining….

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


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Controls – Process Selection joining….

Fume Generation Rate (g/min)

Fiore,S. Welding Journal, 2006, August, 38-42.


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Controls – Fume Extractions Guns joining….

Wallace, M., et al Applied OEH (2001), 16(8),771-779


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Effects of Ventilation joining….

  • 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


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Effect of Ventilation – Confined Spaces joining….

  • Success of either ventilation depends on

    • Work practices

      • backing out

      • backing in

    • Equipment maintenance

Wurzelbacher,S. Applied OEH, 17(11):735-740(2002)


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Welding Processes and Exposure joining….

  • Effect of pulsed power

Wallace, et. Al Applied OEH,16(2), 93-97, 2001


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Hex chromium formation (in MIG welding) joining….

Courtesty John Dennis


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Controls joining….

  • 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




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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.


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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


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Controls Hexavalent Chromium and Ozone in Tubular Wire Arc-welding Processes by Replacement of Potassium by Lithium or by Addition of Zinc.

  • Practical Issues

    • Creativity/ownership

    • Skills

      • To modify

    • Persistence

      • “not sufficiently applicable to moving work”

  • The future

    • Thinking outside the box


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Light Sensing Self-Adjusting Hood Hexavalent Chromium and Ozone in Tubular Wire Arc-welding Processes by Replacement of Potassium by Lithium or by Addition of Zinc.

Ojima, J. JOH,45(2):125-126 (2003)


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Turkem Hexavalent Chromium and Ozone in Tubular Wire Arc-welding Processes by Replacement of Potassium by Lithium or by Addition of Zinc. et. al, AWS, 2005


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Turkem Hexavalent Chromium and Ozone in Tubular Wire Arc-welding Processes by Replacement of Potassium by Lithium or by Addition of Zinc. et. al, AWS, 2005


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