Welding Processes and Exposure Assessment Stephanie R. Carter, CIH University of Washington/Central Washington University CIHC 16th Annual Conference December 4, 2006 San Diego, CA

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Welding Processes and Exposure AssessmentStepha
nie 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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Introduction

• In 2020, welding will continue to be the
  preferred method of joining.
• Increases in
• Plastics, composites, new alloys
• Aluminum
• Robotic welding
• FCAW, GMAW

• RD challenges (heavy industry)
• Make the workplace more attractive by eliminating
  fumes, noise, and radiation
• Materials to replace Cr and Ni (Mn?)

Welding Technology Roadmap Vision, AWS/EWI (2000)
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Introduction

• One California shipyard
• SMAW 50
• GMAW/GTAW 5
• FCAW 20
• SAW 25

• Consumable electrodes purchased in 1991
• SMAW 45
• GMAW 34
• FCAW 17
• SAW 4

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

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

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Health Effects

• Pulmonary
• Decreased lung function
• Asthma
• Lung cancer
• Increase in infections

• Other
• Metal fume fever
• Conjunctivitis
• Nervous system
• Ocular Melanoma/skin cancer
• Fatality

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Health Effects

• 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

• 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 181155-157
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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)

Ocular Clothing
Welders 4 5X 3000X
Nearby workers 9X 13X
Area 5.5X
Tenkata,T. Collins, M. AIHAJ 58(1)33-38
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Tenkata,T. Collins, M. AIHAJ 58(1)33-38
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Sampling and Analysis

• Questions of old
• Placement of sampler
• Grinding influence
• Analysis
• Gravimetric
• Elemental
• As
• Pb
• Co
• Etc

• Newer questions
• Hexavalent chromium
• Particle size
• Analysis
• Radiation

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Sampling and Analysis

• Evaluation of the allowed samplers and procedures
  (ISO 10882-12001)
• 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
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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

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Comparison of Air Samplers to Dummy
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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

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Sampling and Analysis

• 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

• Nanoparticles or ultrafine particles
• lt100 nm
• Arise in workplace through
• Nucleation
• Combustion
• Saturated vapors
• Mechanical processes
• Nanophase technology

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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
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Sampling and Analysis
Process SSA (m2/g)
SMAW-MS 18.0
SMAW-SS 19.4
GMAW-MS 27.2
GMAW-SS 39.6
Process AED(µm)
SMAW-MS 0.59
SMAW-SS 0.46
GMAW-MS 0.25
GMAW-SS 0.25

• 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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Sampling and Analysis

• 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

Nygren,O. JEM,2002, 4,623-627
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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)
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Sampling and Analysis

• Welding
• DC lt 3mBq/m3
• AC lt 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

Gafvert, et al. Radiation Protection Dosimeter,
103(4)pp.349-357 (2003)
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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
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Quantity and particle size of emissions depends

• Welding process itself plus other variables
• Flux
• Gas Composition

• Operating conditions
• Travel speed
• Voltage
• Current
• Arc length
• Polarity
• Welding position
• Electrode angle
• Deposition rate

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By Electrode/Process
Development of Particulate and Hazardous Emission
Factors for Electric Arc Welding (AP-42,Section
12.19), 1994
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Emissions by Current
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
2001 Ship Production Symposium, EWI
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Effects on Particle Size
Zimmer,A. JEM, 2002(4),628-632
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Welding Emissions Control

• 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

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Controls Process Selection
Fume Generation Rate (g/min)
Fiore,S. Welding Journal, 2006, August, 38-42.
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Controls Fume Extractions Guns
Wallace, M., et al Applied OEH (2001),
16(8),771-779
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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
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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)
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Welding Processes and Exposure

• Effect of pulsed power

Wallace, et. Al Applied OEH,16(2), 93-97, 2001
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Hex chromium formation (in MIG welding)
Courtesty John Dennis
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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
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Courtesty John Dennis
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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 461,
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 461, 33-42. 2002
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Controls

• 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
Ojima, J. JOH,45(2)125-126 (2003)
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Turkem et. al, AWS, 2005
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(No Transcript)
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Turkem et. al, AWS, 2005