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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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slide1

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

introduction
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

introduction3
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)

introduction4
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

introduction5
Introduction
  • Emerging Issues
    • Health Effects
    • Sampling/Analysis
    • Process Determinants of Exposure
    • Controls
health effects
Pulmonary

Decreased lung function

Asthma

Lung cancer

Increase in infections

Other

Metal fume fever

Conjunctivitis

Nervous system

Ocular Melanoma/skin cancer

Fatality

Health Effects
health effects7
Health Effects
  • Exposure fatality
    • 2003 fatality in WA/Oregon
    • Oregon sales rep
    • Applied chromium and nickel based thermal sprays for 2 days in WA
health effects8
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

health effects9
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

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

Sampling and Analysis
sampling and analysis12
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.

sampling and analysis14
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
sampling and analysis16
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
sampling and analysis17
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
sampling and analysis18
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

sampling and analysis19
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

sampling and analysis20
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

sampling and analysis21
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)

sampling and analysis22
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)

sampling and analysis23
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

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

Quantity and particle size of emissions depends
slide25

By Electrode/Process

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

emissions by current
Emissions by Current

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

emissions by shielding gas
Emissions by Shielding Gas

2001 Ship Production Symposium, EWI

effects on particle size
Effects on Particle Size

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

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

Welding Emissions Control
controls process selection
Controls – Process Selection

Fume Generation Rate (g/min)

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

controls fume extractions guns
Controls – Fume Extractions Guns

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

effects of ventilation
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

effect of ventilation confined spaces
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)

welding processes and exposure
Welding Processes and Exposure
  • Effect of pulsed power

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

controls
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

slide39

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.

slide40

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

controls41
Controls
  • Practical Issues
    • Creativity/ownership
    • Skills
      • To modify
    • Persistence
      • “not sufficiently applicable to moving work”
  • The future
    • Thinking outside the box
light sensing self adjusting hood
Light Sensing Self-Adjusting Hood

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

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