APPROACHES TO WELDING EXPOSURE ASSESSMENT AND CONTROL

Transcription

1 APPROACHES TO WELDING EXPOSURE ASSESSMENT AND CONTROL Noah Seixas Marissa Baker Chris Simpson Boris Reiss Jeff Walls Chris Warner Jane Pouzou Department of Environmental and Occupational Health Sciences University of Washington

2 Outline Manganese and Welding Mn content of welding fume Particle size distributions/deposition What the literature tells us about exposure Hobson, Liu and Pesche What the literature tells us about Biomarkers Our biomarker study Design Preliminary Findings Potential new directions Hair LA-ICPMS Recommendations for going forward

3 Welding Processes A joining process that produces coalescence of materials by heating them to the welding temperature, with or without the application of pressure alone and with or without the use of filler metal. Jefferson s Welding Encyclopedia, 18 th Edition, Robert L. O Brien, Editor, American Welding Society, Miami, FL >80 Welding Process Types Oxy-Fuel (Welding or Cutting) Arc, or SMAW (Shielded Metal Arc) MIG or GMAW (Gas Metal Inert Gas) FCAW (Flux-Cored Arc) TIG (Gas Tungsten Arc)

4 Welding Risks Overview Estimated 3 million welders and cutters globally About 400,000 in the US; 140,000 full time Estimates 800,000 full-time welders worldwide Most from small employers Risks Acute Injuries Musculoskeletal Electrical Burns UV Gasses CO, CO 2, Asphyxiants Fume Fe, Mn, Cr 6, Ni, Cd, Zn From: Base metal, Filler material Fluxing agents Coatings (Pb, epoxies, etc.)

5 Fume-related health effects Respiratory COPD Siderosis Asthma Cancer Especially lung Presumably from Cr6, Ni in stainless steels Neurological Manganism Parkinson s like syndrome Are welders at increased risk of Parkinson s Disease? At what level of exposure are neurological effects present?

6 Standards and Guidelines Agency Welding Fume Manganese ACGIH 5 mg/m3 (rescinded) 0.1 mg/m3 Inhalable 0.02 mg/m3 Respirable (proposed) NIOSH ALARA 1 mg/m3 OSHA 5 mg/m3 (rescinded) 5 mg/m3 (C) Ger. MAK (TRGS 900) 0.2 mg/m3 Inhalable 0.02 mg/m3 Respirable (proposed) EU 2010 (SCOEL/SUM/127) 0.2 mg/m3 inhalable 0.05 mg/m3 respirable

7 Exposure Assessment Approaches Epidemiologic exposure assessment e.g., Years worked as welder Industrial Hygiene Air Sampling Personal exposure monitoring in breathing zone Total, Inhalable or Respirable fraction sampling? Inside or Outside the hood? Analyte Particulate Mass Concentration Metal-specific concentration Biomonitoring? - especially for Mn Urine Blood* Hair Nails Brain

8 SEM of SMAW fume on polycarbonate filters

9 Particle Size Distributions of Welding Fume From: Hewett, 1995 From: Pesche, et al, 2012 (1-1 line added by eye)

10 PSDs: Primary vs. Agglomerates Richman et al, Journal of Aerosol Science, GMAW samples STEM microscopy Energy dispersive X-ray spectroscopy by primary particle size Primary particles CMD: nm Agglomerates: CMD: nm Mn Abundance (relative to Fe): 6 (+3)% Only slight increase in Mn content with increasing PS Conclusion: Respirable or inhalable fraction samples are adequate: multiple fractions add very little information Primary particle size may be relevant to potential dissolution, absorption, translocation and dose

11 Total Fume Outside Helmet Monitoring: Inside Vs Outside? Some studies show lower levels inside helmet Inside Vs. outside (via PVC & gravimetric) Corr. Coeff.: 0.97 Range inside: 6.6 mg/m 3 to 19.0 mg/m 3. Range outside: 7.1 mg/m 3 to 23.0 mg/m Figure 6 Paired Total Fume Samples Inside Helmet and Outside Helmet with PVC Filters y = 1.067x From Harris, AIHCE PDC, (Total Fume Inside Total Helmet Fume with Inside PVC, Helmet Total Fume Outside Helmet with PVC) Linear ((Total Fume Inside Helmet with PVC, Total Fume Outside Helmet with PVC))

12 Mn vs. Particulate by welding type Overall R 2 =0.51 Coef. CI Oxy (0.001, 0.007) Stick (0.012, 0.020) MIG (-0.008, 0.043) TIG (-0.006, 0.012) Dual Shield (0.018, 0.053) Inner Shield (-0.004, 0.033) Cutting/Grinding (-0.001, 0.003)

13 Estimating exposure Requires quantitative understanding of Factors associated with exposure Including interactions between factors Requires a comprehensive dataset Large number of samples Covering all conditions/processes one might encounter Data on all pertinent factors Repeated measures if possible Exposure Determinants Modeling

14 Factors Associated with (and predictive of) Mn Exposure among welders Hobson Liu Pesche Dataset Published Literature Literature, NIOSH HHEs, TWI Novel dataset, German Industry Years Covered # Samples 1957 (in 60 means) Sample Types Personal Personal/Area Personal Sample Duration Full shift, >6hr ST, FS: <>1hour hours Size Fraction Total Total Respirable Dependent Variable ln(mn) or ln(pm) ln(mn) ln(mn) Model Regression on means Mixed Model on samples Regression on samples Number of Parameters Overall Mean (SD) (mg/m3) 0.26 (+0.36) (+1.49) (IQR, )

15 Modeled Mn (mg/m3) Exposure Estimates

16 What about biomonitoring? For specific constituents (e.g., metals, e.g., Mn) Benefits Closer to biological target Focused on individual-specific dose Accounts for deposition, absorption, etc. Accounts for duration and intensity Accounts for PPE use Disadvantages Individual-only Toxicokinetics confound interpretation Biological regulation may obscure relationships Background levels obscure low levels

17 Selected studies: Air vs. Blood Mn Apostoli et al Blood Mn v. Mn in air Smith et al Blood Mn v. Mn in air by exposure groups, after Luccini, 1999

18 Mean MnB vs. Mn A (n=24 papers)

19 Mean MnB vs. ln Average MnA (n=22 papers)

20 Limitations of current biomarker studies Mostly cross-sectional Poor temporal specificity in relation between airborne and biomarker measures No unexposed baseline LODs are problematic Especially for urine and plasma measures Relationship between Mn and Fe status poorly addressed

21 Mn biomarkers in welding school students Enrolled and tested at baseline Little prior exposure Monitoring over 5 quarter sequence Daily, Weekly, Across Quarter Target 80 Student Welders Air, Blood, Urine, Hair and MRI (subset) Temporally specific modeling for each biomarker

22 Air Mn concentration by weld type

23 Cross shift changes in MnB by Measured Air Manganese Exposure

24 Cross week change in MnB by Estimated Cumulative Air Manganese Exposure

25 Cross Quarter (3 mo) by Estimated Cumulative Air Manganese Exposure

26 Hair as a biomarker Background Pro: Hair has been used as biomarker Growth rate is estimated to be about 1 cm / month Cons: Not all substances have an affinity for hair i.e. Manganese?

27 Descriptive statistics of log transformed hair levels (mg/g) by duration in program N=34 N=22 N=11 N=8 N=4 (180,270] (0,90] (90,180] (270,360] (360,inf]

28 LA-ICPMS for time-resolved metals in hair From Stadlbauer, et al, Anal Bioanal Chem, 2005.

29 Welding Fume Deposition on Hair

30 Suggested Directions for Mn Exposure Assessment Air Sampling Mn and Particulate Mass Combined with Task-specific exposure model Detailed work task and exposure questionnaire Biological monitoring Blood Promising? Hair/nails by LA-ICPMS shows promise In vivo neutron activation analysis also may be possible

31 31 MOTIVATION Shipyard welders routinely receive exposures to weld fume that exceed occupational limits Important determinants: weld method & type of space Barriers to effective fume control Dynamic work environment Work in spaces that restrict air movement Practical general ventilation guidelines relevant to shipyard welding are limited OSHA General Industry 2,000 cfm/worker in spaces < 10,000 ft 3 Unproven and unlikely to be effective overall Local Exhaust Ventilation Ineffective in most dynamic processes Can t effectively position Too close affects weld quality

32 32 Shipyard Ventilation Study AIMS: 1. Develop a set of general ventilation guidelines 2. Teach the guidelines to shipyard welders 3. Evaluate the adoption of the guidelines

33 33 Study Shipyard Vigor Industrial (formerly Todd Pacific Shipyard) USS Polar Star USS Davis Nobel Kulluk Nobel Discoverer WA State Ferry

34 Recommended ventilation guidelines 34

35 Recommended ventilation guidelines 35

36 36 Shipyard observations Randomly observe welders for 10 minutes Measure BZ particular exposure (dataram) Observe Space characteristics Size, configuration, enclosure, location of welding Welding processes Ventilation characteristics Exhaust vs. Supply # mechanical units, estimate CFM Proximity Local, regional, general Mixing/Cross-draft Short-circuiting

37 Exposure by use of ventilation Early results Type of ventilation Area Mixing Volumetric flow rate (Q t ) FCAW SMAW and MIG Oxy-gas welding/cutting Space volume n GM GSD n GM GSD n GM GSD ft 3 All observations No ventilation Exhaust Dilution Unmixed Mixed Low ( ft 3 /min) High ( ft /min) Space ventilation rate Low ( ACM) High ACM ( ACM)

38 Summary Welding is a common industrial process Welding processes have numerous hazards Including metals with significant toxicity Exposures are high and largely uncontrolled Exposure assessment Continue to rely largely on air monitoring Both particulate mass and metal-specific Biomonitoring of great interest, but a largely research enterprise Except for specific issues, e.g., lead Exposure control Ventilation has limited impact, but needs increased attention/use Respiratory protection continues to play an important role

39 Discussion