Levels and control of welding fume exposure to total particulate, hexavalent chromium, and manganese in contracted activities in an oil refinery setting (2008–2018)

Abstract

In response to increasing focus on occupational exposures to welding fume, a 10-year series of personal exposure measurements was analyzed for the two main welding processes (Shielded Metal Arc Welding or Stick and Tungsten Inert Gas welding or TIG) used in an oil refinery setting. Exposures from ancillary gouging and grinding were also analyzed. The operations were conducted under a permit-to-work system, which stipulated control measures in the form of ventilation and respiratory protective equipment (RPE) depending on the work environment, base metal, and welding process. The analysis focused on three health hazards of interest: total particulate (TP); hexavalent chromium (Cr (VI)); and manganese (Mn). The study’s aims were the analysis of exposure levels related to operational conditions to verify the adequacy of required control measures and the generation of quantitative information for the development of predictive exposure models. Arithmetic mean exposures were 2.01 mg/m3 for TP (n = 94), 13.86 µg/m3 for Cr (VI) (n = 160), and 0.024 mg/m3 for Mn (n = 95). Requirements and practices for ventilation and use of RPE appeared adequate for maintaining exposure levels below maximum use concentrations. Predictive models for mean exposure levels were developed using multiple linear regression. Different patterns emerged for TP, Cr (VI), and Mn exposure determinants. Enclosed or confined work environments were associated with elevated exposure levels, regardless of the provision of local exhaust or general dilution ventilation. Carbon arc, used with gouging and grinding, contributed significantly to TP exposure (p = 0.006). The relative TP source strengths of the two main welding processes were comparable to the literature data. For Cr (VI), stick welding was associated with approximately 50-fold (p < 0.001) higher exposure potential than TIG welding. For Mn, this difference was approximately 2.5-fold. Differences were observed across the three analytes in exposure reduction efficiency of local exhaust ventilation (LEV) compared to natural ventilation, possibly due to ineffective use in confined spaces. These findings contribute to the overall understanding of TP, Cr (VI), and Mn exposures from welding and required controls in an oil refinery setting.