Thorium 232 exposure during tungsten inert gas arc welding and electrode sharpening

To assess the exposure of welders to thorium-232 (232Th) during tungsten inert gas arc (TIG) welding, airborne concentrations of 232Th in the breathing zone of the welder and background levels were measured. The radioactive concentrations were 1.11 x 10-2 Bq/m3 during TIG welding of aluminum (TIG/Al), 1.78 x 10-4 Bq/m3 during TIG welding of stainless steel (TIG/SS), and 1.93 x 10-1 Bq/m3 during electrode sharpening, with 5.82 x 10-5 Bq/m3 background concentration. Although the annual intake of 232Th estimated using these values did not exceed the annual limit intake (ALI, 1.6 x 102 Bq), we recommend reducing 232Th exposure by substituting thoriated electrodes with a thorium-free electrodes, setting up local ventilation systems, and by using respiratory protective equipment. It is also necessary to inform workers that thoriated tungsten electrodes contain radioactive material. (author)