Hexavalent chromium content in stainless steel welding fumes is dependent on the welding process and shield gas type

Occupational exposure to welding fumes is a known health hazard. To isolate elements in stainless steel welding fumes with high potential for adverse health outcomes, fumes were generated using a robotic gas metal arc system, using four shield gases of varying oxygen content. The objective was to measure Crⱽᴵ concentrations in a broad spectrum of gas metal arc welding processes, and identify processes of exceptionally high or low Crⱽᴵ content. The gases used were 95% Ar/5% O₂, 98% Ar/2% O₂, 95% Ar/5%CO₂, and 75% He/25% Ar. The welder was operated in axial spray mode (Ar/O₂, Ar/CO₂), short-circuit (SC) mode (Ar/CO₂ low voltage and He/Ar), and pulsed axial-spray mode (98% Ar/2% O₂). Results indicate large differences in Crⱽᴵ in the fumes, with Ar/O₂ (Pulsed) > Ar/O₂ > Ar/CO₂ > Ar/CO₂ (SC) > He/Ar; values were 3000 ± 300, 2800 ± 85, 2600 ± 120, 1400 ± 190, and 320 ± 290 ppm respectively (means ± standard errors for 2 runs and 3 replicates per run). Respective rates of Crⱽᴵ generation were 1.5, 3.2, 4.4, 1.3, and 0.46 µg/min; generation rates were also calculated in terms of µg Crⱽᴵ per metre of wire used. The generation rates of Crⱽᴵ increased with increasing O₃ concentrations. Particle size measurements indicated similar distributions, but somewhat higher >0.6 µm fractions for the short-circuit mode samples. Fumes were also sampled into 2 selected size ranges, a microspatter fraction (≥0.6 µm) and a fine (<0.6 µm) fraction; analysis indicated that Crⱽᴵ is primarily associated with particles <0.6 µm. The conclusion of the study is that Crⱽᴵ concentrations vary significantly with welding type and shield gas type, and this presents an opportunity to tailor welding practices to lessen Crⱽᴵ exposures in workplaces by selecting low Crⱽᴵ-generating processes. Short-circuit processes generated less Crⱽᴵ than axial-spray methods, and inert gas shielding gave lower Crⱽᴵ content than shielding with active gases. A short circuit He/Ar shielded process and a pulsed axial spray Ar/O₂ process were both identified as having substantially lower Crⱽᴵ generation rates per unit of wire used relative to the other processes studied.