Computational Fluid Dynamics (CFD) has been used to model the local shielding gas flow and fume dispersion in Gas Metal Arc Welding (GMAW). Experiments using scale models and salt water have been used to validate the numerical models. These techniques allow a quantitative analysis of GMAW-induced flow patterns and were used to study the dispersion of gas around the weld zone. The numerical and physical modelling show good correlation with real wending conditions, where direct flow visualization is more difficult. The paper describes the approach and its application to the understanding of shielding effectiveness and local fume extraction efficiency. The secondary effects of poor shielding seen in practice are consistent with the numerical modelling results.