This paper reports on the application of Computational Fluid Dynamics (CFD) techniques to the analysis of gas and air flow in Gas Metal Arc Welding (GMAW), so as to estimate the efficiencies of on-torch welding fume extraction system configurations. It is shown that the flow field induced by the GMAW peocess is a combination of an 'impinging fountain' flow and a 'buoyant wall jet' flow. Previously these two flows have been studied individually, but not together in conjunction with GMSW-induced flow fields. CFD simulations for a free jet flow and an extraction flow are presented, and compared to simulations of impinging fountains. The simulations are in excellent agreement with documented experimental evidence. CFD simulations of on-torch fume extraction systems are then presented. It is shown that extraction through concentric sleeves fails to affect the gas-fume flow in the wall jet in any significant way. This appears to be part of the reason for the poor fume extraction efficiancy of on-torch extraction sleeves to date.