The comparison of the killing performance in two industrial gas-liquid-solid stirred reactors, one being a scaled-up version of the other, but with noticeable differences in the mixing devices, has been made using CFD simulations. The work has been devised in three steps. In a first step, the single-phase flows in the two vessels have been compared, the liquid-solid mixture being treated as a pseudo-liquid phase. Then, Eulerian simulations have been performed to investigate the two-phase flow and the gas distribution in the vessels. Finally, the injection of the killing gas has been simulated using a Lagrangian approach. Differences between the two vessels are pointed out as well as the interest of possible modifications. (c) 2005 Elsevier Ltd. All rights reserved.