The research presented in this thesis addresses several aspects of loading operations inunderground mines, in particular tools and equipment selection. It also addresses the flexibilityof the fleet when subject to substantial disturbances, such as ore pass loss, and proposes integration of the scheduling system with discrete event simulation. The thesis begins with a study of discrete event simulation (DES) tools for loading operations in an underground mining system. The results show the benefits of using simulation but also the drawbacks.The thesis presents an analysis of energy consumption and exhaust gas emissions from diesel and electric LHDs. The results show the potential energy savings with the use of electric LHDs. Next, it focuses on the LHD operations affected by long-term ore pass loss (unavailability). It shows the effects on the production system (the ventilation requirements, production and waiting times when too many LHDs operate in the area affected by an ore pass loss) and highlights the need for a flexible solution and a mitigation strategy. Finally, the thesis studies the integration of ABB’s Ability Operations Management System (OMS) with the SimMine simulation model and how this affects LHD operations. The results show the benefits of using the joined platformas a testbed and decision support system.