Conveyor belt systems used in underground mines have the potential to give rise to severe fires unless they are made from a suitable material. Statistical data on such fires show that the most significant risk is from collapsed idler rollers. We have performed a study to assess the characteristics of such fires and to determine their influence on personnel working within an underground system. Cone Calorimeter testing was carried out to determine the combustion properties of typical belt materials. From this information, we used Computational Fluid Dynamics (CFD) to simulate the spread of heat and smoke through the tunnel. These simulations showed that the fire results in a strong plume which causes smoke and hot gases to form a stratified layer along the roof of the tunnel and to curl back down in the region of the fire because of the interaction of the plume with the roof The consequences of the fire on personnel working in the region of the conveyor are considered.