Radiative collapses in the Advanced Toroidal Facility (ATF) torsatron have been studied using the predictive transport code Proctr for realistic shots with moderate radiation levels (Prad/Pin approximately=30%). Simulations to study the influence of density and of different impurity species on the occurrence of thermal collapses have been carried out and it has been found that the impurity cooling rate profiles play a decisive role. A local breaking of the power balance is suggested as the possible origin of the thermal collapse and, once the collapse has started, the rate of increase of the local energy lost by radiation seems to be the important parameter. The lack of efficiency in the radial energy transfer to sustain the local energy balance in the regions with enhanced losses leads to plasma collapse