Previous studies of density limit disruptions in small and medium size tokamaks found that degradation of the plasma energy confinement,characterizing major density limit disruptions,initiates in the neighborhood of the m/n = 2/1 island. A flattening of the electron temperature profile was observed spreading inwards, to the center of the plasma, from the outboard O-point of the 2/1 mode.This event initiates the global destruction of the plasma energy confinement,that if complete results in a major disruption,otherwise only a minor disruption occurs. Generally if the plasma is left to evolve alone then a major disruption will follow after one,or sometimes a few, minor disruptions. Here we report on the observation of this sequence of events, also in JET density limit disruptions. The observation of the same phenomena in three distinct size tokamak plasmas indicates that it may be an intrinsic characteristic of this type of disruptions.