Typical earth systems are used in MV/LV distribution substations often without evaluating their safety performance against the danger of critical electric shock. Earth resistance of a MV/LV substation is periodically monitored and is usually considered as its only safety criterion, assuming that the lower the ground resistance, the safer the substation would be in case of a ground fault. However, this criterion is insufficient in assessing the safety degree of a substation because it doesn't consider safe touch and step voltages limits in fault clearing time. This paper proposes a procedure to assess the safety of substations of a distribution system by defining factor of safety (FoS) and margin of safety (MoS) criteria to recognize the risky substations and classify the safe ones, respectively. These criteria are defined based on EN 50522 standard and are obtained by using advanced modelling of cable sheaths and calculating the portion of the earth fault current contributing to earth potential rise (EPR). The impacts of the type of MV grid (cable/overhead line) and the type of neutral connection of HV/MV on the safety of a distribution system are also investigated.