Abstract The identification of structures, systems and components (SSCs) performing safety functions is of paramount importance for an EU DEMO development in all phases of the project: design, fabrication, commissioning, operation, maintenance, inspections and tests. Early identification of safety relevant SSCs contributes in the correct definition of systems requirements, preliminary layout and design integration. It may also be exploited as a supporting criterion for selection among the plant variants, e.g. alternative blanket concepts. Those SSCs assigned to a safety importance class (SIC) will receive adequate attention during the different developing phases. A graduation of safety important SSCs is adopted for DEMO on the basis of the IAEA Guide No. SSG-30, on SSCs classification. Three safety importance classes (SIC-1, SIC-2 and SIC-3) are assigned on the basis of: a) the consequences the loss of the safety function could lead to, b) the involvement of the SSCs in preventing, detecting or mitigating incident or accident and, c) the involvement of the SSCs in bringing and maintaining the plant in a safe state. In this paper, the provisional safety classification of the Primary Heat Transfer System (PHTS) related to the Helium Cooled Pebble Bed (HCPB) and Water Cooled Lithium Lead (WCLL) blankets of DEMO is presented.