This European Standard describes the calculation of mass flow for sizing pressure relief devices for components of refrigerating systems. NOTE The term "refrigerating system" used in this European Standard includes heat pumps. This European Standard describes the calculation of discharge capacities for pressure relief valves and other pressure relief devices in refrigerating systems including the necessary data for sizing these when relieving to atmosphere or to components within the system at lower pressure. This European Standard specifies the requirements for selection of pressure relief devices to prevent excessive pressure due to internal and external heat sources, the sources of increasing pressure (e. g. compressor, heaters, etc.) and thermal expansion of trapped liquid. This European Standard describes the calculation of the pressure loss in the upstream and downstream line of pressure relief valves and other pressure relief devices and includes the necessary data. This European Standard refers to other relevant standards in Clause 5.