NBN EN 764-7:2003

This European Standard specifies the requirements for safety systems which protect a vessel, a system of vessels, piping, accessories or assemblies from exceeding operating conditions.
It is also applicable to safety related indicators and alarms, signals and warning devices when used in safety systems.
Equipment connected together by piping of adequate capacity, free from potential blockages and which does not contain any valve that can isolate any part from the safety system may be considered as a single pressure system when considering the requirements for overpressure protection.
Safety systems include the interconnections between the equipment to be protected and any discharge location. This location can either be an outlet to atmosphere or the entry into a closed disposal system.
NOTE The scope of this standard and its relationship to the safety accessories and other protective devices described in the Pressure Equipment Directive are shown in annex F.