AADvance Safety Manual - Tuv-fs.com

Chapter 3 Functional Safety ManagementSystem Functional and Safety RequirementsSystem EngineeringA set of system functions and their timing requirements will be specified. Wherepossible, the functions should be allocated to defined modes of operation of theprocess. For each function, it will be necessary to identify the process interfaces.Similarly, where the function involves data interchange with third party equipment, thedata and interface should be clearly identified. Where non-standard field devices,communications interfaces or communications protocols are required, it is especiallyimportant that detailed requirements for these interfaces are established anddocumented at this stage.The client should provide the functional requirements, where this information is notsupplied the System Integrator should define the requirements and agree them with theclient. It is, however, necessary to collate these requirements into a document,including any clarification of the requirements. It is recommended that logic diagramsbe used to represent the required functionality and highly recommended that allrequirements are reviewed, clarified where required and approved by the client.The system safety requirements stage analyses the functional requirements todetermine their safety relevance. Where necessary, additional safety requirements shallbe identified and documented to ensure that the plant will fail-safe in the case offailures of the plant, safety-related system, external equipment or communications, or ifthe safety-related system's environment exceeds the required operating conditions.The appropriate safety integrity level (SIL2 or SIL3) and safety-related timingrequirements shall be defined for each safety-related function. For each function therequired safety failure mode shall be determined. The client should supply thisinformation or it should be defined and agreed with the client as part of this phase.The System Integrator shall ensure that the client approves the resulting safetyrequirements.The system engineering stage realizes the design of the safety-related system. It isrecommended that the engineering be divided into two distinct stages, the first definingthe overall system architecture, and the second detailing the engineering of theindividual architectural blocks.The architectural definition shall define the safety requirements class for eacharchitectural element and identify the safety functions allocated to each element.Additional safety functions resulting from the chosen system architecture shall bedefined at this stage.The detailed engineering design shall refine the architectural elements and culminate indetailed information for system build. The design shall be in a form that is readilyunderstood and allows for inspection and review of each stage of the process and finaldesign.If the possibility of errors cannot be eliminated, the system integrator should makesure that procedural methods are devized and applied to detect them.Document number 553630 Issue 7: February 2010 3-3