The Application of BS IEC 61508 to Legacy Programmable Electronic System

摘要

In order to apply BS IEC 61508 successfully to legacy PES a number of key stages have had to be addressed: 1. Identification of all Safety and Safety Related PES, the safety function they fulfil and the dependency placed upon them. 2. Assessment of the PES to demonstrate that it fulfils these requirements. 3. Development and implementation of a quality and technical process based upon the modification and realisation phases of the overall safety lifecycle to ensure that the PES continues to perform at the required level. 4. Introduction and co-ordination of supporting Management of Safety processes, for example, competency and nomination of personnel. 5. Production of practical solutions and guidelines to deal with the discrepancy between legacy PES and those developed in accordance with BS IEC 61508, for example, in the supporting information and specific documentation available. BS IEC 61508 is a complex standard, which cannot be understood and applied beneficially without significant amounts of review of the document, detailed preparation, and production of specific guidance. Based upon our extensive experience of implementing BS IEC 61508 on 1200 legacy systems we believe the standard is weak in four key areas: 1. The modification model and its relationship back into the overall safety lifecycle. 2. The process for carrying out effective Impact Analysis. 3. The process for carrying out effective Functional Safety Assessment. 4. Knowledge and applicability of the numerous methods and techniques proposed. In all of these cases the overall principles are declared in the standard but detailed guidance on how to apply them has had to be produced. Considerable resource and consultation were required to produce this guidance at a level that allowed effective implementation to be achieved. BNFL has maintained the safety of its plants and processes by the use of formal safety cases, risk reduction techniques and the application of a range of processes and procedures. The adoption of BS IEC 61508 and its structured framework has allowed all of these measures to be drawn together into a cohesive overall lifecycle. This has led to the overall enhancement of the management of safety upon PES.