An Approach to Using Non Safety-Assured Programmable Components in Modest Integrity Systems

  • Peter Bishop
  • Kostas Tourlas
  • Nick Chozos
Part of the Lecture Notes in Computer Science book series (LNCS, volume 6351)


Programmable components (like personal computers or smart devices) can offer considerable benefits in terms of usability and functionality in a safety-related system. However there is a problem in justifying the use of programmable components if the components have not been safety justified to an appropriate integrity (e.g. to SIL 1 of IEC 61508). This paper outlines an approach (called LowSIL) developed in the UK CINIF nuclear industry research programme to justify the use of non safety-assured programmable components in modest integrity systems. This is a seven step approach that can be applied to new systems from an early design stage, or retrospectively to existing systems. The stages comprise: system characterisation, component suitability assessment, failure analysis, failure mitigation, identification of additional defences, identification of safety evidence requirements, and collation and evaluation of evidence. In the case of personal computers, there is supporting guidance on usage constraints, claim limits on reliability, and advice on “locking down” the component to maximise reliability. The approach is demonstrated for an example system. The approach has been applied successfully to a range of safety-related systems used in the nuclear industry.


Programmable components safety integrity safety assurance 


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Copyright information

© Springer-Verlag Berlin Heidelberg 2010

Authors and Affiliations

  • Peter Bishop
    • 1
    • 2
  • Kostas Tourlas
    • 2
  • Nick Chozos
    • 2
  1. 1.Centre for Software ReliabilityCity UniversityLondonUnited Kingdom
  2. 2.Adelard LLPLondonUnited Kingdom

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