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Safety Assessment: Safety Integrity Levels

Safety Assessment: Safety Integrity Levels. ITV Model-based Analysis and Design of Embedded Software Techniques and methods for Critical Software Anders P. Ravn Aalborg University September 2011. Safety Assessment. Find hazards that may lead to incidents or mishaps ,

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Safety Assessment: Safety Integrity Levels

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  1. Safety Assessment:Safety Integrity Levels ITV Model-based Analysis and Design of Embedded Software Techniques and methods for Critical Software Anders P. Ravn Aalborg University September2011

  2. Safety Assessment Find hazardsthat may lead to incidents or mishaps, analyze their relations, and estimate their consequences. May involve probabilistic reasoning (Reliability Engineering). Is PFH < 10-6 per hour (h-1 ) ?

  3. Process & Documents

  4. System Analysis and Definition

  5. Problem domain: That part of a context that is administrated, monitored, or controlled by a system Application domain: The organization that administrates, monitors, or controls a problem domain Model the context Hazards!

  6. System Definition (FACTOR) Functionality: The system functions that support the application-domain tasks. Application domain: Those parts of an organization that administrate, monitor, or control a problem domain. Conditions: The conditions under which the system will be developed and used. Technology: Both the technology used to develop the system and the technology on which the system will run. Objects: The main objects in the problem domain. Responsibility: The system’s overall responsibility in relation to its context.

  7. Determining the Hazards and risks

  8. Hazard DeterminationHAZOP (hazard and operability) -study

  9. Primary Events: Basic event – fault in atomic component Undeveloped Event – fault in composite component (may be analyzed later) External event – expected event from environment Intermediate event: Nodes inside a fault-tree Determine Event SequencesFault Trees

  10. ... ... Fault Tree - Gates condition Inhibit gate

  11. Determining the SIL

  12. Methods • ALARP (As Low As Resonably Possibble) with Quantitative method (Appendix C, D) • Risk Graphs (Appendix E) • LOPA (Layer of Protection Analysis) (Appendix F) • Hazardous Event Severity Matrix (Appendix G)

  13. ALARP – Frequency and Consequence

  14. ALARP – to SIL C a weight of the consequence, eg on a scale [0,1]. Fnp frequency in h-1 or y-1. Fp (Ft) tolerable frequency = PFHavg Fnp

  15. Risk Graphs - SIL

  16. Data for Risk Graph

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