The purpose of this Specification is to define the methodology and the general
principles to be adopted for the Safety Integrity Level (SIL) assignment of Safety Integrated Functions (SIF).
It is not the purpose of this document to define the methodology and principles for SIL
demonstration or SIL achievement.
The purpose of SIL assignment is not to rework the design of installations, but to:
• Validate/ verify the design against the prescriptive requirements of Company’s GS;
• Provide useful information to Operations to set their testing and maintenance
philosophies and schedule;
• Define the performance standards of Safety Critical Elements/ Measures.
 

Contents
1. Scope ....................................................................................................................... 3
1.1 Purpose ............................................................................................................. 3
1.2 Application ......................................................................................................... 3
2. Reference documents............................................................................................. 4
3. Terminology and definitions .................................................................................. 5
4. Overall SIL Concept and Methodology................................................................ 10
4.1 SIL Concept ........................................................................................................... 10
4.2 SIL Assessment Methodology.................................................................... 11
4.3 SIL Assignment Methodology........................................................................ 11
5. Schedule of SIL Assignement.............................................................................. 12
5.1 Pre-requisites/ Preparation works to SIL Assignment Workshop......................... 12
5.2 SIL Assignment................................................................................................... 13
5.3 Next steps....................................................................................................... 13
6. Identification of SIF ............................................................................................... 13
7. Calibrated Risk-Graph Methodology ................................................................... 14
8. LOPA Methodology............................................................................................... 24
8.1 Objectives ............................................................................................... 24
8.2 Application ............................................................................... 24
8.3 Methodology ............................................................................. 25
8.4 LOPA Organization ..................................................................... 28
9. Specific Requirements for HIPS .......................................................................... 28
Appendix 1 SIF and SIL tables.............................................................................. 30
Appendix 2 Rule sets .......................................................................................... 32
Appendix 3 Extracts from  ................................................. 34
Appendix 4 Risk-graph calibration for production outage ........................ 36
Appendix 5 Conducting a SIL assignment workshop................................ 37
Appendix 6 LOPA Worksheet...................................................... 40
Appendix 7 LOPA organisation ..................................................................... 41
Bibliography................................................................................................................. 42