PD CLC/TR 50451:2007

Executive summary
Introduction
1 Scope
2 References
  2.1 Normative references
  2.2 Informative references
3 Definitions
4 Symbols and abbreviations
5 Safety Integrity Levels allocation framework
  5.1 Prerequisites
  5.2 Overview of the methodology
  5.3 Definition of Safety Integrity Levels
  5.4 Qualitative vs quantitative methods
      5.4.1 Qualitative assessment
      5.4.2 Quantitative assessment
  5.5 EN 50126-1 lifecycle context
6 System definition
7 Hazard identification
  7.1 General principles
  7.2 Empirical hazard identification methods
  7.3 Creative hazard identification methods
  7.4 Hazard
  7.5 Existing hazard lists
8 Risk analysis
  8.1 Risk tolerability
  8.2 Determination of Tolerable Hazard Rate
      8.2.1 Qualitative risk analysis
      8.2.2 Quantitative risk analysis
      8.2.3 GAMAB and similar approaches
      8.2.4 The MEM approach
      8.2.5 Other approaches
9 System design analysis
  9.1 Apportionment of safety integrity requirements
      to functions
      9.1.1 Physical independence
      9.1.2 Functional independence
      9.1.3 Process independence
  9.2 Use of SIL tables
  9.3 Identification and treatment of new hazards
      arising from design
  9.4 Determination of function and subsystem SIL
  9.5 Determination of safety integrity requirements
      for system elements
Annex A - Single-line signalling system example
Annex B - Level crossing example
Annex C - Comparison of demand and continuous mode
Annex D - Frequently asked questions

Describes a method to determine the required Safety Integrity Level of railway signalling equipment taking in consideration the operational conditions of the railway, and the architecture of the signalling system.

The scope of this Technical Report is to define a method to determine the required Safety Integrity Level of railway signalling equipment taking in consideration

• the operational conditions of the railway, and

• the architecture of the signalling system.

The following picture may be used in order to detail more precisely the scope of this Technical Report:

From a mechanistic point of view the task of this Technical Report is to define a method of calculation, which determines the integrity requirements (qualitatively and quantitatively) from the inputs stated above.