Page 69 - 捷運技術 第43期

捷運技術半年刊 第43 期 63

and the fail-safe concept. It then goes on to define a management process based on a system life

cycle that has a total of 14 phases, from Concept to De-commissioning and Disposal, with detailed
descriptions of the objectives, inputs, requirements, deliverables and verification of each phase. The

system life cycle as defined in EN 50126 is shown in the typical V-shape curve.

Figure 2cCENELEC Phases

In defining and apportion System Requirements (phases 4 and 5) it was required, that the

concept of Safety Integrity Levels (SIL’s) shall be used and that the overall SIL for the entire Metro

shall be four. The relationship among SIL and Tolerable Hazard rate (THR) is described by the table
below.

Table 2 SIL Levels
Tolerable Hazard Rate Safety Integrity Level
(THR) (SIL)
per hour and function

-9
10 ≤ THR < 10 -8 4
10 ≤ THR < 10 -7 3
-8
10 ≤ THR < 10 -6 2
-7

-6
10 ≤ THR < 10 -5 1