Note: Above diagram is intentionally blurred for conceptional understanding only.
Fig. 1 An example of the architectural assumption
7.3.2 Implementation of Failure Tree Analysis (FTA)
(1) At the initial stage of the design, the component elements in the architectural assumption that are likely to
violate the safety goals shall be extracted by a FTA.
(2) Derivation of FSRs
The FSR shall be derived for each component element that was extracted by the FTA.
In the derivation of the FSR, the following items shall be considered:
a) operating mode b) fault tolerant time interval
c) safe states d) emergency operation interval, and
e) functional redundancies (e.g. fault tolerance).
In addition, also warning and fail-safe action ashall be specified as FSRs.
(3) Preparation of the FTA Table
a) The results of (1) and (2) above shall be summarized by using Form B: FTA Table,
b) However, a customer specific form may be used instead of Form B.
c) Guidelines for completing Form A are shown in Table 4.