Search for:
Base failures causing violations of safety goals without safety mechanisms on any path
Explanation:
Base failures will be searched for
- that are either linked to two or more different violations of safety goals or linked to the same violation of safety goal via single-point fault paths and multiple-point fault paths AND
- which have no safety mechanism on the path to the violations of safety goals.
Example:
Abbreviations:
- The shown sample structure consists of three structure elements. Two safety goals
each with one violation of safety goal 
are assigned to the root
element. The remaining structure elements SE and BSE have safety mechanisms and failure or functions and
failures.
- The following failure graph shows how the base failures BF are linked to the violations of safety goals.
- Two placeholders for the failure type are automatically assigned in the IQ Software to a violation of safety goal. This is represented in the failure graph and the failure net. If you anchor a violation of safety goal in the failure graph or the failure net these placeholders for failure types are automatically shown next to the violation of safety goal in the direction of causes. The failure types tell if the failures leading to a safety goal violation according to ISO 26262 are single-point faults or multiple-point faults.
- The considered Quality Rule (QR) detects base failures (BF), which are linked either to two or more different violations of safety goals or linked to the same violation of safety goal via the single-point fault path and the multiple-point fault path AND have at the same time no safety mechanism on any of their failure paths to the violations of safety goals. Analyzing the failure graph above therefore produces the following search result:
Search result:
All BFs that have safety mechanisms on the paths to the violations of safety goals cannot appear in the search result. For that reason, BF3 is excluded from the search result in advance.
Of the remaining three base failures, BF4 only has a single path to the violation of safety goal TSG2 via the placeholder “multiple-point fault”, which is why BF4 is also excluded from the search result.
The two remaining BFs, on the other hand, fulfill all the filter conditions. BF1 is linked to the two violations of safety goals TSG1 and TSG2. For BF2 it is true that it is only linked to one violation of safety goal, but that link leads there via the single-point fault path as well as via the multiple-point fault path.
Thus, the two base failures BF1 and BF2 are reported as hits.