Independence (Safety Architecture)
Section 06: System Safety & Functional Safety
Definition
A design characteristic ensuring that a failure, error, or external event affecting one element of a system does not propagate to or simultaneously affect another element. Independence is required when redundancy is used to meet safety objectives: two redundant channels provide safety benefit only if they are truly independent such that a single cause cannot defeat both. Independence can be achieved through physical separation (different locations), functional independence (different interfaces and data paths), electrical isolation (separate power supplies), and logical independence (different software, different design teams).
Where This Shows Up
Independence is one of the most important concepts in safety architecture. Without independence, redundancy is ineffective because common causes can defeat all redundant elements simultaneously. The degree of independence required is determined by the severity of the failure condition: catastrophic failure conditions typically require the highest degree of independence between redundant elements, including consideration of systematic common causes (common software, common requirements).
Primary Sources
Addresses independence as a key architectural principle in system development.
Evaluates the adequacy of independence through common cause analysis methods.
Related Terms
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