safetycase

Safety case is a structured, evidence-based argument that a system is acceptably safe for a defined application and operating environment. It comprises safety claims about the system, the argument that links those claims to supporting evidence, and the actual evidence itself. A common way to present the argument is using Goal Structuring Notation (GSN) or similar structured notations to make assumptions, contexts, and dependencies explicit. The evidence may include hazard analyses, design descriptions, failure mode and effects analyses, test results, safety analyses, vulnerability assessments, independent reviews, and operational data.

Purpose and use: The safety case is produced during development and maintained across the system’s lifecycle, updated after design changes, new evidence emerges, or lessons from operation occur. It is used to obtain regulatory approval, authorization to operate, or contract-based assurance in safety-critical industries such as aerospace, rail, automotive (functional safety), medical devices, nuclear power, and process industries. It supports certification or licensing by providing a justified confidence that hazards have been identified and mitigated to an acceptable level within the defined safety envelope.

Relation to standards: The safety case is compatible with risk-based standards such as IEC 61508 (functional safety framework), ISO 26262 (automotive), and EN 50126/50128/50129 (railway), among others. It complements hazard analyses, safety plans, and verification activities by linking evidence to safety claims rather than serving as a stand-alone checklist.

Limitations: A safety case is an argument of justification rather than an absolute proof; its strength depends on the quality and completeness of the evidence and the validity of the underlying assumptions. Independent assessment and rigorous maintenance are essential for credibility.