Hazard Analysis & Risk Assessment (HARA)

Hazard Analysis and Risk Assessment (HARA) is the systematic process defined in ISO 26262-3, Clause 6, that identifies the vehicle-level hazards of an item and classifies their risk. For each hazardous event - a hazard occurring in a specific operational situation - three parameters are rated: severity (S0 to S3), exposure (E0 to E4) and controllability (C0 to C3). Their combination determines the ASIL, from QM through ASIL A to ASIL D. The output is a set of safety goals: top-level safety requirements, each carrying an ASIL, that drive the functional safety concept and everything downstream. HARA is performed on the item definition, before any design decisions.

The three ratings feed a lookup defined in ISO 26262-3: for each hazardous event, the combination of severity, exposure and controllability yields QM, A, B, C or D. The logic is additive - the highest classifications on all three parameters (S3, E4, C3) produce ASIL D, and reducing any one parameter by one class steps the ASIL down one level. That is why justifications matter so much: an optimistic exposure or controllability rating quietly drops the ASIL and with it the required rigor for the whole development. The guide includes interactive ASIL tools and quizzes to make the determination mechanical rather than debatable.

A hazard is a potential source of harm caused by malfunctioning behaviour of the item - for example, unintended full braking. A hazardous event is that hazard combined with a specific operational situation - unintended full braking while driving at high speed on a wet motorway with following traffic. The distinction is load-bearing: risk is rated on hazardous events, not on hazards, because the same malfunction has very different severity, exposure and controllability in different situations. A thorough HARA therefore crosses its hazard list with a structured catalog of operational situations before rating anything.

A safety goal is the top-level safety requirement derived from a hazardous event, inheriting the highest ASIL of the events it addresses. A well-formed safety goal states what must be prevented or achieved (for example, "ensure braking when needed"), carries its ASIL, and is completed by a safe state definition and, where relevant, a fault tolerant time interval (FTTI) within which the system must reach that safe state. Safety goals are the root of the entire traceability tree - the functional safety concept, technical safety concept and all safety analyses argue back to them - so vague or unverifiable goals corrupt everything downstream.

The guide has 14 chapters covering the complete HARA process, supported by 10 interactive diagrams and tools and 3 quizzes on ASIL determination, exposure rating and safety goal formulation. A complete worked example carries an automatic emergency braking system from item definition through S/E/C assessment to ASIL results of D, D, C and A and three safety goals with FTTI and safe states, and a searchable reference catalog of operational situations and hazards accelerates your own analyses. A free account starts you off, and the Pro and Expert plans unlock more of the library.