ASILs

ASILs, or Automotive Safety Integrity Levels, are risk-based safety categorizations defined in ISO 26262 for safety-related electrical and electronic systems in road vehicles. Each ASIL indicates the required level of rigor and safety measures needed to reduce risk to an acceptable level.

The four levels are ASIL A, ASIL B, ASIL C, and ASIL D, with D representing the highest risk and A the lowest. The assignment to a function is based on a hazard analysis and risk assessment that considers three factors: Severity of potential injuries, Exposure probability of the situation, and Controllability by the driver or other actors. The combination determines the required ASIL and the corresponding safety requirements.

In practice, ASILs guide the safety lifecycle, including hardware and software development, reliability targets, safety goals, safety requirements, and verification and validation activities. An ASIL is a property of a safety-related function or a component rather than of a single part, and it can influence both architectural choices and the depth of testing.

ASIL decomposition is a common approach when a function is complex or high risk. Developers may decompose it into multiple elements with lower ASILs to manage complexity while preserving the overall safety objective.

Limitations: ASIL is part of a broader risk-based framework and must be applied in accordance with ISO 26262 across the concept, system development, and production phases. The standard provides the specific criteria and tables used to determine and verify ASIL assignments and safety requirements.