GLOSSARY
ASIL
Automotive Safety Integrity Level
ASIL is assigned during hazard analysis and risk assessment by combining three factors for a given hazardous event: severity of potential harm, exposure to the operating situation, and controllability by the driver or other person. The combination maps to one of four integrity levels, ASIL A through D, or to QM where dedicated safety measures are not required.
The four ASIL levels
| Level | Risk of the hazardous event | What it changes in engineering rigour |
|---|---|---|
| QM | No unreasonable risk identified for the hazardous event | Quality management alone; no ISO 26262 safety measures required |
| ASIL A | Lowest level within scope of the standard | Basic systematic requirements, verification and review |
| ASIL B | Moderate | Added analysis and test coverage expectations, more review discipline |
| ASIL C | High | Stronger architectural measures, diagnostic coverage and independence in verification |
| ASIL D | Highest | Most demanding analysis, coverage, independence and confirmation measures |
How the level is derived
| Parameter | Question it answers | Typical scale |
|---|---|---|
| Severity (S) | How badly could people be harmed? | S0 to S3 |
| Exposure (E) | How often does the operating situation occur? | E0 to E4 |
| Controllability (C) | Can the driver or another person avoid the harm? | C0 to C3 |
How it is used
The assigned ASIL determines the rigour expected of subsequent development activities: the depth of requirements decomposition, the independence expected between development and verification roles, the analysis techniques applied to the architecture, and the coverage expected from testing. A higher ASIL does not change what the system must do; it changes how much confidence the evidence must provide that it does it.
- ASIL decomposition allows a requirement to be split across redundant elements with lower individual levels, provided independence is demonstrated.
- ASIL is attached to safety goals, then inherited by the requirements and architectural elements that implement them.
- Evidence expectations — reviews, analyses, test methods — scale with the assigned level rather than being fixed project-wide.
In practice, the classification is only as trustworthy as the hazard analysis behind it. Assessors expect to see the reasoning for severity, exposure and controllability recorded, not just the resulting letter.