SO 26262 is a functional safety standard used in the automotive industry. It’s titled “Road vehicles — functional safety”.
Complying with this standard is critical for automotive product development. OEMs, their suppliers, and developers of automotive components all need to comply.
Here, we give an overview of the standard and ASIL (Automotive Safety Integrity Level) — plus compliance tips for software development teams.
ISO 26262 is a risk-based safety standard that’s derived from IEC 61508. It applies to electric and/or electronic systems in production vehicles. This includes driver assistance, propulsion, and vehicle dynamics control systems.
The standard covers functional safety aspects of the entire development process:
· Requirements specification
· Design
· Implementation
· Integration
· Verification
· Validation
· Configuration
The goal of the standard is to ensure safety throughout the lifecycle of automotive equipment and systems.
Specific steps are required in each phase. This ensures safety from the earliest concept to the point when the vehicle is retired.
By complying with this standard, you’ll avoid or control systematic failures. And you’ll detect or control random hardware failures. (Or, you’ll mitigate the effects of failure.)
There are 10 parts to the standard:
· Part 1: Vocabulary.
· Part 2: Management of functional safety.
· Part 3: Concept phase.
· Part 4: Product development at the system level.
· Part 5: Product development at the hardware level.
· Part 6: Product development at the software level.
· Part 7: Production and operation.
· Part 8: Supporting processes.
· Part 9: ASIL-oriented and safety-oriented analysis.
· Part 10: Guideline on the safety standard.
The second edition of the safety standard was going to have a section focused on safety of the intended function — SOTIF. However, SOTIF has since been published as its own standard — ISO/PAS 21448.
Part 6 is the most important part for software developers. It details the steps developers must take to ensure the safety of each component.
What's more, Part 6 includes several tables that define the methods that must be considered in order to achieve compliance with the standard.
Any tools used in automotive development need to be qualified. Part 8 provides guidance for tool qualification.
It requires the following:
· Software tool qualification plan.
· Software tool documentation.
· Software tool classification analysis.
· Software tool qualification report.
Some tools are easier to qualify than others. For instance, Helix QAC — a C/C++ static code analyzer — comes with certificates of compliance that make the qualification process easier.
Automotive Safety Integrity Level (ASIL) is a key component of the safety standard. ASIL is used to measure risk of a specific system component. The more complex the system, the greater the risk of systematic failures and random hardware failures.
There are four ASIL values, named A–D. ASIL A is the minimum level of risk. And ASIL D is the maximum. So, ASIL D has stricter compliance requirements than ASIL A.
When determining ASILs, there’s also a fifth option — QM (quality management). This is used to note that there isn’t a safety requirement for that component. (But it’s typically still a good idea to comply in order to improve product quality.)
ASIL is determined by three factors — severity, exposure, and controllability.
Severity measures how serious the damages are of a system failure. Damages include both people and property.
There are four classes of severity:
· S0: No injuries.
· S1: Light to moderate injuries.
· S2: Severe to life-threatening (survival probable) injuries.
· S3: Life-threatening (survival uncertain) to fatal injuries.
Exposure is the likelihood of the conditions under which a particular failure would result in a safety hazard.
The probability of each condition is ranked on five-point scale:
· E0: Incredibly unlikely.
· E1: Very low probability (injury could happen only in rare operating conditions).
· E2: Low probability.
· E3: Medium probability.
· E4: High probability (injury could happen under most operating conditions).
Controllability is a measure of the probability that harm can be avoided when a hazardous condition occurs. This condition might be due to actions by the driver or by external measures.
The controllability of a hazardous situation is ranked on a four-point scale:
· C0: Controllable in general.
· C1: Simply controllable.
· C2: Normally controllable (most drivers could act to prevent injury).
· C3: Difficult to control or uncontrollable.