Introduction

Automotive Safety Integrity Level (ASIL) decomposition is a powerful concept in ISO 26262 that allows a higher ASIL safety requirement to be split into multiple lower ASIL requirements while maintaining overall safety. This enables more cost-effective implementation without compromising functional safety.

However, ASIL decomposition introduces several challenges that can lead to misinterpretation, incorrect application, and potential safety gaps if not handled properly.

Problem Statement

ASIL decomposition aims to optimize system design by reducing over-engineering and cost, but it also brings critical issues that must be carefully managed:

1. Ensuring Independence Between Decomposed Elements

• ASIL decomposition relies on the assumption that the independent elements compensate for each other’s failure risks.
• If these elements are not truly independent (e.g., due to shared resources or failure dependencies), the decomposition does not provide the intended safety benefit.

2. Incorrect Decomposition Leading to Safety Violations

• Some teams decompose ASIL requirements without fully understanding the functional safety implications.
• If lower ASIL paths do not adequately mitigate risks, the overall system may not meet ISO 26262 compliance.

3. Justifying Decomposition in Safety Case Documentation

• Auditors and assessors require solid justification for ASIL decomposition decisions.
• Weak documentation can lead to rejection in assessments, causing delays and rework.

4. Overuse of ASIL Decomposition for Cost Reduction

• Some organizations use ASIL decomposition as a shortcut to reduce cost, without ensuring functional safety integrity.
• This leads to hidden safety gaps that might not be discovered until later validation stages.

Conclusion

ASIL decomposition offers significant advantages when applied correctly, but improper decomposition can compromise safety, lead to compliance failures, and create design inefficiencies.

Need expert guidance on ASIL decomposition? Contact us to ensure your decomposition strategy is optimized for compliance, cost-effectiveness, and safety.