Why?

In the automotive industry, ensuring the safety of complex systems is crucial. As vehicles become more advanced, the systems responsible for maintaining safety grow more intricate, demanding stringent safety measures. ASIL Decomposition emerges as a critical tool that simplifies these complex safety requirements, making it easier to design, implement, and maintain automotive safety systems.
This strategy not only enhances system reliability but also optimizes resource allocation, reduces costs, and ensures compliance with safety standards like ISO 26262. Understanding ASIL Decomposition is essential for engineers and manufacturers working on safety-critical automotive systems.

What

The Concept of ASIL Decomposition?
What is ASIL?
Before we get into decomposition, let’s clarify what ASIL stands for. ASIL, or Automotive Safety Integrity Level, is a risk classification system defined in the ISO 26262 standard, which is specific to the automotive industry. It helps assess the risk of hazards caused by potential system failures in vehicles.
ASIL is categorized into four levels—A, B, C, and D—with ASIL D representing the highest risk (and thus the most stringent safety requirements) and ASIL A the lowest.
ASIL decomposition is a strategic approach that breaks down complex safety requirements into manageable components, allowing for more efficient and effective implementation of safety measures.
Essentially, it’s about spreading the safety responsibility across different components or systems to achieve the same safety goal in a more practical and cost-effective way.
Imagine you have a complex safety requirement that’s classified as ASIL D (the highest risk level). Meeting this requirement can be challenging, expensive, and time-consuming. ASIL Decomposition allows you to split this ASIL D requirement into multiple parts, each with a lower ASIL level, as long as the overall safety goal is still met.

Possible ASIL decomposition scheme as per ISO26262

How?

ASIL Decomposition is guided by specific rules and applied during the early stages of automotive system design to make the development process more practical. Here’s how it works:
When to use ASIL decomposition in the development process?
“ASIL decomposition is typically employed during the early stages of automotive system design. It’s most beneficial when:

Dealing with high-complexity systems
Facing stringent safety requirements
Aiming to optimize resource allocation
Seeking to reduce overall development costs ”
Key Benefits of ASIL Decomposition
“ASIL Decomposition plays a crucial role in making safety requirements more manageable. It allows engineers to design systems that are safer, more reliable, and often more cost-effective. By decomposing a high-risk requirement into lower-risk components, you can:
Simplify design and implementation: Lower ASIL levels are generally easier to design for and test.
Reduce costs: Achieving ASIL D requirements is expensive. Decomposition can lower these costs by spreading the requirement across components with lower ASIL levels.
Increase flexibility: You can use a mix of components with different safety levels, giving more options in design and implementation. ”
The Rules of ASIL Decomposition
“While ASIL Decomposition offers flexibility, it’s governed by certain rules to ensure that safety isn’t compromised. Some key principles include:
Independence: The decomposed elements must operate independently so that a failure in one doesn’t cause the others to fail. For example, if the brake actuator fails, the braking controller should still be able to ensure safety.
Safety Goal Coverage: The sum of the decomposed elements must fully cover the original safety goal. In other words, when combined, the lower-level components must offer the same level of safety as the original high-level requirement.
Traceability: The decomposition process must be well-documented, with clear traceability showing how the original ASIL requirement is satisfied by the lower-level components. “

Conclusion

ASIL decomposition stands as a crucial strategy in enhancing automotive safety. By breaking down complex safety requirements into manageable components, it allows manufacturers to address critical safety concerns more effectively. This approach not only simplifies the development process but also ensures a more robust and reliable safety system in vehicles.