ASIL Decomposition
Learn how to distribute safety requirements across independent architectural elements to reduce individual ASIL allocation while maintaining overall safety integrity. This module covers the full decomposition process with interactive simulators and a Steer-by-Wire case study.
What You'll Learn
Build complete competency in ASIL decomposition from feasibility assessment through quantitative proof to practical implementation.
Evaluate Decomposition Feasibility
Determine whether ASIL decomposition is appropriate for your project using the five-question decision gate and cost/benefit analysis.
Apply Valid Decomposition Schemes
Use the ASIL Algebra point system and ISO 26262-9 Table 1 to select valid decomposition combinations with proper justification.
Prove Element Independence
Demonstrate sufficient independence through DFA, coupling factor analysis, FFI mechanisms, and documented evidence packages.
Perform Quantitative Analysis
Calculate PMHF with beta-factor CCF modeling and validate decomposition against hardware metric targets for each ASIL.
Build FTA for Decomposition
Construct fault trees with AND/OR gates, derive minimal cut sets, and evaluate voting architectures for safety-critical designs.
Distinguish Correctness vs Availability
Separate correctness and availability requirements and apply classical or temporal decomposition strategies appropriately.
12 Comprehensive Chapters
From foundational principles to quantitative FTA and real-world Steer-by-Wire examples, each chapter builds your decomposition expertise systematically.
Orientation
Verify whether ASIL decomposition is right for your project with a five-question decision gate, lifecycle positioning, key vocabulary, and a fast use-or-don't-use checklist.
Introduction & Expectations
Understand what ASIL decomposition is and is not. Explore its origins in IEC 61508, three key benefits, and the top ten misconceptions with interactive flip cards.
Standards & Allocation Matrix
Master the "ASIL Algebra" point system and the ISO 26262-9 permissible decomposition matrix. Use the interactive calculator to explore all valid decomposition options.
Core Decomposition Principles
Learn why decomposition requires the same safety goal AND same safe state, the difference between functional and hardware redundancy, and the comparator pattern for correctness.
Step-by-Step Process
Follow the systematic 5-step process from HARA through strategy definition, DFA, allocation, and V&V. Includes item boundary analysis, SEooC, and legacy component constraints.
Independence Methods
Tackle the hardest aspect: achieving and proving independence. Covers DFA coupling factors, FFI mechanisms, E2E protection, watchdog types, and CascF vs CCF analysis.
Quantitative Analysis
Explore the mathematics of safety: PMHF, SPFM, LFM targets, probability theory, and the beta-factor CCF model with an interactive PMHF calculator.
Fault Tree Analysis
Apply FTA to decomposition with AND/OR gates, minimal cut sets, and voting architectures. Includes an interactive k-out-of-n voting simulator and a Steer-by-Wire example.
Correctness vs Availability
Master the critical distinction between correctness and availability decomposition. Explore classical vs temporal approaches and the 3-path redundancy simulator.
Practical Examples
See how theoretical principles become real engineering solutions with detailed Steer-by-Wire decomposition examples showing architecture, independence, and failure modes.
Limitations & Pitfalls
Understand when decomposition cannot or should not be applied. Explore combinatorial complexity, homogeneous redundancy limits, and technology-based ASIL alternatives.
References & Further Reading
Access the complete bibliography with 20 references covering ISO standards, supporting standards, and academic resources for deeper ASIL decomposition study.
8 Interactive Simulators & Tools
Experiment with decomposition calculators, fault injection, voting architectures, and redundancy simulators that bring abstract concepts to life.
Animated Decomposition Visualization
Click to animate ASIL D splitting into decomposed elements with particle effects, hover tooltips showing PMHF targets and point values.
ASIL Decomposition Calculator
Select any ASIL to see all valid decomposition options as clickable cards, with symmetric filter toggle and detailed combination descriptions.
Comparator Architecture Simulator
Animated data flow through a dual-channel comparator architecture with fault injection controls. Click any component for detailed info.
PMHF / Beta-Factor Calculator
Adjustable sliders for beta factor, failure rates, and detection time with real-time PMHF calculation and independence quality assessment.
k-out-of-n Voting Simulator
Toggle channel failures with adjustable n and k values. See cut set generation, system status, and decomposition feasibility in real time.
3-Path Redundancy Simulator
Toggle path failures and watch automatic fallover animation. Real-time PMHF display with adjustable detection time slider.
Combinatorial Complexity Calculator
Adjust events, max ASIL, and cut sets to see exponential growth of analysis permutations with feasibility assessment and time estimates.
Interactive Misconception Flip Cards
Ten clickable cards that flip between common misconceptions and the reality, filterable by category (cost, technical, process).
Steer-by-Wire Case Study
Decomposition principles are applied to a complete Steer-by-Wire system, demonstrating how to split an ASIL D requirement into independently implemented elements with full traceability.
- ✓ASIL D decomposed to ASIL C(D) + ASIL A(D)
- ✓Primary steering controller + independent safety monitor
- ✓Independence evidence through DFA and coupling analysis
- ✓FTA with minimal cut sets and CCF evaluation
- ✓PMHF calculation with beta-factor modeling
- ✓Comparator architecture with fault injection demonstration
Steer-by-Wire
ASIL D Decomposition
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Start your journey through 12 comprehensive chapters with interactive simulators, quantitative calculators, and practical Steer-by-Wire examples.
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