Functional safety systems require components that are designed, characterised, and documented to a fundamentally different standard than general-purpose electronics. This guide covers the key standards, safety integrity levels, development process, compliant component selection, and the procurement practices that functional safety demands.
This guide covers what functional safety is and why it requires a different approach to component procurement (POINT 01), the key standards and safety integrity levels compared (POINT 02), the functional safety development process (POINT 03), the compliant components available by category (POINT 04), and the procurement practices specific to functional safety (POINT 05).
Functional safety is a design and development discipline for electronic systems where a failure can cause harm to people, property, or the environment. It differs from reliability engineering in its fundamental premise: the goal is not to prevent all failures — it is to ensure that when failures occur, the system transitions to a safe state rather than an unsafe one.
This "safe on failure" requirement drives every aspect of component selection. A standard MCU selected for performance and cost is designed without failure mode characterisation documentation — its internal failure modes, failure rates, and diagnostic coverage are not published by the manufacturer. A functional safety MCU is designed specifically with those properties documented, tested, and certified by a third-party assessor. Without this characterisation, the system safety analysis required by every functional safety standard cannot be completed.
Each functional safety standard uses its own safety integrity level scale. The scales are not identical in their requirements, but they express the same fundamental concept: a quantified probability of dangerous failure per hour, with higher integrity levels requiring lower failure rates and more rigorous design and verification processes.
| Property | SIL 1 (IEC 61508) |
SIL 2 (IEC 61508) |
SIL 3 (IEC 61508) |
ASIL A/B (ISO 26262) |
ASIL C/D (ISO 26262) |
PL c/d/e (ISO 13849) |
|---|---|---|---|---|---|---|
| Dangerous failure rate (per hour) | 10⁻⁵–10⁻⁶ | 10⁻⁶–10⁻⁷ | 10⁻⁷–10⁻⁸ | ASIL A: lowest | ASIL D: <10⁻⁸ | PL e: <10⁻⁷ |
| Typical application | Low hazard risk systems | Medium risk, non-life critical | High risk, reversible harm | Low–medium risk ADAS | Steering, braking, airbag | Industrial safety stops |
| Lockstep / redundancy requirement | No (single channel) | Optional | Typically required | ASIL B: often optional | ASIL D: lockstep mandatory | PL e: dual channel |
| FMEDA documentation required | Yes | Yes | Yes | Yes | Yes | Yes (PFHD) |
Component procurement does not happen independently of the development process — the safety level required for each component is determined in the first stages, and the evidence required for certification is built throughout. Procurement teams who understand the process can anticipate documentation requirements and avoid late-stage surprises.
Functional safety component procurement is fundamentally different from standard electronics procurement: the components must not only function correctly but must be characterised and certified to demonstrate they will fail safely. Determine your required ASIL/SIL level from a completed HARA before selecting any component. Obtain Safety Manual and FMEDA documentation before releasing your design. Verify certification claims against actual certificates — not marketing statements. Implement strict version control for all safety-critical components. And plan for product lifecycles of 10–25 years at the component selection stage. A safety case built on the right components with complete documentation is a manageable engineering problem. A safety case built on the wrong components or incomplete documentation requires the system to be redesigned.
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Denro Keikaku is a cross-border electronics procurement specialist and direct partner of Chengde Technology. We support PCB sourcing for automotive, industrial, and medical applications where quality traceability and long-term supply are non-negotiable.