| Publisher | IEC |
|---|---|
| Type | Standard (multi-part international series, basic safety publication) |
| Scope | Generic requirements for the functional safety of electrical, electronic and programmable electronic systems that perform safety functions, across their entire lifecycle. |
| Who uses it | Safety system designers, device and software developers, functional safety assessors, certification bodies and engineers in sectors without a dedicated sector standard. |
| Edition note | Refer to the publisher for the current edition. |
What It Is
IEC 61508 is the international foundation standard for functional safety: the part of overall safety that depends on a system or equipment operating correctly in response to its inputs. It applies to electrical, electronic and programmable electronic (E/E/PE) systems that carry out safety functions, and it is designated by the IEC as a basic safety publication, meaning other standards are expected to build on it.
The standard is published in seven parts. Part 1 sets general requirements, including the overall safety lifecycle. Part 2 covers hardware requirements, Part 3 software requirements, and Part 4 definitions and abbreviations. Parts 5 to 7 provide guidance and examples, including methods for determining safety integrity levels and an overview of techniques and measures. Many sector standards are derived from it, including IEC 61511 for the process industry and IEC 62061 for machinery.
Why It Matters
Safety functions implemented with electronics and software can fail in ways that are not obvious, including random hardware failures and systematic errors in specification, design or code. IEC 61508 provides a risk-based framework to manage both kinds of failure, setting requirements in proportion to the risk reduction required.
Manufacturers of sensors, logic solvers and valves commonly develop and certify products against IEC 61508 so that end users can apply them in safety instrumented systems with documented failure data and systematic capability. Engineers who understand the standard can read those certificates and safety manuals critically. For end users, the most practical contact with IEC 61508 often comes through product certificates and safety manuals. These documents state the conditions, assumptions and failure data under which a device may be used in a safety function, and they must be respected in the final application.
Key Concepts
- Functional safety — safety that depends on systems or equipment performing their safety functions correctly.
- Overall safety lifecycle — a structured sequence of phases from concept and hazard analysis through realization, operation, modification and decommissioning.
- Safety integrity level (SIL) — four levels, SIL 1 to SIL 4, expressing the required degree of confidence that a safety function will perform.
- Modes of operation — low demand, high demand and continuous modes, each with different measures of failure, such as average probability of failure on demand or probability of dangerous failure per hour.
- Random and systematic failures — hardware failures occurring at random times versus failures built in through errors in specification, design or software.
- Architectural constraints — requirements on hardware fault tolerance and diagnostic coverage, including the concept of safe failure fraction.
- Systematic capability — a measure of confidence that a component's systematic safety integrity meets a given SIL, based on the development process used.
Who Should Know It
- Functional safety engineers and assessors
- Instrumentation and control system designers
- Embedded hardware and software developers for safety products
- Certification and compliance specialists
- Engineering managers responsible for safety-critical products
Related Standards
- IEC 61511 — the process industry implementation of IEC 61508.
- IEC 62061 — the machinery sector functional safety standard derived from IEC 61508.
- ISO 26262 — the automotive functional safety standard, adapted from IEC 61508 principles.
- ISO/IEC 17025 — competence requirements for laboratories that test safety-related equipment.
How ASEEE Uses It
ASEEE instrumentation and functional safety programs map learning outcomes and assessments to IEC 61508 concepts, including the safety lifecycle, SIL, failure types and architectural constraints. See related ASEEE programs.
ASEEE Programs Referencing This Standard
- Certified Valve Instrumentation Inspector
- Electrical QA/QC Inspection and Quality Management
- Fixed Gas Detection Systems (FGDS)
- Installation and Commissioning of Process Field Instruments
- Instrumentation and Control Systems Level 1: Field Instruments
- Instrumentation and Control Systems Level 2: Commissioning & Maintenance
- Override Control Systems: Design and Implementation
- QA/QC Instrumentation Level 1: Field Instrument Measurements
Educational summary only. ASEEE is not the publisher of this document and this page does not reproduce or replace it. Always consult the current official edition from IEC for requirements.