> iec_61508:2010
IEC 61508:2010
Functional Safety of Electrical/Electronic/Programmable Electronic Safety-related Systems
IEC 61508 is the foundational global standard for functional safety across all electrical, electronic, and programmable electronic (E/E/PE) systems. It introduces the concepts of Safety Integrity Levels (SIL 1 through SIL 4), systematic capability, probabilistic hardware metrics (PFDavg and PFH), and a rigorous safety lifecycle governing design, fault injection, architectural constraints, and diagnostic coverage.
Scope & Applicability
Applicable to safety-related equipment containing electrical, electronic, or programmable components where system failures could cause physical harm, environmental catastrophe, or loss of life.
Non-Coverage Boundaries
Does not cover basic electrical safety (shocks/burns) or purely operational efficiency; sector-specific adaptations (IEC 61511 for process, ISO 26262 for automotive) govern downstream application engineering.
Key Clauses & Control Requirements
Safety Integrity Levels (SIL 1 to SIL 4)
Defines target failure measures: Probability of Dangerous Failure on Demand (PFDavg) for low-demand modes and Frequency of Dangerous Failures per Hour (PFH) for continuous modes.
Part 3: Software Requirements & Systematic Capability (SC)
Mandates defensive programming, formal design methods, static analysis, full MC/DC code coverage, and independent software verification based on target SIL.
Hardware Fault Tolerance (HFT) & Safe Failure Fraction (SFF)
Architectural constraints specifying mandatory redundancy configurations (1oo2, 2oo3) and diagnostic coverage thresholds.
Required Regulatory & Audit Evidence Artifacts
- [✓]Safety Requirement Specification (SRS) with traceable hazard log
- [✓]Functional Safety Assessment (FSA) report signed by an accredited independent assessor (e.g., TÜV, exida)
- [✓]FMEDA (Failure Modes, Effects, and Diagnostic Analysis) calculation worksheets
- [✓]Software verification plan, traceability matrix, and tool qualification records
“SIL is not a badge of quality for an entire factory; it is a calculated statistical property of a specific safety instrumented loop. Never accept 'SIL 3 certified' without verifying whether it applies to the device, the subsystem, or the full loop.”
Cross-Surface Ecosystem Relationships
- IEC 61508 Functional Safety Standards Suite ↗(International Electrotechnical Commission)
Frequently Asked Questions
What is the difference between SIL 1, 2, 3, and 4?
Each SIL tier represents an order of magnitude reduction in the probability of dangerous failure on demand: SIL 1 requires PFDavg between 0.1 and 0.01 (10x risk reduction), while SIL 4 requires PFDavg between 0.0001 and 0.00001 (10,000x to 100,000x risk reduction).
How does IEC 61508 relate to cybersecurity standards like IEC 62443?
IEC 61508 ensures physical safety under random component failures and design bugs. However, if an attacker maliciously tampers with safety logic, functional safety is compromised. Modern engineering mandates that IEC 61508 safety systems be hardened under IEC 62443.