IEC 61508 Parts 1 to 7, Mapped and Explained
IEC 61508 is cited constantly but rarely navigated, and engineers often do not know that it is seven parts with very different weights: some are binding requirements and some are catalogs of techniques you consult, not comply with. This page maps the seven parts so you know which ones a certificate rests on and which ones are guidance. It is a structural explainer, assuming you already know the base standard's purpose.
IEC 61508 parts map in one line: IEC 61508 has seven parts. Parts 1 to 3 are the normative requirements: part 1 general and management, part 2 hardware, part 3 software. Part 4 is definitions and abbreviations. Parts 5 to 7 are informative guidance: part 5 on determining SIL targets, part 6 on applying parts 2 and 3, and part 7 a catalog of techniques and measures. Compliance rests on parts 1 to 3.
Normative Versus Informative Parts
The single most useful distinction across the seven parts is normative versus informative. Normative parts contain requirements you comply with; informative parts contain guidance you consult. Parts 1, 2, and 3 are normative, and a compliance claim rests on them. Parts 5, 6, and 7 are informative, valuable for understanding and applying the standard but not themselves a compliance target. Part 4 is the vocabulary.
Mistaking an informative part for a requirement, or vice versa, causes real confusion in audits. Part 7's long lists of techniques and measures are recommendations graded by SIL, not a checklist every project must fully implement. Knowing which parts bind is what lets you focus effort correctly. The base-standard overview on the site, IEC 61508 functional safety, frames why the split exists.
What Each Part Covers
The map below lists all seven parts and their status.
| Part | Status | Covers |
|---|---|---|
| 61508-1 | Normative | General requirements and the overall lifecycle |
| 61508-2 | Normative | Requirements for E/E/PE hardware |
| 61508-3 | Normative | Software requirements |
| 61508-4 | Definitions | Terms and abbreviations |
| 61508-5 | Informative | Methods to determine SIL targets |
| 61508-6 | Informative | Guidance on applying parts 2 and 3 |
| 61508-7 | Informative | Overview of techniques and measures |
Parts 2 and 3 are where a device's certification lives: part 2 sets the hardware requirements, including the architectural constraints from hardware fault tolerance and safe failure fraction, and part 3 sets the software requirements that underpin systematic capability. Together they carry the technical burden of a SIL claim.
Part 6 is the practical companion most engineers actually read, because it shows worked approaches for applying parts 2 and 3, including reliability calculation methods. Part 5 helps at the front end when you are deriving a SIL target, connecting to the site's page on SIL allocation.
Reading a Certificate Against the Parts
A device certificate to IEC 61508 is really a claim against parts 2 and 3: that the hardware meets part 2 and, where programmable, the software meets part 3. When you evaluate a certificate, you are checking the part 2 architectural and failure-rate evidence and the part 3 systematic-capability evidence. The site's explainer on how IEC 61508 determines a SIL walks how those combine into the claimed capability.
Parts 5 through 7 will not appear as compliance points on a certificate because they are informative. If a specification demands compliance with part 7 as if it were a requirements clause, that is a misreading worth correcting, since part 7 is a menu of techniques recommended by SIL rather than a mandatory list.
The takeaway is to weight your attention by part status: parts 1 to 3 for what must be met, part 4 for what terms mean, and parts 5 to 7 for how to do the work well. That weighting keeps an assessment focused on the clauses that actually bind.
Frequently Asked Questions
How many parts does IEC 61508 have?
Seven. Parts 1 to 3 are normative requirements covering general and management aspects, hardware, and software. Part 4 is definitions and abbreviations. Parts 5 to 7 are informative guidance: part 5 on determining SIL targets, part 6 on applying parts 2 and 3, and part 7 an overview of techniques and measures. A compliance claim rests on the normative parts 1 to 3, while the informative parts help you understand and apply them.
Which parts of IEC 61508 does a device certificate rely on?
Primarily parts 2 and 3. Part 2 sets the hardware requirements, including the architectural constraints and failure-rate evidence, and part 3 sets the software requirements behind systematic capability. Part 1 provides the overall management and lifecycle framework. Parts 5 to 7 are informative and will not appear as compliance points on a certificate, so when evaluating a device you focus on its part 2 and part 3 evidence rather than the guidance parts.
Sources and verification
This page references the standards, specifications, and official documentation published by the organizations below. Editions, product capabilities, and documentation change over time - confirm current requirements and specifications directly with the source.
- IEC 61508, Functional safety of E/E/PE safety-related systems - International Electrotechnical Commission
Merobix is not affiliated with, endorsed by, or sponsored by these organizations; their names are used only to identify the standards and products discussed.
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