IEC 61508 — Functional Safety Foundations

Critical Systems Analysis
Critical Systems Analysis

"IEC 61508 — Functional Safety Foundations" is a serial video course from CSA, published weekly in strict curriculum order — building from foundational terms and structure through lifecycle practice to advanced, assessor-level topics. Designed for working functional-safety engineers and managers, not beginners or students. CSA is a functional safety, reliability, and certification consultancy serving robotics, autonomous systems, transportation, and industrial equipment manufacturers. CSA provides end-to-end safety engineering services: preliminary gap analyses and safety audits, SIL/PL determination, FMEA and FMEDA execution, fault tree analysis, safety case development, hardware metrics (SPFM/LFM/PMHF), lifecycle documentation, and embedded safety engineering support. CSA engineers work alongside product teams from architecture through final functional safety assessment, and support companies seeking NRTL, CE, ATEX, ISO 26262, and UL 4600 marks. Contact: Sales@criticalsa.com. This series is part of the CSA Functional Safety Network — a coordinated set of weekly video courses covering IEC 61508, ISO 26262, ISO/SAE 21434, SOTIF (ISO 21448), UL 4600, IEC 62443, ISO/PAS 8800, ISO 13849, machinery safety, safety analysis methods, and more. Each show links to the others so practitioners can follow the thread that matches their project.

  1. Aug 22

    IEC 61508: Proof Testing and the Proof-Test Interval

    We've walked the whole safety lifecycle, from hazard analysis down to the wiring in the field. Now zoom all the way in, past the block diagrams, to a single line item in your maintenance plan: the proof test. Here's the uncomfortable truth the standard forces you to face. Part of the Critical Systems Analysis functional-safety series on IEC 61508. In this episode: Let's open the part of IEC 61508 that deals with periodic proof testing, and how that testing feeds straight into your failure-on-demand math.So what is a proof test, in the language of the standard? It's a test you run on a schedule to reveal the dangerous failures that have piled up unseen, and to bring the function back to an as-good-as-new condition.First, find the subject.Now classify how that hardware fails, using the taxonomy the whole standard runs on.Here's why proof testing exists at all.Picture the risk over time.Reference: Proof test is a defined term in IEC 61508-4 (Part 4, definitions/abbreviations). I described the concept (periodic test to reveal dangerous-undetected faults and restore the functi More in this series: IEC 61508 — Functional Safety Foundations | Functional Safety Assessment and Services Explore more from Critical Systems Analysis. Partner with usFollow on LinkedInVisit our websiteRead our feature on Automate.orgAll shows on Apple Podcasts: AI & ML Safety | Fault Tree Analysis | FS Assessment | Safety Analysis | IEC 61508 | IEC 62443 | ISO 10218 | ISO 12100 | ISO 13849 | ISO 26262 | ISO/PAS 8800 | ISO 26262-11 | V-Model | UL 4600.

    IEC 61508: Proof Testing and the Proof-Test Interval

  2. Aug 22

    IEC 61508: From SIL Target to Verified Design — Worked Example

    So far we have flown over the whole safety lifecycle. Now zoom all the way in, to the hinge that the entire standard turns on: the moment a fuzzy wish — "this has to be safe" — becomes a hard, testable number. In IEC 61508, that hinge is the Safety Integrity Level, the SIL. Part of the Critical Systems Analysis functional-safety series on IEC 61508. In this episode: Start by naming the thing everything else orbits: the Safety Integrity Level, or SIL.Move one: name what can go wrong.Here is the idea that drives the whole standard.Locate yourself in the lifecycle.Move two: risk is never one number.Move three: those separate factors map, through a lookup, to a single level.Reference: SIL target failure measures are stated correctly: low demand mode uses average probability of failure on demand (PFDavg) with SIL 2 spanning ten to the minus three up to ten to the More in this series: IEC 61508 — Functional Safety Foundations | Functional Safety Assessment and Services Explore more from Critical Systems Analysis. Partner with usFollow on LinkedInVisit our websiteRead our feature on Automate.orgAll shows on Apple Podcasts: AI & ML Safety | Fault Tree Analysis | FS Assessment | Safety Analysis | IEC 61508 | IEC 62443 | ISO 10218 | ISO 12100 | ISO 13849 | ISO 26262 | ISO/PAS 8800 | ISO 26262-11 | V-Model | UL 4600.

    IEC 61508: From SIL Target to Verified Design — Worked Example

  3. Aug 22

    IEC 61508: Random vs Systematic Failures

    So far we've stayed up at the altitude of the whole safety lifecycle. Now zoom all the way in, to the single idea that the rest of IEC 61508 is built around. The standard splits every dangerous failure into two families, and it treats them in completely opposite ways. Part 4 gives you the definitions: random hardware failure, and systematic failure. Part of the Critical Systems Analysis functional-safety series on IEC 61508. In this episode: Picture your development pipeline as a row of gates: review, integration test, validation.Here's the core split.The standard is precise about that right-hand column.Now here's the line that matters, and it's the whole reason this video exists.So if you can't calculate your way out of a systematic fault, what do you do instead? You apply rigor, and you scale it.Reference: Definitions of 'random hardware failure' and 'systematic failure' live in IEC 61508-4 (definitions and abbreviations); I described the concepts and edition rather than citing speci More in this series: IEC 61508 — Functional Safety Foundations | Functional Safety Assessment and Services Explore more from Critical Systems Analysis. Partner with usFollow on LinkedInVisit our websiteRead our feature on Automate.orgAll shows on Apple Podcasts: AI & ML Safety | Fault Tree Analysis | FS Assessment | Safety Analysis | IEC 61508 | IEC 62443 | ISO 10218 | ISO 12100 | ISO 13849 | ISO 26262 | ISO/PAS 8800 | ISO 26262-11 | V-Model | UL 4600.

    IEC 61508: Random vs Systematic Failures

  4. Aug 22

    IEC 61508: Fault Avoidance vs Fault Control

    So far we've walked the whole safety lifecycle, cradle to grave. Now zoom all the way in on one idea that sits underneath every single phase of it. IEC 61508 fights failure two different ways at once, and it never, ever lets you blur them together. One way is keeping faults out in the first place. The other is catching faults once they're already in. Part of the Critical Systems Analysis functional-safety series on IEC 61508. In this episode: Here's the confusion this episode kills.Quick re-anchor on scope, so we're all standing in the same place.So here are the two approaches laid side by side.Now the key that unlocks the whole thing.Draw it as a two-by-two.Let's make the boundary concrete.Reference: Specific clause and annex numbers were intentionally not asserted. In IEC 61508-2 the 'techniques and measures' tables for control of failures and for avoidance of failures live in More in this series: IEC 61508 — Functional Safety Foundations | Functional Safety Assessment and Services Explore more from Critical Systems Analysis. Partner with usFollow on LinkedInVisit our websiteRead our feature on Automate.orgAll shows on Apple Podcasts: AI & ML Safety | Fault Tree Analysis | FS Assessment | Safety Analysis | IEC 61508 | IEC 62443 | ISO 10218 | ISO 12100 | ISO 13849 | ISO 26262 | ISO/PAS 8800 | ISO 26262-11 | V-Model | UL 4600.

    IEC 61508: Fault Avoidance vs Fault Control

  5. Aug 22

    IEC 61508: Residual Error Rate of Safe Communication

    Zoom all the way in now. Past the standards family, past the safety lifecycle, past the big hardware chapters, until you land on one quiet requirement in Part 2 of IEC 61508 : the rules for safe data communication. Here is the problem it solves. Your sensor and your logic solver almost never sit in the same box. Part of the Critical Systems Analysis functional-safety series on IEC 61508. In this episode: IEC 61508, safe communication.Start with the loop every safety function runs: sense, decide, act.Let's define that idea.Every failure sorts into the same two-by-two this whole hardware pack uses: safe or dangerous, detected or undetected.The standard makes you enumerate the ways a message can go wrong and pair each one with a defense.That question has a name: the residual error rate, written with the Greek letter lambda.Reference: Clause location: IEC 61508-2:2010 contains the data-communication requirement (widely cited as clause 7.4.11, 'Requirements for data communication process'). The narration names it More in this series: IEC 61508 — Functional Safety Foundations | Functional Safety Assessment and Services Explore more from Critical Systems Analysis. Partner with usFollow on LinkedInVisit our websiteRead our feature on Automate.orgAll shows on Apple Podcasts: AI & ML Safety | Fault Tree Analysis | FS Assessment | Safety Analysis | IEC 61508 | IEC 62443 | ISO 10218 | ISO 12100 | ISO 13849 | ISO 26262 | ISO/PAS 8800 | ISO 26262-11 | V-Model | UL 4600.

    IEC 61508: Residual Error Rate of Safe Communication

  6. Aug 22

    IEC 61508: Common Cause Failures and the Beta Factor

    We've zoomed a long way down. From the whole family of safety standards, into IEC 61508 along its safety lifecycle. Now we drop into one specific, uncomfortable corner of the hardware world. Here's the setup. When one channel isn't reliable enough, you add a second one. Two channels, either can do the job, and now both have to fail before the safety function is lost. Part of the Critical Systems Analysis functional-safety series on IEC 61508. In this episode: So let's name the clause.First, locate the hardware.Here's the promise you were sold.But there are two very different ways for that pair to die.What actually ships the same fault to both channels? Almost always something they share.So the standard gives you one number to capture all of that.Reference: The common cause failure quantification method is in IEC 61508-6:2010, Annex D (the beta-factor model with a scored checklist and conversion tables). Confirm the exact edition/anne More in this series: IEC 61508 — Functional Safety Foundations | Functional Safety Assessment and Services Explore more from Critical Systems Analysis. Partner with usFollow on LinkedInVisit our websiteRead our feature on Automate.orgAll shows on Apple Podcasts: AI & ML Safety | Fault Tree Analysis | FS Assessment | Safety Analysis | IEC 61508 | IEC 62443 | ISO 10218 | ISO 12100 | ISO 13849 | ISO 26262 | ISO/PAS 8800 | ISO 26262-11 | V-Model | UL 4600.

    IEC 61508: Common Cause Failures and the Beta Factor

  7. Aug 22

    IEC 61508: Risk Reduction and the ALARP Principle

    You've walked the lifecycle. Now zoom all the way in on the one question every safety function exists to answer: how much is enough? IEC 61508 doesn't let you guess. It draws a line from the risk your equipment poses when nothing protects it, down to a level of risk people can actually live with. The distance between those two lines is the necessary risk reduction. Part of the Critical Systems Analysis functional-safety series on IEC 61508. In this episode: This is IEC 61508, the standard for functional safety of electrical, electronic, and programmable electronic safety systems.Start with what can go wrong.Where are we in the work? You've already identified the hazards and estimated the risk each one carries.Here's the trap: risk is not one number.Picture two levels stacked up.How do you turn those factors into a target level? One method in Part 5 is the risk graph.Reference: ALARP is not a core normative requirement of IEC 61508; the ALARP model and the three risk regions (intolerable / tolerable-if-ALARP / broadly acceptable) are presented in the info More in this series: IEC 61508 — Functional Safety Foundations | Functional Safety Assessment and Services Explore more from Critical Systems Analysis. Partner with usFollow on LinkedInVisit our websiteRead our feature on Automate.orgAll shows on Apple Podcasts: AI & ML Safety | Fault Tree Analysis | FS Assessment | Safety Analysis | IEC 61508 | IEC 62443 | ISO 10218 | ISO 12100 | ISO 13849 | ISO 26262 | ISO/PAS 8800 | ISO 26262-11 | V-Model | UL 4600.

    IEC 61508: Risk Reduction and the ALARP Principle

  8. Aug 22

    IEC 61508: Functional Safety Assessment (FSA)

    Movement four. We stop circling the safety lifecycle and drop the camera straight onto one clause. Open part 1 of IEC 61508 turn to clause 8. Its title is Functional Safety Assessment. Part of the Critical Systems Analysis functional-safety series on IEC 61508. In this episode: So here is where we are standing.Start with what the phrase actually means, because it is easy to misread.It is tempting to blur assessment into verification and validation, so let us split them.The assessor works across the whole picture, not one document.Here is the move that makes clause 8 bite.Those three levels have precise meanings.Reference: IEC 61508-1:2010 Clause 8 is titled 'Functional safety assessment' (objectives in 8.1, requirements in 8.2). High confidence, but confirm exact sub-clause numbering before final re More in this series: IEC 61508 — Functional Safety Foundations | Functional Safety Assessment and Services Explore more from Critical Systems Analysis. Partner with usFollow on LinkedInVisit our websiteRead our feature on Automate.orgAll shows on Apple Podcasts: AI & ML Safety | Fault Tree Analysis | FS Assessment | Safety Analysis | IEC 61508 | IEC 62443 | ISO 10218 | ISO 12100 | ISO 13849 | ISO 26262 | ISO/PAS 8800 | ISO 26262-11 | V-Model | UL 4600.

    IEC 61508: Functional Safety Assessment (FSA)
See All (55)

About

"IEC 61508 — Functional Safety Foundations" is a serial video course from CSA, published weekly in strict curriculum order — building from foundational terms and structure through lifecycle practice to advanced, assessor-level topics. Designed for working functional-safety engineers and managers, not beginners or students. CSA is a functional safety, reliability, and certification consultancy serving robotics, autonomous systems, transportation, and industrial equipment manufacturers. CSA provides end-to-end safety engineering services: preliminary gap analyses and safety audits, SIL/PL determination, FMEA and FMEDA execution, fault tree analysis, safety case development, hardware metrics (SPFM/LFM/PMHF), lifecycle documentation, and embedded safety engineering support. CSA engineers work alongside product teams from architecture through final functional safety assessment, and support companies seeking NRTL, CE, ATEX, ISO 26262, and UL 4600 marks. Contact: Sales@criticalsa.com. This series is part of the CSA Functional Safety Network — a coordinated set of weekly video courses covering IEC 61508, ISO 26262, ISO/SAE 21434, SOTIF (ISO 21448), UL 4600, IEC 62443, ISO/PAS 8800, ISO 13849, machinery safety, safety analysis methods, and more. Each show links to the others so practitioners can follow the thread that matches their project.

Information

More From Critical Systems Analysis