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59 contributions to Functional Safety Play Book
7d •
Quick question for the group 👇
I’ve always been interested in the management side of functional safety rather than the calculations. If you’re currently managing functional safety on a project, what is the one thing that causes you the most frustration? Don’t give me the textbook answer — tell me what actually annoys you. What do you find yourself repeatedly chasing, checking, updating or worrying about? I’m looking at ways we could make the management of functional safety significantly easier, so I’d really value some real-world examples from the group. Even if it seems like a small problem, put it below. 👇
0 likes • 6d
@Ross Benton that’s a great one.
0 likes • 3d
@Ross Benton completely agree it would be extremely useful if everyone just attended a one day course.
6d •
NEW: Incident Autopsy Live 🔍
Starting next Friday, we'll review a US Chemical Safety Board incident reconstruction together and look at it from a functional safety point of view. For each incident we'll work through: ➡️ What the hazard was and what should have prevented it ➡️ Where the SIS, alarms or other safeguards failed ➡️ Where in the safety lifecycle the failure started ➡️ Whether it could happen on your project After each session I'll post a short summary of the lessons from experience, so we build up a library over time. First session: 📅 Friday 2nd October ⏰ 10:00 UK 📍 Link in the calendar Comment below if you're wanting to attend. I’ll put a link to the case beforehand
1 like • 6d
https://youtu.be/-UoyIV6oZEc?is=Xwd7KNPLbyMRLCMU
0 likes • 6d
This will be the incident to discuss. I watched it the other day and there was so many lessons to learn from it
7d •
One SIF or two SIFs?
I would like to present a very common analytical scenario for discussion. It's related to a hazardous scenario which requires us to cut off the flow of the process medium to a some part of the installation. This is achieved by shutting down the pump. However, the system comprises two pumps (A and B) where one is in operation and the other in a standby mode. When verifying SIL, should we assume a single SIF with a 2oo2 configuration for the pump shutdown, or should we analyze two separate functions, each responsible for shutting down an individual pump?
0 likes • 6d
Good point, Ross, and I agree if the standby can't start. Then the SIF only needs to trip the duty pump, and 2oo2 would be overly conservative. The caveat is auto-changeover. Sometimes the duty/standby sets the standby starts on low pressure or a duty trip, so the SIF trips one pump and the other picks up the flow. In that case holding the standby off isn't a secondary action. It's part of the safe state, so it needs to be inside the SIF, in the PFD calc and in the proof test. I think that’s where Tomasz's 2oo2 is correct. Tomasz, does this pump set have auto-changeover?
22d •
Valve SIL Calculation
Good morning Everyone, For valve SIL calculations, do we need to include the failure rates of all valve components, such as the solenoid, actuator, and valve body? Should the actuator and valve body also be included?
2 likes • 21d
Hi Khalid, yes, all of it. Solenoid, actuator and valve body. Clause 3.2.22 of 61511-1 defines the final element as the part of the SIS that implements the physical action to reach the safe state, and the note underneath spells out that this includes the auxiliaries the solenoid and actuator used to operate the valve. So "the valve" in a SIL calculation means the whole assembly, not just the body in the line. Simple test: if a dangerous undetected failure of that component stops the valve reaching its safe position, it goes in. They're in series, so add the λDU values first, then convert the total. Two things that catch people out. Instrument air 11.9.2 l) asks you to account for the reliability of any utility the SIS depends on. And certificate boundaries check the safety manual before adding vendor numbers, because some cover actuator and valve together, some only the body. Have a look at Annex F of 61511-2 as well. The worked example models the solenoid (MTTFd 35 years) and the vent valve (60 years) as separate events in the fault tree. Both counted, separately. The final element is usually the biggest contributor to SIF PFD, so it's the one worth getting right.
25d •
Free lesson for Premium members: Nuclear Runs on a Safety Case
Quick one for Premium members. I've just published a lesson called "Nuclear Runs on a Safety Case" as part of the Get into Nuclear Foundations unit — it's included free with your Premium membership, no VIP upgrade needed. It's the piece that explains why nuclear safety works on argued cases rather than checklist compliance, which is a key concept to grasp when coming into the industry. I want to make sure it's actually landing before I finalise the full course, so if wouldnt mind, go through it and tell me: Did the "argument vs. compliance" distinction make sense, or did you have to reread it? Was there a point where you thought "wait, what?" Anything you'd want explained differently to make it click faster? Drop it in the comments here, or reply directly on the lesson. Genuinely want the rough edges
0 likes • 24d
Thanks Bachir, really appreciate the feedback and glad you liked it. I’m still preparing the full course but I’ll let you know when it’s ready.
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@richard-kelly-4141
Functional Safety Expert with 15+ years in Nuclear Defence, simplifying FS to what’s needed—no more, no less.
Active 9h ago
Joined Aug 18, 2025