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Functional Safety Play Book
230 members • Free
4 contributions to Functional Safety Play Book
17d •
Hi All - Systems that pre date 61508
Hi all thanks for the add, this looks like a really good way to share experience in the functional safety world. Thanks for setting up Richard. I have a question for you all on the requirements when adding a new SIF to an existing SIL2 system that was designed over 40 years ago and was never designed to 61508. What things would we consider to make this possible without a full system redesign.
1 like • 8d
@Tomasz Barnert I just recently completed an audit for an ammonia production facility that has been in existence for over 20 years. HAZOP, LOPA, SRS, and SIL validation were performed. The specialist who performed the SIL confirmation used partial data for some SIF components from analogues, which I think is not correct. However, even using data for analogues, half of the SIF did not confirm the established SIL. I am currently reading the document GN-001_Legacy_Safety_Systems to understand how to properly organize SIL confirmation for older safety systems.
0 likes • 8d
@Richard Kelly Yes, of course it is useful) But I realized that with poor documentation of SIS maintenance, and it is almost everywhere bad, it is not possible to confirm compliance with SIL
Jan 8 •
Mission Time
Hi all, thanks for accepting. First of all, I am new in functional safety and sorry for my bad english😊. Actually I have some doubt about one of variable in PFDavg calculation namely mission time, couple of question to all: 1. What will happen in the end of mission time?should end user decommissioned the plant?or just replace everything and the mission time will get restarted? 2. If it depend on end user, than based on what consideration usually for them to determine the correct mission time?and what is the reason behind that? 3. Since by the time PFDavg will get derated, and SIL claimed may decreased over the time, shouldn't end user decide to set the mission time before the SIL/RRF drops beyond the rating it should be? Hope you guys can share your knowledge. Thanks,
0 likes • 9d
It seemed to me that the time of the mission is determined by the manufacturer of a particular component or device.
1 like • 8d
@Tomasz Barnert Usually, the manufacturer declares two terms, the first warranty period, and the second service life.
Feb 9 •
Shared components
Hi All. Just thought I would post in here to get others thoughts on a scenario I have come across recently. I know it’s best practice to avoid a single element being used in multiple SIFs, but are there any factors to take into consideration for the calculation. For example, several vessels have a common feed supply and whilst each have their own level sensor and logic solver, the common feed line overfill trip valve is shared for all vessels. Each SIF will have a calculation of all components, but all are actually using the same valve. My understanding is no common cause can really be applied as all have a 1oo1 output function. On another note, the configuration would also result in more demands on the valve with it being shared. Downtime and maintenance would also be impacted if shared. Again, just to get other thoughts on other factors that should be taken into account in this scenario. Thanks, Craig
1 like • 9d
Thanks, interesting question. I think that since one valve controls the level in three tanks, the risk of valve failure will be higher than if the valve controlled one tank, i.e. the RRF for these safety functions will be higher.
1 like • 8d
@Tomasz Barnert OK, then, if the reasons for the overflow of the tanks are independent, well, for example, different BPCS circuits for each tank, then it's okay that one valve enters different SIFS, because the SIS controller also enters different SIFS, but we don't see anything wrong with that.
8d •
Hello
Hello everyone, I recently started working on functional security, after 10 years of experience in HAZOP and LOPA. I have a couple of questions. 1. How are systematic constraints determined, especially for architectures with HFT=1 2. at what stage is the SIL confirmation carried out, what is regulated it and does it include checking the SIF response time
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