SIL Evaluation in HAZOP? (Easy) LOPA needed for SIL determination? (No)
“Are You conducting SIL assessment session along with HAZOP?” Note that this question does not include the term LOPA. We do not use LOPA during a HAZOP (unless clients make us) and yet we identify most of the SIFs and we set the needed SIL at that time (no numbers; no other analysis). We do the same as we discuss a relief valve and make sure it has the capacity for the scenario under concern. LOPA is not required for either of these tasks (and many other similar tasks) of judging IPLs worthy or not, unless the scenario is confusing to the HAZOP (PHA) team. So, we can state a SIF is needed or not in a HAZOP and we can state the SIL there as well. Period. This is also allowed by IEC and ANSI/IEC. But, we (the HAZOP team) will recommned a LOPA when we are confused; LOPA will almost always clear up the confusion so that QRA (like FTA, ETA, consequence modeling, BowTie, etc.) are practically never needed (except to calibrate a site on certain scenarios, or to resolve questions on 1 out of 10,000 scenarios.)
We have done LOPA during the HAZOP many hundreds of time; becuase some clients force us to it that way. But, if you drop the explicit requirement for doing a LOPA everytime a SIF is discussed, you will find better efficiency in your HAZOPs.
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