Discussion on SILa or SIL0 automatic control modes
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Guys, what are your thoughts on whether the automatic control interlock methods of SILa or SIL0 should be part of the DCS system or the SIS system?
SIL0 can be implemented using either DCS or SIS; in fact, this interlock may not even be necessary； SILa indicates that the risk remaining in the current scenario is 10 times or less; if DCS is already in use, then SILa can only be represented by SIS ； If DCS has not been used, it can be implemented either with DCS or with SIS.
Strictly speaking, there are no SIL0 and SILa; the standards only mention SIL1, SIL2, and SIL3
Yes, the standards do not define SILa or SIL0, but some LOPA analyses mention them; I’d like to understand what that means. Thank you very much!
Yes, according to the specifications, there are subsequently the four levels of SIL1, 2, 3, and 4
What I understand is that at this point, even if an accident occurs, it will not pose a significant threat to the equipment or personnel. In this case, the rating will not be very high, and interlocked instruments are not required for protection.
Yes, if there is no SIL rating, it is generally sufficient to use DCS interlocks; this is the common practice. I also consulted experts in HAZOP analysis and design firms, and I received the same answer. However, some people believe that since the system is rated as SILa or SIL0, there is no need for a SIS system, but the instruments used must still have safety rating certifications. But I lean more towards the first explanation.
SILa or SIL0 refers to circuits that are on the edge of the risk spectrum. In my opinion, although they do not need to be managed as SIS circuits, they still represent a protection layer against moderate to high risks, and they are considered critical circuits in DCS systems.
Yes, I tend to set SILa or SIL0 in the DCS system