Should SIL0 and SILa be integrated into the SIS system?
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I would like to ask everyone: 1. Should SIL0 and SILa be integrated into the SIS system? 2. If SIL0 and SILa are integrated into the SIS system, are there any requirements regarding the SIL level of the associated instruments? What is the basis? Thank you~
It’s optional whether to use SILa or not; we’ve chosen not to use it. As for the relevant documents, ask the design institute – they usually have them
If SILa doesn’t proceed, what about the remaining risks? Are there any other alternative suggestions?
The requirement for SILa level is that it can be integrated into either a DCS or a SIS – either one will do. For ratings above SILa, integration into a SIS is necessary; moreover, maintaining a SIS is very complicated, and it’s unlikely that many organizations are able to meet the standards for such maintenance
Where does this requirement come from?
Furthermore, the scenario-independent protection layer of SILa already takes DCS into account; is it possible to go further with DCS? Is it equivalent to unlimited use of DCS?
No relevant documents showing the direct output were found for this; however, the definition of SILa implies that the functionality of the SIF circuit should be preserved, with no requirements specified regarding the SIL level； Previously, my company’s requirements for Sila-level management did not specify any specific functional safety requirements; safety functions could be integrated into the process control system, but it was recommended to manage them in accordance with functional safety standards
Please take a look at these two screenshots. When conducting a LOAP analysis, if process control systems are taken into consideration, it is theoretically recommended to either proceed with SIS or eliminate the associated risks; this is based on the evaluations of those who prepare the LOAP reports for you
The term SILa appears only in the graphical method of IEC61511-3, where it is defined as having no special safety requirements. Apart from this, no other documents contain definitions for SILa/SIL0; these are merely customary terms used within the industry. So you’re right; the interpretation of SILa’s definition is to retain the function of the SIF circuit, which actually means it becomes part of the SIS system. Can something that becomes part of the DCS be called an SIF circuit?
The views expressed in this article are the same as those I mentioned earlier. The premise for using DCS in SILa is that DCS was not utilized in the analysis of the independent protection layers conducted earlier