Is a SIL assessment required for the interlocks set in the DCS?
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RT: The company is planning to conduct SIL assessments for existing installations in the near future. SIL assessments are required for two key installations and one major installation. For those that already have a SIS or ESD system, grading verification can be carried out based on the interlock circuits. If there are no interlock circuits in the device, or if the interlock circuits are located in the DCS system, how should the SIL assessment be carried out? Based on what should the SIL assessment be conducted? I would appreciate some guidance from those with expertise.
Shouldn’t a HAZOP be conducted first to determine the hazard level, so as to decide on the required SIL level?
There should be no problem. First, a HAZOP analysis is conducted, followed by SIL classification; then, an assessment of the SIL level is carried out for each control loop. If some interlocks are located within the DCS system, as long as the SIL level requirements are still met, there is no issue. Each issue needs to be analyzed on its own.
It doesn’t matter whether the interlock circuit is in a SIS or a DCS. The main approach is to conduct regular Hazop analyses, followed by LOPA analyses; based on the results of these analyses, the SIF circuits are determined. Nowadays, those rated as SIL1 or higher must be integrated into the SIS system, while other less important circuits that do not reach the SIL1 level can be incorporated into the DCS. The focus is on the LOPA analysis to determine the SIL level; it has nothing to do with where it was originally located!
In accordance with the requirements for closely monitoring hazardous processes, safety instrumentation systems are designed for those hazardous processes that meet the relevant criteria. If a process is hazardous and lacks an SIS system, such a system must be installed. For specific regulatory provisions, please refer to the standards.
The SIL level evaluates the safety integrity of an SIF function; that is, as long as a certain interlock constitutes a safety instrumented function, a LOPA analysis can be conducted based on the risk assessment. If the SIL level is 1 or higher, it is necessary to incorporate it into a SIS system. The most crucial difference between the SIS system and BPCS is that they are independent of each other; moreover, the SIS has a higher safety integrity level, which results in higher costs.
We are Beijing United Puken Engineering Technology Co., Ltd. Our company specializes in providing consulting services for process safety management in the petrochemical industry. Our services include HAZOP analysis for facilities related to the “two key areas and one major hazard,” SIL assessment of safety instrument systems, safety diagnostics for chemical enterprises (identification of potential hazards), establishment and implementation of dual-prevention mechanisms, development of safety standardization systems, and establishment of Process Safety Management systems (PSM). We have a professional team dedicated to ensuring the safe operation of your company. Contact number: 18513759261 (Jia Kun).