Is the SIL assessment of instruments applied to all instruments in all control loops, or only to those in the SIS and ESD systems?

Only instruments for SIS and ESD systems are covered; the rest fall under the scope of DCS

Does the instrument of the compressor’s built-in shutdown protection system need to undergo a SIL assessment?

Additionally, does the fire and gas detection system require a SIL assessment?

Theoretically, an evaluation is required; in practice, it constitutes the second evaluation (mainly for complete sets of equipment), while the first evaluation is aimed at the process itself and utility systems. However, the compressor features a \"modular\" design from the manufacturer’s side, so there are no major safety concerns. Potential differences between the owner and the manufacturer may relate to the options for pallet configuration and redundancy configuration. Fire systems do not require SIL certification ； The gas system does not require a SIL certification either, as there is no “output interlock function”. I’m not familiar with whether the fire and gas systems on offshore oil platforms require SIL certification (it might be required). @jiaguoyun

**Document No. 116 issued by the State Administration of Work Safety states that a chemical process safety instrumented system (SIS) includes safety interlock systems, emergency shutdown systems, as well as detection and protection systems for toxic and harmful gases, flammable gases, and fires. According to this definition, when conducting a SIL assessment for safety instrumented systems, it is also necessary to assess toxic and hazardous substances, flammable gases, as well as fire detection and protection systems. So how is a SIL assessment carried out for toxic and hazardous substances, flammable gases, and fire detection and protection systems?

**Order No. 116 issued by the State Administration of Work Safety categorizes gas detection systems and fire protection systems under Safety Instrumented Systems (SIS), which is a rather broad approach. 1. To set up an SIS system, it is first necessary to evaluate the protected assets and classify the interlock circuits as SIL 1–3. Once the instrumentation team has received this information, they can proceed with designing the SIS system; without the necessary prerequisites, such SIS design is merely theoretical. 2. A SIS system without safety interlock outputs is of little use. (The gas alarm light does not belong to the safety interlock outputs) 3. Indeed, there are manufacturers that have obtained SIL and fire safety certifications, but not many; these certifications are mainly intended for offshore oil platforms. Gas entering the SIS encountered this once: the interaction between the gas outside the explosion-proof control room and the air conditioning system. Since there is an output, it has been classified under the SIS system. Safety systems are new technologies, and implementing them is difficult because people used to think of them in simple terms (just replace it with an SIS-PLC). In fact, this is a broad field, and the SIS system is just one component within it. As far as I know, the work safety authorities are piloting the implementation of SIS in the Wuxi Development Zone by hiring a large number of experts, with the aim of gaining experience in how to evaluate, characterize, design, and supervise SIS systems, and of finding a reasonable approach for this purpose. In the long run, it would be fine to incorporate interlocks for the tank area into the SIS, which will reduce troubles in the future. @jiaguoyun

Does that mean the SIL assessment applies only to SIS systems that include ESD systems, and not to gas detection systems and fire protection systems?

FGS (Fire and Gas System) is one of the application areas of SIS; it refers to what we call fire protection and detection of toxic and harmful gases. In China, I am aware of its use on CNOOC’s offshore platforms (Honeywell SM and Yokogawa ProSafe), as well as at the Puguang gas field (Honeywell SM).

Based on my sources, after the incident in Tianjin, the work safety supervision authorities held a meeting with the aim of strengthening the enforcement of rule 116. It is estimated that the gas system of the new project should be classified under the SIS category (regardless of whether there are outputs or not), with the aim of having everything configured in advance (as more interlock outputs might be required in the future). Fire systems involve fire safety certification; there are many domestic products (but few with SIS certification). This requires some time for a transition, once there are more certified products. The roadmap is still unclear at the moment, and in the long run, there’s no escape. @jiaguoyun

This depends on the design; it is necessary to determine which level among SIL1 to SIL3 the design’s interlock circuit falls into, and the circuit must be configured accordingly. For SIL calculations, manufacturers of each component are required to provide SIL certificates, which contain the PFD coefficients needed for these calculations； It should be noted that although each component possesses an SIL certificate of the corresponding level, the entire circuit may not meet the SIL requirements as a whole.