Is the SIL assessment of instruments applied to all instruments in all control loops, or only to those in the SIS and ESD systems?
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Which instruments need to be included in the SIL assessment for refinery units? Do the instruments of the compressor’s built-in shutdown protection system require a SIL assessment? Do fire and gas detection systems require a SIL assessment? **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?
Theoretically, it is required in all cases; at the very least, the manufacturer should provide the SIL assessment results themselves
SIL certification is divided into 4 levels in total: SIL1, SIL2, SIL3, and SIL4, covering both the product and system levels. It includes aspects such as on-site instruments; this concept is too broad in scope, and given my limited skills, I am unable to explain it.
This is how I understand it; I’m not sure if it’s correct. The safety level SIL is a concept related to a system, and it includes safety controllers (with redundancy and fault tolerance), field sensors, final actuation elements, etc. In this SIF, none of them may fail to meet the required SIL. For combustible gas detection, the specifications allow for the use of a separate secondary alarm instrument, or for integration with an I/O card in the DCS system. This card operates independently, so that a failure in the DCS process monitoring instruments does not affect combustible gas detection. If connected using either of the above methods, I don’t think it’s necessary for the combustible gas detector to have a SIL rating, since neither your DCS nor the secondary instruments have such a rating. Another approach is to use F&GS; F&GS consists of a PLC and a fire alarm system. Generally, outdoor devices such as combustible gas detectors, flame detectors, temperature sensors, and fire valves are connected to the PLC, while indoor smoke and temperature sensors are connected to the fire alarm controller. The fire alarm controller communicates with the PLC. The PLC specifications here require safety-rated PLCs that meet SIL certification standards; therefore, instruments such as flammable gas detectors on site must also comply with SIL requirements, so that the corresponding SIF meets the required SIL level!
Do fire and gas detection systems require a SIL assessment? All SIFs in the SIS system that require a SIL level must be evaluated. A complete SIF includes systems such as the sensor, the logic solver, and the final element F&G GDS; these belong to safety instrumented systems. However, without an actuator, it is not a complete SIF. There is no need to perform SIL verification for the system circuit. However, hardware requires SIL level specifications.
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