Basis and reasons for including Class I and II major hazard sources in the SIS system

Thread Content

1. Method for determining whether a unit should be included in the SIS system: Whether a unit needs to be part of the SIS system is determined in two ways. One method is to conduct a Hazard and Operability Study (HAZOP) on the unit’s processes, flow diagrams, equipment, piping, instruments, etc., in order to assess whether it has SIL1, SIL2, or SIL3 rated circuits; if such circuits exist, then a SIS system is necessary, otherwise it is not. Secondly, the managers (owners or insurance companies) have the right to decide on their own whether to use an SIS system; they can make this decision without conducting a HAZOP analysis. If the managers decide that an SIS is necessary, it is also up to them to determine the SIL level, as stated in IEC61511. If SIS is not needed, then it can be omitted, with the risks and disaster consequences borne by the decision-makers themselves. Among them, the series of directive documents, notices, and guiding principles issued by the former **Work Safety Supervision Bureau (which are equivalent to laws and regulations) fall into the second category; examples include Order No. 3116 and Order No. 40 issued by the Work Safety Supervision Bureau. 2. **Instructions from the Ministry of Emergency Management (including the former **General Administration of Work Safety): ① “Guiding Opinions of the General Administration of Work Safety on Strengthening the Management of Chemical Process Safety Instrumented Systems” (No. An Jian Zong Guan San 116): Article 1 states that chemical process safety instrumented systems (SIS) include safety interlock systems, emergency shutdown systems, as well as systems for detecting and protecting against toxic and harmful gases, flammable gases, and fires. The safety instrumented system is independent of the process control systems (such as distributed control systems, etc.). It remains in a dormant or inactive state during normal production, but can act instantly and accurately once a situation that could lead to a safety accident occurs in the production facility, thereby stopping the production process safely or bringing it into a predetermined safe state. It must have high reliability (i.e., functional safety) as well as proper maintenance and management. If the safety instrumented system fails, it can often result in serious safety accidents; most of the major chemical (hazardous chemicals) accidents that have occurred in developed countries in recent years have been related to failures in the safety instrumented systems or improper installation of these systems. Based on the consequences and risks resulting from the failure of safety instrument functions, these functions are classified into different safety integrity levels (SIL1-4, with level 4 being the highest). Safety instrumented systems of different levels have varying technical requirements in terms of design, manufacturing, installation and commissioning, as well as operation and maintenance. Article (III) requires further improvement of the technical standards and certification system for chemical process safety instrument systems. Accelerate the formulation and revision of the technical standard system for chemical process safety instrumented systems. In accordance with \"Functional Safety of Electrical/Electronic/Programmable Electronic Safety-Related Systems\" (GB/T20438) and \"Functional Safety of Safety Instrumented Systems in the Process Industry\" (GB/T21109), a functional safety certification service system for relevant personnel, products, and organizations is being established step by step. Article (XIII) requires that, as of January 1, 2018, all newly constructed chemical processing units and hazardous chemicals storage facilities involving the \"two key areas and one major concern\" must be designed with safety instrument systems that meet the specified requirements. For the safety instrument systems of other newly built chemical processing units and hazardous chemical storage facilities, starting from January 1, 2020, it is necessary to comply with the requirements of functional safety standards and design safety instrument systems that meet those requirements. Article (XIV) requires that chemical enterprises and hazardous chemicals storage units dealing with operational production units or facilities that fall under the category of “two key points and one major issue” shall, on the basis of conducting comprehensive process hazard analyses (such as Hazard and Operability Studies), determine the functions of safety instruments and the requirements for risk reduction through risk analysis, and promptly assess whether the existing safety instrument functions meet those risk reduction requirements. ②\"Standards for Identifying Major Safety Hazards in Chemical and Hazardous Chemicals Production and Operation Units (Trial)\\" (Safety Supervision Administration Order No. San121): Article 5 requires that hazardous chemical storage areas that constitute level 1 or level 2 major hazard sources must have an emergency shutdown function in place ； The hazardous chemical storage areas that constitute Class I and Class II major hazard sources involving toxic gases, liquefied gases, and highly toxic liquids are not equipped with independent safety instrument systems. Interpretation of Article 5: In chemical storage areas that constitute major hazard sources of Level 1 or Level 2, due to the severe consequences that can result from accidents, emergency shutdown systems must be installed in each storage tank to enable emergency isolation. For storage tanks directly connected to upstream production units, if installing an emergency shut-off valve could lead to abnormalities such as overpressure in the production units, an emergency switching mechanism can be employed to prevent issues like excessive liquid level or overpressure in the tanks, thereby achieving the function of emergency shutdown. Interpretation of the fifth criterion for key counties: a. In chemical storage areas that constitute major hazard sources of level 1 or level 2, emergency shut-off valves must be installed at the inlets and outlets of each storage tank; otherwise, it is considered a serious safety hazard. b. For hazardous chemical storage areas that constitute primary or secondary major hazard sources, if a main emergency shut-off valve is installed on the main inlet and outlet pipelines of the storage area but no such valves are installed on individual storage tanks, it is considered a serious safety hazard. c. For hazardous chemical tank areas that constitute level 1 or level 2 major hazard sources, if an emergency switching mechanism is installed between storage tanks of the same purpose to prevent situations such as overfilling or overpressure in the tanks, they are not considered to be major safety hazards. d. For hazardous chemical storage areas that constitute level 1 or level 2 major hazard sources, if the storage tanks do not have an emergency shutdown function, but the enterprise has conducted HAZOP analyses and SIL assessments and the results show that safety requirements are met, then it may not be considered a major safety hazard. e. Hazardous chemical storage areas that are classified as major hazard sources of level 1 or 2 and involve toxic gases, liquefied gases, or highly toxic liquids do not have an independent safety instrumented system, which is considered a serious safety hazard. ③The Interim Provisions on the Supervision and Management of Major Hazard Sources of Hazardous Chemicals (**Order No. 40 of the State Administration of Work Safety**): Article 13 requires that hazardous chemical enterprises shall, based on the types and quantities of hazardous chemicals that constitute major hazard sources, as well as the production and usage processes (methods) or relevant equipment and facilities, establish and improve safety monitoring systems in accordance with the following requirements to enhance control measures: (1) Major hazard sources shall be equipped with systems for continuous collection and monitoring of information such as temperature, pressure, liquid level, flow rate, and composition, as well as detection and alarm devices for leaks of flammable gases and toxic and harmful gases; such systems shall also have functions such as remote data transmission, continuous recording, accident early warning, and information storage ； Primary or secondary major hazard sources are equipped with an emergency shutdown function. The electronic data recorded shall be retained for no less than 30 days ； (II) Automated control systems for chemical production facilities and equipment with major hazard sources that meet safety production requirements ； For Class 1 or Class 2 major hazard sources, an emergency shutdown system is required ； (III) Install emergency shut-off devices for key facilities such as toxic gases, highly toxic liquids, and flammable gases among the major hazard sources ； For facilities handling toxic gases, emergency devices for dealing with leaks must be installed. For major hazard sources of level 1 or 2 involving toxic gases, liquefied gases, or highly toxic liquids, an independent Safety Instrumented System (SIS) is required ； ④“Notice of the General Office of the State Council on Issuing the Comprehensive Management Plan for the Safety of Hazardous Chemicals” (Guo Ban Fa No. 88): Article 21 – New chemical processing units must be equipped with automated control systems. Chemical processing units that fall under the category of “two key areas and one major hazard” must be equipped with safety instrumented systems, and major sources of hazard related to hazardous chemicals must have sound safety monitoring and control systems in place. 3. How are relevant standards and specifications specified? ①According to Clause 3.2.3 of \"Functional Safety of Safety Instrumented Systems in the Process Industry – Part 1: Framework, Definitions, Systems, Hardware, and Application Programming Requirements\" (GB/T21109.1-2022/IEC61511-1:2016), a Basic Process Control System (BPCS) is a system that responds to input signals from the process and its associated equipment, other programmable systems, and/or operators, and generates output signals to ensure that the process and its related equipment operate in the desired manner; however, it does not implement any SIFs. ②Clause 3.2.3 of \"Functional Safety of Safety Instrumented Systems in the Process Industry – Part 1: Framework, Definitions, System, Hardware, and Software Requirements\" (GB/T21109.1-2007/IEC61511-1:2003) requires that DCS systems shall not perform any instrument safety functions designated with a SIL ≥ 1. ③According to Article 8.2.1 of the \"Code for Design of Safety Instrumented Systems in Petrochemical Industries\" (GB/T50770-2013), for SIL1 level safety instrumented functions, it is advisable to separate the logic controllers from the basic process control system. 8.2.2 For SIL2 safety instrumented functions, the logic controller shall be separated from the basic process control system. ④Article 8.2.1 of the \"Code for Design of Safety Instrumented Systems in Petrochemical Industries\" (GB/T50770-2013) (revised version in 2023, not yet officially issued): For SIL1-level safety instrumented functions, the logic controller should be separated from the basic process control system. In summary, in accordance with current standard requirements, for those SIF circuits related to major hazard sources of level 1 and 2, if their integrity level is SIL1, and given the current standards’ recommendations that such circuits should be installed separately either as a matter of preference or as a requirement, it is likely that in the future such separation will become a mandatory requirement. It is therefore recommended to install an independent SIS system to fulfill the safety functions associated with these circuits. In accordance with **regulatory requirements, Order No. 40 stipulates that primary or secondary major hazard sources must be equipped with an emergency shutdown system ； For major hazard sources of level 1 or 2 involving toxic gases, liquefied gases, or highly toxic liquids, an independent Safety Instrumented System (SIS) is required ； Document No. 116: The Safety Instrumented System (SIS) includes safety interlock systems and emergency shutdown systems; all newly constructed chemical processing units and hazardous chemical storage facilities that fall under the category of “two key areas and one major hazard” must be equipped with Safety Instrumented Systems that meet the required standards. Document No. 88: Safety instrument systems shall be installed in chemical plants classified as “two key items and one major item”.