How to set up alarms and interlocks for tank farm level and emergency shut-off valves in DCS and SIS systems

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►How to set up alarms and interlocks for tank level and emergency shut-off valves in DCS and instrument safety systems? **What do the standards and documents require in this regard? ►Industry expert Engineer Fan Yongfeng provides an in-depth analysis of the knowledge related to alarms and interlocks for tank farm levels and emergency shut-off valves. ►Natural answers are available to the common problems that instrument technicians encounter regarding tank area level monitoring, as well as alarms and interlocks for emergency shut-off valves! I hope you read the article with these questions in mind: ① How many different types of level detection instruments should be installed in the same storage tank? ②Must key storage tanks such as liquefied gases and highly toxic liquids, which constitute major hazard sources, be equipped with emergency shut-off devices? ③Do all storage tanks require high and low liquid level alarms as well as interlocks? ④If an emergency shut-off valve is installed, are there any requirements regarding its installation location? ⑤Is it necessary to install an emergency shut-off valve interlock button on site? Are there any requirements for the installation location? GB50074-2014 \"Code for Design of Oil Depots\" ◆ Installation Requirements 15.1 Automatic control systems and instruments 15.1.1 Storage tanks with a capacity greater than 100 m3 shall be equipped with remote liquid level measurement instruments, which shall comply with the following provisions: 1 The continuous liquid level measurement signals shall be transmitted to the automatic control system in either analog form or via communication methods ； 2 High and low liquid level alarms should be installed in the automatic control system ； 3 The set level for the high liquid level alarm in storage tanks shall comply with the relevant provisions of the current industry standard \"Design Code for Tank Areas in Petrochemical Storage and Transportation Systems\" SH/T 3007 ； 4 The set level for the low liquid level alarm in storage tanks should be such that cavitation does not occur in the pumps. For external floating roof tanks and internal floating roof tanks, the set level for the low liquid level alarm (measured from the bottom of the tank) should be at least 0.2m higher than the height at which the floating roof touches the bottom of the tank. 15.1.4 The level measuring instruments used for high-high and low-low level alarm signals of storage tanks shall be separate continuous level measuring instruments or level switches; alarms and interlocks shall be set up in the automatic control system. ◆Interlock requirements 15.1.2 The following storage tanks shall be equipped with high liquid level alarms and interlocks; the high liquid level alarm shall be capable of simultaneously interlocking to close the control valve of the tank’s inlet pipeline: Storage tanks for Class A B and Class B liquids with a turnover rate of more than 6 times per year and a capacity of 10,000 m3 or more ； Type A-B and Type B liquid storage tanks with a turnover rate of 2 years less than or equal to 6 times, and a capacity exceeding 20,000 m³ ； 3 Storage tanks for liquids of toxicity grades I and II. 15.1.3 External floating roof tanks and internal floating roof tanks with a capacity of 50,000 m3 or more shall be equipped with a low-low liquid level alarm. The set height for the low-low liquid level alarm (measured from the bottom of the tank) should not be lower than the height at which the floating roof touches the bottom; the low-low liquid level alarm should also be capable of triggering pump shutdown via interlock. 15.1.4 The level measuring instruments used for high-high and low-low level alarm signals of storage tanks shall be separate continuous level measuring instruments or level switches; alarms and interlocks shall be set up in the automatic control system. 【Explanation of the provision】15.1.4 “Separate level continuous measurement instrument or level switch” refers to a level measurement instrument that, in addition to the “requirement for a remote-level measurement instrument,” is also used specifically for providing alarms and interlocks for high and low levels in the storage tank. ◆Setting and interlock requirements 15.1.2 The following storage tanks shall be equipped with high-high liquid level alarms and interlocks; the high-high liquid level alarm shall be capable of interlocking to close the control valve of the tank’s inlet pipeline as well ； 15.1.7 For the important process pumps, fire pumps, tank agitators and other electrical equipment, as well as control valves in Class I oil depots, in addition to being operable on-site, they should also be able to be controlled and have their status displayed from the control room. For the important process pumps, fire pumps, tank agitators and other electric equipment, as well as control valves in secondary oil depots, in addition to being operable on-site, it is also desirable that they can be controlled and their status monitored from the control room. 15.1.11 The start and stop of the fire pumps in primary oil storage facilities, as well as the operation of the control valves on the fire water pipelines and foam liquid pipelines, shall all be capable of being controlled remotely from the fire control room. The main control panel shall display the operating status of the pumps and the valve positions of the control valves. [Explanation of the provision] 15.1.7 This provision allows for real-time monitoring of the status of electric equipment, enabling timely handling of any abnormalities ； 15.1.11 This provision is intended to ensure the rapid activation of the fire suppression system in order to extinguish fires promptly. GB 50737-2011 \"Code for Design of Oil Reserve Tanks\" ◆ Installation requirements 11.1 Automatic control systems and instruments 11.1.2 Each oil tank shall be equipped with continuous level measurement instruments as well as high-level and low-level switches, and shall comply with the following provisions: 1 The accuracy of the level gauge shall be better than ±1mm ； The 2-channel continuous level gauge should have the functions of high-level alarm, low-level alarm, and interlock shutdown of the tank inlet valve at extremely high levels; the set point for the low-level alarm (measured from the bottom of the tank) should not be less than 2 meters ； 3 The high level switch should have the function of interlocking to close the oil tank inlet valve when the level is too high ； 4 The low-low level switch should have the function of interlocking to stop the oil pump and closing the pump outlet valve when a low-low level is reached; the setting height of this switch (measured from the bottom of the tank) should be no less than 1.85 m ； 【Explanation of the provision】11.1.2 Liquid level is the most important parameter that needs to be monitored in oil tanks; therefore, it is required that \"a continuous liquid level measuring instrument shall be installed in each oil tank.\" The high liquid level interlock to close the inlet valve prevents oil spillage when oil is being filled into the tank, and it is a necessary safety measure. The low liquid level switch is installed to prevent the floating roof legs from dropping to the bottom of the tank. In a floating roof tank, the floating roof generally floats on the surface of the oil and is in direct contact with it, which helps to prevent the evaporation of oil vapor. Moreover, there is no gas space except at the sealing rings, thus significantly eliminating the possibility of an explosive environment. During operation, it should be noted that except when servicing the oil tank, the floating roof must be prevented from dropping to the bottom. Once the floating roof settles to the bottom, a gas space is created between the oil surface and the floating roof. In the case of crude oil, the presence of this gas space means there are explosive gases present, which **increases the risk of fire. In the large oil depot fire that occurred in the north in 2010, several oil tanks with a capacity of 10×104 m3 were exposed to the flames from a distance of just over 10 meters; however, only tank No. 103 caught fire and was ultimately destroyed. The main reason for this was that the floating roof of that tank had been lowered at that time, and there was a small amount of oil inside the tank. Under the influence of the flames, the oil vapor present in the gas phase easily ignited, causing the fire. The typical height of the floating roof legs is 1.8 m; therefore, it is specified that the setting height of the \"very low liquid level switch (from the tank bottom plate) shall be no less than 1.85 m\"” ； Considering that there is a processing time of 10 minutes to 15 minutes after an alarm is triggered, it is specified that \"the set height for the low liquid level alarm (from the bottom of the tank) should not be less than 2 meters.\" ◆Requirement 11.1.10: The start and stop of fire pumps, as well as the operation of control valves on fire water pipes and foam pipelines, should be able to be controlled programmatically from the fire control room. The main control panel should be able to display the operating status of the pumps and the valve position signals of the electric valves. GB 50160-2018 \"Code for Fire Protection Design of Petrochemical Enterprises\" – Requirements 6.2.23: Storage tanks for flammable liquids shall be equipped with level gauges and high-level alarms; where necessary, automatic interlock systems to shut off the feeding facilities shall also be installed ； An automatic dehydrator should also be installed. Interlock requirements: 6.3 Above-ground storage tanks for liquefied hydrocarbons, flammable gases, and oxidizing gases ； 6.3.11 Liquefied hydrocarbon storage tanks shall be equipped with level gauges, thermometers, pressure gauges, safety valves, as well as high-level alarms and automatic interlock shutdown mechanisms for extremely high levels to cut off feed. 【Explanation of the provision】6.3.11 The NFPA 58 Code for Liquefied Petroleum Gas stipulates that: \"A high liquid level alarm shall be installed on refrigerated liquefied petroleum gas containers.\" “Refrigerated liquefied petroleum gas containers should be equipped with a high liquid level flow cut-off device, which should be independent of all instruments. ”Even for ambient-temperature storage tanks, such a regulation is safer. The automatic interlock shutdown device for high liquid levels is the most effective means to prevent oil tanks from overflowing; it is widely used nowadays and represents a reasonable setup. ◆Setting and interlock requirements 6.3.14 Full-pressure liquefied hydrocarbon storage tanks should be equipped with a secondary dehydration system that includes anti-freezing measures, and an emergency shut-off valve should be installed at the base of the tank. 6.4 Loading and unloading facilities for flammable liquids and liquefied hydrocarbons 6.4.1 An easily operable emergency shut-off valve shall be installed on the inlet pipeline for flammable liquids (excluding lubricating oils), at a distance of 10 m from the edge of the loading dock ； 6.4.2 When there are no buffer tanks at the station, an emergency shut-off valve that is easy to operate should be installed on the loading and unloading pipelines at a distance of more than 10 m from the loading/unloading cranes ； 7 Pipeline Layout 7.2 Process and Utility Pipelines 7.2.15 For pipelines leading from liquefied hydrocarbons and combustible liquids with an operating temperature equal to or above their auto-ignition point to the pump inlet, a shut-off valve should be installed near the base of the equipment. When the volume of the equipment exceeds 40 m3 and the distance between it and the pump is less than 15 m, this shut-off valve should be a remotely operated valve with a manual function; the control button for this remotely operated valve should be located at a distance of no less than 15 m from the pump. 7.4.7 When the length of an inter-plant pipeline exceeds 5 km, emergency shut-off valves as well as flow and pressure monitoring devices shall be installed on the pipelines located within the enclosure walls or land boundary lines of the enterprises upstream and downstream of it. 8.4.5 Vertical above-ground storage tanks for flammable liquids shall be equipped with a fixed or mobile fire cooling water system; the scope of water supply, flow rate, and installation method shall comply with the following provisions: 5 The control valves shall be located outside the fire dike, at a distance of not less than 15 m from the wall of the tank to be protected. The fire cooling water pipes installed behind the control valve and on the storage tank should be made of galvanized steel pipes. 8.10.10 The installation of fixed fire cooling water pipelines for fully pressurized and semi-refrigerated liquefied hydrocarbon storage tanks shall comply with the following provisions: 2 The fire cooling water system may use manual or remotely controlled valves; when the volume of the storage tank is equal to or greater than 1000 m3, remotely controlled valves shall be used ； 3 The control valve should be located outside the fire dike, at a distance of not less than 15m from the wall of the tank to be protected ； 【Explanation of the provision】 6.3.14 Installing an emergency shut-off valve at the base of the storage tank can reduce losses in the event of an accident in the pipeline system. 7.2.15 This provision is intended to allow for the timely shutdown of the material flow in the event of a fire in the downstream equipment directly connected to the tank. For example, if an accident and fire occur in the pump located downstream of the liquefied hydrocarbon tank in a plant’s product refining unit, it becomes impossible for personnel to approach the pump in order to shut off the isolation valve. Moreover, there is no isolation valve on the pipeline near the base of the tank between the pump and the tank, which results in the liquefied hydrocarbon in the tank being completely burned out before the fire can be extinguished, causing significant losses. API Std 2510, \"Design and Construction of Liquefied Petroleum Gas (LPG) Facilities\", specifies that isolation valves on liquefied hydrocarbon pipelines should be located as close as possible to the tanks, preferably at the tank wall nozzles. For ease of operation and maintenance, the shut-off valve should be installed in a location that is easily accessible. When the volume of a liquefied hydrocarbon tank exceeds 10,000 gal (≈38 m3), all isolation valves located on pipes below the highest liquid level in the tank must be able to close automatically or via remote control within 15 minutes of a fire breaking out. The control system for the isolation valve shall be fire-resistant, and the isolation valve shall be operable manually. In accordance with API standards, the volume of the liquefied hydrocarbon equipment has been adjusted to 40 m3. Given the higher likelihood of accidents involving pumps for flammable liquids whose operating temperature is equal to or above their auto-ignition point, it is necessary to add a requirement to install shut-off valves near the base of the equipment in the inlet pipes leading to pumps for such flammable liquid devices. GB 17681-1999 \"Technical Requirements for Acceptance of Safety Monitoring and Early Warning Systems for Flammable and Explosive Tank Areas\" ◆ Installation requirements 5.5 Liquid storage tanks must be equipped with level detection instruments, and at least two different types of such instruments shall be installed in each tank. Storage tanks holding flammable and explosive materials should be equipped with high and low liquid level alarm circuits; where necessary, they should also have an interlock system linking the liquid level to relevant process parameters. AQ 3036-2010 \"Code for the Installation of On-site Safety Monitoring Equipment in Tank Areas for Major Hazardous Sources of Hazardous Chemicals\" ◆ Installation requirements 6.3.1 Storage tanks shall be equipped with level monitors that have the capability to issue alarms when the liquid level is too high or too low. ◆Interlock requirements 6.3.7: Large combustible liquid storage tanks (over 5000 m3) and pressure storage tanks for hazardous chemicals (over 400 m3) shall be equipped with separate high-high liquid level monitoring, alarm, and interlock control systems. ◆Setup requirements 5 – Setup requirements for interlock control equipment 5.1 Interlock automatic control equipment can be installed to regulate parameters such as the temperature, liquid level, pressure of storage tanks, as well as the ambient temperature, based on actual conditions; this includes systems for automatic shutdown or transfer of materials, as well as spray cooling equipment. SH/T 3007-2014 \"Code for Design of Tank Areas in Petrochemical Storage and Transportation Systems\" ◆ Requirements for installation 5 Atmospheric and low-pressure tank areas 5.4 Selection and installation of instruments 5.4.1 Tanks with a capacity greater than 100 m3 shall be equipped with remote transmission instruments for continuous level measurement. 5.4.2 High and low liquid level alarms shall be provided in the automatic control system, and they shall comply with the following requirements: a) The set point for the high liquid level alarm in the storage tank shall not be higher than the designed maximum liquid level of the tank ； b) The set level for the low liquid level alarm in the storage tank should not be lower than the designed minimum liquid level for storage in that tank. 5.4.5 The high and low level alarm signals for the storage tank, as well as the level measurement instruments, shall be provided by separate continuous level measurement devices or level switches; the alarm signals shall be transmitted to the automatic control system. 6 Pressure Storage Tank Area 6.3 Selection and Installation of Tank Instruments 6.3.2 For level measurement in pressure storage tanks, one remote transmission instrument and one local indication instrument shall be provided. Glass plate level gauges shall not be used as local indication instruments. 6.3.3 Level measurement remote transmitters shall be equipped with high and low level alarms. The set level for the high liquid level alarm should be the designed maximum liquid level of the storage tank ； The set level for the low liquid level alarm should ensure that the pump will not experience cavitation within 10–15 minutes after the alarm is triggered. ◆Interlock requirement 5.4.3: Storage tanks for liquids of toxicity levels I and II, storage tanks for flammable liquids of categories A B and A C with a capacity of 3000 m3 or more, and storage tanks for other liquids with a capacity of 10000 m3 or more shall be equipped with high-high liquid level alarms and interlocks. The high-high liquid level alarm shall trigger the interlock to close the control valve of the tank’s inlet pipeline. 5.4.4 The raw material storage tanks of the unit should be equipped with a low-low level alarm, and the low-low level alarm should interlock to shut down the pump. 5.4.5 The high and low level alarm signals for the storage tank, as well as the level measurement instruments, shall be provided by separate continuous level measurement devices or level switches; the alarm signals shall be transmitted to the automatic control system. 6 Pressure Storage Tank Area 6.3 Selection and Installation of Tank Instruments 6.3.4 Pressure storage tanks shall be equipped with a separate set of level measurement instruments or level switches dedicated to detecting extremely high liquid levels and triggering the interlock to shut off the valves in the tank’s feed pipelines. The set height for the high-level alarm should not exceed the height at which the liquid volume reaches 90% of the calculated capacity of the tank. [Explanation of Provisions] 5.4.1 Liquid level is the most important parameter that needs to be monitored in storage tanks; therefore, this provision requires that “storage tanks shall be equipped with remote liquid level measuring instruments”. 5.4.2 The purpose of setting high/low level alarms is to give a warning that the liquid level in the tank is about to rise/fall to the specified limit level. Upon hearing the alarm, operators must switch to another storage tank within the prescribed time frame to prevent any accidents from occurring. 5.4.3 The interlock to close the inlet valve at high liquid levels can prevent overflow when feeding the tank; more stringent safety measures are required for the three situations listed in this clause. SH 3136-2003 “Safety Design Code for Spherical Storage Tanks of Liquefied Hydrocarbons” ◆ Installation requirements 5.3.1 Spherical storage tanks for liquefied hydrocarbons shall be equipped with local and remote level gauges; however, glass plate level gauges are not recommended. The level gauge used should be safe and reliable, and the number of openings in the spherical liquefied hydrocarbon storage tank should be minimized as much as possible. 5.3.2 Liquefied hydrocarbon spherical storage tanks shall be equipped with a high liquid level alarm and a high-high liquid level interlock. A low liquid level alarm should be installed if necessary. ◆Interlock requirements: 5.3.2 Spherical storage tanks for liquefied hydrocarbons shall be equipped with a high-level alarm and a high-high level interlock. A low liquid level alarm should be installed if necessary. 5.3.3 For spherical storage tanks for liquefied petroleum gas used in the loading and unloading of tank trucks under intermittent operation, an automatic interlock emergency feed cutoff device for high-high liquid level shall be installed. For spherical storage tanks used for the continuous operation of single-component liquefied hydrocarbons or petroleum refining units, the interlock requirements shall be determined based on the requirements of the upstream and downstream process flows. ◆Settings and interlock requirements 6.1 Emergency shut-off valves Emergency shut-off valves shall be installed at the liquid-phase inlet and outlet of LPG spherical storage tanks; their location should be close to the spherical tank. AQ3053-2015 \"Safety Technical Specifications for Vertical Cylindrical Welded Steel Storage Tanks\" ◆ Installation requirements 12.2.2 Level control accessories For storage tanks holding flammable liquids, level gauges as well as high and low level alarm devices, and high-high level alarm devices must be installed in accordance with the specifications and operational requirements; the alarm signals and level information must be transmitted to the control room. Storage tanks that are operated frequently should be equipped with automatic interlock emergency shut-off devices. Large tanks should be equipped with low and high liquid level alarm devices, high-high liquid level alarm devices, and emergency shut-off devices. Interlocking measures should be implemented between the high-high liquid level alarm and the emergency shut-off device, and interlock buttons for the emergency shut-off valves should be provided outside the fire dike as well as at the control room operation stations. When a high level alarm or a fire occurs in the storage tank, it is possible to remotely or manually close the feed cut-off valve; once the cut-off valve is closed, the feed pump should be automatically shut down via interlock. ◆Interlock requirements 12.2.2 Level limitation accessories: Large tanks shall be equipped with high and low level alarm devices, high-high level alarm devices, and emergency shut-off devices. Measures shall be taken to interconnect the high-high level alarm device with the emergency shut-off device; emergency shut-off valve interlock buttons shall be provided outside the fire dike and at the control room operation station. When a high level alarm or a fire occurs in the storage tank, it is possible to remotely or manually close the feed cut-off valve; once the cut-off valve is closed, the feed pump should be automatically shut down via interlock. ◆Requirements 6.13 Isolation valves: A main isolation valve should be installed near the inlet and outlet pipes of the tank’s contents at the tank body. For large storage tanks, valves equipped with pneumatic, hydraulic, or electric actuators should be used. When the actuator is of electric type, its power cable, signal cable, and electric actuator shall be provided with fire protection. The cut-off valve should have automatic and manual shutdown functions, with manual shutdown including remote manual shutdown and on-site manual shutdown. Circular No. 368 issued by the Chief Safety Supervisor: “Notice on Further Strengthening the Safety Management of Chemical Storage Areas” ◆ Requirements for installation: (1) Further improve the monitoring and control facilities in chemical storage areas. In accordance with regulatory requirements, high and low liquid level alarms are installed in the storage tank; automatic interlocks are employed to shut down the tank’s feed valve when the liquid level is too high, and to stop material transfer when the liquid level is too low. Ensure that the alarm systems for leaks of flammable, explosive, toxic, and harmful gases are in good working condition. Emergency shut-off valves must be installed on key storage tanks such as large-scale ones, those storing liquefied gases, and highly toxic chemicals. ◆Setup and interlock requirements: (1) Further improve the monitoring and control facilities in the chemical tank area. In accordance with regulatory requirements, high and low liquid level alarms are installed in the storage tank; automatic interlocks are employed to shut down the tank’s feed valve when the liquid level is too high, and to stop material transfer when the liquid level is too low. Ensure that the alarm systems for leaks of flammable, explosive, toxic, and harmful gases are in good working condition. Emergency shut-off valves must be installed on key storage tanks such as large-scale ones, those storing liquefied gases, and highly toxic chemicals. Circular No. 376 of the Supervisory Authority: “Notice on Further Strengthening the Safety Design Management of Hazardous Chemicals Construction Projects” ◆ Requirements for setup: (14) The design unit shall determine the standards and specifications to be applied in this project, based on the characteristics of the hazard sources associated with the construction project as well as the scope of application of relevant standards and regulations. For construction projects involving the \"two key areas and one major issue,\" they must meet at least the requirements of the following current standards and specifications, with the strictest safety provisions taking precedence. (19) Newly built chemical plants must be designed with automated control systems. It should be determined whether a safety instrumented system is necessary based on the results of the hazard and risk analysis of the process. For large and medium-sized new projects involving hazardous chemical processes that are under strict supervision, the design of safety instrument systems shall be carried out in accordance with relevant standards such as \"Functional Safety of Safety Instrument Systems in the Process Industry\" (GB/T21109) and \"Design Code for Safety Instrument Systems in Petrochemical Industries\" (GB50770). (22) Emergency shutoff devices that can be operated automatically or remotely by hand should be installed on the pipelines for feeding and discharging materials from toxic material storage tanks, cryogenic storage tanks, and pressure spheres. ◆Interlock requirements: (19) New chemical plants must be designed with an automated control system. It should be determined whether a safety instrumented system is necessary based on the results of the hazard and risk analysis of the process. For large and medium-sized new projects involving hazardous chemical processes that are under strict supervision, the design of safety instrument systems shall be carried out in accordance with relevant standards such as \"Functional Safety of Safety Instrument Systems in the Process Industry\" (GB/T21109) and \"Design Code for Safety Instrument Systems in Petrochemical Industries\" (GB50770). (22) Emergency shutoff devices that can be operated automatically or remotely by hand should be installed on the pipelines for feeding and discharging materials from toxic material storage tanks, cryogenic storage tanks, and pressure spheres. Order No. 40 of the State Administration of Work Safety: Interim Provisions on the Supervision and Management of Major Hazard Sources of Hazardous Chemicals ◆ Requirements for Establishment Article 13 Hazardous chemical enterprises shall, in light of 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. Major hazard sources of grade 1 or 2 involving toxic gases, liquefied gases, or highly toxic liquids are equipped with an independent Safety Instrumented System (SIS) ； ◆Interlock requirements Article 13: 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 a safety monitoring and control system in accordance with the following requirements to enhance control measures: (3) Install emergency shut-off devices for key facilities within major hazard sources, such as toxic gases, highly toxic liquids, and flammable gases ； For facilities handling toxic gases, emergency devices for dealing with leaks must be installed. Major hazard sources of grade 1 or 2 involving toxic gases, liquefied gases, or highly toxic liquids are equipped with an independent Safety Instrumented System (SIS) ； Safety Supervision General Administration No. 362 **Notice from the Safety Supervision General Administration on Issuing Guidelines for Curbing Serious Accidents Involving Hazardous Chemicals and Fireworks and Firecrackers ◆ Requirements for installation (4) As of January 1, 2017, all hazardous chemical storage areas that constitute Class I or Class II major hazard sources and do not have an emergency shutdown (emergency isolation) function must cease to be in use ； Su An Jian No. 109, “Opinions on Standardizing the Technical Renovation of Automatic Control Systems in Chemical Enterprises” ◆ Requirements for installation: 1. New production units or storage facilities that fall within the scope of renovation must be equipped with automatic control systems. Safe and reliable automatic control instruments and interlock protection systems should be used, along with necessary detection and alarm systems for leaks of toxic, harmful, flammable, and explosive gases, as well as fire alarm systems. For production facilities with an investment scale of 100 million RMB or more, as well as those involving highly hazardous processes (pyrolysis, hydrogenation, polymerization, fluorination, nitration, peroxidation processes, etc., the same below), emergency shutdown systems must be installed in addition to automated control systems. 2. Existing production units involving hazardous processes must complete the transformation to automatic control technology within the specified time frame, in order to achieve automatic control of the process and automatic alerting for key parameters such as temperature and pressure. Systems with high risk or under certain conditions must be equipped with distributed control systems and emergency shutdown systems to enable remote operation. Hazardous chemical manufacturing enterprises must complete the renovations before renewing (obtaining) their safety production licenses. 3. The existing storage facilities within the scope of the renovation must complete the upgrade to automatic control technology within the specified time frame. Storage areas for highly toxic and flammable/explosive chemicals must be equipped with alarms for excessive levels of liquid, temperature, and pressure, as well as gas leak detection alarms and fire alarm systems ； Key storage tanks such as liquefied gases and highly toxic liquids, which constitute major hazard sources, must be equipped with emergency shut-off devices. Sinopec An No. 635 (November 17, 2010): Interim Provisions on the Safety Technology Management of Liquefied Hydrocarbon Spherical Tank Areas in Sinopec Group ◆ Installation Requirements 3.2.4 Instrumentation and Automation 3.2.4.1 An instrumentation control system shall be installed in liquefied hydrocarbon spherical tank areas to carry out tasks such as data collection, monitoring, alarm generation, and process control during production. Control systems can include programmable logic controllers (PLC), distributed control systems (DCS), supervisory control and data acquisition systems (SCADA), and fieldbus control systems (FCS), among others. When safety interlock requirements are present in tank farm operations, safety interlock circuits and safety instrumented systems should be installed. The measuring elements (including sensors, transmitters, etc.), logic controllers, and actuating elements (including solenoid valves, control valves, shut-off valves, etc.) in the safety interlock circuit must all meet the Safety Integrity Level (SIL) requirements. 3.2.4.3 Liquefied hydrocarbon spherical tanks shall be equipped with local and remote level gauges. Local level gauges can be magnetic flap level gauges, steel belt level gauges, radar or servo level gauge indicators mounted beside the tank; glass tube (plate) level gauges should not be used. When the on-site level gauge is a radar or a servo tank-side indicator, the spherical tank shall also be equipped with a different type of remote level measuring instrument. ◆Interlock requirement 3.2.4.4: Liquefied hydrocarbon spheres should be equipped with low and high liquid level alarms, as well as interlock mechanisms to shut off feeding at extremely high liquid levels. The sensing elements for the high liquid level interlock should be installed separately; ultrasonic, tuning fork, float, or capacitive level switches can be used. It is advisable to combine these with the high liquid level signals from radar and servo-type remote level gauges to implement a \"two-out-of-three\" interlock system that shuts off feed flow. ◆Settings and interlock requirements 2 Terminology 2.2 Emergency shut-off valve: A valve installed on the inlet and outlet pipes of spherical tanks, capable of shutting off quickly and tightly in the event of an accident or abnormal condition. The allowable leakage rate for emergency shut-off valves should meet ANSI B16.104(FCI 70-2) CLASS V or a higher standard. The valve shall have the capability to be closed thermally, manually, and remotely via manual control (remote control with a handle). 3.2.4 Instrumentation and automatic control 3.2.4.4 Liquefied hydrocarbon spherical tanks shall be equipped with low and high liquid level alarms, as well as interlock systems to shut off feed when the liquid level reaches critical levels. The sensing elements for the high liquid level interlock should be installed separately; ultrasonic, tuning fork, float, or capacitive level switches can be used. It is advisable to combine these with the high liquid level signals from radar and servo-type remote level gauges to implement a \"two-out-of-three\" interlock system that shuts off feed flow. 3.2.4.5 Emergency shut-off valves a) Emergency shut-off valves shall be installed at the liquid inlet and outlet of liquefied hydrocarbon spherical tanks; the actuation mechanism for these valves can be pneumatic, hydraulic, or electric (pneumatic type is preferred). When the actuator of the shut-off valve is a pneumatic actuator, a single-acting cylinder actuator (fault-safe type) should be selected ； If a pneumatic double-acting cylinder actuator is used, an emergency air tank should be provided. When the actuator is of electric type, its power supply should be provided by an electrical UPS, and its power cables, signal cables, and electric actuator should be protected against fire. b) Emergency shut-off valves should be distinguished from process control valves. Its sealing structure shall be of fire-resistant design and comply with ANSI/API STD607 standards ； The allowable leakage rate shall meet ANSI B16.104 (FCI 70-2) CLASS V or higher. c) Outside the fire dike of the liquefied hydrocarbon sphere tank area, as well as at the control room operation stations (hard switches or soft switches), emergency shutoff valve interlock buttons should be installed. In the event of a high liquid level alarm in the spheres or a fire, operators can remotely or manually shut down the emergency shutoff valve; once the valve is closed, it automatically triggers the shutdown of the feed pump. The shutdown time of the emergency shut-off valve is as follows: ________________________________________ Nominal size DN (mm) Full shutdown time (s) ________________________________________ ≤50 ≤5 65~350 ≤10 _______________________________________ d) The emergency shut-off valve must be capable of shutting off automatically when the temperature of the fusible element automatic shutdown device reaches 75±5°C. e) The selected emergency shut-off valve shall be fail-safe. \"Regulations on Safety Technology Management for Liquefied Hydrocarbon Spherical Tank Areas in Sinopec\" ◆ Installation requirements: 4.4 Instrumentation and automation 4.4.1 An instrumentation control system shall be installed in liquefied hydrocarbon spherical tank areas to carry out tasks such as data collection, monitoring, alarm generation, and process control during production. Control systems can include programmable logic controllers (PLC), distributed control systems (DCS), supervisory control and data acquisition systems (SCADA), and fieldbus control systems (FCS), among others. 4.4.3 Liquefied hydrocarbon spheres should be equipped with local and remote level gauges. Local level gauges can include magnetic flap level gauges, steel belt level gauges, or radar or servo level gauges as tank-side indicators. When the on-site level gauge is a radar or a servo tank-side indicator, the spherical tank shall also be equipped with a different type of remote level measuring instrument. ◆Interlock requirement 4.4.4: Liquefied hydrocarbon spheres should be equipped with low and high level alarms, as well as interlocks that shut off feed when the level reaches extremely high values. The sensing elements for the high liquid level interlock should be installed separately, and options such as ultrasonic sensors, tuning fork sensors, float switches, and capacitive level switches can be used. ◆Requirements 4.4.5.4: The control of emergency shut-off valves shall allow for remote control from the control room as well as local control on-site. The time required to close these valves is specified in the table below: ________________________________________ Nominal diameter DN (mm) Time to fully close (s) ________________________________________ ≤50 ≤5 65~350 ≤10 ________________________________________ According to Sinopec Document No. 518, “Specifications for the Selection and Design of Emergency Shut-Off Valves for Liquefied Hydrocarbon Spheres” ◆ Requirements 3.1: Emergency shut-off valves are designed specifically for installation on the inlet and outlet pipelines of liquefied hydrocarbon spheres; they serve as valves that can quickly and completely shut off and isolate flammable and toxic materials in the event of fires or leaks within the tank area. When the liquid level in the spherical tank reaches or exceeds the high-high level limit, the emergency shut-off valve can be used to prevent the material from overflowing the tank. No other fittings or valves shall be installed between the emergency shut-off valve and the tank outlet except for the connecting pipes, and the spacing therebetween shall meet the requirements for piping installation, valve maintenance, and the process. The emergency shut-off valve shall have automatic and manual shutdown functions, with the manual shutdown function including remote manual shutdown from the control room and on-site manual shutdown. 4.5.11 An on-site operation switch for the emergency shut-off valve shall be installed outside the fire hazard area of the liquefied hydrocarbon spherical tank area; the signal from its contacts is sent directly to the solenoid valve of the pneumatic actuator, or to the ESD activation terminals of the electro-hydraulic or electric actuator, so as to enable manual shutdown of the emergency shut-off valve on site in emergency situations. (November 20, 2018) Sinopec Anfei No. 477: “Guidelines for the Rectification of Atmospheric Pressure Storage Areas for Flammable and Combustible Liquids at Sinopec” ◆ Interlock Requirements 4.1.4 The emergency shut-off valve on the tank feeding pipeline shall be interlocked with the high liquid level alarm instrument of the tank ； Installation and interlock requirements: 4.1 Installation of emergency shut-off valves 4.1.1 Emergency shut-off valves shall be installed on the inlet and outlet pipelines of storage tanks containing extremely hazardous liquids (Class I) and highly hazardous liquids (Class II), storage tanks for flammable liquids of Class A B and Class B A with a capacity of 3000 m3 or more, storage tanks for other flammable liquids with a capacity of 10000 m3 or more, as well as on the pipelines of tank farms that constitute major hazard sources of Class I or Class II. The emergency shut-off valve should be able to be closed remotely from the control room. 4.1.2 Emergency shut-off valves for storage tanks in refineries, petrochemical plants, and petroleum fiber plants should preferably be pneumatic valves and should have a fail-to-close function ； Electric valves can be used as emergency shut-off valves for storage tanks in crude oil depots, refined oil depots, and pipeline auxiliary stations. 4.1.3 The emergency shut-off valves on the inlet and outlet pipelines of the storage tank can share the same process control valves. 4.1.4 The emergency shut-off valve on the tank feed pipeline shall be interlocked with the tank high liquid level alarm instrument. 4.1.8 The time required for the emergency shut-off valve to open or close completely via a pneumatic or electric actuator shall not exceed 180 seconds. 4.2.1 Storage tanks for bulk hydrocarbons, liquefied hydrocarbons, and liquid ammonia shall be equipped with an independent Safety Instrumented System (SIS). No. 39: Sinopec’s “Guidelines for Addressing Hidden Dangers in Tank Areas” ◆ Requirements for installation and interlocking: IV. Low-low liquid level interlocking, high-high liquid level interlocking 1. Storage tanks with a volume of more than 100 m3 shall be equipped with continuous liquid level measurement and transmission instruments for high, high-high, low, and low-low liquid levels. However, whether interlocking should be used to shut off the inlet and outlet valves or to stop the pumps depends on the effects such interlocking may have; it must comply with the following regulations: (1) Storage tanks that are classified as major hazard sources of level 1 or 2 shall be equipped with high-high liquid level interlocking to shut off the inlet valve. It is also necessary to verify that the design pressure of the inlet pipes and related pipelines meets the requirements of the most severe operating conditions (such as the head at the pump’s shut-off point), and that appropriate safety measures are in place. (2) When the high liquid level interlock of a storage tank containing a certain material shuts down the feed valve, in order not to affect the normal operation of the upstream units (facilities), an alarm should be triggered and the feed valve of another storage tank should be opened promptly. (3) For tanks for which the automatic interlock shutdown of the pump is triggered when the low-low liquid level is reached, and which could cause significant disruptions such as shutdowns and restarts to downstream facilities or stations (such as feed tanks and intermediate feed tanks in processing units, as well as tanks at oil transfer stations), it is advisable to implement a secondary alarm system: the discharge valve should be closed via interlock when the liquid level reaches the low-low level, and the alarm should trigger the opening of the discharge valve of another tank. (4) For tanks in which automatic interlock shutdown of the pump is triggered when the low-low liquid level is reached, and which do not cause significant disruptions such as stops and restarts to downstream operations (loading onto vehicles or ships) – such as finished product tanks in petrochemical plants or storage tanks in fuel depots – it is possible to use interlocks to close the discharge valve or to shut down the pump when the liquid level reaches the low-low level. ◆Settings and interlock requirements: 2. For storage tanks that are classified as major hazard sources of level 1 or 2, in addition to high and low liquid level alarms, corresponding alarms and interlock protection measures should also be installed for low-low liquid level and high-high liquid level. For storage tanks that require a separate SIS system, tank base valves should be installed on their inlet and outlet pipelines (emergency shut-off valves must have fire protection measures, be capable of manual operation, and also have fire protection features); the SIS system is used to interlock and shut off feed in emergency situations such as high liquid levels in the tank or fires ； For storage tanks that do not require a separate SIS system, the tank base valves on their inlet and outlet pipelines should be control valves equipped with manual operation capabilities; in emergency situations such as high liquid levels in the tank or fire accidents, feed can be shut off through interlocks in the basic process control system. Q/SH 0749-2018 \"Technical Standards for the Storage and Transportation of Liquefied Hydrocarbons\" ◆ Requirements for Installation and Interlocking 12.2.5 The selection of level measurement instruments shall comply with the following provisions: a) Two servo level gauges shall be installed in low-temperature vertical storage tanks for level measurement ； A separate servo level gauge should be installed in the low-temperature vertical storage tank, to enable interlock functions for high and low levels by using the level alarm signals from those two servo level gauges. b) For each spherical tank, one servo level gauge and one radar level gauge shall be installed for level measurement. Additionally, one level switch shall be installed to perform high-high level interlock control based on the level alarm signals from the aforementioned two level gauges ； An additional level switch is installed to provide a low-low level interlock with the level alarm signals from the two level gauges. f) The emergency shut-off valve (ESDV) should preferably be equipped with a pneumatic single-acting actuator or an electro-hydraulic actuator. g) The selection of emergency shut-off valves at the base of liquefied hydrocarbon spheres shall comply with Sinopec Document Jian 518, \"Specifications for the Selection and Design of Emergency Shut-Off Valves for Liquefied Hydrocarbon Spheres\" ； The fire shield for the emergency shut-off valve at the base of the spherical tank should be a rigid fire protection shield suitable for outdoor use; such a shield must be able to keep the temperature inside it below 80°C for 30 minutes in the presence of hydrocarbon fires at 1093°C. General Office of Work Safety Administration, Letter No. 27** General Office of Work Safety Administration (February 7, 2018) ◆ Requirements for installation and interlocking: (I) Jiangsu Tianjiayi Chemical Co., Ltd. (13 items): 5. Some of the DCS and SIS pressure transmitters in the dinitration reactors share the same pressure sensing point. 6. The benzene tank area and methanol tank area, which constitute secondary major hazard sources, are not equipped with emergency shut-off valves at the base of the tanks. 8. The cabinet room and monitoring room were improperly located within the nitration plant. (II) Kunpeng Chemical Co., Ltd. in Xiangshui County (15 items): 6. The distillation system does not have automatic control. 11. The doors and windows of the control room and cabinet rooms face devices with fire and explosion hazards. 12. The ESD system does not have dual-circuit power supply. (III) Jiangsu Dahua Chemical Industry Co., Ltd. (11 items): 4. The DCS control room of the facility is not of explosion-proof design, and its doors and windows face Workshop No. 1, which is at risk of fire and explosion. 8. The tank farm, which constitutes a first-level major hazard source, is not equipped with emergency shut-off valves at the base of the tanks. 9. The procedures for disabling the instrument interlock were not followed. (IV) Jiangsu Yongtai Technology Co., Ltd. (9 items) 3. The tank farm classified as a Level 1 major hazard source has numerous safety hazards; for instance, emergency shut-off valves are not installed at the base of the storage tanks ； The storage tanks are not equipped with on-site level indicators; some of them have only one static grounding point ； (II) Jiangsu Sierbang Petrochemical Co., Ltd. (9 items): 4. The interlock devices for pumps at the plant site do not indicate the interlock function in a prominent location on the coupling guards. 7. The gland openings of some instrument junction boxes are not sealed, and they are not explosion-proof ； The static bonding wires of certain instrument housings and junction boxes have come loose. (III) Jiangsu Hailirui Technology Development Co., Ltd. (17 items): 8. The units involving hazardous chemical processes that are under strict supervision do not have emergency shutdown systems. 17. The control room is located within the production facility. (IV) Jiangsu Xincheng Chemical Co., Ltd. (13 items): 6. The units involving hazardous chemical processes that are under strict supervision do not have automated control systems in place, nor are emergency shutdown functions available. (1) Jiangsu Zhongneng Silicon Industry Development Co., Ltd. (12 items): 3. The control measures for major hazard sources are inadequate; for example, since the enterprise constitutes a first-level major hazard source, the assessment in the current status evaluation report places the acceptable social risk curve in the area where risks should be minimized as much as possible. The potential risks present were not analyzed as required, nor were any measures to address those risks established. 7. The safety instrument systems are inadequate; for example, units involving hazardous chemical processes do not have emergency shutdown systems that are independent of the process control system, as required. Safety Supervision Administration Order No. 3121: “Standards for Identifying Major Potential Hazards in Production Safety Incidents in Chemical and Hazardous Chemicals Production and Operation Units (Trial)” ◆ Requirements for installation and interlocking: IV. Facilities involving hazardous chemical processes that are subject to strict supervision do not have automated control systems; the systems do not possess emergency shutdown functions, and the automated control systems and emergency shutdown systems installed are not in use. V. The hazardous chemical storage areas that constitute Class I and Class II major hazard sources do not have an emergency shutdown function ； 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. 10. Operating chemical plants have not undergone formal design nor safety design diagnostics. 13. The side of the control room or cabinet room facing devices with fire and explosion hazards does not meet the fire and explosion prevention requirements of the **standard. 14. The chemical production facilities do not have dual-power supplies installed as required by **standards; no uninterruptible power supply has been provided for the automation control system. 19. Newly developed production processes for hazardous chemicals are put into industrial production directly, without going through pilot tests, scale-up tests, or industrial trials ； The chemical process used for the first time in the country had not undergone safety and reliability assessments organized by the relevant provincial people’s government departments ； No trial production plan has been established for the newly installed unit, so it has not been put into operation with materials fed in ； Fine chemical enterprises have failed to conduct reaction safety risk assessments as required by regulatory documents. Notice No. 368 from the Chief Safety Officer: Further Strengthening the Safety Management of Chemical Tank Areas ◆ Requirements for Installation and Interlocking (1) Further improve the monitoring and control facilities in chemical tank areas. In accordance with regulatory requirements, high and low liquid level alarms are installed in the storage tank; automatic interlocks are employed to shut down the tank’s feed valve when the liquid level is too high, and to stop material transfer when the liquid level is too low. Ensure that the alarm systems for leaks of flammable, explosive, toxic, and harmful gases are in good working condition. Emergency shut-off valves must be installed on key storage tanks such as large-scale ones, those storing liquefied gases, and highly toxic chemicals. (II) Strengthen the production and operation management of chemical tank areas. Under normal operating conditions, it is strictly prohibited to allow any space to form between the floating disk of an internal floating roof tank and the material contained within it. In special cases where operation at an extremely low liquid level is necessary, it is essential to ensure that the feed flow rate is below the specified limit when resuming feeding, in order to prevent accidents caused by static electricity. When high or low level alarms occur, immediate action must be taken. (VI) Tank farms handling hazardous chemicals under strict supervision shall conduct hazard and operability analyses on a regular basis. Guiding Opinions No. 388 issued by the Head of Work Safety Supervision on Strengthening the Safety Management of Chemical Processes (July 29, 2013) ◆ Requirements for installation and interlocking (V) Establish a risk management system. Enterprises should establish a risk management system for chemical processes, defining the scope, methods, frequency, and responsible parties for risk identification, specifying the requirements for applying the results of risk analysis and implementing improvement measures, and conducting risk identification and analysis throughout the entire production process. For production and storage facilities involving highly regulated hazardous chemicals, highly regulated hazardous chemical processes, and major hazard sources of hazardous chemicals (collectively referred to as \"two key areas and one major hazard\"), risk identification and analysis should be carried out using the Hazard and Operability Study (HAZOP) technique, generally once every 3 years. For the risk identification and analysis of other production and storage facilities, depending on the degree of complexity of those facilities, methods such as safety checklists, job hazard analyses, preliminary hazard analyses, Failure Mode and Effects Analysis (FMEA), and HAZOP techniques, or combinations of several such methods, can be used; this analysis can be carried out every 5 years. In the event of significant changes in the enterprise’s management structure, personnel composition, production facilities, or in the occurrence of production safety accidents, risk identification and analysis must be carried out promptly. Enterprises should involve all their employees in risk identification and analysis, striving to ensure comprehensive coverage of such activities. (7) Establish acceptable risk standards. Enterprises shall, in accordance with the requirements of the Interim Provisions on the Supervision and Management of Major Hazard Sources of Hazardous Chemicals (**Order No. 40 of the State Administration of Work Safety), determine their own acceptable risk criteria based on relevant regulations or by referring to international standards. For the unacceptable risks identified through the risk assessment, enterprises should promptly formulate and implement measures to eliminate, reduce, or control these risks, so as to keep them within an acceptable range. Notice No. 53 from Jiangsu Provincial Emergency Management Department on Issuing the \"Basic Requirements for Inherent Safety Diagnosis and Management\" – Issued by the Office of Jiangsu Provincial Emergency Management Department on June 6, 2019. ◆ Requirements for installation and interlocking: I. Diagnosis of major hazards: In accordance with the \"Criteria for Identifying Major Safety Hazards in Chemical and Hazardous Chemicals Production and Operation Units (Trial)\" (Safety Supervision General Administration Document No. 3 [2017] 121), major hazards shall be identified strictly, without any omissions or misidentifications. 5. In accordance with the “Notice of the **General Administration of Work Safety on Publishing the List of Key Hazardous Chemical Processes Subject to Special Supervision” (An Jian Zong Guan San [2009] No. 116), the “Notice of the **General Administration of Work Safety on Publishing the List of the Second Batch of Key Hazardous Chemical Processes Subject to Special Supervision and Making Adjustments to Some Typical Processes Among the First Batch” (An Jian Zong Guan San [2013] No. 3), as well as standards such as GB/T50770, GB/T20438, and GB/T21109, and based on the recommendations from HAZOP analyses, a list is prepared to assess the compliance of the safety functions related to automatic control systems (including DCS, PLC, ESD, SIS) in production facilities involving key hazardous chemical processes; any non-compliance issues are listed separately. 6. In accordance with the requirements of documents such as the Interim Provisions on the Supervision and Management of Major Hazard Sources of Hazardous Chemicals (formerly Order No. 40 issued by the State Administration of Work Safety) and the Guiding Opinions of the State Administration of Work Safety on Strengthening the Management of Safety Instrumented Systems in the Chemical Industry (An Jian Zong Guan San [2014] No. 116), a list should be prepared to assess the compliance of safety functions such as automated control systems, safety instrumented systems, emergency shutdown systems, and emergency isolation devices in the production units (storage facilities) that constitute major hazard sources; any non-compliance issues should be listed separately. (1) Automatic control of raw material and product storage tanks as well as plant storage tanks: 1. Flammable liquid storage tanks, toxic liquid storage tanks, cryogenic storage tanks, and pressure vessels with a volume of 100 m3 or more shall be equipped with remote transmitters for continuous level measurement and local level indicators, as well as high-level alarms. Floating roof storage tanks and storage tanks equipped with extraction pumps shall also be fitted with low-level alarms ； Pressure vessels containing flammable and toxic media are equipped with high liquid level or high pressure interlocks to stop feeding. If the design plan or HAZOP analysis report specifies the need to install an automatic interlock to shut down the pump and close the discharge valve at very low liquid levels, such requirements must be met. 2. For liquid raw material and product storage tanks containing 16 types of hazardous chemicals that are explosive by nature and with a volume of less than 100 m3, a high liquid level alarm should be installed. If the design plan or HAZOP analysis report specifies the need for a high-high liquid level alarm that triggers the interlock to shut off the feed valve, as well as a low-low liquid level alarm that triggers the interlock to stop the pump, these requirements must be met. 3. Storage tanks for liquids of toxicity levels I and II, storage tanks for flammable liquids of categories A B and B A with a capacity of 1000 m3 or more, and storage tanks for other flammable liquids with a capacity of 3000 m3 or more shall be equipped with high-level liquid level alarms and interlocked control valves to shut off the inlet pipes of the tanks. 4. Liquid storage tanks in hazardous chemical tank areas that constitute primary or secondary major hazard sources shall be equipped with high and low liquid level alarms, as well as high-high and low-low liquid level interlock systems to urgently shut off the control valves of the inlet and outlet pipelines. 5. Storage tanks for flammable or toxic liquids should be equipped with high liquid level alarms, as well as interlocks that shut off feeding when the liquid level reaches an extremely high level. The high-level tank of the unit should be equipped with an alarm for high liquid levels, and interlocks that shut off feeding when the level is too high; an overflow pipeline should also be provided. It is advisable to have interlocks that stop the extraction pump or shut off the discharge system when the liquid level is too low. 7. Hazardous chemical storage areas that are classified as Class I or Class II major hazard sources and involve toxic gases, liquefied gases, or highly toxic liquids shall be equipped with an independent safety instrumented system. The sensing elements and actuating elements of each circuit should be installed independently, with the Safety Instrumented Level (SIL) being no less than Level 2. 9. Flammable liquid and highly toxic liquid storage tanks equipped with high-level interlock functions shall be fitted with two types of level gauges or level switches based on different principles; the high-level interlock measuring instrument and the level gauge used in the basic control circuit shall be installed separately. The liquid level measurement of the pressure storage tank should be equipped with a set of remote transmitters and local indicator instruments; in addition, another set of liquid level measuring instruments or level switches dedicated to detecting extremely high or extremely low liquid levels and triggering interlocks to shut off the tank’s feed (discharge) valves should be provided. 14. Major hazard sources of Class 1 and Class 2 hazardous chemicals shall be equipped with an emergency shutdown system, and key facilities such as toxic gases, highly toxic liquids, and flammable gases within these major hazard sources shall be fitted with emergency isolation devices. The safety functions of the emergency shutdown (emergency isolation) system can be implemented either through basic process control (DCS or SCADA) systems or through Safety Instrumented Systems (SIS). For systems with a Safety Integrity Level (SIL) of 1, the safety functions of their emergency shutdown systems can be implemented either through basic process control systems (DCS or SCADA) or through Safety Instrumented Systems (SIS). For systems with a SIL of 2 or higher, the emergency shutdown functions must be implemented through Safety Instrumented Systems (SIS). Document No. 88 issued by the General Office of the State Council: Notice on the Issuance of a Comprehensive Plan for the Safe Management of Hazardous Chemicals ◆ Requirements for installation and interlocking: (1) The chemical process safety instrument 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. The Safety Instrumented System operates independently of the process control system (such as a Distributed Control System). Under normal operating conditions, it remains dormant or inactive. However, in the event that any situation arises within the production equipment or facilities that could potentially lead to a safety incident, it must be capable of responding instantly and accurately to safely halt the production process or automatically bring it into a predetermined safe state. Therefore, it must possess a high level of reliability (i.e., functional safety) as well as proper maintenance and management procedures. Based on the consequences and risks arising 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. (11) Design and implement toxic, hazardous, and flammable gas detection and protection systems in strict accordance with relevant standards; to ensure their reliable operation, such systems should be independent of the basic process control system. (12) Starting from January 1, 2016, qualified chemical enterprises such as large-scale enterprises and those wholly owned by foreign investors that construct new chemical plants or hazardous chemicals storage facilities related to the \"two key areas and one major project\" must design safety instrument systems that comply with relevant standard requirements in accordance with the provisions of these guiding principles. (13) Starting from January 1, 2018, all newly constructed chemical processing units and hazardous chemical storage facilities related to the \"two key areas and one major project\" must be designed with safety instrument systems that meet the required standards. 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. (14) Chemical enterprises and hazardous chemicals storage units that operate production facilities or plants classified as “two key items and one major item” 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 these risk reduction requirements. (15) Enterprises shall, on the basis of assessment, formulate management plans for safety instrumented systems and regular inspection and testing plans. For safety instrumented functions that do not meet the requirements, relevant maintenance plans and rectification programs must be formulated. The evaluation and improvement of the safety instrumented system should be completed by the end of 2019. Other chemical processing units and hazardous chemical storage facilities shall be implemented in accordance with the requirements of these guidelines. AQSIQ General Administration No. 113 **Notice of the State Administration of Work Safety on Issuing the “Guidelines on Key Aspects of Safety Inspections for Chemical (Hazardous Chemicals) Enterprises” ◆ Installation and interlock requirements ◆ Management of equipment and facilities 19. Oil and gas storage tanks that do not meet the following requirements: (1) Storage tanks for liquefied hydrocarbons must be equipped with level gauges, thermometers, pressure gauges, safety valves, as well as high-level alarms and automatic interlock mechanisms to cut off feed at excessively high levels ； Fully refrigerated liquefied hydrocarbon storage tanks should also be equipped with vacuum relief facilities and high/low temperature monitoring, and should be connected to an automatic control system ； (2) The gas holder shall be equipped with upper and lower limit alarm devices, and it is advisable to have automatic interlock shutdown devices for the inlet and outlet pipes ； (3) Emergency shut-off valves should be installed at the liquid inlet and outlet of the spherical LPG storage tank, and their location should be as close as possible to the spherical storage tank ； (4) Spherical storage tanks for propylene, propane, mixed C4, stripped C4, and liquefied petroleum gas shall be equipped with water injection measures. Article 33 of the Work Safety Law ； Articles 6.3.11 and 6.3.12 of the Code for Fire Protection Design of Petrochemical Enterprises (GB50160) ； Articles 6.1 and 7.4 of the \"Code for Safe Design of Spherical Storage Tanks for Liquefied Hydrocarbons\" (SH3136) ； 20. Automatic control systems are not installed in facilities involving hazardous chemical processes or chemicals that are subject to strict supervision ； Or large chemical plants that involve hazardous chemical processes and do not have an emergency shutdown system in place. Article 9 of the **Implementation Measures for Safety Production Licenses of Hazardous Chemicals Production Enterprises** (Order No. 41 of the State Administration for Work Safety). 25. Hazardous chemical process production units involving exothermic reactions that do not have a dual power supply, or whose control systems lack an uninterruptible power supply (UPS). Article 38 of the Work Safety Law, “Technical Code for Electrical Design of Production Facilities in Petrochemical Enterprises” (SH3038), and “Code for Design of Power Supply and Distribution Systems” (GB50052). ◆Safety Management 28. The control room or cabinet room shall have doors and windows on the side facing devices with fire and explosion hazards. (Must be rectified by 2017) ； Article 38 of the Work Safety Law; Article 5.2.18 of the Code for Fire Protection Design of Petrochemical Enterprises (GB50160).