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I. Definition of emergency shut-off valves Regarding the definition of emergency shut-off valves, several standard specifications currently provide definitions for this term. For example, Article 3.1 of “Emergency Shut-Off Valves for Liquefied Gas Equipment” (GB/T 22653-2008) states: “Emergency shut-off valve: A valve installed on tank trucks, tank containers, storage tanks, or pipelines, which can be quickly closed manually or automatically in emergency situations.” Article 3.1 of “Emergency Shut-off Valves for Cryogenic Media” (GB/T 24918-2010) defines an emergency shut-off valve as “a valve installed on tank trucks, storage tanks, or pipelines, which can be quickly closed manually or automatically in the event of an accident”. Notice on the Interim Provisions for the Safety Technology Management of Liquefied Hydrocarbon Spherical Tank Areas of Sinopec Group Company (issued under Sinopec Safety Document No. 635), Article 2.2: “Emergency shut-off valves: Valves installed on the inlet and outlet pipelines of spherical tanks, capable of being quickly and tightly closed in the event of an accident or abnormal condition. The allowable leakage rate for such emergency shut-off valves shall meet the standards of ANSI B16.104 (FCI 70-2) CLASS V or a higher grade.” The valve shall have the capability to be closed thermally, manually, and remotely manually (via a remote control with a handle).” Article 3.1 of the \"Regulations on the Selection and Design of Emergency Shutoff Valves for Liquefied Hydrocarbon Spheres\" (Sinopec Document No. 518) states: \"Emergency shutoff valve: A valve used to be installed on the inlet and outlet pipelines of liquefied hydrocarbon spheres, enabling rapid and thorough isolation (TSO) of flammable, irritating, and corrosive materials in the event of accidents such as 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 process needs. The emergency shut-off valve shall have automatic and manual shutdown functions, and the manual shutdown function shall include remote manual shutdown from the control room as well as on-site manual shutdown. From the above definition, it can be seen that in terms of type, as long as a valve can fulfill the function of shutdown, a gate valve, ball valve, or butterfly valve can all be used as an emergency shut-off valve. Furthermore, in terms of function, an emergency shut-off valve is a type of valve that allows for rapid remote shutdown; its purpose is to isolate the flow of material in case of an emergency (such as a fire or leak), thereby preventing potential accidents and containing them within certain limits. II. Requirements for the setup of emergency shutdown functions: The implementation of emergency shutdown functions in any production system must be based on safety principles. This is achieved by making appropriate choices regarding instrumentation, applying structural constraints (such as redundancy and fault tolerance), establishing regular inspection and testing schedules, and utilizing diagnostic techniques, all of which help to optimize the design of safety instruments and ensure that the requirements for risk reduction are met. Article 13 of the Interim Provisions on the Supervision and Management of Major Hazard Sources of Hazardous Chemicals, issued in 2011 (Order No. 40 of the State Administration of Work Safety), stipulates that “major hazard sources of Grade 1 or Grade 2 shall be equipped with an emergency shutdown function,” and that “emergency shutoff devices shall be installed for key facilities within such 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. For Class 1 or Class 2 major hazard sources involving toxic gases, liquefied gases, or highly toxic liquids, an independent Safety Instrumented System (SIS) must be installed.” The “Notice of the General Administration of Work Safety on Issuing Guidelines for Curbing Serious and Catastrophic Accidents Involving Hazardous Chemicals and Fireworks” issued in 2016 (An Jian Zong Guan San [2016] No. 62) further emphasizes that “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 used.” In February 2022, the Ministry of Emergency Management issued a notice titled \"Basic Requirements for Emergency Shutoff Systems in Oil and Gas Storage Enterprises (Trial)\), which set out requirements for retrofitting emergency shut-off valves in large above-ground atmospheric pressure storage tanks in use by such enterprises; it stipulated that \"emergency shut-off valves must be installed on all process pipelines that are directly connected to the storage tanks.\" Several other documents also mention the requirements for implementing an emergency stop (emergency shutdown) function. To implement the emergency shutdown function, an emergency shutdown system must be installed, using emergency shut-off valves to ensure the safe shutdown of the production equipment. So, under what circumstances is it necessary to install an emergency shut-off valve? It can be summarized as the following situations in which installation is required: (1) Chemical storage areas that constitute major hazard sources of level 1 or 2 ； (2) Key storage tanks such as large-scale ones, those for liquefied gases, and those containing corrosive and irritating chemicals ； (3) Liquid-phase inlet and outlet of spherical LPG storage tanks ； (4) Facilities such as corrosive and irritating gases, corrosive and irritating liquids, and flammable gases that constitute major hazard sources of level 3 and level 4 ； (5) Inlet and outlet pipelines for materials in corrosion-irritating material storage tanks, low-temperature storage tanks, and pressure spherical tanks ； (6) Material inlet and outlet pipes at the bottom of liquefied hydrocarbon storage tanks (non-spherical tanks are also included) ； (7) Loading and unloading pipelines without buffer tanks in the loading and unloading station ； (8) There is also a process isolation system based on the results of HAZOP analysis/LOPA analysis. III. Selection of emergency shut-off valves Article 10.1.6 of the \"Code for Selection and Design of Automation Instruments in Petrochemical Industries\" (SHT 3005-2016) states that \"when the process requires tight shutdown (TSO) of the control valve or when it is involved in emergency shut-off interlocks, the allowable leakage class of the control valve should be selected as grade V or above as specified in the GB/T 4213 or ANSI/FCI 70-2 standards\"” ； Article 10.3.6.7: A fusible plug shall be able to be installed on the cylinder used in the actuator of pneumatic emergency shut-off valves. The melting point of this fusible plug should be 75°C ± 5°C. When the temperature of the cylinder reaches or exceeds this melting point, the fusible plug melts, allowing the pressure inside the cylinder to be released; subsequently, the spring on the other side of the cylinder or the compressed air in the air reservoir pushes the piston to close the valve” ； Article 10.3.6.14: “The pneumatic actuators and their accessories used for emergency shut-off valves shall have fire protection measures; fire protection covers shall be installed, and these covers must comply with UL 1709 standards, enabling them to resist hydrocarbon fires for 30 minutes at 1093°C”” ； Article 10.3.7.11: “The actuators and accessories used for electric emergency shut-off valves shall have fire protection measures; fire protection covers shall be installed, and such covers shall comply with UL 1709 standards, enabling them to resist hydrocarbon fires for 30 minutes at 1093°C”” ； Article 10.3.7.12: “The power cables and signal cables of the electric actuator used for emergency shut-off valves should be provided with fire protection measures.” Article 6.4.1 of the \"Design Code for Tank Areas in Petrochemical Storage and Transportation Systems\" (SH/T 3007-2014) stipulates that remote-operable emergency shut-off valves shall be installed on the inlet and outlet pipelines for liquefied hydrocarbons at the bottom of liquefied hydrocarbon storage tanks. “The actuator of the emergency shut-off valve shall have fail-safe measures.” Regarding these fail-safe measures, the explanations in the regulations take the following forms: (1) Use a fail-safe single-cylinder pneumatic actuator ； (2) When using a double-acting cylinder pneumatic actuator, install an emergency air tank ； (3) When selecting an electric actuator, use one equipped with a UPS backup power supply or one that has its own energy storage device. Article 9.4.1 of the \"Code for Installation and Design of Petrochemical Instruments\" (SH/T 3104-2013) states that \"adjustment valves and control valves used for emergency shutdown interlocks do not require isolation valves or bypass valves.\" Article 5.4.1.13 of the \"Design Code for Automation Systems of Petrochemical Tank Areas\" (SH/T 3184-2017) stipulates that \"emergency shut-off valves used to interlock and cut off feed should be equipped with on-site manual valve closing buttons or switches outside the fire hazard area, so as to allow manual operation in emergency situations.\" Item (XXII) of the \"Regulations on Further Strengthening the Safety Design Management for Projects Involving Hazardous Chemicals\" (Safety Supervision General Administration Document No. San [2013] 76) states that \"emergency shutoff devices that can be operated automatically or remotely manually should be installed on the pipelines for feeding and discharging materials from storage tanks containing corrosive or irritating substances, low-temperature storage tanks, and pressure spheres.\" Article 6.4.2 of the \"Code for Fire Protection Design of Petrochemical Enterprises (2018 Edition)\\" (GB50160-2008) states that \"when there are no buffer tanks on site, 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 and unloading cranes.\" By summarizing the above provisions and standard specifications, the selection criteria that emergency shut-off valves must meet are as follows: (1) The actuator used for the emergency shut-off valve and its accessories shall have fire protection measures; a fire protection cover should be installed, and this cover must comply with UL 1709 standards, enabling it to resist hydrocarbon fires for 30 minutes at 1093°C ； (2) The power cables and signal cables of electric actuators should be provided with fire protection measures ； (3) The allowable leakage class for the isolation valve should be selected as Class V or higher as specified in the GB/T 4213 or ANSI/FCI 70-2 standards ； (4) The actuator of the emergency shut-off valve shall have a fail-safe shutdown function ； (5) On-site manual valve shutdown buttons or switches should be installed outside the fire hazard area ； (6) The emergency shut-off valves for storage tanks containing corrosive and irritating materials, low-temperature storage tanks, and pressure spheres shall have automatic or manual remote control functionality ； (7) An isolation valve and a bypass valve may not be provided when installing an emergency shut-off valve. IV. The relationship between emergency shut-off valves and the SIS system. The SIS system (Safety Instrumented System) falls within the category of automation for industrial production processes; it is a system designed to ensure safe operation, and its safety level is higher than that of DCS-based automation control systems. When abnormalities occur in the automated production system, the SIS intervenes to reduce the likelihood of accidents. The SIS system mainly consists of structural sensors, a logic solver, and terminal actuators, with the emergency shut-off valve being one of such actuators.