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I. Introduction Crude oil, from its extraction to processing in refineries, and refined products, from their production in refineries to consumption by end-users, usually go through several storage and handling processes. During these processes, due to factors such as temperature, air pressure, and changes in the volume of the gas and liquid phases in the containers holding the oil, a portion of the oil and gas evaporates into the atmosphere, resulting in losses of such materials. From the perspective of oil and gas recovery, oil and gas losses can be broadly divided into three main categories: the first is the breathing loss of oil and gas in storage tanks, which occurs mainly at crude oil transfer stations, refineries, and oil depots ； The second is the loss of oil and gas caused by the loading and unloading processes of transportation vehicles such as trains, cars, and ships ； Third is the oil and gas loss at automobile gas stations, which consists of losses that occur during the transfer of oil from tankers to the stations and during refueling using fuel pumps. The evaporation of oil products directly threatens the human living environment. Since most light oils are volatile, flammable, and explosive substances that tend to accumulate, they form explosive mixtures with air and settle in low-lying areas or ducts; when exposed to fire, they can easily cause explosions or fires, resulting in severe losses of life and property. Due to the wide explosion range of oil and gas and their extensive dispersion, fire and explosion accidents resulting therefrom occur from time to time. Explosion accidents are particularly likely to occur in oil tanks, oil depots, oil ship holds, and tank cars that are in a sealed state. Oil and gas molecules released into the atmosphere pollute the environment; they cause photochemical smog and also damage the ozone layer. Oil and gas losses during storage and transportation result in the waste of valuable petroleum resources. According to years of research both domestically and internationally, during the loading process, the average hydrocarbon content in the gases released into the atmosphere is 1.3 kg/m3. In 2005, China’s gasoline consumption was over 50 million tons, with gasoline volatilization losses amounting to nearly 900,000 tons, resulting in direct economic losses of 5 billion yuan. As early as the 1960s, foreign countries began researching technologies for recovering oil and gas lost through evaporation during loading processes. By the 1970s, technologically advanced countries around the world, such as the United States, Japan, and Western Europe, had widely adopted oil and gas recovery technologies, thereby solving the problem of oil loss during loading. In the United States, not only do refineries and oil storage facilities implement measures for oil vapor recovery, but all gas stations also have closed-system unloading and refueling systems, resulting in virtually no oil vapor emissions from these stations. Refineries and oil storage facilities in the EU have generally adopted measures for vapor recovery, and efforts to address vapor pollution at gas stations have also begun; by 2005, all gas stations in the EU had implemented vapor recovery measures. In China, oil and gas recovery is still an emerging industry with limited practical applications. With the growing awareness of safety, environmental protection, and energy conservation, the widespread application of oil and gas recovery in China has been put on the agenda. Since the main locations where oil and gas recovery devices are used are flammable and explosive hazardous sites such as refineries, oil depots, and gas stations, people pay close attention to the safety aspects of these devices, while also having some concerns. In February 2006, Hubei Chuguan Industrial Co., Ltd., located in the Wuhan East Lake High-Tech Development Zone in \"China’s Optics Valley,\" successfully developed China’s first set of oil and gas recovery devices using adsorption technology, with independent intellectual property rights, as a result of years of research. After rigorous on-site testing by Sinopec’s environmental protection experts, its oil and gas recovery rate exceeds 99%, and the concentration of non-methane hydrocarbons in the exhaust gases is below 3 g/m3. Its performance meets the strict emission standards abroad, filling a gap in domestic capabilities. This unit is of skid-mounted design, featuring a compact structure. One of its key advantages is that the entire system – including the equipment, instruments, and electrical components located on the skid, as well as the electrical control cabinets and operation consoles outside the skid – incorporates a rigorous safety and explosion-proof design, ensuring high levels of safety and eliminating concerns for users. At present, the company’s adsorption-based oil and vapor recovery units come in a range of different specifications as part of a series of products, and strict corporate standards have been established to ensure the quality of these units in terms of design, manufacturing, and installation. They are suitable for use in flammable and explosive hazardous environments such as refineries, oil depots, and gas stations (see Figures 1 and 2). This article explores, from a safety perspective, the safety measures and precautions to be taken in the design of adsorption-based oil and vapor recovery systems. II. Device Composition At present, the oil and vapor recovery devices using adsorption methods, whether in foreign countries or in China, consist mainly of two parts: the adsorption section and the absorption section. The adsorption section mainly consists of two adsorption tanks used alternately; one tank is in the stage of adsorbing oil and gas, while the other tank is in the stage of desorbing the saturated adsorbent. Adsorbents generally consist of activated carbon or silica gel specifically designed for oil and gas recovery. The desorption process is carried out by a vacuum pump. The absorption section uses gasoline or light diesel as the absorbent (refineries can send the recovered rich oil back to the refinery for reprocessing), and the absorption process takes place in a packed tower. The exhaust gas that has not been fully absorbed at the top of the tower is sent back to the inlet of the adsorption tank for further cyclic adsorption. The absorption stage mainly converts the rich gas into liquid gasoline; condensation can also be used to achieve phase transformation. The process flow of Chu Guan Company’s adsorption-based oil and vapor recovery unit is described as follows (see Figure 2): The oil and vapor coming from the filling nozzles of train tank cars and road tank cars enter the condensation tank, where free liquid droplets are separated from them. Subsequently, this mixture enters activated carbon adsorption tank A; the hydrocarbon components in the oil and vapor are absorbed by the activated carbon in its pores, while air passes through the carbon layer. The exhaust gas that meets the emission requirements is discharged into the atmosphere through the outlet at the top of the adsorption tank, after passing through a flame arrester. When the hydrocarbon adsorption capacity of carbon adsorption tank A reaches a certain value and is on the verge of being saturated at the top of the tank, the PLC control system automatically switches to the other carbon adsorption tank B to carry out adsorption work at a pre-set and adjusted time, while carbon adsorption tank A enters the regeneration phase; a desorption vacuum pump is used to create a vacuum in it down to a pressure of less than 10 KPa, thereby releasing the hydrocarbons adsorbed in the pores of the activated carbon. To ensure that the hydrocarbons in the carbon bed are removed as thoroughly as possible, a small amount of air is introduced later to purge the carbon bed. The activated carbon bed is equipped with multiple temperature measurement points at the upper, middle, and lower levels. When activated carbon absorbs oil and gas, the temperature of the bed rises due to the adsorption heat. When this temperature reaches a certain level, the control system issues an alarm; if necessary, it automatically switches to another carbon canister or shuts off the oil and gas inlet valve to ensure safety. When activated carbon desorbs oil and gas, it is an endothermic process, and the bed temperature drops again. The highly concentrated oil and gas (enriched gas) released during desorption enters the vacuum pump, where it is separated from the working fluid and some of the condensed liquid gasoline in the separator at the vacuum pump’s outlet. The oil-gas mixture (rich gas) separated in the separator at the vacuum pump outlet is sent to the lower part of the packed absorption tower, where it comes into full contact with gasoline that is sprayed from above; the high-concentration oil-gas mixture is then absorbed by the gasoline. The small amount of low-concentration oil and gas that remains unabsorbed in the absorption tower is led from the top of the tower to the main oil and gas pipeline before the activated carbon tank, where it is sent to the carbon adsorption tank for cyclic adsorption. III. Standards and Specifications Strict compliance with **relevant standards and specifications is a fundamental principle in design. The relevant standards and specifications adopted in the safety design of adsorption-based oil and gas recovery systems include: GB50156-2002 Code for Design and Construction of Automobile Gasoline and Gas Filling Stations; GB50074-2002 Code for Design of Oil Depots; GB50160—92 Code for Fire Protection Design of Petrochemical Enterprises; SH3097－2000 Code for Electrostatic Grounding Design in Petrochemical Industries; SH3063-1999 Code for Detection and Alarm Systems for Flammable and Toxic Gases in Petrochemical Enterprises; JTJ 237－99 Code for Fire Protection Design of Oil Loading and Unloading Terminals; GB50058-92 Code for Design of Electrical Installations in Explosive and Flammable Environments. IV. Explosion Prevention Measures When the concentration of gasoline vapor reaches its explosive limit (0.6%-8.0% V), an explosion and combustion will occur upon contact with an open flame. Therefore, starting from the process characteristics of recovery by adsorption method and the various potential safety hazards it may pose, we take targeted measures one by one, exercising strict control over aspects such as scheme selection, process arrangement, workflow organization, equipment layout, and process piping. 1. Process control measures: High-quality and efficient activated carbon specifically designed for oil and gas recovery is used, having been carefully selected through repeated processes. This coal-based activated carbon is highly suitable for applications involving repeated adsorption and desorption of gasoline vapors. It exhibits excellent desorption properties, with a temperature resistance of up to 450°C. This allows it to effectively ensure the regeneration of the system while also reducing the frequency of hot spots, thereby offering the best safety levels for industrial use ； Temperature alarms and interlocks are installed in multiple locations within the activated carbon bed. Since the temperature of activated carbon rises during adsorption and drops during desorption, the control system automatically issues an alarm and switches to the desorption mode before the temperature rises to a dangerous level during adsorption, thereby ensuring that the temperature of the activated carbon does not continue to increase and pose a safety risk ； A condensation tank and a level gauge are installed before the oil and gas inlet of the activated carbon tank, thereby preventing liquid gasoline from entering the activated carbon bed ； A liquid ring vacuum pump is used, resulting in a low operating temperature within the pump that does not exceed the auto-ignition temperature of the oil and gas, thereby effectively eliminating potential hazards ； Both the separation tank and the absorption tower are equipped with level alarms and interlocks ； It features an advanced control system with a high degree of automation; during normal operation, the key processes are carried out fully automatically, and all parameters such as temperature, pressure, and flow rate can be monitored for both real-time and historical trends ； The alarms and operational information generated during the device’s operation are stored over the long term to help monitor and manage various production and operational failures. The automatic control system is configured in parallel with a manual control system ； The system is equipped with flame arresters and shut-off valves, and automatic control valves are installed on the gasoline pipelines leading to and leaving the unit; in the event of a fault or shutdown, gasoline is prevented from entering the unit ； All equipment, electrical systems, instruments, and control cabinets located on site are designed with strict explosion-proof features and selected in accordance with **relevant standards ； The concentration of hydrocarbons in the exhaust gases is strictly kept below 10 g/m3, to stay well below the lower limit of the flammability range of oil and gas. For the monitoring of exhaust gas concentration, a combustible gas detection and alarm system can be installed, with the high-limit alarm setting to be less than or equal to 0.15% or 5 g/m3. The alarm is installed in the control room or duty room. The selection and installation of combustible gas detectors and alarms shall comply with the relevant provisions of SH3063 \"Design Code for Detection and Alarm of Combustible and Toxic Gases in Petrochemical Enterprises\" ； Pipelines for transporting oil, gas, and gasoline should have an appropriate diameter selected based on the flow rate in order to maintain a suitable flow velocity; the flow velocity of the liquids within the pipes should not exceed 4.5 m/s, and static electricity should be avoided as much as possible. 2. Equipment, pipelines, and piping layout: When designing the adsorption tank, since it operates alternately between normal pressure and high vacuum conditions, fatigue analysis of the areas subject to alternating stress concentrations must be carried out in accordance with the requirements of JB4735-1995 \"Steel Pressure Vessels – Design Criteria for Analysis\". The outlet of the vent pipe should be at a height of more than 2.5 meters above the ground, and also at a height of more than 2.5 meters above the operating platform within a radius of 3 meters from the vent pipe. There should be no open flames or sparks within a radius of 15 meters around the exhaust pipe ； The slope of the pipe section should not be less than 2‰, with 1% being the typical value ； Seamless steel pipes are preferred for fixed process pipelines. The connection of buried steel pipes should be achieved by welding; when necessary, composite pipes that are resistant to oil and soil corrosion as well as capable of conducting static electricity should be used ； The oil and gas recovery connection hose should be an antistatic, oil-resistant hose ； Sufficient space for maintenance and safety should be reserved around vacuum pumps, oil pumps, etc. V. Anti-static measures Static electricity can easily cause fires; therefore, anti-static grounding devices are installed at gas stations, oil depots, and loading sites. The medium flowing within the equipment pipes in the oil and gas recovery unit is gasoline and oil vapor; if the oil pipes are not grounded to eliminate static electricity, the accumulation of static charge can lead to discharge, which can easily ignite the vapor. The voltage of static electricity generated in oils due to friction can reach hundreds of thousands of volts; improper handling can lead to discharge, resulting in explosion and combustion accidents. Connections such as flanges on pipes and the ends of hoses in areas at risk of explosion should be bridged with metal wires. (When there are no fewer than 5 connection bolts on the flange, bypass wiring is not required in non-corrosive environments.) For metal pipes laid parallel on the ground or in trenches, when the clear distance between them is less than 100 mm, metal wires should be used for bridging. When the clear distance between pipe intersections is less than 100 mm, metal wires should be used to bridge those intersections. Bridging is used to equalize the potential, preventing spark discharge caused by a potential difference between them. The grounding resistance of the anti-static grounding device should not exceed 30Ω. Filters are installed on the inlet pipelines of the vacuum pump and oil pump in the process flow, but precision filters should not be installed arbitrarily, as this will significantly increase the amount of static electricity generated in the oil, sometimes by 10 to 100 times. Ensure good grounding. Static grounding reduces the resistance to the leakage of charge into the earth’s crust, thereby accelerating the leakage of charge from the oil. VI. Lightning Protection Measures Direct strikes of lightning on the oil and gas recovery equipment, or indirect discharges resulting from lightning hitting such equipment, can both lead to the combustion of oil products or explosions of oil and gas mixtures. Gas stations, refineries, and oil storage facilities have very strict safety measures, typically equipped with lightning arresters, down conductors, grounding systems, and lightning rods. The oil and gas recovery unit must be equipped with lightning protection and grounding; the tanks, pipelines, flanges, and other metal components must all be electrically connected and grounded, with no fewer than two grounding points. Grounding for lightning protection, anti-static purposes, the operational grounding of electrical equipment, protective grounding, and the grounding of information systems should all make use of the same grounding system, with a grounding resistance not exceeding 4Ω. When separate grounding devices are installed for each component, the grounding resistance of the metal sheaths at both ends of the wiring cables, as well as that of the grounding devices at both ends of the protective steel pipes, should not exceed 10Ω; the protective grounding resistance should not exceed 4Ω. Information systems should use armored cables or wires routed through steel pipes. The metal outer covers at both ends of the wiring cable, as well as both ends of the protective steel pipe, should be grounded. When the beginning and end of the power distribution circuit are connected to electronic devices, overvoltage (surge) protectors suitable for the voltage tolerance of those electronic devices should be installed. In a 380/220V power supply and distribution system, the metal outer sheath of the cables or both ends of the cable metal conduits must be grounded. An overvoltage (surge) protector suitable for the voltage tolerance level of the equipment should be installed at its power supply end. The wiring cables for information systems should be armored shielded cables, and it is preferable to lay them directly underground. The metal outer sheath of the cable should be grounded at both ends and where it enters the building. When the cable is laid in a steel pipe, both ends of the pipe as well as the point where it enters the building should be grounded. Oil unloading operations should be halted during thunderstorms, as well as the operation of the oil and gas recovery system. The vent pipe should be within the protection range of the lightning protection device and have proper grounding. VII. Conclusion The safety of oil and gas recovery systems must be ensured from the very beginning, during the design phase. In addition to strictly adhering to relevant standards and specifications, it is necessary to implement proactive, thorough, and reliable process control measures based on the specific characteristics of such systems. In particular, given the potential dangers associated with the use of activated carbon for oil and gas adsorption and desorption, appropriate safeguards must be put in place. Moreover, measures for explosion prevention, static electricity control, and lightning protection are all essential; safety must always be given top priority, and no reliance on luck should be allowed.