How to prevent and control safety risks during the loading of flammable liquids?

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On March 23, an accident occurred at a company in Dengzhou, Henan, when a methanol tank truck caught fire during filling, resulting in one person being burned. Domestic petrochemical products are frequently loaded and unloaded. The materials handled at loading sites are mostly flammable and explosive, which imposes high requirements on site selection and layout, process design, selection of equipment and facilities, as well as operation safety management. If any aspect is neglected and risk control is inadequate, it may result in material spills in mild cases, or fires and explosions in severe cases, leading to casualties. Regarding the risks associated with loading, the author suggests controlling these risks from the following aspects: First, pay attention to the layout of the loading and unloading areas. The principle of centralized layout by zone is emphasized; grouping functions that are the same or similar together facilitates production and safety management. If the loading/unloading areas and tank groups are arranged in a cross pattern with multiple loading/unloading sites, the fire lanes within the warehouse area become transportation roads, which not only hinders safe management but also makes it difficult to extinguish fires in the event of an accident; in such cases, a fire can easily spread to adjacent areas. Strictly comply with the relevant standard requirements for pump area layout. Some companies locate tank loading and unloading trucks in the pump area of the tank farm, without taking into account the fire separation requirements between the loading/unloading areas, the pump area, and the storage tanks. In the event of a fire or explosion in the pump area or the tank trucks, it can pose safety risks to the tank farm. Optimize the layout of crane positions at the loading and unloading quays. The distance between crane positions should not be less than 4 meters. The distance between adjacent crane positions on the loading and unloading platforms on both sides, or between adjacent crane pipes at the same crane position, must meet the requirements for the proper operation and maintenance of those crane pipes. The dedicated pumps for each crane position can be arranged collectively with the crane pipes; when the number of pumps in operation at the same time exceeds 2, single-sided loading and unloading should be employed. Second, pay attention to the safety of the loading process. Selection of loading method. Chemical liquid materials can be loaded onto vehicles by pumping or gravity flow. For flammable liquids such as gasoline, diesel, naphtha, solvent oil, and alcohols, splash loading is strictly prohibited; bottom-sealed loading methods should be used, as this helps to reduce vaporization of oils and gases and facilitates their recovery. If upper loading is used, a submersible loading dip pipe should be employed; the vertical part of the dip pipe must extend to the bottom of the container, and the distance between the dip pipe opening and the bottom of the tank must not exceed 200 millimeters. The submersible filling method helps to reduce oil and gas losses and also prevents static electricity from accumulating due to splashing during filling. Implement anti-overpressure measures for the loading system. The loading pump should have local and remote emergency shutdown functions. Methods such as motor frequency control and regulation of backflow volume are employed to address pressure buildup that can occur during pumping due to faulty valve operation or cessation of the loading process. The backflow pipes for volatile light liquids such as naphtha and pentane should be connected to the tank inlet pipes, while those for heavy liquids can be connected to the pump’s inlet pipes. Implement measures to prevent backflow and overpressure in gas pipelines. A blast suppression type flame arrester should be installed on the gas branch pipe that connects the oil and gas collection system to the tank truck, in order to prevent the spread of flames in case of an accident and avoid explosions caused by backflow. To prevent blockages in the flame arrester or failures in the recovery system, flow or pressure monitoring instruments can be installed for online detection, and they can be interlocked with the loading system. For operations involving bottom loading of diesel fuel and similar substances where vapor recovery is not employed, the vapor vent should not be discharged on-site; instead, it should be discharged at a elevated location to prevent the formation of explosive gases near the bottom loading port. Third, focus on improving the level of automation control in loading. Equipped with an automated control system. The system features control functions such as programs for the filling process, quantitative loading, interlock with the electronic key box, interlock for releasing human body static electricity, anti-overflow interlock, anti-static grounding interlock, gas detection and alarm interlock, gas flow rate detection interlock, and interlock for checking the proper positioning of the transfer hose. Equipped with a pipeline emergency shut-off device. An accident isolation valve that is easy to operate shall be installed on the liquid-phase main pipe for loading and unloading flammable liquids, at a distance of more than 10 meters from the loading/unloading crane position. In the event of emergencies such as leaks, fires, explosions, or poisonings involving equipment, pipelines, or a certain area, operators will, based on the location and conditions of the incident, activate control buttons either on-site or remotely to close the shut-off valves and halt loading operations, thereby preventing or reducing the spread of the damage caused by the incident. Fourth, pay attention to preventing and controlling the hazards of static electricity. The top priority in preventing fires and explosions when loading flammable liquids is to avoid the accumulation and discharge of static electricity; anti-static measures must be implemented at the loading site: the loading speed must be strictly controlled ； Accelerate static electricity dissipation ； Regular grounding inspections should be carried out; the grounding resistance of anti-static grounding systems should not exceed 100 ohms. If the resistance value of the equipment under inspection does not meet the requirements, it should be repaired immediately. Anti-static grounding equipment capable of detecting the grounding condition can be used at the loading site. Fifth, pay attention to the safety management of loading operations. Develop an intelligent supervision system for the loading of hazardous chemicals. It includes modules such as vehicle reservation, video surveillance, risk warning, and emergency management. Remote vehicle reservation enables safety pre-inspections, including preliminary checks of the qualifications of both drivers and vehicles as well as their safety conditions. For safety verification when vehicles enter, license plate recognition technology is used to compare and verify the pre-inspection information; only vehicles that pass these checks are allowed to enter. Establish and improve the loading management system, clarify the requirements for checking vehicle qualifications and safety conditions, as well as the safety requirements at various stages before, during, and after the operation. At the work site, operational procedure boards or schematic diagrams can be installed to prevent incorrect operations. Before loading a multi-compartment tank truck, it is necessary to verify the amount and type of material in each compartment to avoid loading the wrong materials or causing spills. Divide into different functional areas. Based on the nature of the tasks, areas such as loading zones, waiting zones, and inspection areas are designated. Vehicles should be parked in accordance with the requirements of each zone, and a certain distance should be maintained between vehicles that are being loaded and those that are waiting, so as to enable timely evacuation and rescue in the event of an accident. The measurement and sampling of tank trucks should be carried out in the inspection area; self-made measuring and sampling tools shall not be used, and measures must be taken to eliminate static electricity from personnel and equipment. No vehicle maintenance, tank inspection, or other operations unrelated to loading shall be carried out within the loading yard. Control sources of ignition at the work site. Electrical equipment in the loading area must meet the explosion-proof requirements of the area. Vehicles entering the loading and unloading area must be equipped with exhaust spark arresters and use them properly. Persons entering explosive hazard areas must not carry any ignition sources; they must wear anti-static work clothes and must not wear shoes with metal studs. They are also prohibited from putting on or taking off clothes, shoes, hats, etc., at the workplace. Loading operations should be suspended during extreme weather conditions such as severe convective weather, thunderstorms, typhoons, and high temperatures. During the hot summer weather, it is advisable to adjust the loading schedule in order to avoid carrying out loading operations under such conditions. Attach importance to the training of personnel for respective positions. Loading operators should be familiar with the physical and chemical properties of the chemicals they handle during operations, be acquainted with equipment, facilities, and process operating procedures, and proficiently master emergency response plans for situations such as leaks and fires. (Author: Jiang Kui, an expert from the China Chemical Industry Safety Association)