Lightning: a deadly threat in summer that chemical companies must beware of!

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Lightning protection is a particularly important component of the safety measures in petrochemical enterprises. During production, petrochemical enterprises store and use large amounts of flammable materials, which generate flammable gases and dusts, creating an environment filled with explosive gases or dust. In the event of a lightning strike that causes a fire, it can ignite these explosive mixtures; this may result in production shutdowns and equipment damage, leading to economic losses, or it could even cause casualties and have serious social consequences. Lightning accident at a chemical plant: Around 22:25 on the evening of April 21, 2005, a massive explosion occurred in the emulsification **pharmaceutical production facility of Chongqing Dongxi Chemical Co., Ltd., located on the edge of Ershe, Gunan Town, Qijiang County, Chongqing. The explosion was caused by lightning, resulting in 12 deaths, 7 people missing, and 12 injuries. 　　At 23:04 on March 22, 2013, the Jiudou Fireworks Materials Factory in Dahu Town (which processed single-base powder) experienced an explosion in its drying kilns as a result of a rare lightning strike. No injuries were reported, but the doors and windows of more than 500 houses in the surrounding area were damaged to varying degrees. 　　A gas manufacturing company was struck by lightning, which damaged the gas flow sensor; the direct economic loss amounted to about 20,000 yuan, resulting in an emergency shutdown, while the indirect losses were 80,000 yuan. 　　A chemical manufacturing company was struck by lightning, which damaged 1 oxygen controller, 1 capacitive level transmitter, 1 hydrogen analyzer, 1 magnetic flap level gauge, 2 intelligent alarms, the circuit board of the boiler electrostatic precipitator DAVC controller, and the 366 switch on the 35KV step-down line in the substation. The direct economic loss amounted to about 90,000 yuan, resulting in a suspension of production across the company for 2 days; the indirect losses were 200,000 yuan. Why are lightning accidents more likely to occur in chemical plants during the summer? Composition of equipment and installations in petrochemical enterprises: Tank farms and pump stations. This is a standard component of petrochemical enterprises. The tank area is used to store various raw materials and products; the tanks are connected to each other as well as to the pump area through pipelines. The pumping area is usually combined with the tank area; it is used to transfer the substances inside the tanks to the production site using mechanical pumps, or to remove those substances from the tanks for transportation. 　　Production plant area. This is a core component of petrochemical enterprises. The composition of production facilities is relatively complex; different process flows require a wide variety of equipment. Various chemical or physical reactions take place within the production equipment; during this process, various flammable substances are involved. Flammable gases may be generated during production, or it may be necessary to emit flammable waste gases. 　　Chimneys and flares. This is a prominent feature of chemical enterprises. Chimneys serve as exhaust channels for heating systems, while flares are used to discharge various flammable gases that have been burned. Through facilities such as compressor gas tanks, the pressure inside the flare is kept always higher than the external air pressure. 　　Piping rack. Pipe racks are used for pipeline transportation or as a location for installing outdoor cable trays. Pipelines are used for transporting materials between the production area and the storage area, while cable trays are used for transmitting electrical power between power distribution facilities and electrical equipment. 　　Production control room. The control room is used to manage the production process; it contains a large number of microelectronic devices that are used to control the start-up and shutdown of various equipment, monitor their operating status, issue alerts in case of dangerous situations, as well as monitor the liquid level and temperature of the tanks within the tank area. 　　Wastewater treatment plant. During the production process, petrochemical enterprises generally generate large amounts of industrial wastewater, which must be treated to meet specified standards before it can be discharged. 　　Fire pump room. It has fire-fighting facilities such as fire pumps inside. 　　Substation. Due to the power requirements of some high-power equipment, petrochemical companies generally build their own substations, drawing at least two high-voltage lines from public substations into these stations. After voltage transformation in the substation, power is distributed to the distribution rooms in various areas, from where the cables lead to the various electrical devices. 　　Loading and unloading facilities. It consists of loading/unloading platforms, storage tanks, pipelines, metering facilities, and other components. The hazards of lightning to petrochemical enterprises 1. Direct lightning strike A direct lightning strike refers to a situation in which lightning strikes directly on buildings, other structures, the ground, or external lightning protection systems, thereby generating electrical effects, thermal effects, and mechanical forces. Direct lightning strikes can damage buildings and cause injuries or deaths, as well as damage to equipment that leads to production shutdowns. During a direct lightning strike, the high temperature of the lightning channel can ignite flammable materials in the vicinity, leading to accidents such as explosions. The principles for protecting against direct lightning strikes are as follows: first, use lightning rods to control the location where lightning strikes occur, thereby directing the lightning away from the objects or areas that need to be protected; second, safely dissipate the lightning current into the ground. During this process, it is necessary to avoid the risk of backflow to surrounding metal objects or systems. This requires a low grounding resistance, with the down conductors being short and straight, and having a low inductance value, in order to reduce the voltage across the down conductors and grounding devices. 　　Direct lightning strikes can cause damage to all buildings and structures within petrochemical enterprises, primarily by destroying or damaging those buildings, structures, or equipment. The impact is particularly severe in hazardous areas such as tank farms, outdoor production facilities, and loading/unloading station equipment, as the high temperatures generated by lightning strikes can directly ignite or explode the hazardous materials present in these areas. Therefore, it is necessary to control the locations where lightning strikes occur and keep them within safe zones. When using metal tanks or metal devices themselves as lightning arresters, it is necessary to meet the requirements of relevant lightning protection codes; if these requirements are not satisfied, lightning arresters must be installed for protection. 2 Lightning induction Static electricity induction. Since the bottom of thunderstorm clouds carries a net charge, when such clouds are present in a certain area, the metal conductors in that area will, due to the effect of the electrostatic field, induce charges with a nature opposite to that of the charge at the bottom of the thunderstorm clouds. When the main discharge occurs in a thundercloud, the charge at the bottom of the thunderstorm cloud is neutralized. The induced charges on metal conductors lose their restraint and become charges that can move freely; if these charges are not promptly discharged into the ground nearby, they will generate a very high voltage that breaks down the air gap between them and any nearby metal objects, resulting in spark discharge with those metal objects. If these spaces are filled with flammable materials, sparks may ignite them or cause explosions, leading to serious consequences. 　　Electromagnetic induction. Since a lightning strike is a pulse wave with a duration of milliseconds or microseconds, the lightning current rises from zero to several dozen or even hundreds of kiloamperes in an extremely short time, and then drops back to zero in another extremely short period of time; as a result, the fluctuation of the lightning current is very large. The induced voltage on the nearby loop is proportional to the fluctuation of the lightning current. This induced voltage can overheat the conductor, or cause spark discharge due to an interrupted circuit, or spark discharge can occur as a result of back-discharge with other nearby metals. If combustible materials are present in these areas, the sparks may ignite them or cause explosions, leading to serious consequences. 　　The harm caused by lightning strikes to petrochemical enterprises is primarily manifested in the hazards to hazardous areas. For example, when a pipe accumulates a large amount of charge due to electrostatic induction, if the pipe is not grounded or has an excessively high grounding resistance, or if there is excessive transition resistance at the pipe connections, it may prevent the static electricity from being discharged into the ground. This can result in discharge of electricity to nearby objects, and if flammable gases or liquids are present, they could be ignited as a result. Furthermore, if the loop area between adjacent pipes is too large, electromagnetic induction may generate excessive voltage between them; this voltage could cause the pipes to break down, and if there are flammable gases or liquids inside the pipes, it becomes extremely dangerous. Therefore, it is specified that for pipes laid parallel to each other with a spacing of less than 100 mm, they should be bridged every 30 m or less in order to reduce the area of the induced loop and thus lower the induced voltage. 3 Intrusion of lightning waves Lightning waves are essentially high-voltage pulse waves; they can be caused by lightning directly striking the pipeline lines, or they may result from lightning inducing voltages in those pipeline lines. When lightning waves penetrate indoors along pipelines, high voltages can cause backfeed to equipment or people along that path. 　　Due to the special nature of petrochemical enterprises, there are numerous pipes and cable trays within the plant premises, most of which are installed overhead. Many of these pipelines lead inside buildings; if lightning strikes these pipelines directly or if overvoltage is generated along them as a result of thunderstorms, this overvoltage will penetrate the buildings through those pipelines, causing damage to the equipment connected to them. Additionally, people who come into contact with these pipelines may suffer injuries or death due to contact voltage. If grounding is performed before the pipeline enters the building (with the live conductor being grounded indirectly through an SPD), it can significantly reduce the pulse voltage that enters the room, thereby reducing the risk. 4 Lightning Electromagnetic Pulse A lightning electromagnetic pulse refers to the electromagnetic effects generated by the coupling of lightning current with resistance, inductance, and capacitance, and includes lightning surges and radiated electromagnetic fields. The impact of lightning-induced electromagnetic pulses on petrochemical enterprises mainly affects microelectronic systems such as the production control systems, DCS monitoring systems, and fire alarm systems within these facilities, as well as their electrical systems. The overvoltages and overcurrents caused by such electromagnetic pulses can lead to malfunctioning of these systems or permanent damage to them, thereby disrupting production and resulting in severe economic losses. Implementing proper internal lightning protection measures such as shielding, equipotential bonding, and the installation of SPDs can significantly reduce the impact of lightning-induced electromagnetic pulses on microelectronic systems.