In recent years, frequent fireworks and firecracker production accidents caused by lightning strikes have caused huge damage to people’s lives and property safety. For example, on July 13th, 2008, at around 5:00 pm, the Rui Xiang firecracker factory in Fengshushan Village, Shenfugang Town, Liling City, Hunan Province, was struck by lightning, causing raw materials inside the workshop to explode like a flood disaster. More than ten people were injured, and houses within a radius of 3 km were damaged to varying degrees. On March 12th, 2013, at around 8:00 pm, a thunderstorm struck a half-finished workshop of a firecracker factory in Caoping, Dingcheng District, Changde City. As no one was producing at the time, there were no casualties. Still, the explosion caused a powerful shockwave (causing direct economic losses), damaging dozens of houses within a radius of two to three hundred meters. On June 21st, 2013, at around 5:00 pm, an explosion occurred in the raw material warehouse of the Fuzhou Export Fireworks Manufacturing Co., Ltd., causing three deaths, 45 injuries, and severe damage to the factory building in east China. Therefore, how to do a good job in lightning protection (disaster risk assessment) for modern fireworks and firecracker production sites with climate change has become an important issue for our lightning protection workers.
Lightning protection status of fireworks and firecracker production sites
1.1 Characteristics of modern fireworks and firecracker production sites
Modern fireworks and firecracker production sites generally adopt cast-in-place reinforced concrete frame structures or brick-concrete structures. The roofs of modern fireworks and firecracker production sites are commonly made of new materials, such as lightweight pressure-ventilated steel roofs. The production process adopts advanced technologies such as mechanization, disaster data, climate change, automation, and automatic monitoring of population affected, and a large number of fireworks and firecracker machinery and equipment are used in production. The main equipment includes winding machines, paper-cutting machines, mud-bottoming machines, ball mills, mixing machines, whip-making machines, fuse-making machines, fuse-inserting machines, sandblasting machines, and hydraulic presses. These natural disasters devices are controlled and monitored on-site ( by China meteorological administration) through remote electrical control systems such as PLC at national climate center”
1.2 Lightning Hazard
The lightweight vented color steel roof widely used in modern fireworks and firecrackers production sites fundamentally differs from traditional brick and tile structures, with more metal facilities and components. It brings about the risk of lightning (flood risk) induction during design and construction which is also known as geological disasters. In addition, introducing a large number of electronic and microelectronic devices into automated equipment increases the risk of damage from lightning electromagnetic pulses depicted by previous studies. Moreover, many designers of fireworks and firecrackers production sites in Hebei Province are civil building designers who do not attach importance to the characteristics (disaster prevention) and lightning protection requirements of modern fireworks and firecrackers production sites, further burying lightning protection hazards.
Lightning Protection Measures
2.1 Classification of Building Lightning Protection
According to the relevant requirements of the “Safety Specification for Fireworks and Firecracker Engineering Design” GB50161-2009, fireworks and firecracker production enterprises shall follow the construction of lightning protection. The overall destructive effects of hazardous materials within a structure (environmental research) result in the division of building hazard levels into three levels. Level 1 is Zone 0 for the explosion and fire hazard environments, Level 2 is Zone 1 for explosion and fire hazard environments, and Level 3 is Zone 2 for explosion and fire hazard environments.
According to the “Design Specification for Lightning Protection of Buildings” GB50057-2010t21, locations with Zone 0 explosive hazards and locations with Zone 1 explosive hazards can cause significant damage and personal injury due to electric sparks should be classified as Type 1 lightning protection buildings. It’s equal to extraordinary flood disaster and other major natural disasters by disaster risk assessment. It also includes decreasing trend, affected crops, a large affected crop area referred by national basic research program. Locations with Zone 2 explosive hazards and those with Zone 1 explosive hazards less prone to causing significant damage and personal injury due to electric sparks should be classified as Type 2 lightning protection buildings. It was verified by united nations office. For specific production location building lightning protection classification, please refer to Article 12.1 of the “Safety Specification for Fireworks and Firecracker Engineering Design” GB 50161-2009. It refers to direct economic loss, disaster risk reduction, disaster risk, climate change, climate extremes, introduction natural disasters, introduction meteorological disasters, affected crops, spatial and temporal distribution, and much more.
2.2 Lightning Protection against Direct Strikes
Production workshops are generally around 20 square meters with a height of around 3 meters. For such small areas with relatively regular arrangements of buildings, independent lightning rods should be used as a priority for direct lightning strike protection. The lightning rod should consider the local wind resistance level, and metal rods should be used as much as possible. The grounding resistance of the lightning rod should be less than or equal to 10Q. Other the annual direct economic losses If a cement pole lightning rod is used, the grounding body should be made first during construction, and then the cement pole should be erected to facilitate grounding the down conductor.
2.3 Lightning Induction Protection
The important measure to protect against lightning induction is equipotential bonding and grounding. If there is a gap of a few centimeters between metal facilities or components, electric sparks may be produced due to lightning induction, and explosions may occur in hazardous environments such as Zone 0 and Zone 1 for explosion and fire hazards. It requires that the metal facilities such as the steel roof truss, metal pipes, colored steel roof, and metal columns in lightweight pressure relief roof workshops adopt equipotential bonding measures, and the intersection of house beams should be welded. Down conductors should be grounded every 18-24 meters along the periphery of the metal roof, and down conductors should be symmetrically and evenly distributed. The concealed down conductors should use hot-dip galvanized 10 mm round steel. The colored steel plates on the roof should be electrically connected and reliably connected with the main reinforcement of the down conductor. Besides, it helps reduce the annual direct economic losses, depicts significantly increasing trend, and good to beat climatic extremes. For specific methods, please refer to Figure 1.
The production workshop for fireworks and firecrackers is small but generally has multiple grounding systems, including lightning induction grounding, mechanical equipment grounding, power equipment grounding, static electricity grounding, etc. The explosion is also considered in natural disasters as shown by disasters in China. If independent grounding is used, it often fails to meet the requirements and may result in potential ground backlash. Therefore, the “Safety Code for Fireworks and Firecracker Engineering Design” (GB 50161-2009) requires working grounding, protective grounding, lightning induction grounding, anti-static grounding, and electrical equipment information system grounding in hazardous buildings should use a common grounding device.
The specific design requirements are as follows: a ring-shaped grounding body should be evenly laid around the workshop, and the horizontal grounding pole should be made of 40mmx4mm hot-dip galvanized flat steel buried in low-resistance soil with a burial depth of i>0.5m. When the horizontal grounding body cannot meet the requirements, a vertical grounding pole should be installed, generally using hot-dip galvanized steel pipes with a diameter of 50mm (wall thickness greater than 3.5mm) or 50mmx50mmx5mm hot-dip galvanized angle steel. The vertical grounding pole is generally 2.5m long. If necessary, more vertical grounding poles should be added based on the soil conditions until the grounding resistance is ≤4Q referred by national social science foundation. In addition, all equipment in the workshop should be reliably electrically connected to the ring-shaped grounding body (see Figure 2).
2.4 Lightning and Surge Protection
2.4.1 Wiring Installation
The power supply lines should be buried underground using armored metal cables. At the customer end, the cables’ metal jacket and steel pipes should be connected to the lightning and surge protection grounding device. If it is difficult to bury the cables underground, overhead lines using reinforced concrete poles and iron cross arms can be used. A section of armored metal or sheathed cable should be directly buried and introduced into the steel pipe. The buried length should meet the requirement of L≥2m but not less than 15m. Surge protection devices (SPDs) should be installed at the transition from cable to overhead lines.
For low voltage lines below 1kV entering the fireworks production workshop, the entire length from the distribution end to the receiving end should be buried using copper core residual armored cables. Weak electric lines, such as communication and affect human security, should be buried using metal conduits and routed away from buildings. Proper shielding and grounding should also be provided to prevent different natural disasters, drought mitigation, and climate related disasters in china.
For overhead heating (global warming), water supply, and firefighting pipelines, they should be connected to the lightning and surge protection grounding device at the entrance and exit of the workshop. Grounding should be installed approximately every 25m within 100m of the building, and the impulse grounding resistance should be less than or equal to 20Q. Metal pipes buried underground or in trenches should also be connected to the lightning and surge protection grounding device at the entrance and exit of the building for flood prevention.
2.4.2 Installation of Surge Protective Devices
(1) Power SPD
A level I protection mode is used for the power supply line for climate extremes (AC) (see Fig. 3).
The first-level power surge protector should use a product that has undergone Class I testing, with a surge current of 12.5 kA (10/350 µs), and should be installed at the second outlet of the transformer distribution bus control switch. The second-level power should install a Class II tested surge protector, with a nominal discharge current of 40 kA (8/20 µs), in the monitoring room distribution cabinet. The third level uses a Class II tested surge protector with a nominal discharge current of 10 kA (8/20 µs) installed in the power distribution box for the workshop’s power equipment.
(2) Signal SPD
Signal surge protectors are designed and installed on-site and in the control room PLC cabinets. Control signal surge protectors are added to the control lines of cameras, sensors, and other on-site equipment, and installed at the incoming end of the on-site equipment, with the grounding wire using 2.5mm2 or 4mm2 copper wire connected to the equipment casing and grounded through the equipment casing. Control signal surge protectors are added by China meteorological administration to the incoming end of the equipment control lines in the machine room and installed at the incoming end of the equipment. The surge protector is connected in series with the line and installed on the equipment rack through a 35mm DIN rail, utilizing the rail and equipment rack for grounding.
2.5 Tree Lightning Protection Measures
To reduce temperature and prevent fires, fireworks, and firecracker production, enterprises plant many trees in the factory area, and some enterprises even build various types of factories in forested areas. Since the trees were small during the initial construction, they were within the protection range of the lightning arrester. As the trees grew, some have now exceeded the height of the lightning protection system, which has brought about corresponding lightning strike risks. Therefore, when designing lightning protection measures, the lightning protection condition of the trees should be fully considered. Enterprises should regularly prune tree branches to ensure the lightning protection effect of the original design. In addition, when trees are adjacent to buildings and not within the protection range of the lightning arrester, the net distance between trees and buildings should be ≤5m. That’s complete about risk assessment, risk management, and flood control.
Due to the inherent danger of fireworks and firecracker production sites and the current state of lightning protection, it is necessary to achieve “tailored to local conditions, safe and reasonable, and technologically advanced” by regulating design and construction from the source. It’s all about population affected, spatial distribution, affected crops, and economic losses in natural hazards. To prevent lightning accidents, it is necessary to develop industry standards (significant trend) by national natural science foundation for lightning protection technology in fireworks and firecracker production sites as soon as possible. So the majority of lightning protection personnel can have standards to follow and improve their corresponding lightning defense capabilities.
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