Abstract At 8:37 on August 2, the automobile wheel hub polishing workshop of Zhongrong Metal Products Co., Ltd. of Kunshan Development Zone in Jiangsu Province exploded during the production process, which has caused 65 deaths. According to the Public Security Administration of the Ministry of Public Security, the Ministry of Public Security "play four black and four evils"
At 7:37 on August 2nd, the automobile wheel hub polishing workshop of Zhongrong Metal Products Co., Ltd. of Kunshan City, Jiangsu Province exploded during the production process, which has caused 65 deaths. According to the official Weibo news of the Public Security Administration of the Ministry of Public Security and the Ministry of Public Security’s “Fighting Four Blacks and Four Dangers†special operations office, it was initially found that the explosion was caused by a fire accident caused by dust. The company has 450 employees and its core business is electroplated aluminum alloy wheels. What is a dust explosion?
Dust within the limits of the explosion, encountering a heat source (open flame or temperature), the flame instantaneously propagates through the entire mixed dust space, the chemical reaction speed is extremely fast, and at the same time releases a large amount of heat, forming a very high temperature and a large pressure, the system Energy is converted into mechanical work as well as light and heat radiation, which is highly destructive.
Any solid substance in a fine powder state is called dust. Dust that can be burned and exploded is called combustible dust; dust that floats in the air is called suspended dust; dust that settles on the solid wall is called deposited dust.
The following seven types of substances have been found to be explosive: metals (such as magnesium powder, aluminum powder); coal; food (such as wheat, starch); feed (such as blood meal, fish meal); agricultural and sideline products (such as cotton, tobacco); Products (such as paper powder, wood powder); synthetic materials (such as plastics, dyes).
The dust generated in the production process of some factories and mines, especially the dust generated in the processing of some organic materials, may explode and burn under certain conditions.
The research results at home and abroad show that there are generally three kinds of conditions: (1) flammable dust is suspended in air at an appropriate concentration to form a dust cloud; (2) there is sufficient air and oxidant; (3) Fire source or strong vibration and friction.
It is generally believed that as long as the explosive dust meets the conditions (1) and (2), it means that there is a possibility that an accident may occur.
Explosion process
The explosion of dust can be regarded as the following three steps: the first step is that the suspended dust is quickly retorted or vaporized by the heat source to produce a combustible gas; the second step is that the combustible gas is mixed with air to burn; The three steps are the heat released by the dust combustion, which is transmitted to the nearby suspended or blown dust by heat conduction and flame radiation. The dust is heated and vaporized to make the combustion cycle. As each cycle progresses, the reaction speed gradually increases, and through intense combustion, an explosion is formed. This explosion reaction, as well as the speed of the explosion flame, the speed of the explosion wave, the pressure of the explosion, etc., will continue to accelerate and rise, and will leap forward.
Explosion characteristics
(1) Multiple explosions are the biggest feature of dust explosions; (2) The minimum ignition energy required for dust explosions is high, generally above tens of millijoules. (3) Compared with the explosion of flammable gas, the dust explosion pressure rises slowly, the higher pressure lasts for a long time, the energy released is large, and the destructive power is strong.
The main hazard of dust explosion
(1) It is extremely destructive. Dust explosions cover a wide range of sectors, including coal, chemical, pharmaceutical processing, wood processing, food and feed processing. For example, between 1952 and 1979, there were 209 kinds of dust explosion accidents in Japan, and there were 546 casualties. Among them, the crushing and milling project and the dust separation project were more prominent, each with 46 cases. In the Federal Republic of Germany, there were 768 dust explosion accidents from 1965 to 1980. The most serious ones were wood powder and wood products dust and food and feed explosion accidents, accounting for 32% and 25% respectively. In recent years, the frequency of dust explosions in China every year is: local explosions 150-300 system explosions 1-3 times, and showing an increasing trend. These dust explosions in our country, especially the system explosion, caused serious losses. In 1987, the linen dust explosion accident of Harbin Flax Factory killed 58 people, 177 people were light and serious, and the direct economic loss was 8.82 million yuan.
(2) It is easy to produce a secondary explosion. The first explosion of air waves blows the dust deposited on the equipment or the ground. In the short time after the explosion, the central area of ​​the explosion will form a negative pressure, and the surrounding fresh air will be filled in from the outside to the inside, forming a so-called "return". The wind, mixed with the raised dust, caused a second explosion under the igniting of the first explosion. In the second explosion, the dust concentration is generally much higher than in an explosion, so the power of the second explosion is much larger than the first time. For example, in a sulphur powder plant, an internal explosion occurs in the grinder, and the blast wave diffuses from the grinder to the cyclone along the gas pipe. A secondary explosion occurs in the cyclone, and the blast wave is generated on the cyclone after passing the explosion. The crack spread to the workshop, sulphur dust settled on buildings and process equipment, and an explosion occurred.
(3) It can produce toxic gases. One is carbon monoxide; the other is a toxic gas that is decomposed by explosives (such as plastic). The generation of poisonous gas often causes a large number of human and animal poisoning casualties after the explosion, and must be fully taken seriously.
How to prevent dust explosion?
One is to reduce the concentration of dust in the air. Use equipment with good sealing performance to minimize dust flying and escaping. At the same time, install effective ventilation and dust removal equipment to enhance cleaning. The second is to control the indoor temperature. The third is to improve equipment and control the source of fire. Explosion-proof motors, explosion-proof lights, and explosion-proof switches are required in places where there is a danger of dust explosion. Fourth, the scope of the explosion should be controlled in advance. The fifth is to control the temperature and oxygen level. For containers with dust deposits, cooling measures should be taken, and if necessary, inert gas can be charged to dilute the oxygen content.
How can chemical companies strengthen explosion-proof measures?
In the explosion accident of Hebei Funing Starch Factory, it can be seen that the factory enterprises need a complete set of explosion-proof measures. The following 8 measures are worth learning.
(1) Explosion-proof measures in the design of storage structure
When designing the silo workshop, consider the dust explosion problem, try to make the silo road line away from the office area and living area, the distance is not less than 30m, in the work room less than 150m, the staff is no more than 10 people, and two safety can be set. For export, the width of the evacuated stairway is not less than 1.1m, the width of the corridor is not less than 1.4m, and the width of the evacuated door is not less than 0.9m. Each silo shall be provided with independent manholes and air displacement devices, which shall not be connected to each other. The main dust-producing workshop shall be Set the venting device, the manhole is not less than 800 × 800mm.
(2) Main explosion-proof measures taken from the selection and layout of electrical equipment in the production process
The principle is reasonable process design, correct selection, normal maintenance, compliance with operating procedures, control and elimination of fire source, prevention of friction and heat, impact and ignition, elimination of ignition and detonation parts, simplification of process flow, avoidance of multiple lifting, use of explosion-proof bucket Lifting machine, equipment must have reliable grounding, with automatic alarm, automatic parking and other protection devices, design and manufacture of storage and transportation equipment should be considered detachable or easy to repair. At the same time, it is necessary to consider the convenience of ventilation and dust removal and explosion-proof system work properly. From the production equipment, it is necessary to select electrical appliances that meet the requirements of the National Electrical Law, equipment with dustproof and explosion-proof performance, reduce the line speed of the hoist and other conveyors, reduce grain damage, install permanent magnets on the original grain conveyor, and remove the grain in the grain. Metal.
(3) Reduce production and dust spots and control environmental dust concentration
For dust-producing or dust-producing positions in the storage and transportation production process, dust and dust generation points should be reduced, dust diffusion should be controlled, dust concentration in the surrounding space should be reduced, and the dust concentration should not exceed 10 mg/m. We control the dust concentration far beyond the explosion limit. Naturally, it also controls the occurrence of dust explosions.
(4) Explosion-proof measures for dust removal and dust-producing equipment
For dust-generating or dust-removing systems, focus should be placed on eliminating ignition points, increasing wind speed, or grading to reduce dust concentration.
It should be emphasized here that some people often think that with a ventilation and dust removal system, the danger of dust explosion can be eliminated. This is wrong. Because the ventilation and dust removal can only change the environmental dust concentration, and the harmfulness of the dust explosion is transferred to the dust removal system, the dust removal system is often a dangerous source of dust explosion, such as not being collected in the dust removal system. Effective explosion-proof technical measures, it is difficult to prevent dust explosion by ventilation only. This is a point proved by the scene of dust explosion accidents at home and abroad. Because the dust concentration in the dust removal system is basically within the explosion limit, it is also a relatively closed space, and various impacts, friction, static electricity, open flame, smoldering and the like are high.
In this condition and environment, it is not objective and economical to change the dust concentration. We can only increase the operating wind speed and negative pressure work, use explosion-proof fans and explosion-proof motors to eliminate the ignition point, and adopt flame retardant and anti-fire in the system. Electrostatic material, with good grounding, venting and cleaning port, and pressure and temperature warning and monitoring system, when the system is in danger, the host will automatically stop working, and each explosion-proof and explosion-proof system will work automatically. The dust removal system is started 10 minutes before the production equipment starts, and the production equipment stops working for 10 minutes before stopping the dust removal system.
(5) Remove dust and prevent explosion.
To prevent dust explosions in other parts of the dust-producing workshop, it is necessary to strengthen the cleaning of the workshop and eliminate dust from equipment and the environment. It is best to use a vacuum suction cleaning method to avoid dust “moving†or not having a dead Angle. It is not advisable to use wet cleaning such as spraying. Because combustible dust is flammable at a certain temperature, it will be volatilized in space.
The damage to dust can not be underestimated, because it is the most important and dangerous source of dust. For the dust explosion, the dust is more dangerous than the suspension. The explosion pressure rises the most and the damage is the biggest.
Therefore, effectively eliminating dust is one of the main measures to prevent dust explosion.
(6) Explosion, explosion and explosion-proof measures
For dust explosion: on the one hand, it eliminates the formation of dust explosion factors and prevents the occurrence of dust explosion. On the other hand, it is to control the scope of the explosion and reduce the damage caused by the explosion. Explosion, explosion suppression and flameproofing will alleviate or control the damage caused by the explosion in cases where an environment has formed an explosive condition or temporarily unable to eliminate the explosion factor.
In the building or production equipment of the production workshop producing flammable and explosive dangerous materials, there should be a venting opening with sufficient venting area, and some can be equipped with a box type pressure relief fire extinguisher at the venting port. A partial explosion occurs, the venting diaphragm is broken down, and the fire extinguishing agent in the box is mixed with the flame to achieve the purpose of automatic pressure relief, fire extinguishing and protection equipment.
Explosion is the initial stage of the explosion, detecting the occurrence of an explosion and preventing the development of the explosion, and controlling the explosion within a predetermined range. At present, there is a suppression controller, which is connected to the optical signal of the dust explosion through two infrared probes, and can immediately start the sound and light alarm, and cut off the power supply, stop, close the explosion-proof door, and open the fire extinguisher and other protection equipment. Its action time is less than 10μs, and it can also be used to prevent secondary explosions. Explosive pressure detectors and temperature detectors are also available.
Explosion is to break the explosion through a certain device to prevent the spread and spread of the explosion. Explosion-proofing can use chemical and physical explosion-proof or other explosion-proof devices. In the grain processing, lifting, transportation and production, the photoelectric control explosion-proof door is used to close the inlet and outlet, and to block the explosion of gas, flame and spread to avoid causing another explosion.
(7) Fire fighting measures
The grain storage and production environment should be equipped with corresponding fire protection facilities. When extinguishing a fire, 1) avoid lifting the dust. 2) It is not easy to extinguish with water. Water easily reacts with heat and burning food to produce an explosive mixture. At the same time, water will swell the grain, causing the silo to burst. There must be a complete fire alarm device, and the motor vehicle should be equipped with a spark extinguisher and fire extinguishing equipment.
(8) Strengthen management, clarify the system, adhere to implementation, carefully examine and improve the quality of employees
To establish a sound responsibility system for the safety production of explosion-proof work, this work should be included in the plan, layout, inspection, summary, and evaluation. Investigate and study accidents, conduct technical analysis, and summarize lessons learned.
Regular or irregular safety inspections should be carried out to check whether there are aging, heat, wear, impact sparks, strong vibration, poor contact, poor grounding, leakage, and dust removal efficiency of process equipment, various electrical and ventilation dust removal, etc. Check the holes in the workshop for dust, check the personnel's knowledge of explosion prevention and implementation.
It is necessary to carry out explosion-proof safety education, explain the mechanism and hazard of dust formation and explosion, food storage equipment is easy to form explosive factors, electrical easy to detonate factors, learn to master various techniques to prevent dust explosion.
To strengthen the safe operation management of maintenance operations, employees must understand the relevant regulations on inflammable and explosive on-site operations, and have the operation permit for this project before they can be employed. Before the hot work, it is necessary to remove the dust on the site, especially inside and outside the equipment, the ground wall, and stop and block the mouth, holes and pipes at the same time. Be sure to leave without remaining Mars or overheating.
Explosion-proof vacuum cleaners are required to remove dust.
Fire-fighting facility management, safe and reasonable selection of fire-fighting equipment, reasonable allocation of quantity, reasonable position, proper storage and maintenance, correct operation and use. According to the production post system, clear responsibilities, adhere to implementation, carefully check, explain to workers the basic knowledge of preventing dust explosion, improve their technical quality and safety awareness, and raise awareness of dust explosion. Don't mistake the original production process and management method as an explosion-proof measure. For example, some people think that removing dust and dust from the dust-producing workshop can prevent dust explosion, or use a lot of labor instead of mechanical equipment to prevent dust explosion. These methods are neither scientific nor a fundamental way to eliminate the explosion, but rather a backward and negative practice that hinders the development of productive forces.
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