Fire source

1. The ignition source of the conveyor itself

(1) Roller failure

The metal structure of the roller during high speed operation of the conveyor, which form a bearing failure damage. The bearing damage is first manifested by the bearing rolling element falling off, and the running form between the inner and outer rings of the bearing is converted into sliding friction by rolling friction. The second step is that the outer ring of the bearing falls off. Because of the transitional fit between the outer ring of the bearing and the bearing hole, the inner ring and the roller shaft have an interference fit, and the outer ring is operated at a high speed, so that the outer ring falls off earlier than the inner ring. After the outer ring is detached, the relative sliding speed between the bearing ring of the roller body and the inner ring of the bearing is further improved, and a large amount of friction heat is transmitted to the surface layer of the roller body, so that the surface temperature of the roller is as high as 700 ° C, which is dark red. During the operation of the conveyor, the heating point of the red-hot idler to the conveyor belt is constantly changing, which is insufficient to ignite the conveyor belt. After the conveyor belt stops running, it is easily ignited by contact with the red-hot roller.

A belt conveyor at the dock of a coal terminal in the port had a fire accident that burned more than 1,500 m belts and nearly 1000 m wooden trestle channel pedals. The cause of the accident was that the roller cylinder of the bearing failure was frictionally heated during the operation of the conveyor. After the conveyor was stopped, the heat source ignited the conveyor belt.

Therefore, during the operation of the belt conveyor, the idler should be inspected in time, and the roller with abnormal sound should be replaced in time; within half an hour after the conveyor is stopped, the operator cannot leave the conveyor site, and the conveyor must be Full-length inspection, timely detection of fire signs; In addition, in order to timely and accurately determine and find damaged rollers, when designing the conveyor windshield, the windshield should be avoided to cover the rollers.

(2) Abnormally operating roller bearings

During the drum running process, the roller bearing is used for heavy-duty low-speed rolling operation. If the bearing is poorly lubricated or the assembly is unreasonable, the bearing and the housing may be abnormally hot. Because the bearing housing is not fixed, it is easy to adhere and ignite low-temperature flammable materials such as oil-cotton yarn.

A coal mine wagon belt conveyor had a fire accident. Due to the poor lubrication of the tension roller bearing housing, the bearing produced dry friction inside the rotating process. The friction heat was transmitted to the outer surface of the bearing housing, which ignited the adhesion of the bearing housing. With oil-cotton yarn, the conveyor belt, frame and system accessories at the drive section tensioning roller bearing housing are scrapped.

The method to prevent such fires from being fired is to establish strict standards for drum repair and maintenance to ensure the correct installation of the bearings; to lubricate the roller bearings in accordance with the “five fixed” lubrication requirements of “regular, fixed, fixed, fixed and quantitative” When you find an abnormal sound at the drum and housing, check it in time.

(3) Electrical control circuit

There are a large number of control cables on the conveyor, which are generally arranged in the cable trough on the side of the rack. These cables may be short-circuited due to aging, ablation by electrical welding slag, and mechanical damage, resulting in an open flame.

When designing the cable trough, the cable trough cover should be designed to protect the cable; when engaging in the work unrelated to the control cable, try not to disassemble the cable trough; keep the cable trough cover intact, clean the cable trough, and avoid the attachment of flammable materials; Replace the cable that has expired in service in strict accordance with the cable design life.

2. Other sources of ignition

(1) hot fire repair

It is easy to ignite the conveyor belt by performing maintenance work on the conveyor or in the vicinity. The welding slag of the electric welding work falls on the conveyor belt and can immediately ignite the conveyor belt. Under normal circumstances, such sources of ignition can be detected and extinguished in time, but if the operator is busy leaving the site during the time of the work, and the fire is not noticed, it may cause a conveyor belt fire. In addition, the welding slag falls in the uncovered cable trough and may burn the cable.

Enterprises should establish and strictly implement the fire management system. Before carrying out hot work on or near the conveyor, you should carefully check whether there are conveyor belts, cables and other combustibles under the fire position, and strictly enforce “one fire certificate, one guardian, one fire extinguisher, one responsible person” The "four ones" dynamic fire system timely discovers and eliminates fire hazards.

(2) Cigarette

The cigarette butts left by smoking have a temperature of up to 800 ° C. Although the heat is not enough to ignite the conveyor belt and the cable, it can ignite flammable articles such as oil-cotton yarn and cause a belt conveyor fire.

Enterprises should ban smoking on-site workers and hang "no smoking" signs on obvious parts of the site to prevent outsiders from smoking.

(3) Lightning strike

High-power, long-distance belt conveyors are generally empty, although the height is not high, but because of the isolation, there are no other prominent lightning devices around, it is more susceptible to lightning strikes. Multiple lightning strikes may occur after a lightning strike, and the induced lightning can be transmitted to a remote location with the control cable next to the conveyor. The induced lightning voltage can reach thousands of volts or even higher, and gap discharge may occur. It is a very dangerous source of ignition for conveyors with explosion-proof requirements.

Regardless of the explosion-proof requirements, belt conveyors should consider lightning protection measures, especially anti-induction lightning measures, especially between adjacent large metal structural parts in the conveyor room where the bulk grain is transported, equipotential bonding should be carried out. To prevent gap discharge phenomenon.

Combustible

There are two types of combustibles that are likely to cause fire in the conveyor system: one is the combustibles in the system, including conveyor belts and cables, which are inherent, uncontrollable and eliminated by the system itself; the other is the extra-combustible items outside the system. The process of causing a conveyor fire in such combustible materials is complicated, and it is generally not easy to detect and find at the beginning. For example, the flammable materials near the high temperature surface of the bearing and the bearing housing can be ignited, and the fire will expand to form a conveyor fire; the self-igniting articles that have been attached to the control cable for a long time (especially the inaccessible cable line position) may be caused by spontaneous combustion. Cable and conveyor fires; dust explosions cause conveyor fires, etc. Therefore, timely elimination of combustible materials outside the conveyor system is an important part of preventing the conveyor system from catching fire.

1. Flammable and easily pyrophoric articles

On belt conveyors, flammable materials are mainly from residual materials after being transported and repaired. When flammable materials encounter fire sources, they can expand the fire, ignite cables and conveyor belts; easy self-igniting items can generate fire sources and expand the fire. Coal with high heat, wood chips, cotton wool yarn and fabric, etc., both flammable and easy to spontaneous combustion. Although the chemical properties of these self-igniting materials are relatively stable, the spontaneous combustion point is low. If the accumulation is long-term, the ventilation is poor, and the heat released in the air will not accumulate, which may cause the temperature to rise and reach the spontaneous ignition point. Especially in the rivers, rivers and coasts where the air is humid, the water can promote the heat accumulation and biochemical processes, and it is easier to accelerate the oxidation process and spontaneous combustion of spontaneous combustion articles.

The main measure to prevent such fires is to strengthen the inspection and cleaning of the belt conveyor system. Before, during, and after the conveyor operation, the electromechanical maintenance or vulcanization of the conveyor system, timely inspection of flammable materials around the moving parts along the line, especially the driving parts, to remove flammable and easily self-igniting items. Prevent high temperature moving parts from igniting flammable materials. Regular inspection and removal of dead corners, especially foreign objects on the cable, to prevent self-ignition of spontaneous combustion articles for long periods of time, causing fires such as cables and other combustibles.

2. Conveying materials that are prone to explosive dust

Among the materials to be transported, there may be organic dust such as coal dust and loose grain dust that may form explosive dust. These dusts may accumulate between the conveyor belt and the windshield, in the funnel, in the conveyor corridor, and in the transfer machine room. They are well mixed with the air during the formation process. If the mixed concentration reaches the explosion limit, the dust may easily lead to dust. explosion. On January 13, 2008, the three-ring branch of Kunming Yuntianhua International Chemical Co., Ltd. of Yunnan Province, in the process of transporting sulfur by conveyor belt, suffered a sulfur dust explosion accident, causing 7 deaths. Preliminary investigations show that it is precisely because of the dry weather in winter, the air humidity is low, and the operation is late at night, the wind speed is low, and the air flow is poor, causing the concentration of sulfur dust in the pit of the belt conveyor to increase and reach the explosion limit.

For conveyors with explosion-proof requirements, it is impossible to completely eliminate explosive dust. Only by strengthening the management of fire source can the fire source be eliminated. The main measures are: to ensure that the conveyor system meets the explosion-proof design requirements throughout the use process, such as lightning protection. Anti-static and anti-explosion of electrical components; workers are required to wear anti-static labor protection products; regulate mechanical and electrical maintenance management, prohibit dangerous work in electrical environment and mechanical sparks in dusty environment; prohibit fire source Bring into an explosion-proof place.

For conveyors without explosion-proof requirements such as coal conveyors, dust removal management of the materials to be conveyed should be strengthened to ensure that dry or wet dust removal equipment is effective.

Emergency fire fighting measures

Once the conveyor is in a fire, it should be saved in time to eliminate the fire in the initial stage. For the initial fire, the existing fire protection facilities of the conveyor system can be extinguished in time. However, for major fires in which the conveyor belt and cable are severely burned, an alarm should be given immediately and further emergency fire-fighting measures should be taken.

1. Eliminate the chimney effect

Some special arrangements of the conveyor system can cause the fire to burn intensely under the effect of the chimney. One is that the conveyor with a lift has a chimney effect between the windshield and the conveyor belt after a low fire; the second is a conveyor room with a head (or tail) that is horizontally arranged, a high-grade transfer room, a funnel, and a windproof There is a chimney effect between the hood and the conveyor belt; the third is that the corridor conveyor is prone to chimney effects after a fire.

The unit used by the conveyor should fully predict these various risk factors and precautions. Once the conveyor belts in these areas are in a fire, immediately close the “three doors” (the machine room door, the funnel door and the gallery door) under the conditions of the site conditions. And remove the windshield and other measures to lift or weaken the chimney effect. The initial fire of the conveyor in the corridor is easy to extinguish in time, but after reaching the violent burning stage, it is difficult to save. At this time, the personnel should leave the corridor as soon as possible, close and manually block the corridor to prevent the fire from spreading outward.

2. Isolation conveyor

Since the belt conveyor fire in the violent combustion stage is not easy to extinguish, emergency isolation measures should be taken to isolate the long-distance conveyor from the middle to prevent the fire from spreading along the conveyor. The method is: usually reserve sufficient fire-fighting sand, fire Before the spread, the downstream part of the fire conveyor is separated by fire sand. For wireless conveyor belts, the downstream conveyor belt can be cut with a vulcanizing tool.

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