Electrical fires

With the development of modern science and technology, people's material living standards have changed greatly, and electrical energy has been widely developed and utilized accordingly. The application of electric energy not only benefits human society, but also brings the danger of electric shock and electrical fire accidents to mankind. In the 80s, electrical fires in our country accounted for about 15% of the total number of fires, ranking third in the world. In recent years, with the widespread development and utilization of electric energy, electrical fires have increased sharply in both rural and urban areas, accounting for more than 20% of the total number of fires, ranking first in the world. Among electrical fires, electrical line fires account for about 60%, and low-voltage electrical line fires account for more than 90% of electrical line fires. Obviously, we have many problems in the use of low-voltage electrical lines, and it is urgent to reduce or even eliminate electrical fires. To solve this problem, we must first understand how fires occur, what are the main reasons for their occurrence, and what measures we should take to prevent it when it is the peak of electricity consumption in winter.

1. Short circuit fire

When the two wires are short-circuited, the current increases, the wire insulation layer is destroyed, the core temperature rises rapidly, and the insulation spontaneously ignites and causes fire. For example, the electrical acceptance specification stipulates that the area occupied by the wire in the pipe cannot exceed 40% of the cross-sectional area of the pipe, which is mainly to leave a certain space to ensure air circulation to facilitate the heat dissipation of the wire, and to prevent the aging of the wire insulation layer over time, and the collision of the two wires to cause a short circuit. In the process of supervising the project, we often find that the construction unit cannot strictly follow the regulations, such as the problem of overloading the pipes, some thread seven or eight wires in the pipes with a diameter of 10 mm, and even more, the joints in the pipes appear in the pipes, which is absolutely not allowed.

The main measures to prevent short circuit fire are as follows:

• 1. Avoid short circuit and make the insulation intact. For example, the wire must be piped, not exposed, and cannot be directly wiped in the wall, and the wire should be laid with sheaths, grooves, cables, etc.; Buried cables should be careful to have a large enough bending radius to prevent the cable from damaging the insulation during the pulling process.

• 2. Maintain the insulation level. The wire should avoid overload, overvoltage, high-temperature corrosion and being soaked in water. With the improvement of material living standards, the number of household appliances continues to increase, and the line load is getting larger and larger, and users should not arbitrarily increase the line load without the permission of the design department, especially some old buildings, the cross-sectional area of the wire is small, if you must increase the load, you must also lay another power supply; For new buildings, it is recommended that the design department leave some room in the selection of the cross-sectional area of the wire according to the increasing trend of line load to ensure the normal level of line insulation.

• 3. When laying wires, flame-retardant piping, fireproof cables, fireproof trunkings, etc. should be used.

• 4. If a short circuit has occurred, the circuit should be quickly cut off to limit the spread of fire along the line and prevent the lines from intertwining. It should be noted that water should not be splashed when the power supply is not cut off to avoid causing some undue losses and casualties.

2. Grounding fault voltage fire

This is a more dangerous cause of fire than a short circuit. Generally speaking, when the ground fault circuit impedance is large, and the wire grounding connection is poor, the loop impedance is increased, and arc faults are easy to occur, commonly known as sparks. We require that when the entry line enters the distribution box, the box must be reliably connected to the ground, the grounding bolt must be galvanized gasket, and if it is a multi-strand wire, the nose must be added, which is the reason.

To prevent grounding fault fires, first of all, insulation damage should be prevented as much as possible in the selection and installation of electrical lines and equipment to avoid the occurrence of grounding faults. In this regard, in addition to taking measures to prevent short-circuit fires, the following measures should also be taken:

• 1. At the power supply main line of the building, a leakage protector should be installed, and it should be noted that the leakage protection for fire prevention must be installed at the power supply main line to play a fire prevention role in the whole building;

• 2. Implement total equipotential connection in the electrical installation of the building. When the fault voltage enters the line along the PE line, it is at the same fault voltage on the line in the building, which eliminates the potential difference and prevents arc sparks from occurring, which also meets the fire protection requirements.

3. Install an electrical fire alarm monitoring system

The electrical fire monitoring system saves power and reduces consumption, protects equipment, predicts hidden dangers, and reduces fire prevention and disaster for users.

In addition, gas explosion accidents also have a lot to do with electrical sparks. Generally speaking, when the gas in a certain space reaches a certain concentration, if there is a spark at this time, a gas explosion will occur. When people come home from get off work, if they smell a smell of gas or liquefied gas, it means that there is a leak of gas or liquefied gas, at this time do not rush to turn on the switch of the light, the first thing to do is to open the window, so as not to contact the bad switch to spark, cause gas or liquefied gas explosion, cause undue economic losses and casualties.

The prevention of electrical fires is mainly to do the following things in daily life:

• 1. Inspect the power lines to find problems in time.

• 2. When designing and installing electrical lines, the insulation strength of wires and cables should not be lower than the rated voltage of the network, and insulators should also be selected according to the different voltages of the power supply.

• 3. During the installation of the line and construction, it is necessary to prevent scratches, wear, and collision of the wire insulation, and pay attention to the quality of the wire connection joints and the quality of insulation bandaging.

• 4. In places with particularly humid, high temperature or corrosive substances, it is strictly forbidden to lay insulating wires openly, and casing wiring should be used.

• 5. It is strictly forbidden to connect and pull wires indiscriminately, and when installing the line, the wire of the corresponding section should be reasonably selected according to the load of the electrical equipment. In addition, the distance between the wires, between the wires and the building components, and between the insulators used to fix the wires should meet the requirements of the regulations.

• 6. Check the circuit fuse regularly, choose the appropriate fuse, do not arbitrarily thicken the fuse, and do not use aluminum wire and copper wire instead of fuse.

• 7. Check whether all connection points on the line are firm and reliable, and require that flammable and commendable materials should not be stored nearby.

precursor

• Before an electrical fire, there is a kind of precursor, which should be paid special attention, that is, the wire will first scorch the insulating skin due to overheating, emitting an unpleasant smell of burning rubber and plastic. Therefore, when smelling this smell, you should first think that it may be caused by electrical reasons, if no other reason is found, you should immediately pull the gate to cut off the power until the cause is found and properly dealt with, before closing the power transmission.

measure

• 1. In the event of a fire, the power supply should be cut off first to avoid electric shock, and the short circuit between electrical equipment and the line should be expanded.

• 2. The insulation capacity of electrical equipment in the fire area is reduced due to moisture and smoke, so insulation tools should be used when opening the switch.

• 3. When cutting the wire, different lines should be cut in different parts to avoid two-phase or three-phase short circuits, and the overhead lines should be disconnected near the support objects.

• 4. A warning area should be set up when the wire is grounded to prevent personnel from entering and being electrocuted.