Generally speaking, the spark temperature is very high, especially the arc, the temperature can be as high as 6000 ℃. Therefore, they not only cause combustible combustion, but also melt and splash metal, which is a dangerous source of ignition. Electric sparks can be divided into work sparks and accident sparks.

1. Overheating of electrical installations, dangerous temperatures cause fire and explosion

When the electrical equipment is running, it always has to be heated. When the current passes through the conductor, it must consume a certain amount of electric energy, the magnitude of which is ΔW≤I2RT. This part of the electric energy will cause the conductor to heat up and the temperature to rise. The larger the resistance R, the longer the time t in the current path, and the more heat is released by the conductor. Once dangerous temperatures are reached, it may cause a fire under certain conditions.

2. The general conditions of electrical equipment overheating are as follows:

(1) Overload

Overloading is when an electrical device or wire draws more current than it is rated for. After an overload, the current increases for a long time, which will cause the electrical equipment to overheat.

(2) Short circuit

Short circuit is one of the most serious fault conditions of electrical equipment. Most fires in the grid are caused by short circuits. After a short circuit, the line current is several times or even dozens of times that of the normal situation, causing the temperature to rise sharply. If the ignition temperature of the surrounding combustible material is reached, a fire will occur.

(3) Poor contact and poor heat dissipation

Bad contacts mainly occur on conductor joints, such as the connection of the fixed joint is not firm, the welding is not good, or the dirt on the surface of the joint increases the insulation resistance, causing the joint to overheat. Removable electrical connectors that become loose due to vibration or heat can also cause the connectors to overheat. All kinds of electrical equipment will have certain ventilation and heat dissipation devices in the design and installation. If these equipments fail, it will also lead to overheating of the lines and equipment.

(4) Leakage

After the insulation of electrical lines or equipment is damaged, leakage will occur under certain conditions, and the leakage current is generally not large enough to make the line fuse work, so it is not easy to find. When the leakage current is evenly distributed, the fire hazard is small, but when the leakage current is concentrated at a certain point, it may cause more serious local heating and fire.

When designing power for explosive atmospheres, electrical equipment, especially equipment that has sparks in normal operation, should be located in a less hazardous or non-explosive environment as much as possible. Equipment with high surface temperatures in fire environments should be kept away from flammable materials. Under the premise of satisfying production safety, the use of explosion-proof electrical equipment should be minimized. Electrical heating devices should not be used in fire hazard environments and should be isolated with non-combustible materials if necessary. Explosion-proof electrical equipment should have an explosion-proof certificate, use less portable electrical equipment, and take measures in the building to limit the explosive environment to a certain range, such as using the partition method.