As we all know, the switches installed in flammable and explosive places should be explosion-proof. However, in some cases, explosion-proof switches can also cause fire and explosion. On August 26, 1999, a chemical company in Liaoning Province had a combustible gas burning and explosion accident, which caused casualties and property losses of tens of thousands of yuan. After investigating the incident, the accident investigation team focused on the explosion-proof switches installed on site after eliminating other factors that may cause combustion and explosion accidents. The investigators found that there was a discharge trace at the end of the switch, and the discharge area of ​​the cast aluminum shell was broken down. There were 3 irregular holes with a diameter of about 6 mm. The surface of the concrete wall was imprinted with about 5 mm2 of molten metal splashing. Therefore, it was determined that the explosion-proof switch was the starting point for this explosion.
So, why is the explosion-proof switch not explosion-proof?
The investigation team analyzed that the following three conditions can lead to discharge of the explosion-proof switch: First, the switch is overloaded for a long time, resulting in electric shock to the hair and aging of the insulating bakelite of the switch. The contact slides out of the gap of the bakelite due to various reasons such as operation, vibration or collision. At this time, a strong discharge occurs between the charged wire end and the well-grounded metal shell, thereby breaking through the shell and opening the open flame to detonate the combustible gas. Second, there is a quality problem in the explosion-proof switch itself, which means that the switch insulation performance is poor and there is a leakage phenomenon. Third, corrosive gas may infiltrate the inside of the switch. The insulation bakelite of the switch is damaged, which accelerates the aging of the bakelite, resulting in internal discharge of the switch. It caused fire and explosion accidents.
In addition, the investigation also found that the loss of overload protection is obviously one of the causes of this combustion and explosion accident. How to choose the type of explosion-proof electrical appliances?
At this stage, hazardous industries usually choose some explosion-proof switches, explosion-proof cabinets and other explosion-proof electrical appliances when selecting electrical equipment. With the development of the times, the use of explosion-proof electrical appliances is also becoming wider and wider. For some companies, when they first choose explosion-proof electrical appliances, the problem they face in general is selection. So, what principles do explosion-proof electrical appliances need to follow?
Explosion-proof electrical selection should pay attention to the following principles: 1, the principle of selection of equipment selection burst electrical equipment must be compatible with the risk of explosive mixtures. The degree of danger of a so-called explosive mixture refers to the group of explosive levels and ignition temperature of an explosive mixture. The selected explosion-proof electrical equipment must be compatible with the detonation level, group, and level of the hazardous area of ​​the explosive mixture. Otherwise, the safety cannot be guaranteed. In addition, if there are two or more explosive substances of different risk levels in the same area, the explosion-proof structure must be selected in accordance with the highest degree of risk of explosion and natural temperature level.
In non-hazardous areas, ordinary electrical equipment is generally used. However, when a container containing explosive substances is placed in a non-hazardous area, there is a possibility of danger in abnormal situations. For example, spillage of dangerous substances due to container corrosion, or accidental operation of hazardous materials by workers, or due to abnormal reactions
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