It is possible to meet the requirements of both static electricity accumulation and the formation of explosive mixtures in the environment. There are generally two situations: one is that the accumulation of static electricity comes from combustibles or explosive mixtures themselves, such as the transportation or scouring of combustible liquids or gases; One is that the generation of static electricity is independent of the explosive mixture. For example, people take off their sweaters or perform other operations that generate static electricity in places where flammable gas leaks. The formation of explosive mixture system generally has four situations:
① Combustible gas and combustion-supporting gas are mixed and reach the explosive limit.
②The mixing system of vapor and air of flammable liquid whose working temperature is higher than the flash point temperature.
③Atomized combustible liquid mixed with air.
④ Mixing system of combustible material dust and air reaching the explosion limit range.
According to the formation of electrostatic spark discharge conditions, several common processes in the chemical production process can be found in the electrostatic fire and explosion hazard places or parts:
①The transportation of flammable liquid: the flowing liquid is charged, the electric charge exists in the liquid, and the liquid flowing in the pipeline Even with a higher average charge density, the liquid will not show a higher electrostatic potential because of the larger capacitance. The flammable liquid is mainly charged in the space where the liquid just comes into contact with the air, that is, the outlet of the conveying pipeline.
②Loading, unloading or storage of flammable liquids: When flammable liquids are loaded, unloaded or stored, static electricity will enter the tanker or storage tank along with the liquid, guide the inner wall of the container from the liquid level, and then be guided away by the grounding device. During this process, if sampling on the liquid surface, gauging operation, or incomplete grounding device, it is easy to cause spark discharge.③The flow of flammable gas: If flammable gas such as hydrogen is mixed with air during the flow, it can discharge in the pipeline and cause static electricity to cause fire and explosion accidents. Valves and flanges leak during pipeline transportation of flammable gas, and the leaking surface is not connected with equipotential body or high-pressure injection, which may easily cause electrostatic fire and explosion accidents on the leaking surface.