Methods for preventing and controlling the harm caused by static electricity in bulk bags
1. The packaging materials should be controlled to avoid generating static electricity as much as possible. For example, when transporting flammable liquids, it is necessary to limit the violent shaking in the packaging barrel, control the loading and unloading methods, prevent leakage and mixing of different oil products, and prevent water and air from entering the steel barrel.
2. Take measures to dissipate the generated static electricity as soon as possible to avoid accumulation. For example, install good grounding devices on tools such as handling, increase the relative humidity in the workplace, lay conductive floors on the ground, spray conductive paint on certain tools, etc.
3. Add a certain amount of counter-charge to the charged body to avoid the increase of static voltage (such as induction static neutralizer).
4. In some cases, static electricity accumulation is inevitable, and the rapid increase of static voltage may even produce static electricity sparks. At this time, measures should be taken to prevent explosion accidents from occurring even though it is discharged. For example, inert gas is used in the space where flammable liquids are stored, alarm devices are installed, and efficient exhaust devices are used to prevent flammable gases or dust in the air from reaching the explosion limit.
5. In places with fire and explosion hazards, such as chemical hazardous goods storage places, workers wear conductive shoes and anti-static work clothes to eliminate static electricity on the human body in time. From the perspective of electrostatic ignition hazards, container bags are usually divided into four categories according to their structure. This classification method is widely used in Europe.
Container bags
In June 2003, the European Committee for Electrotechnical Standardization CENELEC published the document CLC/TR50404 "Electrostatics-Code of Practice for the avoidance of hazards due to static electricity". This is a very comprehensive electrostatic operation standard for various fields of industry, and one chapter points out the electrostatic safety use specifications of container bags in detail. The standard divides container bags into four categories: Type A, Type B, Type C, and Type D.
Type A container bags have no special electrostatic safety characteristics, so they are not recommended for the treatment of sensitive flammable dusts and powders. In addition, they cannot be used in places where dust clouds or flammable solvent vapors are present. This type of container bag is usually made with ordinary woven polypropylene cloth and is an insulator. Sometimes, depending on the requirements of use, Type A bulk bags are lined with inner bags or coated on the surface.
Type B bulk bags are similar to Type A and are also made of ordinary woven polypropylene cloth. However, the breakdown voltage of the woven cloth of Type B bags cannot be higher than 4KV. This means that Type B bulk bags will not produce propagating brush discharges. This is an important classification; that is, the discharge that can be produced on the bulk bag is a low-energy brush discharge. If propagating brush discharges can be excluded and the energy of the brush discharge is 4mJ, it is reasonable to believe that this type of bulk bag is safe for flammable gas environments with a minimum ignition energy of no more than 4mJ. Similarly, this type of bulk bag is safe for combustible dusts with an ignition energy of no more than 4nd. However, Type B bulk bags cannot be used in flammable hydrocarbon vapor environments. It must be noted that some factory-made bulk bags meet the classification criteria for Type B and still cause accidents. For example, when tested by a testing agency, it meets the Type B standard, but in actual use, due to the coating on the liner and the bag surface, the breakdown voltage is higher than 4KV, which makes the Type B bag become Type A.
Type C bulk bags are designed for sensitive and flammable environments, including flammable hydrocarbon solvent vapor environments. This type of bulk bag is made of conductive cloth or woven cloth coated with conductive/anti-static coating. Conductive cloth is woven cloth with conductive fibers/flat wires interwoven. In some designs, the conductive wires are parallel, and the spacing is 20mm. In other designs, the conductive wires are woven into a network, with the wires intersecting vertically. The conductive wires are usually flat wires or conductive metal wires.
Type D bulk bags have anti-static or static dissipative properties and do not require grounding. Most Type D bulk bags on the market today are made of thin, semi-conductive wires interwoven into the woven cloth. Unlike the design of Type C bulk bags, these semi-conductive wires are parallel but not cross-linked. This type of bulk bag may have a static dissipating coating. Since fires and explosions caused by bulk bags are generally attributed to static electricity, to solve this problem, some new "static safe" bulk bags have been developed and commercialized.