The control of static electricity in the laboratory is not only for safety, but also for the purpose of improving product quality. For example, in the grinding operation, the electrostatic charge can affect the quality of the finished product, or in the operation of some textile mills, the electrostatic charge can cause the fiber to be vertical. Not lying flat, resulting in defective products. As we all know, the transportation of materials in chutes or pipelines will accumulate static charges, causing the materials to adhere to the inner walls of the chutes or pipelines, which will cause blockages.
1. Minimum ignition energy
The fire or explosion disaster caused by the discharge of static electricity is the result of the discharge energy generated in the combustible mixture being converted into heat energy, which causes the temperature of the combustible gas to rise and exceed the ignition temperature. The minimum energy that raises the temperature to the ignition temperature is called the minimum ignition energy, and this value is used as a target value for explosion or fire.
2. Countermeasures to prevent static electricity disasters
Static electricity disasters occur due to the existence of four conditions: the generation of electric charges, the accumulation of electric charges, the phenomenon of discharge, and the existence of flammable substances. Therefore, if one of these conditions is eliminated, disasters can be prevented. The important thing is to accurately judge which of these four paragraphs to stop and take appropriate countermeasures. As a basic measure to prevent static electricity disasters, we plan to introduce specific methods from the viewpoint of preventing and suppressing static electricity.
(1) Suppress the generation of static electricity: Since the source of static electricity is friction or separation between objects, these effects should be suppressed as much as possible. For example, in operations such as liquid pipeline transportation, dust air transportation or plastic extrusion, the best way is to reduce the speed. In fact, this will affect the efficiency of the operation. The safe flow rate of petroleum is below 1m/s. Static electricity differs in charge or polarity due to different substances. Therefore, a feasible measure is to avoid using insulators that are easy to charge, and use materials that are difficult to generate static electricity by combining them.
(2) Promote leakage of electric charge: In disaster countermeasures, the simplest method is to ground. This method is to make the generated charge quickly disappear to the earth through the metal conductor. However, with this method, if the charged body is a conductor, it can be easily eliminated, while insulators such as plastic, chemical fiber, petroleum, etc., because the charge of the charged part is difficult to move, the effect is not great.
In addition, there is also a method of adding a conductive substance to the object to cause the charge to leak. This includes adding metal powder or carbon black to tires or operator's boots and floor materials of chemical plants, and using hydrophilic oils in chemical fibers or plastics to prevent electrification. If the relative humidity in the air is increased, a water-absorbing layer will be formed on the surface of the object to enhance conductivity, and it will hardly be charged at a humidity above 80%. For this reason, in places where there is a possibility of electrification, the humidity can be increased by increasing the humidity adjustment device or sprinkling water. But the problem is that people may feel unwell, or have an adverse effect on equipment and products.
(3) Elimination of charged charges: In the case where static electricity is still charged even if the generation of charges is suppressed and the leakage of charge is promoted, the static electricity should be actively eliminated. Static eliminators can be used for this, and various eliminators are currently being developed and sold. The currently developed static elimination device uses ions to eliminate static electricity. According to the way of generating ions, there are three types: self-discharge type separator, voltage-added type separator, and radioisotope type separator.
3. Electrostatic protection grounding
In places where flux, powdery substances or other flammable products are handled, there is often a dangerous potential because static electricity accumulates on the equipment, the processed materials, and even the operators. Electrostatic charge discharges to the ground or other equipment. When it encounters flammable or explosive materials, it will inevitably cause fires and explosions, causing many casualties and a large amount of property losses every year.