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STATIC ELECTRICITY F. \u00dcnal TOKTA \u015e. Electrical Engineer, Technical Safety Consultant 1) WHAT IS STATIC ELECTRICITY AND HOW DOES IT FORM? Static electricity (or static electricity) is electricity that occurs due to certain reasons (cid:1) and, as the name suggests, is useless and discharges in the form of arcs from time to time. This discharge is generally uncontrollable (cid:1) and static electricity cannot be utilized. This uncontrolled power can naturally create some dangers. Static electricity is spontaneously formed in nature due to the contact and subsequent separation (contact separation) or friction (friction generation) of two different or the same, conductive (cid:1) or insulating substances. Between substances in contact (cid:1), electron transfer occurs along the contact surface. The electrical characteristics of this boundary layer differ from those of the two materials in contact. If these two materials are separated, the boundary layer disappears, resulting in an electron surplus (negative charge) in one and a electron deficiency (positive charge) in the other. Consequently, these two separate charges attract each other and attempt to discharge (discharge) by forming an arc (spark) across an insulating layer such as air, thus balancing the charge difference. This arc formation can be very dangerous in some environments. If the resistance of the boundary layer is very small and the potential difference is also small, this discharge process occurs without causing an arc (cid:1) between the two materials. As a result, the intensity of the spark that may occur is directly proportional to the potential difference between the two surfaces and the resistance of the transition medium. Furthermore, if the contact and separation of two substances turns into friction, the potential difference and consequently the discharge arc caused by the excess static electricity charges accumulating on the surfaces will be even greater. Static electricity charges can also be induced on surfaces. If a negatively charged surface passes near a neutral surface, the moving surface becomes positively charged due to the transfer of electrons to the neutral surface. Because of this induction, for example, a cloud passing over a building causes a charge to build up on the building. In practice, we can give the following examples of events where static electricity charges occur: a) In vehicles with rubber tires, static electricity accumulates due to friction with the air while in motion. This charge is greater in vehicles with fiberglass bodies (not metallic) because the resistance of the passage surface is higher. In tankers carrying flammable liquids, a significant amount of static electricity accumulates due to the agitation of the liquid by friction with the air (cid:1). Therefore, grounding chains must be used in these vehicles to prevent this static electricity charge from reaching dangerous levels and to continuously discharge the resulting charge to the ground. Additionally, b) During stormy weather, static electricity accumulates in the clouds in the atmosphere. This charge is formed from friction in air movements (cid:1) and the continuous cracking (cid:1) of raindrops. As a result, the discharge of these static electricity charges (cid:1) between clouds of different polarities (cid:1) and between the cloud and the ground manifests itself as lightning. c) If our hair is very clean and dry, and the ambient air is dry and electrically charged, crackling sounds (discharges) are heard as a result of the static electricity charges discharging and balancing (cid: 1) between the hair, which has insulating properties, and a plastic comb. d) In aircraft traveling at very high speeds, a large amount of static electricity accumulates due to high friction. These are continuously discharged (cid: 1) in certain parts of the aircraft, especially through the pointed tips on the wings. As is known, pointed tips spread excess electrical charge around. If this discharge process were not carried out continuously in the air, the aircraft would explode due to the violent discharges that could occur when landing. 60 ELECTRICAL ENGINEERING \u2014 330\/331 e) An example from industry is the spray painting process. Static electricity charges are generated in the spray nozzle due to the friction between the compressed air and the paint mixture. These charges must be discharged continuously. Otherwise, a discharge arc that may occur could ignite the flammable environment. f) Another example from industry is the static electricity charge accumulated on shafts, bearings, belts, and pulleys in transmission assemblies (cid:5). This charge is also generated due to friction. Grounded metal combs (cid:5) should be used to discharge this charge. g) An example from the chemical industry is the static electricity charge that arises during the transport, storage, and transfer of liquids, especially flammable liquids (cid:5), through piping systems. The same electrical charge also occurs when powdered solid particles are transported through piping systems. 2) HAZARDS OF FLASHING, EXPLOSION, AND FIRE CAUSED BY STATIC ELECTRIC DISCHARGE: If a flammable, explosive, or combustible environment exists where a static electric arc is present, it is obvious that this arc can cause major explosions and fires. In general, for a fire hazard, fuel (combustible material), oxygen, and heat (combustible element) must be present simultaneously. If the fuel is not in vapor form, the heat factor must first vaporize the fuel and then bring it to its explosion temperature. For combustion to continue, the relationship between fuel, air, and heat must be such that the heat of combustion continues to vaporize the fuel and burns enough fuel to maintain and increase the reaction temperature. Normally encountered electrostatic sparks cannot vaporize liquid or solid fuels. Thus, if there are no flammable or explosive vapors in the environment, there is no or very little fire hazard due to this arc (cid:5). However, in paint shop environments, such as in spray painting, there is a flammable and explosive paint (cid:5)-air mixture coming from the spray gun. Therefore, the discharge arc can easily ignite this mixture. Thus, the first step to prevent fire is to prevent static electricity (cid:5) discharge and then to prevent the presence of vapors or homogeneously dispersed organic or inorganic dust (cid:5) in the environment at concentrations ready to ignite and explode. For this purpose, liquids with low flash points can be kept in closed containers, while those with high flash points can be kept below this temperature level. In addition, an appropriate ventilation system can be implemented to prevent the formation of vapor or dust concentrations at flammable and explosive levels in the environment. Furthermore, removing or reducing the oxygen in the environment is another measure that can be taken. In an environment where the oxygen level (cid:5) is reduced to between %8 and , combustion can no longer continue. 3) OTHER DANGERS AND HAZARDS THAT STATIC ELECTRICITY CAN CREATE: Other dangers and hazards (cid:5) that static electricity can create are as follows: 3(cid:5)1) High potential difference static electricity discharges can create effects similar to electric shocks. Workers exposed to such electric shocks, if they are working near rotating machinery (cid:5) or in risky places where there is a risk of falling (cid:5), may be exposed to work accidents (cid:5) due to involuntary reflex movements. 3(cid:5)2) The accumulation of static electricity charges can be annoying in some cases. For example, in printing and similar work where lightweight and non-conductive materials (cid:5) are processed or used, the accumulation of static electricity can cause layers to stick together or separate, negatively affecting production. 3(cid:5)3) Static electricity can cause sensitive electrical tools and devices to malfunction. In fact, applying sufficient levels of static electricity to these devices or exposing them to static electricity can cause some of their components to break down and be damaged. 3(cid:5)4) Excessive accumulation of static electricity in the human body can disrupt the normal electrical balance in the body and affect the nervous system. 4) SAFETY MEASURES TO PREVENT STATIC ELECTRICITY DISCHARGE: In general, the formation of static electricity charges cannot be prevented. However, it is possible to prevent these charges from reaching a dangerous level and discharging in the form of sparks, creating a potential difference. The main methods that can be applied to prevent static electricity discharge are as follows: 1) BONDING AND GROUNDING: This method is used only to prevent static electricity discharge between conductive objects. In this method, all conductive parts that may have a potential difference due to the difference in static electricity charge between them are electrically connected to each other, i.e., short-circuited, and also connected to the ground. As a result of short-circuiting, the two objects with different charges reach the same potential (equipotential) level through charge transfer. Therefore, since there is no potential difference between them, an arc discharge is not an issue. With grounding, the charges of these objects (cid:5) are discharged to the ground, bringing them to the ground potential (cid:5). Thus, a discharge between these objects and the ground is prevented. It is not easy to remove static electricity charges accumulated on insulating surfaces in this way. There must be a real conductive surface at the points where the short circuit occurs. As stated in Article 341 of the Occupational Health and Safety Regulations, large synthetic fuel containers must be coated with conductive materials and subsequently grounded. The main application areas of this method are listed below (cid:5): 4(cid:5)1(cid:5)a) All storage tanks, piping systems and connections containing flammable liquids must be properly grounded to discharge any static electricity that may occur. This grounding must be permanently done during the construction of the storage tank or reservoir. During the transfer of flammable liquids (liquids with a flash point below 38\u00b0C) from storage tanks to land and sea tankers, the metal parts of the grounded storage tanks and the metal parts of the tankers must be short-circuited to bring them to an equipotential surface. Short-circuiting and grounding must also be done during the transfer of flammable liquids from one container to another. High flow rates, splashing, and high-pressure filling of flammable and explosive liquids should be avoided (cid:5). Otherwise, the accumulation of static electricity will be excessive. In piping systems, the formation of this charge depends on the flow rate (liters\/min), fluid velocity (meters\/sec), pipe diameter, and length. 4(cid:5)1(cid:5)b) Static electricity also occurs during the transport of powdered materials by pneumatic conveyors. To ensure that the static electricity charges (cid:5) that occur are continuously discharged without arcing, the detailed metal pipes of the conveyor must be connected to each other along the entire line, i.e., short-circuited, and also grounded. 4(cid:5)1(cid:5)c) In spray painting, there should be no potential difference between the spray gun, the metal parts to be painted, all the metal parts of the paint cell, the aspiration systems, and the paint containers. For this purpose, all these parts must be grounded and brought to the same ground potential. 4(cid:5)1 (cid:5)d) Static electricity charges accumulate in the shafts, bearings, belts, and pulleys of the transmission assemblies (cid:5) of machines and equipment. If the machine and equipment have proper grounding (cid:5), and the shafts, bearings, and pulleys are made of metal and are in good contact with the conductive and grounded part, the charge in these parts is transferred to the ground. However, since transmission belts are generally made of non-conductive material (cid:5), grounded brush or comb-shaped static electricity collectors should be placed at the point where the belt leaves the pulley (cid:5) to ensure the discharge of charges generated due to friction, as shown in Figure 1. The width of these brushes and combs should be the same as the width of the belt, they should be placed within 1\/4 inch (6.35 mm) of the belt, and also 4 inches (101.6 mm) from the pulley where the belt leaves it. In addition, the belts can be made of or coated with a special conductive material to prevent the accumulation of static electricity charges on them. COPPER CONDUCTIVE GROUNDED BRUSH Note: The brush is attached or mounted with grounded conductors. [PULL CYLINDERS] GROUNDED METAL PLATE GAP 6.35 mm GROUNDED BRUSH GROUNDED PULLEY BETWEEN 6.35 mm AND 25.4 mm Figure 1: Correct placement of static electricity collectors in the form of a grounded brush 4(cid:5)2) HUMIDIFICATION: Insulating materials cannot easily discharge the static electricity charge present on them. In addition, the distribution of the electric charge on insulating materials is not homogeneous(cid:5). 62 ELECTRICAL ENGINEERING (cid:3) 330\/331 For example, to explain this with an experiment: when a rod made of glass, plastic, or sealing wax is rubbed against a charged cloth or mail, static electricity accumulates on the rod due to the friction. If the rod is made of glass, it becomes positively charged, and if it is made of sealing wax, it becomes negatively charged. However, this charge only accumulates on the part of the rod that is rubbed against the mail. It does not spread homogeneously along the rod. When this end of the rod is then brought close to small pieces of paper, it attracts the paper pieces. However, this process cannot be done with a conductive metal rod, because the static electricity generated in the metal rod is distributed homogeneously across the entire surface of the rod and goes to the ground through the hand holding the rod. However, this process can be done by coating the part of the metal rod held with an insulating material. Therefore, in non-conductive materials, the static electricity charge generated tends to remain stable within the environment in which it is created. To eliminate charge accumulation, a conductive layer that transfers the charge to the ground can be provided on many materials. In practice, the most common conductive layer can be achieved through moisture. As is known, the insulating properties of insulators decrease in humid and wet environments. In fact, materials such as fabric, wood, paper, concrete, etc., contain a certain amount of moisture. If the amount of moisture in the environment is increased, the moisture adheres to the surfaces of the object and forms a thin conductive layer. Thus, it becomes easier to remove the charge from such a layer. The same conductive surface can also be provided by means of antistatic sprays. Another purpose of humidification is that static electric charges are generated in smaller amounts in a humid environment. As the humidity in the air increases, the charge generated due to friction decreases. Furthermore, as the humidity in the air increases, the insulating property of the air decreases, and the resulting charges are discharged through the slightly conductive, humid air environment before reaching a dangerous level (cid:5) and without arcing, passing through another object or the ground (cid:5). Generally, at 70\u00b0F (21\u00b0C), if the humidity level is 60% or higher, static electricity charges will not reach a dangerous level (cid:5). In practice, proper humidification can be done using special humidifiers. An example of this method in practice is the application of a water curtain in areas where spray painting is done. It is applied to eliminate the potential difference that may occur. In certain situations, for example, it is not possible to discharge charges that may accumulate on non-conductive objects in a dry environment. In such an environment, the air around the surface where static electricity may accumulate is ionized. Thus, by creating positive and negative ions in the environment, a temporary conductivity is achieved in an insulating medium such as air, and the charges move freely, establishing equilibrium and neutralizing the objects (cid:5). This movement of ions is definitely not an electric current. However, its effects are the same as those of an electric current. That is, it is the transfer of energy that occurs to eliminate the difference between two objects at two different potential levels. Ionization can be done mainly in the following ways: 4(cid:5)3(cid:5)1) Electrical Ionization: The medium to be ionized (e.g., air) is passed through a high-concentration electric field. For this, high-voltage AC static electricity neutralizers are used. These create an electric corona (corona discharge). Thus, orbital electrons (cid:5) in the atomic structure are easily attracted, creating positive and negative ions (cid:5). The ionization potential required to ionize each substance is different. "Ionization Potential" is the energy required to pull an electron from a neutral and isolated atom. Its unit is electron volt. Electrical ionization generators are not suitable for flammable environments because they release more energy into the environment than they consume. This energy constitutes an ignition source in a flammable environment. 4) Radioactive Ionization: In this ionization, radioactive static eliminators are used to detach electrons from the atom and obtain positive and negative ions in the environment. These are generally sources that emit alpha particles. However, radioactive sources that emit beta particles and gamma radiation are also used. A radioactive ionization generator does not create an ignition source, and the dangers can be easily controlled if alpha particles are used. Alpha radiation can be easily stopped by a sheet of paper or skin (cid:5) and does not pose an external radiation hazard. However, beta and gamma radiation do pose an external radiation hazard. The main way to explain this danger is to stand at a certain distance from the source and place a shield in between. 4(cid:5)3)IONIZATION: This method discharges the static electricity charge accumulated on surfaces before it reaches a dangerous level and between objects (cid:5). The amount of air that this type of generator can ionize depends on the intensity of the source (cid:5) and is limited. A radioactive-headed lightning rod is an application of this method. The air around the head is continuously ionized, and the charges in the air are drawn through a provided conductive medium and discharged to the ground before reaching a dangerous level (cid:2). 4(cid:4)3(cid:4)3) Ionization by Gas Flame or Infrared Heaters: Air can also be ionized by means of gas flame or infrared heaters. A small flame or infrared heater is applied near the environment where static electricity is to be dissipated (cid:2). Unbalanced charges are balanced by being transferred to the flame frame or heating device through the created ionized field (cid:2). This method should not be used where flammable vapors and dusts may be present. 5) PROTECTION OF PERSONNEL: The naked human body is generally considered a fairly good conductor. However, clothing of synthetic origin used as a result of technological development (cid:2) not only isolates the human body from the ground but also causes the formation of electrostatic charges (cid:2). As a result, the capacitance of the human body relative to the ground increases, and the resulting charge creates a risk of arcing and discharging through a nearby conductive surface or the ground (cid:2). Table 1 shows the amount of energy released to the environment (cid:2) due to the electrostatic charge that can accumulate on a person depending on the type of clothing and humidity level, as determined by a study conducted in America. Table 1: Some Example Values for Charge Accumulation on the Human Body Clothing Type Relative Humidity Energy (Joule) Wool Cotton (cid:2) Wool Dynel Cotton 0.087 0.056 0.047 0.025 Tables 2 and 3 show the energy required to ignite some of the most common dusts and vapors, the explosion limits for vapors, and the oxygen levels (cid:2) required for combustion. Table 2: Ignition Sensitivities of Some Commonly Encountered Dusts Ignition Energy (joules) Dust Type Dung Sucrose Corn Starch Relative Explosion Hazard Strong Strong Severe Aspirin Charcoal Epoxide Resin Phenolic Resin Aluminum 0.03 0.02 0.02 0.02 0.015 Severe Strong Severe Severe Severe Table 3: Explosion Limits and Ignition Energies of Some Commonly Encountered Vapors Minimum Oxygen Levels Required for Combustion Vapor Type Benzene Acetone Ethyl Alcohol Ethyl Ether Lower Explosion Limit (%) Upper Explosion Limit (%) Ignition Energy (Joules) 13 2.6 33 1\u00a3 7.1 13.0 19.0 36.5 0.0011 As shown in Table 1, measurements were taken at low humidity levels (cid:2) and when the person was standing on a non-conductive plastic acrylic layer (cid:2). At higher humidity levels, the charge will discharge without excessive accumulation due to the conductivity provided by the humidity (cid:2). If the person wears shoes that can be considered conductive with antistatic (cid:2) properties and also stands on a conductive surface (cid:2), the charge generated in the body will go to ground in this way and will not create a potential difference. Grounding the body in this way eliminates the capacitance of the human body, but some accumulated static energy is stored in the non-conductive layers (cid:2) of the clothing. A large part of the charge on the human body comes from the clothing worn. As seen in Table 1, the best fabric is cotton. Furthermore, because cotton has moisture-absorbing properties, the conductivity of the fabric will also increase. Recently, special work clothes made of conductive polyethylene material containing fine metal threads have been developed. Tables 2 and 3 show how small the ignition energies of many dusts and vapors are. In the past, making and maintaining the floor conductive was considered a very expensive method, but nowadays, new materials have been developed for this purpose, taking their effectiveness into account. As a general precaution, workplace areas containing flammable, explosive gases, vapors, and dusts should be separated from other areas, entrances should be controlled, and "neutralizers" that discharge static electricity from the human body should be present at these entrances. When entering such an area, workers should discharge their static electricity by touching their hands and bodies to this neutralizer. 64 ELECTRICAL ENGINEERING (cid:3) 330\/331<\/pre>\n
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