(A) the basic knowledge of safe use of electricity
1. The significance of safe use of electricity
The so-called safe use of electricity refers to the premise of ensuring the safety of persons and equipment, the correct use of electricity and the scientific measures and means adopted for this purpose.
In modern production and life, electricity plays a very important role, to the benefit of mankind. However, if you can not use electricity safely, there will be personal electric shock accidents, the heaviest cause of death, but also damage to equipment. Therefore, the safe use of electricity as a professional knowledge, should be publicized to all electricity users, should also be mastered by all electricity staff.
2. The cause of human electrocution
The human body touches the electrified body and withstand excessive voltage, resulting in death or localized injuries caused by the phenomenon known as electrocution.
Electrocution according to the degree of injury, can be divided into two kinds of electric shock and electric injury. Electric shock refers to the current through the body and the internal organs of the phenomenon of injury, which is the most dangerous electric shock. Through the human body of the industrial frequency current exceeds 10mA or direct current current exceeds 50mA, will produce breathing difficulties, muscle spasm, central nervous system suffered damage, so that the heart stops beating, so that death. Electrical injury refers to the human body due to the external arc or fuse meltdown when the splash of metal and other burns caused by the phenomenon.
The main cause of electric shock injury is the current. The size of the current is determined by the role of the human body voltage and resistance of the human body. Various parts of the human body resistance size varies, about 2k ~ 20MΩ. Generally speaking, the skin's resistance is larger; but because the skin surface of the moisture will make its resistance lower. Thus, the human body electrocution voltage size and electrocution when the situation, is to determine the degree of electrocution injury is an important factor.
Electrocution occurs in a variety of cases, but the form of electrocution can be summarized as a single line of electrocution and double line of electrocution two. In Figure 4-29a shows, the human body at the same time contact with the two end of the line, the formation of double line electrocution, when the human body to withstand the role of the line voltage is the most dangerous. As shown in Figure 4-29b for the center line grounded single-phase electrocution, then the human body to withstand the role of phase voltage, is also very dangerous. As shown in Figure 4-29c for the center line is not grounded single-phase electric shock, when the charged body insulation and capacitance to ground is very large, the human body is also dangerous.
(B) prevention (prevent) methods and safety measures to prevent electric shock
1. protective grounding and protection of zero
In the process of power generation, power supply and use of electricity, electrical installations due to the aging of the insulation, over-voltage breakdown or wear and tear, resulting in the original should not be part of the charged (such as the metal base, shell, etc.) charged, or the original part of the low voltage with high voltage power, by these Accidental abnormal charge caused by electrical equipment damage and personal injury accidents often occur. In order to avoid the occurrence of such electrical accidents, the most commonly used protective measures are grounding and zero.
Figure 4-29 various electric shock
(1) grounding
Electrical equipment, any part of the earth and the earth to make a good electrical connection, known as grounding. Safety grounding is to ensure that the normal operation of electrical equipment and staff safety is the most important measure. With the earth in direct contact with the metal body or metal body group, known as the grounding body or grounding pole. Grounding body and electrical equipment connected to the metal wire known as the grounding line, the grounding line can be divided into the grounding trunk and grounding branch line. The grounding body and the grounding wire is known as the grounding device.
The grounding voltage is the grounding part of the electrical equipment and the earth fog potential between the rhyming potential difference. Usually can be considered from the grounding body 20m and above the earth for the zero potential point. In addition, the grounding resistance refers to the grounding body of the ground resistance and grounding wire resistance of the sum, it is also equal to the ground voltage and through the grounding body into the ratio of the current in the ground.
Grounding can be divided into protective grounding and work grounding. Protective grounding, which is taken to ensure personal safety grounding, such as electrical equipment metal casing grounding; work grounding, which is taken for normal work grounding, such as power transformer neutral grounding, over-voltage protection grounding and so on.
The following low-voltage IT systems and TT systems for the protection of grounding were introduced:
1) IT systems for the protection of grounding. In the power neutral point is not grounded three-phase three-wire system of low-voltage IT systems (Figure 4-30), all electrical equipment shells were connected to the earth for the implementation of protective grounding. IT system, people touching the single-phase shell of the equipment, through the human body's current Ib is only a part of the grounding current IE, that is, Ib = IERE / (RE + Rb). If a 2.5m long, 50mm diameter steel pipe into the sandy clay, the soil resistivity of 100Ω - m, so its grounding resistance RE ≈ resistivity / length = 100Ω - m / 2.5m = 40Ω, and the human body resistance according to the worst environment can be taken into account Rb = 1000Ω, the current through the human body only accounted for 1/25 of the grounding current, so that the human body can be avoided! The risk of electric shock, play a protective role.
Figure 4-30 IT system
For the equipment, because the IE is only no fault two-phase leakage current (capacitive current) and its value is very small, will not jeopardize the safety of the equipment, will not cause a fire and other accidents, so do not have to cut off the power supply, the faulty equipment in the specified time can continue to run. For petrochemical, mining, shipping and other industrial production of flammable and explosive gases and the requirement of continuous power supply characteristics, the use of IT systems, not only to improve the reliability of power supply, but also play a role in electric shock protection. In order to timely detection and troubleshooting, to prevent the simultaneous occurrence of two-phase ground faults, IT systems must be equipped with insulation monitoring devices, so that in the event of single-phase grounding in the system to send an alarm signal, timely processing.
2) TT system of protective grounding. In the power supply neutral point directly grounded three-phase four-wire TT system, all the shell of the power equipment by their respective PE wire grounded, constituting the TT system, also known as the protective grounding (Figure 4-31). TT system of a device touching the shell, its single-phase grounding current IE = 220 / (4 + 40) = 5A (assuming that the neutral point of the power supply grounding resistance R0 = 4 Ω, the shell of the equipment grounding resistance RE = 40 Ω), the shell of the equipment grounding resistance RE = 40 Ω ), equipment shell to ground voltage UE = 200V, IE is small, UE is a large TT system is characterized. This single-phase grounding short-circuit fault current generally does not make the line overcurrent protective device action, so the equipment shell may be charged for a long time, there is a danger of electric shock to people. For this reason, this TT system must usually be installed leakage protection. Leakage protection action current is generally set at 30mA (safe current value), so that the equipment shell in the event of a single-phase ground fault voltage to ground does not exceed 50V (safe voltage value). This equipment shell protective grounding resistance RE = 50V / 30mA = 1.667Ω. In practice, take RE ≤ 100Ω, which is very easy to realize. So protective earthing as a safety measure has been widely used in the neutral point directly grounded three-phase four-wire system, especially in the wide range of power supply, load imbalance, zero line voltage is higher, the use of TT system is reasonable. This kind of system is widely used in foreign countries, and has been popularized in China. GB50096-2011 Residential Design Code" on the provisions: residential power supply system "should be used TT, TN CS or TN S grounding method".
Figure 4-31 TT system
(2) Zero
Zero refers to the metal casing or frame of electrical equipment insulated from the live part, and the neutral point of the direct grounding system in the zero line (i.e., PEN line or public **** PE line) connected to avoid the risk of electric shock to the human body. In order to ensure that the equipment is reliable, to prevent the risk of electric shock, in the neutral point of direct grounding and lead out of the PEN line or PE line in the TN system must be taken to protect the zero. TN system according to the different ways of zeroing is divided into: TN-C system, TN-S system and TN-C-S system.
1) TN-C system. TN-C system in the N line and PE line into a PEN line, the exposed conductive part of all equipment are connected to the PEN line (Figure 4-32). Its PEN line can have current through, so through the PEN line can produce electromagnetic interference on some equipment. If the PEN line breaks the line, but also can make the equipment connected to the PEN line exposed conductive parts (such as shell) charged, there can be a danger of electric shock to people. Therefore, the system is not suitable for the fight against electromagnetic interference and safety requirements of higher places. But because of the N line and PE line together, thus saving non-ferrous metals (wire materials) and investment. The system used to be the most common in China's low-voltage power distribution system, but now in the safety requirements of higher places, including residential buildings, office buildings and the requirements of anti-electromagnetic interference are not allowed to use the place.
Figure 4-32 TN-C system
2) TN-S system. TN-S system in the N line and PE line is completely separate, all the equipment of the exposed conductive part are connected to the PE line (Figure 4-33). PE line in the current through the PE line, and therefore do not have electromagnetic interference with the PE line of equipment. If the PE line breaks, under normal circumstances will not be connected to the PE line of the exposed conductive part of the equipment charged; but in the event of a phase of the equipment shell failure, will make the other equipment connected to the PE line of the exposed conductive part of the equipment charged, so that there is a risk of electric shock. Due to the separation of N and PE lines, compared with the above TN-C system, in non-ferrous metal consumption and investment have increased. The system is now widely used in places with high safety requirements and anti-electromagnetic interference requirements, such as important offices, experimental sites and residential premises.
Figure 4-33 TN-S system
3) TN-C-S system. TN-C-S system, N line and PE line can be based on the load characteristics and environmental conditions of a combined or separate PEN line, PEN line is not allowed to merge (Figure 4-34), the advantage of its solution to the TN-C system line end of the zero line of too high a voltage to the ground, both the two previous The characteristics of the system, suitable for distribution systems at the end of poor environmental conditions or data processing occasions. It must be pointed out that: the same low-voltage power distribution system, can not be taken to zero protection of another and take grounding protection. Otherwise the use of grounding protection of the equipment shell failure, all the equipment using zero protection of the shell may be dangerous with the ground voltage.
Figure 4-34 TN-C-S system
2. Prevent electric shock safety measures
(1) blackout operation and safety measures
1) disconnect the power supply. Maintenance of electrical lines, should first disconnect the low voltage switch, and then disconnect the high voltage switch. For multiple circuits of the line to prevent from the low voltage side of the equipment to be repaired back to the power supply.
2) power test. With the voltage level of the same checker, the maintenance of the equipment in and out of the line respectively check the power, confirm that no power before work.
3)Installation of grounding wire. The power supply has been disconnected from the output side of each phase, as well as the maintenance of each phase of the line should be installed to carry a temporary grounding wire. Installation of grounding wire, should be connected to the grounding end, and then connected to the conductor end. Remove the grounding wire, should first remove the conductor end, and then remove the grounding end. When installing and removing the grounding wire, should wear insulated gloves, hold the insulated pole operation of the temporary grounding wire, the human body shall not touch the grounding wire, and someone to monitor.
4) in more than six winds, heavy rain and lightning and other circumstances, it is strictly prohibited to board the pole operation and reverse operation.
5)Before boarding the pole work must check whether the root of the pole is firm. Newly erected pole in completely solid before climbing is strictly prohibited.
6)When working on the pole, the ground should be supervised; materials, tools to use the rope to pass; 2m below the pole is not allowed to stand, the site staff should wear a helmet.
7) pole work must use safety belts. Safety belt should be tied to the pole and solid components, not chained to the crossbar wood, should prevent the safety belt from the top of the pole out.
8) the use of ladders should be supported or anti-slip measures.
(2) charged operation of the anti-electrocution measures
1) charged operation must follow the relevant safety regulations, by the trained, examined and qualified electricians, and sent experienced electrical professionals to monitor.
2)Use well-insulated tools, wear no broken, oil-insulated shoes, stand on dry insulation.
3) should first distinguish phase line, zero line. Disconnect the wire, should first disconnect the phase line, then disconnect the zero line. Can not use insulated pliers at the same time clamp off the phase line and the zero line to avoid a short circuit. When connecting the wires, the zero line should be connected first, and then connected to the phase line. Do not make the human body contact two wires at the same time.
4) has been disconnected from the phase line and the charged body should take insulation or isolation measures.
5)Maintenance of low voltage lines erected on high-voltage poles, maintenance personnel from the high-voltage line distance should be in line with Table 4-9.
Table 4-9 safety distance
3. Airport safety instructions
1) It is strictly prohibited to use a line (phase line) a ground (earth) installation of electrical appliances, the fire wire must be into the control switch.
2)In a socket can not be connected to too much or too much power of electrical appliances. Do not tie the power cord with metal wire.
3)Do not use wet hands to touch the charged equipment, not to use a wet cloth to wipe the electrical appliances.
4) electric motors and electrical equipment shall not be placed on the clothing and sitting on; electrical equipment should be kept away from wet, corrosive environment; electrical equipment should have a certain insulation resistance, the use of insulating materials must be frequently checked for damage and aging; airport electrical equipment load should be matched with the power supply capacity.
5) the introduction of drilling airport power line shall not use bare wire; close to the airport poles should be higher than 2.5m above, and will be on the pole insulator iron foot into the grounding wire; if the cable, should be intact, no joints in the middle of the cable should be laid under the floor in the engine room.
6) airport power switch must be intact, reliable insulation, into the box, trigger switch should wear good insulating gloves; working lamp voltage should be less than 36V, moving electrical appliances must cut off the power supply, the fuse is not allowed to use copper, aluminum wire instead.
7) electrical equipment in the airport must be installed grounding device, start the motor to the airport personnel to issue a password, and always pay attention to the motor and other equipment operating conditions, such as smoke, sparks, etc. should be immediately disconnected to check.
8) Thunderstorms, airport staff should not go outside the airport activities to avoid lightning injuries, do not approach the pole and lightning grounding conductor around to prevent lightning into the ground around the existence of step voltage caused by electric shock.
9) airport power distribution equipment (such as transformers) should be far away from the airport and take effective protective measures, so that the general public can not approach the high-voltage equipment, and hang warning signs.
10) telephone facilities in the airport, should be installed lightning protection devices; do not use the phone when the thunder, to prevent the introduction of lightning injuries.
11)In the event of a power failure, all power switches should be turned off to prevent accidents caused by the sudden arrival of electricity.
12)Electrical equipment must be installed in accordance with the norms, the electrified part should be protected. After a long period of inactivity to restart, should be re-measured grounding resistance and insulation resistance value. Drill tower shall not be too close to the high-voltage lines.
(C) electrocution first aid
1. electrocution scene first aid
In the electrocution scene first aid, we should follow the eight-point policy; quickly, accurately, in situ, adhere to.
(1) make the electrocuted person quickly from the power supply
The faster the better, because the longer the electrocution time the more serious the injury, but pay attention to the correct operation.
1) from the power supply is to contact the electrocuted part of the switch of the electrified equipment or try to make the electrocuted person and the electrified equipment to disengage. The electrocuted person is not off the power supply before the rescuer shall not touch the electrocuted person directly with his hands. When disengaged from the power supply rescuer not only to save people, but also pay attention to protect themselves from electrocution.
2) If the electrocuted person touches the low-voltage energized equipment, the rescuer should try to quickly cut off the power supply. For example, pull the power switch or unplug the power supply, or the use of insulated tools, dry sticks and other non-conductive objects to free the electrocuted. Can also grasp the electrocuted person dry and not close to the body of the clothes will be dragged away. You can also wear insulated gloves or hands with dry clothing and other insulation wrapped up to free the electrocuted person. Rescuers can also stand on insulated mats or wooden boards. In order to make the electrocuted person and the electrified body free, it is best to use one hand to rescue.
3) If the electrocuted person touches the high-voltage energized equipment, the rescuer should quickly cut off the power supply and use the insulated tools suitable for the voltage level (wearing insulated gloves, insulated boots and insulated rods) to free the electrocuted person. Rescue personnel in the rescue process, should pay attention to maintain their own and the surrounding electric part of the necessary safety distance.
4) If the electrocuted person is in a high place, the electrocuted person may fall from a high place after releasing the power supply, so it is necessary to take appropriate safety measures to prevent the electrocuted person from falling or dying.
5) in cutting off the power to rescue the electrocuted, should take into account the rescue necessary emergency lighting, in order to continue to carry out first aid.
(2) the electrocution of the local rescue
1)If the electrocution of the consciousness is still awake, it should be made to lie down on the ground under close observation, do not let it stand or walk around for the time being.
2)If the electrocuted person has been confused, it should be made to lie down on the ground on its back, and to ensure that the airway is open, and with 5s time, call the casualty or tap his shoulder to determine whether the loss of consciousness. It is forbidden to shake the head of the casualty to call the casualty.
3)If the electrocuted person loses consciousness and stops breathing, but his heart beats slightly (two fingers can be used to test the carotid artery in the depression next to the knot of the injured person's throat to see if there is any beating), mouth-to-mouth or mouth-to-nose artificial respiration should be carried out immediately after the airway is cleared.
4) If the electrocution injury is quite serious, heartbeat and respiration have stopped, completely unconscious, then after clearing the airway, immediately at the same time, mouth-to-mouth (nose) artificial respiration and chest compression of the heart of the artificial circulation. If there is only one person on the scene rescue, you can alternate artificial respiration and artificial circulation, first chest compression of the heart 4 to 8 times, and then mouth-to-mouth (nose) blowing 2 to 3 times, and then compression of the heart 4 to 8 times, and mouth-to-mouth (nose) blowing 2 to 3 times ...... so that the cycle is repeated.
(3) the first aid process must: adhere to
In the medical personnel in the future to take over the rescue before, should not give up on the scene rescue, more can not only according to the lack of breathing and pulse on the unauthorized determination of the casualty died, give up rescue. Only the doctor has the right to make a diagnosis of death.
2. Electrocution first aid cardiopulmonary resuscitation
The following introduction to the electrocuted person cardiopulmonary resuscitation of the two first aid methods:
(1) Artificial respiration
Artificial respiration method of supine chest pressure, prone pressure back method and mouth-to-mouth (nose) blowing method, etc. Here is only recognized as a simple and easy method. Here only introduced now recognized as simple and easy to implement and the effect is better mouth to mouth (nose) blowing method.
1)First of all, quickly untie the electrocuted person's clothes, pants, loosen the upper body of the corset, bra, scarf, etc. so that the chest can be free to expand, so as not to impede breathing.
2)Make the electrocuted person lie on his back, not padded pillow, head first side to side, remove the blood clots in his mouth, dentures and other foreign objects. If the root of the tongue is sunken, the tongue should be pulled out, so that the airway is open; if the electrocuted person's teeth are closed, the rescuer should use both hands to hold the back corner of the mandible, thumbs on the edge of the angle of the mandible, the hand will slowly move the mandible forward, so that the lower teeth to the upper teeth before; also available open-ended pliers, small pieces of wood, metal, etc., carefully from the corner of the mouth into the gap between the teeth pry open the teeth to remove the oral cavity of the foreign body. Then pull its head upright, so that it tilted back as far as possible, nostrils to the sky, so that the airway is open.
3)The rescuer is located in the electrocuted person - side, with a hand pinch the nostrils, do not make the leakage of air; the other hand will be pulled forward and down the jaw, so that the mouth open. Can cover a layer of gauze on his mouth, ready to receive blowing.
4) After the rescuer takes a deep breath, press the electrocuted person's mouth and blow into him (Figure 4-35a). If you can not break the mouth, you can also pinch the mouth, close to the nostrils blowing, blowing, to make their chest expansion.
Figure 4-35 mouth-to-mouth artificial respiration
5) rescuer for air, should immediately leave the electrocuted person's mouth (or nostrils), and relax the tightly pinched nose (or mouth), so that it is free to exhaust (Figure 3-35b).
Blow and breathe into the electrocuted person repeatedly, about 12 times per minute, as described above. When this method is applied to young children, the nose is not pinched tightly, allowing them to leak freely, and the blowing should not be too strong to avoid the lungs from bursting.
(2) chest compression of the heart of the artificial circulation method
1) and artificial respiration method of the same requirements, first of all, to untie the electrocution of clothing, pants and bra, scarf, etc., and clear the mouth of foreign bodies, so that the airway is open.
2) make the electrocuted person lying on his back, posture and the above mouth-to-mouth blowing method, but the back of the ground must be flat and solid, for the hard ground or wooden boards and so on.
3)The rescuer is located in the side of the electrocuted person, preferably across the waist kneeling at the waist of the electrocuted person, two hands folded (for children can only use one hand), the root of the palm of the hand on the heart a little higher place (such as the lower third of the sternum) (Figure 4-36).
4)After the rescuer finds the correct pressure point of the electrocuted person, he/she presses down with vertical and balanced force from the top to the bottom to press out the blood inside the heart (the force should be appropriately small for children) (Figure 4-37a).
Figure 4-36 Chest compression of the heart method
Figure 4-37 Artificial chest compression of the heart method
5) After the compression, the root of the palm is quickly relaxed (but the palm should not leave the chest), so that the chest of the electrocuted person is automatically restored, the heart expands, and the blood comes back to the heart (Figure 4-37b). Repeatedly press and relax the electrocuted person's heart according to the above operation requirements, about 60 times per minute. Position yourself accurately and apply appropriate force when applying compressions. During artificial respiration and cardiac compressions, the rescuer should closely observe the reaction of the electrocuted person. As long as the electrocuted person is found to have signs of awakening, such as flickering eyelids or lips, should be terminated for a few seconds to allow the electrocuted person to breathe and heartbeat. Artificial respiration and cardiac compression for the electrocuted person; it is very tiring for the rescuers, but in order to save the electrocuted person, they should persist until the medical personnel come to rescue the electrocuted person. As long as the correct and timely adherence to the implementation of artificial treatment, electrocution false death of people are rescued into the possibility of life is very large.