I. Current damage to the human body and the factors affecting
When the human body touches the electrified body, the current passes through the human body, so that part of the body or the whole body was electrically stimulated and harmed, resulting in electrical injuries and electric shock. Electrical injury refers to the external part of the human body is subjected to electrical damage, such as arc burns, electric branding and so on. When the human body is in the vicinity of high-voltage equipment, and the distance is less than or equal to the discharge distance, in the person and the charged high-voltage equipment will occur between the arc discharge, the human body in up to 3000 ℃, or even higher arc temperature and the current of the thermal and chemical effects of the role of the arc burns will cause serious and even death can be caused. Electric shock refers to the body's internal organs are harmed, such as the role of electric current in the body's nerve center, so that the heart and respiratory system functions of the normal work of the destruction, convulsions and spasms, unconsciousness and other phenomena, but also may make the respiratory organs and the blood circulation organs of the activities of the body to stop or greatly weakened, the formation of the so-called pseudo-death. At this time, if not timely use of artificial respiration and other medical methods of rescue, people will not be able to come back to life.
The degree of victimization of human electrocution and the role of the body's voltage, the body's resistance, the value of the current through the body, the frequency of the current, the current through the time, the current in the human body in the circulation of the pathway as well as the human body and other factors, and the value of the current is harmful to the human body's direct factors.
Second, safe current and safe voltage
1, safe current
In order to ensure personal safety, generally to the human body does not produce harmful physiological effects after electric shock as a safety benchmark. Therefore, through the human body generally no harmful physiological effects of the current value, known as the safety current. Safety current can be issued as allowable safety current and continuous safety current. When the human body is electrocuted, the current value through the human body is not greater than the current value of the current known as the permissible safety current, 50 ~ 60Hz AC 10mA (mining and other types of work is required 6mA), DC 50mA for the permissible safety current; when a person is electrocuted, through the human body is greater than the current value of the current value of the current value of the human body and the corresponding duration of the corresponding duration of time known as the duration of the safety current. AC continuous safety current value and continuous energization time of the relationship between:
Iac = 10 + 10/t (0.03 seconds & lt; = t & lt; = 10 seconds)
T - continuous energization time in seconds
2, safe voltage
In a variety of different environmental conditions, the human body is exposed to a certain voltage of the voltage of the body, the voltage of the body's electrical system, the voltage of the body's electrical system, the voltage of the body's electrical system. Under a variety of different environmental conditions, the human body after contact with a certain voltage of the charged body, its parts do not occur any damage, the voltage seconds known as the safety voltage.
The safe voltage is expressed as the product of the current allowed to pass through the body and the resistance of the body. Normally, a voltage below 40V to ground can be considered as a safe voltage. The International Electrotechnical Commission stipulates that the limit value of the contact voltage is 50V, and stipulates that when it is below 25V, there is no need to consider safety measures to prevent electric shock. China's provisions of the safety voltage level: 42V, 36V, 24V, 12V, 6V, rated value of five levels, the current use of safety voltage to 36V and 12V more. Power plant production sites and substations, such as the use of running lights are generally 36V, in more dangerous places or narrow workplace, surrounded by a large area of grounding body, the environment of hot and humid places, such as cable trench, coal hopper tanks, etc., the use of running lights are not permitted to exceed the voltage of 12V.
It is important to point out that these voltages can not be considered as absolutely safe, if the human body in the sweat and wet, skin rupture, etc., and so on. If the human body in wet sweat, skin breakage, etc., not long touch the power supply, electric shock injury may also occur.
Third, the human body electrocution mode
The basic mode of human electrocution single-phase electrocution, two-phase electrocution, step voltage electrocution, contact voltage electrocution. In addition, there are human beings close to high-voltage electricity and lightning electrocution.
1, single-phase electrocution
refers to the human body standing on the ground or other grounded body, a part of the human body touches a phase of the electrocution caused by a charged body. It is the degree of danger and the high and low voltage, the neutral point of the grid is grounded or not, the size of each phase of the ground capacitance, is a more common type of electrocution.
In daily work and life (three-phase four-wire system), low-voltage electrical equipment, switches, plugs and lamps, as well as electric motors, electric irons, washing machines and other household appliances, if their insulation is damaged, the charged part of the exposed shell, skin charged, when the human body touches these devices, a single-phase electrocution will occur. If the human body is standing on the insulating plate or wearing insulated shoes, the resistance between the human body and the earth will be very large, the current through the human body will be very small, then there will be no danger of electric shock.
2, two-phase electrocution
refers to the human body has two places at the same time in contact with any two-phase electrocution charged power supply. When two-phase electrocution occurs, the current flows from one wire through the human body to another wire, the voltage acting on the human body is equal to the line voltage, if the line voltage is 380V, the current flowing through the human body up to 268mA, such a large current as long as after 0.186s may cause electrocution to the death of the person. Therefore, two-phase electrocution is more dangerous than single-phase electrocution.
3, step voltage electrocution
When the electrical equipment grounding fault or when the line occurs a wire fault, and the wire falls to the ground, the fault current will flow into the earth from the grounding body or wire landing point, and to the earth in a hemispherical dispersion, from the current into the location of the closer, the higher the potential from the current into the location of the farther, the lower the potential into the location of the 20M outside the ground, the potential is nearly zero. The ground potential is approximately zero 20M away from the entry point. If someone enters this area at this time, the potential difference between the two feet is the step voltage. Electrocution caused by step voltage, known as step voltage electrocution. The human body to withstand step voltage, the current is generally along the lower body, that is, from the feet to the crotch to the feet flow through, and the earth to form a pathway, the current is rarely through the human heart vital organs, it seems to be less harmful, but, step voltage is higher, the person will be due to the foot cramps and fell to the ground, which will not only make the action of the body on the voltage increases, there may be a change in the current through the human body path through the human body and vital organs, thus greatly increasing the electric shock. The first thing you need to do is to get a good look at the body, and you will be able to see what is going on.
Therefore, electrical workers in the usual work or walking, must be extra careful. When the equipment found to have ground faults or wire breaks down to the ground, to stay away from the disconnected area; once accidentally have stepped into the disconnected area and feel the voltage across the step, you should quickly put your feet together or use one leg to jump out of the disconnected area; when you have to go into the disconnected area to save or troubleshooting, you should wear insulated boots.
4, contact voltage electrocution
Contact voltage refers to the person standing next to the occurrence of short-circuit fault equipment, touching the shell of the leakage equipment, its hands, feet between the voltage. Electrocution caused by contact voltage is called contact voltage electrocution.
In power plants and substations, general electrical equipment shell and seat are grounded, normal, these equipment shell and seat are not charged. But when the equipment insulation breakdown, grounding part of the damage, equipment and the earth between the potential difference, the human body if contact with these devices, their hands, feet will be subjected to contact voltage and electrocution. In order to prevent contact voltage electrocution, it is often necessary to a workshop, a substation, all the equipment are individually buried grounding body, each motor using a separate protective grounding.
5, arc discharge electrocution
Due to carelessness or failure to take safety measures and close to the exposed high-voltage energized equipment, there will be a serious discharge electrocution accident.
6, power outages caused by the sudden arrival of electrocution
In the power outage on the maintenance of equipment, if you do not take reliable safety measures, such as not installed to hang the temporary grounding and hanging the necessary signage, when the wrong equipment is under repair to send electricity, resulting in electrocution of maintenance personnel.
Fourth, to prevent personal electric shock technical measures
When the shell of the electrical equipment due to insulation damage and charged, and no charged symbols, people will not have any premonition of the danger of electrocution, which is often prone to electrocution. But as long as you master the laws of electricity and take appropriate measures, many electrocution can still be avoided.
1, protective grounding
Protective grounding is to prevent damage to the insulation of electrical equipment when the human body suffers electric shock hazards, and in the metal casing of electrical equipment or frame, etc., and the grounding body to make a good connection between. Protective grounding is applicable to the neutral point is not grounded in the low power grid. The use of protective grounding, can only reduce the degree of risk of electric shock, but can not completely guarantee personal safety.
2, protection of zero
In order to prevent personal electric shock due to insulation damage to electrical equipment, the metal casing of the electrical equipment and the grid zero line (transformer neutral) is connected, known as protection of zero. Protection zero for three-phase four-wire system neutral point directly grounded in the low-voltage power system.
For the use of protective zero system requirements:
① Zero line can not be installed fuses and circuit breakers to prevent the zero circuit break, the zero line phase voltage caused by electric shock accidents;
② in the same low-voltage power grid, is not allowed to use part of the electrical equipment to protect the grounding, and another part of the electrical equipment using the protection of zero;
③ in the connection of the Three-eyed socket, the socket is not allowed to connect the zero line of the power supply with the grounding hole in series. The correct connection is to connect the power supply zero hole with the grounding of the hole were connected to the zero line with a wire;
④ In addition to the neutral point must be well grounded, but also must be repeated grounding of the zero line.
3, work grounding
A point in the power system directly or by special equipment and ground for metal connection, known as work grounding. Work grounding can reduce the contact voltage of the human body, quickly cut off the power supply, reduce the insulation level of electrical equipment and transmission lines, to meet the special needs of the operation of electrical equipment.
4, leakage protector
Its role is to prevent electrical equipment and lines and other leakage caused by personal electrocution, can also be used to prevent equipment leakage caused by fire accidents as well as used to monitor or excise a phase of ground faults, and in the case of leakage of equipment, the shell presents a dangerous ground voltage automatically cut off the power supply.
V. First aid on the scene of electrocution
Electrocution accidents often occur in an instant, the situation is critical, there must be no hesitation, time is life.
The human body after electrocution, some although the heartbeat, breathing stopped, but may belong to the dying or clinical death. If the rescue is correct and timely, generally still possible to save life. Electrocution of the life can be saved, the key is to be able to quickly from the power supply and the correct emergency care.
1, off the power supply
When a person is electrocuted, the first thing to do is to make the electrocuted person off the power supply, which is the key to first aid for the electrocuted person. But in the electrocuted person is not off the power supply before the first aid personnel are not allowed to use their hands to pull the electrocuted person directly, in order to prevent the first aid personnel electrocuted. In order to make the electrocuted person out of the power supply, the first-aiders should decisively take appropriate methods and measures according to the conditions of the scene. The methods and measures to disengage from the power supply generally have the following kinds.
(1) low-voltage electrocution from the power supply
① In the vicinity of the low-voltage electrocution power switch or plug, you should immediately pull the switch or plug off to cut off the power supply.
② If the power switch is far away from the place of electrocution, the wire can be cut off with insulated tools, but the power side of the wire must be cut off, and should be prevented from being cut off by accidental contact with others.
③ When the electrified low-voltage wire falls on the electrocuted person, may be insulated objects to move the wire away from the electrocution from the power supply. However, it is not allowed to use any metal rods or wet objects to move the wire to prevent first aiders from being electrocuted.
④ If the clothes of the electrocuted person is dry, the first-aider can use the accompanying dry clothes, dry scarf, etc. will be strictly wrapped in their own hands, and then use the wrapped hands to pull the electrocuted person dry clothes, or the first-aider's dry clothes knotted together, drag the electrocuted person, so that the electrocuted person out of the power supply.
⑤ If the electrocuted person is far away from the ground, it should be prevented from falling down from the high place after cutting off the power to cause trauma.
(2) high-voltage electrocution from the power supply
When a high-voltage electrocution occurs, you should quickly cut off the power switch. If you can not cut off the power switch, you should use insulated tools suitable for the voltage level, so that the electrocuted person from the power supply. First aiders in the rescue, should be the voltage level to protect a certain safety distance to ensure the personal safety of first aiders.
(3) overhead line electrocution from the power supply
When someone is electrocuted on the overhead line, it should be quickly pulled off, or use the phone to inform the local power supply department to stop the power. If you can not immediately cut off the power supply, you can use the method of throwing a short circuit to make the power side switch tripped. When throwing the short circuit line, should prevent the arc burns or broken line endanger personal safety. After the electrocuted person on the pole is detached from the power supply, use the rope to send the electrocuted person to the ground.
2, the scene of first aid treatment
When the electrocuted person from the power supply, the first aiders should be based on the electrocuted person's different physiological response to the scene of first aid treatment.
(1) The electrocuted person is conscious, but feel weak, panic, shortness of breath, pale. At this time should be electrocuted to lie flat on the ground quiet rest, do not let the electrocuted to move to reduce the burden on the heart, and should be closely observed respiratory and pulse changes. If you find that the electrocuted person's pulse is too fast or too slow, you should immediately ask the medical staff to check the treatment.
(2) the electrocuted person is confused, there is a heartbeat, but respiratory arrest or very weak respiration, should be used in a timely manner to lift the chin method to make the airway open, and mouth-to-mouth artificial respiration. If not timely artificial respiration, will be too long due to lack of oxygen and thus cause cardiac arrest.
(3) the electrocution of the loss of consciousness, cardiac arrest, but there is a weak breath, should immediately carry out cardiopulmonary resuscitation first aid. Can not think of still very weak breathing only to do chest compressions, because this weak breathing is not to play the role of gas exchange.
(4) electrocution heartbeat, respiratory arrest, should be immediately CPR first aid, in moving or sent to the hospital on the way should still be in accordance with the provisions of cardiopulmonary resuscitation first aid.
(5) electrocution heartbeat, respiratory arrest, and accompanied by other injuries, should be quickly CPR first aid, and then deal with trauma. For electrocution accompanied by cervical spine fracture, when opening the airway, the head should not be tilted back to avoid high paraplegia, so the application of the jaw method.
(6) When a person suffers a lightning strike, due to the lightning current will make the heart depolarization, the brain produces a transient metabolic quiescence and central non-respiratory. Therefore, the lightning struck person's heartbeat, respiratory arrest, CPR should be carried out first aid, otherwise hypoxic cardiac arrest and death will occur. Can not be because of the lightning struck person's pupils have been dilated, and do not insist on first aid with cardiopulmonary resuscitation.