1. Accidental contact with live parts under voltage as a result of:
erroneous actions during work;
malfunctions of protective equipment with which the victim touched current-carrying parts, etc.
2. The appearance of voltage on the metal structural parts of electrical equipment as a result of:
damage to the insulation of current-carrying parts; network phase closure to ground;
falling wire under voltage on the structural parts of electrical equipment, etc.
3. The appearance of voltage on disconnected current-carrying parts as a result of: erroneous switching on of a disconnected installation;
short circuits between disconnected and energized live parts;
lightning discharge into an electrical installation, etc.
4. The occurrence of step voltage on the land where the person is located, as a result of:
phase-to-earth short circuit;
removal of the potential by an extended conductive object (pipeline, railway rails);
malfunctions in the protective earthing device, etc.
Step voltage - the voltage between two points of the current circuit, located one from the other at a step distance, at which a person is simultaneously standing.
The highest step voltage is near the fault, and the lowest is at a distance of more than 20 m.
At a distance of 1 m from the ground electrode, the step voltage drop is 68% of the total voltage, at a distance of 10 m - 92%, at a distance of 20 m - almost equal to zero.
The danger of step voltage increases if the person who has been exposed to it falls: the step voltage increases, since the current no longer passes through the legs, but through the entire body of a person.
42. The most important factors affecting the outcome of electric shock are:
the amount of current flowing through the human body; duration of current exposure; current frequency;
current path; individual properties of the human body. The magnitude of the current. Under normal conditions, the smallest power frequency current that causes physiological sensations in a person is on average 1 milliamp (mA); for direct current, this value is 5 mA. Duration of current exposure. Prolonged exposure to electric current with parameters that did not initially pose a danger to the body can lead to death as a result of a decrease in the resistance of the human body. It has already been noted above that when an electric current is applied to the human body, the activity of the sweat glands increases, as a result of which the moisture content of the skin increases, and the electrical resistance decreases sharply. As experiments have shown, the initially measured ohmic resistance of the human body, amounting to tens of thousands of ohms, decreased under the influence of an electric current to several hundred ohms. Type of current and frequency. Currents of various kinds (ceteris paribus) represent a different degree of danger to the body. The nature of their impact is also not the same. A direct current produces a thermal and electrolytic effect in the body, and an alternating current mainly causes contraction of muscles, blood vessels, vocal cords, etc. increases the danger of exposure to direct current. The role of the current path. The current path in the human body is important for the outcome of the lesion. The passing current is distributed in the body throughout its volume, however, the largest part of it passes along the path of least resistance, mainly along the flows of tissue fluids, blood and lymphatic vessels and the membranes of the nerve trunks. Features of the individual properties of a person. The physical and mental state of a person at the time of exposure to an electric current is of great importance. Persons suffering from heart disease, lung disease, nervous disease, etc. are more susceptible to the danger of electric shock. Therefore, labor legislation establishes a professional selection of workers servicing electrical installations, depending on their state of health.
43. The main measures of protection against the defeat of email. current are:
Ensuring the inaccessibility of current-carrying parts under voltage for accidental contact, eliminating the risk of damage when voltage appears on cases, casings; - protective grounding, grounding, protective shutdown; - use of low voltages; - the use of double insulation. Analysis of the causes of electrical injury reveals the following basic conditions for the occurrence of electric shock to a person: 1. Contact with live parts under voltage. 2. Damage to the insulation of electrical equipment and wiring, creating the possibility of voltage transfer to their structural parts. Touching live parts can cause electrical injury. 3. High voltage transition to low voltage system.
The main causes of accidents from exposure to electric current are as follows.
1. Accidental contact or approaching a dangerous distance to live parts under voltage.
2. The appearance of voltage on the metal structural parts of electrical equipment - cases, casings, etc. - as a result of damage to the insulation and other reasons.
3. The appearance of voltage on the disconnected current-carrying parts on which people work, due to the erroneous switching on of the installation.
4. The occurrence of a step voltage on the earth's surface as a result of a wire shorting to the ground.
The main measures of protection against electric shock are: ensuring the inaccessibility of current-carrying parts under voltage for accidental contact; network security separation; elimination of the danger of damage when voltage appears on cases, casings and other parts of electrical equipment, which is achieved by the use of low voltages, the use of double insulation, potential equalization, protective grounding, grounding, protective shutdown, etc .; the use of special protective equipment - portable devices and devices; organization of safe operation of electrical installations.
Classification of premises according to the danger of electric shock. The environment and surroundings increase or decrease the risk of electric shock. With this in mind, the “Electrical Installation Rules” divide all premises according to the degree of danger of electric shock to people into three classes: 1 - without increased danger; 2 - with increased danger and 3 - especially dangerous.
Premises without increased danger are dry, dust-free premises with normal air temperature and with insulating (for example, wooden) floors, i.e., in which there are no conditions inherent in premises with increased danger and especially dangerous.
An example of premises without increased danger are ordinary office premises, tool rooms, laboratories, as well as some industrial premises, including workshops of instrument factories, located in dry, dust-free rooms with insulating floors and normal temperature.
Hazardous premises are characterized by the presence of one of the following five conditions that create increased danger:
dampness, when the relative humidity of the air exceeds 75% for a long time; such premises are called damp;
high temperature, when the air temperature exceeds +30°C for a long time; such rooms are called hot;
conductive dust, when, according to the conditions of production, conductive technological dust (for example, coal, metal, etc.) is released in the premises in such an amount that it settles on wires, penetrates into machines, devices, etc.; such rooms are called dusty with conductive dust;
conductive floors - metal, earthen, reinforced concrete, brick, etc.;
the possibility of a person simultaneously touching the metal structures of buildings connected to the ground, technological devices, mechanisms, etc., on the one hand, and to the metal cases of electrical equipment, on the other.
An example of a high-risk room is stairwells of various buildings with conductive floors, unheated storage rooms (even if they are located in buildings with insulating floors and wooden shelving), etc.
Particularly dangerous premises are characterized by the presence of one of the following three conditions that create a particular danger:
special dampness, when the relative humidity of the air is close to 100% (walls, floors and objects in the room are covered with moisture); such rooms are called especially damp;
chemically active environment, i.e. rooms in which, according to the conditions of production, vapors are contained or deposits are formed that act destructively on the insulation and current-carrying parts of electrical equipment; such rooms are called rooms with a chemically active environment:
the simultaneous presence of two or more conditions characteristic of premises with increased danger.
Particularly dangerous premises are most of the industrial premises, including all workshops of machine-building plants, testing stations, galvanizing shops, workshops, etc. The same premises include work areas on the ground in the open air or under a canopy.
The inaccessibility of current-carrying parts of electrical installations for accidental contact can be ensured in a number of ways: by insulating current-carrying parts, placing them at an inaccessible height, fencing, etc.
Protective separation of the network. In an extensive electrical network, i.e., having a large length, fully serviceable insulation can have low resistance, and the capacitance of the wires relative to the ground can be large. These circumstances are extremely undesirable in terms of safety, since in such networks with a voltage of up to 1000 V with an isolated neutral, the protective role of wire insulation is lost and the threat of electric shock to a person increases if he touches the wire of the network (or to any object that is under the phase voltage).
This significant drawback can be eliminated by the so-called protective separation of the network, i.e., the division of an extensive (extended) network into separate small and electrically unconnected sections.
Separation is carried out using special isolating transformers. Isolated sections of the network have a high insulation resistance and low capacitance of wires relative to earth, which significantly improves safety conditions.
Application of reduced voltage. When working with a portable hand-held power tool - a drill, a wrench, an electric chisel, etc., as well as a hand-held portable lamp, a person has prolonged contact with the bodies of this equipment. As a result, the danger of electric shock sharply increases for him in case of damage to the insulation and the appearance of voltage on the case, especially if work is done in a room with increased danger, especially dangerous or outdoors.
To eliminate this danger, it is necessary to power hand tools and portable lamps with a reduced voltage not exceeding 36 V.
In addition, in especially dangerous rooms under especially unfavorable conditions (for example, work in a metal tank, work sitting or lying on a conductive floor, etc.), an even lower voltage of 12 V is required to power hand-held portable lamps.
The impact of electric current on a person depends primarily on the value of the current strength and the time it takes to pass through the human body and can cause discomfort, burns, fainting, convulsions, cessation of breathing and even death. A current of 0.5 mA is considered acceptable. a current of 10-15 mA a person cannot independently break away from the electrodes, break the current circuit into which he has fallen. A current of 50 mA affects the respiratory organs and the cardiovascular system. A current of 100 mA leads to cardiac arrest and circulatory disorders and is considered fatal . Numerous surveys of accidents have shown that the outcome of the lesion is not directly dependent on the magnitude of the current, but is determined by many factors and circumstances and the individual properties of the victim. Therefore, the same magnitude of current, regardless of other factors, has a different effect on different people and different on the same person, depending on his condition at the time of the lesion, the degree of excitation of the nervous system, its physiological endurance and reactivity.
Attention. Remember that the current flowing in a household electrical network is 5-10 A and far exceeds the lethal one.
The main causes of electric shock:
. accidental contact with current-carrying parts under voltage (bare wires, contacts of electrical equipment, tires, etc.);
. unexpected occurrence of voltage where, under normal conditions, it should not be;
. the appearance of voltage on disconnected parts of electrical equipment (due to erroneous switching on, voltage induction by neighboring installations, etc.);
. the occurrence of voltage on the surface of the earth as a result of a short circuit of the wire with the earth, a malfunction of grounding devices, etc.
To prevent electric shock, you should strictly follow the rules for electrical installations (PUE), the rules for technical operation (PTE) and the safety rules (PTB). Persons who have been trained and have the appropriate certificate are allowed to work on electrical installations. When a person gets energized, the electric current usually flows from one hand to the other, as well as from hand to foot. Therefore, you should not touch the elements of the device with both hands at the same time, and also hold on to the heating or water pipe with your hand; it is advisable to put it under your feet at the workplace rubber mat as an insulator. In some cases, when the phase is shorted to the case and the protection fails (for example, due to a malfunction of the circuit breaker or an incorrectly selected fuse), the voltage of the case relative to earth exceeds the permissible value of the contact voltage. The voltage that appears on the human body when two points of conductors or conductive parts, including when the insulation is damaged, is called the touch voltage. The touch voltage increases with distance from the grounding point and outside the current spreading zone is equal to the voltage on the equipment case relative to the ground. The spreading zone is understood as the ground zone, outside of which the electric potential that has arisen due to the short circuit of current-carrying parts to the ground can be conditionally accepted equal to zero.
In the late 70s of the century before last, the first death of a person from electricity was recorded. A lot of time has passed since then, but the number of people affected by the same cause is only increasing. In connection with these events, people were forced to create a list of rules for dealing with electricity. For many years, future electricians have been trained in specialized educational institutions and immediately after which they undergo an “internship” in production and, of course, pass the final test exam, after which they receive a license and can independently work with electric current. What is most amazing is that no one in this world is immune from mistakes. Even a highly qualified specialist can easily get injured due to inattention. Can you say with confidence that for any problem related to electricity, you will solve it with ease and accuracy? If not, then this article is for you! Next, we will talk about what are the causes of electric shock and the main protective measures in everyday life.
What is electric current?
The concentrated movement of charged particles in space under the action of an electric field. This is how the term electric current is explained. What about particles? So they can be absolutely anything, for example: electrons, ions, etc. It all depends only on the object in which this very particle is located (electrodes / cathodes / anodes, etc.). If we explain according to the theory of electrical circuits, then the cause of the occurrence of an electric current is the “purposeful” course of charge holders in a conductive environment when exposed to an electric field.
How does electricity affect the human body?
A strong electric current that is passed through a living organism (human, animal) may cause a burn, or may cause an electrical injury by fibrillation (when the ventricles of the heart do not contract synchronously, but each “by itself”) and eventually this will lead to to lethal outcome.
But if you look at the other side of the coin, electric current is used in therapy, for resuscitation of patients (during ventricular fibrillation, a defibrillator is used, a device that, by means of electricity, simultaneously contracts the muscles of the heart, and thereby causing the heart to beat in its “familiar” rhythm), etc. etc., but that's not all. Every day, since our birth, electricity “flows” in us. It is used by our body in the nervous system to transmit impulses from one neuron to another.
Rules for handling electrical appliances
In fact, we will offer you a list of rules of what cannot be and what must be done when children interact with electrical appliances, BUT this does not mean that as an adult you can neglect these rules! So, let's begin!
When interacting with electrical appliances IT IS FORBIDDEN:
- Touch exposed wires.
- Activate broken electrical appliances, because in which case they can cause a fire or shock you.
- Touch the wires with wet hands (especially if they are bare).
NECESSARY:
- Remember that in no case should you pull on the wire in order to pull it out of the socket.
- When leaving home, check to see if any electrical appliance has been left on.
- If you are a child, then be sure to call an adult if, while plugging in an electrical appliance, you saw that the wire or the electrical appliance itself began to smoke.
The main causes of electric shock
An electric shock can occur while a person is near the place where the current-carrying parts included in the network are located. It can be described as irritation or interaction of body tissues with electricity. In the end, this will lead to absolutely involuntary (convulsive) contractions of the human muscles.
There are a number of reasons for electric shock to a person, such as: the possibility of damage when replacing a light bulb in a lamp connected to the network, the interaction of the human body with equipment that is connected to the network, long (continuous) operation of electrical appliances, and of course people who repair everything themselves do not depending on whether it is successful or not (in other words, "Homemade"). Let's start by listing the main causes of electric shock, and then we'll figure out in order what the essence of these problems is.
The main causes of electric shock are:
- Human interaction with faulty household electrical appliances.
- Touching bare parts of the electrical installation.
- Wrong voltage supply to the place of work. That is why in production you need to hang out a special one, as in the picture below:
- The appearance of voltage on the body of equipment, which, under normal conditions, should not be energized.
- Electric shock due to a faulty power line.
- Replacing a light bulb in a luminaire connected to the network. People can be injured due to the fact that during the banal replacement of a light bulb, they simply forget to turn off the lights. It must be remembered that before changing the light bulb, the first thing to do is turn off the light.
- The interaction of the human body with equipment that is connected to the network. There were cases when people were injured from this option. Everything is simple here. When interacting with an electrical appliance (for example, a washing machine), you hold on to a fragment of the house that is grounded (for example, a pipe) with your other hand. Thus, a current will pass through your body, which will cause damage. To prevent this from happening, it is recommended.
- Long (continuous) operation of electrical appliances. In fact, the cases of damage in this way are minimal. The problem is this: appliances such as a washing machine can break down from long work and, in the case of a washing machine, at least leak. To avoid such incidents, simply check to see if the instruments are working properly more frequently. About that, we talked about in the corresponding article.
- People who do everything themselves. This is considered the most common problem of all, because today with the help of the Internet you can find a lot of instructions like "How to do ...", even on our website in the section. However, the majority of people who start designing something do not have the proper knowledge and, due to ordinary carelessness, are injured or even maimed.
- can be very dangerous for you or your equipment, after all, power surges can cause a fire or, worse, cause an electric shock. So how do you deal with it? To date, there are three main ways to reduce the effects of power surges, namely:, well, and. These three things in everyday life will serve as protection for you and your equipment from power surges.
Statistics show that electric shocks are commonly found in the home and at work. How to protect yourself and what to do in case of exposure to current?
What is an electrical injury?
Cases of electric shock are rare, but at the same time they are among the most dangerous injuries. With such a lesion, a fatal outcome is possible - statistics show that it occurs on average in 10% of injuries. This phenomenon is associated with the effect of electric current on the body. Therefore, representatives of professions related to electricians can be attributed to the risk group, but they are not excluded among people who accidentally encountered the action of current in everyday life or on sections of power lines. As a rule, the cause of such a defeat is technical problems or non-compliance with safety regulations.
Types of electric shock
The nature of the impact on the body and its degree can be different. The classification of the lesion is based precisely on these features.
Electrical burn
Electric shock is one of the most common injuries. There are several variants of such an injury. First of all, it should be noted the contact form, when an electric current passes through the body upon contact with a source. An arc lesion is also distinguished, in which the current itself does not pass directly through the body. The pathological effect is associated with an electric arc. If there is a combination of the forms described above, such a lesion is called mixed.
Electrophthalmia
An electric arc leads not only to a burn, but also to irradiation of the eyes (it is a source of UV rays). As a result of such exposure, inflammation of the conjunctiva occurs, the treatment of which can take a long time. In order to avoid such a phenomenon, special protection against electric shock and compliance with the rules for working with its sources are necessary.
Metallization
Among the types of skin lesions, metallization of the skin stands out with its clinical features, which occurs due to the penetration of metal particles melted under the action of an electric current. They are the smallest in size, penetrate into the surface layers of the epithelium of open areas. Pathology is not fatal. Clinical manifestations soon disappear, the skin acquires a physiological color, and pain stops.
electrical signs
Thermal and chemical action leads to the formation of specific signs. They have sharp contours and color from gray to yellowish. The shape of the signs can be oval or round, as well as resemble lines and dots. The skin in this area is characterized by the occurrence of necrosis. It becomes hardened due to the necrosis of the surface layers. Due to cell death in the post-traumatic period, there are no complaints among complaints. The lesions disappear after some time due to regeneration processes, while the skin acquires a natural color and elasticity. This type of injury is very common and usually non-fatal.
Mechanical damage
They occur with prolonged exposure to current. Mechanical injuries are characterized by ruptures of muscles and ligaments, which occurs due to muscle tension. In addition, the neurovascular bundle is additionally damaged, and such severe injuries as fractures and complete dislocations are also possible. More serious and highly qualified assistance is required in case of electric shock with such a clinic. In case of untimely assistance or too long exposure, a fatal outcome is possible.
As a rule, these types do not occur separately, but are combined. This factor makes it difficult to provide first aid and further treatment.
What determines the degree of electric shock?
This indicator depends not only on the strength, duration of action and the nature of the current, but also on the resistance of the body. The skin and bones have a high resistance index, while the liver and spleen, on the contrary, have a low resistance index. Fatigue contributes to a decrease in resistance, and therefore, in such cases, a fatal outcome is most likely. Wet skin also contributes to this. Clothes and shoes made of leather, silk, wool and rubber will help protect the body from harmful effects, as they will act as an insulator. It is these factors that affect the risk of electric shock.
Effects
Electrical current causes multiple damage. First of all, it acts on the nervous system, due to which motor activity and sensitivity worsen. In addition, there are, for example, severe convulsions and loss of consciousness can cause death due to respiratory arrest. After saving the victim, deep lesions of the central nervous system are sometimes noted. The main ones lead to this.
Impact on the heart can also lead to death, as the current leads to impaired contractility and causes fibrillation. Cardiomyocytes begin to work inconsistently, as a result of which the pumping function is lost, and the tissues do not receive the necessary amount of oxygen from the blood. This leads to the development of hypoxia. Another formidable complication is rupture of blood vessels, which can lead to death from blood loss.
Muscle contraction often reaches such a force that a fracture of the spine is possible, and, consequently, damage to the spinal cord. On the part of the sense organs, there is a violation of tactile sensitivity, tinnitus, hearing loss, damage to the eardrum and elements of the middle ear.
Complications do not always appear immediately. Even with a short exposure, electrical injury can make itself felt in the future. Long-term effects - arrhythmias, endarteritis, atherosclerosis. From the side of the nervous system, neuritis, vegetative pathologies and encephalopathy can occur. In addition, contractures are possible. That is why means of protection against electric shock are important.
The reasons
The main etiological factor is the action of the current. Additional conditions are the state of the body and the presence or absence of any protection. Electrical shock is usually caused by improper use or lack of protection when working with wiring. The risk group includes professions related to working with current. However, electrical injury can happen to anyone. Cases of defeat in everyday life are not uncommon, but they mostly end favorably. In addition, episodes of contact with such lesions are frequent. Attention and knowledge of safety precautions will protect against such phenomena.
Clinical manifestations of electrical injury
Symptoms depend on the type of lesion, while their complex is based on a combination of manifestations of the described types of injuries. Also, the clinic depends on the severity. It should be noted that the most dangerous functional deviations of the respiratory, nervous and cardiovascular systems. The victim is in severe pain. A characteristic suffering expression appears on the face, and the skin becomes pale. Under the action of current, muscle contraction occurs, the duration of which depends on the preservation of their integrity. All this can cause loss of consciousness, and in a more severe case - death. Protecting against electric shock will help prevent this condition.
The effect of current on the body
The changes that occur in the body under the influence of current are associated with the versatility of its effects. It has a thermal effect by converting electrical energy into thermal energy due to tissue resistance. This is due to the formation of burns and marks. Thermal action adversely affects the body, as it inevitably leads to the destruction of tissues.
Electrochemical action mainly affects the circulatory system. This leads to a change in the charge of many molecules, and also sticks together blood cells, thickening the blood and promoting the formation of blood clots.
The biological effect is associated with a violation of organs and systems - the effect on muscle tissue, the respiratory system, and nerve cells.
The multiple effect of the current on the body aggravates the condition of the victim, increasing the risk of death. The combined factors of electric shock can lead to a different outcome. Even the action of 220 volts on the body will cause irreversible damage.
First aid
All types of electric shock require otherwise a fatal outcome is possible. First of all, it is necessary to stop the effect of current on the victim, that is, turn it off from the circuit. To do this, the rescuer should definitely protect himself with insulating materials and only after that pull the victim away from the source. After you need to call an ambulance team and start providing first aid. These activities are carried out before the arrival of specialists. A person exposed to current does not tolerate cold, so it must be transferred to a warm, dry surface. First aid is aimed at restoring vital functions - breathing and blood circulation. This requires cardiopulmonary resuscitation. Every person should be trained in it or have at least the slightest idea. Resuscitation is carried out on a hard surface. The rescuer combines artificial respiration and cardiac massage. It is required to observe the ratio - 2 breaths and 30 clicks. Salvation begins with a massage, since the restoration of blood circulation is a priority. It is performed with straight arms, placing the palms on top of each other (pressure is applied to the area of the wrist on the lower part of the sternum). The recommended frequency is 100 compressions per minute (the chest should move 5 cm). After the oral cavity is cleaned of secretions and artificial respiration is carried out. To protect the rescuer, it is recommended to manipulate through a handkerchief. Resuscitation can be carried out by two rescuers, while maintaining the ratio of 2 breaths and 15 clicks. When one person takes a breath, the second is contraindicated to touch the chest. When inhaling, the chest of the victim must necessarily rise - this indicates the correctness of the procedure.
Treatment
Electric shock requires prompt resuscitation and subsequent treatment. The therapy is carried out in a hospital. Even if the victim feels satisfactory, and the damage is minor, preventive monitoring is required to help avoid complications.
Treatment is aimed at the speedy healing of skin lesions, as well as the elimination of other disorders associated with the harmful effects of current. Observation in the hospital is carried out until complete recovery.
Prevention
To prevent all types of electric shock will help compliance with safety regulations. Do not use electrical appliances that are defective. It is also contraindicated to touch them with wet hands, as this will improve the conduction of current. Working with electrical appliances and wiring requires the use of protective equipment against electric shock. These include gloves, special pads. Tools must have an insulated handle. Also, for prevention, the public should be informed about the possibility of such an injury. A special role is played by informing in the media, as well as conducting conversations with schoolchildren. This will reduce the risk of electric shock.
Electrical injuries are very dangerous, and their outcome depends on many factors. It is influenced not only by current indicators (voltage, duration), but also by the body's defenses. For example, a current of 220 volts, depending on the conditions of exposure, can lead to both non-fatal injuries and death. It is very important to observe safety precautions - this will help to avoid such defeats.
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