Ways of electric current passing through the human body. The most dangerous way. What is a current loop? What current loops are most dangerous to humans

The most dangerous is the passage of current through the respiratory muscles and heart. Paths:

"Hand-hand" through the heart passes 3.3% of the total current,

"Left arm - legs" through the heart is 3.7% of the total current,

"Right arm - legs" through the heart passes 6.7% of the total current,

"Leg - leg" through the heart passes 0.4% of the total current,

"Head - legs" through the heart passes 6.8% of the total current,

"Head - hands" through the heart passes 7% of the total current.

The most severe damage is likely if the heart, lungs, chest, brain or spinal cord are in the path of the current, since the current acts directly on these organs. If the current passes in other ways, then its effect on the organs can be reflex, and not direct. At the same time, although the danger of severe injury remains, its probability is sharply reduced.

The most dangerous are the head-arms and head-legs loops, when current can pass through the brain and spinal cord (but these loops are relatively rare).

The least dangerous path is the leg-to-leg path, which is called the lower loop and arises when a person is exposed to the so-called step voltage. In this case, a small current, obviously, passes through the heart. But it must be borne in mind that there were facts of a fatal outcome when a current flowed through the finger, from one side to the other.

According to statistics, disability for 3 days or more with the current path "hand-arm" in 83% of cases, "left arm-legs" in 80%, "right arm-legs" -87%, "leg-leg" in 15 %. Thus, the path of the current affects the outcome of the lesion; the current in the human body does not necessarily follow the shortest path, which is explained by the large difference in resistivity

Fig.1 Paths of current passage: a) left arm - legs; b) hand - hand; c) right hand - legs; d) leg - leg

The influence of direct and alternating currents of various frequencies on the outcome of the lesion

The values ​​of the current passing through a person, mA	The nature of the impact
	Alternating current, 50-60 Hz	D.C
	Onset of sensation, slight trembling of the fingers	Not felt.
	Violent trembling of fingers. The sensation reaches the wrist.	Not felt.
	Light cramps in the hands, pain.	Itching. Feeling of heat.
	Hands are difficult, but you can still tear them off the electrodes. Severe pain in fingers, hands and forearms.	Enhanced heating sensation
	Paralysis of the hands, it is impossible to tear them off the electrodes. Very severe pain. Breathing is difficult.	An even greater increase in heating. Slight contraction of the arm muscles.
	Stop breathing. Onset of cardiac fibrillation.	Strong heating sensation. Contraction of the arm muscles. Convulsions, difficulty breathing.
	Stop breathing. When the duration is more than 3 sec. Heart failure.	Stop breathing.

When the circuit breaks quickly, even a small direct current (below the sensation threshold) gives very sharp blows, sometimes causing muscle cramps in the arms. The most dangerous current is 50-60 Hz. The danger of the action of the current decreases with increasing frequency, but the current at 500 Hz is no less dangerous than at 50 Hz.

The effect of high voltage current on the body

Long ago there have been astonishing cases of human survival when exposed to high currents at high voltages. The founder of the science of the dangers of electricity, the Austrian scientist Jellinek, at the beginning of the 20th century, described a case of a victim's recovery after a defeat, which led to the burning of a 40A fuse.

Such a paradoxical discrepancy between the strength of the current and the results of its action on the body found, however, an exhaustive explanation when testing the action of a strong current on animals.

These tests showed that the action of a high voltage current does not cause fibrillation, but only a temporary cardiac arrest, which, after switching off the current, resumes its normal activity. Measurement of the current flowing directly through the heart (in experiments on dogs) showed that a current of 10-15mA causes fibrillation; a current of 0.8A (through wide electrodes placed on both sides of the heart) does not cause fibrillation, and a current of more than 1A is able to stop fibrillation of the heart. The ability of the current of the indicated (and greater) value to stop fibrillation is widely used at present in clinics to restore the activity of the heart, disturbed during the operation and from other reasons.

Thus, the survival of people who are under high voltage and exposed to a current of tens of A can be explained by the fact that no cardiac fibrillation occurs under the influence of such a current. So contradictory at first glance, the consequences of the action of a weak and strong current on the body are associated with the peculiarities of the heart's reaction to the action of a current of various strengths.

The passage of a current of 0.1-5A through the body causes fibrillation of the heart and disrupts its work; a stronger current does not cause such a disturbance in the work of the heart. The short-term action of a strong current causes a dysfunction of the nervous system, which leads to prolonged respiratory arrest. However, the victim can survive if artificial respiration is started in a timely manner.

With a longer exposure to high voltage current, death can occur due to physical damage caused by such a current (extensive and deep burns, as well as destruction of the internal structure of body tissues). However, there are cases of people recovering from electrical injuries that even cause charring and subsequent loss of significant areas of the bones of the skull.

Painful condition of the human body as an aggravating factor in electrical injuries

The diseased state of the human body causes changes in the course of biochemical, biophysical, physiological and other processes, which cannot but affect the outcome of an injury in case of electrical injury.

Variants of paths for the passage of electric current through the human body:

1 - "hand-hand"; 2 - "hand-feet"; 3 - "hand leg"; 4 - "hands-legs"; 5 - "leg-leg"; 6 - "head-legs"; 7 - "head-hand"; 8 - "head-foot"

The path of electric current through the human body largely determines the degree of damage to the body. The most common options in practice are:

a person touches with two hands to live wires or parts of equipment that are energized. In this case, the movement of the current goes from one hand to the other through the lungs and heart. This path is usually called "hand-hand";

when touching the current source with one hand, standing with two feet on the ground; path of current flow "hand-foot";

when current flows to ground from faulty electrical equipment. The ground within a radius of up to 20 m receives a voltage potential that decreases with distance from the ground electrode. A person standing with both feet in this zone is under a potential difference, since each of his legs receives a different voltage potential, depending on the distance from the ground electrode. The result is a leg-to-leg electrical circuit, the voltage of which is called stepping;

touching live parts with your head can create an electrical circuit, where the path of the current will be: "head-hands" or "head-feet".

The most dangerous are those options in which the vital organs and systems of the body - the brain, heart, lungs - fall into the affected area. These are the chains: "head-hands", "head-legs", "arms-legs", "hand-arm " .

Human electrical resistance.

Factors of a person's condition that significantly increase the likelihood of a fatal electric shock to a person:

everything that increases the rate of work of the heart - fatigue, excitement, alcohol, drugs, certain medications, smoking, illness;

anything that reduces skin resistance - sweating, cuts, alcohol consumption.

The total electrical resistance between two electrodes applied to the body of the same person should be divided into two parts: the resistance of the skin and blood vessels and the resistance of the nerves. The resistance of the human body is an active quantity consisting of internal and external components. The internal resistance of all people is approximately the same and amounts to 600 - 800 ohms. The resistance of the human body is mainly determined by the magnitude of the external resistance, and specifically - by the condition of the skin of the hands with a thickness of only 0.2 mm (primarily its outer layer - epidermis).

There are many examples of this, here is one of them. The worker lowers his middle and forefinger into the electrolytic bath and receives a fatal blow. It turned out that the cause of death was a cut in the skin on one of the fingers. The epidermis did not exert its protective effect, and the defeat occurred with an apparently safe current loop.

If we take the resistance of the skin as 1, then the resistance of internal tissues, bones, lymph, blood will be 0.15 - 0.20, and the resistance of nerve fibers is only 0.025 (“Nerves” are excellent conductors of electric current!).

Body resistance is not a constant value: in conditions of high humidity, it decreases 12 times, in water - 25 times, sharply reduces its intake of alcohol.

But during sleep, it increases 15-17 times. As the minimum resistance of the human body, a value of 1000 ohms is taken, but in general this value can vary from several hundred ohms to several megohms. Dry, intact, clean skin has this resistance.

Cardiocycle phase.

Danger of coincidence of the moment of passage of current through the heart with phase T of the cardiocycle

Each cycle of cardiac activity consists of two periods: one, called diastole when the ventricles of the heart, being in a relaxed state, fill with blood, and another, called systole when the heart, contracting, pushes blood into the arterial vessels.

The most vulnerable heart is in the T phase, which lasts about 0.2 s. Therefore, if during phase T a current passes through the heart, then, as a rule, cardiac fibrillation occurs; if the time of passage of the current does not coincide with the phase T, then the likelihood of fibrillation decreases sharply.

T - the period when the contraction of the ventricles ends and they go into a relaxed state.

When the duration of the passage of the current is equal to or exceeds the time of the cardiocycle (0.75 - 1 s), the current “meets” all phases of the heart, including the most vulnerable phase T; it is very dangerous for the body. If the time of exposure to the current is less than the duration of the cardiocycle by 0.2 s or more, then the probability of the coincidence of the moment of passage of the current with the phase T, and, consequently, the danger of injury decreases sharply.

If the time of passage of the current coincides with the phase T, then in this case the likelihood of cardiac fibrillation depends on the duration of exposure to the current.

In the investigation of accidents associated with exposure to electric current, first of all, it is found out in what way the current flowed. A person can touch live parts (or metal non-live parts that may be energized) with a variety of parts of the body. Hence - the variety of possible paths of current.

The most probable are the following:

"Right arm - legs" (20% of cases of defeat);

"Left arm - legs" (17%);

“Both hands are legs” (12%);

“Head - legs” (5%);

Hand - hand (40%);

Leg - leg (6%).

All loops, except for the last one, are called "large" or "full" loops, the current captures the region of the heart and they are the most dangerous. In these cases, 8-12 percent of the total current flows through the heart. The leg-to-leg loop is called “small”, only 0.4 percent of the total current flows through the heart. This loop occurs when a person is in the area of ​​current spreading, falling under a step voltage.

Step is called the voltage between two points of the earth, due to the spreading of current in the ground, while simultaneously touching them with the feet of a person. Moreover, the wider the step, the more current flows through the legs.

This path of current does not pose a direct danger to life, however, under its action, a person can fall and the path of current flow will become life-threatening.

To protect against step voltage, additional means of protection are used - dielectric bots, dielectric rugs. In the case when the use of these means is not possible, you should leave the spreading zone so that the distance between the legs standing on the ground is minimal - in short steps. It is also safe to walk on dry boards and other dry, non-conductive objects.

1. Electrical safety in existing electrical installations up to 1000 Volts. Manufacturing jobs.

Electrical installations such installations are called in which electricity is produced, converted and consumed. Electrical installations include mobile and stationary sources of electricity, electrical networks, switchgear and connected pantographs.

Operating electrical installations Installations are considered to be fully or partially energized or to which voltage can be applied at any time by switching on the switching equipment.

According to the degree of danger of injury to personnel by electric current, electrical installations are subdivided into electrical installations up to 1000 Volts and above 1000 Volts .

An employee of management personnel who has an electrical safety group of at least the 4th has the right to give an order to perform work in existing electrical installations up to 1000 Volts.

Work in electrical installations in relation to safety measures is divided into those performed:

with stress relief;

without removing the voltage on live parts and near them.

TO stress relief work includes work performed in an electrical installation (or part of it), in which voltage is removed from live parts.

TO work without removing voltage on live parts, and near them includes work performed directly on these parts or near them. In installations with voltages above 1000 Volts, as well as on overhead lines up to 1000 Volts, the same work includes those that are performed at distances from live parts that are less than permissible. Such work must be performed by at least two persons: the manufacturer of work with a group of at least IV, the rest - below III.

In practice, it has been established that the path of current passage through the human body plays a significant role in the outcome of the lesion. So, if vital organs - the heart, lungs, brain - are in the path of the current, then the danger of injury is very high, since the current acts directly on them.

If the current passes in other ways, then its effect can only be reflex, and not direct.

There are a lot of possible paths of current through the human body, which are also called current loops. The most common current loops are shown in table. 1 .

Table 1

Characteristics of the most common paths of electric current through the human body *

Current path	How often this path occurs,%	The proportion of those who lost consciousness during exposure to current,%	Fraction of current passing through the heart area,%
Hand - hand
Right arm - legs
Left arm - legs
Leg - leg
Head - legs
Head - hands

* The table shows data on a person's electric shock that caused disability, i.e. leading to an accident.

Most dangerous are the loops: head - arms and head - legs when an electric current can pass through the brain and spinal cord. Fortunately, these loops are relatively rare.

Next in danger is the way right arm - legs, which ranks second in frequency.

Least dangerous is the way leg - leg, which is called the lower loop and occurs when a person is exposed to the so-called step tension.

3. The effect of electric current on a person

Electric current, passing through the human body, has a thermal, chemical, biological and mechanical effect on his body.

Thermal- leads to dangerous heating of tissues and the occurrence of injuries such as burns, electrical signs, metallization of the skin.

Chemical- leads to electrolysis of blood and other solutions contained in the body, a change in their chemical composition, a violation of their physiological functions.

Biological- It is expressed in irritation of living tissues of the body, sharp, involuntary convulsive muscle contractions, reflex excitation of the nervous system and disruption of internal bioelectric processes.

The variety of actions of electric current on the human body often leads to various electrical injuries, which can be reduced to two types: local damage to the body and general electrical injuries - the so-called electrical shock, when the entire body is affected due to disruption of the normal activity of vital organs and systems. It has been established that the most vulnerable organ of the human body when an electric current passes through it is the heart (Table 2).

Local electrical injuries include:

electric burns of two types- current (contact) and arc. There are four degrees of burns: Ι - skin redness; ΙΙ - the formation of bubbles; ΙΙΙ - necrosis of the entire thickness of the skin; ΙV– tissue carbonization. Currents arise at a voltage not exceeding 1–2 kV and are in most cases Ι and ΙΙ degree burns. Arc arcs between the live part and the human body (an arc with a very high energy and a temperature of over 3500 ° C) cause severe burns of ΙΙΙ and ΙV degrees;

electrical signs- clearly defined spots of gray or pale yellow color on the surface of human skin exposed to the current. Signs are also in the form of scratches, wounds, cuts or bruises, warts, skin hemorrhages, and calluses;

electrophthalmia- eye damage caused by intense radiation of an electric arc, the spectrum of which contains ultraviolet and infrared rays harmful to the eyes;

mechanical damage- arise as a result of sharp involuntary convulsive muscle contractions under the action of a current passing through the human body; as a result, ruptures of the skin, blood vessels and nerve tissues can occur, as well as dislocation of joints and even bone fractures.

Electric shocks (excitation of living tissues of the body by an electric current passing through it, accompanied by involuntary convulsive muscle contractions), depending on the outcome of the effect of the current on the body, are of four degrees:

Ι degree- convulsive muscle contraction without loss of consciousness;

ΙΙ degree- convulsive muscle contraction, loss of consciousness, but preservation of breathing and heart function;

ΙΙΙ degree- loss of consciousness and impaired cardiac activity and / or breathing;

ΙV degree- clinical death, i.e. lack of breathing and blood circulation.

D

table 2

the effect of electric current on the human body

Types of electrical injuries				Clinical manifestations
Local electro-injuries	Electrical burn (60-65%) from all electrical injuries		Current burn (contact)	Burns of I and II degrees of the skin at the point of contact of the body with the live part. Occur on electrical installations with a voltage not higher than 1-2 kV.
			Arc burn	Skin burns of III and IV degree, can be extensive with tissue burnout to a great depth. They arise in networks with voltages above 1-2 kV.
	Electrical signs; current signs; electrical tags (19-21% of all electrical injuries)			The appearance of spots of gray or yellow-gray color on the skin at the point of touching live parts (sometimes the form of scratches, cuts, warts, calluses)
	Skin metallization (10% of all victims)			Penetration of metal inclusions into the skin in places of contact with an electric arc, accompanied by pain due to burns and tension of the skin
	Electrophthalmia (1-2% of all victims)			Inflammation of the mucous membranes of the eyes caused by ultraviolet radiation when an electric arc occurs; manifests itself after 2-6 hours. Accompanied by lacrimation, photophobia, partial blindness
	Mechanical damage (rare)			Tears of the skin, blood vessels, nerve fibers, dislocations due to convulsive muscle contractions under the influence of an electric current
Electric shock	I degree			Convulsive muscle contraction without loss of consciousness
	II degree			Convulsive muscle contraction and loss of consciousness. Preservation of breathing and work of the heart
	III degree			Loss of consciousness, impaired heart activity or breathing
	IV degree	Clinical (imaginary) death; lack of breathing and heart function; pupils are dilated, do not react to light		Termination of the heart (direct action of the current on the heart muscle), fibrillation of the heart muscle (the coincidence of the action of the current with T-phase of the heart). Cessation of breathing, paralysis (direct or reflex action of the current on the muscles of the chest). Electric shock (severe neuro-reflex reaction, accompanied by disorders of blood circulation, respiration, metabolism); lasts from several tens of minutes to a day

For alternating current, its frequency also plays a role. With an increase in the frequency of the alternating current, the impedance of the body decreases, which leads to an increase in the current passing through the person, and, consequently, the risk of injury increases. The greatest danger is the current with a frequency of 50 to 100 Hz; as the frequency increases further, the risk of fatal injury decreases. The decrease in the risk of electric shock with increasing frequency becomes practically noticeable at a frequency exceeding 1 ... 2 kHz, and completely disappears at a frequency of 45 to 50 kHz. However, at these current frequencies, the risk of burns remains.

The path of the current through the human body... The path of current passage through the human body plays a significant role in the outcome of the lesion, since the current can pass through vital organs: the heart, lungs, brain, etc. The effect of the passage of the current path on the outcome of the lesion is also determined by the resistance of the skin in different parts of the body.

There are many possible paths for the passage of current in the human body, which are also called current loops. The most common current loops and their characteristics are shown in Table 2.

Table 2 - Characteristics of current paths in the human body

Loop name	Current path	Path occurrence frequency	Share of those who lost consciousness at defeat,%
	Hand - hand
Right full	Right arm - legs
Left full	Left arm - legs
	Leg - leg
Straight vertical	Head - legs
Straight horizontal	Head - hands

The most dangerous loops are "head-arms" and "head-feet", but these loops are relatively rare. In the design, calculation and operational control of protective systems, they are guided by the permissible current values ​​for a given path of its flow and the duration of exposure in accordance with GOST 12.1.038-82. With prolonged exposure to a person, more than 30 s, the value of the permissible current is taken equal to 1 mA, with a duration of exposure from 30 s to 1 s - 6 mA, and with exposure less than 1 s, the value of the permissible current is taken equal to 50 mA.

However, the given values ​​of currents cannot be considered as ensuring complete safety and are taken as practically permissible with a rather low probability of defeat. These currents are considered permissible for the most probable paths of their flow in the human body: "hand - arm", "arm - legs".

Individual properties of a person in case of electric shock, it is mainly determined by the electrical resistance of the human body, which is the sum of the resistances of the skin and internal tissues. The current passing through the human body can be estimated according to Ohm's law:

where I people- current passing through a person, A;

U - voltage applied to a person, V;

R people- resistance of the human body, Ohm.

The resistance of the human body with dry, clean and intact skin ranges from 3 to 100 kOhm or more, and the resistance of the internal organs of the body is only from 300 to 500 Ohm. Neglecting the capacitive component of the human body, the value of the active resistance of the human body, equal to 1000 Ohm, is taken as a calculated value when exposed to an alternating current of industrial frequency.

2.2 Analysis of electric shock in electrical networks

The defeat of a person with an electric current is possible only when the electrical circuit is closed through the human body. The voltage between two points of the current circuit that a person touches at the same time is called tension of touch... The danger of such a touch is estimated by the amount of current passing through the human body. The magnitude of the current depends on the touch voltage and a number of factors: the resistance of the human skin, the circuit for closing the current circuit through the human body, the voltage of the network, the circuit of the network itself, the mode of its neutral, the degree of isolation of live parts from the ground, the value of the capacitance of live parts relative to the ground, etc.

There are two possible cases of closing the current circuit through the human body: a person touches two phase wires at the same time and a person touches only one phase wire. With regard to AC networks, the first circuit is usually called two-phase touch (Figure 2a), and the second - single-phase (Figure 2b, c).

a - two-phase touch; b - single-phase contact in a network with an isolated neutral; c - single-phase contact in a network with a grounded neutral

Figure 2 - Schemes of the possible inclusion of a person in a three-phase current network

Two-phase touch a person to the current circuit occurs quite rarely, but it is the most dangerous and often fatal, since the highest voltage in this network is applied to the human body - linear U l =
U f... In networks with line voltage U l= 380 V ( U f= 220 V) with a resistance of the human body R h = 1000 Ohm, the current through a person is

This current is deadly for a person, because almost four times the value of the threshold fibrillation current I fib= 100 mA. With a two-phase touch, the current passing through a person practically does not depend on the neutral mode of the network.

Single phase touch occurs many times more often than two-phase, but it is less dangerous, because the phase voltage is 1.73 times less than the linear voltage, while the current passing through the person will also be less. The amount of current passing through a person is significantly influenced by the insulation resistance of the wires relative to the ground, the resistance of the floor on which the person is standing, the resistance of his shoes, the neutral mode of the electrical network and some other factors. In Russia, only two types of three-phase networks are used up to 1000 V: a three-phase three-wire network with an isolated neutral and a three-phase four-wire network with a dead-grounded neutral. Consider the conditions of electric shock, depending on the neutral mode of the network.

In a network with an isolated neutral, when a person touches a wire of one of the phases, the current passes through the human body, the ground and then through the insulation resistance into the network (see Figure 2b). If the electrical capacitance of the wires relative to the ground is small, which usually occurs in short-range overhead networks, the value of the current passing through a person is determined as

,

where U f- phase voltage, V;

R h , R about , R n , R from- resistance of a person, shoes, flooring and insulation of wires relative to the ground, kOhm.

U f= 220 V, R h= 1 kΩ,
R about= 20 kΩ, R n= 30 kΩ and R from= 150 kOhm, the current through a person will be equal to I h= 2.2 mA, which is more than the threshold perceptible, but less than the threshold non-releasing current, and the likelihood of a favorable outcome is very high.

In a network with a grounded neutral, when a person touches the phase wire, it also turns out to be under phase voltage (Figure 2c), but the current in this case passes through the human body to the ground and then through the neutral ground to the network. Then the current through the person is

,

where R O- neutral grounding resistance, usually R O= 4 ohms.

When substituting numeric values U f = 220 V, R h= 1 kΩ,
R about= 20 kΩ, R n= 30 kΩ and R O = 4 Ohm, we get a slightly higher current value than in a network with an isolated neutral and equal

I h= 4.4 mA, which is also very likely safe for humans.

As can be seen from the calculations, under normal operating conditions of electrical installations, a single-phase connection of a person to a network with an isolated neutral is less dangerous than to a network with a grounded neutral.

Any contact with live parts of electrical installations with voltages above 1000 V is dangerous regardless of the power supply circuit. Therefore, in such networks, all measures are taken to make live parts inaccessible to accidental human touch. They are located at an inaccessible distance, reliably fenced, strictly regulate the procedure for admission to electrical installations, etc.

The contact voltage when a person touches energized equipment depends on the state of grounding, the person's distance from the grounding electrode and resistance
the foundation on which a person stands. This is clearly shown in Figure 3. The contact voltage is

U NS = φ max –φ H ,

where φ max- the maximum potential that will be at the grounded housing and the grounding electrode;

φ n- the potential of the earth's surface at the point where the legs of a person are located.

If a person's feet are above the grounding electrode, the touch voltage is zero, since the potentials of the arm and legs are the same and equal to the potential of the ground electrode. When a person moves away from the grounding electrode, the touch voltage tends to the maximum value, since the potential of the legs tends to zero. Almost at a distance of 20 m from a single earthing switch, the contact voltage reaches its maximum value.

The amount of touch voltage is also determined by the resistance of the shoe and the sub-floor or ground directly under the feet. Therefore, the use of dielectric gloves, galoshes or a bot will increase the total resistance of a person and, therefore, significantly reduce the amount of current passing through the human body.

In the area of ​​the electric current spreading zone in the ground, for a single earthing switch, the radius of the zone is about 20 m, there is a danger of shock from the step voltage (Figure 3).

A - potential curve; K - touch curve

Step voltage is called the potential difference between two points in the area of ​​spreading of an electric current, located at a distance of a person's step, and on which the person's legs are located at the same time. Step voltage is

U NS = φ 1 –φ 2 ,

where φ 1 - potential of one human leg, V;

φ 2 - the potential of a person's other leg, V.

Even with a small step voltage (from 50 to 80 V), an involuntary convulsive contraction of the leg muscles may occur, and a person may fall to the ground. At the same time, he is forced to simultaneously touch the ground with his hands and feet, the distance between which is greater than the length of the stride, so the tension increases. In this case, a new pathway for the passage of current is formed, affecting the vital organs, and there is a real threat of fatal injury. As the stride length decreases, the step voltage decreases. Therefore, in order to get out of the zone of action of the step voltage, you should move in as short steps as possible.

2.3 Classification of premises according to the danger of electric shock

The condition of the surrounding air and environment can significantly affect the risk of electric shock. In this regard, all rooms are divided according to the degree of danger of electric shock to people into three classes: without increased danger, with increased danger and especially dangerous.

To rooms with increased danger includes premises characterized by the presence of any of five factors: 1) the relative humidity of the air exceeds 75% (damp premises); 2) the air temperature exceeds 35 0 С (hot rooms); 3) the presence of conductive dust (for example, coal, metal, etc.); 4) the presence of a conductive floor (for example, metal, concrete, earthen, clay); 5) the ability to simultaneously touch the body of electrical equipment and a grounded object.

Examples of hazardous premises are staircases of various buildings with conductive floors; warehouses; workshops or workshops for the machining of metal or wood, etc.

To especially dangerous premises m includes rooms characterized by the presence of any of three conditions: 1) the relative humidity of the air is close to 100% (especially damp rooms); 2) the presence of a chemically active and organic environment that destroys insulation and live parts of electrical installations; 3) the presence of two or more factors , in rooms with increased danger, for example, a damp room with conductive floors or a hot one with conductive dust, etc.

Particularly dangerous premises are the majority of industrial premises, including all power plant shops, battery room and electrolysis room, etc. The territories for the location of outdoor electrical installations in relation to the danger of electric shock are equated to especially dangerous premises.

To premises without increased danger includes all other rooms characterized by the absence of conditions that create an increased or special danger in case of electric shock. An example of such premises is the accounting room, classrooms, some laboratories, etc.

Taking into account the class of the premises for the danger of electric shock, the choice of electrical equipment and structures of electrical installations is made, which must successfully withstand the effects of the environment and provide a high degree of safety during maintenance.

3 First aid for defeat

electric shock

Everyone who works in electrical installations should be able to provide first aid to an injured person. First aid for electric shock consists of two stages: the release of the victim from the action of the current and the provision of first aid to him. Since the degree of electric shock depends on the duration of its passage through the human body, it is very important to release the victim from the current as soon as possible and, if necessary, immediately begin to provide him with medical care. This requirement also applies in the case of fatal electric shock, since the period of clinical death lasts several minutes. In all cases of electric shock to a person, it is necessary, without interrupting the provision of first aid, to call a medical worker and, if necessary, provide assistance in delivering the victim to a hospital.

3.1 Releasing the victim from the action of electric current

In case of electric shock, it often turns out that the victim cannot independently free himself from the action of the electric current. The release of the victim from the action of the current can be done in several ways.

In all cases, the most reliable way to release the victim is to quickly disconnect the electrical installation. Disconnection of the electrical installation is carried out using the nearest knife switch, switch or other disconnecting device, as well as by removing the fuses, connection connector, etc. If the victim is at a height, then you need to take measures against his fall when the current is turned off. With artificial lighting, you need to be prepared for the lack of lighting when the current is turned off.

If it is impossible to turn off the electrical installation quickly, it is necessary to free the victim from live parts in other ways. With a voltage in the network up to 1000 V, release from live parts can be done by throwing the wire away from the victim or pulling the victim away from the wire. Throwing away the wire can be done with any dry object made of non-conductive material (dry stick, board, rope), with a hand in a dielectric glove, in a canvas glove, or with a hand wrapped in a dry cloth. The victim can be dragged away only by his dry clothes, and if this is not possible, then the releasing person pulls the victim off with his hands protected from electric current.

If the victim convulsively squeezes the live wire with his hand, then to release him from the action of the current, you can unclench his hand, bending each finger separately. To do this, the caregiver must have dielectric gloves on his hands and stand on an insulating base - a dielectric mat, dry board, etc. You can also interrupt the action of the current by isolating the victim from the ground, for example, by placing a dry board under him. If necessary, you can cut or cut the wires with a dry-handled ax or a tool with insulated handles.

With a voltage in the network above 1000 V, you can release the victim only by disconnecting the electrical installation or use the main insulating means for networks above 1000 V (insulating rods, insulating pliers):

- put on dielectric gloves, rubber boots or galoshes;

- take an insulating rod or insulating pliers;

- short-circuit the wires of the 6-20 kV overhead line by the throw method, according to special instructions;

- drop the wire from the victim with an insulating rod;

- pull the victim by the clothes at least 10 meters from the place where the wire touches the ground or from the equipment that is energized.

3.2 Provision of first pre-medical aid

The measures of the first pre-medical aid to the victim of electric current depend on his condition. To determine the condition of the victim, he must be laid on his back and check for breathing and heartbeats.

Disturbed breathing characterized by indistinct or irregular rises of the chest during inhalation, rare, as if gasping for air, inhales or the absence of visible respiratory movements of the chest. All these cases of respiratory distress lead to the fact that the blood in the lungs is insufficiently saturated with oxygen, as a result of which oxygen starvation of tissues occurs and
organs of the victim. Therefore, in these cases, the victim needs artificial respiration.

The presence of heartbeats indicates the work of the heart, i.e. about the presence of blood circulation in the body, it is determined by listening to heart sounds, putting the ear to the left half of the victim's chest, or by checking the pulse. The presence of a pulse is checked on the large arteries, where it is more pronounced - on the radial, femoral and carotid.

Checking the condition of the victim, including giving his body an appropriate position, checking breathing, pulse and pupil condition should be done quickly - within 15 ... 20 s.

Possible first aid measures:

- if the victim does not have breathing and pulse, then immediately you need to start reviving him by artificial respiration and external (indirect) heart massage;

- if the victim breathes rarely and convulsively, but his pulse is felt, start doing artificial respiration;

- if the victim is conscious with stable breathing and pulse, you need to put him on clothes or other mat, unbutton clothes that hinder breathing, give fresh air, warm when cooled and give cool in the heat;

- if the victim is unconscious in the presence of breathing and pulse, it is necessary to observe his breathing; in case of respiratory failure when the tongue falls, push the lower jaw forward and maintain it in this state until the tongue sinks.

In all cases of electric shock, it is necessary to call a doctor, regardless of the condition of the victim.

Doing mouth-to-mouth artificial respiration, the person providing assistance is located on the side of the victim's head, puts one hand under his neck, and with the palm of the other hand presses on his forehead, throwing his head back as much as possible. In this case, the root of the tongue rises and frees the entrance to the larynx, and the victim's mouth opens.

The caregiver leans towards the victim's face, takes a deep breath with his open mouth, then completely tightly covers the victim's open mouth with his lips and exhales vigorously; simultaneously covers the victim's nose with his cheek or fingers on his forehead. As soon as the victim's chest has risen, the air injection is stopped, the assisting raises his head, and the victim exhales passively. In order for the exhalation to be deeper, you can gently press your hand on the chest to help air out of the victim's lungs.

electrical installations Consumers Section 1, Chapter 1. ... every Consumer atexploitationelectrical installations? (*) Manufacturing instructions for exploitationelectrical installations... (*) Official ...

Document

... atexploitationelectrical installations atexploitationelectrical installations... to personnel in relation to electrical safety

Interindustry rules on labor protection (safety rules) during the operation of electrical installations with changes and additions

Document

... atexploitationelectrical installations(2nd ed., Revised and supplemented - M .: Energoatomizdat, 1989) and Safety regulations atexploitationelectrical installations... to personnel in relation to electrical safety are minimal and the decision of the head ...

Document

... atexploitationelectrical installations(2nd ed., Revised and supplemented - M .: Energoatomizdat, 1989) and Safety regulations atexploitationelectrical installations... to personnel in relation to electrical safety are minimal and the decision of the head ...

Interindustry rules on labor protection (safety rules) during the operation of electrical installations pot r m-016-2001 rd 153-34 0-03 150-00

Document

... atexploitationelectrical installations(2nd ed., Revised and supplemented - M .: Energoatomizdat, 1989) and Safety regulations atexploitationelectrical installations... to personnel in relation to electrical safety are minimal and the decision of the head ...