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What are the causes of electric shock? Electric shock Causes of electric shock to personnel

29.05.2020

Characteristics of human lesions electric shock. Electrical resistance of the human body. 2

The main causes of electric shock. 3

Methods and means used. 4

for protection against electric shock. 4

when touching metal non-current-carrying parts, 4

under tension. 4

Organizational measures to ensure the safety of work in electrical installations. 4

Technical measures to ensure the safe performance of work in existing electrical installations. 4

Characteristics of electric shock to a person. Electrical resistance of the human body

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

The biological effect of current is manifested in irritation and excitation of tissues and organs. As a result, skeletal muscle spasms are observed, which can lead to respiratory arrest, avulsion fractures and dislocations of the limbs, and spasm of the vocal cords.

The electrolytic effect of the current is manifested in the electrolysis (decomposition) of liquids, including blood, and also significantly changes the functional state of cells.

The thermal effect of electric current leads to burns of the skin, as well as the death of underlying tissues, up to charring.

The mechanical action of the current is manifested in the stratification of tissues and even the separation of body parts.

Electrical injuries can be conditionally divided into local, general (electric shocks) and mixed (local electrical injuries and electrical shocks at the same time). Local electric shocks make up 20% of the considered electric injuries, electric shocks - 25% and mixed - 55%.

Local electrical injuries- clearly expressed local disorders of body tissues, most often these are superficial injuries, i.e. damage to the skin, sometimes soft tissues, as well as articular bags and bones. Local electrical injuries are cured, and a person's working capacity is restored completely or partially.

Typical types of local electrical injuries- electrical burns, electrical signs, skin plating, electrophthalmia and mechanical damage.

The most common electrical injury is electrical burns. They make up 60 - 65%, and about 1/3 of them are accompanied by other electrical injuries.

There are burns: current (contact) and arc.

Contact electrical burns, i.e., tissue damage at the points of entry, exit and on the path of movement of the electric current arise as a result of human contact with the current-carrying part. These burns occur during the operation of electrical installations of relatively low voltage (not higher than 1-2 kV), they are relatively light.

arc burn due to exposure to an electric arc that creates a high temperature Arc burn occurs when working in electrical installations of various voltages, often the result of accidental short circuits in installations above 1000 V and up to 10 kV or erroneous operations of personnel. The defeat occurs from the flame of an electric arc or clothing caught fire from it.

There may also be combined lesions (contact electric burn and thermal burn from the flame of an electric arc or ignited clothing, electric burn in combination with various mechanical damage, electric burn simultaneously with thermal burn and mechanical injury).

According to the depth of the lesion, all burns are divided into four degrees: the first - redness and swelling of the skin; the second - water bubbles; the third is the necrosis of the superficial and deep layers of the skin; the fourth - charring of the skin, damage to muscles, tendons and bones.

electrical signs are clearly defined spots of gray or pale yellow color on the surface of the skin of a person who has been exposed to current. Signs are round or oval with a depression in the center. They come in the form of scratches, small wounds or bruises, warts, skin hemorrhages, and calluses. Sometimes their shape corresponds to the shape of the current-carrying part that the victim touched, and also resembles the shape of lightning. In most cases, electrical signs are painless and their treatment ends well. Signs occur in about 20% of those affected by the current.

Skin metallization- penetration into its upper layers of particles of metal melted under the action of an electric arc. This is possible in case of short circuits, trips of disconnectors and knife switches under load, etc.

The affected area of the skin has a rough surface, color
which is determined by the color of the metal compounds on the skin:
green - in contact with copper, gray - with aluminum, blue -

green - with brass, yellow-gray - with lead.

Metallization of the skin is observed in approximately 10% of the victims.

Etectroophthalmia- inflammation of the outer membranes of the eyes as a result of exposure to a powerful stream of ultraviolet rays. Such exposure is possible in the presence of an electric arc (for example, during a short circuit), which is a source of intense radiation not only of visible light, but also of ultraviolet and infrared rays. Electrophthalmia occurs relatively rarely (in 1-2% of victims), most often during electric welding.

Mechanical damage occurs as a result of sharp, involuntary, convulsive muscle contractions under the influence of current passing through the human body. In this case, ruptures of the skin, blood vessels and nervous tissue are possible, as well as dislocations of the joints and bone fractures. Mechanical damage - serious injuries; their treatment is long. They occur relatively rarely.

electric shock- this is the excitation of body tissues by an electric current passing through it, accompanied by muscle contraction.

Distinguish four degrees of electric shock:

I - convulsive muscle contraction without loss of consciousness;

II - convulsive muscle contraction with loss of consciousness, but with preserved breathing and heart function;

III - loss of consciousness and impaired cardiac activity or breathing
niya (or both together)

IV - clinical death, i.e. lack of breathing and blood circulation,
The danger of exposure to electric current on a person depends on

the resistance of the human body and the voltage applied to it, the strength of the current, the duration of its impact, the path of passage, the type and frequency of the current, the individual properties of the victim and other factors.

The electrical conductivity of various tissues of the body is not the same. Cerebrospinal fluid, blood serum and lymph have the highest electrical conductivity, followed by whole blood and muscle tissue. The internal organs, which have a dense protein base, brain substance and adipose tissue, conduct electrical current poorly. The skin and, mainly, its upper layer (epidermis) has the greatest resistance.

The electrical resistance of the human body with dry, clean and intact skin at a voltage of 15 - 20 V is in the range from 3000 to 100,000 ohms, and sometimes more. When the top layer of the skin is removed, the resistance decreases to 500 - 700 ohms. With complete removal of the skin, the resistance of the internal tissues of the body is only 300 - 500 ohms. When calculating, the resistance of the human body is taken equal to 1000 ohms.

The resistance of the human body depends on the sex and age of people: in women, this resistance is less than in men, in children it is less than in adults, in young people it is less, NR IN THE ELDERLY: THIS is due to the thickness and degree of coarsening of the upper layer of the skin.

On the electrical resistance the type of current and its frequency also affect. At frequencies of 10 - 20 kHz, the upper layer of the skin practically loses resistance to electric current.

The main causes of electric shock

1. Accidental contact with live parts under voltage as a result of: erroneous actions during work;

malfunctions protective equipment with which the victim touched current-carrying parts, etc.

2. The appearance of stress on metal structural parts
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 in re
Result:

erroneous inclusion of a disabled installation;

short circuits between disconnected and energized live parts;

lightning discharge into an electrical installation, etc.

4. Emergence step voltage on the land where
person as a result:

phase-to-earth short circuit;

removal of the potential by an extended conductive object (pipeline, railway rails);

malfunctions in the device protective earth and etc.

Step Voltage - the voltage between two points in a current circuit that are one step apart from one another and where a person is standing at the same time.

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.

Methods and means used

for protection against electric shock

when touching metal non-current-carrying parts,

under tension

To protect against electric shock when touching metal non-current-carrying parts that are energized, the following methods and means are used:

protective earthing, grounding, potential equalization, system of protective conductors, protective shutdown, isolation of non-current-carrying parts, electrical separation of the network, low voltage, insulation control, compensation of earth fault currents, personal protective equipment.

Technical methods and means are used separately or in combination so as to provide optimal protection.

Organizational measures to ensure the safety of work in electrical installations

Organizational measures that ensure the safety of work in electrical installations are:

registration of work with a work permit, order or list of works performed in the order of current operation;

work permit;

supervision during work;

registration of a break in work, transfers to another workplace, end of work.

Technical measures to ensure the safe performance of work in existing electrical installations

In accordance with the requirements of the Safety Rules for the operation of consumer electrical installations, to prepare the workplace during work with stress relief, the following technical measures must be performed in the specified order;

the necessary shutdowns have been made and measures have been taken to prevent the supply of voltage to the place of work due to erroneous or spontaneous switching on of the switching equipment;

prohibitory posters are posted on the manual drives and on the remote control keys of the switching equipment;

the absence of voltage on current-carrying parts, on which grounding must be applied to protect people from electric shock, was checked;

grounding is applied (grounding knives are turned on, and where they are absent, portable grounding devices are installed);

Electrical safety.

The main causes of electric shock to a person:

Violation of insulation or loss of insulating properties;
Direct contact or dangerous approach to live parts under voltage;
Action inconsistency.

The action of electric current on living tissue is versatile and peculiar, there are several of them:

Thermal action: burns of certain parts of the body are possible, heating of blood vessels, nerves, heart, brain and other organs to high temperatures, which causes serious functional changes in them. According to the Joule-Lenz law, the amount of heat released is directly proportional to the square of the current strength, the resistance of the human body and the exposure time.
The electrolytic action is expressed in the breakdown of blood and lymph molecules into ions. The physico-chemical composition of these liquids changes, which leads to disruption of the life process.
The mechanical action of the current leads to stratification, rupture of body tissues as a result of the electrodynamic effect, as well as instantaneous explosive formation of steam from tissue fluid and blood.
Biological action - excitation of living tissues, causing convulsive contraction and disruption of internal bioelectric processes.

There are two types of injury:

Local electrical injury causing local damage to the body.

Electrical burn is the most common electrical injury:

two types - current (or contact), resulting from the passage of current through the human body as a result of contact with live parts, contact burn most often occurs at a voltage of no more than 2000 volts;

– arc burn is possible at different voltages. As a result of electric arc injury when passing through the human body, a fatal outcome is possible.

Electric signs are sharply defined spots of gray or pale yellow color on the surface of the body of a person who has been exposed to an electric current.
Metallization of the skin occurs when the smallest particles of metal, melted under the action of an electric arc, penetrate into the upper layers of the skin.
Mechanical damage is a consequence of sharp involuntary muscle contractions under the influence of current (rupture of tendons, skin, blood vessels, sometimes dislocations and fractures are possible).
Electrophthalmia - inflammation of the cornea and conjunctiva of the eye caused by ultraviolet rays from an electric arc.

General electrical injuries lead to the defeat of the whole organism, they are divided into four degrees:

I - convulsive muscle contractions;

II - convulsive muscle contractions with loss of consciousness;

III - loss of consciousness with impaired respiratory and cardiac activity;

IV - clinical death (the length of time from the moment the heart and breathing stop until the death of brain cells starts is about 4-6 minutes, during this period a person can be helped)

Factors affecting the risk of electric shock:

The main damaging factor is the strength of the current, the greater the current, the more dangerous its impact.

Three threshold values are set to characterize the impact:

Threshold perceptible current 0.5 - 1.5 mA for AC 50 Hz and 5 - 7 mA for DC - the minimum current that causes pain (itching, tingling).
Threshold not releasing 8 - 16 mA 50 Hz and 50 - 70 mA 0 Hz - the minimum current value at which the convulsive contraction of the muscles of the hand does not allow a person to independently get rid of current-carrying parts.
Threshold fibrillation 100 mA 50 Hz and 300 mA 0 Hz - causes heart fibrillation - chaotic multi-temporal contractions of the heart muscle, at which blood circulation stops.

The resistance of the human body is made up of the resistance of the skin and internal organs, whereby:

Rskin = 3000 - 20,000 Ohm,

Internal organs Rin = 500 - 700 Ohm,

Rch \u003d 2Rn + Rv

The resistance of the skin depends on its condition: dry - wet, whether there are any damages, impurities, time and density of contact.

The duration of the impact.
Path, type and frequency of the current.
Individual characteristics of a person (age, psychological, physical).
Environmental conditions.

Classification of premises according to the degree of danger of electrical shocks.

The safety of electrical equipment maintenance depends on environmental factors. Based on these factors, all premises are divided into three classes:

The first - without increased danger (dry, without dust, with normal temperature, with insulating floors, humidity up to 70%).
The second - premises with increased danger are characterized by one of the following features: relative humidity > 75%, the presence of conductive dust, the presence of conductive floors, high air temperature (> 30, periodically > 35 and briefly > 40), the possibility of simultaneous contact of a person with the metal parts of electrical installations and to metal structures connected to the ground.
The third one is especially dangerous premises: the presence of humidity close to 100%, the presence of a chemical aggressive environment, the presence of two or more signs of premises with increased danger at the same time.

Electrical installations are classified by voltage into two groups:

Electrical installations with rated voltage up to 1000 V.
Electrical installations with voltage over 1000 V.

Electrical products according to the method of protecting a person from electric shock are divided into five classes: 0; 01; I; II, III.

Class 0 - products with a rated voltage of more than 42 V with working insulation and not having devices for grounding or grounding (household appliances).

Class 01 - products with working insulation and a grounding (grounding) element.

Class I - products with working insulation, a grounding element and a power wire with a grounding (neutral) bus.

Class II - products that have double or reinforced insulation on all accessible parts.

Class III - products without internal and external electrical circuits with voltages above 42 V.

Electric shock is a consequence of the simultaneous touch of a person to two points of the electrical circuit, between which there is a potential difference. The danger of such a touch depends on the characteristics of the circuit and the scheme for including a person in it, by determining the current strength taking into account these factors, it is possible to select protective measures with a high degree of accuracy.

Possible schemes for including a person in an electrical circuit:

Two-phase switching is more dangerous than single-phase, because. the greatest voltage in this network is applied to the body - linear: J \u003d Ul / Rch,

where Ul - line voltage (V);

Rh - the resistance of the human body (Ohm), in the calculations they take 1000 Ohm.

Single-phase switching - various factors affect the current passing through a person, which reduces the risk of damage: Jh \u003d U / (2Rh + r),

where U is the voltage in the network (V);

R is the insulation resistance (Ohm).

Or: Jh = U/R0; R0 - shoe resistance; floor resistance; wire insulation resistance; human body resistance.

Touch voltage - occurs as a result of touching electrical installations under voltage.

Upr \u003d * (ln - ln) * α,

where is the ground fault current (A);

ρ - specific resistance of the base of the floor (Ohm * m);

L and d are the length and diameter of the earth electrode (m);

X is the distance from a person to the grounding point (m);

α is the touch voltage coefficient.

Step voltage - the voltage on the human body when the legs are positioned at the points of the current spreading field with a ground electrode or from a wire that has fallen to the ground.

When a person moves to or from a source of an electric field, the step length is taken equal to 0.8 m in calculations.

The maximum value of the voltage at the point where the electric current closes to the ground and decreases with distance from it. It is assumed that at a distance of 20 m from the fault, the potential is zero.

X is the distance of a person from the closing point;

A - step length;

ρ is the resistivity of the soil.

Therefore, it is necessary to leave the voltage zone in as short steps as possible.

Protective measures against electric shock:

Organizational events

Recruitment;
Training in electrical safety rules, certification;
Appointment of responsible persons;
Carrying out periodic inspections, measurements and tests of electrical equipment.

Use of personal protective equipment

Basic insulating protective equipment (dielectric gloves, insulated tool);
Additional protective equipment (dielectric mats and stands);
Auxiliary devices (screens, fitters, etc.).

Technical measures

Protective earthing - intentional electrical connection with earth or its equivalent, metal non-current-carrying parts of electrical installations that may be energized.

According to the rules, all electrical installations operating at a rated AC voltage of more than 50 V and a constant voltage of more than 120 V are grounded (except for lamps suspended indoors without increased danger at a height of at least 2 m).

As artificial grounding conductors, buried in the ground are used. steel pipes, corners, pins. The natural ones include water pipes laid in the ground and sewer pipes, metal sheathed cables.

The principle of operation of grounding is the reduction to safe values of touch or step voltages in the event of a current short circuit on metal cases of electrical equipment.

Given that the resistance of the human body is much greater than the resistance of the grounding device, the main current in the event of a short circuit will pass through the ground electrode.

There are disadvantages:

Part of the current will pass through the human body.
In the event of a fault in the grounding device circuit, the risk of electric shock increases dramatically. According to the norms, the resistance of the grounding device is checked at least once a year, in especially dangerous rooms - at least once a quarter.

Zeroing is a deliberate connection with a zero protective conductor of metal non-current-carrying parts of electrical equipment that may be energized.

The principle of operation of protective neutralization is to turn a short circuit to the case into a single-phase short circuit (between the phase and zero protective conductor) in order to create a large current that can ensure the operation of a protective shutdown device (fuses, magnetic starters with thermal protection, etc.).

To provide automatic shutdown emergency equipment, the resistance of the short circuit network should be small (about 2 ohms).

Disadvantages - deprivation of protection of electrical consumers in the event of a break in the neutral wire.

Protective shutdown - quick shutdown of electrical installations (up to 1000 V) in the event of a dangerous electric shock in it.

The RCD response time does not exceed 0.03 ... 0.04 s.

With a decrease in the time of current flow through a person, the danger decreases.

Due to the ubiquitous use of electricity, as in production processes, and for solving everyday problems, a significant threat of electric shock is created. To prevent such situations, there are a number of rules that allow you to protect personnel and ordinary people from the deplorable consequences of illiterate handling of electricity. To do this, it is important to understand the causes of electric shock and the measures necessary in certain situations to prevent electric shock.

The concept of electric shock

An electric shock should be understood as such a situation when an electric charge from a current source uses as one of the flow paths or the only path human body. In this case, the directed movement of particles creates a spontaneous contraction of the muscles that fall under its influence on the flow path, the current destroys tissues and causes other damage.

Electric shock can occur both during normal operation of electrical installations and in emergency situations (damage to wire insulation, breakdown of dielectrics, destruction of insulators, when an electric arc burns, etc.). In addition to interaction with current in everyday life, there is the possibility of being struck by lightning. But whatever the current flow, it can cause a number of adverse consequences for the human body.

How does electricity affect the human body?

If we do not consider planned electric shocks, during medical or cosmetic procedures with devices whose action is aimed at passing electric current through the tissues of the body, then in all cases of electrical injuries, the body receives three main current effects:

Thermal- lead to burns at the points of electric current. Unlike the usual one, an electric burn is further complicated by tissue damage by small particles of hot metal. Which after the impact remain in the skin, respectively, and the healing of such wounds takes longer and requires additional effort. Light, medium, or severe burns may occur, depending on the conditions under which the shock occurs.
dynamic- causes contraction and subsequent damage to muscles and ligaments. Since all the muscles in the body are controlled by electrical impulses, when current flows, their spontaneous contraction occurs. What can happen due to mechanical damage tissues - breaks. As well as convulsive compression of the limbs, in which a person cannot unclench his fingers on his own and free himself from the action of the current. The same effect occurs with the heart, which can cause a fatal shock.
electrolytic- when current flows, blood vessels have the lowest resistance, which are the conductors in the body. When an electric current passes through the vessels, the blood acts as a conductor, which, with prolonged exposure, decomposes into plasma and blood cells.

Depending on the situation, damage may also result in electrical shock. The condition of the victim is characterized by the lack of an adequate response to the events and dilated pupils. In this state, it is difficult to judge the damage done to the body, due to the fact that a person cannot report his own well-being. Therefore, his condition is determined by indirect factors (pulse, respiration, etc.).

The main causes of electric shock

The reasons may be due to various factors and situations. Because of these differences in situations, the rules regulate the use of certain remedies or impose obligations on the implementation of certain measures. In this connection, the causes of damage are divided into those that can occur in domestic conditions, and those that can occur at work.

At home

The most common causes of damage in the domestic environment are any malfunctions or careless handling of the operated devices by the person himself. The strength of the current acting on a person depends on the resistance of the electrical circuit, which includes the resistance of the skin, shoes, current spreading in the floor or some other point. The lowest resistance value is obtained in the case of wounds on the skin, a wet surface of the hands, or when a person touches grounded elements.

Particular attention should be paid to such causes of damage:

Insulation failure inside appliances- for the most part, all home vacuum cleaners, kettles, microwaves, washing machines and other helpers are equipped with reliable insulation at the factory. However, due to natural aging or damage, the insulation resistance may deteriorate, resulting in electric shock. This problem is characterized by a potential transfer to the case or metal parts of electrical appliances and causes the occurrence.
Damage to the insulating sheath of wires- applies to both wiring and all kinds of power cords and extension cords. There is a possibility of electric shock from places where kinks, blows or chafing occurred, especially if water gets on them.
Contact with improvised devices and exposed live parts. Both do not guarantee a person any compliance with the standards. Therefore, interaction with questionable devices or bare wires can lead to severe electric shock.
Spontaneous repair attempts- when people without the necessary skills and knowledge try to repair some appliances or electrical wiring. At the same time, they expose themselves to the danger of accidentally touching the elements under voltage, which is the cause of the defeat. For example, when replacing an electric lamp in a lamp, when the voltage is not removed from the cartridge.
Using switches or sockets with a damaged housing. The case of these devices acts as a natural barrier, which, if damaged, opens access to current-carrying elements and there is a threat of electric shock.
Attempts to replace lamps in the presence of voltage in the cartridge– due to negligence, a person may touch the internal components, which will lead to electric shock. It is also possible that a burnt-out lamp is destroyed and disintegrates in the hands, and some parts can become conductors of electric current. In this case, the disconnected switch is not a guarantee of the absence of voltage due to the fact that it may not break the phase.
Operation of electrical appliances in conjunction with water– attempts to dry your head with a hairdryer and use an electric shaver while in the bathroom, adding water to the switched on electric kettle and other options when the device comes into contact with water can cause electric shock.
Temporary wiring on twists- often in everyday life, in order to speed up the supply of voltage and not spend a lot of time on a full-fledged laying in the wall, or at least a channel, make the connection in an open way. It is these "snot" hung in the context of all norms around the house, barn or garage that can cause electric shock.

In production

The vast majority of work that is performed in production provides for a number of measures aimed at preventing electric shock. But, due to the violation of these measures and rules, personnel in contact with electrical installations or simply performing work in the immediate vicinity may be exposed to voltage.

Consider the most common causes electric shock at work:

- Lack of protective equipment or use of unsuitable. This is especially true in situations where any devices remain energized while working on them.
- Insulation failure and lack of grounding- in power circuits, this is damage to insulators, cable insulation and other severe damage to equipment. They cause the presence of potential on the hull, load-bearing structures, which can lead to fatal injury in case of contact. Initially, grounding is provided as insurance in case of damage to the insulation, so electric shock is possible only if there is no or faulty grounding.
- Electric arc burning- can occur as an integral part of the operation of the same switches, welding machines or short circuits, and an emergency. An arc strike can cause burns, characterized by the transfer of part of the charge and the subsequent passage of current through a person.
- Falling wires to the ground- creates a danger zone, which is 10 m for open areas and 8 m for indoors. In this space, currents spread if the protection does not turn off the line. Due to the spreading of currents on the ground surface, a potential is formed, which decreases in proportion to the distance from the point of incidence. In such a zone, the cause of the lesion is formed by the potential difference between the feet of a person.
- Violation of safety signs– most of the dangerous places at the enterprise are fenced off. On the fence itself or in places where voltage is possible, temporary or permanent signs or posters are installed. In the event that a person intentionally or negligently violates the requirements of the signs, an electric shock may occur.
- If switching or operation has not taken place or is not completely. Since most high-voltage equipment is controlled remotely, and the nodes electrical contacts in switches and disconnectors it is quite difficult to control, information about the absence of voltage is obtained through pointers or signaling devices. In the case when, for mechanical reasons, the switch or disconnector did not turn off at least one of the phases, there is a threat of electric shock in some section of the network, so it is imperative to use the pointer.
- Wrong voltage supply- when performing work with the removal of voltage, a potential can be accidentally applied to the line or to the electrical installation both by employees and as a result of an emergency. If the personnel goes beyond the protective zone, fenced with grounding, or does not install them at all, then there is a danger of electric shock for them.
- Induced voltage- It is the most dangerous factor in de-energized wires and neutral elements (sections of the conductor enclosed by two insulators). In production, the most dangerous is the defeat of direct current. Because the frequency of the alternating current drops to zero on its own and rises again, due to which its effect is inconsistent.
- Violation of the procedure for removing or hanging grounding- according to the requirements of the rules, when installing the ground, it is first connected to the ground, and then hung on the conductor. Otherwise, if there is a potential in the line, the worker will first bring the ground to the line potential, and when he tries to connect it to the ground loop, he himself will become an element in the current flow circuit. Grounding is removed in the reverse order - first it is removed from the current-carrying elements, and then disconnected from the circuit. When removed, there is also a similar threat.

What to do in case of electric shock?

If you witness someone being electrocuted and still under its influence, you need to get them free as soon as possible. Since the outcome of an electrical injury directly depends on the duration of contact, the response speed should be maximum.

First, it is necessary to de-energize the electrical installation or its parts with which a person interacts. The best for this are automatic switches, switches or fuses located in the immediate vicinity. For high-voltage networks, their analogues are switches and disconnectors. If these are not available, other measures may be used to reduce the duration of exposure.

by the most important rule upon release, it is the observance of the safety rules by the rescuer himself, so that he does not get struck by the current. Otherwise, to prevent death, any means will do.

Release up to 1000 V

For lines up to 1 kV, any dry clothing wrapped around the hand can be suitable, ideally these should be dielectric gloves. They can pull off the victim by the lagging ends of just dry clothes. Use a tool with insulated handles to cut through the wire. It is also possible to break the electrical circuit by placing a dielectric sheet between the victim and the ground.

In devices above 1 kV, it is dangerous to approach the victim already because the rescuer himself can fall under step voltage. But, at the same time, you can make a sketch of any uninsulated wire between the source and the victim. Try to pull the wire with an insulating rod, but with dielectric gloves. The cable, also with gloves, is allowed to cut phase by phase with an ax.

Measures for protection against electric shock

To avoid electric shock and minimize the causes that can cause it, it is enough to follow a number of simple rules:

Don't touch electrical appliances, switches, plugs, sockets with wet hands;
Do not allow faulty devices or devices that do not have case grounding to be connected to the network (absence is allowed only for devices designed for very low voltage);
Do not violate the instructions prescribed by electrical signs that regulate certain actions;
Do not leave appliances turned on when leaving the house, do not allow the plug to be pulled out by the cord;
When working in electrical installations, it is imperative to comply with the requirements of the rules, instructions, the order of technological processes;
Work in electrical installations should only be carried out using necessary funds protection.

Video in the development of the topic

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, short circuit of the network phase to the 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 current-carrying parts; * lightning discharge into electrical installation, etc. 4. The occurrence of step voltage on the plot of land where the person is located, as a result of: * phase short circuit to the ground; * removal of potential by an extended conductive object (pipeline, railway rails); *faults 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.

146. The concept of step voltage and touch voltage

In any electrical networks a person in the zone of current spreading may be under step voltage and touch voltage. Step voltage(step voltage) is the voltage between two points of the current circuit, located one from the other at a step distance (0.8 m) and on which a person is simultaneously standing. 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. The touch voltage is the voltage between two points of the current circuit, which are simultaneously touched by a person. The danger of such a touch is estimated by the value of the current passing through the human body, or by the voltage of the touch, and depends on a number of factors: the circuit for closing the current circuit through the human body, the network voltage, the circuit of the network itself, the mode of its neutral.

Passing through the body, the electric current causes thermal, electrolytic and biological effects.

thermal action It is expressed in burns of certain parts of the body, heating of blood vessels and nerve fibers.

Electrolytic action expressed in the decomposition of blood and other organic fluids, causing significant violations of their physico-chemical compositions.

Biological action manifests itself in irritation and excitation of living tissue of the body, which may be accompanied by involuntary convulsive contraction of muscles, including the muscles of the heart and lungs. As a result, various disorders in the body may occur, including a violation and even a complete cessation of the activity of the respiratory and circulatory organs.

The irritating effect of current on tissues can be direct, when the current passes directly through these tissues, and reflex, that is, through the central nervous system, when the current path lies outside these organs.

All the variety of action of electric current leads to two types of damage: electrical injuries and electric shocks.

electrical injury- these are clearly defined local damage to body tissues caused by exposure to electric current or an electric arc (electric burns, electrical signs, skin plating, mechanical damage).

electric shock- this is the excitation of the living tissues of the body by an electric current passing through it, accompanied by an involuntary convulsive contraction of the muscles.

Distinguish four degrees of electric shocks:

I degree - convulsive muscle contraction without loss of consciousness;

II degree - convulsive muscle contraction with loss of consciousness, but with preserved breathing and heart function;

III degree - loss of consciousness and impaired cardiac activity or respiration (or both);

Grade IV - clinical death, that is, the absence of breathing and blood circulation.

Clinical ("imaginary") death It is a transitional process from life to death that occurs from the moment the activity of the heart and lungs ceases. The duration of clinical death is determined by the time from the moment of cessation of cardiac activity and respiration until the onset of death of cells of the cerebral cortex (4-5 minutes, and in the case of death of a healthy person from random causes - 7-8 minutes). Biological (true) death- this is an irreversible phenomenon, characterized by the cessation of biological processes in the cells and tissues of the body and the breakdown of protein structures. Biological death occurs after the period of clinical death.

Thus, causes of death from electric shock there may be a cessation of the heart, cessation of breathing and electric shock.

Cardiac arrest or fibrillation, that is, chaotic rapid and multi-temporal contractions of the fibers (fibrils) of the heart muscle, in which the heart stops working as a pump, as a result of which blood circulation in the body stops, can occur with the direct or reflex action of an electric current.

The cessation of breathing as the root cause of death from electric current is caused by a direct or reflex effect of the current on the muscles of the chest involved in the breathing process (as a result - asphyxia or suffocation due to lack of oxygen and excess carbon dioxide in the body).

Types of electrical injuries:

- electrical burns –

Skin electroplating

electrical signs

Electric shocks

Electrophthalmia

Mechanical damage

Electrical burn and arise under the thermal action of an electric current. The most dangerous are burns resulting from exposure to an electric arc, since its temperature can exceed 3000 ° C.

Skin electroplating- penetration into the skin under the action of an electric current of the smallest particles of metal. As a result, the skin becomes electrically conductive, i.e., its resistance drops sharply.

electrical signs- spots of gray or pale yellow color, arising from close contact with a current-carrying part (ps of which an electric current flows in working condition). The nature of electrical signs has not yet been sufficiently studied.

Electrophthalmia- damage to the outer shells of the eyes due to exposure to ultraviolet radiation from an electric arc.

Electric shocks - a common lesion of the human body, characterized by convulsive contractions muscles, disorders of the human nervous and cardiovascular systems. Often, electrical shocks are fatal.

Mechanical damage(tissue tears, fractures) occur with convulsive muscle contraction, as well as as a result of falls when exposed to electric current.

The nature of electric shock and its consequences depend on the value and type of current, the path of its passage, the duration of exposure, the individual physiological characteristics of a person and his condition at the time of the defeat.

electric shock- this is a severe neuro-reflex reaction of the body in response to strong electrical stimulation, accompanied by dangerous disorders of blood circulation, respiration, metabolism, etc. This state can last from several minutes to a day.

	At AC 50 Hz	At DC
	The appearance of sensation, slight trembling of the fingers	Not felt
	Cramps in the hands	Sensation, heating of the skin Increasing heating
	Hands are difficult, but still can be torn off the electrodes; severe pain in the hands and forearms	Heating boost
	Hands become paralyzed, it is impossible to tear them off the electrodes, breathing is difficult	Slight muscle contraction
	Stopping breathing. The onset of cardiac fibrillation	Strong heating; contraction of the muscles of the hands; shortness of breath
	Respiratory and cardiac arrest (with exposure duration of more than 3 s)	Respiratory arrest

43. The impact of electric current on the human body. General and local injuries

Passing through the human body, the electric current has a thermal, electrolytic, mechanical and biological effect on it.

An electric shock occurs when an electrical circuit is closed through the human body. The most common cases of electric shock in cases where a person touches two or one wire, while having contact with the ground. In the first case, the touch is called two-phase, in the second - single-phase.

With a two-phase touch (Fig. 10-1), a person is exposed to line voltage, so a large current flows through him

where is the line voltage and the average (with good contacts) resistance of the human body. The current in this case is deadly, although a person can be well isolated from the ground.

In the case of a single-phase contact in a network with a grounded neutral wire (Fig. 10-2), a series circuit is formed from the resistances of the human body, shoes, floor and grounding of the neutral (neutral wire) of the current source. A phase (and not linear, as in the previous case) voltage is applied to this circuit. However, if a person in wet or nailed shoes stands on damp ground or on a conductive floor, then these resistances, like the resistance (10 ohms), are negligible compared to the resistance of the human body. Current will flow in this circuit:

This current is deadly.

However, if a person is wearing special rubber shoes and is on a dry wooden floor, then, assuming the resistance of the shoes is 45,000 ohms and the floor is 100,000 ohms, in the circuit under consideration we get the current value:

i.e. harmless to humans. The last case shows how important it is for safety reasons to use non-conductive shoes and especially an insulating floor.

In the case of a single-phase contact with a network with an isolated neutral, the circuit closes through the human body and through the imperfect insulation of the network wires (Fig. 10-3). In good condition, the insulation has a very high resistance, so such a touch should not be dangerous. This is true only for normal (fail-safe) networks. In networks with a voltage of 1000 V or more, the capacitance between phases and ground can create a large capacitive current that is dangerous to humans.