What are the causes of electric shock? Electrical safety at work What determines the degree of electric shock

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, however, to 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 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:

1. Touch exposed wires.
2. Activate broken electrical appliances, because in which case they can cause a fire or shock you.
3. Touch the wires with wet hands (especially if they are bare).

NECESSARY:

1. Remember that in no case should you pull on the wire in order to pull it out of the socket.
2. When leaving home, check to see if any electrical appliance has been left on.
3. 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 shocks 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:

1. Human interaction with faulty household electrical appliances.
2. Touching bare parts of the electrical installation.
   
3. 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:
   
4. The appearance of voltage on the body of equipment, which, under normal conditions, should not be energized.
5. Electric shock due to a faulty power line.
6. 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.
7. 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.
   
8. 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.
9. 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.
10. 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.

The causes of electrical accidents are many and varied. The main ones are:

1) accidental contact with open live parts under voltage. This can occur, for example, during the production of any work near or directly on live parts: in the event of a malfunction of protective equipment, through which the victim touched live parts; when carrying long metal objects on the shoulder, which can accidentally touch uninsulated electrical wires located at an accessible height in this case;

2) the appearance of voltage on the metal parts of electrical equipment (housings, casings, fences, etc.), which are not energized under normal conditions. Most often, this can occur due to damage to the insulation of cables, wires or windings of electrical machines and apparatus, which, as a rule, leads to a short circuit to the case;

3) the appearance of voltage on the disconnected current-carrying parts as a result of the erroneous switching on of the disconnected installation; short circuits between disconnected and energized live parts; lightning discharge into the electrical installation and other reasons

4) an electric arc that can form in electrical installations with a voltage of over 1000 V between a live part and a person, provided that the person is in close proximity to the live parts;

5) the occurrence of a step voltage on the earth's surface when the wire is shorted to the ground or when current drains from the ground electrode into the ground (in the event of a breakdown to the body of grounded electrical equipment);

6) other reasons, which include such as: uncoordinated and erroneous actions of personnel, leaving electrical installations energized without supervision, admission to repair work on disconnected equipment without first checking for a lack of voltage and a malfunction of the grounding device, etc.

All cases of electric shock to a person as a result of an electric shock are possible only when the electrical circuit is closed through the human body, that is, when a person touches at least two points of the circuit between which there is some voltage.

The voltage between two points in the current circuit, which are simultaneously touched by a person, is called the touch voltage.

A touch voltage of 20 V is considered safe in dry rooms, because the current passing through the human body will be below the threshold non-letting one, and the person who received an electric shock will immediately tear his hands off the metal parts of the equipment.

In damp rooms, a voltage of 12 V is considered safe.

The step voltage is the voltage between the points of the earth, due to the spreading of the fault current to the ground while simultaneously touching the person's legs. The greatest electrical potential will be at the point of contact of the conductor with the ground. As we move away from this place, the potential of the ground surface decreases and at a distance of approximately 20 m, it can be taken equal to zero. Damage with step voltage is aggravated by the fact that due to convulsive contractions of the muscles of the legs, a person can fall, after which the current circuit closes on the body through the vital organs.

safety vital activity injury current fire

The most widely used at the moment are three-phase three-wire networks with a solidly grounded neutral and three-phase four-wire networks with an isolated neutral of a transformer or generator.

Solidly grounded neutral - the neutral of a transformer or generator, connected directly to the grounding device.

Isolated neutral - the neutral of a transformer or generator that is not connected to an earthing device.

To ensure safety, there is a division of the operation of electrical installations (electrical networks) into two modes:

• - normal mode, when the specified values ​​of the parameters of its operation are provided (there are no short circuits to the ground);
• - emergency mode in case of a single-phase earth fault.

In normal operation, the network with isolated neutral is the least dangerous for a person, but it becomes the most dangerous in emergency mode. Therefore, from the point of view of electrical safety, a network with an isolated neutral is preferable, provided that a high level of phase isolation is maintained and emergency operation is prevented.

In a network with a solidly grounded neutral, it is not required to maintain a high level of phase isolation. In emergency mode, such a network is less dangerous than a network with an isolated neutral. A network with a solidly grounded neutral is preferable from a technological point of view, since it allows you to simultaneously receive two voltages: phase, for example, 220 V, and linear, for example, 380 V. In a network with an isolated neutral, you can get only one voltage - linear. In this regard, at voltages up to 1000 V, networks with a dead-earthed neutral are more often used.

There are a number of main causes of accidents caused by exposure to electric current:

• - accidentally touching or approaching a dangerous distance to live parts under voltage;
• - the appearance of voltage on the metal structural parts of electrical equipment (casings, casings, etc.), including as a result of damage to the insulation;
• - the appearance of voltage on disconnected current-carrying parts on which people work, due to the erroneous switching on of the installation;
• - 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 the following:

• - ensuring the inaccessibility of live parts under voltage;
• - electrical separation of the network;
• - elimination of the danger of damage when voltage appears on cases, casings and other parts of electrical equipment, which is achieved by using low voltages, using double insulation, potential equalization, protective grounding, grounding, protective shutdown, etc.;
• - the use of special electrical protective equipment - portable devices and devices;
• - organization of safe operation of electrical installations.

double insulation- this is electrical insulation, consisting of working and additional insulation. Working insulation is designed to isolate the current-carrying parts of the electrical installation and ensures its normal operation and protection against electric shock. Additional insulation is provided in addition to the working insulation to protect against electric shock in case of damage to the working insulation. Double insulation is widely used in the creation of manual electric machines. In this case, grounding or zeroing of the cases is not required.

Protective earth- this is an intentional electrical connection to earth or its equivalent of exposed conductive parts (accessible to the touch conductive parts of an electrical installation that are not energized in normal operation, but may be under it if the insulation is damaged) to protect against indirect contact, from static electricity accumulating during friction of dielectrics, from electromagnetic radiation, etc. The equivalent of land can be river or sea water, quarry coal, etc.

With protective earthing, the earthing conductor connects the open conductive part of the electrical installation, for example, the housing, to the earthing conductor. A grounding conductor is a conductive part that is in electrical contact with the ground.

Since the current follows the path of least resistance, it is necessary to provide a small resistance of the grounding device (grounding conductor and grounding conductors) compared to the resistance of the human body (1000 Ohm). In networks with voltage up to 1000 V, it should not exceed 4 ohms. Thus, in the event of a breakdown, the potential of the grounded equipment decreases. The potentials of the base on which the person stands and the grounded equipment are also equalized (by raising the potential of the base on which the person stands to a value close to the value of the potential of the open conductive part). Due to this, the values ​​of the touch and step voltages of a person are reduced to an acceptable level.

As the main means of protection, grounding is used at voltages up to 1000 V in networks with isolated neutral; at voltages above 1000 V - in networks with any neutral mode.

Zeroing- intentional electrical connection with a neutral protective conductor of metal non-current-carrying parts that may be energized, for example, due to a short to the housing. It is necessary to provide protection against electric shock in case of indirect contact by reducing the voltage of the case relative to the ground and limiting the time for the passage of current through the human body by quickly disconnecting the electrical installation from the network.

The principle of zeroing operation is that when a phase wire is closed to a zeroed housing of an electrical consumer (electrical installation), a single-phase short-circuit current circuit is formed (that is, a short circuit between the phase and neutral protective conductors). The single-phase short-circuit current causes the overcurrent protection to operate. Fuses, circuit breakers can be used for this. As a result, the damaged electrical installation is disconnected from the mains. In addition, before the operation of the overcurrent protection, the voltage of the damaged case decreases relative to the ground due to the action of re-grounding the zero protective conductor and the redistribution of voltage in the network during the flow of a short circuit current.

Zeroing is used in electrical installations with voltages up to 1000 V in three-phase AC networks with a grounded neutral.

Safety shutdown- this is a high-speed protection that provides automatic shutdown of an electrical installation when there is a danger of electric shock to a person in it. Such a danger may arise, in particular, when a phase is shorted to the case, the insulation resistance drops below a certain limit, and also if a person touches directly live parts that are energized.

The main elements of the residual current device (RCD) are the residual current device and the executive body.

Residual shutdown device - a set of individual elements that perceive the input value, react to its changes and, at a given value, give a signal to turn off the switch.

The executive body is an automatic switch that ensures the shutdown of the corresponding section of the electrical installation (electrical network) upon receipt of a signal from the residual current device.

The action of the protective shutdown as an electrical protective agent is based on the principle of limiting (due to a quick shutdown) the duration of the current flow through the human body when it inadvertently touches the electrical installation elements that are energized.

Of all the known electrical protective equipment, the RCD is the only one that protects a person from electric shock by direct contact with one of the current-carrying parts.

Another important property of the RCD is its ability to protect against fires and fires that occur at facilities due to possible damage to the insulation, faulty wiring and electrical equipment.

Scope of RCD - networks of any voltage with any neutral mode. But they are most widely used in networks with voltages up to 1000 V.

Electrical protective equipment - these are portable and transportable products that serve to protect people working with electrical installations from electric shock, from the effects of an electric arc and electromagnetic field.

By appointment, electrical protective equipment (EPS) is conditionally divided into insulating, enclosing and auxiliary.

Insulating EZS serve to isolate a person from parts of electrical equipment under voltage, as well as from the ground. For example, insulating handles of a fitter's tool, dielectric gloves, boots and galoshes, rubber mats, tracks; stands; insulating caps and linings; insulating stairs; insulating pads.

Enclosing EZS are designed for temporary fencing of current-carrying parts of electrical installations under voltage. These include portable fences (screens, barriers, shields and cages), as well as temporary portable grounding. Conditionally, warning posters can also be attributed to them.

Auxiliary protective equipment is used to protect personnel from falling from a height (safety belts and safety ropes), to safely climb to a height (ladders, claws), as well as to protect against light, thermal, mechanical and chemical influences (safety glasses, gas masks, gloves , overalls, etc.).

The most frequent cases:

• accidental contact with live parts under voltage (bare wires, contacts of electrical equipment, tires, etc.);
• the sudden appearance 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.
• electric shock to a person who accidentally found himself under voltage. Currents through the human body of the order of 0.05-0.1 A are dangerous, large values ​​​​can be fatal;
• overheating of wires or an electric arc between them during short circuits, which leads to human burns or fires;
• overheating of damaged areas of insulation between wires by currents, leakage through the insulation, which can lead to spontaneous combustion of the insulation;
• overheating of electrical equipment cases due to their overload.

To ensure security, you must:

eliminate the possibility of a person touching live parts, which is achieved by concluding electrical equipment in closed cases and turning it off during repairs;

if possible, use safe low voltages up to 36 V when using portable electrical equipment;

maintain a high level of isolation relative to earth;

reduce the effect of wire capacitance;

use protective earth (ground wire);

use network-wide leakage protection devices in networks with deaf neutral grounding.

In a network with grounding, the connection of electrical equipment cases to separate grounding conductors that are not connected to the neutral wire is prohibited.

The effect of electric current on the human body

The action of electric current on the human body is manifested in the following forms: thermal, electrolytic, mechanical, biological.

Thermal impact manifests itself in the form of current and arc burns.

Degrees of burn: redness, blistering, tissue necrosis, charring. In this case, the area of ​​damage should be taken into account.

In case of electric shock, a person may receive local electrical injury or electric shock.

Local electrical injuries: burns, metallization of the skin, electrical signs, electrophthalmia.

The electrolytic effect is manifested in the form of damage to internal organs due to electrochemical reactions in the human body.

Mechanical action can be direct or indirect. Direct mechanical action manifests itself in the form of a rupture of muscle tissues and walls of blood vessels due to the transformation of lymph or blood into steam. Indirect mechanical impact is manifested in the form of bruises, dislocations, fractures with sharp involuntary convulsive muscle contractions.

The biological effect is manifested in the form of an electric shock - the impact of an electric current on the central nervous system.

Electric shock has several degrees:

slight trembling in the joints, mild pain,

severe pain in the joints,

loss of consciousness and disturbance of cardiac activity or breathing,

loss of consciousness and cardiac arrest or respiratory arrest,

loss of consciousness, cardiac arrest, respiratory arrest, i.e. state of clinical death.

The degree of electric shock to a person is significantly affected by: the magnitude of the current, the duration of the current flow through the human body, the flow path, and the condition of the skin.

According to the magnitude and effect of the current on the human body, a tangible current and a non-releasing current are distinguished, in which the victim cannot unclench his hand on his own. Perceptible current - constant about 5 - 8 mA, variable - about 1 mA.

The value of the non-releasing current is about 15 - 30 mA. Currents greater than 30 mA are considered dangerous.

The value of the resistance of the human body, depending on external conditions, can vary over a wide range - from several hundred ohms to tens of kilohms. A particularly sharp drop in resistance is observed at voltages up to 40-50 V, when the resistance of the human body decreases tenfold. However, when carrying out calculations for electrical safety in networks with voltages above 50 V, it is customary to consider the resistance of the human body to be 1000 ohms.

The duration of the current flow and the magnitude of the allowable current are related by the empirical formula

The shorter the duration of current flow, the greater the value of the allowable current. If At \u003d 16 ms, then the value of the permissible current is 30 mA.

This current value determines the insulation requirements. So, for example, for a network with a phase voltage of 220 V, the insulation resistance must be at least

What is the general characteristic of the distribution of electrical injuries in railway transport?

On railways, more than 70% of cases of electrical injury occur in the power supply and locomotive facilities. It is necessary to pay maximum attention to the prevention of electrical injuries here, since electrical installations and power lines are the main object of service and the subject of labor.

More than 8% of cases of electrical injury occur in places with increased danger and especially dangerous (contact network, overhead power lines, etc.).

An analysis of the distribution of electrical injuries depending on the month, day of the week, decade and time of the incident during the day shows the following trend. The main share of electrical injuries falls on the period from June to September, when the largest amount of work is planned for all the facilities of the Ministry of Railways. On the days of the week, electrical injuries are distributed almost evenly, with the exception of Saturday and Sunday, when the amount of work is significantly reduced and mainly troubleshooting is carried out in emergency cases. The most unfavorable is the second decade. It accounts for 44 to 52% of all injuries. In terms of work completion time from their start, the largest number of cases occurs at the approaching lunch break (after 3-4 hours from the start of work). A large percentage of electrical injuries occur at the end of the working day due to fatigue, as well as haste at the end of work.

The largest number of accidents occurs during repair work - about 50%. The number of accidents during installation work is increasing. This indicates the insufficient use of existing protective equipment by maintenance personnel.

What are the causes of electric shock?

The main causes of accidents in the economy of electrification and power supply are non-shutdown of electrical installations, non-use of portable grounding and protective helmets, violation by workers of the dimensions of zones that are dangerous in relation to approaching live or grounded parts when working with de-energized or energized, lack of supervision on the part of work managers for performing operations in high-risk areas. Due to gross violations of safety regulations, when work is carried out without removing the voltage on live parts and near them, more than 88% of all accidents occur.

The cause of electrical injuries is often the inconsistency of work with the task, specialty and qualification group of the employee. Their share is more than 9%. The number of cases of electrical injuries occurring due to the supply of voltage to the work area without warning is from 22 to 32%. Electrical injuries also occur when wires sag or are very close together - up to 10-15% of cases, which indicates poor-quality maintenance of this line.

Accidents mainly occur along the external current circuit along the “phase-ground” path, therefore it is necessary to use protective grounding of electrical installations, follow the requirements of the instructions for grounding power supply devices on electrified railways.

The most frequent cases of current flow through the human body along the path "arm - arm" and "arm - legs". To prevent this, it is imperative to use special work shoes.

What organizational measures are required to be taken to prevent electrical injuries?

To prevent electrical injury, you must:

• improve the system of training in safe work practices;
• improve the quality of the briefing before starting work;
• improve the system of legal education;
• improve the qualifications of personnel in order to master safe labor practices;
• strengthen control over the implementation of fundamental standards;
• systematically conduct certification and certification of workplaces.

The education system should be improved by using a variety of visual aids and technical means in the educational process: photo showcases, operating layouts, control and teaching machines. movies, video recorders. The acquisition of safe work skills is facilitated by the creation and use of training grounds equipped with operating models of structures that imitate electrical equipment.

To increase the responsibility of personnel in terms of the unconditional implementation of safety regulations in accordance with the briefing, it is advisable to issue warning cards. In case of violation of safety regulations, it is necessary to withdraw coupons and assign violators a re-examination in safety regulations.

The improvement of legal education is facilitated by the quarterly holding of the day of labor law, when consultations are given on issues of labor legislation.

Improving the quality of vocational training, reducing the number of errors in the preparation of orders, reducing the time for their execution is also facilitated by the widespread introduction of technological cards for the maintenance and repair of power supply devices and the introduction of training cards and knowledge testing.

What technical means increase the safety of maintenance of power supply devices?

To prevent injuries when working in KSO-type chambers, a blocking lock is installed on the drives of the grounding knives, as a result of which access to the chamber with disconnected grounding knives is impossible.

A special device has been created to monitor the insulation and condition of AC and DC operational circuits without disconnecting their power source.

A device for monitoring the serviceability of 110 kV bushings has been developed and is being used to detect partial breakdowns, moisture and complete overlaps in the main insulation of power transformer bushings.

Hazardous voltage signaling device type SOPN-1 allows you to remotely and directionally control the presence of voltage (working or induced) in electrical installations of alternating current and contact network from the ground

direct current.

A device for signaling the danger of approaching high-voltage installations has been developed and is being used.

These and some other tools have been developed by scientists and specialists from the electrical laboratory of the Moscow Institute of Railway Engineers.

The Department of Power Supply of Electric Railways of the Rostov Institute of Railway Engineers, in collaboration with specialists from the research and production laboratory of the North Caucasus Road, developed and introduced into trial operation a non-contact voltage indicator BIN-BU (universal). It is designed to remotely detect the presence of voltage on the current-carrying parts of AC and DC electrical installations with voltages from 3.3 to 110 kV. The objects of indication can be a contact network, traction substations, as well as power lines.

When preparing a workplace with de-energizing the contact network, there are cases when it remains energized due to the rotation of the shaft of the mast disconnector, shunting of the air gap and false tele-alarm. The Zlatoust power supply distance of the South Ural Road has created an RKN voltage control relay, which is installed at a substation or on a stage at the points of parallel connection of the contact network with the output of the RKN contacts to the TU-TS rack for remote signaling to the energy dispatcher about the presence or absence of voltage in the contact network.

Polymer insulating elements are widely used in contact network devices, on overhead lines and other electrical installations. The service life and reliability of their operation depend on the influence of ultraviolet rays, dust, snow, ambient temperature, relative humidity, contact with water and mechanical stress. By analogy with porcelain insulators, it is possible to overlap them in cases of contamination, and when the protective cover (coating) is depressurized and moisture gets on the supporting fiberglass rod, small currents can flow through it. This can lead to a deterioration in the electrical insulating properties and a decrease in mechanical strength. To control the tick along the entire insulating element, especially on sectional and mortise insulators (without their dismantling), a device for monitoring the insulating properties of polymer insulating elements (UCIP) has been developed.

For grounding wires of both the contact network and overhead lines (with a cross section of 6 to 18 mm2), a clamp was developed by rationalizers of the Petropavlovsk power supply section. The clamp allows you to hang the grounding rod also on the strip clamp. The principle of attaching the rod clamp to the wires is self-tightening. The clamp is removed from the wire by a sharp upward movement of the rod. The design of the clamp is convenient to use and ensures reliable contact with the wire.

A device for ensuring electrical safety during track work during the overhaul of one of the tracks of a multi-track section of a seamless track, electrified by an alternating current system. when trains continue to run on the existing tracks, it allows to ensure the safety of workers involved in the repair of the track.

In parentheses after the question are the numbers of regulatory documents on labor protection used in the formation of the answer -

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