Action Email current on the human body, types of exposure, types of damage

electrical safety b is a system of organizational and technical measures and means that ensure the protection of people from the harmful and dangerous effects of electric current, electric arc and static electricity in order to reduce electrical injuries to an acceptable level of risk and below.

A distinctive feature of electric current from other industrial hazards and hazards (except radiation) is that a person is not able to detect electrical voltage remotely with his senses.

In most countries of the world, the statistics of accidents due to electrical shock shows that the total number of injuries caused by electrical current with loss of ability to work is small and amounts to approximately 0.5-1% (in the energy sector - 3-3.5%) of the total number of accidents. in production. However, with a fatal outcome, such cases in the workplace are 30-40%, and in the energy sector up to 60%. According to statistics, 75-80% of fatal electric shocks occur in installations up to 1000 V.

Electric current flows through the human body if there is a potential difference between its two points. The voltage between two points in a current circuit touched by a person at the same time is called touch voltage

The effect of electric current on the human body

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: electric 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, metallization of the skin, 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 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.

In this way, 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 fast 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.

Basically, the value and type of current determine the nature of the lesion. In electrical installations up to 500 V, alternating current of industrial frequency (50 Hz) is more dangerous for humans than direct current. This is due to complex biological processes occurring in the cells of the human body. With an increase in the frequency of the current, the danger of injury decreases. At a frequency of the order of several hundred kilohertz, electric shocks are not observed. Currents, depending on the value, according to their effect on the human body, are divided into tangible, not letting go and fibrillatory.Sensible currents- currents that cause perceptible irritations when passing through the body. The person begins to feel the impact alternating current(50 Hz) at values ​​from 0.5 to 1.5 mA and direct current from 5 to 7 mA. Within these values, slight trembling of the fingers, tingling, heating of the skin (with direct current) are observed. Such currents are called threshold sensible currents.

Non-release currents cause convulsive contraction of the muscles of the hand. The smallest current value at which a person cannot independently tear his hands off current-carrying parts is called threshold non-release current. For alternating current, this value lies in the range from 10 to 15 mA, for direct current - t 50 to 80 mA. With a further increase in current, damage to the cardiovascular system begins. It becomes difficult, and then stops breathing, the work of the heart changes.

fibrillation currents cause fibrillation of the heart - fluttering or arrhythmic contraction and relaxation of the heart muscle. As a result of fibrillation, blood from the heart does not enter the vital organs and, first of all, the blood supply to the brain is disturbed. The human brain, deprived of blood supply, lives for 5-8 minutes, and then dies, so in this case it is very important to provide first aid to the victim quickly and in a timely manner. Fibrillation current values ​​range from 80 to 5000 mA

Factors influencing the outcome of the defeat El. current

The outcome of the impact of electric current on the human body depends on a number of factors, the main of which are: the electrical resistance of the human body; the magnitude of the electric current; the duration of its effect on the body; the amount of stress acting on the body; type and frequency of current; path of current flow in the body; psychophysiological state of the body, its individual properties; condition and characteristics environment(air temperature, humidity, air pollution and dust content), etc.

Current strengthI. Currents:

0,6 – 1,5 mA: there is a sensation (of change), not felt (constant)

5 - 7mA: convulsions in the hands (of change), there is a feeling (constant)

20 -25mA: threshold, not letting go - hands are paralyzed, it is impossible to tear them off the equipment, slowing down breathing (of change), slight muscle contraction (constant)

50 - 80mA: fibrillatory - arrhythmic contraction or relaxation of the heart muscles

The duration of the impact of current on the human body is one of the main factors. The shorter the exposure time, the less the danger.

If the current does not let go, but does not yet disrupt breathing and heart function, a quick shutdown saves the victim, who could not free himself. With prolonged exposure to current, the resistance of the human body drops and the current increases to a value that can cause respiratory arrest or even heart fibrillation.

Respiratory arrest does not occur instantly, but after a few seconds, and the greater the current through a person, the shorter this time. Timely shutdown of the victim helps prevent the cessation of the respiratory muscles.

Thus, the shorter the duration of the action of the current on a person, the less likely it is to coincide with the time during which the current passes through the heart with phase T.

The path of current in the human body. The most dangerous is the passage of current through the respiratory muscles and the heart. So, it was noted that along the “hand-hand” path, 3.3% of the total current passes through the heart, “ left hand- legs" - 3.7%, "right arm - legs" - 6.7%, "leg - leg" - 0.4%, "head - legs" - 6.8%, "head - arms" - 7 %. According to statistics, disability for three days or more was observed with the current path "arm - arm" in 83% of cases, "left arm - legs" - in 80%, "right arm - legs" - 87%, "leg - leg" - in 15% of cases.

Thus, the current path affects the outcome of the lesion; the current in the human body does not necessarily pass along the shortest path, which is explained by the large difference in the resistivity of various tissues (bone, muscle, fat, etc.).

The smallest current through the heart passes when the current travels along the lower loop "leg - leg". However, one should not draw conclusions from this about the low danger of the lower loop (the action of step voltage). Usually, if the current is large enough, it causes leg cramps and the person falls, after which the current can already pass through the chest, i.e. through the respiratory muscles and heart. Most dangerous- this is the path passing through the brain and spinal cord, heart, lungs

Type and frequency of current. It has been established that alternating current with a frequency of 50-60 Hz is more dangerous than direct current. since the same effects are caused by greater values ​​of direct current than alternating current. However, even a small D.C.(below the threshold of sensation) when the chain breaks quickly, it gives very sharp blows, sometimes causing cramps in the muscles of the hands.

Many researchers argue that the most dangerous is alternating current with a frequency of 50-60 Hz. The danger of the action of the current decreases with increasing frequency, but a current with a frequency of 500 Hz is no less dangerous than 50 Hz.

human body resistance inconstant and depends on many factors - the condition of the skin, the size and density of the contact, the applied voltage and the time of exposure to the current.

Usually, when analyzing the danger of electrical networks and in calculations, it is customary to consider the resistance of the human body as active and equal to 1 kOhm.

The nature of the damage also depends on the duration of the current. With prolonged exposure to current, the heating of the skin increases, the skin is moistened due to perspiration, its resistance drops, and the current passing through the human body increases sharply.

The nature of the lesion is also determined by the individual physiological characteristics of a person. If a person is physically healthy, then the electrocution will be less severe. With diseases of the cardiovascular system, skin, nervous system, with alcohol intoxication, electrical injury can be extremely serious even with small acting currents.

An important influence on the outcome of the lesion is exerted by the psychophysiological preparedness of the worker for the impact. If a person is attentive, focused when doing work, prepared for the fact that he may be exposed to electric current, then the injury may be less severe.

Environment PARAMETERS: temperature, humidity, dust

Physiological characteristics of the body at the time of injury

Applied voltage dependence is directly proportional

The phenomenon of current flowing into the ground

The foot-to-foot path is least dangerous. Most often, such a path occurs when a person falls under the influence of the so-called step voltage, that is, between points on the earth's surface that are at a step distance from each other.

If a ground fault occurs in any circuit - an accidental electrical connection of the current-carrying part directly to the ground or through metal structures, then an electric current will flow along the ground, called earth fault current. The potential of the earth, as it moves away from the place of the circuit, will change from the maximum to zero value,

because the ground resists the earth fault current.

Fig.1 Turning on a person for step voltage

If a person enters the zone of current spreading, then there will be a potential difference between his feet, which will cause the current to flow along the “foot - foot” path. The result of the action of the current may be the contraction of the muscles of the legs, and the person may fall. The fall will cause the formation of a new, more dangerous current circuit through the heart and lungs.

On fig. 3.1 shows the formation of a step voltage and shows the distribution curve of the potential on the surface of the earth. At a distance of 20 m from the fault, the potential can be considered equal to zero. Rice. 3.1. Turning a person on step voltage

The value of the current passing through the human body depends on the applied voltage and the resistance of the body. The higher the voltage, the more current flows through the person.

(I 2 - the path of passage is more dangerous and the current strength is higher)

Touch and step voltages

Step voltage - the voltage on the earth's surface between points that are at a step distance from each other.

Touch voltage - the potential difference of two points of electric. the chains of which a person touches at the same time.

To reduce the difference φ 2 -φ 1, you need to leave the spreading zone in small steps

Classification of premises according to the degree of danger of electric shock

electrical installations are the installations in which electrical energy is produced, converted, distributed and consumed. Electrical installations include generators and electric motors, transformers and rectifiers, wired, radio and television communication equipment, etc.

The safety of work in electrical installations depends on the electrical circuit and parameters of the electrical installation, rated voltage, environment and operating conditions. From the point of view of ensuring safety, all electrical installations according to the PUE are divided into installations up to 1000 V and installations above 1000 V. Since installations above 1000 V are more dangerous, they have more stringent requirements for protective measures.

Electrical installations can be located indoors and outdoors. Environmental conditions have a significant impact on the state of insulation of an electrical installation, on

the resistance of the human body, and therefore, to the safe? service personnel. Working conditions according to the degree of electrical safety are divided into three categories: with increased danger of electric shock to people; especially dangerous; without increased risk.

Terms with heightened danger the presence of one of the following features is characterized: - conductive bases (reinforced concrete, earthen, metal, brick);

Conductive dust that impairs cooling and insulation conditions, but does not cause a fire hazard;

Dampness (relative humidity exceeding 75%);

Temperature exceeding +35°C for a long time;

The possibility of simultaneous contact of a person with grounded metal structures, on the one hand, and with metal cases of electrical equipment, on the other.

To reduce the risk of electric shock under these conditions, it is recommended to use low voltage (no more than 42 V).

Particularly hazardous conditions characterized by the presence of one of the following features:

special dampness (relative humidity close to 100%);

chemically active environment that destroys insulation and current-carrying parts of electrical equipment;

at least two signs of increased danger.

In conditions without increased danger, the above signs are absent

Today we have a very interesting and informative article about the effect of electric current on the human body.

I think that each of you at least once thought about the danger of electric current and its consequences. And someone can (God forbid, of course) experienced it on himself.

Introduction

The environment in which we live, as well as everything that surrounds us, contains a potential danger to us. One such threat is electric shock. Except natural environment(), there are also household and industrial ones, which are constantly developing and progressing (improvement of technology and the use of new developments), which means that they carry an even greater threat.

Despite the fact that the check of devices is carried out very high quality, no one is immune from errors and unforeseen situations.

Unfortunately, most often electric shock, both at work and at home, happens because precautions and elementary precautions are not followed.

The causes of malfunction and breakdown of appliances (when using an electric kettle, microwave oven, and other household appliances; , or at, or at and much more), used in everyday life, and electrical units and used directly in production.

As statistics show, the percentage of injuries received from electric shock is much lower compared to injuries received in other ways.

But with electric shock, the percentage of severe injuries and death is much higher.

What is electric current?

The effect of electric current on a person, as well as its consequences, can be better understood after we consider in more detail what a current is.

Electricity is the orderly movement of electrons in a conductor or semiconductor.

In a section of the circuit, the current strength is directly proportional to the voltage at the ends of the section (potential difference) and inversely proportional to the resistance of this section of the circuit -.

In the case when a person touches a conductor that is energized, he thereby includes himself in the circuit. A current will pass through the human body if it is not isolated from the ground, or if it touches the conductor simultaneously with another object that has the opposite potential.

This formula is applicable to two-phase, or it is also called two-pole contact with live parts under voltage. It looks like this:

When a person touches two phases of an electrical installation, a circuit appears through the human body, through which an electric current passes. The magnitude of the electric current in this case depends ONLY on the voltage of the electrical installation and the internal resistance of a person.

For example, the phase voltage of an electrical installation is 220 (V), the line voltage is 380 (V), respectively. Under normal conditions, the average human resistance is approximately 1000 (Ohm).

In this case, the current that will pass through a person when he simultaneously touches two phases (A and B) will be equal to 380 (mA). And this is deadly!

A little differently, the calculation of the current passing through the human body will occur if it touches one phase in a network with an isolated neutral.

In this case, the current circuit will close through the human body, then to the ground and through the phase capacitances.

What threatens the action of electric current?

Electric current produces the following effects on the human body passing through it:

1. Thermal

With such an impact, overheating occurs, as well as a functional disorder of the organs located in the path of the current.

2. Electrolytic

With the electrolytic action of the current in the liquid, which is in the tissues of the body, electrolysis occurs, including in the blood, due to which its physico-chemical composition is disturbed.

3. Mechanical

During mechanical action, tissue rupture and stratification occurs, impact action from the evaporation of fluid from the tissues of the human body. This is followed by a strong contraction of the muscles, up to their complete rupture.

4. Biological

The biological effect of the current carries irritation and overexcitation of the nervous system.

5. Luminous

This action causes damage to the eyes.

Consequences under the action of electric current

The depth and nature of the impact depends on:

• kind of current (alternating or direct) and its strength
• the time of its exposure and the path it takes through the person
• psychological and physiological state of the person.

So, for example, under normal conditions and the presence of dry, intact skin, the resistance of a person can reach several hundred (kOhm), but if the conditions are unfavorable, then the value can drop to one kiloohm.

Below, I will give you an example of a table of how an electric current of various sizes acts on the human body.

A current with a strength of about 1 (mA) will already be quite noticeable. At higher readings, painful and unpleasant muscle contractions in humans will be experienced.

With a current of 12-15 (mA), a person can no longer control his muscular system and is not able to independently break away from the damaging current source.

If the current is higher than 75 (mA), then its effect will lead to paralysis of the respiratory muscles and, consequently, to respiratory arrest.

If the current continues to increase, then the heart will fibrillate and stop.

More dangerous than direct current is alternating current.

It is also of no small importance what parts of the body a person touches the current-carrying part. The most dangerous are those paths during which the spinal cord and brain (head-legs and head-arms), lungs and heart (legs-arms) are affected.

The main damaging factors

1. Electric shock

It excites the muscles of the body, leads to convulsions, and then to respiratory and cardiac arrest.

2. Electrical burns

They result from the release of heat after the passage of current through the human body.

There are several types of burns that occur depending on the parameters of the electrical circuit, as well as the state of the person at that moment:

• skin redness
• blistering burns
• tissue charring is possible
• metallization of the skin, accompanied by the penetration of pieces of metal into it, in case of melting of the metal.

Contact voltage is the voltage that acts on a person during his contact with one pole, or with the phase of a current source.

The most dangerous areas of the body are the areas of the temples, back, backs of the hands, shins, back of the head, and also the neck.

Read my article about the group that happened to two electricians when switching in an electrical installation with a voltage of 10 (kV).

P.S. If you have any questions while reading the material, then ask about it in the comments.

The ordered movement of charged particles - electrons, ions, etc. is called electric current. For mankind for many years, electricity has been a mysterious phenomenon, because it cannot be seen. Electricity is generated when electrons move from one atom to another. The electrons carry negative charges, and the nuclei of atoms have a positive charge.

There are two types of electric current - direct and alternating. DC current moves in one direction. The movement of the alternating current changes at certain time intervals equal to fractions of a second.

How current affects the body

The human body contains many water and salt substances. Therefore, in direct contact with an electric current, it becomes a member of the electrical circuit.

The degree of consequences for a person in contact with a conductive element of electricity can be of different severity, up to fatal cases. The following factors matter:

• Duration of contact between the current and the body.
• Type of current. Variable is more dangerous.
• Areas of contact. Greatest Danger is formed if the heart muscle, respiratory organs, brain are included in the affected area.

The human body can react differently to electrical influences. The main varieties are presented in the table.

Which value is non-dangerous, dangerous and critical

The human body painfully reacts to contact with a current of more than 1 mA. Up to this value, exposure is considered non-hazardous.

• With an increase in current strength to 10 mA, a person experiences discomfort, muscles begin to contract painfully.
• With an electrical impact of 15 to 25 mA, convulsions develop, and a person is not able to free himself from a current-carrying source or object.
• If the values ​​reach from 25 to 80 mA, as a result of tonic spasms of the respiratory muscles and the glottis, respiratory arrest and paralysis of the nerve center responsible for respiratory function occurs.
• The current, the strength of which is more than 100 mA, disrupts the coronary blood supply, can cause fibrillation. Ventricular fibrillation is especially likely in situations where the electrical loop passes through the region of the heart muscle.

Symptoms:

When exposed to electric current, severe muscle pain occurs, convulsions begin. The injured person can be thrown away from the current-carrying source. Possible:

• Loss of consciousness for a short or long time.
• Sharp excitement.
• Headache.
• Confusion of consciousness, retrograde memory loss.
• Feeling of fear.
• Involuntary natural excretions - urination, defecation.
• Sharp weakness.

Heart sounds are muffled, bradycardia or tachycardia occurs, falls arterial pressure. Human breathing is difficult, asphyxia, the development of a terminal state and clinical death are possible.

Local signs are "current signs" - areas of necrosis on the skin, wounds or swelling, burns up to charring. When struck by lightning, a characteristic pigmentation appears on the skin, resembling a branched tree, which is of forensic significance.

Interesting! After an electrical injury, a violation of cardiac activity can occur within a few days, up to its termination.

First aid and treatment

When a victim is found, first of all, it is necessary to remove the electrical wires from him or get rid of contact with other electrical sources. The wire must be dropped with a wooden object, you need to stand on a rubber mat, put on rubber gloves on your hands. The electrical appliance is turned off.

The person should be taken to the hospital as soon as possible.

If the injury did not cause loss of consciousness, the injured person should be laid down, calmed down, and antihistamines - pipolfen, clemastine, dimedrol - should be administered.

For pain in the chest, give valocordin, validol.

If a person's cardiac and respiratory functions are suddenly disturbed, an indirect heart massage and artificial respiration begin. Do this until the person begins to breathe on their own.

In a hospital setting, the patient is intubated and artificially ventilated. If necessary, all resuscitation measures.

It should be remembered that even with a short-term loss of consciousness, a person must be hospitalized under medical supervision. To avoid long-term consequences.

The electrical saturation of modern production creates an electrical hazard, the source of which can be electrical networks, electrified equipment and tools, computer and organizational equipment that runs on electricity. This determines the relevance of the problem of electrical safety - the elimination of electrical injuries.

Electrical safety is a system of organizational and technical measures and means that ensure the protection of people from the harmful and dangerous effects of electric current, electric arc, electromagnetic field and static electricity.

In comparison with other types of industrial injuries, electrical injuries make up a small percentage, however, it occupies one of the first places in terms of the number of injuries with a severe and especially fatal outcome.

An analysis of industrial injuries in the meat industry shows that, on average, about 18% of all severe and fatal cases occur as a result of electric shock.

The largest number of electrical injuries (60-70%) occurs at work on electrical installations with voltage up to 1000 V. This is due to widespread such installations and the relatively low level of training of persons operating them. There are much fewer electrical installations over 1000 V in operation and they are serviced by specially trained personnel, which causes a smaller number of electrical injuries.

1. The effect of electric current on the human body

Electric current, passing through the human body, has a biological, electrolytic, 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.

Electrolytic action 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 subcutaneous tissues, up to charring. The mechanical action of the current is manifested in the stratification of tissues and even the separation of body parts.

There are two main types of damage to the body: electrical trauma and electrical shock. Often both types of damage accompany each other. However, they are different and should be considered separately.

Electrical injuries are clearly defined local violations of the integrity of body tissues caused by exposure to electric current or an electric arc. Usually these are superficial injuries, that is, lesions of the skin, and sometimes other soft tissues, as well as ligaments and bones.

The danger of electrical injuries and the complexity of their treatment are determined by the nature and degree of tissue damage, as well as the body's response to this damage. Usually, injuries are cured, and the victim's working capacity is restored completely or partially.

Sometimes (usually with severe burns) a person dies. In such cases, the immediate cause of death is not electric current, but local damage to the body caused by current.

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

Electrical burns are the most common electrical injury. They make up 60-65%, and 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 electric current flow occurs 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.

An arc burn is caused by the action of 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 from 1000 V to 10 kV or erroneous operations of personnel. The defeat arises from a change in the 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).

Electric 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 wrinkles.

In most cases, electrical signs are painless, and their treatment ends safely: over time, the top layer of the skin and the affected area acquire their original color, elasticity and sensitivity. Signs occur in about 20% of those affected by the current.

Metallization of the skin is the penetration into its upper layers of particles of metal that has 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 has a rough surface, the color of which is determined by the color of the metal compounds that have fallen under the skin: green - in contact with copper, gray - with aluminum, blue-green - with brass, yellow-gray - with lead. Usually, over time, the diseased skin disappears and the affected area becomes normal. At the same time, all the painful sensations associated with this injury also disappear.

Metallization of the skin is observed in approximately one in ten of the victims. Moreover, in most cases, simultaneously with metallization, an electric arc burn occurs, which almost always causes more severe injuries.

Electrophthalmia is an inflammation of the outer membranes of the eyes as a result of exposure to a powerful stream of ultraviolet rays, causing chemical changes in the cells of the body. 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 visible light but also ultraviolet and infrared rays. Electrophthalmia occurs relatively rarely (in 1-2% of victims), most often during electric welding.

Mechanical damage is the result of sharp, involuntary convulsive muscle contractions under the influence of a current passing through a person. As a result, ruptures of the skin, blood vessels and nervous tissue can occur, as well as dislocations of the joints and even bone fractures. These injuries are usually serious injuries that require long-term treatment. Fortunately, they rarely occur - no more than 3% of those affected by the current.

Electric shock is the excitation of living tissues by an electric current passing through the body, accompanied by involuntary convulsive muscle contractions.

Depending on the outcome of the negative impact of current on the body, electric shocks can be conditionally divided into the following four degrees:
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 respiration (or both);
IV - clinical death, that is, the lack of breathing and blood circulation.

Clinical (or "imaginary") death is a transitional period from life to death, occurring from the moment of cessation of activity and lungs. A person who is in a state of clinical death lacks all signs of life, he does not breathe, his heart does not work, pain stimuli do not cause any reactions, the pupils of the eyes are dilated and do not react to light. However, during this period, life in the body has not yet completely died out, because its tissues do not die immediately and the functions of various organs do not immediately die out.

The cells of the brain, which are associated with consciousness and thinking, are the first to die, which are very sensitive to oxygen starvation. Therefore, 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 the cells of the cerebral cortex; in most cases, it is 4-5 minutes, and when a healthy person dies from an accidental cause, for example, from an electric current, it is 7-8 minutes.

Biological (or true) death 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; it occurs after the period of clinical death.

Causes of electrocution death include cardiac arrest, respiratory arrest, and electrical shock.

The cessation of cardiac activity is a consequence of the effect of current on the heart muscle. Such an effect can be direct, when the current flows directly in the region of the heart, and reflex, that is, through the central nervous system, when the current path lies outside this area. In both cases, cardiac arrest can occur or its fibrillation occurs, that is, chaotically fast and different-time 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.

The cessation of breathing as the root cause of death from electric current is caused by a direct or reflex effect of current on the muscles. chest involved in the process of respiration. A person begins to experience breathing difficulties already at a current of 20-25 mA (50 Hz), which increases with increasing current. With prolonged exposure to current, asphyxia can occur - suffocation as a result of a lack of oxygen and an excess of carbon dioxide in the body.

Electric shock is a kind of severe neuro-reflex reaction of the body in response to strong irritation with an electric current, accompanied by dangerous disorders of blood circulation, respiration, metabolism, etc.

The state of shock lasts from several tens of minutes to a day. After this, either the death of the body may occur as a result of the complete extinction of vital functions or complete recovery as a result of timely active therapeutic intervention.

2. Factors affecting the outcome of human electric shock

The severity of electric shock depends on a number of factors: the value of the current strength, electrical resistance the human body and the duration of the current flow through it, the path of the current, the type and frequency of the current, the individual properties of a person and environmental conditions,

The strength of the current is the main factor that determines one or another degree of damage to a person (path: hand-hand, hand-feet).

Fibrillation is called chaotic and multi-temporal contractions of the fibers of the heart muscle, completely disrupting its work as a pump. (For women, the current threshold values ​​are 1.5 times less than for men).

Direct current is about 4-5 times safer than 50 Hz alternating current. However, this is typical for relatively low voltages (up to 250-300 V). At higher voltages, the danger of direct current increases.

In the voltage range of 400-600 V, the danger of direct current is almost equal to the danger of alternating current with a frequency of 50 Hz, and at a voltage of more than 600 V, direct current is more dangerous than alternating current.

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 3,000 to 100,000 ohms, and sometimes more.

When the upper layer of the skin is removed, the resistance decreases to 500-700 ohms. When the skin is completely removed, 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. If there are various injuries on the skin (abrasions, cuts, abrasions), the

its electrical resistance in these places. The electrical resistance of the human body decreases with an increase in current and the duration of its passage due to increased local heating of the skin, which leads to vasodilation, and, consequently, to an increase in the supply of blood to this area and an increase in sweating.

With an increase in the voltage applied to the human body, the resistance of the skin decreases, and, consequently, the total resistance of the body, which approaches its lowest value of 300-500 ohms. This is due to the breakdown of the stratum corneum of the skin, an increase in the current passing through it, and other factors.

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 than in the elderly. This is due to the thickness and degree of coarsening of the upper layer of the skin. A short-term (for several minutes) decrease in the resistance of the human body (20-50%) causes external, unexpected physical irritations: pain (blows, injections), light and sound.

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

In addition, there are particularly vulnerable areas of the body to the action of electric current. These are the so-called acupuncture zones (the area of ​​the face, palms, etc.) with an area of ​​2-3 mm2. Their electrical resistance is always less than the electrical resistance of the zones lying outside the acupuncture zones.

The duration of the current flow through the human body greatly affects the outcome of the lesion due to the fact that over time the resistance of the human skin decreases, and heart damage becomes more likely.

The path of the current through the human body is also essential. The greatest danger arises with the direct passage of current through the vital organs.

Statistics show that the number of injuries with loss of consciousness during the passage of current along the "right arm-leg" path is 87%; along the “leg-leg” path - 15%, The most characteristic current circuits through a person are: arm-legs, arm-arm, arm-torso (respectively 56.7; 12.2 and 9.8% of injuries). But the most dangerous are those current circuits in which both hands are involved - both legs, left arm-legs, arm-arm, head-legs.

The type and frequency of the current also affect the degree of damage. The most dangerous is alternating current with a frequency of 20 to 1000 Hz. Alternating current is more dangerous than direct current, but this is typical only for voltages up to 250-300 V; at high voltages, direct current becomes more dangerous. With an increase in the frequency of the alternating current passing through the human body, the impedance of the body decreases, and the passing current increases. However, a decrease in resistance is possible only within frequencies from 0 to 50-60 Hz.

A further increase in the frequency of the current is accompanied by a decrease in the danger of damage, which completely disappears at a frequency of 450-500 kHz. But these currents can cause burns both when an electric arc occurs, and when they pass directly through the human body. The decrease in the risk of electric shock with increasing frequency is practically noticeable at a frequency of 1000-2000 Hz.

The individual properties of a person and the state of the environment also have a noticeable effect on the severity of the lesion.

3. Conditions and causes of electric shock

The defeat of a person by electric current or electric arc can occur in the following cases:
with a single-phase (single) touch of a person isolated from the earth to non-insulated live parts of electrical installations that are energized;
when a person simultaneously touches two non-insulated parts of electrical installations that are energized;
when approaching a person who is not isolated from the ground, at a dangerous distance to current-carrying parts of electrical installations that are not protected by insulation, which are energized;
when a person who is not isolated from the ground touches non-current-carrying metal parts (cases) of electrical installations that are energized due to a short circuit on the case;
under the action of atmospheric electricity during a lightning discharge;
as a result of the action of an electric arc;
when releasing another energized person.

The following causes of electrical injuries can be distinguished:
Technical reasons - non-compliance of electrical installations, protective equipment and devices with safety requirements and conditions of use, associated with defects in design documentation, manufacturing, installation and repair;
malfunctions of installations, protective equipment and devices that occur during operation.

Organizational and technical reasons - non-compliance with technical safety measures at the stage of operation (maintenance) of electrical installations; untimely replacement of faulty or obsolete equipment and the use of installations that have not been put into operation in the prescribed manner (including home-made ones).

Organizational reasons - non-fulfillment or incorrect fulfillment of organizational security measures, inconsistency of the work performed with the task.

Organizational and social reasons:
overtime work (including work to eliminate the consequences of accidents);
inconsistency of the work of the specialty;
violation of labor discipline;
admission to work on electrical installations of persons under 18 years of age;
attraction to work of persons who have not been issued an order for employment in an organization;
admission to work of persons with medical contraindications.

When considering the causes, it is necessary to take into account the so-called human factors. These include both psychophysiological, personal factors (lack of individual qualities necessary for this work, violation of his psychological state, etc.), and socio-psychological (unsatisfactory psychological climate in a team, living conditions, etc.).

4. Measures for protection against electric shock

According to the requirements of regulatory documents, the safety of electrical installations is ensured by the following main measures:
1) inaccessibility of live parts;
2) proper, and in some cases increased (double) insulation;
3) grounding or grounding of electrical equipment cases and elements of electrical installations that may be energized;
4) reliable and fast automatic protective shutdown;
5) the use of low voltages (42 V and below) to power portable current collectors;
6) protective separation of circuits;
7) blocking, warning signaling, inscriptions and posters;
8) the use of protective equipment and devices;
9) carrying out scheduled preventive repairs and preventive testing of electrical equipment, apparatus and networks in operation;
10) carrying out a number of organizational activities (special training, certification and re-certification of electrical personnel, briefings, etc.).

To ensure electrical safety at the enterprises of the meat and dairy industry, the following technical methods and means of protection are used: protective grounding, zeroing, the use of low voltages, winding insulation control, personal protective equipment and safety devices, protective shutdown devices.

Protective earth is an intentional electrical connection to earth or its equivalent to non-current-carrying metal parts that may be energized. It protects against electric shock when touching the metal cases of the equipment, the metal structures of the electrical installation, which, due to the violation of electrical insulation, are energized.

The essence of protection lies in the fact that during a short circuit, the current passes through both parallel branches and is distributed between them in inverse proportion to their resistances. Since the resistance of the person-to-ground circuit is many times greater than the resistance of the body-to-ground circuit, the current flowing through the person is reduced.

Depending on the location of the grounding conductor relative to the equipment to be grounded, remote and contour grounding devices are distinguished.

Remote grounding switches are located at some distance from the equipment, while the grounded enclosures of electrical installations are on the ground with zero potential, and a person, touching the enclosure, is under the full voltage of the grounding conductor.

Electric current has a thermal, electrolytic and biological effect on the human body.
Thermal effect of current manifests itself in burns of certain parts of the body, as well as in heating up to high temperatures other organs.
Electrolytic action of current manifests itself in the decomposition of organic liquids, causing significant violations of their physico-chemical composition.
Biological effect of current manifests itself in irritation and excitation of living tissues of the body, as well as in violation of internal bioelectrical processes.

Types of human electric shock

There are two main types of electric shock to a person:
electrical injuries and electrical shocks.
Types of electrical injuries: local electrical injuries (electric burns, electric signs, skin plating, mechanical damage, electrophthalmia).
Of particular danger are electrical injuries in the form of burns. An electrical burn appears at the point of contact of the human body with the current-carrying part of an electrical installation or an electric arc. Electric burns are cured much more difficult and slower than conventional thermal burns, they are accompanied by sudden bleeding, necrosis of certain parts of the body.
Metallization of the skin is the penetration into its upper layers of the smallest particles of metal that has melted under the action of an electric arc. The victim at the site of the lesion experiences skin tension from the presence of a foreign body in it and pain from a burn due to hot metal. Metallization is observed in approximately 10% of the victims.
Mechanical damage occurs as a result of sharp, convulsive muscle contractions under the influence of current passing through the human body. As a result, ruptures of the skin, blood vessels, nervous tissue, as well as dislocations of the joints and bone fractures can occur.
Electrophthalmia is an inflammation of the outer membranes of the eyes that occurs as a result of exposure to a powerful stream of ultraviolet rays that are absorbed by the cells and cause chemical changes in them. Such exposure is possible in the presence of an electric arc.
Electric signs are clearly defined spots of gray or pale yellow color, round or oval in shape with a depression in the center, sometimes in the form of scratches, bruises, warts, hemorrhages in the skin, calluses, sometimes they resemble the shape of lightning. Basically, electrical signs are painless. Signs occur in 20% of those affected by the current.

The consequences of the impact of electric current on a person. electric shock