The influence of electric current on the human body. The effect of electric current on the human body: features and interesting facts

Business game No. 8

PROVIDING FIRST PRE-MEDICAL AID IN THE EVENT OF ELECTRIC SHOCK.

Theoretical knowledge required to perform business game No. 8.

EFFECT OF ELECTRIC CURRENT ON THE HUMAN BODY. TYPES OF ELECTRIC SHOCK.

Widespread use of electricity in all industries National economy increases the number of people who operate electrical equipment. Therefore, the problem of electrical safety during the operation of electrical equipment is of particular importance.

An analysis of accidents in industry indicates that the number of injuries caused by electricity is relatively small and amounts to 0.5-1% of total number accidents. However, it should be noted that of the total number of fatal accidents at work, 20-40% occur due to electric shock, which is more than due to other causes, and about 80% of fatal electrical injuries occur in an electrical installation with voltage up to 1000 V. Such electrical installations are very common, and they are serviced by almost all persons who work in industry, and electrical installations with voltage more than 1000 V served by a small number of highly qualified personnel.

Electrical injury is an injury caused by an electric current or arc.

Electrical injuries are divided into two types :

Electrical injuries that occur when current passes through the body of the eyelid,

Electrical injuries, the occurrence of which is not associated with the passage of current through the human body. A person's injury in this case is associated with burns, blinding by an electric arc, a fall, and, as a consequence, significant mechanical damage.

Types of effects of electric current on humans:

Thermal effect of current

Burns of certain parts of the body,

Heating to a high temperature of blood vessels, nerves, heart, brain and other organs that are in the path of the current, causing significant functional disturbances in them.

Electrolytic effect of current characterized by the breakdown of organic fluids, including blood, which is accompanied by significant changes in their physicochemical composition.
Mechanical (dynamic) action - this is delamination, ruptures and other similar damage to body tissues, including muscles, walls of blood vessels, vessels of the lung tissue due to the electrodynamic effect, as well as instantaneous explosive formation of steam from overheating by the flow of liquid and blood.
Biological effects of current manifests itself through irritation and excitation of living tissues of the body, as well as due to disruption of internal biological processes, occurring in the body, which are closely related to its vital functions.

Types of electrical injuries:

Local electrical injuries that cause local damage to the body;

General electrical injuries (electrical shocks), when the entire body is affected (or there is a threat of injury) due to disruption of the normal functioning of vital organs and systems.

Ø Local electrical trauma - a pronounced violation of the integrity of body tissues, including bones, caused by the influence of electric current or electric arc. Most often, these are surface injuries, that is, damage to the skin, and sometimes to other soft tissues of ligaments and bones. Local electrical injuries are cured and the victim’s performance is restored fully or partially. However, with severe burns the person dies. In this case, the direct cause of death is not the electric current, but local damage to the body caused by the current. Typical local electrical injuries:

Ø electrical burns, This is damage to the surface of the body caused by an electric arc or large currents that pass through the human body.

Ø electrical signs, this is a clearly defined mark with a diameter of 1-5 mm of gray or pale yellow color, which appears on the surface of human skin at the site of current passage. In most cases, electrical signs are painless (the top layer of skin comes off, and the affected area returns to its original color, plasticity and sensitivity are restored).

Ø Electrometalization - penetration of metal particles into the skin due to its splashing and evaporation under the influence of current. It can occur during short circuits, power outages by disconnectors and switches under load. In this case, small particles of molten metal, under the influence of dynamic forces and heat flow, scatter in all directions from high speed. Each of these particles has a high temperature with a small reserve of heat, and therefore is not capable of burning through clothing. Therefore, exposed parts of the body are affected: hands and face. If the eyes are damaged, treatment can be lengthy and difficult, and in some cases the victim may lose their vision. Therefore, work in which an electric arc may occur must be performed with safety glasses.

Ø Mechanical damage are in most cases the result of sharp convulsive muscle contractions under the influence of current that passes through the human body. As a result, ruptures of tendons, skin, blood vessels and nerve tissue, and even bone fractures can occur. Mechanical damage occurs when working in installations with voltages up to 1000 V when a person remains under voltage for a long time.

Ø Electroophthalmia - this is an inflammation of the outer membranes of the eyes, which occurs under the influence of a powerful stream ultraviolet rays. Such irradiation is possible when an electric arc forms (during a short circuit).

Electroophthalmia develops 4-8 hours after ultraviolet irradiation. In this case, redness and inflammation of the skin, mucous membranes of the eyelids, tears, purulent discharge from the eyes, eyelid spasms and partial loss of vision occur. The victim feels a headache and sharp pain in the eyes, which intensifies in the light. Prevention of electroophthalmia when servicing electrical installations is ensured by the use of safety glasses with ordinary glass, which almost do not transmit ultraviolet rays, and at the same time protect the eyes from infrared radiation and splashes of molten metal.

Ø Electric shock - This is the stimulation of living tissues of the body by electric current, which is accompanied by convulsive muscle contractions. Such a blow can lead to disruption and even complete cessation of the functioning of the lungs and heart. At the same time, a person may not have external local damage, that is, electrical injuries.

Depending on the severity of the lesion electric shocks conditionally possible divided into 5 degrees:

I - convulsive, barely perceptible muscle contractions;

II - convulsive muscle contractions, which are accompanied by severe, barely bearable pain without loss of consciousness;

III - convulsive muscle contractions with loss of consciousness, with preservation of breathing and heart function;

IV - loss of consciousness and impaired cardiac function or breathing

V - clinical death, that is, stoppage of the heart and lungs.

Approximately 75% of cases of electric shock to people are accompanied by local electrical injuries.

2. CAUSES OF DEATH FROM ELECTRIC CURRENT .

Causes of death from electric shock can be :

Stopped heart function

Stopping breathing

Electric shock.

The simultaneous action of two or even three of these causes.

Cessation of cardiac activity from electric current is the most dangerous, since bringing the victim back to life in this case is, as a rule, a more difficult task than in case of respiratory arrest or shock.

The effect of current on the heart muscle can be:

Direct, when the current passes directly into heart area,

Reflex, that is, through the central nervous system, when the current path lies outside this area. In both cases, cardiac arrest or fibrillation may occur. In case of electric shock, cardiac fibrillation occurs much more often than complete cardiac arrest.

Heart fibrillation - chaotic multi-temporal contractions of cardiac muscle fibers (fibrils), in which the heart is unable to drive blood through the vessels. My heart fibrillation occurs as a result of an alternating current of more than 50 mA with a frequency of 50 Hz passing through the human body along the arm-arm, or arm-leg path for several seconds.

For cardiac fibrillation , which occurs due to short-term action of current, breathing can continue for 2-3 minutes. Since the supply of oxygen to the body stops along with blood circulation, a person experiences a rapid, sharp deterioration. general condition and breathing stops. Fibrillation continues for some time and ends in complete cardiac arrest. Clinical death occurs.

Stopping breathing occurs due to the direct influence of the current on the muscles of the chest, which are involved in the breathing process. A person begins to feel difficulty breathing due to convulsive muscle contractions already at a current of 20-25 mA with a frequency of 50 Hz. At higher value current strength, this effect is enhanced. In the case of prolonged passage of current, a person experiences asphyxia - a painful condition due to a lack of oxygen and excess carbon dioxide in the body. With asphyxia, consciousness, sensitivity, and reflexes are gradually lost, then breathing stops, and after some time the heart stops or fibrillation occurs, that is, clinical death occurs.

The cessation of cardiac activity in this case is due not only to the related influence of the current on the heart, but also to the cessation of oxygen supply to the body, including the cells of the heart muscle due to respiratory arrest.

Electric shock - a kind of severe neuro-reflex reaction of the body due to irritation by electric current, which is accompanied by profound disorders of blood circulation, breathing, and metabolism. The state of shock lasts from several tens of minutes to a day. After this, the death of a person may occur due to the complete extinction of vital important functions, or recovery - due to timely active medical intervention.

The causes of electrical injuries can be grouped according to the following factors :

1. Touching live parts due to non-compliance with safety rules, design defects and installation of electrical equipment;

2. Touching non-current-carrying parts that accidentally become energized (damage to insulation, short circuit of wires);

3. Incorrect supply of voltage to the installation where people work;

4. Lack of reliable protective equipment.

3. FIRST MEDICAL AID IN CASE OF ELECTRICAL INJURY.

First health care - is a set of measures aimed at restoring or preserving the health of victims, carried out non-medical workers (mutual help) or the victims themselves (self-help).

Electrical injury is a consequence of the human body coming into contact with a voltage source.

If you touch a live conductor, a person becomes part of the electrical network through which electric current flows.

It is no secret that the human body contains a lot of fluid and salts. And this is an excellent current conductor. Because electricity can affect him. A long-term and intense current effect on the human body can lead to his death.

How can electric current affect our body?

The outcome to which the effect of electricity on the human body will lead depends on many circumstances. It is affected by:

1) magnitude (current strength, voltage) and type of electricity (alternating current is more dangerous than direct current);

2) duration of action (the longer the current acts on a person, the more severe the outcome may be);

3) the path of flow (the most dangerous is the current that passes through the spinal cord and brain, heart and respiratory organs);

4) psychological and physical state victim at the time of impact. Our body has some resistance. It directly depends on our condition.

The action of direct current is faster than alternating current. But alternating is very dangerous, even if the voltage is low and the frequency is low. Fabrics resist alternating current less than direct current.

Alternating current 100-150 V can have a strong effect on a person, even causing death. Alternating current 500 V is more dangerous than direct current with the same voltage. But direct current above 500 V is more dangerous than alternating current. The latter, with a frequency of 40-60 periods per second, poses the greatest threat human life. If you increase the frequency of periods, the harmful effects of electricity will decrease. High frequency current is used in medicinal purposes(D'Arsonval's current).

Passing through the human body, the current has such types of impacts:

Biological.
Electrolytic.
Thermal.

The first disrupts normal operation muscular system. The muscles contract convulsively. There can be a huge danger to the respiratory and circulatory organs (heart, lungs). They may cease to function normally; their functioning may cease completely.

During electrolytic action, blood and other organic liquids in tissues are broken down, and significant physical and chemical changes in composition occur.

During thermal exposure, burns appear on the body different shapes. Blood vessels overheat, functionality internal organs is violated.

The main factors of damage arising due to the action of current on the human body

Electrical injury is local damage to body tissue due to the action of a current or electric arc. This includes electrical burn, skin plating, electrical mark, mechanical damage.

The most common electrical injury is an electrical burn. 60% of all accidents involve electric shock. Electrical burns can be either arc or current.

An electric sign appears on the skin of a victim who has been exposed to current, in the form of an oval spot of a pale yellow or gray hue. Usually such a sign does not hurt, it hardens, like a callus. Dead layers of skin gradually come off on their own.

Metallization of the skin is caused by the penetration into the upper skin layer of small particles of metal that have melted due to an electric arc. The affected area hurts and becomes hard. The skin becomes a dark metallic shade.

Mechanical damage occurs when the current causes the muscles to involuntarily contract convulsively. Skin, nerve tissue and blood vessels may rupture.

But the most dangerous is electric shock. Living tissues of the body are excited by current. At this time, the muscles contract convulsively.

Four degrees of action of current on the human body:

I – muscles contract convulsively, the person does not lose consciousness;

II – the muscles contract convulsively, the victim loses consciousness, the heart and respiratory organs work;

III – there is no breathing, heart function is disrupted;

IV – clinical death occurs, there is no breathing, the heart stops.

What affects the severity of an electrical injury?

A person’s individual qualities greatly influence the outcome of an electrical injury. A healthy and physically strong person can more easily tolerate the effects of current compared to those who have various diseases. But not only the physical, but also the mental health of the victim matters at the time of electrical injury. A person with a nervous disease, heart disease, organ disease internal secretion, tuberculosis and so on, as well as victims with overwork, fatigue, drunkenness is more likely to suffer severe electrical injury. Therefore, electrical installations are serviced by persons who have completed special courses and a medical examination.

Factors influencing the severity of electric shock. Types of electric shock. Resistance of the human body.

Electrical installations represent a large potential danger for humans, since during operation there may be cases of touching live parts.

Features of electric shock are:

absence external signs impending danger that a person could detect in advance: see, hear, smell, etc. In most cases, a person is included in electrical network either with the hands (hand-to-hand current path), or with the hand and feet (hand-to-foot current path). The current passing through this leads to serious damage to the central nervous system and vital organs such as the heart and lungs.

severity of electrical injuries. Temporary disability due to electrical injuries is usually long-lasting. Thus, in case of damage in 220/380 V networks, it averages 30 days. Overall, electrical injuries account for 12-16% of all workplace fatalities.

industrial frequency currents of 10-25 mA can cause intense muscle cramps, resulting in a non-releasing effect, i.e., “chaining” a person to live parts, in which the victim cannot independently free himself from the effects of electric current. Prolonged flow of such current can lead to serious consequences.

the effect of current on a person causes a sharp withdrawal reaction, and in some cases, loss of consciousness. When working at height, this can cause a person to fall. As a result, there is a danger of mechanical injury caused by exposure to current.

A specific danger of electric shock lies in the fact that live parts of electrical installations that become energized as a result of insulation damage do not produce any signals that would warn a person about the danger. A person’s reaction to electric current occurs only when the latter flows through the human body.

Effects of current on the human body

Passing through the human body, electric current has thermal, chemical, mechanical and biological effects on it.

The thermal effect of current manifests itself in burns of individual parts of the body, heating of tissues and biological environments, which causes functional disorders in them. Chemical exposure is expressed in the decomposition of organic liquid, blood and manifests itself in a change in their physical and chemical composition; mechanical leads to rupture of muscle tissue; biological is the ability of current to irritate and excite living tissues of the body.

Any of the following electrical current may cause injury. Injury caused by exposure to electric current or electric arc is called electrical injury (GOST 12.1.009-76).

Types of electric shock

In practice, electrical injuries are conventionally divided into local and general. Local electrical injuries cause local damage to the body - electric burn, electric sign, metallization of the skin with particles of metal melted under the influence of an electric arc, mechanical damage caused by involuntary muscle contractions under the influence of current, and electroophthalmia (inflammation of the outer membranes of the eyes under the influence of an electric arc).

General electrical injuries, more often called electric shock, cause disruption of the normal functioning of the most vital organs and systems of the body or lead to damage to the entire body.

Factors Affecting the Severity of Electric Shock

These factors include: strength, duration of exposure to current, its type (constant, alternating), paths of passage, as well as factors environment and etc.

Current strength and duration of exposure. An increase in current strength leads to qualitative changes in its effect on the human body. With increasing current strength, three qualitatively different responses of the body clearly appear: sensation, convulsive muscle contraction (non-release for alternating current and pain effect for direct current) and cardiac fibrillation. Electric currents that cause a corresponding response in the human body are called tangible, non-releasing and fibrillation, and their minimum values are usually called threshold.

Experimental studies have shown that a person feels the effects of alternating current of industrial frequency with a force of 0.6-1.5 mA and direct current with a force of 5-7 mA. These currents do not pose a serious danger to the human body, and since under their influence a person’s independent release is possible, their prolonged flow through the human body is permissible.

In cases where the damaging effect of alternating current becomes so strong that a person is unable to free himself from contact, the possibility arises of a prolonged flow of current through the human body. Such currents are called non-releasing currents; prolonged exposure to them can lead to difficulty and breathing problems. The numerical values of the non-releasing current strength are not the same for different people and range from 6 to 20 mA. Exposure to direct current does not lead to a lasting effect, but causes severe pain, which occurs in different people at a current strength of 15-80 mA.

When a current of several tenths of an ampere flows, there is a danger of disruption of the heart. Cardiac fibrillation may occur, i.e. erratic, uncoordinated contractions of the heart muscle fibers. In this case, the heart is unable to circulate blood. Fibrillation usually lasts several minutes, followed by complete cardiac arrest. The process of cardiac fibrillation is irreversible, and the current that causes it is fatal. As experimental studies conducted on animals show, threshold fibrillation currents depend on the mass of the body, the duration of the current flow and its path.

Current path.

The damage will be more severe if the heart, chest, brain and spinal cord are in the path of the current. In the practice of servicing electrical installations, the current flowing through the body of a person exposed to voltage usually follows the “arm-to-arm” or “arm-to-leg” path. However, it can also flow along other paths, for example, “head-legs”, “back-arms”, “leg-leg”, etc. The degree of damage in these cases depends on which human organs are affected by the current, as well as on the strength of the current passing directly through the heart. Thus, when current flows along the “leg-to-leg” path, 0.4% of the total current passes through the heart, and 3.3% passes through the “arm-to-arm” path. The strength of the non-releasing current along the "hand-to-hand" path is approximately 2 times less than along the "hand-to-hand" path. right hand-legs".

Type of current

Power frequency current is the most unfavorable. As the frequency increases (more than 50 Hz), the values of the sensible and non-releasing current increase. As the frequency decreases from 50 Hz to 0, the values of the non-releasing current also increase and at a frequency equal to zero (direct current), they become approximately 3 times larger.

The fibrillation current values at frequencies of 50-100 Hz are equal. With an increase in frequency to 200 Hz, the strength of the fibrillation current increases approximately 2 times, and up to 400 Hz - almost 3.5 times. Increasing the frequency of the supply voltage of electrical installations is used as one of the electrical safety measures.

Environment.

Air humidity and temperature, the presence of grounded metal structures and floors, and conductive dust have an additional impact on electrical safety conditions.

The degree of electric shock largely depends on the density and area of human contact with live parts. In damp rooms with high temperatures or in outdoor electrical installations, they are folded unfavourable conditions, in which the area of human contact with live parts increases. The presence of grounded metal structures and floors creates increased danger damage due to the fact that a person is almost constantly connected to one pole (ground) of an electrical installation. In this case, any human touch to live parts immediately leads to its bipolar inclusion in the electrical circuit. Conductive dust also creates conditions for electrical contact with both live parts and the ground.

Electrical resistance of the human body

The strength of the current Ich passing through any part of the human body depends on the supplied voltage Upr (touch voltage) and electrical resistance zt provided to the current by a given part of the body,

Ich = Upr / zt

In the area between two electrodes, the electrical resistance of the human body mainly consists of the resistance of the two thin outer layers of skin touching the electrodes and the internal resistance of the rest of the body.

The outer layer of skin adjacent to the electrode, which is a poorly conductive current, and the inner tissue located under this layer, as it were, form the plates of a capacitor with a capacitance C with a resistance rn. In the outer layer of the skin, current flows along two parallel paths: through the active external resistance rn and capacitance C, (Figure 1) the electrical resistance of which

where ω = 2nf - angular frequency, Hz; f - current frequency, Hz.

Then the total resistance of the outer layer of skin for alternating current zн = rn xc /√ rn2 +xc 2

Resistance rn and capacitance C depend on the area of the electrodes (contact area). As the contact area increases, rn decreases; and capacity C increases. Therefore, an increase in the contact area leads to a decrease in the total resistance of the outer layer of skin.

Flowing through the human body, electric current causes thermal, electrochemical and biological effects.

The thermal effect of the current manifests itself in heating and burns of individual parts of the body; electrochemical in the decomposition of blood and other organic liquids; the biological effect of the current is associated with irritation and excitation of living tissues of the body, which is accompanied by involuntary convulsive contractions of muscles, including the muscles of the lungs and heart muscles, and can cause cessation of the activity of the circulatory and respiratory organs.

These effects of current can lead to two types of damage: electrical injury and electrical shock.

Electrical injuries include electrical burns, electrical marks, electroplating of the skin, electroophthalmia, and mechanical injuries.

The cause of electrical burns can be the action of an electric arc (arc burn) or the passage of current through the human body as a result of contact with a live part (electric burn). An electric burn is, as a rule, a skin burn at the site of contact of the body with a live part due to transformation electrical energy to thermal. Since human skin has many times more resistance than other body tissues, it generates most of the heat. Electrical burns occur in electrical installations, mainly with voltages up to 1000 V.

An arc burn is caused by exposure to an electric arc on the body, which is created during a discharge when a person approaches live parts energized above 1000 V, or during short circuits in electrical installations

voltage up to 1000 V. High temperature electric arc can cause extensive burns to the body and lead to death.

Electrical marks, also called shock marks or electrical marks, are dead spots on the skin of a person who has been exposed to an electrical current. In most cases, electrical signs are painless and treatable.

Electrometallization of the skin is caused by the penetration of tiny metal particles into its upper layers, melted under the action of an electric arc. Subsequently, the damaged area is restored and takes on a normal appearance, and the pain disappears. Cases of eye damage can be very dangerous, often leading to loss of vision. Therefore, work in which such cases are possible must be performed with protective glasses. At the same time, the worker’s clothing must be buttoned with all buttons, the collar must be closed, and the sleeves must be lowered and buttoned at the wrists.

Often, simultaneously with metallization of the skin, an electric arc burn is possible.

Electrophthalmia is an inflammation of the outer membranes of the eyes that occurs as a result of exposure to a stream of ultraviolet rays. Such irradiation is possible when an electric arc occurs, for example, during short circuits, which is a source of intense radiation not only visible light, but also ultraviolet and infrared rays.

Prevention of electrophthalmia when servicing electrical installations is ensured by the use of special safety glasses, which simultaneously protect the eyes from splashes of molten metal.

Mechanical damage occurs as a result of sharp involuntary convulsive muscle contractions under the influence of current. This can lead to falls from heights, joint dislocations, fractures, etc.

Electric shocks refer to the type of injuries that occur when exposed to low currents (of the order of several hundred milliamps) and voltages up to 1000 V. With electric shocks, the outcome of the impact of current on a person can vary from a slight, barely noticeable convulsive contraction of the muscles of the fingers to a fatal injury, associated with cessation of cardiac or respiratory function.

The degree of electric shock from electric shocks is characterized by its threshold value. The following currents are characteristic: threshold palpable, threshold non-releasing, threshold fibrillation.

Threshold perceptible current smallest value a tangible current that causes tangible irritation when passing through the human body.

Threshold non-releasing current is the smallest value of non-releasing current that, when passing through a person, causes irresistible convulsive contractions of the muscles of the arm in which the conductor is clamped.

Threshold fibrillation current is the lowest value of fibrillation current that causes cardiac fibrillation when passing through the body.

As will be shown below, the current flowing through a person fluctuates widely and depends on numerous physical and physiological phenomena that are difficult to account for. Unlike previous years, the prevailing opinion in electrical safety engineering is that it is inappropriate to standardize dangerous and safe threshold values for voltage and current in industry and in everyday life.

Table 1. The nature of the effect of electric current on the human body


Current value, mA	AC, 50 Hz	D.C
	Beginning of feeling a slight itching, tingling of the skin under the electrodes	Not felt
	The feeling of current spreads. and on the wrist, slightly cramps the hand	Not felt
	The pain intensifies throughout the entire hand, accompanied by cramps; mild pain is felt throughout the entire arm, up to the forearm. Hands, as a rule, can be removed from the electrodes	The beginning of the sensation is the impression of heating the skin under the electrode
	Severe pain and cramps in the entire arm, including the forearm. It’s difficult, but you can still tear your hands away from the electrodes	Increased feeling of heating
	Barely bearable pain in the whole arm. In many cases, it is impossible to take your hands off the electrodes. As the duration of the current increases, the pain intensifies	An even greater increase in the sensation of heating both under the electrodes and in adjacent areas of the skin
	The hands are instantly paralyzed and it is impossible to tear them away from the electrodes. Severe pain, difficulty breathing	An even greater sensation of skin heating. Minor contractions of the ARM MUSCLES
	Very severe pain in the arms and chest. With prolonged current, respiratory paralysis or weakening of the heart with loss of consciousness may occur	Feelings of intense heating, pain and cramps in the hands. When you remove your hands from the electrodes, barely bearable pain occurs as a result of convulsive contractions of the arm muscles
	Breathing becomes paralyzed within a few seconds, and heart function is disrupted. With prolonged current flow, cardiac fibrillation may occur.	Sensations of very strong heating, severe pain in the entire chest area. Difficulty breathing. It is impossible to take your hands off the electrodes
	Cardiac fibrillation after 23 seconds, a few seconds later cardiac paralysis	Respiratory paralysis due to prolonged current flow
	Same action in less time	Cardiac fibrillation after 23 s, after a few seconds respiratory paralysis
	Breathing becomes paralyzed immediately within seconds. Cardiac fibrillation, as a rule, does not occur. Temporary cardiac arrest is possible during the current flow. If current flows for a long time (several seconds), severe burns and tissue destruction	Increased feeling of heating

The main factors influencing the outcome of electric shock to a person are as follows.

The path of current in the human body.

The path of current in the human body affects the lesion in different ways. For some time now this issue has been given great importance, since the analysis of accidents made it possible to establish their dependence on the type of so-called current loop, i.e., on the path of the current through the human body. The most common four loops are: right arm, leg, left hand legs, arm arm, leg leg. In most cases, the current circuit occurs along the path of the right hand and foot. The most common and usually accompanied by severe damage is the current path (current loop) hand hand, where the current passes through vital organs, in particular the heart.

Accident analyzes show that approximately 55% of all electrical shocks occur along two main paths: from the hand or hands to the feet and from one hand to the other hand. However, fatal injuries account for half of the reported number of accidents.

The danger is determined not by whether current flows or does not flow through the heart area, but by what part of the body a person touches live parts. Most vulnerabilities human body are the back of the hand, neck, temple; front of leg, shoulder. Education electrical circuit through vulnerabilities leads to fatalities even at very low currents and voltages.

Electrical resistance of the human body.

The electrical resistance of the circuit through which current passes through the human body consists of the electrical resistance of the active and inductive wires; electrical resistance of machines, devices or devices that are connected in series with the human body; electrical resistance of the transition contact between live parts of the equipment touched by a person; the human body's own electrical resistance.

The resistance of the human body is a complex complex of biophysical, biochemical and other phenomena. It is usually divided into two parts: skin and blood vessel resistance and nerve resistance. Upper layer The skin has a noticeable resistance compared to the resistance of the internal organs. The presence of sweat glands in the skin greatly changes its electrical resistance. There is very little nerve resistance. It is this component of the total resistance that plays the most significant role in current conduction, and therefore in the outcome of electrical injury. The electrical resistance of a living organism is influenced by big number factors. The condition of the skin is of significant importance: damage to the stratum corneum (pores, scratches, abrasions and other microtraumas); hydration with water or sweat; pollution various substances and especially well-conducting electric current (metal or coal dust, scale, etc.).

The resistance of the human body, i.e. the resistance between two electrodes applied to the surface of the body, can be conventionally considered to consist of three series-connected resistances: two resistances of the outer (horny) layer of the skin and one called internal resistance body, which includes the resistance of the inner layer of the skin and the resistance of the internal tissues of the body. In general, these resistances have active and capacitive components.

In practical calculations, it is necessary to know and evaluate the numerical values of the resistance of a human electrical circuit between two electrodes applied to the body. Type of current and voltage. Research (see Table 1) and the practice of operating electrical installations show that direct current, compared to alternating current of the same values, is less dangerous for humans. This is explained primarily by the fact that due to the presence of a capacitive component in the electrical resistance of the human body, the current density, and therefore the field strength in the tissues, will be greater at equal voltages in the case of alternating current damage than in the case of direct current damage. Another significant circumstance is that with alternating current the damaging amplitude voltage can be 1.4 times greater than the effective voltage. And finally, the probability of the formation of an electrical circuit through vulnerable points with alternating current is greater than with direct current, because alternating current networks cover incomparably larger number installations, moreover, the most varied, while DC networks have more limited and specialized applications.

What has been said about the relative danger of injury from direct and alternating currents is true only for small voltages of the order of 250 - 300 V. At higher voltages, direct current is more dangerous than alternating current with a frequency of 50 Hz, due to the possibility of throwing the victim away from live parts under high voltage , which is extremely rarely observed with similar alternating current injuries. The thrown person may receive a mechanical injury, which may result in death (for example, in a fall).

In general, it should be noted that the question of the comparative danger to humans of alternating and direct current needs further study, which will expand our understanding of the biophysics of electrical injury.

Voltage applied to an electrical circuit leads to the transformation of electrical phenomena into other phenomena, the impact of which on the human body directly causes one or another outcome of the lesion. There is an opinion that the outcome of electric shock depends on the network voltage: the higher the voltage, the more dangerous consequences electrical injuries. IN statistical reports Electrical injuries are recorded and subdivided according to network voltage values. Based on the same criteria, data are analyzed and electrical injuries are classified, research and experiments are conducted. Meanwhile, such a study of electrical trauma does not always give a correct idea of this damaging factor.

Our current Rules divide all installations into voltages below and above 1000 V. In installations with voltages above 1000 V, the main cause of fatal injuries is burns caused by the passage of electric current. In installations below 1000 V, the main cause of damage is due to the direct effect of current. Statistics show that fatal electrical injuries occur predominantly in installations up to 1000 V.

Fatal injuries also occur at low voltages (65, 36, 24, 12 V). Their analysis shows that they are caused not only by fibrillation current, which cannot be obtained at these voltages. Damages from 12 to 65 V can be fatal only under special circumstances, for example, if the electrical circuit occurs through points vulnerable to current, if conditions are unfavorable external environment. Other reasons are also possible fatal outcome, which have not yet been sufficiently studied.

Summarizing what has been said regarding the absence of a direct relationship between the outcome of the injury and voltage, current, we state that it is impossible to standardize with high accuracy in industry (and in everyday life) dangerous and safe threshold values of current and voltage.

The duration of the existence of an electrical circuit through the human body.

The outcome of electric shock is related to the time factor. When analyzing accidents, much attention is paid to this parameter, especially considering the presence of contradictions in the assessment of the dangerous (and safe) time of current passing through a person. On the one hand, there are injuries with a severe outcome even with small currents and a very short duration of current passing through a person (fractions of a second), on the other hand, cases with a favorable outcome (excluding burns) with a duration of injury of several seconds or more.

Due to the above contradictions, it is not possible to strictly substantiate the dependence of the outcome of the lesion on the duration of the existence of the electrical circuit.

Effect of frequency

From the above formula for the total resistance of the human body, it follows that as the frequency of alternating current increases, the resistance decreases, which leads to an increase in current and an increase in the danger of injury. However, practice shows that this conclusion is valid only within certain frequencies. For a long time It was believed that in the low frequency region the 50-cycle current is most dangerous. With a further increase in frequency within the range of 50 - 400 Hz, the current maintains approximately the same values. Further increase in frequency reduces the risk of injury. But whether it is harmful or not harmful to the human body, there is no affirmative answer yet.

There is a comparative danger to humans from rectified current. The presence of frequency components in it aggravates the outcome of electrical injury. So far this is a little-studied section of electrical safety.

Environmental impact.

The environment can in many cases influence the risk of electric shock to a person. Factors of this influence include atmospheric pressure, temperature, humidity, electrical or magnetic field and etc.

An increase in air temperature affects a person's sweating, as a result of which the electrical resistance of his body drops and the danger of electric shock increases.

Similar phenomena are also associated with high humidity. Here there is a decrease not only in electrical resistance, but also in the body’s overall resistance to electric current.

The influence of these two factors, temperature and humidity, is recorded in regulatory documents.

The third atmospheric factor, ambient air pressure, also affects sensitivity to electric current. As the pressure increases, the risk of injury decreases. For example, statistics show that no fatal or severe electrical injuries have been recorded during underwater electric welding, although cases of contact of divers working underwater with live elements and contacts have been noted repeatedly.

The opposite picture was found for reduced atmospheric pressure, which is especially important in connection with the electrification of mountainous areas. It has been experimentally proven that low atmospheric pressure increases the danger of electric current for living organisms.

Medical and biological properties of humans

Analysis of accidents involving electric shock shows that the outcome of the injury is related to the medical and biological characteristics of a person and his state of health. Physically healthy and strong people tolerate electrical injuries more easily than unhealthy and weak people. People suffering from skin diseases, cardiovascular, and nervous diseases are more susceptible to electric current.

Therefore, safety regulations for the operation of electrical installations provide for the medical selection of personnel to service electrical installations. Selection is carried out upon admission to work, periodic examinations are carried out within the time frame established by the Ministry of Health in accordance with the list of diseases and disorders that prevent access to work. Selection also has another goal: to prevent people with diseases from servicing electrical installations that may interfere with their production work or cause erroneous actions that are dangerous for other persons (failure to distinguish the color of a signal due to a visual impairment, inability to give a clear command due to a sore throat or stuttering, etc.).

In addition, safety regulations do not allow persons under 18 years of age and without specific knowledge in the field of electrical safety corresponding to the scope and conditions of the work they perform to service electrical installations.

Accidents associated with exposure to electric current on the human body occur as a result of direct contact of the human body with conductive elements or exposure to a current discharge when approaching conductors at the minimum distance for a discharge to occur.

The mechanism of electric shock to the body is quite complex and has not yet been fully studied.

Its effects on the body can be divided into four categories:

thermal – burns;
chemical – electrolysis;
mechanical – bone cracking, tissue rupture;
biological – disruption of the functioning of the nervous system and related processes.

Types of damage to the body caused by electricity:

external – burns and metallization;
internal – electric shock.

Electrical shocks are the most severe type of electrical injury.

As a result of studies of injuries from electric current, it was found that the following factors play a decisive role in their outcome:

the amount of electric current passing through the human body;
voltage value in electrical installations;
time of exposure to electric current on the human body;
current path;
frequency and type of electric current;
the state of the human body at the time of injury;
state of the external environment.

Magnitude of electric current

Despite many studies, the exact amount of electric current that is dangerous or fatal to the human body has not been established.

Safe current is understood to be such a value that makes it possible to independently break away from conductive parts. Its magnitude depends on the applied voltage and the resistance of the human body.

The maximum output AC current at a frequency of 50 cycles per second is about 20 mA. In general average value This indicator for different frequencies is in the range of 60-70 mA.

The approximate dependence of the nature of the action of electric current on the body on its magnitude has the following indicators:

1.Alternating current (55 cycles per second):

current strength from 0.6 to 1.5 – slight trembling of fingers;
from 2 to 3 – strong trembling of fingers;
from 5 to 7 – cramps in the hands;
from 8 to 10 – pain in the hands and fingers, it is difficult to lift hands from wires or cables;
from 20 to 25 – difficulty breathing, hands are paralyzed and cannot be torn away from the wires or cable;
from 50 to 80 – paralysis of breathing and flutter of the heart ventricles;
from 90 to 100 – with exposure for more than three seconds, cardiac paralysis occurs.

2.Constant current:

from 0.6 to 3 – the effect is not felt;
from 5 to 7 – itching, slight heating;
from 8 to 10 – increased heating;
from 20 to 25 – slight muscle contraction;
from 50 to 80 – convulsions, difficulty breathing;
from 90 to 100 – paralysis of the respiratory tract.

Electric current exposure time

The duration of exposure to electric current on the body also plays a significant role on the body. Body resistance has an inverse relationship with duration: than longer person comes into contact with conductive parts, the lower the resistance, which in turn leads to an increase in the amount of current passing.

Electric current path

The path that stress takes through the body also significantly influences the outcome of injuries. The longer the path, the more severe the consequences. The passage of current through the body leads to various pathological processes and the more important organs it affects, the greater the likelihood of death.

Frequency and type of electric current

Many studies of the nature of the effects of direct and alternating current on humans show that the danger of the latter is much higher at low voltages. Moreover, with increasing frequency, the probability of damage decreases. The most dangerous frequency is in the region from 50 to 60 Hz.

Higher frequency currents do not pose a significant danger to the body, but can cause burns.