Causes of injury by technical electricity. Defeat by technical electricity. Lecture plan and distribution of study time
The effect of electric current at work and in everyday life can cause severe and even fatal injuries from contact with faulty household appliances (table lamps, kettles, irons, etc.) connected to a network with a voltage of 127 or 200 V. In industry, a three-phase current with a voltage of 380 V is used and a frequency of 50 Hz. At this voltage, severe electrical injury often occurs. Distinguish between direct and alternating current. AC and DC voltages, equivalent in their effect on the body, are respectively equal to 120 and 42 V. Direct current is less dangerous than alternating current, only up to a voltage of 500 V. At a voltage of 500 V, the danger of both types of current is equalized, and at voltages of more than 500 DC is more dangerous. In practice, direct current injuries are rare. The severity of injury from an electric current depends mainly on its physical parameters, but often the circumstances under which the current acts, as well as the state of the body, are of great importance. The greatest danger of injury exists when exposed to alternating current with a frequency of 40-60 Hz.
With an increase in the frequency of electrical vibrations, the risk of injury decreases, and at high-frequency currents (more than 10,000 and up to 1,000,000 Hz) and even at high voltage (1500 V) and high force (2-3 A), no damaging effect on the body is observed. This is the basis for the widespread use of high-frequency currents in medical practice - for physiotherapy procedures.
Depending on the magnitude of the voltage, the primary damage to the respiratory or circulatory organs occurs. The international standard for safe voltage, the so-called reduced voltage, is a potential difference of 24 V. Fatalities are possible even at a voltage of 40 V. High voltage currents - over 3000 V, are less dangerous and rarely lead to death. This is due to the fact that at high voltages between the body and the electrode, the effect of an electric arc flash occurs and most of the electrical energy is converted into heat, causing local lesions in the form of burns. The most frequent deaths are caused by current from 100 to 1500 V.
The magnitude of the current is of great importance in the development of electric damage; exposure to a current of 100 mA is in the vast majority of cases fatal.
The effect of the biological action of the current depends on the time during which the body is exposed to a current of a certain intensity, which is an important factor for the occurrence of ventricular fibrillation. Prolonged contact with electrical conductors at a current strength of 0.25-80 mA (minimum "non-letting" current) can lead to death, causing convulsions of the respiratory muscles and, as a consequence, acute asphyxia.
The spread of electric current throughout the body is possible if there are conditions for the input and output of current. This occurs when a person simultaneously comes into contact with two electrodes - a two-pole connection or contact with one of the electrodes, and any part of his body is grounded - a single-pole connection. Turning on can be partial when a person isolated from the ground touches opposite poles with one hand. Under these conditions, the current passes through the included arm section, which is usually not dangerous. At high voltage, electric current can strike a person without directly touching the conductor - at a distance, through an arc contact that occurs when dangerously approaching it. As a result of air ionization, human contact is created with current-carrying installations or wires. The danger of injury from a distance increases significantly in wet weather due to the increased electrical conductivity of the air. At ultra-high voltages, the arc can reach a length of 35 cm.
Electrical injury can occur from the so-called step voltage. Defeat in this case occurs when a person's feet touch two points on the ground that have different electrical potentials. Step voltage occurs when a high-voltage wire falls to the ground, when faulty electrical equipment is grounded, when lightning is discharged to the ground, etc. When a step voltage is hit, the current passes from one leg to the other along the lower "loop". This path of current through the human body is less dangerous. In the same case, when a person falls due to a convulsive contraction of the muscles of the lower limb, the lower loop turns into a full, more dangerous one. It is considered dangerous to enter the area of \u200b\u200ba dropped high-voltage network wire within 10 steps. At the same time, the wider the step, the greater the potential difference and the more stress a person gets.
Fatal injuries can occur from low voltage currents, and, conversely, a person can survive when exposed to very high voltage currents. The degree of damage by technical electricity is influenced by the path of the current in the body. In the literature, they are conventionally called current loops. The most dangerous path is when an electric current passes through the brain or heart, which can be observed when the left arm and leg, right arm and left leg, left and right arm, chest or back and arm, head and leg or arm are connected to the electrical circuit and others. Electric current passes mainly through tissues with the highest electrical conductivity and least resistance.
The resistance of tissues to electric current increases in the following sequence - blood, mucous membranes, liver, kidneys, muscles, brain matter, lungs, tendons, cartilaginous, nervous, bone tissue, skin. Dry skin has the greatest resistance. Damp skin and increased sweating can contribute to electric shock.
The state of the body at the time of exposure to current is of great importance. Persons suffering from diseases of the cardiovascular system, kidneys, endocrine glands and anemia, old people, children, pregnant women, as well as those who are intoxicated, are especially susceptible to electric current. Deep asphyxia and overheating reduce the body's resistance to electric current.
Electrical energy has an effect not only at the point of contact, but also on the entire body, which can manifest itself in various symptoms depending on the defeat of a particular organ system. The mechanism of the general effect of electricity is considered as shock, leading to respiratory and circulatory disorders.
The shock that develops as a result of the action of an electric current belongs to the pain group. With a longer passage of current, shock occurs due to a sharp painful irritation of receptors, nerve trunks, painful muscle cramps and vasospasm (ischemic pain).
When an electric current of significant intensity spreads in the body, death occurs, as a rule, instantly as a result of the primary cessation of breathing or cardiac activity. Sometimes the so-called delayed death is observed, when the victim has convulsions for some time after the electric shock, he screams and tries to get rid of the current conductor. Often, the victim is freed from the guide, but soon dies. The death of an injured person can also occur after a considerable period of time after exposure to the current. During the closure of the electric current, maximum exhalation occurs, for the power of the expiratory muscles is greater than that of the respiratory muscles. This greatly aggravates the course of electrical injury, since the oxygen reserve in the body is greatly reduced.
Changes in the place of contact with the conductor along the current are associated with the transition of part of the electricity to other types of energy, which determines its warm, mechanical and physicochemical action.
The action of an electric current in a short circuit leads to the formation of an electrometric, and in the event of an electric arc flash, significant burns may occur, as well as carbonization of soft tissues and bones.
Electric tags: a - at the entrance; 6 - at the current outlet
With the local action of the current, in addition to electrodes and burns, edema, necrosis, metal impregnation and damage can be noted. The thermal effect of an electric current is also manifested by the death of the underlying tissues, up to charring. Sometimes it is possible to see in the bone tissue peculiar formations - "pearl beads", resulting from the melting of bone substance with the release of calcium phosphate. The mechanical action is associated with convulsive muscle contractions, which can even lead to their rupture. An electric arc, which sometimes occurs between the body and the conductor, ignites the clothing and, consequently, the formation of extensive burns on the body. The remains of burnt clothing should be especially carefully examined to establish the place of contact with the current-carrying conductor. It is necessary to examine the shoes, as with a single-pole connection, there may be traces of current on them. As a rule, electro-markers are pale yellow, gray-white or gray-yellow in color. They are dense to the touch, have a sinking bottom and roller-like raised edges, usually without inflammatory exudative phenomena in the surrounding tissues. Electro tags can look like scratches, small wounds, calluses, skin hemorrhages, small-dot tattoos. Sometimes electro-marks are reminiscent of gunshot entrance holes. The epidermis in the area of \u200b\u200bthe electrometric can be exfoliated and raised. One of the signs of an electrometric is metallization, which is formed both when an object under voltage is in close contact with the skin, and in the case of an electric arc. Metal traces in the area of \u200b\u200belectro-marks can be detected by the method of color prints. Microscopic changes in the skin from electric shock are common. In the stratum corneum and lustrous layers of the epidermis, numerous voids are visible, giving the epidermis a cellular appearance. The shape of the various sizes of voids can be round, oval and angular. They are often found in groups, but they can meet alone. The stratum corneum and lustrous layers of the epidermis are completely separated from the granular layer. In the granular and thorny layers of the epidermis, voids in the form of cracks can also occur, separating the surface layers of cells from the deep ones. Sometimes the altered epidermis can completely exfoliate from its own skin, rising above it like a bubble, the upper part of which is often torn. More often, the exfoliated epidermis is separated from the skin itself only by a narrow gap. The boundaries of epidermal cells are not defined, the nuclei of the basal and partially prickly and granular layers are elongated, located perpendicular or obliquely to the skin surface. Sometimes the nuclei deviate in two directions, as if in the form of panicles, in some places there are vortices of the nuclei. When the epidermis separates from the skin itself, the cells remaining in the depressions between the papillae are also elongated. Using special methods of staining preparations, it is possible to establish the presence of metals during microscopic examination. Under the action of an electric current, no morphological changes in the skin can be detected in 10-20% of cases. Under the action of electricity, the phenomena of congestive plethora, edema of the wall and bed of the gallbladder, hemorrhages are observed. Congestion, edema, and sometimes punctate hemorrhages are detected in the pia mater and the substance of the brain. In difficult cases, to study current sources, conductors and obtain other data, it is necessary to carry out technical expertise, without which it is sometimes impossible to judge the cause of death. Of particular importance in case of electric shock is the statement of the actual onset of death, since there are cases of imaginary death, in which, first of all, it is necessary to carry out measures to provide medical assistance aimed at restoring vital functions (artificial ventilation of the lungs, heart massage and other resuscitation measures).
The action of atmospheric electricity
The action of atmospheric electricity is a giant electrical discharge in the atmosphere. The voltage reaches a million volts, the current strength is hundreds of thousands of amperes. The striking factors of lightning are electric current, light and sound energy, and shock wave. The duration of the impact of lightning can be very short, limited to fractions of a second, however, the extremely large amount of energy at the time of its action causes various bodily harm and even death. The action of lightning does not differ in principle from the action of a high voltage electric current.When struck by lightning, damage occurs on the skin, mainly in the form of burns, hair loss, as well as tree-branched figures of red or pink color - the so-called lightning figures. The appearance of "figures of lightning" is explained by a sharp expansion of the superficial vessels of the skin and small hemorrhages along their course. In survivors, such changes can be noted for several days, and on the corpse they turn pale and disappear rather quickly. The action of lightning is characterized by the symmetry of the lesion - paresis of both limbs, paraplegia with deep long-term loss of consciousness, respiratory arrest, and suppression of cardiac activity.
Occasionally, there are skin lesions in the form of small holes with burnt edges (they can be mistaken for an entrance hole for a firearm), and sometimes gross injuries up to extensive skin burns, bone fractures, tearing of limbs and ruptures of internal organs. There are frequent cases of the complete absence of visible traces of lightning on the human body.
The pathomorphological picture of the internal organs at the onset of death from the action of atmospheric electricity is similar to the picture observed with the defeat of technical electricity.
When struck by lightning, clothing can be torn in different directions or have small holes. The edges of the defects can be burnt or remain completely unchanged. Holes in the soles of shoes are characteristic, as well as charring of the skin around the metal nails on the sole. Metal objects often melt completely or melt, resulting in metal impregnation of the skin, which is of expert diagnostic value.
In the absence of signs of lightning, it is very difficult to decide the cause of death. Of great importance is the participation of an expert in the inspection of the place where the corpse was found, since traces of lightning are often visible at the scene of the incident, for example, in the form of splitting trees, fire, etc. A lightning strike can be direct or occur through any objects, for example, through a radio or telephone ... There are known cases of being struck by lightning when talking on the phone during a thunderstorm or when working with radios. Being struck by lightning does not always end in death. It can cause health problems or leave no consequences.
The action of electric current on the body is based on the sum of electrochemical, thermal and mechanical effects, accompanied by a sharp disorder of cardiac activity (fibrillation of the ventricles of the heart) and respiration, as well as the occurrence of shock reactions. In forensic practice, there are two types of electric shock: technical and atmospheric. Defeat by technical electricity. Severe and fatal electric shocks are possible from contact with faulty household appliances (table lamps, kettles, irons, etc.) connected to a network with a voltage of 127 or 220 W. Depending on the magnitude of the voltage, the primary damage to the respiratory or circulatory system occurs. The severity of an electric shock depends mainly on its physical parameters (strength, type, voltage, frequency), the time of contact with the current-carrying surface, the density and area of \u200b\u200bcontact, the circumstances of the injury, as well as the individual characteristics of the organism. The degree of injury by technical electricity depends on the path of the current in the body, that is, the electric current passes mainly through the tissues that have the highest electrical conductivity and the least resistance with their damage.
The resistance of tissues to electric current increases in the following sequence: blood, mucous membrane, liver, kidneys, muscles, brain, lungs, tendons, cartilaginous, nervous, bone tissue, skin. The local action of technical electricity at the point of contact of the body with the conductor leads to the formation of an electrometry, and with an outbreak of an electric arc, burns and charring of soft tissues and bones are possible. When examining a corpse externally at the place of its discovery or in a morgue, the expert must carefully examine the shoes for moisture, the presence of metal parts on the plantar surface with traces of melting. When examining the body of a corpse, the presence of electro-marks is established.
A typical electrometric is small in size, pale yellow or gray-yellow in color, dense to the touch, mainly oval in shape, with a sunken bottom and roller-like raised edges, without inflammatory exudative phenomena in the circumference. One of the signs of an electrometric is metallization, which is formed both during close contact with the skin of a current-carrying object, and in the case of an electric arc. Traces of metal in the area of \u200b\u200belectro-marks can be detected by the method of colored prints, for example, metallization from copper conductors gives a bluish, greenish color, iron H yellow, yellow-brown, black, lead H gray-yellow, gray, gray-black. An internal investigation reveals signs of an acutely frowning death. Damage by atmospheric electricity. Lightning is a giant electrical discharge in the atmosphere.
The voltage reaches a million volts, the current strength is H hundreds of thousands of amperes, the lifetime is 0.0001 s. On the skin when struck by lightning, injuries occur in the form of burns, scorching of hair, as well as "lightning figures" H treelike branches of red or pink figures, which is explained by the expansion of the superficial vessels of the skin and small hemorrhages along their course. Occasionally, there are skin lesions in the form of small holes with burnt edges (they can be mistaken for an entrance hole for a firearm), and sometimes gross injuries, up to extensive skin burns, bone fractures, detachment of limbs and ruptures of internal organs. There are frequent cases of complete absence of visible traces of lightning on the human body, which greatly complicates the work of an expert in determining the cause of death. The main issues to be resolved during the forensic medical examination of electrical injuries:
- 1. Properties of electrical energy: X atmospheric electricity; X mains electricity; X electrical discharge; X electric arc; X combination of selected species.
- 2. Features of current-carrying contacting parts: X material; X form; X size; X relief.
- 3. Mechanism of damage formation: X places of electrical energy application; X paths of current in the victim's body; X features of the biological effects of electrical energy on the victim's body; X duration of exposure; X the possibility of getting an electrical injury under specified conditions.
EFFECT OF HIGH AND LOW BAROMETRIC PRESSURE
Significant changes in internal organs from the action of high and low barometric pressure are associated with special types of human activities: diving and caisson work, alpine climbs, flights in airplanes, spaceships, and underwater sports. action of high barometric pressure. this type of effect on the body occurs during deep diving, underwater sports.
It has been established that the hydrostatic pressure doubles at a depth of 10 m, triples by 20 m H compared to atmospheric, etc. The increased hydrostatic pressure reduces the sensitivity of skin receptors to traumatic influences, therefore, damage caused under water is detected only upon ascent. As a result of the large difference between external and internal pressure, anatomical cavities and organs containing air (lungs, gastrointestinal tract, middle ear, etc.) are subjected to greater damage (compression). The main injuries from the action of high barometric pressure include: rupture of the alveoli, bronchi, lung tissue, damage to the tympanic membrane. With an internal examination, the expert discovers enlarged lungs, multiple hemorrhages, liquid and coagulated blood in the cavities of the heart and large vessels and in the lumen of the respiratory tract, signs of bleeding. When examining the corpses of persons who died from barotrauma, the organo complex is removed from the chest with tied arteries and veins, after which it is necessary to inflate the lungs under water and determine the places of lung tissue ruptures by the emerging air bubbles. With a rapid rise from depth to the surface, gases dissolved in blood and body fluids begin to be released in the form of free gas bubbles and gas emboli. Blockage of blood vessels with gas bubbles leads to the appearance of various symptoms, which is called decompression sickness (decompression sickness). When examining the corpses of persons who died from decompression sickness, observe: the presence in the right half of the heart and veins of blood convolutions with small bubbles of gases, the formation of subcutaneous emphysema. the effect of low barometric pressure on the human body occurs when working in high mountain regions, flying on airplanes and spaceships. The main mechanism for the development of this process is a decrease in the partial pressure of oxygen (hypoxia), decompression disorders and "boiling" of the body's fluids.
The first symptoms include: dizziness, rapid breathing, palpitations, fatigue, muscle weakness, and bleeding from the nose and ears. When examining the corpses of persons who have died from acute hypoxia, only general signs of asphyxial or rapidly occurring death are found. When examining corpses found in the mountains, one should take into account the possibility of sudden death in persons suffering from cardiovascular diseases, as well as the likelihood of being struck by lightning, falling from a height, sun or heat strokes. In these cases, a zone of significant pressure increase alternates with a zone of sharp air rarefaction, which causes a variety of damage, mainly of a mechanical nature.
temperature pressure electricity organism
Damage from the action of electricity: lecture / Yu.V. Galtsev. SPb .: VMA,
Associate Professor of the Department of Forensic Medicine of the Military Medical Academy Yu.V. Galtsev. Head Department of V.D. Issakov
Damage from the action of electricity: lecture / Galtsev Yu.V. -.
bibliographic description:
Damage from the action of electricity: lecture / Galtsev Yu.V. -.
html code:
/ Galtsev Yu.V. -.
forum embed code:
Damage from the action of electricity: lecture / Galtsev Yu.V. -.
wiki:
/ Galtsev Yu.V. -.
Target setting: To provide a forensic characterization of electrical damage.
Place of occupation: educational-methodical complex of the department.
Lesson time: 2 hours (90 min).
PLAN OF THE LECTURE AND ALLOCATION OF LEARNING TIME
Introduction ............................................. - 5 min
1. Conditions for the action of electricity on a person .......... - 15 minutes
2. Damage from technical electric current ..... - 30 min
3. Damage to atmospheric electricity .............. - 20 min
4. Features of forensic medical examination in case of electrical injury ....................................... - 15 min
Conclusion ........................................... - 5 min
INTRODUCTION
Local and general changes in the body caused by the action of electrical energy are called electrical trauma. Distinguish between technical and atmospheric electricity lesions. Not studied and represent a great rarity of damage by electric discharges, produced by special organs of some species of marine animals.
1. Conditions for the action of electric current on a person
The problem of electrical injury is currently very relevant. The specific gravity of electrical injury is relatively low and accounts for 1-2.5% of all mechanical damage (M.A. Sarkisov, 1972).
Electrical injury is more often fatal than other injuries. The frequency of deaths from electric shock in different countries ranges from 9-10%. The figures given refer mainly to severe cases, while minor lesions were not taken into account at all. Even less often, electrical injuries received in everyday life are recorded. Consequently, electric shock occurs much more often than it is given in official statistics.
In military affairs, electrical energy can be used as a weapon of war. For example, even during the defense of Port Arthur in 1904-1905, high voltage installations were used, to which wire barriers were connected. Electrical energy was widely used by almost all countries that participated in the First World War. Electrification of wire fences, camouflaged wires and other obstacles was used mainly in defensive operations. In the war with Finland and during the Great Patriotic War, our troops had to face electrified obstacles. The problem of electrical injury is no less urgent for the Navy. (Electrical defense of a breakwater, coastal areas, etc.). Finally, electricity is a special-purpose combat weapon, and due to its invisibility and quietness of action, as well as the effectiveness of destruction, it can be used as an "electric weapon".
The nature of electrical injuries depends on many conditions, the main of which are:
- a) the physical properties of the current;
- b) the external conditions of its action;
- c) features of the state of the organism.
When evaluating an electrical injury, the following properties of the current must be taken into account: _voltage. (low currents 120-220 and high voltage currents over 280 V). However, a direct relationship between the magnitude of the voltage and the onset of death cannot be established.
Current strength... It is believed that with 0.08 A, the current is deadly. A person begins to feel a current of 1 mA, at 5-7 mA pain and cramps appear, at 15 mA it is impossible to unclench his hands and get rid of the electrode.
Current type (variable - technical and lighting of the order of 40-60 periods per second is considered more dangerous than constant). An alternating current of 500 V is more dangerous than a direct current of the same voltage, and at voltages above 500 V, direct current turns out to be more dangerous.
The conditions for the action of this current are as follows: the properties of the current to overcome the resistance, the duration of the action of the current, the density, the area and the number of contacts, the path of the current. The outcome of an electrical injury is also determined by the state and characteristics of the organism. Children, tired people, the sick and the elderly have an increased sensitivity to electric shock. Inhibition of the cerebral cortex with the help of narcotic substances, as well as sleep, reduce the body's sensitivity to current.
For example, ether anesthesia reduces the mortality of experimental animals from the action of 500 V alternating current by 15 times. An increase in sweating dramatically reduces the body's resistance to current.
There are thermal, mechanical and electrolytic effects of current on the body. Thermal the action of the current is due to the conversion of electricity into thermal energy according to the Lenz-Joule law. The higher the strength of the currents and the stronger the resistance, as well as the time of action, the stronger the heating of the tissues. In places of contact with current conductors, burns occur, up to carbonization of tissues and fusion of bones ("bone beads"). Non-contact thermal effect of current occurs when an electric arc is formed (temperature 3000-4000 degrees). In such cases, clothing may ignite, hair may be scorched, certain parts of the body may be charred, etc. Electromechanical Action arises due to the direct transfer of electrical energy to mechanical energy. Tears and holes appear in the skin due to the formation of steam and gas. Electrolytic the action of the current causes the decomposition of sebum with the formation of fatty acids at the site of the current entry with the formation of electro-marks on the skin. Electric current can also cause electrolysis of tissue solutions, disrupt ion exchange in cells, up to the coagulation of cellular protein.
The mechanism of death in electrical trauma is not yet sufficiently understood and can be different. Death can occur from primary paralysis of the heart or respiration, as well as simultaneously from paralysis of respiration and heart. at high currents, people die from primary paralysis of the central nervous system.
The morphological changes found during the autopsy of those who died from electrical injury are rather scarce and nonspecific. At this stage in the development of science, they have not yet been fully studied. Apparently, changes occur at the molecular or submolecular level and are not detected by traditional forensic and pathological studies. find: hyperemia, edema and hemorrhage in the heart muscle, lungs, brain and other organs.
With electrical trauma in the gastrointestinal tract, acute gastric ulcers, perforation of the sigmoid colon, edema and necrosis of the gallbladder, hemorrhagic pancreatitis, etc. can be found. Current marks or electro-marks represent skin lesions, sometimes corresponding to the outline of the current-carrying part, of a pale yellow color, of hard consistency, with a depression in the center, usually without inflammatory exudative phenomena in the circumference. The hair around is usually intact or just curled. Sometimes electro-marks have the appearance of scratches, cut wounds, calluses and warts, skin hemorrhages, pinpoint tattoos, or, finally, similar to the figures of lightning.
Sometimes the signs of the current look like foci of destruction going deep, like a gunshot wound. They show: (histological examination) honeycomb voids in the stratum corneum of the skin, small foci of decay, stained with chromatin in the basal layer of the epidermis, elongation, elongation of cells and nuclei of the malpighian layer in the form of "brushes". Often, there is an extension of the cells of the hair bags towards the surface of the skin, as well as the excretory ducts of the sebaceous and sweat glands. With the local action of the current, the process of decay and rejection is not limited to pronounced areas, but goes further 2-3 times exceeding the boundaries of the affected area. For the survivors, this process is favorable. Wounds are not prone to suppuration, the temperature usually remains normal, and the general condition is not disturbed. The dead areas are mummified and rejected, forming a soft scar, usually not showing a tendency to shrinkage and degeneration. Healing proceeds smoothly, without maping and suppuration.
Using special histochemical reactions, it is possible to determine the chemical composition of the deposited metals, i.e. metallization of the epidermis.
During an internal examination of the corpses of persons who died from electrical injury, there are signs of acute death (plethora of internal organs, a liquid state of the blood, pronounced edema of the hepatoduodenal ligament, bed and wall of the gallbladder.
The main clinical symptoms in electrical injury are, depending on the severity of the lesion, more or less pronounced disorders of the cardiovascular and nervous system, psyche, less often of the internal organs. Very often, with severe electrical burns in the kidneys, changes are typical for acute renal failure.
2. Damage from technical electric current
Electric shock almost always occurs through direct contact with an electric current conductor. Rarely, a person can be struck by a high voltage electric shock without touching the conductor through the arc contact that occurs when approached at close distance. Electric shock can occur from "step voltage", which occurs due to the potential difference between the two feet touching the ground near a high voltage conductor lying on the ground. The damaging effect of an electric current depends on the cumulative effect of the properties of the current, contact conditions and the properties of the organism. Speaking about lesions of the properties of the current, first of all, they mean the strength, voltage, type of frequency.
Fatal electric shock is most often found at a voltage of 110-240 volts, which is to some extent associated with the predominant distribution of these voltages in everyday life and at work.
The body becomes more sensitive to the action of electricity with a decrease in the general resistance of the body due to physical overstrain, overwork, injury, disease, intoxication, prolonged general action of high temperature, etc.
Some meaning is given to the "factor of attention" or "the factor of expectation." It has long been noted that favorable outcomes are observed in cases where a person is struck by current. But here, most likely, it is necessary to speak with the readiness of a person to pull away from the conductor at the moment of electric shock and thereby reduce the contact time, and, consequently, the power of the electrical impact. The mechanism of the damaging effect of technical electricity is complex and consists of the specific and nonspecific action of the current.
The specific effect of the electric current is significant. It is expressed in biological, electrochemical, thermal and mechanical action.
The biological effect is expressed in irritation of all excitable tissues of the body: skeletal and smooth muscles, glandular tissues of nerve recipes and conductors. The consequences of this action can be tonic spasms of skeletal muscles, which can cause respiratory arrest, spasm of the vocal cords, and avulsion fractures. The action of an electric current on vascular smooth muscles leads to its contraction and an increase in blood pressure. Action on the muscle of the heart, electric current can cause ventricular fibrillation. The organs of internal secretion respond to electrical stimulation by releasing catecholamines. Electric current can affect the potassium-sodium gradient of cells, membrane potentials and disrupt the processes of excitation transmission, which can, in particular, lead to cardiac arrest.
The electrical effect is expressed: a) in the consequences of disruption of ionic equilibrium in tissues in the form of coagulation (at the anode) and callivation necrosis (at the cathode), b) in the formation of steam and gas, c) in the impregnation of the skin with the metal of the conductor. Thermal action is directly related to tissue resistance and the conversion of electrical energy into heat (Joule-Lenz law). The consequences of this action are burns of varying degrees. Bones can form "pearl beads", which are molten and then solidified calcium phosphate in the form of white balls 1-1.5 mm in diameter with voids due to the evaporation of the liquid in the bones.
The mechanical action of electric current is associated with ruptures and layering of tissues. Mechanical action of great force can lead to dislocation and even separation from the limbs. The influence on the body of secondary phenomena accompanying electrical processes refers to a nonspecific action: burns from the action of a volt arc, a hot conductor, hot clothing, acoustic trauma, mechanical injury when falling after an electric shock, etc.
The local action of technical electricity leads to the appearance of electro-marks or current signs. they are formed at the point of contact with the current conductor. A typical electrical injury is small and crater-shaped: its edges are raised, the bottom sinks. The surface of the electric mark is dry. Its outer walls are light gray, sometimes almost white, and are surrounded by a corolla of pink hyperemia. The inner walls are dark gray, impregnated with the conductor metal. The shape and size of the electrodes can vary depending on the shape, size and relief of the contacting part of the conductor. Sometimes electro-marks do not differ in appearance from abrasions. The differential diagnosis in such cases is based on the study of the microscopic picture. The histological map of the electrometric is specific: in the stratum corneum, less often in the granular and prickly layers of the epidermis, honeycomb-like voids and slit-like breaks are visible, located parallel to the skin surface; the cells of the basal, thyroid and granular layers are elongated perpendicularly at a slight angle to the skin surface and are presented in the form of a "picket fence", "brush" or "panicles". The embedded metal particles of the conductor affect the surface and deep in the stratum corneum. In 10-12% of mortal electrical injuries, electric markers are not found. Changes in internal organs during electric shock are uncharacteristic and are reduced to a picture of impending death: plethora of internal organs, dark liquid blood in the cavities of the heart and large vessels, multiple small dark red hemorrhages under the serous membranes of the heart, lungs and other parenchymal organs. Death from electric shock can occur both from primary respiratory arrest, as well as from primary cardiac arrest. The cause of respiratory arrest can be oppression and paralysis of the respiratory center of the medulla oblongata, tonic contraction of the diaphragm, tonic contraction of the glottis contractors. Primary cardiac arrest can be caused by paralysis of the vasomotor center of the medulla oblongata, reflex spasm of the coronary arteries of the heart, cessation of the transmission of excitation processes due to a violation of the sodium-potassium gradient and membrane potentials, fibrillation of the ventricles of the heart.
Forensic medical examination in case of electric shock involves, first of all, establishing the cause of death. To judge the cause of death, one should use, firstly, objective sectional and histological data on the presence on the body of the deceased electric tags and signs of a quick death, on the absence of signs of injuries, diseases and poisoning that can independently lead to death, and secondly, data technical expertise, information about the situation of the scene and the nature of the work performed by the deceased before death, indicating a real possibility of contact with a conductor under voltage.
The identification of the conductor metal is carried out using the method of color imprints and microchemical reactions to metals in histological sections.
3. Defeat by atmospheric electricity
Damage by atmospheric electricity occurs when lightning strikes. Lightning is an electrical spark discharge in the atmosphere, characterized by a current of about 100,000 amperes and a voltage of several million volts and a lifetime of less than 0.0001 seconds.
Lightning has mainly thermal and mechanical damaging effects on the body. In places of contact, lightning causes deep carbonization of tissues, and sometimes tears of the skin. Clothing is usually burnt and torn, and metal objects are melted. Sometimes skin burns can be superficial. Singing of the hair is always expressed over a large area. When a person is directly struck by lightning, gross destruction of the body occurs from separation of limbs to fragmentation of the body. Specific to the action of atmospheric electricity are "lightning figures" - reddish tree-like branches that can be found on any part of the body surface, sometimes occupying a significant area. They are not always found on the corpse, since they often disappear by the end of the first day, they stay on the body of the survivors for several days. The situation at the scene can support the opinion about a possible lightning strike: open areas, not far from the corpse, split and charred wood with other wooden objects, melted metal objects, scraps of burnt clothing around the corpse.
4. Features of forensic medical examination in case of electrical injury
When establishing death from electric shock, the forensic expert must use preliminary information and data from the initial examination of the corpse at the place of its discovery. A number of questions arising during the examination of electric shock are of a technical nature and therefore it is advisable to inspect the scene of the accident in conjunction with a specialist of the relevant profession. Diagnostics is based mainly on current signs. In 10-15% of cases of fatal electrical injury, there is no damage to the skin. Most authors consider electrometrics to be specific changes inherent only to electrical injury. In the diagnosis of electric shock, great importance is attached to the detection of metallization at the point of entry of current into the human body, to the histological examination of electrometrics.
When opening a corpse, pay attention to minor hemorrhages in various organs and tissues, as well as the signs set forth in the previous section of this lecture. Moreover, it is these signs that can only be indirect evidence of death from electric current, provided that other possibilities of causes of death, for example, from diseases or other injuries, are completely excluded.
Sometimes an electric shock is accompanied by a fall from a height and severe bodily injury. In these cases, there is a need for differential diagnosis. Electric injuries are more often in the nature of an accident. However, in judicial practice, there were cases of murder and suicide with the help of electricity.
CONCLUSION
This lecture concludes the forensic treatment of injuries from external physical actions. With all the variety of damage arising from this, two main tasks are solved as the main ones: determining the properties of the traumatic agent, and also establishing the mechanism of its action. The next lecture will be devoted to the forensic characteristics of poisoning.
LITERATURE
- a) Used in preparing the text of the lecture:
- Kaplan A.G. Electric shock and lightning. - M., 1948.
- Aitvak A.S. Programmed training in forensic medicine. - M., 1970.
- Druzhinin V.E. Forensic medical examination in case of electric shock. Diss.kand., - L., 1972.
- Sarkisov M.A. Electrical trauma. - L., 1972.
- Orlov A.N. and other Electrical injury. - L., 1977.
- Popov V.L. Forensic Medicine. - SPb, 1984.
- b) materials of this lecture are recommended for independent work.
Visual aids
- Tables: "Factors that determine the nature of the damaging effect on the body of electric current."
- Set of slides "Damage from electricity".
- Overhead projector of the "Proton" type.
Damage by technical electricity is possible with direct contact with an electric current conductor and at a distance, without touching a high-voltage current conductor, which allows the formation of a volt arc through an arc contact at a close distance from the conductor and "step voltage" due to the potential difference between two feet touching the ground near a high voltage conductor lying on the ground.
Most often, damage is the result of direct contact with an electric current conductor (household items, parts of electric machines, tools), as well as with a person or animal in contact with current conductors, weak current installations (telephone, telegraph, etc.), accidental connection with networks of strong current, induction, lightning strikes, etc.
The causes of electric shock are extremely varied. They can be accidents, breaks in electrical wires, malfunctioning electrical appliances, short circuits as a result of improper installation or damage to insulation, violation of safety rules, inappropriate jokes with electricity.
The defeat of a person with electricity is possible in cases of the presence of a current source, a conductor and two opposite poles (phases), which, when closed, make up an electrical circuit. If the circuit is open, no electric shock will occur. A person can come into contact with a current source with two poles at once (two-pole connection) or one (single-pole connection). A two-pole connection is especially dangerous when current flows through the human body from one phase to another. With a single-pole connection (with grounding), a person comes into contact with the current source with one pole, and the current goes through the body to the ground (the second pole). With a single-pole connection (without grounding), the current does not pass through the human body and the person is not injured by an electric current, the circuit remains open.
The place of contact of a person with the current source is the entry point, and with the second conductor or ground, the exit point.
For one reason or another, the human body surrounded by insulators - clothing, shoes, skin - can become a kind of conductor of electric current. In some cases, they lose their insulating properties and turn into current conductors between the current source and the ground, being a kind of means for grounding the current. Most often, the action of the current is manifested by direct contact with a current-carrying object. The action of a high voltage current can strike someone located at some (close) distance from the current source due to the transfer of electrons from it to the body.
Sometimes electric current does not cause damage, but causes changes associated with the transition of electrical energy to other types - heat, light, acoustic.
From a physical point of view, the human body is a complex conductor of electric current, to which the general laws of physics are applicable. The current power or energy generated in cases of current passing through the human body mainly depends on the voltage of the current, the resistance of the body and insulators, and the time of exposure.
The resistance of the human body to the action of the current and the severity of the injury are influenced by the state of the body, the conditions of the external environment and the action of the current, voltage, magnitude (strength) of the current, frequency, exposure time, density and contact area, type (type) of current (direct or alternating) , the presence and nature of insulators, environmental humidity, one- or two-pole connection in an electrical circuit, the path of current passage in the body.
Physical factors
Frequency (type or kind) of current. The most dangerous is an alternating low-frequency current with a frequency of 40-60 Hz (oscillations per second). The frequency of oscillations of such a current coincides with the frequency of the heartbeat, and a life-threatening violation of the rhythm of cardiac activity occurs.
As the vibration frequency increases, the risk of injury decreases. A current with a frequency of more than 70 kHz is safe, since its thermal effect prevails. Currents with a frequency of 100 kHz and above do not have a damaging effect on the body and are used in medical practice.
Long-term exposure to high-frequency currents causes rapid fatigue, a decrease in the efficiency and resistance of the body, which must be remembered by the investigator investigating this category of cases.
Voltage. A current with a voltage of more than 50 V and a force of more than 0.06-0.1 A. is considered dangerous for human life.In persons with increased sensitivity to current, death can occur at a voltage of more than 30 V. Currents with a voltage of 110 to 500 V.
High voltage currents of more than 1000 V may not lead to death, since a volt arc arises at the point of contact, burning and charring the tissues, causing a sharp increase in their resistance and a decrease in the current strength. Deep carbonization can lead tissues to a state of dielectric and thereby interrupt the contact between the current and the body.
In case of electric shock above 380 V, burns occur in 70-80% of victims. A shock of very high voltage (over 10 kV) is also observed without direct contact with the current conductor. A high voltage power line wire that falls to the ground generates an electric field with a potential difference, the so-called "step" voltage. A person caught in such a zone may be standing in different parts of the electric field, thereby closing the circuit and getting injured.
Amount (strength) of the current. A person begins to feel the current from the value of one milliampere (threshold reaction). A further increase in the magnitude of the current causes the appearance of pain, convulsive muscle contraction (convulsive reaction). The current of 12-15 mA does not allow the hand to be released in contact with the current source due to convulsive contractions. A current of 100 mA is lethal (lethal reaction). It can be both at low voltage (up to 100 V) and low resistance of the human body (about 100 Ohm), and at a voltage above 100 V and high body resistance. However, in the latter cases, fatalities are more often caused by burns, and not by the direct action of the current. The current of very small strength and high voltage may not cause harm to health.
The comparative danger of alternating and direct current depends on voltage: up to 400 V - alternating current (50 Hz) is more dangerous, about 500 V - the danger is the same, above 500 V - direct current becomes more dangerous.
Resistance. The main resistance to electric current is provided by the skin, followed by hair, bones, tendons, poor in blood vessels and tissue fluid, in descending order. Muscles, adipose tissue, nerves, mucous membranes, and especially blood, are good conductors of current. The body's resistance to the action of the current is due to the reactivity of the body, the state of tissues and organs, the nervous and endocrine systems, health, age, body size.
Leather. The resistance of the skin to the action of electric current depends on the voltage (the higher the voltage, the lower the resistance) and can range from 2,000 ohms to 200,000 ohms, as well as the body area. The greatest resistance is provided by the skin of the palmar and plantar surfaces of the extremities.
Thick, with a thickened stratum corneum and epidermal layer, callous, rough and dry skin has the greatest resistance to the action of the current.
Thin and delicate, with a thinned stratum corneum, soft, moist, perspiring, devoid of epidermis, damaged skin has less resistance to the action of electric current. The resistance of leather moistened with water drops by 40%.
The number of sweat glands, blood vessels of the skin, pallor and redness, natural or formed under the influence of physical (heat or cold) factors or mental reasons (fear, etc.), as well as the state of internal organs can change the electrical conductivity of the skin in one direction or another ...
The presence of insulators - dry clothing and shoes, protective gloves and rubber shoes - increases the resistance of the fabrics. The absence of insulators and the presence of conductors - wet clothes and shoes, metal fittings (fasteners), nails in shoes, metal objects in clothing pockets sharply reduce the resistance of fabrics, increasing the risk of injury.
The outcome of the action of the current is influenced by the local resistance of the tissues and the general resistance of the organism. The greater the resistance of the skin, the less damage, the weaker the general phenomena, but the more pronounced the local effect. In this regard, the skin with high resistance suffers the most, since heat is generated here according to the Joule-Lenz law, which causes deep destruction and drying of tissues. The burned and charred skin surface directly adjacent to the current source does not conduct current well, and the burning of the skin area interrupts it.
Electrode distribution and current path. The severity of an electric shock is largely determined by the passage of current through the body or by a current loop from the point of entry to exit. The most dangerous are the upper full current loops passing through the heart and brain. Such a move occurs when hinges head - legs, left hand - right hand, left hand - legs. The lower current loops passing through both legs are less dangerous (Fig. 285).
Figure: 285. Ways of propagation of electric current in the human body (according to VM Smolyaninov, 1975). Loop name: a - full; b - right full; в - left full; g - right oblique; d - left oblique; e - right; g - left; h - top; and - bottom; k - transverse
The time of exposure of the conductor to the body increases the reaction of the muscles, which is manifested by convulsive contraction of the fingers squeezing the wire or instrument. The duration of the contraction of the extensor group of the skeletal muscles under the influence of the following stimuli, separated by a short period of time, makes the victim touch the live part with his back or the back of his head and remain, as it were, chained to the current.
The high voltage current causes a sharp contraction of the muscles in cases of approaching the current source, and due to the joining reflex evasion from the current, the victim is thrown away.
The longer the exposure time, the area and density of the contact, the more energy passes through the body, the more dangerous is the effect of electric current, which affects the intensity of lesions and injuries, their morphology, volume and area.
The density of the contact and the conductor deserves special attention. Close contact leads to the appearance of an electrometric, incomplete contact causes burns of varying degrees.
Environmental conditions. Wet rainy weather, high ambient temperature, high humidity of premises, condition of the floor, clothes, shoes contribute to the occurrence of electrical injury. High humidity imparts conductivity to common insulators: rubber, glass, concrete floor. Therefore, there is a concept of current-hazardous premises: basements, bathrooms, saunas, sheds, dugouts, etc. Cotton and linen fabrics conduct electricity well. Silk, leather, rubber, etc. have insulating properties.
The state of the body. A person becomes more sensitive to the action of electricity with a decrease in the overall resistance of the organ
nism due to physical overstrain, overwork, overheating, trauma, diseases of the cardiovascular system, kidneys, nervous system, a tendency to hysterical seizures, increased excitability, anemia, intoxication, alcoholic intoxication, exhaustion or cooling.
The elderly, children and pregnant women are especially susceptible to current.
Other factors worth mentioning are training, the moment of surprise (“surprise”), problem or attention factor, or expectation factor. There are known cases of death of persons who were repeatedly exposed to electric current without damage to their health, but died from unexpected exposure to electricity, which must be remembered by the investigator interrogating persons related to the incident.
Electric current action. Electric current, passing through tissues and organs, causes changes at the entry point, along the current and exit loop. Its action at the point of entry and exit is manifested by local electrical, thermal and mechanical action, and along the current loop - by a general specific action that causes general changes in organs, tissues, cells.
Local action occurs when part of the electricity is transferred to other types of energy during the passage of an electric current through the body. Electrolytic, thermal and mechanical damage can occur depending on a number of conditions. Local changes are caused by the current itself, thermal energy, into which the electric current is transformed, by objects heated by the electric current that the victim touches.
The general effect of the current consists of a direct effect on the cells and tissues of the body and an indirect, reflex action on the central nervous system, leading to respiratory and circulatory disorders, manifested by stopping and fibrillation of the ventricles of the heart.
The specific effect of the current is reduced to irritation of skeletal and smooth muscles, glandular tissues, nerve receptors and conductors. Skeletal muscle irritation is manifested by tonic convulsions causing respiratory arrest, spasm of the vocal cords, avulsion fractures, and irritation of vascular smooth muscles leads to its contraction and an increase in blood pressure. Acting on the heart muscle, the current causes ventricular fibrillation. The organs of internal secretion respond to electrical stimulation by releasing catecholamines. The electric current affects the potassium-sodium gradient of cells, membrane potentials and disrupts the processes of excitation transmission, which leads to cardiac arrest.
Depending on the voltage and duration of exposure, clinically general changes are manifested by minor pain sensations, the absence of any changes in the skin. Longer exposure leads to a variety of nervous symptoms, some mental disorders, manifested by confusion, disorientation, sharp motor excitement, etc. Continued action of the current causes respiratory and circulatory disorders, leads to shock, sometimes ending in death.
The clinical picture of electrical injury. At the moment of exposure to the current, most victims experience convulsive contraction of certain muscle groups or (more often) muscles of the whole body. Victims cannot scream due to spasm of the glottis caused by the passage of current. Most of the victims lose consciousness for a period of several minutes to several hours. After the termination of the action of the current, headache, dizziness, nausea are felt.
On examination, marked pallor, cyanosis of the lips, cold sweat.
Severe forms of electrical trauma are accompanied by torpid shock with loss of consciousness, respiratory arrest, and extremely weakened cardiac activity.
In the future, many of the victims are inhibited, lethargic, drowsy, some of them have retrograde amnesia and symptoms of peripheral nerve damage.
Depending on the severity of the listed symptoms, electrical injury is divided into four degrees: I - convulsive muscle contraction without loss of consciousness; II - convulsive muscle contraction with loss of consciousness;
- loss of consciousness and impaired cardiac activity and breathing;
- clinical death.
The physicochemical (electrolytic) effect is manifested by electrolysis - the decomposition of the constituent parts of the body's liquid media into their chemical components, as a result of which the formation of fat decomposition products is observed on the skin at the point of contact. As a result of electrolysis, severe disorders of tissue metabolism, changes in the structure of cells and tissues, and deposition of the metal of the conductor in the area of \u200b\u200belectrometrics occur.
The electrolytic effect is expressed in the violation of ionic equilibrium in tissues in the form of coagulation necrosis (at the anode) and colliquation (at the cathode); the formation of steam and gas; impregnation of the skin with the metal of the conductor.
Thermal action is associated with tissue resistance and the conversion of electrical energy into heat. According to the Joule-Lenz law, the greater the voltage, magnitude, current and resistance, the longer the contact time, the more the conductor heats up. At the point of contact of the conductor with the skin, depending on the density of contact, time, characteristics of the skin at the time of exposure and other conditions, the temperature rises significantly, and electric burns are formed from minor necrosis, called electro-marks, to carbonization of tissues and focal fusion of the bone with the formation of round, hollow inside. "Bone beads" or "pearls" the size of a pea, representing molten and then solidified calcium phosphate in the form of white balls up to 0.5 cm in diameter with voids due to the evaporation of the liquid in the bones. They are specific to electrical injury. The incidence of concomitant burns increases with increasing current strength and voltage. The thermal effect is especially characteristic of the action of high voltage current, the defeat of which causes deep burns.
and IV degree.
Mechanical action. It is caused by the transfer of the kinetic energy of the electron flow to those tissues with which it comes in contact. It is manifested by abrasions, skin breaks, holes of various depths, isolated bone cracks, dislocations, tears, delamination, holes in clothing and shoes, and even detachment of limbs, as well as the introduction of metal particles of the conductor into the skin at the site of contact, called metallization.
The effect on the body of secondary phenomena accompanying electrical processes is attributed to the nonspecific action of the current: burns from a volt arc, a hot conductor, burning clothes, acoustic trauma, mechanical damage caused by a fall after an electric shock, etc.
Local changes from electrical shock. The direct effect of the current is most pronounced in the tissues with the greatest resistance. Such tissue is the skin, in which typical and atypical injuries can occur during the passage of electric current. These injuries were divided by Jellinek into electrodes, edema, burns, metal impregnation, mechanical damage, “lightning figures”.
A typical electro-marking (Fig. 286), or a current sign, is a superficial burn of the skin or mucous membrane, formed as a result of the release of heat at the point of contact of the conductor with the body. It is manifested by coagulation
Figure: 286. Typical electric markers
and drying the surface layers of the skin. For the first time, the electrometric was described by Jellinek in 1903. It is characteristic of the action of a low voltage current (10-220 V) on dry skin with a thickened stratum corneum. Its appearance is associated with the thermal and electrolytic action of the current conductor, which has a temperature not higher than 120 ° C. From the action of a higher temperature, the electrometry takes the form of burns of the III-IV degree. Electric tags are resistant to decay.
Electro-tags are localized at the points of current entry and exit, as well as along the current loop, as a rule, on the flexor surface of the joints.
At the point of entry, the electric network occurs due to contact with a conductor, at the exit point - with the ground or a grounded object. Most often, it is a nail in the heel or sole of the shoe. Current signs are formed along the shortest path of current flow, far from the entrance and exit in the natural folds of the skin, on the flexor surfaces of the joint areas or on two contacting areas of the body. The current, spreading along the surface of the body or leaving the depth to the surface, meets resistance in two contacting areas of the skin and overcoming it, turns into heat or, slipping between them, forms an electric arc or spark.
Typical electrometrics are dry and dense crater-like thermal damage, various in configuration and size, reflecting the shape and size of the conductor, which is due to the tightness of contact with the body. Often they have a rounded shape, less often the shape of an ellipse or a socket, sometimes an irregular shape, which is explained by the shape of the contacting surface of the current conductor and the angle of contact with the conductor, concomitant thermal and traumatic effects.
Their edges rise in a roller-like manner above the level of the skin. The walls are chamfered. The outer walls are light gray, sometimes almost white, surrounded by a corolla of pink hyperemia. The inner walls are dark gray, impregnated with conductor metal. The bottom is crater-shaped. Sometimes the edges of the electrometric pass into a canal that penetrates to the bone.
The spatter of the metal of the conductor forms multiple randomly spaced electro-marks resembling splashes. The pattern of papillary lines in the epidermis is indistinct.
The color of the electrometric, as a rule, depends on the material of the conductor and is due to the metallization. Iron gives the electro-tag a brown color, copper - a grayish-green.
The color of the electro-mark on the corpse changes under the influence of drying and other influences. The color change is influenced by various impurities passing to the conductor.
Close contact with the conductor clearly delimits the edges of the electrometric, the surrounding skin is not altered in appearance, the hair is not singed. Bubbles, unlike thermal burns, are not formed. With a less tight contact, its edges are surrounded by a corolla of pink hyperemia, the hair is somewhat twisted, and with loose contact and the action of a high voltage current (more than 380 V) and high force, a thermal burn is formed. It captures the entire thickness of the skin and can be accompanied by charring, sometimes reaching the bone and even penetrating the finger, forming a tunnel. Depending on the temperature of the conductor, the skin becomes dark yellow, brown or black. The damaged area has clear boundaries. Hair is singed.
In cases of high voltage technical electricity, so-called "lightning figures" may occur, which must be borne in mind when investigating cases related to electrical trauma.
In 10-30% of those affected by electric current, electro-markers are not detected. This happens in case of damage by low voltage currents (110 V, 220 V, 380 V) with low resistance of wet and thin skin, tight contact of the conductor on a large surface, skin contamination with plaster particles, machine lubricant, which prevent the formation of an electro-net or make it difficult to detect.
The combination of an electric tag with a burn often obliterates the signs of electrical injury.
The specificity of the course of electric burns in living persons is due to the depth of coagulation necrosis, damage to the tissues surrounding the burn, and changes in the body associated with the passage of current through it.
There are the following types of electric burns: current signs (electro-markers), contact electric burns, volt arc burns, combined electrothermal burns (Fig. 287).
Figure: 287. Electrothermal burn of the thigh
According to the depth of the lesion, electric burns are divided into 4 degrees: 1 degree - electro-tags, 2 degree - the formation of bubbles (rarely observed). After bursting of the bubble, a gray-white burn of deep-lying tissues is exposed, usually combined with thermal; Grade 3 - damage to the entire thickness of the skin and underlying soft tissues; Grade 4 - bone damage.
The difference between electric burns and thermal burns is a large depth of necrosis not only of the skin, but also of the underlying tissues.
Electric tags are usually painless. In the absence of a thermal burn, pain and an inflammatory reaction of the surrounding tissues are mostly absent. This is due to damage to the Meissner bodies in the skin, as well as the absence of an inflammatory response. The cone-shaped propagation of electricity causes a crater. After 10-12 days, the dead epidermis is rejected, leaving no wound or scar. That is why electric markers do not require special treatment. Longer exposure to the current with significant heat generation leads to carbonization and combustion of tissues. The muscles that better conduct the electric current are exposed and the limb takes on the appearance of a spent anatomical specimen.
Electro-tags impregnated with metal particles are detached without inflammation and suppuration, except for the palmar surface of the hands and fingers. Sweating promotes maceration and superficial suppuration.
Contact burns are caused by high voltage currents. Most often, the upper limbs (especially the hands) and the head are affected, then the trunk and lower limbs. Typically, these burns reflect the contours of the contacting surface of the current conductor. Burn areas are characterized by white or black (charred) necrosis. Charring is surrounded by a white rim (area of \u200b\u200bIII degree burn). In the place where the current with a voltage of more than 1000 V exits, there is a burn resembling the exit hole of a gunshot wound. Muscles of a dark color will stand out from its depths. Around the electric burn, tissue edema immediately develops, resulting from an increase in the permeability of the skin capillaries caused by the action of the current. The depth of tissue damage is determined by the voltage and the affected area. Currents below 1000 V affect areas with significant muscle mass.
In the area of \u200b\u200bthe fingers and joints, tendons, blood vessels, muscles and bones are injured.
Electric burns disturb the sensitivity of the skin around the lesion, damage nearby nerves and disrupt tissue nutrition, which is explained by the general effect of the current and the depth of the lesion. Necrotized tissues are rejected within 5-7 weeks. The wound granulates sluggishly, the purulent discharge is insignificant, the inflammatory reaction in the circumference is weak.
Electric burns of the head by high voltage currents are accompanied by charring of the skin and bone, penetrating or not penetrating into the cranial cavity. The victims have severe lesions of the nervous system in the form of paresis of the extremities, visual impairment and especially prolonged loss of consciousness. These complications can occur immediately or later.
Contact electric burns are usually not extensive, but deep. Dry necrosis occurs at the site of the lesion. Plasma loss through the burn surface is almost absent, the wound is less painful than with a thermal burn. Therefore, the typical picture of shock caused by an electric burn does not always develop. Necrotic soft tissues are rejected within 2-3 weeks, bone tissues - after 4-6 weeks.
Severe electrical burns of the extremities are often accompanied by acute circulatory disorders and secondary bleeding caused by compression of the vessels by contracted muscles, charred skin, reflex vasospasm and damage to their walls by Joule-Lenz heat, if the vessel directly enters the burn zone.
The action of the current on the more strongly developed flexors of the muscle group causes a sharp bending of the limbs in the joints. This contributes to even greater vascular compression and the formation of flexion contractures. Vascular spasm during the passage of current occurs as a consequence of the direct action of the current on the vessels, and by reflex. These changes lead to persistent circulatory disorders in one or another part of the limb, which causes a slowdown in blood flow, which can cause a blood clot.
Distinctive properties of electric burns located near large vessels are arterial bleeding, which occurs at 3-4 weeks. as a result of a previous sharp change in the vascular wall under the influence of current and a low ability of the thrombus to organize.
The vessels burnt with soft tissues in the zone of the IV degree burn are the cause of ischemia of the limb region located below the burn. Violation of the limb's circulation is expressed in its cold snap and cyanosis.
Voltaic arc burns occur as a result of a flash of thermal energy arising from a current short circuit. The flame temperature is 3,000-4,800 ° C with a very short exposure time. Combustion of metal is accompanied by splashing of hot particles, smokiness and metallization of the burnt areas.
Another damaging factor is the light emission from the volt arc. A flash of a voltaic arc mainly affects the face and back surfaces of the hands, and ultraviolet rays - the eyes, which must be remembered when determining the position and articulation of the victim at the time of an industrial injury. These burns damage the surface layers of the skin. The epidermis coagulates to form a brown thin scab. The sebaceous and sweat glands, hair follicles, the network of blood vessels in the deep layers of the skin remain intact. This causes the rapid demarcation and rejection of necrosis, epithelialization of the wound within 3-4 weeks.
Combined electrothermal burns occur when injured by a high-voltage current or volt arc with a voltage of more than 1,000 V, which causes a fire in clothing and surrounding objects. In these cases, the victim receives electrical and thermal burns, which heal within 10-12 days.
Atypical electric tags are manifested by burns of the II-III degree and occur during the formation of Joule heat, voltaic arc, ignition of clothing; sometimes they look like bruises, areas of punctate hemorrhages in the skin, small-point tattoos, abrasions, wounds, healings, scratches, drops of stearin, roseol (Fig. 288). In some cases, they represent wounds with burned edges, reminiscent of the entrance holes of blind gunshot injuries. The presence of such markers makes it difficult to recognize them. The diagnosis is established by laboratory tests. In survivors, atypical electro-tags are manifested by non-healing wounds and scab-covered scratches.
One of the signs of electrical injury is electrogenic metallization.
It occurs both in close contact with the conductor and from a volt arc, spraying the conductor metal and the introduction of its particles into the skin. In the place of loose contact with the skin, the metal of the conductor heats up, heats up, melts, sometimes flares up, splashes and burns, turning into gas. For the most part, under the influence of a voltaic arc, the skin is impregnated with the smallest metal particles (metallization of the skin). Metallization color in the presence of an iron conductor - brown, yellow-brown, black, copper - yellow-brown, brown, copper salts - bluish, bluish, green, aluminum - gray, yellowish, yellow-brown, brownish-black, tin - brown, brown-gray.
Sometimes in the area of \u200b\u200bthe electrometric there is a detachment of the epidermis - epidermolysis. It occurs secondarily, especially with wet skin.
Secondary damage is caused by a volt arc, fire, explosion of parts of the electrical installation, throwing by a current source, accompanied by a fall.
Secondary injuries are manifested by voltaic arc burns that ignite clothing, causing damage to the body. The most easily burned cotton (especially wadded quilted) clothing, which emits a lot of heat, which can cause deep burns up to charring. The voltaic arc melts and sprays the metal. Drops
it, getting on the clothes and body, burns through them characteristic small rounded holes and freezes in the depths.
The action of ultraviolet rays of the voltaic arc causes blinding, inflammatory diseases of the conjunctiva, cornea and retina of the optic nerve.
Electric shock is accompanied by electric burns and flammable clothing. Extensive skin burns with carbonization and damage to deep tissues and bones occur at the point of contact of the conductor under the action of a current of about 1,000 V and above. They are often combined with burns from a voltaic arc, reaching 3,000-3,500 ° C, and ignited clothing. Under the influence of this temperature, tissue combustion, a large release of heat at the point of contact and melting of phosphate salts contained in the bone with the formation of "pearls" occurs.
Sometimes electrical trauma is complicated by the development of electrogenic edema or electrical necrosis. Electrogenic edema is formed from the penetration and passage of electric current in the deep layers of the skin and subcutaneous tissue. Simultaneously with thermal, its chemical action also occurs - electrolysis with the formation of steam-gas, as a result of which zigzag cavities with charred walls can arise. The cells of the vascular endothelium are stretched, the walls of the capillaries rupture and hematomas appear, as well as electrical edema, indicating damage to the vessels and nerves of the affected area. The affected tissue can take on a cellular structure with flattening of the cells of the skin epithelium into characteristic bundles.
Electrogenic edema is most often located in the area of \u200b\u200belectro-tags, surrounding them mainly at the entrance. The amount of edema is determined by the area of \u200b\u200bthe affected area and other conditions. The skin in the area of \u200b\u200bedema is dense, pale, the tissues are sharply edematous due to vascular thrombosis, permeability of the vascular wall, stagnation of blood circulation and lymph circulation.
Necrosis of the extremities is caused by severe lesions of the vascular walls, fragility of the latter and the formation of blood clots, stagnation of blood circulation and lymph circulation. The tissues at the border of the affected area are sharply edematous, as if welded, necrotic, and in the future are not very viable, so that the process of necrosis extends beyond the visible borders of the burn. At first, changes in the tissue are not visible, and then, for 3-4 weeks, the border of the dead tissue is determined, which begins to undergo rejection. Healing occurs with a scar.
The ingress of an electric current of a higher voltage than the usual working current into the hearing devices of telephone operators, radio operators due to high voltage network failures, a lightning strike and other causes fainting, inflammatory and atrophic processes of the inner ear, etc.
Lability of the cardiovascular system and the appearance of its disorders at a later time is characteristic of electrical trauma. Occasionally, severe headaches and symptoms of increased intracranial pressure, post-traumatic encephalopathy are noted. Sometimes there is dizziness, easy fatigue, fatigue, fright, depressed mood, irritability, decreased memory and attention, disorders of the inner ear (dizziness), refractive and conductive environments of the eyes, which must be remembered when conducting an examination of working capacity.
Mechanical damage
Mechanical damage can be caused by the direct action of an electric current, being thrown from a current source, falling from a height due to electric shock, which must be taken into account when conducting differential diagnostics.
Injuries at the site of current entry look like deep and extensive wounds that can be confused with cut and bruised.
Cracks and fractures of the bones of the extremities, dislocations in the joints are associated with a sharp contraction of muscles during convulsions accompanying electric shock.
An insignificant effect of an electric current causes a convulsive contraction of muscles, a reflex twitching of the limbs, recoil from a current source, a fall from a pillar, a roof, which causes a complex of typical injuries.
In the majority of victims, the course of electric burns is rather favorable, the wounds are quickly cleared of necrotic masses, epithelialized, leaving behind thin, delicate scars. Sometimes a local or general infection joins, secondary bleeding due to destructive changes in the walls of blood vessels with subsequent necrosis of the wall and trophic disorders. Due to tissue decay and severe intoxication, secondary shock and mental disorders can occur in persons with an unstable nervous system, disappearing after a few days or months, which must be borne in mind when establishing the severity of bodily injury.
Diagnosis of electrical damage, especially in production, presents significant difficulties due to an attempt to change the situation by officials before the arrival of the task force. Therefore, in the diagnosis of electrical injury, a thorough examination of the scene, examination of the corpse with the use of the entire complex of laboratory studies and a detailed study of the case materials are of decisive importance.
Inspection of the scene
Before proceeding with the inspection of the scene, the investigator must make sure that the scene of the incident and the corpse is de-energized and that the situation is unchanged by the persons concerned.
In cases of electrical injury, in addition to the investigator, forensic expert and forensic expert, an electrical engineer is involved in the inspection of the scene. Inspection can be started only after the source of injury is de-energized.
Examining the scene, the investigator, with the help of specialists, must identify:
source of damage: current-carrying wire or object; physical parameters of current, fresh damage and reflow on electrical products;
the degree of serviceability of insulation, protective devices;
conditions that contributed to the defeat, created a current-hazardous environment, which includes, first of all, the increased humidity of the air and surrounding objects that acquire the ability to conduct current; high voltage current, when it is possible to strike at a distance, etc.;
the nature of the victim's inclusion in the electrical network: single-pole, double-pole; by direct contact with a current-carrying source or mediated with objects and liquids. Most often, an electrical injury occurs from a single-pole connection, when the victim is in contact with one pole of the current-carrying wire, and the circuit is closed by contact with grounded objects;
contact time and degree of its density;
changes in the environment that could mask the manifestations of electric shock or cause it (fire, wire breaks, etc.).
The efforts of the forensic expert during the inspection of the scene of the incident should be aimed at finding damage from the action of electric current on clothing and shoes, electro-marks on the victim's body, overlays of human tissue and traces of biological origin on current sources and objects that could be sources of current.
In the passport part of the protocol of inspection of the scene, it is necessary to reflect the temperature and humidity of the air at the time of inspection. The scene of an accident can be residential buildings, outbuildings, industrial premises, cellars, basements, storage facilities, open air, etc.
It is more expedient to start the inspection of the scene from the corpse, when it has not been moved from the scene, if the corpse is moved to another place, then it is better to start the inspection from the scene.
At the scene of the accident, the position and position of the corpse in relation to current-carrying conductors, grounding and fixed landmarks are carefully recorded.
By examining the corpse, in addition to general data, the expert must record:
posture and articulation of the corpse, what area and part of the body it contacts with a current-carrying conductor (wire, object, part) and ground (grounded object); if the posture was changed before arriving at the scene, then it is necessary, according to eyewitnesses, to clearly imagine the original posture;
list the items and nature of clothing, indicate its insulating properties (dry, wet, contaminated with oil, metal, the material from which it is made, the presence of metal fittings and items in the pockets of clothing);
note the presence or absence of shoes, their dryness or moisture, their intactness, the nature of the attachment of the sole or outsole;
to establish the nature of damage (thermal, mechanical) to clothing and items in pockets, as well as shoes;
determine the origin of injuries on the body: mechanical, thermal, electrical (electric tags);
to identify the correspondence of damages caused by the action of current on the body, clothes and shoes, melting, damage to the current-carrying wire (object), insulating devices,
Inspection of clothing and shoes is essential to determine the nature of the incident.
When examining them, it is necessary to remember about the different ability of materials to withstand the action of heat and electricity. So, cotton materials burn, woolen materials are scorched, synthetic materials are melted.
The action of high voltage current causes rupture of clothes and shoes without traces of scorching, magnetization, melting or melting of metal fittings, nails and shoe shoes, metal objects in pockets.
After listing the items of clothing, it should be noted the presence of damage, scorching and melting, remembering that the ignition of clothing causes a voltaic arc arising from loose contact between the power source and the victim. Therefore, when searching for the source of injury, it is necessary to pay attention to the current sources that cause a volt arc.
The presence of multiple holes in synthetic garment materials indicates metal splashing from the conductor. Melted metal and molten plastic items can be found in clothing pockets.
Particular attention should be paid to the inspection of shoes. From a single-pole connection of the victim to an electrical circuit, the current exit is most often the legs. Therefore, the expert must reflect the material from which the shoes are made, their condition at the time of inspection. Rubber shoes, as a rule, exclude the possibility of current flowing through them. In this case, the place of current exit should be sought in other areas of the body, taking into account the posture and position of the victim in relation to grounded objects. If you have leather shoes on your feet, you need to pay attention to the moisture of it and the socks, the presence of nails in the soles reaching the insole, indicate the material from which they are made and its moisture content, note the presence or absence of melting of nails or other metal parts of the shoes.
When starting to examine a corpse, it is necessary to focus on the moisture content of the skin and especially to emphasize the moisture of the hands and the imposition of foreign substances on them.
The main task during the examination of a corpse is the detection (search) of electro-marks. Most often they are found on the palmar surface of the hands at the points of contact of the fingers. This localization is explained by convulsive flexion of the fingers under the action of an electric current and the formation of many folds. Persons who constantly work with electricity, knowing about the convulsive contraction of the muscles, touch the source of the current with the back surface of the hands, where the electrometry is revealed by examination. Somewhat less often, electrodes are found on the plantar surface of the feet and sometimes in places covered with clothing, as well as on the flexor surfaces of the joints.
Particular attention should be paid to damage that has a peculiar shape and a certain pattern of the surface relief. This will make it possible to purposefully conduct a search for a current-carrying object with which the victim was in contact. If such is found, a large-scale survey is carried out for subsequent identification.
Damage revealed by body inspection by area should be compared with damage to clothing and shoes. The presence of injuries on the body under undamaged clothing indicates the direct effect of electric current.
On the scalp, single patches of scalp can be seen without visible skin changes. Sometimes the opposite picture is also possible, which is explained by the density of the contact. In these cases, the hair is not singed, but has a characteristic curl.
Anisocoria is of great diagnostic value for determining the lifetime of electrical injury. A narrower pupil is observed on the side of current entry. In cases of electric shock to the head, the pupil on the injured side is more dilated.
In addition to electro markers, during an external examination of the corpse, electrogenic edema, metallization, various kinds of burns (clothing, skin, hair), epidermolysis, necrosis, mechanical damage, lightning figures, and occasionally bubbles can be found.
Examination of the corpse in the open air in the protocol reflects the state of the weather at the time of injury (rain, sleet, hot, humid weather), the nature and moisture of the soil. Particular attention should be paid to high ambient temperatures that cause sweating and increase the risk of electric shock.
When inspecting residential premises, note whether electrical appliances are included in the network, whether the insulation of current-carrying conductors is broken. If the corpse is found in the bathroom, then it is imperative to indicate the presence or absence of water in the bath, the degree of filling with water, the material from which the floor is made, the humidity of the floor, the presence of homemade electrical devices.
Inspection of industrial premises pay special attention to the places of connection of current-carrying conductors, their grounding, air and floor humidity.
When inspecting damp rooms, basements, cellars, pay attention to the insulation of wires, moisture, the protection of the light bulb with shades, the floor (earthen, concreted, wooden, dry or wet).
A thorough examination of current-carrying objects can reveal remnants of the epidermis, subcutaneous fat, blood, hair, parts and fibers of clothing. In these cases, in the protocol of the inspection of the scene, it is necessary to fix the height of their location from the floor level.
Clothes and shoes with traces similar to the action of electric current are removed from the scene of the incident and sent for investigation to the Department of Medical Forensics.
Subjects with human tissue overlays are sent for examination to a forensic laboratory.
Information necessary for an expert to conduct an examination
In the installation part of the decision on the examination, the investigator must indicate: air humidity, the presence or absence of the smell of ozone in the air at the place of detection of the corpse, the location of the victim at the time of the incident (on the pole, in the bathroom, in the field), what he did (repair of electrical wiring , watering the garden, etc.), what is the floor in the room, wet or dry ground, is there melting of the soil, damage, burning and melting of household items, buildings, what areas of the body the victim came into contact with the current-carrying conductor, at what distance was found from the current source, what is its voltage and current strength, what diseases the victim suffered during his lifetime, whether he received help, who and what.
On autopsy, there are no specific changes in internal organs caused by the action of electric current, but signs of asphytic death are revealed.
In cases of electric shock, various additional studies are widely used, carried out in the departments of the forensic medical examination bureau.
Histological studies are carried out in order to establish the diagnosis of electrical injury.
When examining the skin from an electrometric and a proposed electrometric, flattening of the upper layers of the skin, swelling and homogenization of the stratum corneum, the presence of honeycomb-like voids in it, formed under the influence of the transformation of water contained in the tissues into vapor, slit-like breaks located parallel to the skin surface, are found. Sometimes traces of metal particles left by the current conductor are found on the surface and in the depths of this layer.
Under the microscope, the cells of the main layer (or embryonic, germ, malpighian and partly prickly) are elongated perpendicularly or at a slight angle to the skin surface in the form of a "picket fence", "brush" or "panicles", bulging vortex-like. The hairy sacs and endothelial cells of the capillaries are elongated, the epidermis is exfoliated, the skin papillae are flattened.
Sometimes there is fragmentation and disappearance of elastic fibers and transverse striation of muscle fibers, swelling of nerve fibers.
In the deeper layers of the skin, cavities with charred walls are found - current paths that are also observed in the bone.
An invisible electric tag can be detected by placing the skin in contact with an electric current for 1 hour in a 20% solution of acetic acid, which causes tissue swelling and the electro tag becomes distinguishable (T. Odtaga, 1968).
Differential diagnosis of electrical injury is based on the identification of damage and changes characteristic of the action of electric current.
Hot metal burns are characterized by continuous heat.
Electric tags have the form of multiple point burns with a wide metallization border.
With prolonged passage of high voltage current in the internal organs, small necrotic foci and hemorrhages, often perivascular, can be found.
In the muscles, the absence of transverse striation and multiple foci of necrosis are often revealed.
If the victim has lived for several hours after the injury, then a picture of pigmentary nephrosis appears in the kidneys.
By examining urine in a clinical laboratory, by the end of the first hour after the injury, myoglobin is detected, which, after extensive muscle damage from high voltage shock, enters the bloodstream, and from there enters the urine.
X-ray examination in the bones reveals: cleavage, macular osteoporosis, bone fusion, the formation of bone pearls, etc.
By medical and forensic examination of clothing, changes are established that are typical for the action of an electric current.
By examining electro-marks and damage on clothing, the metal of the conductor is determined by the simplest and most accessible method - the method of color prints, as well as X-ray examination in soft Bucca rays. Microcrystalline and spectral research methods establish the qualitative composition of the conductor.
The charred areas and traces of melting of the metal of the conductor (the action of Joule's heat) in the form of blackish dots, sometimes merging with each other in a grayish cloud or repeating the shape of the contacting surface of the conductor, are determined by research in ICL (infrared rays) using an image intensifier (image intensifier) \u200b\u200b(electronic optical converter).
Evaluating the results of laboratory tests for metals, it is required to exclude the possibility of accidental contamination of the skin, especially palms and clothing, in persons working with metal.
When stereomicroscopic examination of clothing items, it is found in the places of breaks without traces of burning, as it were, a smooth cutting off of the ends of the fibers of the threads (SD Kustanovich, 1965).
Establishing a causal relationship between injury and death is important for the investigation. In this regard, there are several types of death caused by electric shock:
instant, or instantaneous, death occurs at the moment of electric shock, and the person dies immediately after exposure to it at the scene;
delayed death occurs at the scene, when, after an electric shock, the victim still shows signs of life for a short time after the injury;
interrupted death occurs after removal from a serious state, when from the moment of switching on until the moment of death, a certain short period passes, during which a person regains consciousness, signs of improvement in health appear, and then he dies;
late death occurs many hours and even days after electric shock, most often from changes, complications and diseases caused by the passage of current.
The causes of death from electrical injury are different and are due to the nature of the current, by its passage, the reaction and state of the body, as well as other factors.
One of three causes of death or a combination of them are possible: impaired cardiac activity (fibrillation), respiratory and circulatory arrest, shock. They can occur both under the direct action of an electric current, respectively, on the heart or brain, and as a reflex effect on other areas and organs of the body. Acute oxygen starvation of tissues is of great importance in the mechanism of development of these conditions.
In most cases, the cause of instant death is a violation of cardiac activity caused by the action of a current of low voltage and small magnitude.
Cessation of cardiac activity occurs as a result of developing myocardial fibrillation or from reflex cardiac arrest due to a depressing effect through the vagus nerve on the vaso-motor center of the medulla oblongata, reflex spasm of the coronary arteries of the heart, termination of the transmission of excitation processes due to disturbances in the sodium-potassium gradient and membrane potentials, ventricular fibrillation.
The action of high voltage alternating current causes damage to the central nervous system. In these cases, respiratory arrest is the leading cause of death. It occurs as a result of reflex irritation of the respiratory center of the medulla oblongata, or a direct action on the respiratory center of the current at the moment it passes through the head, causing paralysis of the respiratory center, or tonic contraction of the diaphragm and muscles of the glottis contractors, or spasm of the respiratory muscles.
The immediate cause of late death (after a few days or weeks) is usually burns or massive bleeding from necrotic vessels, sometimes located at a distance from the main lesion.
A feature of the examination of an industrial electrical injury is the study of the conclusion of a technical inspector, safety rules, departmental instructions for a given profession, an accident report, medical documentation. The expert receives the necessary information from the case materials submitted by the investigator. In the explanations and interrogation protocols, the investigator is obliged to find out how the victim was feeling shortly before what happened, whether he was overworked, what diseases he suffered in general, whether he suffered from diseases contraindicated for this work, whether the deceased was intoxicated. Comparing and evaluating expert data with investigative ones, the expert must explain the presence or absence of electro-marks and other changes characteristic of the action of the current, exclude or confirm the presence of diseases and poisoning, and also reconstruct the incident, restoring the posture and position of the victim, the lifetime of the injury, the duration of exposure.
Mostly, these accidents in everyday life and at work occur due to a violation of safety regulations, technical malfunction of electrical equipment, devices and electrical equipment, damage to electrical insulation. Cases of murder and suicide by electric shock are rare.
Forensic medical examination is carried out in cases of the need to determine the degree of disability in persons affected by electric shock.
Factors and conditions for the action of technical electricity on the body
The damaging effect of electric current on the body is due to its physical properties, conditions of action and the state of the body.
More often, electric shock occurs due to direct contact with a current-carrying object, less often - at a short distance from the current source.
The physical properties of an electric current are determined by its voltage, strength, type and frequency. Low voltage - 110–220 V, high - over 250 V. On electric railways, the voltage reaches 1500–3000 V. Mostly, there are cases of low voltage shock, with which a person is more often in contact in everyday life and at work.
A current of 50 mA is life-threatening, and above 80-100 mA, it is fatal.
By type, alternating and direct current are distinguished. Alternating current injury is more common. Alternating current with voltage up to 500 V is more dangerous than direct current. The latter is more harmful at voltages above 5000 V.
Low-frequency alternating current is dangerous (40-60 oscillations per second). High-frequency currents (from 10 thousand to 1 million Hz and more) are not dangerous for the body and are used in medical practice during physiotherapeutic procedures.
Conditions for the action of the current. These include: the value of the resistance of body tissues, the area and density of contact with the electrical conductor, the time of exposure to the current, the path of the current in the body.
The resistance of the body is due to the moisture of the skin, its thickness, blood circulation, the state of the internal organs.
Human skin resistance ranges from 50,000 to 1 million ohms. The resistance of damp skin is sharply reduced. Wet clothing does not protect well from electric current. The resistance of the internal organs (especially the brain and heart) is much lower than that of the skin. Therefore, the passage of current through organs with low resistance is very dangerous, especially when both hands are included in the electrical circuit, the systems "head - legs", "left arm - legs".
There is a concept of hazardous premises - with high humidity (baths, washrooms).
The tighter the contact with the current-carrying conductor and the longer the time of exposure to the current, the greater its damaging effect.