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Action of electric current

  • Action of atmospheric electricity
  • The electric current, unlike other traumatic factors that cause damage to a person in direct contact, can act on a person and indirectly, through objects, at a distance, through arc contact and step voltage. In forensic medical examinations, one has to meet more often with electric shock at work and at home, much less often with the action of atmospheric electricity (lightning). The effect of electric current on the body is manifested in electrical, thermal and mechanical effects and often leads to the development of extreme conditions, accompanied by a sharp breakdown of cardiac activity (ventricular fibrillation of the heart) and respiration, as well as to the occurrence of shock reactions. Electric shock damage is 1–2.5% of all types of injuries, but in the number of deaths and disability occupy one of the first places.

    The effect of electric current in the workplace and in the home can cause severe and even fatal damage from contact with faulty household appliances (table lamps, teapots, irons, etc.) connected to the network of 127 or 200 V. In industry, it uses three-phase current of 380 V and a frequency of 50 Hz. At such a voltage, a severe electrical injury often occurs. There are direct and alternating current. DC and AC voltages, equivalent in their effect on the body, are 120 and 42 V, respectively. DC current is less dangerous than AC, only up to 500 V. At 500 V, the danger of both types of current is equalized, and at voltages above 500 The more dangerous is the direct current. In practice, direct current lesions are rare. The severity of the lesion from the electric current depends mainly on its physical parameters, but often the circumstances under which the current acts, as well as the condition of the body, are of great importance. The greatest danger of injury exists when exposed to alternating current frequency of 40- 60 Hz.

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    With an increase in the frequency of electrical oscillations, the danger 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 strength (2-3 A), there is no damaging effect on the body. This is the basis for the widespread use of high-frequency currents in medical practice - for physiotherapeutic procedures.

    Depending on the magnitude of the voltage, there is a predominant lesion of the respiratory or circulatory organs. The international standard for safe voltage, the so-called reduced voltage, is a potential difference of 24 V. Fatal outcomes are possible even at a voltage of 40 V. High voltage currents are over 3000 V, less dangerous and rarely fatal. This is explained by the fact that at high voltages between the body and the electrode, an electric arc flash effect occurs and most of the electrical energy is converted into heat, causing local damage in the form of burns. The most frequent deaths under the action of current voltage from 100 to 1500 V.

    The value of current is important in the development of an electric shock; the impact of a current of 100 mA is in most cases fatal.

    The effect of the biological action of 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 onset of ventricular fibrillation of the heart. Prolonged contact with electrical conductors with a current of 0.25–80 mA (minimum “non-admitting” current) can lead to death, causing cramps in the respiratory muscles and, as a result, acute asphyxiation.

    The propagation of electric current throughout the body is possible if there are conditions for the input and output current. This happens when a person simultaneously contacts two electrodes — a bipolar inclusion or contact with one of the electrodes, and any part of his body is grounded — a single pole inclusion. Inclusion may be partial, when a person isolated from the ground touches opposite poles with one hand. Under these conditions, the current passes through the included segment of the arm, which is usually not dangerous. At high voltage, an electric current can hit a person without directly touching the conductor - at a distance, through an arc contact, which occurs when there is a dangerous approach to it. As a result of air ionization, a person creates contact with live installations or wires. The danger of a lesion at a distance increases significantly in wet weather due to the increased electrical conductivity of the air. At extremely high voltages, the electric arc can reach a length of 35 cm.