How does electric current affect the person?
Electric current strikes the person suddenly. The current flow through the body of the person causes elekyotrichesky injuries of different character: electric blow, burns, electric signs tags.
The electric blow nazyyovatsya defeat by current at which there is shock, i.e. svoyeyoobrazny heavy reaction of the organism on strong the razdrazhiyotel — electric current.
The outcome of shock is different. In the hard case shock is followed by disorder of blood circulation and the dykhayoniya. Fibrillation of heart is possible, i.e. instead of simultaneous rhythmical (about 1 time a second) reductions of the cardiac muscle there is the chaotic twitching separate it волокон — fibrilla. It stops normal work of heart, the blood-groove stops, and there can come death.
Defeat of the person current at the voltage up to 1000 V in the majority случаев is followed by electric blow.
Burns arise at influence of current of the considerable veliyochina (about 1 And yes more) or from the electric arc. So, at approach to current carrying parts over 1000 V on unacceptably small distance between the current carrying part and the body of the person there is the spark discharge, and then the elektricheyosky arch which causes the heavy burn. At accidental contact with the current carrying part up to 1000 V of prokhodyayoshchiya through the body of the person current heats fabrics to 60 — 70 °C. It causes protein folding. Burns electric current recover difficult. They take the big surface of the body and get deeply.
Electric signs (tags) are the necrosis of skin in the form of the callosity of yellow color with the gray border in the place of the entrance and exit of current. If defeat got deeply, then body tissues gradually die off.
The nature of influence of variable electric current in the zayovisimost from its size is given in tab. 1
Follows from tab. 1 that current more than 15 mA at which the person cannot independently osvoyoboditsya is dangerous to the person. Current in 50 mA causes severe defeat. The current in 100 mA influencing more than 1 — 2 with is deadly.
The factors influencing the result of defeat
The size of the elektriyochesky current passing through the body of the person and consequently, the result of defeat depend on many circumstances.
The most dangerous is alternating current with the frequency of 50-500 Hz. Most of people keep ability to be exempted samostoyayotelno from currents of such frequency at its very small sizes (9 — 10 mA). The direct current is dangerous too, but independently it is possible to be exempted from it at a little big sizes (20 — 25 mA).
The size of current depends on tension of the electric unit and on resistance of all elements of the chain on which current, including from resistance of the body of the person proceeds. Resistance of the body develops of active and capacity resistance of skin and vnuyotrenny bodies. The dry, undamaged skin has soprotivleyony about 100 000 Ohms, wet — about 1000 Ohms, and soprotivleyony internal fabrics (at the removed horn layer) makes about 500 — 1000 Ohms. The smallest resistance face skin and axillary hollows has.
Resistance of the body of the person - size nonlinear. It sharply, disproportionately decreases at increase in tension, priloyozhenny to the body, increase in time of influence of current, at the unsatisfactory physical and mental soyostoyaniye, at the big and hard contact with the current carrying part, etc. Follows from fig. 1 that at increase in voltage from 0 to 140 V attached to the body body resistance not linearly falls from tens of thousands to 800 Ohms (the curve 1). Respectively, the current passing through the body increases (the curve 2).
Resistance of the body of the person (Ohm) is determined approximately by the formula
Zchel = Upr/Ichel
where Upr — voltage drop on resistance of the body of the person - Century.
In calculations for electrical safety it (too it is approximate) is accepted equal:
Zchel = 1000 Ohms
The way of current through heart, the brain, lungs is most dangerous. Harakyoterny ways: the palm — the foot, the palm — the palm, the foot — the foot. However deadly defeat is possible also at the current prokhoyozhdeniye on the way which, apparently, does not mention zhizyonenno important bodies, for example through the shin to the foot. These are yavleyony has a talk that current in the body proceeds on the way of naimenyyoshy resistance (to nerves, blood), but not on the straight line — through fabrics with the big resistance (muscles, fat).
It is established that the result of defeat by current depends on the fizicheyosky and mental condition of the person. If it is hungry, tired, got drunk or is not healthy, then the probability of the heavy porayozheniye increases. Women, teenagers, men with poor health are capable to sustain considerably smaller currents (in limits of the mA), than healthy muzhchiyona (12 — 15 mA).
Influence duration - one of the major factors influencing the result of defeat. The cycle of work of heart is equal priyomerno to 1 page. In the scraper there is the phase T equal 0,1 with when the muscle of heart is relaxed and it is most vulnerable for current: there can be the fibrillation. The time of influence of current is less (less than 0,1 c), the probability of fibrillation is less. Long (several seconds) influence of current leads to the heavy outcome: resistance of the body decreases, and current of defeat increases.
Mechanism of impact of electric current on the person сложен. On the one hand, in high-voltage installations there were sluyocha when short-term (the 100-th fractions of a second) influence of current in several ampere did not lead to death. On the other hand, ustayonovleno, that death is possible at the voltage of 12-36 V when current in several milliampere influences. It proyoiskhodit as a result of touch to the current carrying part naiboyoly the vulnerable part of the body - the palm back, the cheek, the neck, the shin, the shoulder.
Considering danger of electric units tension as to 1000, and higher than 1000 V, each working has to remember firmly that it is impossible to touch current carrying parts независимо from under what tension they are, it is impossible to approach close current carrying parts in high-voltage installations, it is impossible to touch without need metal designs of distributing devices, support of lines of the elekyotroperedacha, to the equipment body able it to appear energized at short circuit on them current carrying parts.
Maximum permissible it is necessary to consider current at which человек can independently come off the electric circuit:
Ground faults in electric units otyoklyuchatsya, as a rule, by the main relay protection for fractions of a second. Therefore electrical safety devices (grounding, etc.) are allowed to be calculated, proceeding from big sizes of the permissible current. In this case the current which is not causing the fibrilyolyation in 99,5% of experimental animals is considered admissible, the body weight and hearts kotoyory is close to human. The admissible sizes of current and napryayozheniye of touch received at laboratory issledoyovaniye are specified in tab. 2
Follows from tab. 3-2 that currents more than 65 mA and voltage more than 65 V are allowed less than 1 page.Top