Action of electric current on a human body ofReaction to electric current arises only after its passing through tissues of the person. In these cases there are spasms of muscles or respiratory standstill and hearts that does not allow the person to be exempted from contact with the installation (or wires) which is energized independently. Extent of defeat of the person depends on a sort and the size of tension and current; frequencies of electric current; ways of current through the person, durations of action of current; environmental conditions.
As is shown by practice, rescue of the person is possible if time during which the person is under the influence of electric current does not exceed 4... 5 min.
the Body of the person have the electric resistance which consists of resistance of skin and resistance of internals. In the calculations connected with definition of the current passing through the person, resistance of a body of the person of Rchel is accepted equal 1000 Ohms. The size of the current passing through the person is the factor determining weight of defeat by electric current. Electric current, passing through the person, the physics - biological impact on the main systems of an organism which is expressed in excitement of muscular and nervous tissues, burns of internal and external bodies, blood electrolysis renders difficult.
of People begins to feel passing of current with a frequency of 50 Hz with the force of 0,6... 1,5 ma. At current 10... 15 ma there are spasms of muscles of hands which the person cannot independently overcome, i.e. the person is not able to unclench a hand which touches current carrying part of installation. It is accepted to call the size of such current threshold not releasing. When passing current in 25... 50 ma there are spasms of muscles of a thorax that causes violation or the termination of breath. At long influence of current of such size (5... 7 min.) can come death owing to termination of work of lungs. Current with a force of 50 ma and more causes a stop or chaotic reductions of heart that leads to the blood circulation termination. Such current is considered deadly.
Diverse influence of electric current can be reduced to two types of defeat; to electric injuries and electric blows. Electric injuries are the damages of body tissues under the influence of the passing electric current which are expressed as an electric burn, metallization of skin, mechanical damages, electric signs. The electric blow causes the excitement of living tissues of an organism under the influence of the passing electric current which is followed by involuntary reductions of muscles.
The factors determining the result of defeat
by the Major striking factor electric current is. At long (more than 1 with] course of alternating current of industrial frequency mark out the following characteristic values: threshold current of feeling (0,8 - 1,2 ma), the threshold not releasing (arresting) current (10 - 16 ma), threshold fibrillyatsionny current. The domestic scientist Kiselyov A. P. the settlement ratio for definition of the striking current as function of mass (G) of a body of the person is offered: / ““, = 1,2 (30 + 3,7G)
Resistance of a body of the person. Allocate internal and external resistance. The main component is external resistance - skin resistance (namely epidermis) the person. So, in relative units if to accept resistance of skin for 1, then resistance of internal fabrics will make 0,15 - 0,20 (600 - 8000M). resistance of nervous fibers - 0,025. Sweat, moisture reduce resistance of the person by 12 times, in water it decreases by 25 times. As a calculated value of resistance of a body the size 1000 0 of m
the Way (loop) of current is accepted. Distinguish so-called big (full) loops which occupy the area of heart (through heart 8 - 12% of a general meaning of current proceed) and small loops when through heart 0,4% of a general meaning of current proceed. Treat big loops: the right hand - legs (statistically they arise in 20% of cases), the left hand - legs (17%), both hands - legs (13%), the head - legs (5%), a hand - a hand (40%). A small loop is the loop a leg - a leg (6%).
Threshold values of the striking currents depend on duration of influence of current: lasting influence 0,1 with they make 500 ma (400 ma); at 0,2 with - 250 ml (190 ma); at 0,4 with ~ 125 ma (140 ma); at 0,5 with - 100 ma (125 ma); at 0,7 with - 70 ma (90 ma); at 1,0 with - 50 ma (50 ma). In brackets values of currents taking into account nonlinearity of change of values of resistance of a body depending on the enclosed tension are specified.
the Direct current is less dangerous, than variable (by 4 - 6 times in comparison with current of industrial frequency). The most dangerous to the person is current with a frequency of 70 Hz. The industrial frequency of 50 Hz is equivalent on danger with a frequency of 100 Hz. With growth of frequency of value of the striking currents increase, i.e. danger of defeat decreases.
Other factors. It is established that everything that increases rate of work of heart promotes increase in probability of defeat (fatigue, excitement, a fright, thirst, alcohol, drugs, diseases, etc.). Not a smaller role is played by readiness for electric blow. In more detail this question is considered in the " magazine; Labor protection and social insurance “ No. in, 1997.