Measures of prevention of electrotraumatism
As the statistics shows, accidents from defeat by electric current become less. However to lead it to self-complacency, on the contrary, it should not is necessary to strengthen fight for elimination of traumatism from defeat by electric current.
How there is the damage of the human body electric current?
The body of the person should be considered as the carrying-out weight surrounded with dielectric — the outside integument.
Resistance of the body of the person to electric current depends mainly on the condition of the outside integument.
Resistance — size variable, different not only at different people, but even at the same person, depending on the number of factors (moistening of skin, stalemate allocations, availability of metal dust and so forth).
Resistance of the body of the person changes in wide limits (from several hundred thousands to one thousand ohms), and sometimes (in especially adverse conditions) and up to 400 — 500 Ohms. Rated resistance it is considered to be 1000 Ohms.
Deadly size is current intensity from 0,1 A and above, dangerous size — current from 0,05 A and above. Alternating current with a frequency from 40 to 60 Hz is considered the most dangerous.
Current makes the strongest impact on the central nervous system, breaking the electric processes inherent to live matter with which its life activity is connected. At defeat such phenomena as the mechanical rupture of tissues of the body, burns, the chemical phenomena (blood electrolysis), etc. occur electric current also.
Defeats by electric current separate into electric blows and electric traumas.
The electric blow is most dangerous. He says that when passing electric current through the body of the person all organism is surprised.
Electric traumas are cases at which electric signs and metallization of skin turn out. Also refer damages when falling from height in holding time of electrical units to electric traumas.
Work energized, non-operational condition of electric units, accidental touch to the current carrying parts which are energized directly or metal and other objects are basic reasons of defeat of the person at electric blow.
At direct accidental contact with current carrying parts the greatest danger of defeat is created by electric current. Especially dangerously accidental touch of the person at the same time to two different phases of the installation which is energized. At such touch current reaches the maximum size caused by only resistance of the body of the person. The danger increases also because in most cases the person touches both phases with two hands, and the way of current lies through internals of the person (heart, respiratory bodies, etc.). Besides, the person is influenced in this case by the full operating voltage of installation, and isolation it has no protective action.
All cases of electrotraumatism are subject to registration.
Statistical data of electrotraumatism confirm the possibility of severe defeat with electric current at two-phase inclusion even at the voltage of 65 century.
Electric traumas usually are followed by passing of electric current through the earth.
The personnel servicing the electrical unit or adjoining to it are also connected to the earth through resistance of the bigger or smaller size depending on the condition of the body, material of the floor, properties of footwear, etc. Therefore for the person can constitute danger not only simultaneous inclusion on two phases of the electrical unit, but also touch to one phase as at the same time through the earth there passes the electric circuit which joins the person.
The touch to one phase is possible in many cases during the work energized (for example, when replacing of the fused lamps, touch to the wire with defective insulation and especially during the work with field electric devices and the electric tool).
It is also necessary to mean that in alternating current mains at contact of the person with any phase through his body except the leakage current (wattful current) there passes also the current caused by the capacity of network in relation to the earth (capacity current).
At the isolated installation neutral the body of the person joins on linear stress consistently with the resistance of network. If resistance of network becomes close to zero, then the body of the person is directly included on full linear stress.
Single-phase inclusion can arise when works (for example, on measurements) carry out without protective equipment, when using of devices with unsatisfactory isolation of current carrying parts and also upon transition of tension to metal constructive parts of the equipment.
At the undamaged dielectric galoshes in case of application of the insulating basis the danger of defeat can be minimized.
Electric burns arise at the most various short circuits which are followed by emergence of the electric arc.
Short circuits in installations up to 1000 V happen at connection of phases any metal subject (tool), at the wrong turning on of breakers of asynchronous electric motors to the disconnected rotor rheostat, at installation of safety locks when short circuit in network is not eliminated, at shutdowns, etc.
In installations by tension 1000 V the greatest danger concerning burns are given by shutdown of disconnectors under loading above.
Distinguish three degrees of burns: the first — skin reddening, the second — formation of bubbles, the third — carbonization and the necrosis of fabrics.Top