Electrification (health)

Prevention

The man was always wary of the Foudre. On the other hand, the electricity distributed (domestic or industrial) appears not very dangerous to him first of all. It is thus necessary to take actions of information and sensitizing to avoid the accidents.

With the use of electricity as a source of energy, the men have, progressively accidents, tempted to guard itself against the dangers of this energy as practical as dangerous.

It is recommended to handle a cable in service only with Gant S insulators.
modern equipment and electrical installations, of the strict Norme S must be respected to avoid with the user undergoing an electric shock.
If that arrives despite everything (it is an accident still too frequent), very fast security systems shut off the current, (Disjoncteur).
For as much, protection is never total. Moreover, in the environment industrialists, of the distribution networks high and very high voltage, like for the food of the Train S (Catenary S), an even short exposure is often fatal, worse, the systems of cut being designed to rearm itself automatically (for example to restore the food after a Surtension on the network).

Fields of tension

Comments on classification

One can notice that the more the tension is raised, the more it is classified dangerous, because the current which crosses the body him is proportional (Loi of Ohm) and, it is this electric current circulating in the body which is dangerous. The alternative courses or impulse which cause cardiac Fibrillation S (disordered state of the beats of the heart, with fast risk of death) are more dangerous than the continuous currents (serious internal burns).

The tension is regarded as little or not dangerous in lower part of 50 V approximately.

The table above makes it possible to very highlight the specificity of the high voltage: close to a line with High voltage (including close to the railway installations), no daily insulator is enough to prevent the passage of the current (flash or electric arc). In other words, one should not approach of cables with high voltage (even fallen on the ground). Indeed, an electric arc could occur while approaching with less than 1 or 2 meters! A wood end is not enough either. Only specialized teams can intervene to eliminate the danger. In particular, even after cut of the current, there remains an significant amount of energy stored in the line.

Values of currents and effects

One starts to feel the current from 1 approximately my (thousandths of amp).
It becomes really dangerous towards approximately 10 my (contraction of the muscles).
human traversed by a current of 30 my during 10 seconds has a chance on two to keep serious after-effects of them, however these 30 my would not light a bulb of 25 Watt S!

An impulse of current passing by the heart at the bad time can suffir to kill on the blow. The cardiac arrest is in fact the primary reason of the majority of the deaths by electrification. While an important current will cause serious lesions (by internal burns for example) but with difficulty death (according to the exposure time and the body considered).

Macabre detail: the Electric chair is a tool well badly thought, because much the weakest running well placed would be certainly more “effective”.

Action to be taken in the event of electrification

electrification is always a serious accident . Even if the victim seems to be well, it is necessary:

to protect: to disconnect the defective apparatus, or to better shut off the current; if that is not possible, to prevent the other people from approaching;
for an accident blaming an air line, only a specialized team can intervene in safety, in waiting of its intervention, protection exclusively consists in maintaining the people distant;
First aid: alarm: to alert the helps (“112” in all the European Union. Certain countries have in premium of the specific numbers, example: “18” in France);
according to the state of the victim:

if the person is conscious, to install it in the position where it feels best (by defect lengthened) and the to supervise;
if the person is unconscious and breathes, to turn it on the side in dog of rifle (side Position of safety);
if the person does not breathe, to carry out the cardiopulmonary Réanimation.

The agents of the French company of electricity (Électricité de France) have a particular technique in the event of accident on post: after protection, an agent goes up to the post, positions behind the victim (which is suspended by its harness) and violently plates it against the post, in order to create an effect similar to the Punch sternal; then, it descends the victim. This gesture does not have proven effectiveness, but it does not delay the descent of the victim (the reanimation is not possible in height).

Consequences of electrification

Electrification is a Accident in the home and a frequent Industrial accident. It can have like consequences:

Of the Burn S, either on the Skin (the current skirted the skin and caused surface burns), or interns, one then sees on the skin a burn at the entrance point and a burn at the exit point of the current;
a destruction of the cells inside the body or Rhabdomyolyse;
a ventricular Fibrillation, causing a cardiac arrest;
a contraction of the muscles (Tetany) being able to cause a Asphyxiation. Note that this contraction is perverse: the muscles being contracted, the electrified subject cannot slacken any more the contact (case of a wire in the hand; it is advised to touch the cables with the outside of the hand).
Of the Traumatism S secondaries due to a fall or involuntary movements (Wound, Fracture, Luxation, distorsion).

Effects of the electric current

the factors influencing the physical injuries are:

the type of current (alternate or continuous)
the tension
the resistance of the Human body
the intensity of the current
the duration

the resistance of the human body (i.e. its opposition to the passage of the current) varies with:

the Surface of contact
the contact pressure
the thickness of the Skin
the presence of moisture
the Weight, the size, the Tiredness…

Example of the risk incurred by the human body, crossed by an alternative course (of 15Hz with 1000Hz):

characteristic Values

the indications hereafter come from the experiments made directly on the man until the threshold of contraction. The other phenomena were caused on animals. They summarize the effects produced by a Alternative course (50-60 Hz) according to the intensity of the current and its time of passage.

Effects of the passage of the alternative course:

ventricular fibrillation is regarded as the main cause of Mort by electric shock. There exist also cases of dead by asphyxiation or cardiac arrest.

Of the effects Pathophysiological S, such as muscular contractions, difficulties of breathing, increase in the Blood pressure , disturbances in the formation and the propagation of the impulses in the Heart, including Auricular fibrillation and the provisional stop of the heart, can occur without ventricular Fibrillation. Such effects are then not Mortel S and are usually reversible.

Impedance of the human body

The fabrics of the Human body can be represented by a succession of resistances R and Réactance S (Inductance S and Capacité S) X, the whole constituting a impedance Z: Z ² = R ² + X ² .

the impedance of human body Z results from the geometrical sum of the impedances of the skin or mucous membrane at the contact points Zp1 and Zp2 and of the internal impedance of the Zi fabrics.
the internal impedance (Zi) is appreciably always the same one for the same individual, except if the surface of contact is very weak, in which case it increases.
total resistance decrease quickly when the intensity of the current increases.
the impedance of the skin varies for each individual in function, primarily, of the Paramètre S following:

the Temperature of the skin
the Surface and the Pressure of contact
the tension (force) of contact
the state of moisture and Sudation of the skin
the Time of passage of the running
the Physiological state of the person
the morphology of the individual
the way of the current in the human body

Effects of the frequencies higher at 100 Hertz

electrical energy in the shape of alternative course of frequency higher than 50/60 Hz is used more and more in the modern electrical materials, for example in the Aviation the portable (400 Hz), tools and the electric welding (100-200-300 Hz and up to 450 Hz), the electrotherapy (a few Khz), the food of power of 20 Khz with 1 GHz.

the impedance of the skin is practically inversely proportional to the frequency for tensions of contact of a few tens of volts.

It is estimated that to 500 Hz, the impedance of the skin is approximately the tenth of that to 50 Hz, it can thus be neglected in much case.

Under these conditions, the total impedance of the human body can be comparable with its impedance interns Zi, from where determination of a factor of frequency FF which is equal to the report/ratio of the threshold at the frequency fx on the threshold at frequency 50 or 60 Hz for the same physiological effects. FF = S (fx)/Sf (50/60)

Thresholds of fibrillation at frequencies lower than 1 000 Hz can be represented, but are still unknown for higher frequencies.

Other effects for frequencies higher than 10 000 Hz:

For frequencies ranging between 10 Khz and 100 Khz, the threshold of feeling amounts roughly to 100 my instead of 10 my.

At the frequencies higher than 100 Khz, a feeling of heat instead of tingling characterizes the threshold of feeling for currents of a few hundred milliamperes.
With currents of a few amps, the appearance of burns is probable according to the time of passage of the current.

Effects of the D.C. current

The difference with the alternate one is the excitation two to three times higher of the muscles. At the time of an accident in D.C. current, the most dangerous moment is the powering or the cut of the current.

One often notes K the factor of equivalence between D.C. current and alternative course (report/ratio of intensities in amps between a D.C. current and the alternative course having the same risk of fibrillation).

For (?????), a feeling of Chaleur is felt in the ends during the passage of the current.

the transverse currents of to the more 300 my passer by through the body during several minutes can cause reversible cardiac arrhythmias, visible marks, Brûlures, giddinesses and sometimes the Inconscience.

With the top of 300 my, unconsciousness frequently occurs.

See too

External bonds

Électrocution - electrification, B. - has. Gaüzere, Samu 974
Soins with the electrified people, electrification - Explanation of the phenomenon

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