Electrical Hazards
7. Accidental Electric Arcs
When working in the vicinity of live areas, not only the risk of electrical Contact with active parts will need to be considered, but also the possible formation of electric arcs due to short-circuiting.
It should be noted that the ISASTUR Group generally works at centres where the short-circuit power is very high. Therefore, the electric arcs that may be produced are of a high magnitude.
Of all the electrical accidents that occur, the majority are due to an accidental electric arc.
At normal temperatures, air is an insulator, because the elements it is made up of (atoms and molecules) are neutral. It only becomes a conductor when it is ionized, i.e. when free electrons and ions (the two carriers of electricity) are formed within it due to certain means contributing energy (heat, ultraviolet radiation, etc.).
However, this ionization is generally insufficient to sustain conduction through the air. That is, for an electric arc to be produced, there has to exist a difference in potential between the conductors or between the conductor-ground and an extraction of free conduction electrons from the conductor, either by means of a thermo-ionic effect (the energy needed to overcome the potential barrier) or by electrical field emission (high voltage).
Generally as a result of the effect of a high electric current (short-circuit), high temperatures are produced in the electrical conductors that cause the thermo-ionic effect and ionization of the surrounding air, giving rise to the electric arc that elevates the temperature of the medium where it is primed and reaching temperatures of 4,000ºC.
It is known that 50% of the energy of an electric arc is absorbed by heating the surrounding air, 40% irradiates and the rest is absorbed by the melting of the metallic parts affected by the electric arc.
An electric arc produces ultraviolet, infrared and visible radiation. This confirms the need to use inactinic goggles without loss of vision, with the aim of absorbing the radiations and protecting one’s eyes against possible spattering of metallic particles, such as copper, which are violently projected when melting.
Likewise, the use of face screens and leather gloves as protective elements is mandatory, since these elements act by absorbing part of the heat when a short-circuit is produced, given that the duration of the arc does not exceed a second in time.
The working clothes of electricians and electrical operators is to be heatproof so that the temperature of an accidental arc does not set them alight. Acrylic clothing is not recommendable; cotton or fireproof artificial fibres are recommended.
Voltage checks in the case of breakdowns, repairs, etc., are to be considered as live work and so the aforementioned protective elements are to be used when carrying out such work.
