The study of the hazards, electrophysiology and prevention of electrical accidents requires an understanding of several technical and medical concepts.
The following definitions of electrobiological terms are taken from chapter 891 of the International Electrotechnical Vocabulary (Electrobiology) (International Electrotechnical Commission) (IEC) (1979).
An electrical shock is the physiopathological effect resulting from the direct or indirect passage of an external electrical current through the body. It includes direct and indirect contacts and both unipolar and bipolar currents.
Individuals-living or deceased-having suffered electrical shocks are said to have suffered electrification; the term electrocution should be reserved for cases in which death ensues. Lightning strikes are fatal electrical shocks resulting from lightning (Gourbiere et al. 1994).
International statistics on electrical accidents have been compiled by the International Labour Office (ILO), the European Union (EU), the Union internationale des producteurs et distributeurs d'énergie électrique (UNIPEDE), the International Social Security Association (ISSA) and the TC64 Committee of the International Electrotechnical Commission. Interpretation of these statistics is hampered by variations in data collection techniques, insurance policies and definitions of fatal accidents from country to country. Nevertheless, the following estimates of the rate of electrocution are possible (table 40.1).
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Table 40.1 Estimates of the rate of electrocution - 1988
|
|
Electrocutions |
Total deaths |
|
United States* |
2.9 |
714 |
|
France |
2.0 |
115 |
|
Germany |
1.6 |
99 |
|
Austria |
0.9 |
11 |
|
Japan |
0.9 |
112 |
|
Sweden |
0.6 |
13 |
* According to the National Fire Protection Association (Massachusetts, US) these US statistics are more reflective of extensive data collection and legal reporting requirements than of a more dangerous environment. US statistics include deaths from exposure to public utility transmission systems and electrocutions caused by consumer products. In 1988, 290 deaths were caused by consumer products (1.2 deaths per million inhabitants). In 1993, the rate of death by electrocution from all causes dropped to 550 (2.1 deaths per million inhabitants); 38% were consumer product-related (0.8 deaths per million inhabitants).
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The number of electrocutions is slowly decreasing, both in absolute terms and, even more strikingly, as a function of the total consumption of electricity. Approximately half of electrical accidents are occupational in origin, with the other half occurring at home and during leisure activities. In France, the average number of fatalities between 1968 and 1991 was 151 deaths per year, according to the Institut national de la sante et de la recherche medicale (INSERM).
Physical and Physiopathological Basis of Electrification
Electrical specialists divide electrical contacts into two groups: direct contacts, involving contact with live components, and indirect contacts, involving grounded contacts. Each of these requires fundamentally different preventive measures.
From a medical point of view, the current's path through the body is the key prognostic and therapeutic determinant. For example, bipolar contact of a child's mouth with an extension cord plug causes extremely serious burns to the mouth-but not death if the child is well insulated from the ground.
In occupational settings, where high voltages are common, arcing between an active component carrying a high voltage and workers who approach too closely is also possible. Specific work situations can also affect the consequences of electrical accidents: for example, workers may fall or act inappropriately when surprised by an otherwise relatively harmless electrical shock.
Electrical accidents may be caused by the entire range of voltages present in workplaces. Every industrial sector has its own set of conditions capable of causing direct, indirect, unipolar, bipolar, arcing, or induced contact, and, ultimately, accidents. While it is of course beyond the scope of this article to describe all human activities which involve electricity, it is useful to remind the reader of the following major types of electrical work, which have been the object of international preventive guidelines described in the chapter on prevention:
1. activities involving work on live wires (the application of extremely rigorous protocols has succeeded in reducing the number of electrifications during this type of work)
2. activities involving work on unpowered wires, and
3. activities performed in the vicinity of live wires (these activities require the most attention, as they are often performed by personnel who are not electricians).
Physiopathology
All the variables of Joule's law of direct current-
(the heat produced by an electric current is proportional to the resistance and the square of the current)-are closely interrelated. In the case of alternating current, the effect of frequency must also be taken into account (Folliot 1982).
Living organisms are electrical conductors. Electrification occurs when there is a potential difference between two points in the organism. It is important to emphasize that the danger of electrical accidents arises not from mere contact with a live conductor, but rather from simultaneous contact with a live conductor and another body at a different potential.
The tissues and organs along the current path may undergo functional motor excitation, in some cases irreversible, or may suffer temporary or permanent injury, generally as a result of burns. The extent of these injuries is a function of the energy released or the quantity of electricity passing through them. The transit time of the electric current is therefore critical in determining the degree of injury. (For example, electric eels and rays produce extremely unpleasant discharges, capable of inducing a loss of consciousness. However, despite a voltage of 600V, a current of approximately 1A and a subject resistance of approximately 600 ohms, these fish are incapable of inducing a lethal shock, since the discharge duration is too brief, of the order of tens of microseconds.) Thus, at high voltages (>1,000V), death is often due to the extent of the burns. At lower voltages, death is a function of the amount of electricity (Q=I x t), reaching the heart, determined by the type, location and area of the contact points.
The following sections discuss the mechanism of death due to electrical accidents, the most effective immediate therapies and the factors determining the severity of injury-namely, resistance, intensity, voltage, frequency and wave-form.
Causes of Death in Electrical Accidents in Industry
In rare cases, asphyxia may be the cause of death. This may result from prolonged tetanus of the diaphragm, inhibition of the respiratory centres in cases of contact with the head, or very high current densities, for example as a result of lightning strikes (Gourbiere et al. 1994). If care can be provided within three minutes, the victim may be revived with a few puffs of mouth-to-mouth resuscitation. Next part of the document