Effects of electric shock to the human body

Most critical organ

The most critical organ in the case of electric shock is the heart. Those with any heart problems are more vulnerable. The current passing through the body can produce physiological damage, or trauma. There is the possibility of skin burns and necrosis of the underlying tissue. The degree of burning will depend upon the energy at the point of contact and its duration. That is to say

$I^{2}\times R\times t$ or ${\left({E^{2} \over R}\right)}\times t$

where:

$I$ is the current flowing,

$R$ is the resistance at the point or area of contact, and

$E$ is not the source voltage, but the drop in voltage between the live conductor and the surface of the body.

With a very dry skin, a high voltage shock could produce a severe burn without necessarily electrocuting the victim. A lower voltage applied to a wet or sweaty skin could, however, cause death without any evidence of burning, particularly if the path of the current is across the chest. For obvious reasons most deaths due to electricity occur at consumer voltages and in these cases the only visible injury is typically a slight discoloring of the skin where a live part has been grasped.

Engineering Explanation

From an engineering point of view, the human body is in effect a tank of electrolyte, the tank itself (the skin) having a relatively high ohmic resistance. Most of the burning will therefore be generated on the surface of the body at the point of contact.

Skin resistance can normally only be deduced (on a live subject) from the overall resistance between two places where the electric current enters and leaves the body. Tests have shown that this value can range from a few hundred ohm to several thousand ohm.* It is also found that the resistance is far higher at low voltages. Electrical safety is therefore greatly enhanced by reducing the source potential, since the current flowing will be more than proportional to the applied voltage.

With any electric shock the greatest internal current density will generally be along the shortest path between the two areas of contact — most frequently between one hand and the feet or between the two hands. The density will be greatest in the immediate vicinity of the point of contact and the current may destroy tissue under what appears to be a superficial skin burn. Careful medical attention is necessary here, since a life-threatening infarct may subsequently arise, i.e. an area of dead tissue due to the blocking of the bloodstream which normally nourishes it.

Trauma of the brain

The second type of trauma is by paralysis of the breathing center of the brain.

This of course leads to de-oxygenation of the blood and is equivalent to suffocation. In this condition the pulse may also be irregular, feeble or nonexistent.

It is vitally important that some form of resuscitation is applied. Movement of the lungs will also provide a massaging effect on the heart encouraging it to beat correctly. Patients who have been rendered lifeless by an electric shock can often be revived by artificial respiration which should be applied as quickly as possible and maintained for nee less than an hour before the case can be regarded as hopeless. Any method is better than none since even minor amounts of cardiopulmonary activity can be sufficient to sustain life.

The two other types of trauma concern the heart itself and are therefore likely to be lethal unless some sort of pulse can be rapidly restored. Failure of the heart to deliver oxygenated blood to the head will result in irreversible brain damage and then death within a very short time. One cannot survive more than a few minutes if the brain is deprived of arterial blood. In mechanical terms the human heart is a compact 280 g assembly, comprising two separate 2-stage displacement pumps working in series and in synchronism. It has a continuous rating of about 4·5 W and a short-time rating of at least 20 W. Its 'specification' requires it to be • Self-powered by extraction of energy from the pumped medium (i.e. by using some of the oxygen from the blood) • Completely maintenance-free