The effects of electrocution are due to the effects of the current and the conversion of electrical energy to heat energy on passage through the tissues. Important factors are:

• Energy delivered — heat = amperage2 x resistance x time, i.e. the amperage is the most important determinant of heat production.

• Resistance to current flow-tissues are resistant to current flow in the following decreasing order: bone, fat, tendon, skin, muscle, blood vessels, nerves. A high skin resistance and short duration of contact concentrate the effects locally. However, skin contaminants, moisture and burning reduce resistance.

• Type of current—alternating current is more dangerous than direct current. Tetanic muscle contractions may prevent the victim from releasing the current source whereas the single, strong muscle contraction with direct current often throws the victim clear. Alternating current is more likely to reach central tissues with consequent sustained apnoea and ventricular fibrillation (with as little as 50-100mA for 1-10ms).

• Current pathway—cardiorespiratory arrest is more likely the closer the contact is with the chest and heart.

Lightening strike differs from contact electrocution in that high intensity, ultra-short duration of current may produce cardiac arrest with little tissue destruction.

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