What is the role of the circuit type in the pathogenesis of electrical injuries?

Updated: Mar 09, 2020
  • Author: Tracy A Cushing, MD, MPH, FACEP, FAWM; Chief Editor: Joe Alcock, MD, MS  more...
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Answer

Electrical current can flow in 1 of 2 types of circuits: direct current (DC) or alternating current (AC), in which the flow of electrons changes direction in rhythmic fashion. AC is the most common type of electricity in homes and offices, standardized to a frequency of 60 cycles/sec (Hz).

High-voltage DC often causes a large single muscle contraction that throws the victim away from the source, resulting in a brief duration of contact with the source flow. In contrast, AC of the same voltage is considered to be approximately 3 times more dangerous than DC, because the cyclic flow of electrons causes muscle tetany that prolongs victims' exposure to the source. Muscle tetany occurs when fibers are stimulated at 40-110 Hz; the standard 60 Hz of household current is within that range. If the source contact point is the hand, when tetanic muscle contraction occurs the extremity flexors contract, causing the victim to grasp the current and resulting in prolonged contact with the source.

Table. Physiologic Effects of Different Electrical Currents (Open Table in a new window)

Effect

Current (milliamps)

Tingling sensation/perception

1-4

Let-go current – Children

3-4

Let-go current - Women

6-8

Let-go current – Men

7-9

Skeletal muscle tetany

16-20

Respiratory muscle paralysis

20-50

Ventricular fibrillation

50-120


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