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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Arcing electrical burns through the shoe around the rubber sole. High-voltage (7600 V) alternating current nominal. Note cratering.
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Contact electrical burn. This was the ground of a 120-V alternating current nominal circuit. Note vesicle with surrounding erythema. Note thermal and contact electrical burns cannot be distinguished easily.
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Contact electrical burns, 120-V alternating current nominal. The right knee was the energized side, and the left was ground. These are contact burns and are difficult to distinguish from thermal burns. Note entrance and exit are not viable concepts in alternating current.
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Electrical burns to the hand.
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Electrical burns to the foot.
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High-voltage electrical burns to the chest.
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Superficial electrical burns to the knees (flash/ferning).
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Energized site of low-voltage electrical burn in a 50-year-old electrician.
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Grounded sites of high-voltage injury on the chest of a 16-year-old boy who climbed up an electric pole.
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Energized site of the high-voltage injury depicted in Media File 9 (16-year-old boy who climbed up an electric pole).
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Entrance site of a low-voltage injury.
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Grounded sites of a low-voltage injury in a 33-year-old male suicide patient.
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Grounded site of a low-voltage injury in the same 33-year-old male patient depicted in Media File 12.
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Grounded sites of low-voltage injury on the feet.
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A histologic picture of an electrical burn showing elongated pyknotic keratinocyte nuclei with vertical streaming and homogenization of the dermal collagen (40X). Courtesy of Elizabeth Satter, MD.
Tables
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 |
