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Lightning damage and the human body


Every year in Japan several people are killed by direct lightning strikes. Many people are struck by lightning while standing in comparatively open spaces, with no high building or trees nearby, in rice fields, flat open roads and other open spaces.

What happens to a human body when an impulse voltage is applied o it? The effect of the electric shock on the human body is in fact determined by the size of the current flowing through the body, rather than the voltage.

The size of the current and the extent of the shock

The extent of the electric shock will depend on whether the current is direct current or a commercial frequency, and whether it is high frequency or impulse. In terms of the effects of commercial frequency current on the human body, at rms 1mA, the person would be able to feel it, but not much more. 5mA would be fairly painful, and 10mA intolerably so. 20mA would cause the muscles to contract and the person would not be able to pull their hand away from the circuit by themselves. 50mA would be very dangerous, and 100mA lethal.

Human body resistance and hazardous voltage


The resistance of the human body will depend on the wetness and dryness of the skin that touches the power supply, as well as the voltage value. With voltage of around 50V and dry hands, the human body’s resistance (between hands and feet) would be 5,000Ω, and with wet hands 2,000Ω. Also, the higher the voltage, the lower the body’s resistance will be.

Also, the body’s resistance will differ depending on whether the current is alternating or direct at low voltage (100V or lower). The human body has greater resistance to direct current.

Voltage safety limit of electromagnetic induction

If a power line is a single line grounded, if there are any public telecommunications lines in the vicinity, electromagnetic induction voltage may be generated, with the possibility that line maintenance personnel or equipment users could suffer electric shock. For this reason, the Induction Coordination Committee has set the electromagnetic induction voltage limit at 430V.

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