809: Focus Four - Electrocution Hazards

Contact with Energized Sources

Review the table below to see the reaction the body has to increasing levels of electrical current.

Current	Reaction
1 milliamp	Just a faint tingle.
5 milliamps	Slight shock felt. Disturbing, but not painful. Most people can "let go." However, strong involuntary movements can cause injuries.
6-25 milliamps (women)† 9-30 milliamps (men)	Painful shock. Muscular control is lost. This is the range where "freezing currents" start. It may not be possible to "let go."
50-150 milliamps	Extremely painful shock, respiratory arrest (breathing stops), severe muscle contractions. Flexor muscles may cause holding on; extensor muscles may cause intense pushing away. Heart fibrillation possible. Death is possible.
1,000-4,300 milliamps (1-4.3 amps)	Rhythmic pumping action of the heart ceases. Muscular contraction and nerve damage occur; death likely.
10,000 milliamps (10 amps)	Cardiac arrest and severe burns occur. Death is probable.
15,000 milliamps (15 amps)	Lowest overcurrent at which a typical fuse or circuit breaker opens a circuit!
* Effects are for voltages less than about 600 volts. Higher voltages also cause severe burns. † Differences in muscle and fat content affect the severity of shock.

(1,000 milliamperes= 1 amp; therefore, 15,000 milliamperes = 15 amp circuit)

To further illustrate how easily a person can receive a fatal shock, consider a voltage that is common to every location in the United States, 120-volts. Under average working conditions where a person is perspiring, they have a resistance of only 1000-ohms from hand-to-hand. Using the simple Ohm's Law formula (current equals the voltage divided by the resistance), the current flow will be 0.12 amperes or 120 mA.

Even when the power system is properly grounded, electrical equipment can instantly change from safe to hazardous because of extreme conditions and rough treatment.

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