The Dangers of Electrical Shock
Severity
The severity of injury from exposure to electricity depends on two factors: the level of electrical current (amperage) and the duration of the current passing through the body.
- The level of current is determined by both the voltage and resistance of an electrical pathway. The higher the voltage and lower the resistance, the greater the current.
- The next factor determining severity is the duration of exposure to electricity. The longer the employee is exposed, the greater the severity of injury.
OSHA considers all voltages of 50 volts or above to be hazardous because, as we know, electric current, not voltage, passing through the human body causes injury, and the amount of current passing through an object depends on the resistance of the object.
The internal resistance of the human body is about 500 ohms, which is the minimum resistance of a worker with broken skin at the point of contact. The current through 500 ohms from a live part energized at 60 volts would be 120 milliamperes. This level of current, either AC or DC, is sufficient to cause serious injury.
Although OSHA's standards require guarding starting at 50 volts (AC or DC), it is not necessarily the case that voltages below that level are completely safe. Cases in which auto mechanics have sustained serious injuries working with 12-volt or 24-volt (DC) vehicle batteries. For instance, see these two examples of injuries while working around car batteries (NIH/Pubmed):
A 34-year-old male auto mechanic who was holding a wrench when his gold ring touched the positive terminal of a 12-volt car battery and the wrench touched both his ring and the negative terminal. He felt instant pain and had a deep partial-thickness circumferential burn at the base of his ring finger. No other soft tissues were injured. The cause of ring burns is most likely electrothermal burns.
A 21-year-old man sustained a band of deep burn around the wrist. A metal watchstrap that the patient was wearing, with evidence of the arching phenomenon on it, short-circuited the battery of the vehicle. Although there was an electrical accident, the current did not pass through any part of the patient's body, as what happens in an electrical injury.
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2-1. The severity of injury from electrical shock depends on which two factors below?
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