We're sorry, but OSHAcademy doesn't work properly without JavaScript enabled. Please turn on JavaScript or install a browser that supports Javascript.

715 Electrical Safety for Technicians and Supervisors
Skip to main content

715 Electrical Safety for Technicians and Supervisors

The Dangers of Electrical Shock

Severity

The severity of injury from exposure to electricity depends on two factors:

  1. The level of electrical current (amperage) passing through the body.
  2. The duration of time the current flows through the body.
EMT about to shock a patient with a defibrillator
Currents greater than 75 mA may cause very rapid, ineffective heartbeat. This condition will cause death within a few minutes unless first aid is administered.

Current Level

  • The amount of current depends on both voltage (the electrical “pressure”) and resistance (measured in ohms, the opposition to current flow).
  • As previously mentioned, Ohm’s Law is Current = Voltage ÷ Resistance:
    • Higher voltage or lower resistance increases current.
    • For example, if 60 volts are applied across a human body with about 500 ohms of resistance (typical for broken skin), the current would be:
      • 60 V ÷ 500 Ω = 0.12 A (120 milliamperes).

Duration of Exposure

  • The longer a person is in contact with electricity, the greater the injury.
  • Even relatively small currents can be deadly if they flow for several seconds.

OSHA Guidance

  • OSHA considers all voltages 50 volts or above hazardous.
  • This is because it is current (amperes), not voltage itself, that causes injury. Voltage only determines how much current will flow through the body, depending on resistance.

Internal Resistance of the Body

  • The human body typically has about 500 ohms of resistance at the point of contact if skin is broken or wet.
  • At 60 volts, this produces a current of 120 mA, which is well above the threshold for serious or fatal injury.

AC vs. DC

  • AC (Alternating Current): Current changes direction many times per second (in the U.S., 60 cycles per second or 60 Hz). AC is more likely to interfere with the heart’s rhythm and cause fibrillation.
  • DC (Direct Current): Current flows in one constant direction. DC is more likely to cause sustained muscle contractions, which can make it difficult to let go of the source.
  • Both AC and DC at sufficient levels can cause severe injury or death.

Although OSHA's standards require guarding starting at 50 volts (AC or DC), voltages below that level are not necessarily safe. Auto mechanics, for example, have sustained serious injuries while working with 12-volt or 24-volt DC vehicle batteries. To review two real-life examples of such injuries, click the toggle below (NIH/PubMed):

A 34-year-old male auto mechanic 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 burns around the wrist. A metal watchstrap that the victim 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 victim's body, as what happens in an electrical injury.

Knowledge Check Choose the best answer for the question.

2-1. The severity of injury from electrical shock depends on which two factors below?

Previous Module
Next Section