How Electrical Current Affects the Human Body
Three primary factors affect the severity of the shock a person receives when he or she is a part of an electrical
circuit:
- Amount of current flowing through the body (measured in amperes).
- Path of the current through the body.
- Length of time the body is in the circuit.
Other factors that may affect the severity of the shock are:
- The voltage of the current.
- The presence of moisture in the environment.
- The phase of the heart cycle when the shock occurs.
- The general health of the person prior to the shock.
Effects can range from a barely perceptible tingle to severe burns and immediate cardiac arrest. Although it is not
known the exact injuries that result from any given amperage, the following table demonstrates this general relationship
for a 60-cycle, hand-to-foot shock of one second's duration:
Current level
(in milliamperes) |
Probable effect on human body |
| 1 mA |
Perception level. Slight tingling sensation. Still dangerous under certain
conditions. |
| 5 mA |
Slight shock felt; not painful but disturbing. Average individual can let go. However, strong involuntary
reactions to shocks in this range may lead to injuries. |
| 6-30 mA |
Painful shock, muscular control is lost. This is called the freezing current or "let-go"
range. |
| 50-150 mA |
Extreme pain, respiratory arrest, severe muscular
contractions. Individual cannot let go. Death is possible. |
| 1000-4300 mA |
Ventricular fibrillation (the rhythmic pumping action of the heart ceases.) Muscular contraction and
nerve damage occur. Death is most likely. |
| 10,000 mA |
Cardiac arrest, severe burns and probable death. |
|
|
Wet conditions are common during low-voltage electrocutions. Under dry conditions, human
skin is very resistant. Wet skin dramatically drops the body's resistance.
|
Dry Conditions: Current = Volts/Ohms = 120/100,000 = 1mA
a barely perceptible level of current
Wet conditions: Current = Volts/Ohms = 120/1,000 = 120mA
sufficient current to cause ventricular fibrillation
|
|
Back > |
|
If the extensor muscles are excited by the shock, the person may be thrown away from the
circuit. Often, this can result in a fall from elevation that kills a victim even when electrocution does not.
|
|
Back > |
|
When muscular contraction caused by stimulation does not allow the victim to free
himself from the circuit, even relatively low voltages can be extremely dangerous, because the degree of injury
increases with the length of time the body is in the circuit. LOW VOLTAGE DOES NOT IMPLY LOW HAZARD!
|
100mA for 3 seconds = 900mA for .03 seconds
in causing fibrillation
|
|
Back > |
|
Note that a difference of less than 100 milliamperes exists between a current that is barely
perceptible and one that can kill.
|
|
Back > |
|
High voltage electrical energy greatly reduces the body's resistance by quickly breaking
down human skin. Once the skin is punctured, the lowered resistance results in massive current flow.
|
Ohm's law is used to demonstrate the action.
At 1,000 volts, Current = Volts/Ohms = 1,000/500 = 2 Amps
which can cause cardiac standstill and serious damage to internal organs.
|
|
Back > |
|
Back to Top
www.osha.gov
