The severity of the shock received when a person becomes a part of an electric circuit is affected by three primary factors: the amount of current flowing through the body (measured in amperes), the path of the current through the body, and the length of time the body is in the circuit. Other factors that may affect the severity of shock are the frequency of the current, the phase of the heart cycle when shock occurs, and the general health of the person.
The effects of electric shock depend upon the type of circuit, its voltage, resistance, current, pathway through the body, and duration of the contact. Effects can range from a barely perceptible tingle to immediate cardiac arrest. Although there are no absolute limits or even known values that show the exact injury from any given current, the table shows the general relationship between the degree of injury and amount of current for a 60-cycle hand-to-foot path of one second's duration of shock.
The table also illustrates that a difference of less than 100 milliamperes exists between a current that is barely perceptible and one that can kill. Muscular contraction caused by stimulation may not allow the victim to free himself or herself from the circuit, and the increased duration of exposure increases the dangers to the shock victim. For example, a current of 100 milliamperes for 3 seconds is equivalent to a current of 900 milliamperes applied for .03 seconds in causing ventricular fibrillation. The so-called low voltages can be extremely dangerous because, all other factors being equal, the degree of injury is proportional to the length of time the body is in the circuit.
LOW VOLTAGE DOES NOT IMPLY LOW HAZARD!
A severe shock can cause considerably more damage to the body than is visible. For example, a person may suffer internal
haemorrhages and destruction of tissues, nerves, and muscles. In addition, shock is often only the beginning in a chain of events. The final injury may well be from a fall, cuts, burns, or broken bones.
|Effects of Electric Current in the Human Body|
|1 Milliampere||Perception level. Just a faint tingle.|
|5 Milliamperes||Slight shock felt; not painful but disturbing.|
Average individual can let go. However, strong involuntary reactions to shocks in this range can lead to injuries.
|6-25 Milliamperes (women)||Painful shock, muscular control is lost. |
|9-30 Milliamperes (men)||This is called the freezing current or "let-go" range.|
|50-150 Milliamperes||Extreme pain, respiratory arrest, severe muscular contractions.*|
Individual cannot let go. Death is possible.
|1,000-4,300 Milliamperes||Ventricular fibrillation. (The rhythmic pumping action of the heart ceases.) Muscular contraction and nerve damage occur. Death is most likely.|
|10,000-Milliamperes||Cardiac arrest, severe burns and probable death.|