Safety Manual. Revised Edition 2010

Revised Edition 2010

Electrical Hazards

3. Factors that Intervene in Electrical Accidents

3.5. Electrical resistance of the human body

As the electrical resistance of the human body depends on multiple factors, its value may be considered random to a certain degree.

Among the factors that intervene and which have been determined experimentally, we may list: applied voltage, age, gender, state of the Contact surface - moisture, dirtiness, etc. - the path the current takes, alcohol in the blood, Contact pressure, etc.

The following values may be considered as a basis for calculation for the human organism:

  • Maximum value: 3,000 Ohms
  • Average value: 1,000/2,000 Ohms
  • Minimum value: 500 Ohms

The human body acts as a semiconductor; its resistance therefore varies with voltage.

Low Voltage Electro-technical Regulations (average value) establish the value of electrical resistance of the human body at 2,500 Ohms.

3.6. Applied voltage

We shall now begin to distinguish between fault current, which circulates due to a fault in insulation, and Contact current, which passes through the human body when it is subjected to voltage.

For each type of current, we shall also differentiate between Contact voltage (that applied to the human body) and fault voltage. These are understood as the voltage difference that, due to a fault, may be applied between the hand and foot of a person who touches a ground or element not normally subjected to voltage with the former, or the voltage difference that appears as a result of faulty insulation between two grounds, between a ground and a conducting element, or between a ground and earth, respectively.

From the point of view of hazard, the only voltage to consider is that of Contact, but the voltage that is considered in practice is the fault voltage.

3.7. People’s capacity to react

It is clear that the effect of current when a body is electrified differs greatly depending on the characteristics of the person affected.

Some possible reasons for this would be:

  • a) The person’s physical and psychological state.
  • b) The alcohol the person’s body contains.
  • c) Whether the person is asleep or awake (someone who is asleep can support approximately twice as much current as someone who is awake).
  • d) The state of nervousness or excitation of the person affected.
  • e) Whether the person has cardiac problems or not.
  • f) Others such as: gender, fatigue, etc.

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