Electrical Hazards
3. Factors that Intervene in Electrical Accidents
When electric current circulates through the human body, this behaves like a resistance and, according to Ohm’s Law, the intensity of the passing current will be determined by:
I = V / R
where:
I: the intensity of the current that passes through the human body (Amps).
R: the resistance of the body to the current passing through it (Ohms).
V: the Contact voltage between the current entry and exit points (Volts).
The factors that intervene in electrical accidents may be classified as:
Technical Factors:
- The intensity of the current that passes through the human body.
- The time of exposure to the hazard.
- The path the electric current takes through the human body.
- The nature of the current (alternating/direct).
- The electrical resistance of the human body.
- The applied voltage.
Human Factors:
- Age.
- Illnesses.
- Gender.
- Emotional state.
- Usual profession or trade.
- Experience, etc.
3.1. Intensity of the current passing through the human body
It has been demonstrated experimentally that it is the intensity of the current passing through the human body and not the voltage which may cause injuries due to the electrical accident.
A distinction is made between:
Threshold of perception:
The value of the intensity of current that a person begins to perceive (slight tingling) when their hand comes into Contact with a conductor.
A value of 1 mA has been set for alternating current.
Limit intensity:
The maximum intensity of current at which a person is still able to let go of a conductor.
Its value has been set experimentally at 10 mA for alternating current.
| CURRENT | EFFECTS ON THE HUMAN BODY |
|---|---|
| From 1 to 3 mA | A normal organism perceives a tingling sensation that is not dangerous (threshold of perception). |
| From 5 mA upwards | Prolonged Contact may provoke brusque movements in certain people. |
| From 10 mA upwards | Muscular contractions and tetanization (rigidity and convulsive tension) commence in the muscles of the hand and arm, which may cause the skin to stick to the points of Contact with low voltage parts (stiffening phenomenon). |
| Above 25 mA | In Contact lasting over 2 minutes, tetanization of the chest muscle may be produced if the current passes through the heart region, possibly resulting in the person suffering asphyxia due to muscular blockage of the thoracic cavity. |
| Between 30 and 50 mA | Ventricular fibrillation may be produced if the current passes through the cardiac region, resulting in death if the injured person does not receive attention in a few minutes. |
| Between 2 and 3 A | Respiratory arrest and unconsciousness occur and visible marks appear. |
| For currents above 3 A | The consequences are serious burns and possibly death. |
