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26-02-2011, 10:25 AM
Earthing and shocks.pptx (Size: 417.95 KB / Downloads: 103)
• Occurs when electrical current passes through the body
• Causes devastating injuries or even death
Why are we prone to shocks?
• Because our bodies are good conductors of electricity.
• When a part of our body completes an electric circuit, we get an electric shock
• You will receive a shock if you touch two wires at different voltages at the same time.
Causes of electric shocks
Accidental contact with exposed electrical wiring
Contact with a high voltage source
Contact with a person who is receiving an electric shock
Contact with a live and neutral wires
Due to a lightning strike
Poking metal objects into an electrical outlet
Touching an electrical appliance with wet hands
TYPES OF ELECTRIC SHOCKS
Most common type of shock
Occurs when current flows across intact skin and through the body
Occurs when there is a direct current path to the heart tissue
Usually these shocks are from inside the skin, i.e. a malfunctioning pacemaker, or ungrounded catheter etc.
A basic electric circuit has three components: voltage, current, and resistance.
The killer component is current.
According to Ohm’s law,
Resistance of the body varies from one person to another, moisture content between different layers of skin
Typical skin resistance : 500 Ω (moist skin) to 300,000 Ω (dry skin)
The low resistance of wet skin allows current to pass into the body more easily and give a greater shock.
The severity of an electrical shock depends on –
The amount of electrical current through the body
The duration of the current through the body
The path of the current through the body
The muscle structure of the person
Electrical shocks can occur in several forms, and the given description applies to various levels
Fibrillation level: This is a function of current over time. For example, you will get fibrillation
with 500mA over 0.2 sec or 75mA over 0.5 sec.
Let-go threshold: This is the current level at which humans lose muscle control; the electricity causes muscles to contract until current is removed