March, 2007

Published by Terry Chandler Director of Engineering, Power Quality Thailand LTD/Power Quality Inc., USA. Emails: terryc@powerquality.org, terryc@powerquality.co.th

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Accidental Death is REAL!!

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Electrical Shock Fatalities in the USA

• Electric shocks are responsible for about 1,000 deaths in the United States each year, or about 1% of all accidental deaths.
• Electric shocks cause death in 3-15% of cases. Many survivors require amputation or are disfigured by their burns.

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Electrical Injuries

• Electrical injuries can be caused by a wide range of voltages but the risk of injury is generally greater with higher voltages, and is dependent upon individual circumstances.
• Electric shock
• Electrical burns
• Loss of muscle control
• Thermal burns

Electrical Shock

• A voltage as low as 50 volts applied between two parts of the human body causes a current to flow that can block the electrical signals between the brain and the muscles.
• Stopping the heart beating properly
• Preventing the person from breathing
• Causing muscle spasms

Electrical Burns

• If an electrical current passes through the human body it heats the tissue along the length of the current flow. This results in deep burns that  are permanently disabling.
• Burns are more common with higher voltages but may occur from low voltage.

Loss of Muscle Control

• An electric shock causes painful muscle spasms that can be strong enough to break bones or dislocate joints.
• This  often means the person cannot ‘let go’ or escape the electric shock.
• The person may fall if they are working at height or be thrown into nearby machinery.

Burn Injury Survival

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Thermal Burns

• Overloaded, faulty, incorrectly maintained, or short circuits  get very hot.
• Even low voltage batteries (12V) can get hot and may explode if they are shorted out.

Arc Flash

Arc Flash has 3 issues

• The arc temperature
• The incident energy
• The pressure developed by the expanding gas

The main concern is the arc temperature  and ignition of clothing.

Arc Flash Test

An arc flash test used a circuit adjusted to deliver 20,000 amperes at 480 V, 3 phase. The bright light is the arc.

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Arc Flash Test 2

As the arc develops (second from top), it melts and vaporizes the metal of the electrodes and the box.

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Arc Flash Test 3

This vaporizing metal  expands outward with the pressure wave, and the test stand is enveloped in the arc flash explosion.

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Arc Flash Test 4

The duration of the arc was about 0.045 sec. The test was set up at the Square D High Power Lab in Cedar Rapids, IA.

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Arc Flash Result

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Approach to Energized Part

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Safety Requirements by Category 0 to 4

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Arc Flash Protection

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Dressed for Safety

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Arc Flash labeling in USA

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Safety Review

• Shock hazard
• Burn hazard from electrical current
• Burn from thermal (hot wires)
• Explosions due to Arc Fault

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Some Safety Tips

• Never work alone on electrical circuits.
• Use lock outs to prevent accidental circuit activation.
• Wear protective gloves, eye and face protection and clothing.
• Double check the expected voltage before work.
• Always deenergize circuits if at all possible.
• DO NOT ASS-U-ME the circuit is off.
• Always make sure the area around your feet is clear.
• If a ladder is necessary it should be fiberglass.

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BE SAFE!!!