11.1: Electrical Safety

Electrical Safety Considerations

Electrical Shock

Electricity flows along a circuit that consists of a power source, a load, and conductors. The human body can become a conductor and a part of the electric circuit which can result in electrical shock. Exposure to electrical energy may result in no injury at all or may result in physical and/or neurological damage or death. An minor electrical shock may cause muscle pain and may trigger mild muscle contractions or startle people, causing a fall. However, high resistance contact may cause dielectric breakdown at the skin, lowering skin resistance, causing surface damage, but more often tissues deeper underneath the skin have been severely damaged. Electric shocks can paralyze the respiratory system or disrupt heart action, causing instant death.

The outcome of an electrical shock depends on several factors that are determined by the relationship between current, voltage, and resistance, also known as Ohm’s Law.

Ohm’s Law

Voltage or Electrical Force (V)
Amperage or Current Flow (I)
Resistance or Ohms (Ω or R )

Current=Electrical Force/Resistance or I=V/R

Exposure Conditions play an important role in the extent of injuries sustained as a result of electric shock. These factors include:

• Duration- The longer a human body remains part of an electrical circuit, more tissue and neurological damage can occur.
• Pathway- Electricity is always seeking the path of least resistance to ground. If both hands of a person are part of the pathway, the current has more potential to affect the heart resulting in ventricular fibrillation. If the current chooses another path such as hand-to-foot, tissue and internal organ damage still may occur.
• Humidity/Saturation- Electricity can easily flow through water or moisture in the air. Humidity also can effect how much a body sweats, which can lower a persons resistance to electrical current.
• Skin Condition- The human body’s resistance to current is affected moisture content:
  • Dry Skin- 100,000 to 500,000 ohms of resistance
  • Perspiring (sweaty hands)- 1000 ohms of resistance
  • In Water (completely wet)- 150 ohms of resistance

Amperage Kills

Current	Effect
<1 Milliampere	No sensation
1 Milliampere	Tingling sensation
5 Milliamperes	Slight shock felt
6 to 30 Milliamperes	Definite shock Could cause muscle contraction causing you to hang on
50 to 100 Milliamperes	Painful shock Breathing can stop Severe muscle contractions Possible death
1000 to 4300 Milliamperes	Ventricular fibrillation Respiratory paralysis Possible death
10,000 Milliamperes	Cardiac arrest Severe burns Probable death

Example:
A worker is using a faulty 120 volt tool on a hot and humid day and is sweating heavily. The worker’s body resistance is approximately 1,000 ohms.
Using Ohm’s law:
• Current = 120 volts / 1,000 ohms.
• Current = 0.12 amps or 120 mA.
According to the above table, this amount of current will cause a painful shock, the workers’s breathing may stop, there will be severe muscle contractions, and death is possible.

Arc Flash and Arc Blast

Arc-Flash-Arc- Flash burn can occur when an electrical equipment malfunction causes an extremely high temperature area around the arc that can reach as high as 35,000 degrees Fahrenheit. Electrical burn can also occur any time an electrical current flows through bone or tissue.

Arc-Blast- When an arc occurs, a blast causes molten metal to be thrown through the air and onto the skin or into the eyes. The speed of the molten metal in an arc-blast is estimated at approximately 700 mph.

Donnie’s Accident Story

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General Safety Rules for Electrical Technicians

• Safety glasses, goggles, or face shields must be worn any time a hazard exists that can cause foreign objects to get in your eyes from the front or the sides.
• Head protection must be worn whenever there is a potential for objects to fall from above, for bumps to your head from objects fastened in place, or for accidental contact with electrical hazards.
• Hand protection must be worn any time your hands are exposed to a potential hazard.
• Do not wear clothing with exposed zippers, buttons, or other metal fasteners.
• Remove rings, wristwatches, and any other metal jewelry before beginning work.
• Work with a buddy. Avoid working alone.
• Always turn power off and lock it out before working on any electrical circuits or equipment.
• Never cut off the grounding prong from a three-prong plug on any power extension cord or from a power cord to any piece of equipment.
• Do not defeat the purpose of any safety devices such as fuses or circuit breakers.
• Do not open and close switches under load unless absolutely necessary.
• Assume all electrical equipment to be “live” and treat it as such.

Non-Energized Testing

Never test an energized circuit when individual components of the circuit can normally be tested by other means. Most electrical components and pathways of electrical systems can be individually tested for continuity and resistance.

Remix

This chapter was updated and remixed from content created by

• 
• Clifford Rutherford
• University of Hawaii Maui College via University of Hawaiʻi OER