Course 812 Module 7 OSHA Focus Four Hazards: Electrocution

Electrocution Hazards

BESAFE Poster
Remember to BESAFE to avoid electrocution

Electrocution results when a person is exposed to a lethal amount of electrical energy. An electrical hazard can be defined as a serious workplace hazard that exposes workers to the following:

Therefore, BE SAFE by recognizing, avoiding, and protecting against all of these electrical hazards. These BE SAFE terms are defined as:

B = Burns: A burn is the most common shock-related injury. Burns from electricity are caused by electrical, arc flash, or thermal contact.

E = Electrocution: Electrocution is fatal; it means to kill with electricity. Electrocution results when a human is exposed to a lethal amount of electrical energy.

S = Shock: Shock results when the body becomes part of the electrical circuit; current enters the body at one point and leaves at another. Electrical shock is defined as a reflex response to the passage of electrical current through the body.

A = Arc Flash: An arc flash is the sudden release of electrical energy through the air when a high-voltage gap exists, and there is a breakdown between conductors. An arc flash gives off thermal radiation (heat) and bright, intense light that can cause burns. Temperatures have been recorded as high as 35,000 °F. High-voltage arcs can also produce considerable pressure waves by rapidly heating the air and creating a blast.

An arc flash can be spontaneous or result from inadvertently bridging electrical contacts with a conducting object. Other causes may include dropped tools or the buildup of conductive dust or corrosion. For more information on arc flash/blast, including best practices in electrical safety, refer to NFPA 70E: Standard for Electrical Safety in the Workplace®

F = Fire: Most electrical distribution fires result from problems with "fixed wiring" such as faulty electrical outlets and old wiring. Problems with cords (such as extension and appliance cords), plugs, receptacles, and switches also cause electrical fires.

E = Explosion: An explosion can occur when electricity ignites an explosive mixture of material in the air.

1. What is the sudden release of electrical energy through the air when a high-voltage gap exists?

a. Electrocution
b. An explosion
c. An arc flash
d. A shock

Examples

Construction worker carrying a ladder.
It's easy to forget where the ladder is above you.
  • Two workers were moving an aluminum ladder. The ladder came in contact with the overhead power lines and electrocuted one of the workers.
  • When a worker raised the mast on his water well drilling truck, it came into contact with high voltage overhead lines and electrocuted him.
  • The boom of a rotary drilling truck contacted an overhead power line and electrocuted the worker. The victim and another worker had just finished drilling a water well on a residential property. The victim moved the truck away from the well. The victim was standing at the controls, lowering the boom and was thrown several feet away from the truck.
  • A worker fell to the concrete floor while working from an 8’ fiberglass step ladder. He was fatally injured and electrocuted. The worker was changing an energized ballast on a two bulb fluorescent light fixture, located approximately 11' 6" off the ground.
  • A worker was electrocuted while connecting a replacement electrical service box to the electrical service drop to the building.

2. In a worse-case scenario, what is likely to happen to a worker if he or she contacts a high voltage overhead power line with a metal ladder or pole?

a. Arc flash
b. Electrocution
c. Burns
d. Shock

Contact with Power Lines

Overhead and buried power lines are especially hazardous because they carry extremely high voltage.

Fatalities are possible as electrocution is the main risk; however, burns and falls from elevations are also hazards that workers are exposed to while working in the vicinity of high voltage power lines. Workers may not realize that cranes are not the only equipment that reaches overhead power lines. Working on a ladder or in a man-basket suspended under or near power lines also poses a risk of electrocution. Please click here to review Toolbox Talk 1.

Important to note: The covering on an overhead power line is primarily for weather protection; therefore, workers need to know if they touch a power line, covered or bare, death is likely.

Voltages of overhead lines range from 120 to 750,000 volts. The most reliable way to know the voltage is to ask the utility company that owns the line. OSHA requires that equipment be kept at least 10 feet away from power lines with voltages up to 50 kilovolts (kV).

Practice Identifying Hazards

Try to identify the hazards in the picture below. Then click on the picture to see if you correctly identified the hazards.

Contact with Power Lines Hazards
Click to review hazards

3. OSHA requires that equipment be kept _____ away from power lines with voltages up to 50 kilovolts (kV).

a. a minimum of 5 feet
b. 8 feet or more
c. 3 feet for every 10 kV
d. at least 10 feet

Contact with Energized Sources

The major hazards regarding contact with energized sources are electrical shock and burns. Electrical shock occurs when the body becomes part of the electric circuit. This occurs when an individual comes in contact with both wires of an electrical circuit (one wire of an energized circuit and the ground, or a metallic part that has become energized by contact with an electrical conductor).

Crane working on a bridge.
Be sure the wiring is not live.

The severity and effects of an electrical shock depend on a number of factors, such as:

  • the pathway through the body,
  • the amount of current,
  • the duration of the exposure, and
  • whether the skin is wet or dry.

Water is a great conductor of electricity, allowing current to flow more easily in wet conditions and through wet skin. The table below discusses the effects of electrical shock.

Electrical burns can be arc burns, thermal contact burns, or a combination of burns. Electrical burns are among the most serious burns and require immediate medical attention. They occur when an electric current flows through tissue or bone, generating heat that causes tissue damage. The body cannot dissipate the heat generated by current flowing through the resistance of the tissue. Therefore, burns occur.

Current Reaction
1 milliamp Just a faint tingle.
5 milliamps Slight shock felt. Disturbing, but not painful. Most people can "let go." However, strong involuntary movements can cause injuries.
6-25 milliamps (women)†
9-30 milliamps (men)
Painful shock. Muscular control is lost. This is the range where "freezing currents" start. It may not be possible to "let go."
50-150 milliamps Extremely painful shock, respiratory arrest (breathing stops), severe muscle contractions. Flexor muscles may cause holding on; extensor muscles may cause intense pushing away. Heart fibrillation possible. Death is possible.
1,000-4,300 milliamps (1-4.3 amps) Rhythmic pumping action of the heart ceases. Muscular contraction and nerve damage occur; death likely.
10,000 milliamps (10 amps) Cardiac arrest and severe burns occur. Death is probable.
15,000 milliamps (15 amps) Lowest overcurrent at which a typical fuse or circuit breaker opens a circuit!

*Effects are for voltages less than about 600 volts. Higher voltages also cause severe burns.
†Differences in muscle and fat content affect the severity of shock.

(1,000 milliamperes= 1 amp; therefore, 15,000 milliamperes = 15 amp circuit)

4. The severity and effects of an electrical shock depend on all of listed factors, EXCEPT _____.

a. the pathway through the body
b. the induced reluctance
c. the duration of exposure
d. the amount of current

Examples

To further illustrate how easily a person can receive a fatal shock, consider a voltage that is common to every location in the United States, 120-volts. Under average working conditions where a person is perspiring, they have a resistance of only 1000 ohms from hand-to-hand. Using the simple Ohm’s Law formula (current equals the voltage divided by the resistance), the current flow will be 0.12 amperes or 120 mA. From the table in the previous section, we can see that the reaction can be a painful shock to possible death.

A fault current may travel through a worker's body, causing electrical burns or death if:

  • the power supply to the electrical equipment is not grounded, or
  • the path has been broken, or
  • if there are live parts or bare wires.

Even when the power system is properly grounded, electrical equipment can instantly change from safe to hazardous because of extreme conditions and rough treatment.

Practice Identifying Hazards

Try to identify the hazards in each picture below. Then click on each picture to see if you correctly identified the hazards.

Contact with Energized Sources Hazards
Click to review hazards
Contact with Energized Sources Hazards
Click to review hazards

5. Under average working conditions (120 vac) where a person is perspiring, they have a resistance of only _____ ohms hand-to-hand which can result in death.

a. 1000
b. 2100
c. 2400
d. 3600

Improper Use of Extension and Flexible Cords

Untangling extension cords.
Be sure to untangle extension cords in order to help prevent snags, and abrasions.

The normal wear and tear on extension and flexible cords can loosen or expose wires, creating a hazardous condition. Cords that are not 3-wire type, not designed for hard-usage, or that have been modified, increase the risk of contacting electrical current. With the wide use of power tools on construction sites, flexible extension cords are often necessary.

Because they are exposed, flexible, and unsecured, they are more susceptible to damage than fixed wiring. Hazards are created when cords, cord connectors, receptacles, and cord- and plug-connected equipment are improperly used and maintained.

To reduce hazards, flexible cords must connect to devices and fittings in ways that prevent tension at joints and terminal screws. A flexible cord may be damaged by door or window edges, staples and fastenings, abrasion from adjacent materials, or simply by aging. If the electrical conductors become exposed, there is a danger of shocks, burns, or fire.

When a cord connector is wet, electric current can leak to the equipment grounding conductor, and to anyone who picks up that connector if they provide a path to ground. Such leakage can occur not just on the face of the connector, but at any portion that is wet.

6. How do you reduce the electrical hazards posed by flexible cord connections?

a. Ground all cords at their source
b. Wrap the cords with duct tape
c. Reduce tension at joints and terminal screws
d. Use bonding insulators with the cords

Improper Use of Extension and Flexible Cords (Continued)

Extension cord with damaged insulation.
Example of an exposed wire.

Let’s review an example of an actual accident:

A fan connected to a 120-volt electrical system via an extension cord provided ventilation for a worker performing a chipping operation from an aluminum stepladder. The insulation on the extension cord was cut through and exposed bare wires and energized conductors made contact with the ladder. The ground wire was not attached on the male end of the cord's plug. When the energized conductor made contact with the ladder, the path to ground included the worker's body, resulting in death.

What would you recommend?

Recommendation

Though it is possible to properly repair the extension cord, it is always best to replace an extension cord that is damaged. Yes, it may cost a little money to replace the extension cord. However, if you don't replace the extension cord, and it is not repaired properly a life can be lost and the company will be put at risk.

7. What is the best strategy to eliminate the hazard from an extension cord that is damaged with a section of exposed wire?

a. Wrap the exposed wire with electrical tape
b. Replace the cord
c. Use shrink tubing around the exposed wire
d. Dip the exposed wire into a insulated liquid and dry

Check your Work

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