Safety and health newsletter for the Oregon construction industry

May 14, 2012

faulty extension cord plug

Toolbox talk: Electrocution hazards and how they happen

Contact with overhead power lines, failing to de-energize equipment, and improper use of extension cords are the most common electrocution hazards in construction work. Here are three examples of how relatively simple tasks can have unexpected consequences.

Contact with overhead power lines

Cranes are not the only equipment that can contact overhead power lines.

Example: Workers were installing aluminum window wrapping around the third-floor windows of a residential home. One of them climbed an extension ladder carrying a five-foot by one-foot aluminum strip. As he reached the top of the ladder, a gust of wind blew the aluminum strip upward into electrical power lines running parallel to the residence. He received an electrical shock from the 7,620-volt power line, lost his grip on the ladder, and fell 30 feet to the ground. He went into cardiac arrest and was taken to a nearby hospital, but he did not survive.

The covering on an overhead power line is primarily for weather protection and offers no protection against electrocution.

Electrical shock and burns from failing to de-energize equipment

Electrical shock and burns are the major hazards caused by contact with energized sources such as live parts, damaged or bare wires, and defective equipment. Electrical shock occurs when the body becomes part of an electric circuit. Electrical burns, which include arc burns and thermal contact burns, occur when an electric current flows through tissue or bone, generating heat that causes severe tissue damage.

Example: An electrician's apprentice was standing on top of an eight-foot fiberglass stepladder changing a lighting fixture in a ceiling. A 277-volt power source was still connected to the light fixture. When he touched the live 277-volt wiring, it pulled him inward and he could not release his hand. He managed to shift his weight on the ladder and he fell backward about six feet to the concrete floor. He sustained a contusion to the back of his head, electrical shock, and third-degree burns to his left index finger.

Improper use of extension cords

Because extension cords are exposed, flexible, and unsecured, they're more susceptible to damage than fixed wiring. The normal wear and tear on extension and flexible cords can loosen or expose wires, creating a hazardous condition. Cords that are not three-wire type, not designed for hard use, or that have been modified, increase the risk.

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. Leakage can occur not just on the face of the connector, but also at any wet portion.

Example: A worker was standing on a plastic bucket using a refurbished, double-insulated saw to cut holes in the sheetrock ceiling of a residential home under construction. The saw's power cord, which had an inadequate splice in it, was plugged into a 120-volt extension cord and the extension cord was plugged into a power strip. The power strip was connected to a series of three extension cords that went to an outlet in the house next door. That outlet was equipped with a ground-fault circuit interrupter. But the three extension cords between the power strip and the outlet were missing their grounding pins.

The worker draped the 120-volt extension cord that powered the saw around his neck so that the plug was resting on the left side of his chest. It was a hot day, and he was sweating.

A witness heard the worker yell and saw him throw off the saw and cord. He stepped off the plastic bucket, took two steps, and collapsed. He was rushed to a local hospital where he was pronounced dead. The electrical shock he received was not enough to leave burn marks on his body, but it was enough to disrupt the rhythm of his heart. The medical examiner's report listed the cause of death as acute cardiac dysrhythmia due to low-voltage electrocution.

 

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