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From the Forensic Files of NIOSH

Aug 1, 2008 12:00 PM

Few would argue that electrocution is a serious threat to electrical workers. However, it's only one of the dangers faced by this group of individuals, as evidenced by a tragedy that occurred at a Michigan vehicle transmission plant.

On the afternoon of the incident, a 55-year-old electrician had been asked to strip out a section of wiring and conduit from an overhead electrical service. To access an overhead junction box, he was operating an articulated boom-supported elevated aerial work platform, which had been rented from an equipment rental company.

In accordance with company and plant policy, another worker had been assigned as a ground person during this construction activity. Both the ground person and the electrician had received training and were licensed to operate articulated boom-supported aerial work platforms.

According to the ground person, he had walked to the front of the unit when he heard a scraping sound. He called out to the electrician but received no response. Immediately, he and two other employees looked up saw the man pinned with his back against a 6-inch-diameter iron fire protection water pipe and his chest against the control panel at the front of the platform. The workers on the ground tried to override the basket panel controls but couldn't, because the key that would allow them to access the controls from the ground was missing from the ground control panel switch. An estimated 3 to 4 minutes passed until another employee used a key from a different brand of aerial lift to gain control of the aerial work platform and lower it.

The local fire department and its EMS squad responded to the incident. Emergency treatment was administered at the plant. The victim was then transported to a local hospital, where he was pronounced dead.

Examination of the rented unit after the incident revealed that the hydraulic basket tilt cylinder located on the boom had failed catastrophically. The hydraulic tilt cylinder was bent into a “C” shape, indicating a large amount of pressure had been exerted on the cylinder. The basket controls were found to be in good working order.

Although no one observed the events immediately leading up to the accident, it appears that the victim was close to the junction box he was trying to access near the plant ceiling but could not quite reach it. As he attempted to grab it, either the controls momentarily malfunctioned, driving the articulated arm against a roof truss, or he inadvertently continued to operate the tilt controls after the arm had become wedged against the lower side of a roof truss. Presumably, the hydraulic lift cylinder failed because of excess pressure exerted on it. When the hydraulic lift cylinder failed, the basket snapped backward toward an iron water pipe, crushing the victim.

NIOSH recommends following these guidelines to avoid similar tragedies:

• The American National Standards Institute (ANSI) should evaluate and consider modifying ANSI A92.S standard titled “The American National Standard for Self Propelled Elevating Work Platforms,” and encourage manufacturers and distributors to follow the International Organization for Standardization (ISO) Standard for articulated boom-supported aerial work platforms regarding providing pressure sensor/relief valves on their equipment.

• Limit the number of brands of aerial lifts purchased or leased by a facility.

• Tether the key that operates the equipment from the ground controls to the ground control panel.

• Conduct a written pre-work inspection on equipment and ensure workers do not operate equipment until it is repaired when the pre-work inspection reveals faults, such as defeated or missing safety devices.

• Ensure that employee training is appropriate and specific for each type of equipment workers will be using.

Reprinted with permission from the National Institute for Occupational Safety and Health (NIOSH), Division of Safety Research (DSR). All electrical-related FACE reports can be viewed in their entirety at www.cdc.gov/niosh/face/default.html.

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