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| High-voltage power line contact by a crane hoist cable |
Description of Problem
During the 1990s, about 20% of all mining electrocutions resulted from high-reaching mobile equipment that made contact with overhead electric power lines. A detailed analysis of these accidents revealed that 56% of the injured miners had contacted the equipment and ground simultaneously after the power line contact had occurred and were unaware of the shock hazard. These workers could have avoided injury had they simply known after the fact that the equipment had become energized. An overhead power line contact alarm, while not designed to avoid all related injuries, is a reliable, affordable, and practical alternative to proximity warning systems. Contact alarm technology could also reduce power line-related electrical injuries in other industries, such as construction. This system was developed to warn workers when a piece of mobile equipment becomes energized by a power line.
Research and Development Activities
NIOSH research identified one important aspect of power line electrocution little mentioned in the literature: workers are often killed or injured by electrically energized equipment before they are even aware of the hazard. NIOSH hypothesized that a system to alert operators and nearby ground crew workers could prevent more than half of these injuries in mining. Baseline experiments characterized voltage rises and danger areas on energized cranes and dump-bed trucks for equipment operators and other workers. Follow-on research identified two methods of power line contact detection. Undercarriage electric fields were identified as the most reliable detection method because of their ability to detect power line contact on all common road surfaces. Prototype technology was designed, built, tested, and transferred to industry.
R&D Outputs and Transfer Activities
The results of overhead power line hazard and contact alarm research and recommended hazard mitigations were published in several technical articles. An invited 90-minute workshop on Electrical Safety for Water Well Drillers was held at the National Ground Water Association annual meeting in Las Vegas, NV, December 12, 2004, and twice at the South Atlantic Water Well Driller's Jubilee, Myrtle Beach, SC, July 30-31, 2005. A U.S. patent for the "Alarm System for Detecting Hazards Due to Power Transmission Lines" was awarded on July 29, 2003.
Description of Intermediate Outcome
In 2004, the largest manufacturer of power line proximity warning alarms, Allied Safety Systems, Inc. (Sanford, FL), added undercarriage electric field detection as an option to its existing product line of power line proximity warning devices. This resulted, in part, from discussions with NIOSH engineers regarding the contact alarm concept. Allied plans to add a low-cost, stand-alone undercarriage power line contact alarm to its product line. Another manufacturer, Hirschmann Electronics, Inc./PAT America plans to introduce a power line proximity warning alarm that includes an undercarriage power line contact alarm as both an add-on and a low-cost, stand-alone product. With the market for proximity warning alarms systems estimated at 45,000 worldwide, the potential to reduce power line contact accidents is high.