Safety 2007: Proceedings of the 2007 ASSE Professional Development Conference, Orlando, Florida, June 24-27, 2007. Des Plaines, IL: American Society of Safety Engineers, 2007 Jun; :1-2
Purpose: Electrocution is ranked fifth among occupational fatalities in the United States (1980-1999, 7,271 electrocution deaths). In order to reduce the occupational electrical injury and fatality rates, a proximity warning personal protective device at high and low voltages and an electrical contact activated circuit breaker at low voltage were proposed by a National Institute for Occupational Safety and Health (NIOSH) project. As a component of the project, a prototype worker-worn 60Hz electric field detector was built at the NIOSH to detect a worker's proximity and electrical contact to a nearby electrical power line. To investigate the effectiveness of the electric field detector as the proximity/electrical contact indicator, an experiment was conducted to measure 60- Hz electric field variation on simulated human arms in various proximity to a low/high voltage simulated power line and in electrical contact to a low voltage simulated power circuit. Methods: Ten defrosted hog legs were used in the experiment to simulate human arms. The experiment setup consisted of a simulated power line, a pair of conductive fabric cuffs, a 60- Hz electric field detector, and a PC data acquisition system. The simulated power line was energized with a low voltage (n8 volts) and with a high voltage (8,896 volts). The pair of conductive fabric cuffs were mounted on the hog leg to sense the 60-Hz electric field, which was emitted from the simulated power line to the hog leg. The battery-powered electric field detector, which was connected to the conductive cuffs, measured the magnitude of the 60- Hz electric field on the hog leg. In order to avoid any grounding effect, which would introduce electric field measuring error, the electric field detector had no direct connection to any instruments, and used a radio frequency transmitter to transmit the measured data to a nearby radio receiver, which was connected to a PC data acquisition system to acquire the measured data. During the experiment, the hog legs were moved (one at a time) from 100 cm to 1 cm to the simulated power line through 8 distance steps. The field detector measured the 60-Hz electric field variations on the hog legs. Results: At low voltage (118 volts), as the hog legs were moved from 100 cm, through the steps of 80, 60, 40, 20, 10, 5, 2, to 1 cm to the simulated power line, the mean 60-Hz electric field magnitude monotonically increased 45.6%, 50.7%, 57.0%, 66.9%, 36.1%, 39.2%, 11.4% and 8.16%, respectively. These magnitude increments are large enough for the detector to distinguish the leg proximity to the low voltage power line in 8 steps. Further, as the hog legs were moved from 1 cm to the power line to electrically contacting the bare "line" wire, there was a significant mean magnitude jump of 2612%, which effectively distinguishes the electrical contact from near proximity. At high voltage (8,896 volts), as the hog legs were moved from 100 cm, through the same steps as above, to 1 cm to the simulated power line, the mean 60-Hz electric field magnitude monotonically increased 48.9%, 55.2%, 70-4%, 82.6%, 46.1%, 47.7%, 30.0% and 33.8%, respectively. These magnitude increments are large enough for the detector to distinguish the leg proximity to the high voltage power line in 8 steps. The mean field magnitude on the hog legs as they were 100 cm away from the power line at 8,896 volts is 881% higher than that when they were 1 cm away from the power line at 118 volts. Therefore, there is a distinct electric-field magnitude gap between 1-cm proximity at 118 volts and the 100-cm proximity at 8,896 volts. Conclusions: It is effective for the 60-Hz electric field detector to detect a worker's proximity and electrical contact to a nearby power line. The sensitivity of the device could be configured into two voltage ranges. In the low voltage range (120 volts), the detector detects both the human proximity and electrical contact to an energized low-voltage power line. In the high voltage range (8,900 volts), the device detects only the human proximity to an energized high-voltage power line. The concept of using the 60- Hz electric field detection on the human body to sense the proximity and electrical contact to a nearby power line has been included in a U.S. patent application (Pub. App. No. 20050264427).