Magnetic-Field Exposures of Cable Splicers in Electrical Network Distribution Vaults

Abstract

The purposes of the research reported here were to quantify the power-frequency magnetic-field exposures of cable splicers while they were performing tasks in energized network distribution vaults and to compare these exposures with occupational exposure guideline levels. Network vaults supply electricity to commercial and residential urban areas as well as to large buildings. Participating workers wore a personal exposure monitor at the waist, kept a simple diary to record their work location, and recorded information about the vaults and tasks performed. To capture temporal variability, a stationary meter was deployed in the vault during a task. Load current in the vault was measured. To examine temporal variability over long time periods, stationary meters were deployed in selected vaults for one month. Data were collected during 77 tasks in 69 vaults for 191 person-tasks, representing approximately 400 hours of in-vault personal exposure data. Highest exposures were observed in tasks performed near secondary conductors. Personal exposure variability arises principally from worker movement and activities in the vaults, not from load variability during a task. Maximum field during a person-task exceeded the International Committee on Non-Ionizing Radiation Protection (ICNIRP) (0.42 millitesla) and the American Conference of Governmental Industrial Hygienists (ACGIH) (1.0 millitesla) guideline levels during 14 percent and 8 percent of the person-tasks, respectively. The mean of measurements during a person-task exceeded those guideline levels during 4 percent and 2 percent of the person-tasks, respectively. A large number of person-tasks (40%) had measured fields above the ACGIH recommended limit of 0.1 millitesla for workers with pacemakers or other implanted devices. Based on the frequency and duration of their high exposures, cable splicers working in network distribution vaults are one of the most highly exposed groups in the electric utility industry. Selective assignment of work location and task could minimize the likelihood of exposures for vault workers exceeding guideline limits for wearers of pacemakers or other implanted devices. Scheduling vault tasks during off-peak hours (nights and weekends) may reduce exposures. However, even during these periods exposures in certain vaults can still exceed guideline levels.

Evaluation of Biological Effects, Dosimetric Models, and Exposure Assessment Related to ELF Electric- and Magnetic-Field Guidelines

“…(19) Other studies have targeted speci c occupations and tasks to quantify and better understand the frequency and nature of guideline-level exposures. (131) The most likely candidates for high exposures are occupations within the electric-utility industry that entail work near conductors carrying large currents. Job categories of particular interest are those of line workers, cable splicers, generator mechanics, and substation workers.…”

“…Some PE measurements by cable splicers working in underground distribution network vaults have exceeded guideline levels (>0.42 and >1.0 mT) for extended periods (>1 hr) during tasks. (131) For these workers, exposure to high elds occurs during tasks that involve contact or very close proximity to low voltage (240 and 480 V) service cables (i.e., secondaries) carrying currents of more than 500 amperes (A).…”

Numerical modeling of pacemaker interference in the electric-utility environment

“…Though exposures to magnetic fields of 0.1 mT and above are documented in a number of work scenarios as described above, perception through neurostimulation has a threshold in excess of 50 mT [19]. Any form of interference by a utility work-related power-frequency magnetic field would not be preceded by perception, as the highest documented exposure level we are aware of was approximately 8 mT in a networkvault worker [16]. Worker exposures to contact currents are insufficiently characterized, although scenarios involving exposures of several hundred microamperes would require attention related to interference.…”

“…For repair or replacement of spacers, 0.2 mT was exceeded for over 60% of task time. A subsequent assessment focused entirely on network-vault workers at a single utility [16], a group that had been previously uncharacterized. The results collected from 191 person tasks are summarized in Fig.…”

Peak Inhalation Exposure Metrics Used in Occupational Epidemiologic and Exposure Studies

“…The 13 (12%) studies measuring peak exposure to physical agents (110,(156)(157)(158)(159)(160)(161)(162)(163)(164)(165)(166)(167) included assessments for noise (46%) and electromagnetic frequency (54%). Personal monitoring was conducted in 85% of studies, all utilizing real-time instruments.…”