Evaluating occupational 60-hertz electric-field exposures for guideline compliance

U.K. linesmen's experience of microshocks on HV overhead lines

Linesmen working on high voltage equipment occasionally report unpleasant discharges from equipment. The sensation is known as microshocks, which result from capacitive coupling of the linesmen to high voltage sources and subsequent discharging when in very close proximity to grounded objects. Often, this is just an annoyance, but the levels can become such that work has to cease. Microshocks are unpredictable, and therefore, planning maintenance work around them has not been possible. A survey has been developed to investigate and quantify different factors that may have a direct influence on the frequency and intensity of discharges. Transmission line workers (N = 102) from England and Wales participated in the survey and provided details of personal body characteristics as well as their experiences of microshocks. Survey results suggest a correlation between body mass index and certain work activities to the likelihood of a person experiencing microshocks, and their severity. Higher body mass index reduces the likelihood of experiencing painful microshocks. Climbing lattice towers adjacent to energized conductors is the area most associated with the phenomenon. Microshock incidents have increased or are occurring at the same rate as 5 years ago. Results presented will aid the development of policy statements and mitigation techniques that minimize linesmen's exposure to microshocks. [Supplementary materials are available for this article. Go to the publisher's online edition of the Journal of Occupational and Environmental Hygiene for the following free supplemental resources: a PDF file containing survey questions.].

Electromagnetic effects - From cell biology to medicine

In this review we compile and discuss the published plethora of cell biological effects which are ascribed to electric fields (EF), magnetic fields (MF) and electromagnetic fields (EMF). In recent years, a change in paradigm took place concerning the endogenously produced static EF of cells and tissues. Here, modern molecular biology could link the action of ion transporters and ion channels to the "electric" action of cells and tissues. Also, sensing of these mainly EF could be demonstrated in studies of cell migration and wound healing. The triggers exerted by ion concentrations and concomitant electric field gradients have been traced along signaling cascades till gene expression changes in the nucleus. Far more enigmatic is the way of action of static MF which come in most cases from outside (e.g. earth magnetic field). All systems in an organism from the molecular to the organ level are more or less in motion. Thus, in living tissue we mostly find alternating fields as well as combination of EF and MF normally in the range of extremely low-frequency EMF. Because a bewildering array of model systems and clinical devices exits in the EMF field we concentrate on cell biological findings and look for basic principles in the EF, MF and EMF action. As an outlook for future research topics, this review tries to link areas of EF, MF and EMF research to thermodynamics and quantum physics, approaches that will produce novel insights into cell biology.

60-Hertz electric-field exposures in transmission line towers

This article reports on an investigation of 60-Hz electric-field exposures of line workers in 230- to 765-kV transmission line towers. The exposures were based on computations of the unperturbed electric field along climbing routes and at work positions on the towers and on insulated ladders suspended in towers. Computed exposures were expressed in terms of the unperturbed electric field averaged over the body as stipulated by guidelines. For the realistic on-tower positions, the worker's posture, the uniformity of the field, and the field orientation differed from the guideline exposure scenario of standing erect in a vertical uniform field. These differences suggest the need for care in comparing electric-field exposures in towers with guideline limits. The unperturbed nonuniform fields at discrete points near steel and aluminum lattice structures were computed using Monte Carlo methods that model surface and spatial electric fields on and near standard geometrical elements. To estimate a whole-body average, fields were computed at 10 discrete points positioned on segments of an articulated stick-figure model of the human body. The whole-body average field was computed from fields at all the points weighted by the fraction of body volume that the corresponding segment represented. We estimated the average unperturbed electric field, the space potential at the torso, and the induced short-circuit current for 19 climbing and work positions in six towers. The maximum average electric-field exposure during climbing ranged from 10 kV/m for a 230-kV tower to 31 kV/m for a 765-kV tower. Exposures at on-tower work positions were lower than the estimated maximum exposures during climbing. For 500- and 765-kV towers, computed exposures while climbing and at some on-tower positions exceeded the limit of 20 kV/m given in the recently adopted IEEE Standard C95.6 2002. For lower voltage towers, exposures did not exceed 20 kV/m.