Assessing compliance with power-frequency magnetic-field guidelines

Several organizations have established guidelines for occupational exposure to power-frequency magnetic fields. At 60 hertz, exposure limits are 1.0 millitesla (mT) for the American Conference of Governmental Industrial Hygienists, 0.42 mT for the International Committee on Non-ionizing Radiation Protection, and 1.6 mT for the National Radiation Protection Board guidelines. Adoption of the current guidelines as mandatory standards could dramatically affect electric-utility work practices. Two large personal-exposure monitoring projects have characterized exposures of overhead lineworkers and cable splicers while they perform various tasks near energized conductors. Personal exposure measurements indicate that these two groups are very likely the most highly exposed among utility workers and often experience fields above guideline levels. In addition, survey measurements in utility environments have identified locations where other workers may experience exposures at guideline levels. The nature of high-field exposure scenarios in the utility industry suggests a simple practical method for determining compliance with basic restrictions on internal induced current density [< 10 milliamperes per square meter (mA m(-2))] in the presence of fields that exceed limits to magnetic fields external to the body.