Summary and evaluation of guidelines for occupational exposure to power frequency electric and magnetic fields

Major U.S. and international guidelines for limiting occupational exposures to EMF are evaluated. These safety guidelines are designed to prevent short-term adverse effects by maintaining bulk-tissue current densities below 10 mA m(-2) (rms). Above this level, effects of induced currents and electric fields can include stimulation of neural and cardiac tissues. The models and input data used by guideline-setting organizations to relate 50/60-Hz magnetic-field exposures to induced current densities differ significantly. In order to develop a better understanding of such differences, the current densities derived from exposure guideline models are compared to minimum thresholds for cardiac stimulation and fibrillation. The nominal minimum thresholds for cardiac stimulation and ventricular fibrillation are 100 times and 200 times greater, respectively, than the current density of 10 mA m(-2) used as a dosimetric limit. However, the assumed relationship between the 10 mA m(-2) dose limit and magnetic field exposure limits introduces additional uncertainty. The ratios between the threshold for cardiac stimulation and the calculated induced current density at the exposure limit vary between a low of 50 and a high of 526, depending upon the guideline. These ratios, as indicators of implicit safety factors, are larger than those recommended to protect against adverse effects of induced current density, including cardiac stimulation, in magnetic resonance imaging or against adverse effects of toxic chemical exposures. This review and assessment of EMF occupational exposure guidelines suggests that several scientific and compliance issues remain ambiguous or unresolved. Recommendations are made for guideline organizations to strengthen and clarify the scientific basis for the guideline process. These recommendations include the documentation of supporting data, development of operational definitions for guidelines, examination of dosimetric models, clarification of safety factors, and identification of high priority topics for future research.