Recent advances in research relevant to electric and magnetic field exposure guidelines

Abstract

Limits on exposures to extremely low-frequency electric fields, magnetic fields and contact currents, designated as voluntary guidelines or standards by several organizations worldwide, are specified so as to minimize the possibility of neural stimulation. The limits, which we refer to as guidelines, derive from "basic restrictions" either on electric fields or current density within tissue, or on avoidance of annoying or startling interactions that may be experienced with spark discharge or contact current. Further, the guidelines specify more conservative permissible doses and exposure levels for the general public than for exposures in controlled environments, which most typically involve occupational settings. In 2001 we published an update on guideline science. This paper covers more recent developments that are relevant to the formulation and implementation of the next generation of guidelines. The paper deals with neurostimulation thresholds and the relevance of magnetophosphenes to setting guideline levels; dosimetry associated with contact current benchmarked against basic restrictions; tissue and cellular dosimetry from spark discharge; assessment of exposures to high electric fields in realistic situations (e.g., line worker in a transmission tower); a simplified approach to magnetic field assessment in non-uniform magnetic fields; and a quantitative approach to sampling workplace exposure for assessing compliance.

Possible Influences of Spark Discharges on Cardiac Pacemakers

“…For peripheral nerve, IEEE identifies a population median stimulation threshold for 20 mm diameter neurons of 6.15 V m −1 peak (4.35 V m −1 RMS) at frequencies f < 3.35 kHz, the frequency that corresponds to the membrane time constant, t e , of 0.149 ms (3.35 Â 10 3 = 0.5 t e −1 ); the threshold increases by a factor of f/3.35 kHz for f ≥ 3.35 kHz or to 102 V m −1 peak (72.2 V m −1 RMS) at 55.6 kHz. Based on unpublished 60-Hz dosimetry data provided by Stuchly and Dawson to Kavet (Kavet et al 2008) and using skin and fat tissue as a surrogate for peripheral nerve, the 99th percentile electric field in peripheral nerve of the lower arm of the contacting hand (the anatomical compartment analyzed with the highest in situ electric fields from contact current) is estimated at~8.94 V m −1 peak per mA for an adult model and 23.5 V m −1 peak per mA for a child model. With these estimates, the 99th percentile peak in situ electric field in peripheral nerve from the spark discharge exposure in this study is~10.7 kV m −1 peak for the adult model and~28.2 kV m −1 peak for the child model.…”

The relationship between anatomically correct electric and magnetic field dosimetry and publishedelectric and magnetic field exposure limits

“…The coupling coefficients for the ellipsoidal model, C Ell-BT , and for the 99th percentile electric field in tissue, C BT99 , from anatomical modelling that were selected from the literature are shown in Table 1. Note that coupling coefficients for skin and fat are used as a surrogate for dose to peripheral nerve (8,9) , because the maximum dose to peripheral nerve is assumed to take place in a cutaneous receptor located near the interface between the skin and subcutaneous fat (10) . Dose to peripheral nerve has not been explicitly modelled as also noted by ICNIRP.…”

“…The use of skin and fat as surrogates for peripheral nerve, although used in previous publications (8,9) , and relied on by ICNIRP for the 2010 Guidelines has not to the authors' knowledge, been validated rigorously. Since magnetic field induction is maximal towards the periphery of anatomical structures increasing with cross-sectional area, and the cross-sections of the limbs are small compared with those of the torsos, the 99th percentile induced electric fields associated with fat and skin was expectedly associated with the torso periphery (9) .…”

Transcranial stimulability of phosphenes by long lightning electromagnetic pulses

“…Retinal phosphenes have even lower threshold values than their cortical counterparts [14,15]. Motivated by the availability of many well documented clinical TMS studies on cortical phosphenes, and by the established specifications of TMS induction coils, we restrict to those in the following comparison with lightning electromagnetic pulses (LEMPs).…”