An Alternative Approach for Evaluating Induced and Contact Currents for Compliance with Their Exposure Limits (100...

The Institute of Electrical and Electronics Engineers establishes exposure reference levels ( ERL s) for electric fields ( E -fields) (0-300 GHz) and both induced ( I IND ) and contact currents ( I SC ) (<110 MHz) in its standard, IEEE Std C95.1™-2019 (IEEE C95.1). The "classical" scenarios addressed in IEEE C95.1 include a free-standing, grounded "reference" person ( I IND ) or an ungrounded reference person in manual contact with an adjacent grounded conductor ( I SC ), each exposed to a vertically oriented E -field driving the currents. The ERL s for current from 100 kHz to 110 MHz were established to limit heating in the finger (from touch), ankle ( I IND ), and wrist ( I SC from grasp contact), specifying the 6-min average specific absorption rate ( SAR , W kg -1 ) as the dosimetric reference limit ( DRL ); whole-body E -field ERL s are 30-min averages. The DRLs were established assuming a default "effective" local cross-section (9.5 cm 2 ) and consistent with a composite tissue conductivity of ~0.5 S m -1 . A previous publication described the misalignment of the ERL s for E -fields with the ERL s for I IND (which extends to I SC ) and also proposed a ramped E -field ERL from 100 kHz to 30 MHz. For the frequency range 100 kHz to 110 MHz, this paper proposes temperature increase ( ΔT ) in ankle and wrist as the preferred effect metric associated with I IND and I SC ; applying the E -field ERL s as surrogates for limits to these currents; and adopting the proposed ramp. The analysis of ΔT is based on the tissue mix in realistic anatomic depictions of ankle and wrist cross-sections; relevant tissue properties posted online; published tissue perfusion data; and anthropometric data on a large sample of male and female adults in the US military, allowing an estimate of effects over a range of body size. To evaluate ΔT versus frequency and time, the Penne bioheat equation was adapted with convective cooling from arterial blood as the lone cooling mechanism. The analysis revealed that I IND s and I SC s induced by ERL -level E -fields produce SAR s in excess of the local DRL s (in some cases far exceed). Calculations of time to ΔT of 5 °C, reflective of a potentially adverse (painful) response, resulted in worst-case times for effects in the ankle on the order of minutes but on the order of 10s of s in wrist. Thus, compliance with the E -field ERL , as assessed as a 30-min whole-body average is incompatible with the time course of potentially adverse effects in ankle and wrist from I IND and I SC , respectively. Further analysis of the relevant exposure/dose scenarios and consensus of stakeholders with a multi-disciplinary perspective will enable the development of a revised standard, practical from a compliance perspective and protective of all persons.