INDUCED AND CONTACT CURRENT LIMITS a. Guidance is provided for limiting the RF induced currents in the human body for free-standing conditions (no skin contact with conducting objects), and under conditions of grasping contact with conducting objects to limit the maximum RF current through the human body. For frequencies of 3 kHz to 100 kHz, both induced currents and contact currents are averaged over any 1 second. For frequencies of > 100 kHz to 100MHz, induced currents and contact currents are averaged over any six minute period, subject to a ceiling limit of 500 mA using the square of the induced currents calculated as follows: (I2 max = I2ave (Xxxx/Tmax). Induced current measurements are not necessary at frequencies over 100 MHz.
b. Adherence to the induced body current limits (section B of Table C-I) will prevent localized SAR in the ankles or wrists from exceeding 20 W/kg (see 2.a). In general, between 3 kHz and 100 kHz, the perception threshold is related to a tingling or prickling sensation, while between 100 kHz and 100 MHz, the perception threshold is related to a sensation of heat or warmth. Under some conditions, touching conductive objects that are in the vicinity of a radiating RF antenna could result in a flow of RF current of sufficient magnitude to be painful or to produce a burn at the point of contact.
c. Evaluation of induced RF currents will generally require a measurement to determine the RF current flowing to ground through the feet of the individual, or the RF current flowing through the hand in contact with a conductive surface. To avoid the possibility of further overexposure it is recommended that currents be measured by instruments that simulate the electrical characteristics of the human body. Induced current measurements are not required if the spatially-averaged electric field strength does not exceed the PEL at frequencies of 0.45 MHz or less and does not exceed the limits shown in Figure C-2 at frequencies greater than 0.45 MHz.
d. Under various exposure conditions, application of the field strength limits in Table C-I, Section A in conjunction with the induced current limits in Table C-I, Section B may not be consistent or amenable to analysis. Many variables, such as near-field exposure conditions, physical contact with or close proximity to nearby conductive surfaces, RF absorption enhancement under resonance frequency conditions, and inherent differences in human body sizes, will affect the measured induced currents.
