8.4.4 Current And Contact Current
RF fields can induce currents in conductive structures and in the human body. Induced current in a limb may be measured using an appropriate current-measurement device and is a reference-level quantity over the frequency range specified by the applicable exposure standard.
Contact current occurs when a person touches a conductive object at a different RF potential. It can produce perception, pain, shock, or localized RF burns, even when the surrounding field strengths are not unusually high. RPS S-1 manages contact-current hazards through guidance rather than a numerical exposure restriction. Contact-current risk must therefore be assessed and controlled separately where people may touch large conductive structures near high-power transmitters, industrial RF equipment, or antenna systems.
Currents in accessible conductors and limbs may be measured with suitable probes. Currents distributed within the body cannot normally be measured directly and instead require analytical or computational assessment.
8.4.5 Dosimetric Quantities
Dosimetric quantities describe fields induced or power and energy absorbed within or at the surface of the body. Depending on frequency and exposure duration, they include induced electric field, specific absorption rate (SAR), specific energy absorption, absorbed power density, and absorbed energy density.
Induced electric field is used at the lower end of the RF range where electrostimulation must be considered. SAR describes the rate of energy absorption per unit mass and is used for whole-body and localized exposure below 6 GHz. Specific energy absorption describes energy absorbed per unit mass during a specified short interval. Above 6 GHz, absorbed power density and absorbed energy density describe absorption at or near the body surface.
These quantities cannot normally be measured directly in living people. They are determined using standardized measurements in tissue-equivalent phantoms, validated computational human models, or, where appropriate, analytical calculations. Chapter 6 describes these dosimetric quantities and methods in detail.