6.4 EXPOSURE

Emission describes the RF energy produced by a source, whereas exposure describes the electric and magnetic fields present at the location occupied by a person. The two are related but, as noted at the start of Section 6.3, transmitter power alone does not determine exposure. The fields reaching a person also depend on the operating frequency, antenna gain and radiation pattern, beam direction, distance from the source, transmission duty cycle, and the effects of surrounding structures. Reflections, shielding, diffraction, and absorption can produce field distributions that differ substantially from those expected from distance alone. Exposure may involve the whole body, a limited part of the body, or a very small region immediately adjacent to a transmitting device.

For the purposes of general RF exposure guidelines, people are generally assigned to one of two exposure populations: members of the general public and occupationally exposed workers. Within the general-public category, it is useful to distinguish between exposure associated with the voluntary use of a device and exposure arising from RF fields in the surrounding environment. This distinction helps describe how exposure occurs, but it does not alter the applicable general-public restrictions.

These two populations do not encompass every exposure circumstance. ICNIRP treats the exposure of patients, carers, and comforters during medical procedures managed by qualified medical practitioners, and the exposure of approved research volunteers, as outside the scope of its general exposure restrictions. These circumstances require separate medical or ethical assessment in which potential risks are weighed against the intended benefits. Clinical and research personnel who are occupationally exposed remain within the occupational framework.