8.3 PLANNING AN RF SAFETY ASSESSMENT
A reliable RF safety assessment begins by defining the question that the assessment is intended to answer. The purpose may be to evaluate a product, demonstrate compliance at an installation, assess a workplace task, confirm the effectiveness of an exposure control, or investigate a suspected exposure. The assessment must also distinguish between demonstrating compliance under maximum reasonably foreseeable operating conditions and characterizing exposure during typical operation. These objectives may require different assumptions, methods, and degrees of conservatism.
The next step is source characterization. Relevant information includes operating frequency and bandwidth, transmitter power, modulation, duty cycle, antenna type, gain, radiation pattern, polarization, height, orientation, and any beam-steering or adaptive-power behavior. All operating modes capable of materially affecting exposure should be considered. Where several transmitters can operate simultaneously, their frequencies, locations, operating states, and combined contributions must be identified.
The exposure scenario must then be defined. This includes the people who may be exposed, the locations they can occupy, their minimum separation from the source, the duration and frequency of their presence, and any relevant body orientation or close-body use. The assessment should also identify whether exposure occurs in the reactive near field, radiating near field, or far field and whether reflections, shielding, scattering, or nearby conductive structures may alter the field distribution. Accessible positions and reasonably foreseeable operating or maintenance conditions must be considered, rather than only the nominal operating arrangement.
With the source and exposure scenario established, an appropriate assessment path can be selected. Low-power exclusions, manufacturer data, or conservative analytical calculations may provide sufficient evidence in straightforward cases. Direct measurement is often appropriate when external field quantities can be determined reliably at accessible locations. Strongly nonuniform fields, close-body sources, complex antenna systems, or assessments against basic restrictions may require standardized laboratory measurements or computational dosimetry. Measurements and calculations may also be used together, with each providing a check on the assumptions and limitations of the other.
Where measurement is required, the plan should specify the quantities to be measured, the instruments and probes to be used, the measurement locations, and the required spatial and temporal sampling. Instrument frequency response, dynamic range, isotropy, probe dimensions, calibration, and measurement uncertainty must be appropriate to the field being assessed. The source operating conditions, modulation, duty cycle, traffic loading, beam behavior, and averaging intervals must also be controlled or documented sufficiently for the results to be interpreted.
The completed assessment should present the measured or calculated quantities, explain how simultaneous frequencies or sources were combined, account for uncertainty in the manner required by the applicable assessment method, and compare the results with the appropriate limits. It should identify the conditions represented by the result, the margin relative to the applicable limit, and any limitations that affect the compliance conclusion. The following sections examine the quantities, instruments, measurement techniques, and computational methods used to carry out this process.