7.7 RECOGNITION OF RF OVEREXPOSURE
An RF overexposure is first a compliance question: did the exposure exceed an applicable restriction or legally enforceable limit? An RF injury is a clinical question: did the event impair physiological function or damage tissue? The two questions are related but not identical because exposure restrictions are derived from substantiated effects using adverse-health-effect thresholds or conservative operational thresholds, with reduction factors then applied.
The consequences of an overexposure depend on frequency, field strength, duration, waveform, spatial distribution, the body region exposed, and the person's position relative to the source. A confirmed or suspected exceedance must therefore be investigated even when no symptoms are reported, while nonspecific symptoms alone cannot demonstrate that an exceedance occurred.
Thermal overexposure may be localized or involve much of the body. Localized exposure can produce warmth, discomfort, erythema, pain, or burns; severe heating may cause deeper tissue injury that is not immediately visible. Whole-body heating may resemble heat stress from other causes, with symptoms such as excessive perspiration, weakness, headache, dizziness, nausea, impaired concentration, heat exhaustion, or, in severe cases, heat stroke.
At the lower end of the RF range, sufficiently strong induced fields may produce tingling, painful nerve stimulation, or involuntary muscle contraction. Contact with a conductive object carrying induced RF current may also cause shock, a spark discharge, or a localized burn. A startle response or loss of muscular control can lead to secondary injuries, particularly during work at height or near machinery.
The microwave auditory effect may produce clicking, buzzing, or knocking sensations during exposure to particular pulsed microwave fields. The effect is not itself evidence of tissue injury or proof that an exposure restriction has been exceeded, although an unexpected occurrence in the workplace should prompt a review of the exposure circumstances.
The eyes and other tissues with limited heat removal can require particular consideration during intense localized exposure. People with implanted or body-worn medical devices require a separate device-specific assessment because electromagnetic interference or localized coupling to a lead may occur even when the general human-exposure restrictions are satisfied.