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,BA6 4 e/7oc9or.,c7 ..:Zni F0/20/477 /Y i • . 10/ 19/83 3910.3A UU I J 1481 CHAPTER 3. NONIONIZING RADIATION SECTION 1. RADIOFREQUENCY/MICROWAVE RADIATION 30. GENERAL. The widespread and growing use of high-power output radar, navigational aids, and communications systems has increased the potential for personnel exposure to radiofrequency (RF)/microwave radiation. Therefore, it is important that operating personnel become familiar with the nature of the biological effects of exposure to this form of energy and that certain exaggerations and misconceptions be dispelled. Activities around high power electronics equipment are completely safe provided that the guidance contained in this section is followed. For the purposes of this order, RF radiation shall refer to all electromagnetic radiation ranging in frequency from 300 kHz to 300 GHz and shall include the microwave radiation region ranging in frequency from 300 MHz to 300 GHz. The entire RF portion of the electromagnetic spectrum (Figure 1-1) is far removed from the x-ray and gamma-ray region and is classified as nonionizing radiation. 31. EFFECTS AND HAZARDS. In contrast to the cumulative biological effects associated with exposure to ionizing radiation, the only confirmed harmful effects from exposure to RF/microwave radiation are thermal in nature. It is to protect against the heating effect and its consequent influence upon workers that the permissible exposure limits are set. a. Thermal Effects. The depth of human tissue heating caused by exposure to RF/microwave radiation depends upon the frequency of the incident energy. Above 10 GHz (3 cm wavelength) heating occurs mainly in the superficial tissues (outer skin surface). From 10 GHz to 3 GHz (3 cm to 10 cm) the penetration and heating is deeper, and from 1.2 GHz to 150 MHz (25 cm to 200 cm) penetration and absorption are sufficient to cause heating of internal body tissues. The body attempts to regulate temperature increases through: (1) Perspiration and (2) Heat exchange via blood circulation Those organs which have a limited circulatory system are considered vulnerable to RF/microwave radiation exposure. Two structures in the human body are more susceptible to high radiation intensities than the remainder of the body: (a) The testes are vulnerable due to their sensitivity to temperature change. Intense microwave radiation exposure to the testes of experimental animals has been shown to impart temporary and reversible sterility. Chap 3 Par 30 Page 23