9.3 RADIO FREQUENCY (RF) RADIATION HAZARDS.
The effect of rf radiation on living tissue is thought to be primarily thermal in nature. The most vulnerable
parts of the human body are the eyes and the testes. However, other parts which can be affected are the brain,
nerves, skin, and muscles. The thermal effects can range from a mild heating of the skin or organs to fatal
Below 1000 MHz, rf energy penetrates deeply into the body. These frequencies are extremely hazardous since
the radiation is not detected by the nerve endings located in the skin. The power absorbed in the body tissues
can be as high as 40% of the incident power. The urinary bladder, gall bladder, and parts of the gastro-
intestinal tract are particularly vulnerable since they are not cooled by an abundant flow of blood. Also,
stainless steel and platinum bone implants and fillings in teeth can increase in temperature when subjected to rf
radiation, resulting in burning of tissues.
In the 2-5 GHz region of the rf spectrum, the eyes and the testes are the most vulnerable organs to rf radiation
damage. Damage to the eyes is generally irreversible and can result in blindness from cataracts or loss of lens
transparency. Animal experiments have shown that damage to the testes from low levels of exposure does not
differ from that caused by common forms of heat applied to the testes, and that the reduction in testicular
function due to heating appears to be temporary. It is not known if rf radiation produces any genetic damage.
To minimize possible hazards from rf radiation, Dept of Defense Instruction 6055.11 (9-4) provides
recommendations to prevent possible harmful effects in human beings exposed to radio frequency radiation.
9.4 LASER HAZARDS (9-5).
Biological damage from laser radiation is caused by photochemical, thermal, and pressure effects, acoustic and
ultraviolet shock waves, plasma generation, ultrasonic emission, and even the generation of free radicals. Of
these, the first three are the most hazardous to tissues, organs, and eyes. The damages include tissue
ionization, molecular rearrangements, blood vessel occlusion, corneal opacity, retinal lesion, blindness, and even
death. Lasers are divided into four classes: Class 1 is non-hazardous; Class 2 depends on blink reflex for the
person to turn away to prevent a hazard; Class 3 is a direct or specular reflection hazard; Class 4 is all other
high energy lasers. See ANSI Z136.1 for further information concerning safe use of lasers.
It is believed that damage to eye tissue by visible and infrared light is mainly thermal in nature. The lens of the
eye is practically transparent in these regions, thus increasing the susceptibility to retinal burn or lesion. The
susceptibility is enhanced by the fact that the power density of light converging on the retina is concentrated
by a factor of 105 when it passes through the pupil and lens of the eye.
At near ultraviolet, the eye responds in nearly the same way as it does to visible light, the exception being a
marked decrease in vision between 380 nm
meters) and 420 nm. This decrease is caused by the strong
absorption at the lens of the eye. Extreme exposure to these wavelengths may lead to the development of
cataracts. In the B and C ultraviolet bands, radiation is absorbed by the cornea and its outer layer. Excessive
exposure to these wavelengths can cause a condition called "welder's flash," an effect similar to snow blindness.