a Hya i Wm LE ge ae, gicalPOVeSBo athens: U- B. THERMAL RADIATION — FLASH AND HEATING EFFECTS Background Information Levels of thermal radiation that can produce skin burns are limited to the immediate testing site areas. Effects on the eyes, however, may extend for much greater distances. These effects may be either permanent damage to part of the eye or a temporary flash “blindness.” The latter is only a discomforting effect but can be potentially hazardous in the case of automobile drivers and aircraft pilots. This is one of the reasons why certain areas of highways have been closed for specified periods of time around the Nevada Test Site and also why the same precautions have been taken for the air lanes around the Nevada and Pacific testing sites. Perhaps surprisingly, the amount of heat (calories) received per unit area on the rear portion of the eyeball (retina) does not decrease with increasing distance from the point of burst — except for the absorption (attenuation) effect in the atmos- phere. While the expected decrease in energy per unit area does occur outside the eye (the inverse square law), the image formed on the retina correspondingly decreases in size in the same proportion. The result is that the thermal dose, in cal- ories per unit area, remains constant but it covers a smaller area on the retina. This reduction in imagesize on the retina with increasing distance from the burst continues until it reaches approximately: 0.00018 inch (7 microns) in diameter which is generally taken as about the limit for the maximum focusing effect of the human eye. Of course a dilation of the pupil of the eye, such as at nighttime, will permit more light to enter and, although the retinal image size does not change,it can be relatively more hazardous. Also, it is assumed that any. light gathering devices such as binoculars also would increase the hazard. Any damage to the retina probably would not be detected by an eye examination if it were less than 50 microns in diameter. Actual functional impairment of vision probably would not be noted if the lesions were mild and less than 50 microns in diam- eter on the fovea—the most sensitive portion of the retina. There may beless injury to the retina of the eye if a given total amount of thermal energy is received at a slower rate, i.e., there is more opportunity for the adjacent ceils in the retina to conduct away some of the heat. High yield detona- 50685" . g tions in the lower atmosphere exhibit a slower rate of delivery than low yields (say, a million tons versus 20 thousand tons). At very high altitudes, say above 150 miles, only about %100,000 Of the total yield from a megaton detonation appears 23