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 damageto 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 atmosphere. 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 calories 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 FIGURE 7.— A downtown Las Vegas window, showing how the glass was sucked out by the rarefaction wave, rather than pushed in by the compression wave resulting from the November 1, 1951, nuclear test at the Nevada Test Site. been no significant structural damages from refracted blast waves since good predictive methods have been developed. There has been no known case of direct injury to man or animals from the refracted blast waves. Evaluation The predictive procedures developed resulted in greatly minimizing off-site damage from blast effects. In fact, there have been only incidents of single windows being damaged since 1953. Two occurred in 1955 and a third in 1957. 22 can be relatively more hazardous. Also, it is assumed that any light gathering devices such as binoculars also would increase the hazard. Any damageto the retina probably would not be detected by an eye examination if it were less than 50 micronsin diameter. Actual functional impairment of vision probably would not be noted if the lesions were mild and less than 50 micronsin diameter 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 cells in the retina to conduct away some of the heat. High yield detonations 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 ‘hoo,ooo Of the total yield from a megaton detonation appears 23