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.
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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
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