The Effects of Nuclear War
http://www.fas.org/nuke/intro/nuke/7906/
1-KT TERRORIST WEAPON AT GROUND LEVEL
A terrorist group using stolen or diverted fission material, having general technical competence but lacking direct weapon design experience, could probably build a weapon up to several kilotons. This weapon would be large and heavy, certainly not the often-discussed ?suitcase bomb, ? so is likely to be transported in a van or small truck, with threatened detonation either in the street or the parking garage of a building.
Because of the locations and yield of this weapon, its effects will be much less devasting than those of high-yield, strategic weapons. The range and magnitude of all the nuclear effects will be greatly reduced by the low yields; in addition, the relative range of lethal effects will be changed. At high yields, blast and thermal burn reach out to greater distances than does the initial nuclear radiation. At 1 kt the reverse is true; for example, 5-psi overpressure occurs at 1,450 feet [442 m], while 600 reins of
initial radiation reaches out to 2,650 feet [808 m], For the 1-Mt surface burst, 5 psi occurred at 2.7 miles and 600 reins at 1.7 miles.
In addition to these changes in range, the highly built-up urban structure in which the weapon is placed wilI significantly modify the resulting nuclear environment. This occurs when the lethal range of effects shrink to such an extent that they are comparable to the size of urban structures. It is indeed reasonable to expect that the blast effects of a smalI weapon (5 psi at a range of only 1,450 feet) will be severely infIuenced by nearby structures having comparable dimensions. Preliminary calculations have confirmed this. For example, suppose a device is detonated in a van parked alongside a 1,000-foot high building in the middle of the block of an urban complex of rather closely spaced streets in one direction and more broadly spaced avenues in the other direction. Whereas the 2.5-psi ring would have a radius of 2,100 feet [640 m] detonated on a smooth surface, it is found that this blast wave extends to 2,800 feet [850 m] directly down the street, but to only 1,500 feet [460 m] in a random direction angling through the built-up blocks. These calculations have been made by many approximating factors which, if more accurately represented, would probably lead to
an even greater reduction in range.
Other weapons effects will be similarly modified from those predicted on the basis of a relatively open target area. I n the case of initial nuclear radiation, a lethal 600 rem would be expected to extend to 2,650 feet [808 m] from 1 kt. Because of the great absorption of this radiation as it passes through the multiple walls of the several buildings in a block, it is expected that 600 reins will reach out no further than 800 feet [245 m], thus covering an area onIy one-tenth as great. The thermal radiation will affect only those directly exposed up and down the street, while the majority of people will be protected by buildings.
For the same reason directly initiated fires will be insignificant, but the problem of secondary fires starting from building damage wilI remain. The local fallout pattern also will be highly distorted by the presence of the buildings. The fireball, confined between the buildings, will be blown up to a higher altitude than otherwise expected, leading to reduced local fallout but causing broadly distributed long-term fallout.
In summary, the ranges of nuclear effects from a low-yield explosion in the confined space of an urban environment will differ significantly from large yield effects, but in ways that are very difficult to estimate. Thus the numbers of people and areas of buildings affected are very uncertain. However, it appears that, with the exception of streets directly exposed to the weapon, lethal ranges to people will be smaller than anticipated and dominated by the blast-induced collapse of nearby buiIdings.
