-TAPTER 8 - INTERACTION OF SIMULTANEOUS SURFACE BURSTS 1, The situation discussed in this chapter is the only one in the report which, in effect, could mean that current assessments of the local fallout hazard may not be conservative, i.e., that current methods under certain circumstances predict less local fallout than actually could occur. If two or more nuclear weapons were to be detonated closely in time and space, causing the resulting cloud height to be severely limited, the expected radiation levels in the local fallout pattern could be substantially increased compared to those predicted by DCPA (and other) fallout prediction models. Currently assumed characteristics of the nuclear arsenal of any potential U.S, adversary in a nuclear war are such that near-simultaneous, closely spaced nuclear bursts seem unlikely. Multi-reentry vehicles are not thought to be part of such a potential enemy's current arsenal. If and when such weapons become available for use against us, the probability of such simultaneous-burst circumstances, and thus an enhanced fallout radiation threat, could increase. 2, It is noted that the above assessment is, as pointed out in the report, based on preliminary and inadequate data. Questions of bursts of non-equal yields, or that are not quite simultaneously detonated, have not been answered. Thus, the increased threat of local fallout resulting from interactions of nearby simultaneous bursts is far from having been established. II-14 % uf +