There is a ceiling on the amount of destruction that a single weapon can produce, because the radius of destruction for any given level of blast increases approximately as the cube root of the energy output.
With 7 weapons dropped in a circle, at the midpoint between zero point distance, blast waves would collide at the overpressure points. On interior points of the circle, the blast waves, depending upon the angles at which they met, would be reflected or merge. The key feature of encirclement in terms of blast forces is that the energy on the interior of the circle would be concentrated in a comparatively small area instead of dissipating from the zero point at a 128° angle over an ever larger area [the angle formed at an intersections of a 7 sided polygon]. The result is greater blast destruction on the interior of the circle than is commonly suggested when contemplating single weapon effects.
Paul Cooper's text Explosives Engineering (1996) [p. 216]:
Take the amount of TNT - lets say 1,000 lbs. 4184 Joules = 0.001 Kton. Y^0.4), where Y is yield.
Approximate over pressures and distances for .001 Ktons as follows:
15 Psi - 0.02 miles
10 Psi - 0.02 miles
5 Psi - 0.03 miles
1 Psi - 0.01 miles
0.25 PSI - 0.19 miles
For the METRIC guys:
103 KPa - 0.02 Km
68.9 KPa - 0.03 Km
48.3 Kpa - 0.04...
You get the point. But keep in mind 2PSi is enough to destroy reinforced concrete buildings - but the blast radius falls off rather quickly. Tanks and other cans - at least now a days are sealed up pretty tight - so a close blast might be reflected out. If the tank were not sealed - the shock front would reflect off the interior of the tank walls - and amplify the blast effects to the crew. Hope that helps.
