Editing Little Boy (section)

===Blast===
The blast from a nuclear bomb is the result of [[X-ray]]-heated air (the fireball) sending a shock wave or pressure wave in all directions, initially at a velocity greater than the speed of sound,{{sfn|Diacon|1984|page=18}} analogous to thunder generated by lightning. Knowledge about urban blast destruction is based largely on studies of Little Boy at Hiroshima. Nagasaki buildings suffered similar damage at similar distances, but the Nagasaki bomb detonated {{convert|2.0|mi|km|sp=us}} from the city center over hilly terrain that was partially bare of buildings.{{sfn|Glasstone|Dolan|1977|pages=300, 301}}

[[File:House 1953 Nevada Nuclear Test 5 psi.jpg|thumb|Frame house in 1953 nuclear test, 5 [[Pound per square inch|psi]] overpressure]]

In Hiroshima, almost everything within {{convert|1.0|mi|km|sp=us}} of the point directly under the explosion was completely destroyed, except for about 50 heavily reinforced, earthquake-resistant concrete buildings, only the shells of which remained standing. Most were completely gutted, with their windows, doors, sashes, and frames ripped out.{{sfn|The Atomic Bombings of Hiroshima and Nagasaki, 1946|page=14}} The perimeter of severe blast damage approximately followed the {{convert|5|psi}} contour at {{convert|1.1|mi|km|sp=us}}.

Later test explosions of nuclear weapons with houses and other test structures nearby confirmed the 5&nbsp;psi overpressure threshold. Ordinary urban buildings experiencing it were crushed, toppled, or gutted by the force of air pressure. The picture at right shows the effects of a nuclear bomb-generated 5&nbsp;psi pressure wave on a test structure in Nevada in 1953.{{sfn|Glasstone|Dolan|1977|page=179}}

A major effect of this kind of structural damage was that it created fuel for fires that were started simultaneously throughout the severe destruction region.