What chance factors at Hiroshima added to the inherent destructiveness of the atomic bomb and produced more deaths and devastation than American...

There were several factors that caused the detonation of the atomic bomb over Hiroshima, Japan, on August 6, 1945, to be worse than what scientists had expected. While the Americans had aimed to hit the Aioi Bridge, their bomb missed the target because of crosswinds. Instead, the bomb detonated directly above the Shima Surgical Clinic, which is considered "ground zero" for the blast. As a result, about 90% of the doctors and 93% of the nurses in the city perished instantly, and the hospital was destroyed. Upwards of 70,000 people died immediately from the blast (some estimates are as high as 140,000 people) and thousands died later from radiation sickness, but the medical staff to assist them was killed in the blast. 

In addition, the central part of Hiroshima was flat, causing fires to spread quickly. These fires coalesced into a large "fire storm," causing additional damage to what had been destroyed in the initial blast. Hiroshima was highly flammable, as most of its structures were built of wood frames and tile roofs outside the center of the city (where some buildings had reinforced concrete). In the later atomic bomb detonation at Nagasaki, fires also broke out, but the shape of the city prevented the creation of a fire storm. In Hiroshima, every building within one mile of "ground zero" was destroyed, save for the few that were built with reinforced concrete. The flat contour of the center of the city added to the destructive capacity of the atomic bomb.