<P> 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 . </P> <P> The first effect of the explosion was blinding light, accompanied by radiant heat from the fireball . The Hiroshima fireball was 370 metres (1,200 ft) in diameter, with a surface temperature of 6,000 ° C (10,830 ° F). Near ground zero, everything flammable burst into flame . One famous, anonymous Hiroshima victim, sitting on stone steps 260 metres (850 ft) from the hypocenter, left only a shadow, having absorbed the fireball heat that permanently bleached the surrounding stone . Simultaneous fires were started throughout the blast - damaged area by fireball heat and by overturned stoves and furnaces, electrical shorts, etc . Twenty minutes after the detonation, these fires had merged into a firestorm, pulling in surface air from all directions to feed an inferno which consumed everything flammable . </P> <P> The Hiroshima firestorm was roughly 3.2 kilometres (2.0 mi) in diameter, corresponding closely to the severe blast damage zone . (See the USSBS map, right .) Blast - damaged buildings provided fuel for the fire . Structural lumber and furniture were splintered and scattered about . Debris - choked roads obstructed fire fighters . Broken gas pipes fueled the fire, and broken water pipes rendered hydrants useless . At Nagasaki, the fires failed to merge into a single firestorm, and the fire - damaged area was only one fourth as great as at Hiroshima, due in part to a southwest wind that pushed the fires away from the city . </P> <P> As the map shows, the Hiroshima firestorm jumped natural firebreaks (river channels), as well as prepared firebreaks . The spread of fire stopped only when it reached the edge of the blast - damaged area, encountering less available fuel . </P>

How big was the blast radius of the hiroshima bomb
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