Many have cuts and broken bones from falling debris and burns from the intense heat of the explosion.

VOA: standard.2010.07.26

Theorists believe the rapid collapse generates heat that ignites the explosion.

CNN: Why gamma-ray burst shocked scientists

An explosion is simply an exponential rise in heat.

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Furthermore, it would take a combination of extreme events to make things dangerous in Tokyo (nuclear re-criticality, steam explosion) etc all of which are being rendered less and less likely as time passes and the heat decay process progresses.

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