system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How are Hiroshima and Nagasaki habitable?
gpt
The bombs were detonated half a kilometer high up in the air to maximize the shockwave and blast patterns. So most of the "fallout" would have blown away from the blast site. 

Second, the bombs were small. This isn't like a nuclear core meltdown where there's tons of primary and secondary radioactive dust and material. This was just a few kilograms of fissionable material that vaporized, and since it occurred over such a wide area the radiation hazard declined fairly rapidly.