[niwtsol]

Thank you for this detailed explanation. Given the above, I find it absolutely wild that the closest survivor of Hiroshima was only 170m away (granted he was in a concrete basement). In my head, I always pictured a large area completely obliterated as you described.

"Eiso Nomura (1898-1982) miraculously survived the atomic bombing of Hiroshima, despite the fact that the explosion occurred in the air right above him.On August 6, 1945, Mr. Nomura was in the basement of the Fuel Hall (now, the Rest House in Peace Memorial Park), about 170 meters southwest of the hypocenter."

[VonGuard]

Furthering the original question: the myth says Plumbbob launched a manhole cover into orbit, but the truth is slightly less than that, and it wasn't really a manhole cover.

Still, this is what happens when you use a nuclear bonb as a detonating charge at the bottom of a tube...

https://en.wikipedia.org/wiki/Operation_Plumbbob

[kakacik]

900kg steel cap is a bit more than manhole :)

And it was most probably vaporized, either by blast itself or by rapid compression of air. They estimated if it actually started flying it would have 6x Earth escape velocity (cca 240,000 kmh), no way to survive flight through 100km of atmosphere before reaching semi-vacuum

[mohaine]

He was 170m away from the location the bomb exploded over, not 170m away from the explosion.

That said, the bomb only exploded at roughly 600m in altitude so still pretty close.

[Syzygies]

There is no single accepted definition of "fireball" like the Kármán line where outer space begins, and even that is just a convention.

The "artificial sun" created at Hiroshima, the early-stage plasma fireball at 1 ms, is estimated to have been 5 to 10 meters across.