His main character is Guy Montag. And when he run away from the city. He uses the words "I see the bomb falling in the city and burning down the ashes." The bomb is A-bomb and you have to be away at least 5 miles from the place it explodes.
200 miles? 50? I'm afraid not. Don't get me wrong, an atom bomb produces a tremendous explosion, but the Heroshima and Nagasaki bombs didn't do much major blast damage beyond 5 miles. Both bombs were capable of inflicting burns at a much greater radius than the blast radius, but neither could do much damage of any kind instantaneously beyond 20 miles. Even the most powerful bombs ever devised (some 1,000 times more powerful than Heroshima) could only inflict minor blast damage at 50 miles. But, any way you look at it, being 5 miles from ground zero can't be healthy, and watching the explosion would probably cause blindness.
I've been to Hiroshima and visited the memorial museums there. Some people who were in the city of Hiroshima and its immediate surroundings did survive the A-bomb blast. Many later died of conditions brought on by massive radiation exposure, but some did live for decades later. Some people did see the A-bomb blast and lived to tell the tale. The manga "Barefoot Gen" is a good example of this; it's a semi-autobiographical story told by a survivor.
I think the more relevant issue here is a feature of much Golden Age science fiction: a fascination with atomic power, coupled with a near-total ignorance of its true effects. The short story "Nerves" by Lester Del Ray demonstrates this duality perfectly, with its excellent story and shockingly bad (to modern eyes) physics and medicine.
In other words, I think that Guy Montag's observation is less a slip-up than a feature of that era's SF. If we were to list all the atomic-related slip-ups of Golden Age SF books, we would be here a very long time...
At the time the bomb was dropped on Hiroshima, my mother and her family were living in Kure, approximately 20 miles from Hiroshima. None of her family were affected in any way. My Mum says that they felt a very strong gust of wind from the blast, but that was all.
OK, wait a minute. When in the book does it ever say that it's an A-bomb anyway? I looked, and it's many bombs that they dropped not just one nuke. And, if it was an a-bomb, the fallout would kill the book people once they get to the city, wouldn't it?
I don't see why it really matters how big of a radius an a bomb has. The author was trying to give a visual image of how close Guy really was. You also have to remember this book is fairly old and pin point accuracy didn't matter much.
Fahrenheit 451 is a fantastic book, and i have read it several times. The bomb was never mentioned as an a-bomb. I also have a very hard time believing the Ray Bradbury would make such a careless mistake as such, and mar his gorgeously poetic writing.
I read farenheit451 and the book has no reference to the time period. Bradbury was just making predictions that might happen. When Bradbury wrote the novel they didn't even have the a-bomb yet!