How far do you need to be to survive a nuclear blast?

The question of how far is “safe” from a nuclear explosion doesn’t have a simple answer. It depends on the size of the bomb, whether it explodes in the air or on the ground, and where you are when it happens. But scientific models and emergency planning guidelines do offer a fairly clear picture for a typical 10–20 kiloton detonation, roughly the scale of the Hiroshima bomb.

Close to the point of impact, survival is extremely unlikely. Within about 0.5 to 1 kilometre, buildings are largely destroyed and radiation levels are immediately lethal. The heat alone can cause severe burns in seconds, while the blast wave can flatten most structures. Studies based on past nuclear testing show that people exposed directly within roughly a mile, or 1.6 kilometres, face a high risk of fatal radiation and burn injuries without protection.

Step a little further away and things start to look different. At roughly 1.5 to 3 kilometres from ground zero, the impact is still serious, but survival becomes more likely, especially if you’re inside a well-built structure. This is what emergency planners call the moderate damage zone. Buildings can be badly damaged, but they’re not completely wiped out, and with timely medical help, many of those injured can make it through.

Beyond roughly 4 to 5 kilometres, the immediate blast effects weaken significantly. Windows may shatter and some buildings may be damaged, but the chances of surviving the initial explosion improve sharply. However, this is not a safe zone in the usual sense. Injuries from flying glass, fires, and the shockwave are still common.