How Far Away is Safe from a Nuclear Bomb?

At a distance of 40-45 miles, a person would have a maximum of 3 hours after the rain began to find shelter. Significantly smaller doses of radiation can make people seriously ill, making the prospects for survival of those immediately downwind of the burst point slim unless they can be sheltered or evacuated. Heat and debris in the air created by a nuclear explosion can cause rain; debris is believed to do this by acting as condensation cores for clouds. To date, only two nuclear weapons have been used in war, but there are still approximately 12,700 warheads left in the world today.

Estimating the impact of a single nuclear bomb is difficult, as it depends on many factors such as the weather on the day it's launched, the time of day it's detonated, the geographical distribution of where it impacts, and whether it explodes on the ground or in the air. Studies on the total effect of nuclear explosions on the ozone layer have been, at least tentatively, exonerating following initial discouraging findings. While a serious event, such as a plane crash against a nuclear power plant, could result in the release of radioactive material into the air, a nuclear power plant would not explode like a nuclear weapon. Nuclear devices range from small portable devices carried by an individual to weapons carried by missiles.

This notion referred to the nuclear reaction of two atmospheric nitrogen atoms that form carbon and one oxygen atom, with an associated release of energy. We also know that radioactive particles can travel very far; a recent study found that traces of radioactive carbon from Cold War nuclear bomb tests have been found in the Mariana Trench, the deepest point in the world's oceans. Most of the material damage caused by a nuclear gust of air is caused by a combination of high static overpressures and strong winds. In an instant, the dense shock front obscures the fireball and continues to move beyond it, now expanding outwards, free of the fireball, causing a reduction in light emanating from a nuclear detonation.

The following table summarizes the most important effects of individual nuclear explosions under ideal weather conditions and with clear skies. Large nuclear weapons detonated at high altitude also cause geomagnetically induced current in very long electrical conductors. The explosion of a nuclear explosion also moves air away from the explosion site, creating sudden changes in air pressure that can crush objects and bring down buildings. It is these reaction products and not gamma rays that contain most of the energy of nuclear reactions in the form of kinetic energy.

Approximately 35 percent of the energy released from a nuclear explosion is thermal radiation. To learn more about current state of nuclear weapons in the world, including scale of bombs, visit The Nuclear Notebook in The Bulletin of Atomic Scientists.