The hazardous rain zone can easily extend 10 to 20 miles (15 to 30 kilometers) from detonation, depending on explosive performance and weather conditions. Heat is a problem for those closest to the explosion. Minor first-degree burns can occur up to 11 km (6.8 miles) away, and third-degree burns, which destroy and blister skin tissue, can affect anyone up to 8 km (5 miles) away. Third-degree burns that cover more than 24 percent of the body would likely be fatal if people don't get immediate medical attention.
Those closest to the bomb would face death, while anyone within a distance of up to 5 miles could suffer third-degree burns. People within a maximum distance of 53 miles may experience temporary blindness. The 1963 Limited Nuclear-Test-Ban Treaty ended atmospheric testing for the United States, Great Britain and the Soviet Union, but two major non-signatories, France and China, continued nuclear testing at a rate of approximately 5 megatons per year. Nuclear explosions can produce clouds of dust and radioactive sand-like particles that disperse into the atmosphere, known as nuclear fallout.
However, for more information on the current state of nuclear weapons in the world, including the scale of bombs, you can visit the Nuclear Notebook in the Bulletin of Atomic Scientists. For survivors of nuclear war, this persistent radiation hazard could pose a serious threat for up to 1 to 5 years after the attack. Nuclear explosions produce a powerful phenomenon called a nuclear electromagnetic pulse (PEM), an invisible burst of energy that can cut off power lines, telephone and Internet.