How long would you have to stay underground after a nuclear war?

Unless you are told to go out, it's best to stay still until the risk of contamination decreases. The U.S. Department of Health and Human Services recommends staying home for at least 24 hours after a nuclear explosion. An accident at a nuclear power plant, a nuclear explosion, or a dirty bomb are examples of radiation emergencies.

If something like this happens, you may be asked to enter a building and take shelter for a while instead of leaving. The walls of your home can block much of the harmful radiation. Because radioactive materials weaken over time, staying indoors for at least 24 hours can protect you and your family until it's safe to leave the area. Entering a building and staying there is called sheltering in place.

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. Whether it's North Korea's far-fetched stance, the actions of a US president described by his own military as easily primed and quick to attack, or the growing tensions between a growing number of nuclear states (Russia, India, Pakistan). You wait for the days to pass (at least, you think they are days, it's hard to tell in the permanent twilight of your bunker), you read and reread your copy of The Road, chew a strip of jerky and drink a bottle of whiskey, until, finally, you start thinking that it might be time to return to your new nuclear world. Obviously, the military climate has evolved tremendously since these targets were chosen (otherwise, you guessed it, they wouldn't have been declassified), and a modern nuclear attack is likely to follow a very different pattern than described here.

Instead of hoarding world-destroying nuclear bombs, such as the legendary Soviet-era Tsar Bomb, a giant 50-megaton and the largest nuclear weapon ever built, the world's nuclear states have shifted to smaller reserves, filled mostly with (relatively) small-performing missiles designed for greater precision, surgical attacks. A single nuclear weapon could cause tens of thousands, if not hundreds of thousands, of immediate deaths in a major city like New York or Washington. In the event of a nuclear attack, a conventional one- or two-story house will provide almost no protection; and according to FEMA guidelines, if discovered by surprise, the best thing to do is seek shelter in a basement or subway station. Russian President Vladimir Putin put his nuclear forces on high alert on Sunday, raising concern among defense experts that Russia could unleash a nuclear attack or, in a nightmarish scenario, an all-out nuclear war.

When the nuclear winter comes, you'll be thankful for the warm fleeces and waterproof jackets you saved. Given the uncertainties about the dynamics of a potential nuclear war, cancers induced by radiation and genetic damage together over 30 years are estimated to range from 1.5 to 30 million for the world's population as a whole. It is estimated that more than 500 megatons of nuclear performance detonated in the atmosphere between 1945 and 1971, approximately half of this yield was caused by a fission reaction. From black bears climbing perimeter fences, to the northern lights triggering a state of total alertness, the weakest link in the nuclear chain of command has always been old human incompetence.