Consider this: the unthinkable has happened, and a nuclear attack has made it necessary for you to enter your underground bomb shelter. You’re prepared with plenty of water and food stores, you’ve got adequate ventilation and a plan for waste disposal. You’re set. But how long do you have to stay?
The duration of your stay in your shelter is going to depend on multiple factors, particularly your distance from the initial blast. The nice thing about fallout (that’s not a phrase you read every day, is it?) is that the radiation loses potency over time, and eventually you will be able to leave the shelter safely.
In determining when it will be safe for you to leave, consider your proximity to the blast. The more information you have about the blast, the better. For this reason, plan to keep a variety of communication devices with fresh batteries in your shelter so that you can stay as up-to-date as possible. Was the explosion the result of a missile? A dirty bomb? Decay rates of nuclear fallout are about the same regardless of the type or size of device, but the overall amount of fallout will vary according to the size as well as the device’s proximity to the ground at the time of the explosion. The heaviest fallout would be limited to the area at or downwind from the explosion, and 80 percent of the fallout (that is, the most dangerous period) would occur during the first 24 hours. Individuals several miles or more from the explosion, and especially those upwind, would likely be able to leave their shelter within about 72 hours.
Overall, radioactive fallout poses the greatest threat during the first two weeks after the blast. After this time, it will have decayed to about 1% of its initial radiation level. This is why two weeks is an excellent standard to shoot for when stocking your shelter- if, for some reason, you cannot access any outside communication and you aren’t sure of your distance from or location relative to the blast, your safest bet is to assume that the area outside your shelter is contaminated for two weeks. After this time you can emerge to further assess your situation, evacuating to a further safe distance if necessary.
Emerging From Your Shelter
If you are unable to access emergency information via radio or television and two weeks has passed, it will be necessary to leave your shelter briefly to assess the safety of your surroundings and determine whether it is safe for all inhabitants to emerge. The individual who makes this initial venture out of the safety of the shelter should be one who is the least physically vulnerable- i.e. not elderly, pregnant, etc.
As mentioned, by two weeks’ time the radiation is very likely to have decreased to a safer level, particularly the further you are from ground zero. Still, take as many protective precautions as you are capable of: wear a particulate mask to avoid breathing in any dust or ash lingering in the air. Without specialized equipment and the training to operate it, it will be difficult to determine how much radiation is present, so your goal will be, ideally, to access public health information or determine the location of a more secure shelter. Without exact information regarding the level of radiation still present in fallout, you will want to do as much as possible to avoid contact with any accumulations of dust/ash material. Upon returning to your shelter, it is wise to shake off any dust particles you’re your hair and clothing before re-entry, then bag up all clothing you were wearing in heavy plastic trash bags.
If you are able to obtain one, a dosimeter will tell you the level of radiation that you are being exposed to and will help you to determine whether your surroundings are safe to return to or travel through, or if you should return to the relative safety of your shelter immediately.