Radioactive iodine can result from a nuclear power plant disaster, such as Chernobyl or Fukushima, or from a nuclear bomb explosion. Fallout from either type of disaster, the latter being inestimably greater than the former, can spread for hundreds of miles on the wind. The pattern of areas affected is as unpredictable as the weather and the wind direction.
Obviously, the best approach is to evacuate the affected area, so as to minimize your exposure. But even if you leave the area immediately, you might still be exposed to radioactive iodine. And if you are unable to leave, your exposure will be greater. Radioactive iodine (I-131) emits beta-rays and gamma-rays, making exposure a danger even if it is exterior to the body.
However, inhalation or ingestion of radioactive iodine presents an additional danger to the thyroid. The danger of this exposure is not theoretical. After Chernobyl, the rate of thyroid cancer in children and teens increased to 30, 60, even 100 times the typical rate, especially in areas closer to the disaster.
Potassium iodide (KI) is the potassium salt of iodine. It contains non-radioactive (stable and safe) iodine. The body cannot tell the difference between radioactive and non-radioactive iodine. Taking a dose of KI floods the body with stable iodine, so that uptake of the radioactive iodine is greatly reduced. However, persons over 40 years of age do not usually need to take KI, as their thyroid glands are not very active.
In case of a radiological disaster, affected persons may be told by government health officials to take either one dose of KI, which protects for 24-hours, or a course of KI for a number of days, up to 7 to 14 days. Taking KI is not without health risks, so follow medical advice on how long to take it. Dosages vary based on age. Pregnant or breast-feeding women, and neonates (birth to one month) should take a single dose, and they should be given priority for evacuation over the rest of the population. Otherwise, dosages by age are as follows:
Neonates: birth through 1 month: 16 mg (single dose)
Children: 1 month through 3 years: 32.5 mg per day
Children: 3 years through 12 years: 65 mg per day
Teens: 12 through 18 years: 65 mg per day
but teens who are close to adult size (by body weight) should receive the adult dose of 130 mg per day.
Adults: 18 through 40 years: 130 mg per day
Pregnant or breast-feeding women: 130 mg (single dose)
Adults over 40 do not need KI tablets, unless their exposure is very high; do not take KI if you are over 40, unless recommended by government health officials.
These inexpensive KI tablets, available at Amazon.com, are in the form of 32.5 mg tablets, which is convenient for the dosages needed by children. If KI tablets are in short supply, priority must be given to children and teens; they are at the highest risk for thyroid cancer. And if there is a major nuclear disaster, especially a nuclear bomb explosion, it is almost certain that KI will be in very short supply, so only children should be given the tablets. That is why the 32.5 mg tablets are better than the 130 mg tablets. The KI in the link above is 240 tablets, enough for a 14-day course for 8 children (2 tablets per day per child is 65 mg), or a 7-day course for 16 children.
Much more information in my book, Apocalypse Survival Guide for Christians, available at Amazon in print and in Kindle format.