The Federal government has ordered the production and storage of 1.6 million doses of potassium iodide. The human thyroid gland collects iodine from food; the body needs trace elements of it. But in the event of nuclear fallout (or a "dirty bomb"), radioactive iodine in the air would be absorbed by the thyroid and (trapped inside the body) continue to cause radiation poisoning for weeks. By giving people (especially children) doses of potassium iodide, the thyroid will be flooded with iodine and not try to absorb any more, allowing the radioactive version to pass through with minimal harm.--Stephen V Cole