In addition to what Beachdoc mentioned, I would add that KI is very unlikely to be useful in a dirty bomb incident, as it is unlikely that radioiodine would be used. Half lives for cobalt-60 and cesium-137 (believed to be the most likely sources used) are 5.2 and 30.1 years respectively. So if you are planning to hunker down and wait for it to decay, you would be waiting awhile.

Also in a dirty bomb incident, the powers-that-be will most likely ask the public to shelter in place initially, wait for the dust to settle, and then evacuate those that might be impacted by the resuspension of contamination when the hazmat guys go in to clean things up. At least that's what I told the police officers I trained this morning. <img src="images/graemlins/grin.gif" alt="" />

Greg
(the helpful radiation safety guy)