b. Predicted Fallout Zones. The predicted fallout zones (FM 3-22) are those areas in which exposed, unprotected
personnel may receive significant doses of nuclear radiation within 1 to 4 hours after actual arrival of fallout. A primary
zone of hazard and a secondary zone of hazard are predicted.
(1) Zone I is a primary zone of hazard and is called the Zone of Immediate Operational Concern. In this zone
personnel may receive doses greater than 150 rad (the emergency risk dose) in less than 4 hours after actual arrival of
(2) Zone II is the area of secondary hazard and is called the Zone of Secondary Hazard. In this zone the total
dose to personnel is expected to be less than 150 rad in the first four hours after the arrival of fallout, but is expected to
exceed 50 rad (the negligible risk dose) within the first 24 hours after the arrival of fallout.
(3) Outside the predicted area, exposed unprotected personnel may receive a total dose that does not exceed
50 rad in the first day (24 hours) after actual arrival of fallout. The total dose for an indefinite time of stay outside the
predicted area should not exceed 150 rad (the emergency risk dose).