Evacuation may further reduce radiation exposure (after initial sheltering), but it only makes sense when sufficient information and logistical capacity exist.
Just how long a person in the dangerous fallout zone should stay sheltered before evacuating cannot be predicted in advance.6
The best time for an individual to leave the safety of a shelter will depend on several factors: the quality of the shelter, the levels of radiation around that shelter, and the feasibility of moving to greater safety quickly.6 Precise knowledge of radiation levels and speedy routes to safety, however, will not be available in the early, chaotic hours following a nuclear detonation. Communities implementing a fallout preparedness program nonetheless need a framework with which to educate people in advance about the best course of action to minimize fallout exposure and to save lives. Recognizing that a complicated algorithm does not serve a majority of people in the DFZ, the Expert Advisory Group proposes the following rule of thumb for the sequence of recommended protective actions:
1 Minute ⇒ Shelter: Immediately after a detonation—by minute one, for ease of planning and public communication, the best course of action is to take shelter quickly in a solid structure with the highest protective factor as possible. In some instances, this may have to be a poor shelter. The most extreme radiation levels are present in the first hour following a detonation; being inside a protective shelter at this time is essential to saving one’s life.
1 Hour ⇒ Upgrade: At hour one postdetonation, people who were forced to locate in a poor shelter should relocate quickly to a building with a higher protective factor and resume sheltering.23 Exposure during the brief time spent outdoors seeking a better shelter is an investment in a lower radiation dose overall. For those in an adequate shelter, however, staying put is more important.
1 Day ⇒ Prepare to evacuate: By day one postdetonation (24 hours), potential exposure to radiation will have dropped off by 80%. Those sheltering should be prepared to evacuate according to guidance from authorities who will have mapped the DFZ to determine the safest routes for evacuation. Until information on safe evacuation routes is available, people should stay sheltered. In some instances, this may be 2-3 days or more.
Choices about when and who to evacuate will be very complex and context dependent.
Decisions about who to evacuate, and in what order, should be driven by the hazards faced by survivors and logistical considerations.5 The anticipated impact of a nuclear detonation is immense—in terms of geographic area and potential evacuees—and it could exceed available infrastructure and resources (eg, transportation, hospitals). It may be necessary to relocate in phases according to available assets and accommodations, both in the area being evacuated and in the receiving locations.24 High-priority candidates for early evacuation are people who are located in poor quality shelters in the highest dose regions of the DFZ; who require critical medical attention or who are threatened by building collapse or fire; or who face special circumstances or vulnerabilities, such as children and the elderly.5 Uninjured people in adequate shelters are not priorities for early evacuation, nor are individuals in minimally protective shelters outside the DFZ (unless other threats to survival exist).5 People located in good shelters (ie, large buildings or underground) should be considered candidates for late-phase evacuation (days after a detonation).22 A phased evacuation is a complex undertaking, with the strong possibility for disorganization. Nonetheless, survivors and their families will expect that response professionals and evacuation planners employ a rational approach.
Mass evacuation should be delayed until fallout hazard zones and unobstructed routes are clearly known.
No evacuation should be attempted until basic information is available regarding fallout distribution and radiation dose rates. In general, it is best to assume radioactive material is present and dangerous until measurements show otherwise. Basing evacuation routes on erroneous data about high dose rate regions in the dangerous fallout zone could eliminate the very benefits of evacuation.23 The principal goal is to minimize the time that evacuees spend unsheltered when leaving the DFZ. To develop timely and safe evacuation routes, planners will also need to consider infrastructure status (eg, whether roads are passable and bridges are intact). Officials should not underestimate the time it may take to conduct a mass evacuation under postdetonation conditions. In comparison, estimated times for evacuating many major urban areas in the Atlantic and Gulf Coast regions, in advance of a hurricane and with no damage to infrastructure, exceed 30 hours; in some cases, evacuation time can exceed 48 hours.25