Precautionary action zone

Precautionary Action Zone (PAZ). A precautionary action zone is an area where there is the potential for severe deterministic health effects if protective actions are not taken before or shortly after the start of a severe release. The precautionary action zone is therefore also a response zone. In this zone, automatic protective actions are taken to reduce the risk of... 

Evacuation. Evacuation can be the most effective protective action from all the exposure pathways resulting from a plume. In general, evacuation is the preferred protective action for areas close to any source of hazardous material release, provided that it can be implemented safely and promptly. For example, in the precautionary action zone, evacuation or substantial shelter is appropriate for a severe accident. However, the effectiveness of an evacuation depends on the nature of the release, time to initiate and complete, distance from the source, duration of the release, and other factors. The effectiveness of evacuation relative to shelter must be determined by careful study for each threat category I facility. These studies have come to some counterintuitive conclusions. For example, as shown above under Public Protective Actions, walking (e.g., evacuation by foot) in a plume from close to a... 

Threat category Precautionary action planning zone size (PAZ) Urgent protective action planning zone size (UPZ) Longer-term protective action planning zone size (LPZ)... 

As discussed in Section 5.2, risk decreases rapidly up to a distance of about 2 to 3 miles and decreases more slowly thereafter. Thus, in a core melt accident, early evacuation of the first 2 to 3 miles would markedly reduce individual risks (i.e., the payoffs would be greatest within this distance). Second, the population within this distance is small (at many sites, a few hundred people), and there are normally few impediments to immediate evacuation of the area. Indeed, this area encompasses the low-population zone around most reactor sites. Third, the individual risk of early deaths or injuries for the most severe accident is, in most cases, confined to this area. Immediate evacuation of people near the plant could well prove to be precautionary because most severe accidents (like the Three Mile Island accident) would not be expected to lead to a major release. On the other hand, core damage accidents are expected to be extremely rare, so that precautionary evacuations would also be rare and the results of not taking immediate protective actions could be tragic. 

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