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U.S. Department of Health & Human Services
Radiation Event Medical Management (REMM)

National Council on Radiation Protection and Measurement (NCRP)
Radiation Protection Perimeter Guidelines *
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Zones defined by NCRP Commentary No. 19 *Adapted from Key Elements of Preparing Emergency Responders for Nuclear and Radiological Terrorism
(NCRP Commentary No. 19, December 2005, purchase required; see Free Overview (PDF - 219 KB))

This diagram was created based on recommendations from NCRP, Commentary 19, but the diagram is not a part of the document. The location of the perimeter lines depends on the facts of each incident, and the locations will change over time, as the incident evolves.

Inner perimeter:

  • Establish when 10 Roentgens per hour (R h-1) exposure rate
  • Exposure and activity levels within this perimeter have the potential to produce acute radiation injury.
  • Actions should be restricted to time-sensitive, mission critical activities (e.g. lifesaving).
  • An alarming personal radiation dosimeter should be used by each emergency responder.
  • The cumulative absorbed dose received by an emergency responder working within or near the inner perimeter must be recorded.
  • Fifty (50) rad (0.5 Gy) is the NCRP recommended "decision dose" that triggers a decision on whether to withdraw an emergency responder from within or near the inner perimeter. This dose may also apply to removal from within the outer perimeter.

Outer perimeter:

  • Establish if any of the following are exceeded:
    • 10 milliRoentgens per hour (mR h-1) exposure rate
    • 60,000 disintegrations per minute per square cm (dpm cm-2) for beta and gamma surface contamination
    • 6,000 dpm cm-2 for alpha surface contamination
  • Appropriate actions inside this perimeter are:
    • Evacuate members of the public
    • Isolate the area
    • Ensure all emergency workers inside the area minimize their time spend in the area and follow appropriate protection guidelines.
  • Fifty (50) rad (0.5 Gy) is the NCRP recommended "decision dose" that triggers a decision on whether to withdraw an emergency responder from within or near the inner perimeter. This dose may also apply to removal from within the outer perimeter.