Radiation Control Zones and Perimeters Recommended by Various Agencies for Responding to Radiological Emergencies

Agency Zone Designation Perimeter Designation Exposure Levels Activities and Guidelines


(See diagram)

Inside the inner cordoned area --- Areas with >100 mSv/h
  • Only lifesaving actions should be performed in this area
  • Limit staying time to <30 minutes, or less, depending on measured level of radiation.
Cordoned Area ("Hot zone")
Safety Perimeter >0.1 mSv/h
  • Area around dangerous radioactive source where precautions should be taken to protect the responders and the public from potential external exposure and contamination.
Cordoned Area
Security Perimeter ---
  • Access controlled, secure zone around the inner cordoned area.
  • Ambient dose rates in this area need to be at levels very close to background levels.
  • See diagram for response activities in this zone.


(See diagram)

Dangerous Radiation Zone Inner Perimeter >10 R/h
(>0.1 Sv/h)
  • Actions taken in this area should be restricted to timei-sensitive, mission critical activities such as life saving.
Hot Zone Outer Perimeter >10 mR/h
(>0.1 mSv/h)
  • Appropriate actions include
    • Initiate early, adequate sheltering followed by delayed, informed evacuation using specific instructions from appropriate government officials.
    • Remember that until the level and extent of contamination can be determined, efforts should be made to avoid being outdoors in potentially-contaminated areas.
    • Isolate the area.
    • Minimize time each emergency worker spends inside the area.
    • Ensure that workers follow appropriate personal protection guidelines. (PPE and worker exposure guidelines)
Cold Zone --- Outdoor exposure rates
< 10 mR/h
(<0.1 mSv/h)
  • The area outside the outer perimeter is where the command post and other support functions are located.


(See diagram)

Extreme Caution
Radiation Zone
Extreme Caution
Radiation Boundary
≥10,000 mR/h
(≥10 R/h)
  • Activities restricted to saving lives.
  • Total accumulated stay time for first 12 hours: minutes to hours
Radiation Zone
Radiation Boundary
1000 mR/h
  • Access restricted to authorized personnel performing critical tasks:
    • Firefighting
    • Medical assistance
    • Rescue
    • Extrication
    • Other time-sensitive activities
Radiation Zone
Radiation Boundary
100 mR/h
  • Access restricted to authorized personnel entering the "High Radiation Zone" to perform critical tasks such as saving of lives and property.
  • Serves as a buffer zone/transition area between the "High Radiation Zone" and "Low Radiation Zones"
Radiation Zone
Radiation Boundary
≤10 mR/h
  • Access restricted to essential individuals.
  • Initial decontamination of first responders should occur near the outer boundary of this area.

Note: See original source documents below for additional details, including benchmarks of concern for detecting focal, high levels of gamma, beta, and alpha radiation from radionuclides.

Manual for First Responders to a Radiological Emergency, page 12, (PDF - 2.2 MB) (CTIF, IAEA, PAHO, WHO, October 2006) and
Generic Procedures for Medical Response During a Nuclear or Radiological Emergency (PDF - 2,224 KB) (IAEA, WHO, April 2005)
Key Elements of Preparing Emergency Responders for Nuclear and Radiological Terrorism (NCRP Commentary No. 19), National Council on Radiation Protection and Measurements, Bethesda, MD, December 2005. Purchase required. See Responding to Radiological and Nuclear Terrorism: A Guide for Decision Makers, (PDF - 1.61 MB) (NCRP Report No. 165), Bethesda, MD, 2010.
§ Handbook for Responding to a Radiological Dispersal Device (Dirty Bomb): First Responder's Guide: The First 12 Hours (CRCPD Publication 06-6) Conference of Radiation Control Program Directors, Inc. Frankfort, Kentucky, 2006

mR/hour: milliroentgen per hour
R/hour: roentgen per hour

See also: Planning Guidance for Response to a Nuclear Detonation, Second edition, 6/2010 (PDF - 2.62 MB) (National Security Staff, Interagency Policy Coordination Subcommittee for Preparedness & Response to Radiological and Nuclear Threats)