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Radiation Area Posting Guide

Determine correct area posting and access controls based on measured dose rate per 10 CFR 20

Free radiation area posting reference for RSOs, radiation workers, and compliance officers who need to determine which posting, sign, and access control requirements apply to an area based on the measured dose rate. Enter the dose rate at the location of interest and the calculator identifies the correct posting category per 10 CFR 20 Subpart G: unrestricted area (below 2 mR/hr), radiation area (5 to 100 mR/hr), high radiation area (100 mR/hr to 500 R/hr), and very high radiation area (above 500 R/hr). For each category, the tool displays the required sign, posting, access control, survey, and dosimetry requirements. It also lists the applicable regulatory citations and practical notes for implementation. Correct area posting is a basic regulatory requirement that is frequently cited in NRC inspection findings. Posting the wrong sign, failing to post at all, or posting at the wrong boundary can result in a Notice of Violation. This tool provides a quick reference to ensure your postings match your survey data.

Pro Tip: The boundary between "radiation area" and "high radiation area" at 100 mR/hr is the most operationally important threshold in 10 CFR 20. High radiation areas require locked or continuously attended access controls, conspicuous signs, and written authorization for entry. If your survey reads 80 mR/hr at a boundary, it is good practice to post as a high radiation area anyway, because dose rates fluctuate and survey instruments have a typical accuracy of plus or minus 20 percent. An NRC inspector who measures 105 mR/hr at your "radiation area" posting will write a finding. Posting conservatively costs nothing and avoids citations.

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Radiation Area Posting Guide
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How It Works

  1. Enter the Measured Dose Rate

    Enter the dose rate measured at the location where you need to determine posting requirements. Use the highest reading at accessible locations around the area boundary. Select the unit: mR/hr, R/hr, mSv/hr, or μSv/hr.

  2. Review the Posting Category

    The tool identifies which 10 CFR 20 posting category applies: unrestricted, radiation area, high radiation area, or very high radiation area. Each category shows the required sign wording, the trefoil symbol requirement, and the applicable 10 CFR 20 section.

  3. Check Access Control Requirements

    For each posting category, the tool lists the required access controls: whether the area must be locked or attended, whether written authorization is required for entry, and whether additional dosimetry (such as an alarming dosimeter) is required. Use this information to verify that your area controls match the posting.

Assumptions

  • Dose rate thresholds are per 10 CFR 20.1003 definitions as of the current regulatory text.
  • Dose rate is measured at 30 cm from the source or from any accessible surface, consistent with 10 CFR 20 definitions.
  • Posting categories apply to areas accessible to personnel. Locked, inaccessible areas may have different requirements.
  • This tool addresses gamma and X-ray fields only. Neutron area monitoring and posting may have additional requirements.

Limitations

  • Does not address airborne radioactivity area posting (10 CFR 20.1902(d)) or contamination postings.
  • Does not cover state-specific posting requirements that may differ from NRC regulations in Agreement States.
  • Does not address posting for radioactive materials storage, waste, or transportation containers.
  • Does not calculate dose rate. Use the companion radiation distance or activity-to-dose calculators for that.

References

  • 10 CFR 20 Subpart G - Control of Exposure from External Sources in Unrestricted and Controlled Areas
  • 10 CFR 20.1003 - Definitions (radiation area, high radiation area, very high radiation area)
  • 10 CFR 20.1601 - Control of Access to High Radiation Areas
  • 10 CFR 20.1901-1904 - Caution Signs, Labels, Signals, and Controls

Frequently Asked Questions

Under 10 CFR 20.1003, a radiation area is any area where a person could receive a dose rate greater than 5 mR/hr (0.05 mSv/hr) but less than 100 mR/hr (1 mSv/hr) at 30 cm from the source or surface. A high radiation area is any area where a person could receive a dose rate greater than 100 mR/hr. The practical difference is significant: radiation areas require posting with a caution sign, while high radiation areas require conspicuous signs, locked or continuously attended access points, and positive control measures to prevent unauthorized entry. The jump in control requirements at 100 mR/hr is one of the most important thresholds in radiation protection compliance.
Radiation areas require a sign bearing the radiation symbol (trefoil) and the words "CAUTION, RADIATION AREA" or "DANGER, RADIATION AREA." High radiation areas require "CAUTION, HIGH RADIATION AREA" or "DANGER, HIGH RADIATION AREA." Very high radiation areas require "GRAVE DANGER, VERY HIGH RADIATION AREA." All signs must bear the standard three-bladed radiation symbol (trefoil) in magenta or black on a yellow background per 10 CFR 20.1901 and 1902. The word "CAUTION" or "DANGER" is at the licensee's discretion for radiation and high radiation areas, but "GRAVE DANGER" is mandatory for very high radiation areas.
An unrestricted area is any area to which access is not controlled by the licensee for purposes of radiation protection. Under 10 CFR 20.1301, the dose to a member of the public in unrestricted areas must not exceed 100 mrem (1 mSv) in a year, and the dose rate in unrestricted areas must not exceed 2 mR/hr (0.02 mSv/hr). In practice, if your survey reads below 2 mR/hr at an accessible boundary, no radiation posting is required at that location. However, you must still demonstrate that the annual dose to any individual does not exceed 100 mrem through survey records or dosimetry.
Under 10 CFR 20.1601, each entrance to a high radiation area must have one or more of the following: (a) a control device that energizes a visible or audible alarm upon entry, (b) a control device that prevents unauthorized entry, or (c) continuous direct or electronic surveillance capable of preventing unauthorized entry. Additionally, each individual entering must be provided with a radiation monitoring device. For industrial radiography under 10 CFR 34, the radiographer must maintain direct surveillance of the high radiation area boundary at all times during radiographic operations.
If the dose rate at any accessible surface of the storage location exceeds 5 mR/hr at 30 cm, the area must be posted as a radiation area. Most properly shielded radiography cameras (depleted uranium shielding) produce dose rates well below 5 mR/hr on contact, which means the storage area may not require radiation posting. However, many facilities post the storage area as a precaution and to satisfy license conditions. Always survey the storage location and document the results. Some NRC and Agreement State licenses have specific storage posting requirements that may be more restrictive than 10 CFR 20.
Incorrect or missing area posting is a violation of 10 CFR 20 Subpart G. The NRC classifies most posting violations as Severity Level IV, which can result in a Notice of Violation and, if repeated, civil penalties up to $150,000 per violation per day. Failure to control access to a high radiation area is treated more seriously (Severity Level III or higher) and can result in escalated enforcement, increased inspection frequency, and orders modifying or suspending the license. Agreement States have equivalent enforcement authority. Correct posting is straightforward and inexpensive. There is no good reason to get it wrong.
Disclaimer: This tool provides a reference summary of 10 CFR 20 area posting requirements. It does not replace the full text of the regulations or your facility's radiation protection program. Posting decisions should be based on calibrated instrument surveys and verified by the radiation safety officer. Some Agreement State regulations may differ from 10 CFR 20.

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