NCRP-116: Radiation Exposure Limits

Background

Released in 1993, NCRP 116 is an update to the NCRP 91 (released 1987). NCRP 91 was largely based on study of atomic bomb survivors completed by the Radiation Effects Research Foundation (RERF). Three important factors were recognized as result of RERF’s work. First, excess cancers continued to be observed in atomic bomb survivors into the latest study period, at time of writing. Second, cancer incidence appeared at a rate consistent with a multiplicative projection model. Third, revised risk-dose estimates became available. However, because the risk assessment was incomplete, the limits set by NCRP 91 were considered upper limits rather than radiation safety design goals.  NCRP 116 was created upon completion of risk assessments from several national and international bodies and generally increases the reported risks of radiation exposure.

Definitions

  • Deterministic Effect: a somatic effect which increases in severity with increasing radiation dose above a threshold dose.
  • Stochastic Effects: health effects which occur randomly and for which the probability of the effect, rather than the effect’s severity, is related to dose.
    • “For radiation-protection purposes, the risk of a stochastic effect is proportional to dose without threshold, throughout the range of dose and dose rates of importance in routine radiation protection.”
  • As Low As Reasonably Achievable (ALARA): making every reasonable effort to maintain exposures to radiation as far below the dose limits as is practical

Radiation Risk and Limit Tables

Radiation Exposure Risk Estimates

GroupRisk FactorNCRP Report 91ICRP Publication 60NCRP Report 116
WorkersFatal cancer1.25% per Sv4% per Sv 4% per Sv
WorkersNon-fatal cancer-0.8% per Sv0.8% per Sv
WorkersSevere genetic effects0.4% per Sv0.8% per Sv0.8% per Sv
Members of the PublicFatal cancer-5% per Sv5% per Sv
Members of the PublicNon-fatal cancer-1% per Sv1% per Sv
Members of the PublicSevere genetic effects-1.3% per Sv1.3% per Sv
Embryo/Fetus-20% per Sv-~10% per Sv

Radiation Worker Exposure Limits

 NCRP Report 91ICRP Publication 60NCRP Report 116
Based on Stochastic Effects50 mSv annual effective dose limit

10 mSv × age (y) cumulative effective dose limit for workplace
50 mSv annual effective dose limit

100 mSv in 5 year cumulative effective dose limit
50 mSv annual effective dose limit

10 mSv × age (y) cumulative effective dose limit for workplace
Based on Deterministic Effects150 mSv annual dose equivalent limit to lens

500 mSv annual dose equivalent limit to all other organs (e.g. red bone marrow, breast, lung, gonads, skin, extremities)
150 mSv equivalent dose limit to lens

500 mSv annual equivalent dose limit to skin, hands, and feet
150 mSv annual equivalent dose limit to lens

500 mSv annual equivalent dose limit to skin, hands, and feet
Annual Limits of Intake (ALI)[50 mSv]/[HE (50) Bq-1][20 mSv]/[HE (50) Bq-1]--
Annual Reference Levels of Intake----[20 mSv]/[HE (50) Bq-1]

Public Exposure Limits

 NCRP Report 91ICRP Publication 60NCRP Report 116
Based on Stochastic Effects1 mSv annual for continuous exposure

5 mSv annual for infrequent exposure
1 mSv annual

A higher value may be acceptable if average annual over 5 years is less than 1 mSv
1 mSv annual for continuous exposure

5 mSv annual for infrequent exposure
Based on Deterministic Effects50 mSv annual limit to lens, skin, and extremities15 mSv annual limit to lens

50 mSv annual limit to skin, hands, and feet
50 mSv annual limit to lens, skin, and extremities
Embryo/fetus5 mSv annual limit

0.5 mSv per month once pregnancy is known
2 mSv limit to woman’s abdomen once pregnancy is declared

Limit intake of radionuclides to 1/20 of ALI
0.5 mSv limit per month once pregnancy is known
Negligible Individual Dose (NID)0.01 mSv annual per source or practice--0.01 mSv annual per source or practice

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