Dose limits

ICRPædia Guide to the System of Radiological Protection:

1. The System of Radiological Protection: An Overview · 2. Objectives of Radiological Protection · 3. Fundamental Principles of Radiological Protection · 4. Exposure Categories and Situations · 5. Absorbed, Equivalent, and Effective Dose · 6. Dose limits

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Dose limits help ensure that no person is exposed to an excessive amount of radiation in normal, planned situations.

They are the strongest form of restriction on dose to an individual. Exceeding a dose limit is contrary to regulations in most countries.

Dose Limits Recommended by ICRP

Type of Dose Limit	Limit on Dose from Occupational Exposure	Limit on Dose from Public Exposure
Effective Dose	20 mSv per year, averaged over defined periods of 5 years, with no single year exceeding 50 mSv After a worker declares a pregnancy, the dose to the embryo/fetus should not exceed about 1 mSv during the remainder of the pregnancy	1 mSv in a year In special circumstances, a higher value could be allowed in a single year, provided that the average over 5 years does not exceed 1 mSv per year
Equivalent Dose to the Lens of the Eye	20 mSv per year, averaged over defined periods of 5 years, with no single year exceeding 50 mSv	15 mSv in a year
Equivalent Dose to the Skin Averaged over 1 cm2 of skin regardless of the area exposed	500 mSv in a year	50 mSv in a year
Equivalent Dose to the Hands and Feet	500 mSv in a year	-

Dose limits are primarily from ICRP Publication 103 Table 6. The recommendation for pregnant workers is from ICRP Publication 103 Paragraph 186. The occupational limit for the lens of the eye is from Paragraph 3 of the ICRP Statement on Tissue Reactions in ICRP Publication 118.

Dose limits alone are not enough to ensure adequate protection. They function in combination with the fundamental principles of justification and optimisation.

These limits apply only to doses received above the normal local natural background radiation.

Limits on effective dose, combined with optimisation of protection, are designed to avoid a risk of stochastic effects that would be considered intolerable in a planned exposure situation.

Limits on equivalent dose to an organ, combined with optimisation of protection, are designed to prevent the occurance of deterministic effects.

Dose limits apply only in planned exposure situations. In other situations, restrictions on individual dose are called reference levels. They provide the additional flexibility needed in emergency and existing exposure situations to make sure protection is optimised.

Dose limits do not apply to medical exposures. If they did, the effectiveness of diagnosis or treatment might be reduced, doing more harm than good for the patient. The emphasis is on justification of medical procedures and optimisation of protection.

Quotes from ICRP Publications

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ICRP Publication 103 paragraph 243

Dose limits apply only in planned exposure situations but not to medical exposures of patients. ... dose limits ... recommended in Publication 60 ... continue to provide an appropriate level of protection. ... Within a category of exposure, occupational or public, dose limits apply to the sum of exposures from sources related to practices that are already justified ...

ICRP Publication 103 paragraph 247

Dose limits do not apply in emergency exposure situations where an informed, exposed individual is engaged in volunteered life-saving actions or is attempting to prevent a catastrophic situation. For informed volunteers undertaking urgent rescue operations, the normal dose restriction may be relaxed ...

ICRP Publication 103 paragraph 248

For informed individuals of the general public involved in caring and comforting patients released from a hospital following therapy with unsealed radionuclides, the normal dose restriction may be relaxed and such individuals should in general not be subject to the public dose limit ...

ICRP Publication 103 paragraph 186

... Once an employer has been notified of a pregnancy, additional protection of the embryo/fetus should be considered. The working conditions of a pregnant worker, after declaration of pregnancy, should be such as to ensure that the additional dose to the embryo/fetus would not exceed about 1 mSv during the remainder of the pregnancy ...

See Also

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  ICRPædia Guide to the System of Radiological Protection
• 

  ICRP Publication 103 The 2007 Recommendations of ICRP