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ICRPAEDIA: Dose Limits

  DOSE LIMITS  

Dose limits help ensure that no person is exposed to an excessive amount of ionising 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 regardles 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 optmisation.

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 stochatic 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.

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▶ Further Reading: Quotes from ICRP Publications