Biomedical Engineering Reference
In-Depth Information
The Council no longer recommends specific controls for occupationally exposed
women not known to be pregnant. However, the NCRP adopts the ICRP recom-
mendation of reducing the limits on intake of radionuclides, once pregnancy is
known. ICRP Publication 60 also recommends an equivalent-dose limit of 2 mSv
to a woman's abdomen, once a pregnancy is declared.
Nonoccupational Limits
In Section 14.2 we mentioned briefly some of the considerations that apply to es-
tablishing exposure limits to members of the public. Historically, limits for nonoc-
cupational exposures have been one-tenth those for occupational exposures. That
practice continues. The NCRP makes the following recommendations for the ex-
posure of an individual to man-made sources (natural background and medical
exposures are not to be included):
For continuous (or frequent) exposure, it is recommended
that the annual effective dose not exceed 1 mSv
...
Furthermore, a maximum annual effective dose limit of
5 mSv is recommended to provide for infrequent annual
exposures.
...
For deterministic effects, the NCRP recommends an annual equivalent dose limit
of50mSvforthehands,feet,andskinand15mSvforthelensoftheeye.
The recommendations in ICRP Publication 60 are somewhat different. An indi-
vidual annual effective dose limit of 1 mSv is also set for nonoccupational expo-
sures. There is a proviso that a higher annual limit may be applied, if the annual
average over 5 y does not exceed 1 mSv.
Negligible Individual Dose
In its 1987 Report No. 91, the NCRP defined a Negligible Individual Risk Level
for radiation as that level below which efforts to reduce exposure to an individual
are not warranted. This concept took cognizance of such factors as the mean and
variance of natural background exposure levels, the natural risk for the same health
effects, risks to which people are accustomed in life, and the perception of risk
levels. Also, the magnitude of the implied dose level and the difficulty of measuring
it were considered.
NCRP Report No. 116 defines a negligible individual dose (NID), without a cor-
responding risk level, as follows:
The Council
...
recommends that an annual effective dose of
0.01 mSv be considered a Negligible Individual Dose (NID)
per source or practice.
ICRP Publication 60 does not make a recommendation on the subject.
