(3) ICRP RECOMMENDATIONS ON RADIATION PROTECTION (EXCEPTS) (Adopted on January 17, 1977)
Natural
radiation and dose-equivalent limits
(87)
|
Man has always been exposed to radiation
from his natural environment, the basic sources of natural radiation exposure
being cosmic rays, radioactivity in rocks and soil, and radioactive nuclides
incorporated into his tissues. The does of natural radiation that a person
receives depends on a number of factors such as the height above sea-level at
which he lives, the amount and type of radioactive nuclides in the soil in
his neighbourhood, and the amount that he takes into his body in air, water
and food. The total absorbed dose rate in most human tissues from natural
radiation is about one-thousandth of a gray per year, but absorbed dose rates
up to one-hundredth of a gray per year, or more, have been reported from
certain limited areas of the would.
|
(88)
|
Man-made modifications of the environment
and man's activities can increase the "normal" exposure to natural radiation.
Examples of this include mining, flight at high altitudes, and the use of
building materials containing naturally-occurring radioactive nuclides. Even
living within a house is often sufficient to increase radiation exposure
because restricted ventilation tends to lead to an accumulation of
radioactive gases and their decay products.
|
Dose-equivalent
limits for individual members of the public
(117)
|
Radiation risks are a very minor fraction of
the total number of environmental hazards to which members of the public are
exposed. It seems reasonable therefore to consider the magnitude of radiation
risks to the general public in the light of the public acceptance of other
risks of everyday life. This acceptance (when related to risks that could not
be reduced or avoided entirely) is motivated by the benefits that would not
otherwise be received, by an assessment of the social cost of achieving a
possible reduction of risk, or by an implicit judgment that the risk is
negligible.
|
(118)
|
The acceptable level of risk for stochastic
phenomena for members of the general public may be inferred from
consideration of risks that an individual can modify to only a small degree
and which, like radiation safety, may be regulated by national ordinance. An
example of such risks is that of using public transport. From a review of
available information related to risks regularly accepted in everyday life,
it can be concluded that the level of acceptability for fatal risks to the
general public is an order of magnitude lower than for occupational risks. On
this basis, a risk in the range of 10-6 to 10-5 per year
would be likely to be acceptable to any individual member of the public.
|
(119)
|
The assumption of a total risk of the order
of 10-2 Sv-1 (see paragraph 60) would imply the
restriction of the lifetime dose to the individual member of the public to a
value that would correspond to 1 mSv per year of life-long whole body
exposure. For the reasons given in the following paragraphs, the Commission's
recommended whole body dose-equivalent limit of 5 mSv (0.5 rem) in a year, as
applied to critical groups, has been found to provide this degree of safety
and the Commission recommends its continued use under the conditions
specified in paragraphs 120-128.
|
Statement
from the 1985
Paris Meeting of the International
Commission on Radiological Protection
Dose
Limits for Members of the Public
In the recommendation on effective
dose-equivalent limits* for members of the public, made in its 1977
Recommendations (IRCP Publication 26),
two values were mentioned. The use of the limit of 5 mSv in a year was
endorsed, but only under the conditions described in paragraphs 120 to 128 of ICRP Publication 26. For other
circumstances the Commission recommended that it would be prudent to limit
exposures on the basis of a lifetime average annual dose of 1 mSv.
The Commission's present view is that the
principal limit is 1 mSv in a year. However, it is permissible to use a
subsidiary dose limit of 5 mSv in a year for some years, provided that the
average annual effective dose equivalent over a lifetime does not exceed the
principal limit of 1 mSv in a year.
With this limitation on the effective dose
equivalent, the non-stochastic organ limit of 50 mSv in a year becomes
unnecessary for most organs. However, since the dose equivalents in the skin
and the lens of the eye are not included in the computation of effective dose
equivalent for the individual, organ dose limits are still needed for these two
tissues. The recommended dose-equivalent limit for both the skin and the lens
is still 50 mSv in a year for members of the public.
* The Commission's dose-equivalent limits
apply to the sum of the effective dose equivalent resulting from external
exposure during 1 year and the committed effective dose equivalent incurred
from that year's intake of radionuclides.
|