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Ionising Radiation > Occupational Radiation Protection > Dose Limits
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Dose limits in occupational radiation protection
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In the Federal Republic of Germany, the official monitoring
of workers who are occupationally exposed to radiation began almost five decades
ago. By adopting the "First Radiation Protection Ordinance" in 1960,
Germany had transposed the obligation of "... the health protection of the
population and the workers against the dangers of ionizing radiations" from
the first version of the Euratom Basic Safety Standards into national legislation. This first Radiation Protection Ordinance experienced several amendments by which the set of regulations was adapted to changes of the Euratom Basic Safety Standards or to the latest scientific knowledge of radiation protection research. With the latest amendments of the Radiation Protection Ordinance in 2001 and the X-Ray Ordinance in 2002 the Guideline 96/29/EURATOM was converted into national legislation. This European Guideline brought a substantial reduction of the allowed annual dose limits, included occupational exposure from naturally occurring radiation sources into the monitoring and made
justification, limitation and optimisation to obligate principles in radiation
protection.
Review of criteria for dose limits
There are numerous workplaces in Germany where workers may be exposed to ionizing radiation. These are not only nuclear power stations, but primarily various technical facilities in the medicine, industry or research institutes, where e.g. X-ray-machines, high-radioactive sources or non-contained radioactive substance are used. The radiation, to which the general population may be exposed by these sources, is limited on 1 mSv per person and calendar year. Excluded are radiation exposures which are medically indicated and serve diagnostic or therapeutic purposes or are due to natural environmental radiation, e.g. radon in dwellings or cosmically caused radiation at high altitudes in aircrafts during flights.
Limit of the effective dose per year
In Germany, about 350,000 persons are dose monitored for reasons of occupational radiation protection. These people work e.g. with X-ray units, handle sealed high-radioactive sources, unsealed radioactive substances or are exposed to an enhanced level of civilian (e.g. nuclear power station) or natural radiation (e.g. radon in mines, show caves, drinking water facilities or cosmic radiation during flights) at their workplaces. The permissible occupational radiation exposure for these persons is limited and officially supervised. The dose limit of the permissible effective dose from occupational radiation exposure is 20 mSv per calendar year in all European countries (in the USA 50 mSv/year). Beside the limit for the effective dose there are dose additional limits for organs, e.g. among others for the eye and the lung (150 mSv), skin and hands (500 mSv), gonads and uterus (50 mSv) as well as for the thyroid (300 mSv).
Special dose limits for children, young persons and pregnant women
For juveniles and unborn children are exist additional dose limits. The permitted effective dose from occupational exposure for persons under 18 years must not exceed of 1 mSv per calendar year. The responsible authority can specify a dose limit of 6 mSv for juveniles aged between 16 and 18, if this is necessary for training purposes. For these groups exists also lower organ dose limits. For occupationally radiation exposed women apply the same dose limits as for men, provided they are not pregnant. However, the organ dose of the uterus must not exceed 2 mSv per month. With the notification of an existing pregnancy the unborn child must not receive a higher dose than 1 mSv during the remaining period of the pregnancy. Additionally to the dose limits specified in the Euratom Basic Safety Standards there exists in Germany also an occupational life time dose limit for workers: the sum of all effective doses received during the whole occupational career of a worker must no exceed 400 mSv.
Exceeding dose limits
If a dose limit is exceeded, the responsible regulatory body examines the cause. Dependent on the cause it can impose additional requirements, forbid activities, set penalties and withdraw permission. In justified cases and under defined conditions it can also permit exceptions.
The exceed of a dose limit is very rare in Germany: in 2007 the 20-mSv-limit was exceeded only in 10 cases. In general, the actual exposures remain almost always far below the dose limits. The cause is the legal requirement for optimization. In Europe, it is not only necessary to keep exposure below the dose limit, it is additionally required to keep radiation exposures as low as reasonably achievable, taking the state of science and technology and the circumstances of the individual case into account. The effectiveness of this so called “ALARA-principle” is evident: in the calendar year 2007, 99% of the supervised workers had an annual dose below 3 mSv; the average effective dose of all measurably exposed workers was 0.8 mSv, a value that reached only 4% of the permitted annual limit of 20 mSv.
Occupational life-time dose limit
For the dose measurement of radiation exposure on workplaces officially approved dosimeters are used, in most cases film badges. The dosimeters are distributed to the worker’s companies by officially approved dosimetry services and usually evaluated in a monthly period. The dose fracture which results from natural ambient radiation is subtracted from the measured value. If workers handle open radioactive substances and the possibility of an up-take of radionuclides into their body cannot be excluded, (e.g. through mouth, nose or skin), then these persons are additionally monitored by officially approved dosimetry services for incorporation. These services monitor the workers regularly or at special occasions if they have incorporated radionuclides into their body. All dosimetric results from both external and incorporation monitoring are regularly sent to the Radiation Protection Register of the BfS, which, amongst other things, supervises the keeping of dose limits.
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