Ann. occuf. Hyg. Vol. 20, pp. 313-316. Porgamon Presj 1977. Printed in Great Briuin


National Radiological Protection Board, Scottish Centre, Glasgow Abstract—This paper considers the role of the National Radiological Protection Board in relation to radiological safety by design. It discusses recommendations of the International Commission on Radiological Protection, and describes a general and consecutive procedure of justification, optimisation and comparison with recommended dose limits which can be applied to any industrial and other uses of ionising radiations.

THE MAIN provision of the Radiological Protection Act in 1970 was the establishment of the National Radiological Protection Board (NRPB). The Act provided for the Board, by means of research and otherwise, to advance the acquisition of knowledge about the protection of mankind from radiation hazards, and to provide information and advice to persons (including Government Departments) with responsibilities in the United Kingdom in relation to the protection from radiation hazards either of the community as a whole, or of sections of the community. In order to provide appropriate guidance to users of radiation, and to ensure that radiological protection considerations are taken into account in designing installations, devices and processes, it is first of all necessary to determine what standards should be applied. Radiological protection standards are the subject of widespread study internationally. Recommendations for basic standards, based on biological and epidemiological evidence, are made by the International Commission on Radiological Protection (ICRP). This Commission is generally recognised as the authority on radiation dose limits; it is non-governmental in the sense that its members are appointed every four years by the International Congress of Radiology. The Commission expresses its views in a series of publications. From these recommendations other international bodies derive working standards. Radiological protection in the United Kingdom, as a member of the European Communities, is governed by the Communities' Directive of 1st June 1976 (EUROPEAN COMMUNITIES, 1976), laying down the revised basic safety standards for the health protection of the general public and workers against the dangers of ionising radiation. Such Directives are mandatory on the Member States, who then must apply the objectives in a way which suits their administrative, legal and social systems. The basic objective of ICRP and other bodies, including the U.K. regulatory authorities, is the avoidance of unnecessary radiation exposure by requiring justification for any type of exposure and the minimising of exposure when some exposure is unavoidable (optimisation). There are also numerical limits of dose which should be exceeded only in very exceptional circumstances. Such limits are specified for the occupational exposure of workers, and for the exposure of members of the general public (from sources other than medical radiology). 313

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Dose equivalent limits, one year Organ or tissue

Whole body Skin, hands, forearms, feet, ankles Other organst

adults exposed in the course of their work* (rem)

members of the public (rem)





see ICRP (1977)

see ICRP (1977)

•The previous recommendation that for occupational exposure the magnitude of a single dose equivalent should be limited to one half of the annual limit is not considered necessary. The Commission no longer recommends the use of the former age-related formula 5(N-18). tThe Commission's recommended dose limitation for other organs is now based on the principle that the risk should be equal whether the whole body is irradiated uniformly or whether there is non-uniform irradiation. This condition will be met if

I, w, H, < H^, L, where H>I is a weighting factor (for values, see ICRP, 1977); Hl is the dose equivalent in the organ or tissue; and H^,L is the recommended annual dose equivalent for uniform irradiation of the whole body.

The practical application of this recommendation is discussed by the ICRP (1973) and summarised thus: 'The recommended comprehensive system of dose limitation is aimed at the following principal objectives: (a) to ensure compliance with the dose limits; (b) to avoid the use of unnecessary sources of exposure; (c) to provide for operational control of specific procedures, both individually and in combination, so that resulting doses are as low as is reasonably achievable, economic and social considerations being taken into account; (d) to provide a more general framework, to ensure that these doses are justifiable in terms of benefits that would not otherwise have been received.'

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ICRP recommendations are intended to keep radiation exposures within a level of safety likely to be generally acceptable, e.g. by limiting occupational exposures to levels of risk at least as low as those in occupations which are widely regarded as safe. The system of limiting doses by the consecutive procedures of'justification', 'optimisation' and 'dose limits' is, however, applicable to the control of a wide range of toxic hazards. Table 1 gives a summary of ICRP dose equivalent limits for adults exposed in the course of their work, and for individual members of the general public (ICRP, 1977). As any exposure to radiation may involve some degree of risk, the ICRP include the general and overriding recommendation that any unnecessary exposure be avoided and that where some exposure is unavoidable, any doses should be kept as low as is reasonably achievable, economic and social considerations being taken into account.

Radiological safety by design—II. N.R.P.B. viewpoint


Unless the doses are known to be so trivial as to be negligible, it is necessary to justify the use of radiation in any undertaking or device. The starting point is the evaluation of dose. Taking the occupational scene as a typical example, the evaluation would include doses received during construction, installation, operation and during any subsequent maintenance work when relatively close contact with exposed sources of radiation is sometimes necessary. The total detriment derived from established dose risk relationships can then be balanced against the benefits, and a comparison made with alternative practices available. Downloaded from at University of Iowa Libraries/Serials Acquisitions on July 8, 2015

The benefits may include an improvement in working conditions, increased efficiency and reliability, and greater economy. When it has been confirmed that such advantages clearly exist, installations, equipment and procedures are designed to ensure that doses in normal and accident conditions are kept as low as can reasonably be achieved, and certainly within the ICRP dose limits. These general principles of 'justification', 'optimisation' and 'dose limitation' have been applied in the design of a wide range of industrial and other applications involving the use of ionising radiations. Some examples are thickness gauging, level detection, static elimination, industrial and medical radiography, luminising, other light-emitting devices, and tracer techniques. In all cases, it is essential that the consideration of design features to meet radiological protection standards coincides with consideration of other features. Modifications added as an afterthought to meet radiological protection requirements are usually less than adequate; they either fail to meet fully the necessary standards, or restrict significantly the intended purpose of the equipment or device. The installation, device or process may involve the use of either sealed or unsealed radioactive material or equipment capable of generating ionising radiations. Design considerations in the choice of a radioactive isotope must take account of its radiotoxicity and its half-life. The latter should be the shortest consistent with the useful working life of the process or device. The activity should be the minimum necessary, and the materials should be in an appropriate chemical and physical form offering the highest degree of intrinsic safety under all environmental conditions. Where machines are used for generating ionising radiations, the energy, machine output and filtration must be appropriate for the type of work being undertaken. Radiation equipment, whether using radioactive sources or X-ray generators, must be designed to limit the useful beam to the area of interest by use of collimation, cones and beam stops. The intrinsic shielding of the beam controlling devices must be adequate. Where it is necessary to bring material into the radiation beam, this must be carried out in such a way as to avoid any leakage of scattered radiation; all access points must be appropriately controlled, if necessary by interlock, to avoid accidental entry. If certain aspects of the interlock or control system are essential to the basic safety requirement, then these should be of a fail-safe design. This point may usefully be extended to all the critical components where reliability, failure to safety, ease of access for maintenance must be carefully considered. It may be necessary for alternative or back-up systems to be included where high reliability is required. Once the basic design is complete, consideration must be given to operating procedures to ensure that the process or device can be used safely, account being taken of non-radiation hazards such as electrical or mechanical handling. Routine



maintenance and checking schedules, designed to prevent or give early warning of changes likely to affect safety, must be drawn up. To summarise, a consecutive procedure of 'justification', 'optimisation', and 'dose limit comparisons' should always be carried out. Radiological protection should be taken into account from the outset of the technical design. The criteria on which decisions rest should be periodically reviewed, since factors may change over the useful working life that affect them. Downloaded from at University of Iowa Libraries/Serials Acquisitions on July 8, 2015

REFERENCES EUROPEAN COMMUNITIES (1976) Off. J. Eur. Communities 19 (L 187/1). ICRP (1973) Implications of Committee Recommendations that Doses be kept as low as Readily Achievable: A Report by Committee 4. International Commission on Radiological Protection Publication no. 22. Pergamon Press, Oxford. ICRP (1977) Recommendations of the ICRP: Revision of ICRP 9. International Commission on Radiological Protection Publication no. 26. Pergamon Press, Oxford.

Radiological safety by design--II N.R.P.B. viewpoint.

Ann. occuf. Hyg. Vol. 20, pp. 313-316. Porgamon Presj 1977. Printed in Great Briuin RADIOLOGICAL SAFETY BY DESIGN—II N.R.P.B. VIEWPOINT National Rad...
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