are generally based on the recommendations of the ICRP. Exposure situations The ICRP recognises planned, emergency, and existing exposure situations, as described below; Planned exposure – defined as "...where radiological protection can be planned in advance, before exposures occur, and where the magnitude and extent of the exposures can be reasonably predicted." These are such as in occupational exposure situations, where it is necessary for personnel to work in a known radiation environment. Emergency exposure – defined as "...unexpected situations that may require urgent protective actions". This would be such as an emergency nuclear event. Existing exposure – defined as "...being those that already exist when a decision on control has to be taken". These can be such as from naturally occurring radioactive materials which exist in the environment. Regulation of dose uptake The ICRP uses the following overall principles for all controllable exposure situations. Justification: No unnecessary use of radiation is permitted, which means that the advantages must outweigh the disadvantages. Limitation: Each individual must be protected against risks that are too great, through the application of individual radiation dose limits. Optimization: This process is intended for application to those situations that have been deemed to be justified. It means "the likelihood of incurring exposures, the number of people exposed, and the magnitude of their individual doses" should all be kept As Low As Reasonably Achievable (or Reasonably Practicable) known as ALARA or ALARP. It takes into account economic and societal factors. Factors in external dose uptake There are three factors that control the amount, or dose, of radiation received from a source. Radiation exposure can be managed by a combination of these factors: Time: Reducing the time of an exposure reduces the effective dose proportionally. An example of reducing radiation doses by reducing the time of exposures might be improving operator training to reduce the time they take to handle a radioactive source. Distance: Increasing distance reduces dose due to the inverse square law. Distance can be as simple as handling a source with forceps rather than fingers. For example, if a problem arise during fluoroscopic procedure step away from the patient if feasible. Shielding: Sources of radiation can be shielded with solid or liquid material, which absorbs the energy of the radiation. The term 'biological shield' is used for absorbing material placed around a nuclear reactor, or other source of radiation, to reduce the radiation to a