2. Radiation protection principles for existing exposure situations
2.1 Principles for protection
The system of protection and safety aims to assess, manage and control exposure to radiation so that radiation risks, including risks of health effects and risks to the environment, are reduced to the extent reasonably achievable. The components of the system of protection and safety are illustrated in Figure 2.1.
The Fundamentals for Protection Against Ionising Radiation (RPS F-1) (ARPANSA 2014) sets out the underlying principles that form the basis of the system used to manage risks from ionising radiation in Australia. The ten principles are outlined in Appendix 2. The Fundamentals cover all circumstances of radiation exposure and should be applied to all sources and all individuals exposed to radiation, as well as to environmental exposures. All exposures are classified into the following three types of exposure situations consistent with the 2007 Recommendations of the International Commission on Radiological Protection, ICRP Publication 103 (ICRP 2007) and GSR Part 3 (IAEA 2014).
- Planned Exposure Situations: situations where radiation protection can be planned in advance, before exposures occur and where the magnitude and extent of exposures can be reasonably predicted. Planned exposure situations may result in exposures that are anticipated to occur (normal exposures) and in potential exposures that are not anticipated to occur, but may do so.
- Emergency Exposure Situations: situations that may occur during the operation of planned exposure situations if loss of control or breakdown of radiation protection occurs, or from malicious acts, or from any other unexpected situation that requires urgent action in order to reduce or avoid undesirable consequences. These exposure situations are not planned and exposures may not be able to be controlled.
- Existing Exposure Situations: these are exposure situations that already exist when a decision on control has to be taken, including prolonged exposure situations after emergencies.
The system also considers the three principles of radiation protection, being:
- justification (that any activity involving radiation should do more good than harm)
- optimisation (that actual exposure, likelihood of exposures and number of exposed persons should be as low as reasonably achievable (ALARA), taking into account economic and societal factors)
- dose limits (levels of radiation dose that must not, under normal circumstances, be exceeded).
Under Principle 10 of the Fundamentals (ARPANSA 2014), protective measures to reduce existing or unregulated radiation risks must be justified and optimised.
There are four categories of exposure identified in the Fundamentals (ARPANSA 2014), specifically:
• occupational (all exposure incurred by workers in the course of their work)
• public (exposure incurred by members of the public from radiation sources, excluding any occupational or medical exposure and the normal local natural background radiation)
• medical (incurred by patients undergoing medical diagnosis or treatment)
• environmental (associated with protection of the environment and incurred by non-human biota (or wildlife)).
Dose criteria serve as boundaries within which the optimisation process takes place and serve to reduce inequities of exposure. The three types of dose criteria are the following:
- reference levels (in emergency or existing controllable exposure situations, this represents the level of dose or risk, above which it is judged to be inappropriate to plan to allow exposures to occur, and below which optimisation of protection should be implemented; the chosen value for a reference level will depend upon the prevailing circumstances of the exposure under consideration for the public and non-human biota).
- dose constraints (a prospective and source–related restriction on the individual dose from a source, which provides a basic level of protection for the most highly exposed individuals from a source, and serves as an upper bound on the dose in optimisation of protection for that source).
- dose limits (the value of the effective dose or the equivalent dose from planned exposure situations that shall not be exceeded).
For protection of non-human biota, the Guide to Radiation Protection of the Environment (RPS G-1) (ARPANSA 2015) provides guidance on screening dose rates and methodologies that may assist in reaching a regulatory decision. Further guidance on environmental protection under different exposure situations can be found in ICRP Publication 124 (ICRP 2014).
Figure 2.1: The system of radiological protection, illustrating the interrelationships between the principles of protection, the exposure situations, the categories of exposure, the dose criteria, and the application of the system.
The implementation of the system of radiological protection requires that the exposure situation is well understood through an assessment that considers all relevant aspects of the exposure. The information from the assessment will form the basis for decisions on actions (if deemed necessary). Such decisions need to be taken in a transparent manner including, as relevant, taking the views and knowledge of stakeholders into consideration. Stakeholders are regarded as an asset who will contribute knowledge to the process, and the consultation contributes to informed decisions and the best possible outcomes. Accountabilities need to be established and communicated, so that it becomes clear who the decision maker is and on what grounds decisions are taken.
2.2 Identification of existing exposure situations
Existing exposure situations are exposures from sources that already exist when decisions to control them are made. The source can be natural, such as cosmic radiation in aviation and space flights, naturally occurring radioactive material (NORM), or radon. The source can also be artificial, such as contaminated sites from past activities or accidents.
Existing exposure situations have a number of common features. Exposures often affect places of living and day-to-day activities. The exposures need to be measured and the distribution of individual doses can be very wide. Existing exposure situations do not present a potential for accidents. In many cases, the exposure can be at least partially controlled by exposed individuals themselves (self-help protection).
Protection of the environment should be considered in existing exposure situations. Unlike protection of people, protection of non-human biota addresses protection of populations/ecosystems and not individuals. Further guidance for the protection of non-human biota is provided in RPS G-1 (ARPANSA 2015).
To understand if there is a problem the exposure situation needs to be characterised to determine the nature of the source and the different exposure pathways to people and the environment. This will provide an understanding of the feasibility and net benefits of preventive measures, which would be directed in reducing or preventing exposures. For a national approach to environmental health risk assessment, the enHealth presents a general methodology applicable to a range of environmental health hazards (enHealth 2012).
Some work environments and activities may entail exposures that need to be managed as existing exposure situations, using reference levels to guide optimisation (for example, aircrew exposed to cosmic radiation at cruising altitude and workers exposed to radon in the workplace). In other cases, the nature of the work activity and associated exposures may warrant treatment as planned exposure situations and be subject to dose limits and constraints (e.g. workforce involved in remediation of existing (legacy) situations). The employer in all circumstances has primary responsibility for the protection of workers and the management of exposures. Once an exposure has been identified, careful management is needed, applying a graded approach.
Figure 2.2 shows a systematic way for identifying and managing an existing exposure situation.The decision box titled ‘Is control justified?’ determines whether there is a need to take protective measures (e.g. remedial actions and/or protective actions) If after a risk characterisation has been completed and it is determined that there is no significant potential for radiological exposure, no protective measures are required. If it is determined that there is a significant potential for radiological exposure within an existing exposure situation, a protection strategy should be developed and justified that considers remedial actions and/or protective actions. In some situations, protection must be achieved through management in accordance with RPS C-1 (ARPANSA 2016) on radiation protection in planned exposure situations.
Figure 2.2: A systematic way for identifying an existing exposure situation and choose management strategy. Refer to enHealth guidance for a national approach to environmental health risk assessment (enHealth 2012).
2.3 Protection Strategy
In planned exposure situations, protective actions can be implemented prior to the introduction of a source and are thus effective from the moment a radiation source is introduced. In emergency exposure situations, they must often be implemented urgently in order to be efficient and are sometimes based on incomplete information. In existing exposure situations, protective measures are implemented after characterisation of the exposure situation, and it generally takes time to progressively reduce or maintain exposures through optimisation. However, regardless of the type of exposure situation, protective measures can be envisaged and planned in advance.
When a decision is made not to take protective measures, ongoing review of the situation should be considered as future circumstances of exposure may change and evolve over time.
When an existing exposure situation is identified, responsibilities for protection and safety should be assigned and appropriate reference levels should be established.
Reference levels should be used prospectively in the planning phase and retrospectively as a benchmark for evaluating the effectiveness of the remedial and/or protective actions that have been implemented.
Protection strategies supported by a safety assessment that describes the appropriate remedial action plan or protection plan is aimed at the timely and progressive reduction of the radiation risks. Eventually, if possible, the removal of restrictions on the use of, or access to the area, or the removal of protective actions of a particular situation may be lifted.
A safety assessment should be used as a documented process for the evaluation of safety — for example, evaluation of the magnitude of hazards, evaluation of the performance of safety measures and judgement of their adequacy, or quantification of the overall radiological impact or safety of the existing exposure situation.
Remedial and/or protective actions should be justified, by use of decision-aiding techniques and processes, as necessary, resulting in a net positive benefit, taking account all relevant factors that are to be considered in the planning and implementation of the protection strategy.
Verification of the effectiveness of specific remedial and/or protective actions is important throughout the remedial action plan or protection plan. This involves comparison of the actual radiological exposures against the initial estimates, and the measures established for their control. If the actual exposures significantly differ from the initial estimates, the plan should be revised to account for the actual conditions being experienced. In cases where the actual exposures exceed those predicted, an investigation should be undertaken to improve understanding of the situation, and to prevent exposures that are higher than anticipated.
For exposures in workplaces that persist above the reference level, and it is not possible to reduce exposure below this reference level, then workers should be considered as occupationally exposed. In such cases, the application of the relevant clauses for occupational exposure in planned exposure situations as described in the Code for Radiation Protection in Planned Exposure Situations, RPS C-1 (ARPANSA 2016) apply.
The relevant regulatory body should review the integrity of the final remediation or protection report and use the information that has been provided to verify the nature, extent and duration of any post-remediation or post-protection control measures and their effectiveness.