Executive Summary

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Executive summary 

Basic principles 

(a) The Commission’s 2007 Recommendations (ICRP, 2007) re-state its principles of justification and optimisation as applying to emergency exposure situations. This means that the level of protection should be the best possible under the prevailing circumstances, maximising the margin of benefit over harm. In order to avoid grossly inequitable outcomes of the optimisation procedure, the process should be constrained, to the extent practicable, by restrictions on the dose or risks received by individuals as a result of the emergency.

(b) The reference level represents the level of residual dose or risk above which it is generally judged to be inappropriate to plan to allow exposures to occur. Therefore, any planned protection strategy should at least aim to reduce exposures below this level, with optimisation achieving still lower exposures. Protection against all exposures, above or below the reference level, should be optimised. In the context of developing response plans for emergency exposure situations, the Commission recommends that national authorities should set reference levels between 20mSv and 100mSv effective dose (acute or per year, as applicable to the emergency exposure situation under consideration). Reference levels below 20mSv may be appropriate for the response to situations involving low projected exposures. There may also be situations where it is not possible to plan to keep all doses below the appropriate reference level, e.g. extreme malicious events or low-probability, high-consequence accidents in which extremely high acute doses can be received within minutes or hours. For these situations, it is not possible to plan to avoid such exposures entirely. Therefore, the Commission advises that measures should be taken to reduce the probability of their occurrence, and response plans should be developed that can mitigate the health consequences where practicable.

(c) The Commission now considers that more complete protection is offered by simultaneously considering all exposure pathways and all relevant protection options when deciding on the optimum course of action. While each individual protective measure must be justified by itself in the context of an overall protection strategy, the full protection strategy must also be justified, resulting in more good than harm. This approach may represent a relative increase in operational complexity, but it also provides a significant amount of increased flexibility in designing the optimum protection to address an emergency exposure situation by focusing on the combined effects of all individual protective measures included in the protection strategy rather than on any single protective measure. Moreover, the new approach provides a framework that supports a consideration of how individual protective measures affect one another, and it helps focus resource allocation to where the strongest overall benefit can be achieved. It also recognises that the dose which an individual has already received during an emergency should be taken into consideration when determining what constitutes optimum protection in later response actions.

(d) In order to optimise an overall planned protection strategy, it is necessary to identify the dominant exposure pathways, the time scales over which components of the dose will be received, and the potential effectiveness of individual protective options. Knowledge of the dominant exposure pathways will guide decisions on the allocation of resources. Resource allocation should be commensurate with the expected benefits, of which averted dose is an important component. Knowledge of the time periods over which exposures will be received informs decisions about the lead times available to organise the implementation of protective measures once an emergency exposure situation has been recognised. Where urgent actions are required to reduce exposures, specific legislation would facilitate efficient management of the response (e.g. management of contaminated wastes). Furthermore, it is important to use easily identifiable ‘triggers’ as the basis for decisions to implement urgent protective measures.

(e) The Commission recognises that there is a qualitative difference between the risks of stochastic health effects and the risks of an individual receiving exposures that would result in severe deterministic injury. By ‘severe deterministic injury’, the Commission means injuries that are directly attributable to the radiation exposure, irreversible in nature, and severely impair the quality of life of individuals, e.g. lung morbidity and early death. The Commission recommends that every practicable effort should be made to avoid the occurrence of severe deterministic injuries in an emergency exposure situation. This means that it will be justified to expend significant resources, both at the planning stage and during the response, if this is required, in order to reduce expected exposures to below the thresholds for these effects. Furthermore, where prompt medical intervention has the potential to avert such injury, the Commission recommends that procedures and measures should be included in the emergency response plan to enable those individuals who may have received such high exposures to be identified promptly and receive appropriate medical treatment.

Arrangements for emergency exposure situations 

(f) The Commission recommends that plans should be prepared for all types of emergency exposure situation: nuclear accidents (occurring within the country and abroad), transport accidents, accidents involving sources from industry and hospitals, malicious uses of radioactive materials, and other events, such as a potential satellite crash. The level of detail within a plan will depend on the level of threat posed, and the degree to which the circumstances of the emergency can be determined in advance. However, even outline generic plans should indicate the responsibilities of different agencies, methods for communication and organisation between them during the response, and a framework for guiding decision making. More detailed plans should contain a description of the overall protection strategy, and provide triggers for initiating those aspects of the response that need to be implemented promptly. It is for the relevant national authorities to determine the detail of planning that is appropriate for different situations.

(g) It is essential that all aspects of the plan are consulted with relevant stakeholders, otherwise it will be more difficult to implement them during the response. To the extent possible, the overall protection strategy and its constituent individual protective measures should be worked through and agreed with all those potentially exposed or affected. Such an engagement will assist the emergency plans in being focused on the protection of those at greatest risk in the initial phases, and also on the progression to populations resuming ‘normal’ lifestyles.

(h) In the event of an emergency exposure situation, it is likely that exposure rates will vary in space and time, and that the doses received by individuals will vary, both as a result of the variations in exposure rates and as a result of differences in their physiological characteristics and behaviours. These population groups should be characterised by representative persons, as described in the Commission’s advice on the representative person. In accordance with the Commission’s advice on the representative person, it is important that the dose estimates reflect those likely to be received by the groups at greatest risk, but that they are not grossly pessimistic.

(i) The Commission’s band of reference levels is expressed in terms of effective dose. For many emergency plans, this is an appropriate quantity in which to express the reference level. However, there are situations for which effective dose is not an appropriate quantity to express reference levels. This is the case when the type or scale of an emergency may result in doses in excess of 100mSv effective dose (where the assumption of linearity may no longer hold), when parts of the response need to focus on individuals at risk of incurring severe deterministic injury, and when the resulting exposures are very strongly dominated by irradiation of a single organ for which very specific protective measures are optimum (e.g. releases dominated by radioiodine). For these situations, the Commission advises that consideration should be given to specifying (or providing supplementary) reference levels in terms of organ dose.

(j) In its previous advice, the Commission recommended the use of intervention levels of averted dose to assist decisions on whether/when to include certain protective measures in an overall protection strategy. It should be emphasised that the intervention level is understood as a level above which an action is justified and below which no action (e.g. no optimisation of protection) is needed. This concept is no longer valid. Moreover, the Commission now recommends focusing on optimisation of protection with respect to the overall protection strategy, which includes exposures from all exposure pathways simultaneously, rather than individual measures. However, the levels of averted dose recommended in Publication 63 ICRP, 1991a, ICRP, 1991b for optimisation of protection in terms of individual protective measures may still be useful as inputs to the development of the overall response (see also ICRP, 2005).

(k) In order to develop an emergency plan, it is necessary to evaluate the projected doses for the situations being considered. The purpose of estimating projected doses and their likely spatial and temporal distributions is three fold: first to identify the scale of health consequences that might occur if no protective measures were taken (and, in particular, whether there is a risk of severe deterministic injury), and from this to determine the broad scale of resources it is appropriate to assign to a protection strategy; second, to identify the broad geographical and temporal distribution of the various likely response phases; and third, where, in terms of protection, resources are likely to be spent most effectively. Where it is judged appropriate to develop a detailed emergency response plan, it is important to identify whether specific provisions are required to protect those at risk of severe deterministic injury. If so, this part of the plan should be given priority for focus and resources, and should be separately justified and optimised.

(l) For detailed planning to protect against exposures resulting in stochastic risk, it is useful to begin the development of an overall protection strategy by identifying all protective measures that are likely to be justified, even if they only avert a relatively small component of the projected dose. Once all protective measures that are likely to be individually justified have been identified, each one should be examined for its potential to avert a significant proportion of the projected dose, and for consequences that may interact with those of other protective measures in such a way as to render their combined implementation either significantly more strongly justified or unjustified. From this initial scoping review, a broad outline protection strategy can be developed.

(m) Having identified protective measures that are likely to be included in the protection strategy, it is necessary to evaluate the residual doses (i.e. those to different representative individuals) that would result from implementing the protection strategy. The first step is to scope the residual doses, in order to compare them with the appropriate reference level. If the residual dose is likely to be below the reference level, detailed optimisation of the protection strategy can be undertaken. If not, changes to the protective measures or their implementation need to be considered, and the process of comparison of the reference level with the residual dose repeated.

(n) Some combinations of protective measures can be considered to be largely independent of one another, e.g. commercial food restrictions and the evacuation of populations in close proximity to a radiation source. These types of protective measures can readily be optimised separately and their relevant averted doses can be used as a direct guide.

(o) The resources required to implement protective measures are not the only factors that might interact within an overall protection strategy. Other such factors include individual and social disruption, anxiety and reassurance, and indirect economic consequences. It is important to review the proposed overall protection strategy with relevant stakeholders to ensure that the plan is optimised with respect to these factors, as well as with respect to dose and the resources required. This wider review of the protection strategy may indicate a role for additional measures which, in isolation, may not appear optimum (or even justified).

(p) Once the protection strategy has been optimised, triggers for initiating the different parts of an emergency response plan for the early phase should be developed. Triggers may be expressed in terms of any observable circumstances or directly measurable quantities, such as plant conditions, dose rates, or wind direction. They may be related to dose considerations, but are more likely to be related to key indicators of the occurrence of the emergency situation for which the plan (or a group of protective measures within the plan) was developed. It may not be appropriate to specify triggers for initiating protective measures later in the plan, since these should generally take account of the specific details of the evolving emergency situation. For such protective measures, it may be helpful to include in the response plan an agreed framework for developing triggers in ‘real time’ when needed. The inclusion of such a framework is likely to result in wider acceptance of the ‘real-time’ triggers when they are developed.

Implementing protection strategies 

(q) In the context of the ICRP system of radiological protection, there is one fundamental difference between prospectively planning to address the consequences of a radiological emergency exposure situation, and managing consequences that are in the process of occurring or that have already occurred. In the context of planning, optimisation is performed using the appropriate reference level as the upper bound, eliminating all protection solutions that result in individual residual doses exceeding the reference level. The inherently unpredictable nature of emergency exposure situations, their tendency to evolve rapidly, and the wide possible range of emergency conditions (i.e. weather conditions, geographical location, population habits, etc.) could result in situations that do not match the assumptions that were used to develop the optimised protection strategies, and some actual exposures may exceed the preselected reference level. As such, in the context of managing the consequences of an emergency that is in the process of occurring or that has already occurred, the predefined reference level is used as a benchmark against which the results of implementing an optimised protection strategy can be judged, and for guiding the development and implementation of further protective measures if necessary.

(r) Once an emergency exposure situation has occurred, it is likely that many stakeholders will be very interested in providing input to discussions regarding protective measures. Should the emergency exposure situation require urgent protective measures, the ‘reflex’ use of preplanned protection strategies, implemented on the basis of predefined triggers, will be necessary with no or very little stakeholder involvement beyond the emergency response authorities and those responsible for the site, facility, or source that is causing the emergency exposure situation. Inappropriate involvement of stakeholders or excessive review of the detailed effectiveness of such ‘reflex’ protective actions is likely to reduce their effectiveness by delaying their implementation, and this should be avoided. However, as the emergency exposure situation progresses, it will become increasingly beneficial to involve stakeholders in discussions leading to protection decisions. It is therefore important that part of emergency response planning should be the development and implementation of processes and procedures to inform and involve stakeholders once the most urgent protective actions have been implemented.

(s) In many cases, emergency response planning will broadly fit a large range of possible situations, such that the timely implementation of a planned protection strategy should come close to providing the optimum protection, with divergence most likely being on the conservative side. However, there may be a need to operationally adjust planned protection strategies, justifying new protective measures or significant changes to plans. The need to consider such modifications may increase as the emergency exposure situation progresses, and the magnitude of changes from plans may depend on the nature of the emergency exposure situation that occurs.

(t) If, in application, protective measures do not achieve their planned residual dose objectives, or worse, result in exposures exceeding the reference levels defined at the planning stage, a re-assessment of the situation is warranted to understand why plans and results differ so significantly. New protective measures could then, if appropriate, be selected, justified, optimised, and applied, or existing options could be extended in time and/or space.

(u) As an emergency exposure situation progresses and understanding of the exact circumstances increases, decisions will increasingly be based on actual circumstances rather than on preplanned responses, assumptions, and models. There will also be an increased need to plan future protection strategies in greater detail than included in the initial emergency plan.

(v) The decision to terminate individual protective measures will need to reflect the prevailing circumstances of the emergency exposure situation being addressed in an appropriate manner. For the termination of early protective measures, guidance should have been developed and included in the emergency plan. For later protective measures, wherever possible, the criteria for terminating the measures should be agreed with relevant stakeholders in advance of their implementation. In this case, criteria for termination are best expressed in terms of directly observable or measureable quantities, so that achievement of the criteria can be demonstrated clearly. In planning and in the event of an emergency, decisions to terminate protective measures should have due regard for the appropriate reference level. In planning, this is an integral part of the optimisation of the protection strategy. However, since the actual circumstances of an emergency may deviate from those addressed during planning, it is important to consider the implications for residual dose when making decisions regarding the termination of protective actions, using the reference level as a benchmark.

Transition to rehabilitation 

(w) The Commission recommends that the management of exposures in the long term following an emergency exposure situation should be treated as an existing exposure. This is because the characteristics of response become very different from those at an early stage. The management of existing exposure situations involves accepting that the exposure situation is different from what would normally be considered acceptable, but recognising that, given the circumstances and possibly subject to some ongoing special measures, the exposure can and will be tolerated, i.e. that stability has been achieved.

(x) The change from an emergency exposure situation to an existing exposure situation will be based on a decision by the authority responsible for the overall response. This transition may happen at any time during an emergency exposure situation, although not generally when urgent actions are being taken. Moreover, this transition may take place at different geographical locations at different times, such that some areas are managed as an emergency exposure situation whilst others are managed as an existing exposure situation. The transition may require a transfer of responsibilities to different authorities. This transfer should be undertaken in a co-ordinated and fully transparent manner, and should be understood by all parties involved. The Commission recommends that planning for the transition from an emergency exposure situation to an existing exposure situation should be undertaken as part of the overall emergency preparedness, and should involve relevant stakeholders.

(y) Existing exposure situations which are created by emergency exposure situations can be characterised as having some sort of residual exposure pathways and lingering contamination above previous background levels, but having social, political, economic, and environmental aspects of the situation that will be sustained, and are seen by the affected populations and governments as being their new reality. There are no predetermined temporal or geographical boundaries that delineate the transition from an emergency exposure situation to an existing exposure situation. In general, a reference level of the magnitude used in emergency exposure situations will not be acceptable as a long-term benchmark, as these exposure levels are generally unsustainable from social and political standpoints. As such, governments and/or regulatory authorities will, at some point, have to identify and set a new reference level, typically at the lower end of the range recommended by the Commission of between 1 and 20mSv/year.

(z) For some large emergency situations involving the release of high levels of long-lived contamination over large areas, part of the new reality following the situation may be that some areas will be so contaminated as to be incapable of sustaining social, economic, and political inhabitation as before. In these areas, governments may prohibit human habitation and other land uses. This would mean that any populations evacuated from these areas would not be allowed to return, and that further resettlement or use of these areas would not be allowed. Clearly, it is not easy for a government and its people to make a decision to remove people permanently (or for the long-foreseeable future) from an area and to forbid its use. As such, the social, economic, political, and radiological aspects of such a choice will need to be discussed in a broad and transparent fashion before a decision is reached.

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1. Introduction 

(1) The Commission has set out general principles for planning an intervention in the case of a radiation emergency (ICRP, 1991a, ICRP, 1991b), and additional relevant guidance (ICRP, 2005a, ICRP, 2005b, ICRP, 2005c). More recently, the Commission has published new recommendations relating to its overall system of protection (ICRP, 2007a). The 2007 Recommendations are intended to complement, rather than replace, the Commission’s previous advice. However, the advice contained in the 2007 Recommendations may have implications for emergency preparedness and response. This report discusses the application of the new advice, and explains how the previous advice fits into the revised overall system of protection. Where the Commission’s advice is unchanged from its previous recommendations, or issues are discussed thoroughly in publications by other international organisations, appropriate references are given and no detailed discussion is provided. The report does not cover emergency situations involving unintended exposures of patients; these situations are dealt with separately by the Commission (ICRP, 2007b).

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2. Scope of this advice 

(2) This advice relates to preparedness for, and response to, all radiation emergency exposure situations. The Commission defines radiation emergency exposure situations as: ‘situations that may occur during the operation of a planned situation, or from a malicious act, or from any other unexpected situation and require urgent action in order to avoid or reduce undesirable consequences’. The scope of this advice is preparedness for, and response to, emergency exposure situations. It covers the protection of all those at risk of exposure, whether they are directly involved in mitigating actions (termed emergency ‘workers’ in this report, regardless of whether or not they are routinely exposed to radiation as a result of their normal employment), or are simply in need of protection (termed ‘the public’ in this report).

(3) An emergency exposure situation that includes the release of significant quantities of longer-lived radionuclides may evolve, in time, into an existing exposure situation. The management of emergency exposure situations and the management of existing exposure situations have distinct characteristics. Therefore, the Commission’s detailed advice for these situations is published in two complementary documents (that for emergency exposure situations in this report, and that for existing exposure situations following emergency exposure situations in a forthcoming ICRP publication.

(4) Various design aspects of facilities where radioactive materials are present affect both the likelihood of an emergency arising, and also the magnitude of doses in the event that an emergency occurs. Such design measures, including both passive and active safety features, should be considered in a prior safety assessment that considers all reasonably foreseeable events. Such assessments are outside the scope of this report.

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3. Objectives of protection in emergency exposure situations 

(5) In the event of an emergency exposure situation, the primary concern is the prevention or reduction of radiation dose. However, the potential consequences are wider ranging than the risk of radiation health effects. As demonstrated by the accident at the Chernobyl nuclear power station in 1986, the social and economic consequences may be serious and extend over a prolonged period of time. The goals for response must therefore encompass these wider potential impacts. A number of international bodies have summarised the practical goals of emergency response to radiation emergency as:

(6) The Commission recognises that there is a qualitative difference between the risks of stochastic health effects and the risks to an individual receiving exposures that would result in a severe deterministic injury. By ‘severe deterministic injury’, the Commission means injuries that are directly attributable to the radiation exposure, irreversible in nature, and severely impair the quality of life of that individual, e.g. lung morbidity and early death. The Commission recommends that every practicable effort should be made to avoid the occurrence of severe deterministic injuries in an emergency exposure situation, and that planning to protect against the occurrence of severe deterministic injury should take priority over that to protect against stochastic risks.

(7) The results of an analysis of the lessons learned from the responses to the Chernobyl, Goiania, and other emergencies over the past years lead to the conclusion that while the nature and extent of past emergencies are dissimilar, the lessons concerning emergency response are very similar, see below.

(8) It is important to prepare an agreed framework within which decisions on the optimum response will be made. Such an agreed framework should represent an overall protection strategy which does not focus solely on actions required after the onset of an emergency exposure situation.

(9) For many types of an emergency exposure situation, exposure rates will be greatest immediately following the event and will then decrease with time (or the extent of uncertainty surrounding exposure rates will mean that this is a prudent assumption to make for protection purposes). This means that some protective actions (e.g. sheltering, evacuation) need to be taken promptly in order to be effective. To implement these actions, there is no time to undertake detailed exposure assessments in real time. It is therefore necessary to determine, in advance, a set of internally consistent criteria for taking such actions, and, based on these criteria, to derive appropriate triggers (expressed as readily measurable quantities or observables) for initiating them in the event of an emergency.

(10) As the emergency exposure situation evolves in time, it may become prudent to extend the geographical or temporal spread of initial protective measures, and other protective measures may become appropriate, such as decontamination. Since the initial protective measures will have provided significant protection for those at greatest risk, decisions to implement other, less urgent, protective measures need to consider the actual circumstances of the situation and the optimisation of the overall protection strategy more carefully. Therefore, it will not always be appropriate to define the implementation criteria precisely in advance for less urgent protective actions. Where appropriate, the procedures by which the protective actions implemented by such criteria would be justified and optimised during the emergency should be agreed in advance, in order to facilitate their acceptance by the public during an emergency. Scientifically based recommendations for implementing protective and other measures need to be accompanied by an explanation that enables the decision maker to understand and consider them, and also to explain them to the public.

(11) The Commission recognises that the nature and extent of stakeholder involvement may vary between countries, but suggests that engagement with stakeholders is an important component in the justification and optimisation of protection strategies in emergency exposure situations. In this context, the stakeholders referred to by the Commission may include many different types of people and organisations, e.g. the public affected by the emergency exposure situation, the authority responsible for the emergency response, the licensee – if there is one – of the facility or activity causing the emergency exposure situation, the regulatory authority licensing the facility or activity – if there is one – causing the emergency exposure situation, local public officials within and perhaps near the areas affected by the emergency exposure situation, emergency workers including first responders, and others. The stakeholders involved in any particular aspects of an emergency response situation will vary with the type of situation/facility being considered, the scale of the emergency exposure situation being considered, and the time phase of the emergency exposure situation being addressed.

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4. Protection of emergency workers 

(12) Emergency workers and their roles should be identified in advance. Emergency workers may include radiation workers (e.g. employees of registrants and licensees) and people who are not normally occupationally exposed to ionising radiation, such as police, rescue personnel, fire fighters, and medical personnel.

(13) All workers identified in an emergency plan should have appropriate training sufficient to carry out their emergency role, so that they have sufficient information upon which to base informed consent should that be needed, and so that they can contribute to their own protection. They should also be provided with personal protective equipment, and arrangements should be made to assess any radiation doses received.

(14) The exposure of workers responding to an emergency who are implementing an emergency plan can generally be seen as deliberate and controlled, although this is not always the case; thus, some flexibility is required. Therefore, where feasible, the system of radiological protection consistent with that for planned exposure situations should be applied. Nevertheless, there may be a need to take protective actions promptly during an emergency, necessitating exposures for some workers higher than the dose limit for planned exposure situations (such as to help endangered people or to prevent the exposure of a large number of people). In such cases, it may be acceptable for emergency workers to receive, on the basis of informed consent, doses that exceed the occupational dose limits normally applied. Nevertheless, such doses should be optimised and be below a predetermined dose level appropriate to the type of task undertaken. The predetermined guidance values should take into account the assessment upon which the emergency plan is based, together with expert radiation protection advice.

(15) Previously (ICRP, 1991), the Commission advised that the exposures of emergency workers should be managed by grouping them into three categories:

(16) The Commission’s advice with respect to Categories 1 and 3 is essentially unchanged. With respect to Category 2, the Commission now recommends that protection should be consistent with the full system for planned exposure situations where this is feasible. This is a small change from the advice in Publication 63 (ICRP, 1991), where the focus was on planning exposures so that they did not exceed those ‘permitted in normal conditions’. The new advice can be thought of as requiring the optimisation of protection below a reference level of dose that is equivalent to the occupational exposure dose limit. Workers carrying out Category 2 tasks would be expected to include ambulance crews, medical personnel, drivers of evacuation vehicles, and police (fire fighters and rescue personnel may carry out Category 2 tasks; however, they may also carry out Category 1 tasks).

(17) The Commission’s advice, as set out in Publication 63 (ICRP, 1991), regarding the appropriate provision of training and information to emergency workers, and, for those in Category 1, ensuring that they are undertaking the risks voluntarily, remains unchanged. Furthermore, the Commission now explicitly recommends that women who have declared that they are pregnant, or who are nursing an infant, should not have an emergency role that would be expected to lead to doses greater than 1 mSv or to significant bodily contamination.

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5. Description of emergency exposure situations 

(18) Publication 103 defines an emergency exposure situation as a situation ‘…that may occur during the operation of a planned situation, or from a malicious act, or from any other unexpected situation, and require urgent action in order to avoid or reduce undesirable consequences’ (ICRP, 2007, Para. 176). Emergency exposure situations are characterised by the need to manage a changing situation back to one of ‘normality’, or at least one which is both stable and acceptable. Emergency exposure situations may be characterised by one or more of the following features: significant uncertainty concerning current and future exposures, rapidly changing rates of actual exposure, potentially very high exposures (i.e. those with the potential to cause severe deterministic health effects), or loss of control of the source of the exposure or release. Any or all of these features may continue to dominate how the response is managed for an extended period of time (i.e. months or even years), although, for some types of accident, the emergency exposure situation may be very short (days or even hours).

(19) Emergency exposure situations may be caused by many different types of initiating events and initial locations. Emergencies can occur, for example, at nuclear sites, medical facilities using radioactive materials, industrial sites that use or make radioactive sources or process materials containing naturally occurring radioactive material, or during the transport of radioactive materials, whether for commercial, energy generation or weapons use. For these situations, because the use of the radioactive material is regulated and therefore planned or known about in advance, it is possible to develop a protection strategy tailored for the specific characteristics of the potential accidents. The level of detail required for such plans will be decided by the relevant authorities, with response planning for more likely accidents developed in more detail than accidents judged to be more unlikely.

(20) Exposures could also be caused maliciously, e.g. through the dispersal of radioactive material in a public place, or arise without warning in unexpected locations, e.g. radioactive material that has by-passed regulatory controls such as ‘orphan’ sources. For these, it is not possible to plan a protection strategy in detail because the exact mechanism and location of exposure cannot be known in advance. However, this does not preclude the preparation of generic protection strategies with response plans; the inclusion of flexibility is of paramount importance to enable these generic plans to be adapted to the actual situation that arises. The guidance developed in this report is also applicable to these types of emergencies. Further guidance on response planning for malicious events can be found in Publication 96 (ICRP, 2005).

(21) For planning and response to emergency exposure situations, various time-related ‘phases’ are often used in national response plans. The Commission recognises that different national approaches will be used with respect to various phases of an emergency, and feels that the recommendations as expressed in this report for emergency exposure situations can be appropriately adapted to any national approach that is taken.

(22) It is necessary to define a conceptual set of doses for use in the justification and optimisation of emergency plans and decisions. These doses are as follows.

5.1. Projected dose 

(23) The projected dose is the individual effective (or equivalent) dose that is expected to occur as a result of an emergency exposure situation if no protective measures are employed. Projected doses should be calculated to representative persons. Generally, these will represent population groups, but, where there is a risk that individuals may be exposed above the thresholds for severe deterministic injuries, the representative persons may be assumed to undertake activities leading to the highest potential exposure. Projected doses may be used in several ways within emergency response planning:

5.2. Residual dose 

(24) The residual dose is the effective dose from all exposure pathways remaining after the implementation of an optimised protection strategy. The residual dose is the quantity that is compared with the appropriate reference level when selecting and assessing protection strategies. It can be assessed by estimating the exposure during emergency response planning (e.g. as the difference between the projected dose and the dose averted by implementing a protective measure or combination of protective measures), or by measuring and/or calculating the actual dose after an emergency exposure situation has occurred. The residual dose should be calculated as realistically as possible.

(25) Since emergency plans are developed to protect population groups, rather than specific individuals, the residual dose is derived in planning as the dose to each of a set of representative persons. Guidance on characterising the representative person is provided in Publication 101 (ICRP, 2006). In principle, those populations that may be exposed during an emergency should be divided into groups which are relatively homogeneous with respect to exposure and risk from that exposure, and representative persons should be characterised for each group.

(26) Once an emergency exposure situation has occurred, the residual dose should be assessed for those individuals who have been or may have been exposed. Where reasonably possible, this should be based on the assessment of exposures for real individuals. Where this is not reasonably possible, efforts should be made to characterise actual groups of exposed individuals more directly so that calculations related to representative person exposures are more accurate. As an emergency exposure situation progresses in time, more effort should be made to assess actual individual exposures.

(27) The assessment of residual dose is important when planning the response for an emergency because it is necessary to explore whether or not the dose is radiologically and socially acceptable, given the circumstances. In particular, this is fundamental to the Commission’s approach to emergency response planning, and supports the achievement of Goals 3, 5, 6, 7, and 8, as listed in Section 3. The residual dose should be calculated over the appropriate period of time. For emergency exposure situations where the dose is likely to be received in less than 1 year, the residual dose calculated and compared with the reference level should be the total dose received as a result of the emergency exposure situation. For accidents where the total dose is likely to be received over periods of more than 1 year, the residual dose calculated and compared with the reference level should be the sum of the external dose received over 1 year plus the committed effective dose received from intakes over the same 1-year period. With the exception of high-consequence, low-probability emergencies, the Commission recommends that if the residual dose exceeds the appropriate reference level, additional protective measures should be planned to result in residual doses less than the reference level. Where the implementation of protective measures is being considered during the actual response, the residual dose calculated for comparison with the reference level should include doses already received, those committed through the ingestion and inhalation of radionuclides, and those expected to be received in the future (see Section 8).

(28) The process of constrained optimisation should result in a residual dose which is below the appropriate reference level that is both radiologically and socially acceptable. This is because the process of optimisation involves wider issues than simply the radiation health risks associated with the dose. The process of optimisation must take account of the perceptions and aspirations of those who will continue to live and work in affected areas, and of those who may visit or purchase goods from these areas. Doses that are acceptable in the longer term will be influenced by the doses actually received. Therefore, it is generally the full 1-year residual dose (dose received plus the prospective dose for the remainder of the year) that should be the object of an optimised protection strategy. The optimised outcome may also be influenced by other – non-radiological – measures taken to support those affected, e.g. compensation schemes, health monitoring, infrastructure, and economic support. Therefore, in the planning of a protection strategy, it is important to engage the potentially affected stakeholders and, to the extent possible, explore with them what overall outcome, including residual dose, would be acceptable. This process of constrained optimisation within emergency response planning is discussed in more detail in Section 7.

5.3. Averted dose 

(29) The averted dose is the dose to the appropriate representative person (usually expressed as effective dose or equivalent dose) that is expected to be averted by the implementation of a protective measure or combination of protective measures. The concept of averted dose is an important component of the optimisation of emergency response planning, since it is one measure of the radiological benefit gained from implementing a protective option.

(30) Full response strategies are comprised of a set of individual protective measures (such as evacuation, milk restrictions, etc.). Where a number of different protective measures are relevant, optimisation of the overall protection strategy as a single process is likely to be complex. To assist emergency planners, the Commission has published guidance on setting intervention levels of averted dose for individual protective options (ICRP, 1991a, ICRP, 1991b, ICRP, 2005). These are intended to assist in the optimisation of the component protective measures of an emergency response plan. It should be emphasised that the intervention level is understood as a level above which an action is justified and below which no action is needed. This concept is no longer valid. Thus, the above-mentioned intervention levels should be called ‘triggers’, expressing the effectiveness of a specific protective measure in terms of averted dose in view of its inclusion in an integrated protection strategy of multiple protective measures.

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6. Applying the commission’s system to emergency exposure situations 

(31) The Commission’s 2007 Recommendations (ICRP, 2007) re-state its principles of justification and optimisation, and the requirement to protect against severe deterministic injury, as applying to emergency exposure situations.

(32) In an emergency exposure situation, the source of exposure is not inherently under control, and its magnitude may vary over a large range. It may therefore be impractical to maintain exposures below a predetermined dose level, or, in order to achieve this, the emergency response may require the use of resources well in excess of the risk. As such, the Commission recommends that exposure management should rely on the concept of constrained optimisation rather than on the more rigid concept of dose limits.

(33) Exposures may occur in advance of the emergency being recognised (e.g. covert malicious actions or orphan source material incorporated inadvertently in commodities). Even following recognition of an emergency situation, there may be no practical protective measures that could reasonably be planned to reduce or avoid some exposures (e.g. the initial exposures to those in close proximity to a criticality accident). Furthermore, some emergency scenarios may be so unlikely to occur that detailed planning of protective actions would not constitute an acceptable use of resources. The Commission’s advice on planning protection strategies for emergency exposure situations is only intended for application to those aspects of exposure and protective response for which it is reasonable to plan. It is the role of national authorities to set the regulatory framework for identifying the emergency scenarios for which it is appropriate to develop emergency response plans, and those aspects of the scenarios for which it is not reasonable to plan protective actions that optimise exposures below the appropriate reference level. The principles of justification and optimisation are discussed in more detail below.

6.1. Justification 

(34) Protection strategies are comprised of a series of specific protective measures designed to address, as appropriate, all pathways to which affected populations may be exposed. This concept represents an evolution from the previous ICRP recommendations which suggested that the individual and independent justification and optimisation of individual protective measures was sufficient. The Commission now considers that more complete protection is offered by simultaneously considering all exposure pathways and all relevant protective measures when deciding, during planning, on the optimum course of action to be taken. In more concrete terms, this means that the overall ‘benefit’ and ‘harm’ of a suite of protective measures must be assessed when judging the justification of their application – it will be justified to implement a protection strategy when it results in more benefit than harm. In many cases, the summation of benefit and harm from a series of justified individual protective measures will also result in a net benefit. However, in some cases, particularly for large-scale accidents, the addition of many protective measures, each with a positive net benefit but each resulting in significant social disruption, could result in the collective benefit of the protection strategy being negative. Thus, while each individual protective measure must itself be justified, the full protection strategy must also be justified, resulting in more good than harm.

(35) As an emergency exposure situation evolves, prevailing circumstances may change beyond the range that was considered during emergency planning and preparations. As such, the protection strategy may also require change. In considering these changes, the ‘new’ protection strategy should be justified. The level of detail given to such ‘real-time’ justification will, of course, vary depending on the urgency of the situation at hand, but it would be expected that beyond the need for urgent protective measures, a careful assessment of the justification of proposed actions would take place, as well as their subsequent optimisation. The need to reconsider justification will be a judgemental decision based on the magnitude of any necessary changes to the original plan.

(36) The resources allocated to the process of justification will vary depending on a number of factors. Two of the most important factors are the nature of the likely health effects should an emergency exposure situation occur, and the extent to which the need for protective measures can be ‘deferred’ until the occurrence of the exposure situation (i.e. whether the planned response can largely rely on ‘paper’ planning and training, or whether specialised equipment, e.g. alarm systems, must be purchased and/or installed in advance). The Commission also recognises that the practicability of implementing a protective measure is relevant to determining whether or not an action should be included in the protection strategy.

6.2. Optimisation and the role of reference levels 

(37) When optimising protection strategies, it is necessary to consider all aspects and protective measures to reduce residual dose, questioning whether ‘…the best has been done in the prevailing circumstances, and if all that is reasonable has been done to reduce doses’ (ICRP, 2007, Para. 217). This approach focuses efforts on optimising protection in order that individual exposures, from all pathways, resulting from the emergency exposure situation (i.e. residual doses) are judged to be acceptable in the context of the circumstances being planned for and the expected resources required/allocated for protection. This new approach implies the simultaneous optimisation of all protective measures that are included in the protection strategy, implemented if necessary in a stepwise fashion to address prevailing circumstances appropriately.

(38) While this new approach does represent a relative increase in operational complexity, it also provides a significant amount of increased flexibility in designing the ‘best’ protection to address an emergency exposure situation. This is partly because it enables the influence of one protective measure upon another to be taken into account, and partly because it provides for resources to be focused towards those measures that are expected to achieve the greatest net benefit overall, rather than implying the need to focus equal attention on each single protective measure. The sum of the benefits and harms from all individual, optimised protective measures may not, itself, be positive. Again, this is because the combination of effects of many individual protective measures, each involving large social disruptions, may be too socially disruptive overall. An optimised protection strategy may include protective measures which would not appear optimised if considered in isolation.

(39) The Commission has introduced the concept of constrained optimisation below reference levels in order to ensure that the response, as well as being optimised, avoids inequity of individual exposures. The reference levels define a level of dose above which it is generally unacceptable to plan to allow exposures to occur, and below which one should strive to be as low as reasonably achievable. The level of dose applies to that estimated for representative persons of identified population groups.

(40) In planning, it is necessary to optimise protection with respect to specific population groups and with respect to the overall response. This latter consideration is illustrated in Fig. 6.1. In this figure, the vertical lines represent the spread of residual doses to the representative persons of all population groups considered in the plan, whilst the blocked bars represent the mean of these residual doses. In this case, only Option B is acceptable, as Options A and C result in doses to representative persons that exceed the reference level.

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• Fig. 6.1. 

  The application of dose reference levels in planning protective actions for a number of population groups: Options A and C are unacceptable.

(41) In order to optimise an overall protection strategy during planning, it is necessary to identify the dominant exposure pathways, the time scales over which components of the dose will be received, and the potential effectiveness of individual protective measures. Knowledge of the dominant exposure pathways will guide decisions on the types of protective measures to consider and the allocation of resources; resources allocated to protective measures should be commensurate with the expected benefits, of which averted dose is an important component. Knowledge of the time scales over which exposures will be received informs decisions about the lead times available to organise protective options once an emergency exposure situation has been recognised. The effectiveness of single protective measures can be complex to evaluate, as it includes wider social and economic consequences as well as dose effectiveness.

(42) The optimisation of the overall protection strategy during planning is an iterative process involving stakeholders, in which the proposed protective measures are individually optimised and their contribution to the overall protection strategy is assessed and optimised. For planning, this optimisation needs to be robust as the detailed circumstances of the emergency cannot be known in advance. When an emergency has been recognised, the appropriate protection strategy should be implemented. Once the urgent measures have been implemented, a more detailed iterative optimisation can take into account the exact circumstances and the actual stakeholders. Thus, the process of constrained optimisation is iterative with respect to individual measures and the overall protection strategy, with respect to time and stakeholders. At each stage, comparison of the residual dose expected from the overall protection strategy should be compared with the planned residual dose to gauge the effectiveness of the implemented protection strategy, as well as the appropriate reference level(s) to ensure that the outcome is optimised.

(43) Fig. 6.2 illustrates the application of the reference level once an emergency situation has occurred. Regular review of the expected residual doses as both the emergency situation and the response develop, and consequent re-optimisation of the response may well result in a progressive lowering of the expected residual doses over time. Review of the expected residual doses may also demonstrate that the doses to some population groups will exceed the reference level. In this case, any re-optimisation of the protection strategy should focus on these population groups in order to explore whether it is feasible to reduce their doses. It should be noted, however, that a fully optimised response may result in a distribution of doses where some are above the reference level, as indicated by the second bar in Fig. 6.2.

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• Fig. 6.2. 

  Actual dose distribution after implementing the planned protection strategy (left) and ongoing optimisation (right).

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7. Arrangements for emergency exposure situations 

7.1. The planning process 

(44) The importance of planning for emergency response cannot be over-emphasised. No emergency response can be effective without prior planning. This planning needs to involve identification of the range of different types of emergency situation for which a response may be required, engagement with stakeholders, selection of appropriate individual protective measures and development of the overall protection strategy, agreement of the areas of responsibility of different agencies and how they will interact and communicate, deployment of the necessary equipment for monitoring, supporting the implementation of protective measures, communicating with those at risk, training, and exercising of the plans.

(45) The Commission recommends that plans should be prepared for the types of emergency exposure situation identified in the risk assessment: nuclear accidents (occurring within the country and abroad); transport accidents; accidents involving sources from industry and in hospitals; malicious uses of radioactive materials; and other events. The level of detail within the plans will depend on the level of threat posed¹, and the degree to which the circumstances of the emergency can be determined in advance. However, even outline generic plans should indicate the responsibilities of the different parties involved, methods for communication and co-ordination between them and internationally during the response, and a framework for guiding decision making. More detailed plans should contain a description of the protection strategies for the identified scenarios, and provide triggers to facilitate prompt decision making.

(46) Detailed response plans are likely to place most emphasis on the initial response, as this is when there is least time for developing the response in real time and when uncertainties concerning the overall situation, current exposures, and the likely evolution of exposures will be greatest. However, any actions (or inactions) taken during this phase will impact on what can be, or needs to be, done at a later stage. In addition, the particular characteristics later in an emergency exposure situation, e.g. with regard to the need for widespread monitoring, may mean that unless the protection strategy is addressed adequately during planning, it may not be possible to respond effectively in the event. The optimum protection strategy for emergency exposure situations must address a wide range of issues over a relevant time period. For this reason, the Commission’s reference level for emergency exposure situations refers to the residual dose received/committed over 1 year unless otherwise specified (Para. 27). Optimising the planned protection strategy to aim for the maximum residual doses to be below this level and as low as reasonably achievable requires consideration of the response across all phases (or at least the early and intermediate phases for large events). An emergency protection strategy should therefore address the response during all time periods. For an urgent response, the planned response would be set out in detail with triggers to help guide decisions on implementation. For the later response actions, it is likely that an outline protection strategy would be indicated, rather than a specific response being planned, together with a framework for developing the specific response at the time of the emergency, taking account of the actual circumstances. Whilst the form of planning for the later time periods would be different, and in some cases may be done as part of planning for existing exposure situations, it is important that this planning is undertaken in such a way as to provide confidence that residual doses over a whole year will not exceed the reference level.

(47) Even after an emergency exposure situation has occurred, there will be a need to plan subsequent actions, particularly as time advances and the urgent need to act dissipates and finally disappears. As such, there will be a continual need to reflect relevant experience in selecting, justifying, optimising, implementing, adjusting, and terminating protective measures. The emergency plan will have identified a set of protective measures, and planned their implementation to an appropriate level of detail.

(48) A key concern in the event of an emergency exposure situation is to keep the exposure to individuals from all pathways below the thresholds for severe deterministic health effects (ICRP, 1991a, ICRP, 1991b). In the event of an emergency, it is possible that some individuals may be exposed to radiation doses that are so high that, without prompt medical treatment, they will cause severe, irreversible injury to their health. The Commission calls these ‘severe deterministic injuries’, to distinguish them from deterministic tissue reactions which may be reversible or may only have a minor impact on the individual’s health. The Commission continues to advise that practicable protective measures should always be planned to protect those individuals who would be at risk of suffering severe deterministic injury in the event of an emergency exposure situation. The following paragraphs provide additional advice on a framework to achieve this.

(49) In developing this framework, the Commission recognises that there is a qualitative difference between planning protection for emergencies and protection for unintentional events (e.g. orphan sources) and malicious acts. Accidents occur when events disrupt planned exposure situations. It is therefore possible to design additional safety precautions into a planned activity that would mitigate the doses received in the event of an accident. This is clearly not possible in the case of malicious acts, as such acts are planned deliberately to circumvent any protective measures that might be in place. The Commission recommends that the framework for protection in the case of accidents comprises two steps: one prior to any accident, and one in the event of an accident. The recommended framework for protection in the case of malicious acts may contain a ‘prior’ step for specific locations or activities judged to be at particular risk, but will generally focus on the response phase.

(50) The Commission recommends that postulated emergency situations should be examined to determine whether or not they may result in exposures that could cause severe deterministic injuries. If such exposures are considered possible, all protective options that could be implemented in advance to reduce these exposures, should the emergency exposure situation occur, should be considered. Such options will be dependent on the particular circumstances and may include:

(51) A further step is the preparation of a protection strategy that provides specific protection for those at risk of severe deterministic injury in an emergency exposure situation. The protection of those at high risk should take priority over the protection of others, in terms of both resources and focus. Therefore, this part of the overall response should be separate from the protection of those at risk of lower exposures. Nothing in the emergency plan developed for protecting those at lower risk should compromise the protection of those who are at risk of receiving exposures that could result in severe deterministic injury. The response plan for those at risk of severe deterministic injury should not only include specific measures aimed at reducing exposures, but should include procedures to rapidly identify those most likely to be at high risk, so that they can receive detailed assessment and prompt medical attention. One way of achieving this might be for those in a particular high-risk area to muster separately to others, so that they can be accorded appropriate priority.

(52) In planning protection against malicious acts, it may not be possible to implement protection in advance. However, for specific ‘high-risk’ locations and activities, the Commission recommends that practicable options should be considered for implementation, in order to reduce the exposures that may result from such acts. Response planning for malicious acts should develop procedures that enable the potential for exposures sufficient to cause severe deterministic injury to be assessed rapidly. Where this potential is judged to exist, the emergency plan should also provide procedures for identifying those who may have been exposed at such levels, guidance on exposure assessment and appropriate treatments, and practical plans to enable the individuals to receive treatment in the necessary time scales.

(53) The Commission recognises that the nature and extent of stakeholder involvement may vary between countries, but suggests that engagement with stakeholders is an important component to the justification and optimisation of protection strategies in emergency exposure situations.

(54) During planning, it is essential that the plan is discussed, to the extent practicable, with relevant stakeholders, including other authorities, responders, the public, etc. Otherwise, it will be difficult to implement the plan effectively during the response. The overall protection strategy and its constituent individual protective measures should have been worked through with all those potentially exposed or affected, so that time and resources do not need to be expended during the emergency exposure situation itself in persuading people that this is the optimum response. Such engagement will assist the emergency plans by not being focused solely on the protection of those at greatest risk early in an emergency exposure situation.

(55) Stakeholders are not limited to those groups affected in the country where the emergency occurs; for large-scale emergencies, there may be international consequences. These may result from: international trade and concerns that produce/trade items may be contaminated; the perceived need for protective measures in other countries and therefore the need to harmonise the response across country borders; and the need for authorities to ensure the safety of their nationals in an affected country and to deal appropriately with people from an affected country crossing their borders. It is important that national authorities ensure effective international communication with authorities, particularly in countries that could be affected in the event of an emergency. There would be advantages in co-ordinating the response as much as possible.

(56) A further need for stakeholder engagement centres around the issue of waste containing radioactive material. In any emergency exposure situation involving anything more than the most limited contamination of the environment, it is likely that very large volumes of contaminated waste will be generated, e.g. Goiania (IAEA, 1988). Early in an emergency exposure situation, emphasis should be placed on containment of radioactive waste so as to control impacts on people and the environment. In the longer term, management and disposal of waste will pose significant problems both socially and practically, and may even require changes to legislation. Where agriculture is affected, the problem of large volumes is compounded by the fact that this waste may rapidly become a health hazard, and the production of some food wastes (e.g. milk) is not easily terminated. Engagement with representatives of local communities, producers, and regulators in advance of an emergency can provide an opportunity for solutions to be developed in outline, and any legislative changes required to be identified in advance.

(57) In the event of an emergency exposure situation, it is likely that actual exposure rates will vary in space and time, and that the doses received by individuals will vary, both as a result of the variations in exposure rates and as a result of differences in their physiological characteristics and behaviours. In order to ensure that the optimum protection strategy is developed, it is important to consider the range of doses and other consequences for individuals that may occur, both in the absence of protective measures (projected doses) and following implementation of the protection strategy (residual doses).

(58) The Commission advises that this should be achieved by identifying a set of different population groups who, by their locations, characteristics, and behaviours, represent the full distribution of doses and risks. These population groups should be characterised by representative persons, as described in the Commission’s advice on representative persons (ICRP, 2006). It would be expected that where children and other sensitive groups are likely to be present in an affected area, the consequences and protection strategy for these groups would be explicitly considered as deemed appropriate in the planning arrangements. In accordance with the Commission’s advice on the representative person, it is important that the dose estimates reflect those likely to be received by the groups at greatest risk, e.g. pregnant women and children, but that they are not grossly pessimistic.

(59) The Commission has recommended that reference levels for emergency exposure situations should typically be set in the band of 20–100mSv (acute or per year). This band applies in unusual, and often extreme, situations where actions taken to reduce exposures would be disruptive (ICRP, 2007, Para. 241). Reference levels and, occasionally for ‘one-off’ exposures below 50mSv, constraints could also be set in this range in circumstances where benefits from the exposure situation are commensurately high. Action taken to reduce exposures in a radiological emergency is the main example of this type of situation. The Commission considers that a dose rising towards 100mSv will almost always justify protective measures. In addition, situations in which the dose threshold for deterministic effects in relevant organs or tissues could be exceeded should always require action.

(60) While reference levels for emergency exposure situations may be fixed at values up to 100mSv (ICRP, 2007, Table 5), they would only be set at the upper end of the band 20–100mSv in unusual or extreme circumstances where actions taken to reduce exposures would be very disruptive. Setting reference levels for emergency workers is discussed in Section 4. Reference levels below 20mSv may be appropriate for the response to events involving projected exposures below 20mSv.

(61) The selection of a reference level should fit the type of emergency exposure situation and the protection strategy to which it will be applied. For example, in a large-scale release of radioactive material, the protection strategy will be an evolving set of protective measures aimed at addressing the particular circumstances of populations affected in different ways and to different levels, at different times, and in different places. Part of the role of those authorities responsible for requiring emergency response planning should therefore be to determine the most appropriate reference level for the emergency exposure situation under consideration. This may be achieved by setting a single reference level for all types of emergency, or alternatively, by setting an appropriate reference level to apply to each type of emergency. There may also be situations where it is not possible to plan to keep all doses below the appropriate reference level, e.g. high-consequence emergencies in which extremely high acute doses are received within minutes or hours. For these events, the Commission advises that measures should be taken to reduce the probability of their occurrence, and response plans should be developed that can mitigate the health consequences where practicable. Emergency planners should prepare their protection strategy in accordance with the established reference level.

(62) The preselected reference level against which the optimisation of protection is assessed should be expressed in mSv (acute or per year). The optimisation process may also need to take into account whether or not the optimum protection is being afforded to individuals under various emergency circumstances. The residual dose to be compared with the preselected reference level is that assessed and/or estimated for the exposed populations for the year following the accident. In an emergency exposure situation involving no long-term environmental contamination (e.g. criticality accident), the preselected reference level against which the effectiveness of the protection strategy is assessed is the total dose received via all pathways over whatever time period the exposures may occur.

(63) The type of reference level that is selected should thus be tailored to meet the type of emergency exposure situation under consideration. Depending on the time of year of a release to the environment, as well on the nuclide composition of a contamination, there are major differences in the contributions of the pathways considered (ingestion, inhalation, cloud shine, ground shine) to the projected dose. These differences have to be considered in an appropriate fashion in defining reference levels and developing protection strategies. Regulatory authorities and operators will assess reasonably foreseeable risks, and authorities will preselect appropriate reference levels for the various emergency scenarios that they judge to be relevant.

(64) The Commission’s band of reference levels is expressed in terms of effective dose. There are situations for which effective dose is not an appropriate quantity in which to express reference levels. Such situations include: where the type or scale of the emergency may result in doses in excess of 100mSv effective dose (where the assumption of linearity in its derivation may no longer hold); where parts of the response need to focus on individuals at risk of incurring severe deterministic injury; and where the resulting exposures are very strongly dominated by irradiation of a single organ for which very specific protective measures are optimum (e.g. releases dominated by radioiodine). For these situations, the Commission advises that consideration should be given to specifying (or providing supplementary) reference levels in terms of equivalent or absorbed dose.

(65) In its previous advice (ICRP, 1991a, ICRP, 1991b, ICRP, 2005), the Commission recommended the use of intervention levels of averted dose to assist decisions on whether/when to include certain protective measures in an overall protection strategy. This term was used in the context of a process-based approach system of protection, making a distinction between practices and intervention. In this latter case, the concept of intervention level was understood as requiring an action above the intervention level and no action below; this is not consistent with the 2007 Recommendations (ICRP, 2007). Thus, the Commission believes that it is more appropriate to avoid the use of the term ‘intervention level’. However, the corresponding quantified values can be used as triggers expressing the effectiveness of individual protective measures as an input of the process of optimisation of the protection strategy (ICRP, 2005).

(66) In the context of planning and implementing a protection strategy, the Commission still considers that the levels of averted dose are useful tools to rate the individual protective measures within an optimised protection strategy. However, in an actual emergency exposure situation, the parameters relevant to the situation may be different than the levels of averted dose for individual protective measures, and/or the judgements used in establishing these levels in isolation may not be fully representative. When several actions are combined within an overall protection strategy, the balance of harms and benefits contributed by individual measures is likely to be different than when they are considered in isolation. It is therefore not appropriate to treat the averted dose levels previously defined by the Commission as ‘absolute’ criteria that prescribe when each protective measure should be included a plan. In particular, in circumstances for which it appears that no single protective measure on its own is sufficient to reduce residual doses to below the reference level and as low as reasonably achievable, it may be necessary to combine several protective measures, one or more of which would appear unjustified by simple comparison with its previously defined intervention level, to achieve this outcome. In this case, the level of averted dose would act as a prompt to consider the introduction of that measure more carefully, to determine whether or not an alternative measure or manner of introduction might increase the expected benefits or decrease the expected harms. Triggers, particularly their use for the initiation of urgent protective actions, are further discussed in Section 7.2.5.

7.2. Components of a protection strategy 

(67) A protection strategy will contain a wide range of information and guidance, including information such as contact details, duties and responsibilities of the different organisations involved, reference to legislation, amounts of equipment/resources required etc.; this is beyond the scope of this document. A discussion of these practical and technical issues can be found in publications from other organisations (NEA, 2000, IAEA, 2002, IAEA, 2003). In this document, only those aspects relevant to the application of the Commission’s advice are discussed.

(68) There are different protective measures which could be applied in a radiation emergency. Urgent protective measures are those that must be taken promptly (normally within hours) in order to be effective, and for which the effectiveness will be markedly reduced if there is a delay. The most commonly considered urgent protective measures in a nuclear or radiological emergency are evacuation, decontamination of individuals, sheltering, respiratory protection, iodine thyroid blocking, and restriction of the consumption of foodstuffs that have the potential to give significant exposures to people (e.g. green vegetables grown in the open and milk from animals grazing outdoors). Longer term protective measures (and food restrictions to protect against longer term exposures) include measures such as permanent relocation, agricultural protective measures, and some decontamination measures. The Commission has previously published detailed guidance on most of these protective measures (ICRP, 1991a, ICRP, 1991b); further discussion of individual protective measures in this document is therefore restricted to new aspects of the Commission’s advice.

(69) During an emergency exposure situation, other measures are also likely to be considered. These include public warning, information, advice and basic counselling, dealing with their own national citizens in another affected country, comprehensive psychological counselling, medical management, and long-term follow up. More details are provided in Annex B.

(70) The characteristics of potential exposures and therefore the requirements for the protective response will vary both spatially and in time. In order to be manageable, a protection strategy will sub-divide the area at risk into appropriate sub-areas, based on a number of factors such as: distance from the initiating source; demographic, economic and land use factors; and response phase (early, intermediate, late). This approach enables the broad issues for each sub-area to be treated appropriately within the plan. However, in reality, there will be few, if any, sharp boundaries to delineate the implementation of protective measures.

(71) Aspects that need to be considered when optimising an overall protection strategy are: the impact of actions (or inactions) taken at one point in time on subsequent protective requirements; and the potential need to manage different areas simultaneously in different fashions (e.g. one area with heavy contamination may require urgent protective actions, whilst another area with much lower contamination may require management involving more stakeholder engagement). These types of issues are discussed below.

(a) Influence of actions on subsequent actions

(72) The management of wastes arising from decontamination, food restrictions, and other protective measures (e.g. domestic and commercial refuse left outside in an area that was evacuated) is an example of the need for response planning to consider the wider temporal consequences of actions. A decision to prevent the consumption of fresh milk is straightforward to make and implement, but the consequence is a rapid build up of large volumes of organic liquid waste that are difficult to dispose of safely, from a biological perspective, regardless of the radiation hazard posed. An optimised overall protection strategy should include the identification and prior agreement of appropriate disposal routes and temporary storage sites.

(73) The termination of protective measures is another area where the interaction of urgent protective measures and later protective measures is particularly obvious. Withdrawing all urgent protective measures and then, some time later, initiating new protective measures such as decontamination may, purely from consideration of future doses and dose rates, seem the optimum course of action. It may not be optimum from a practical and ‘cost’ viewpoint. For example, extending evacuation whilst decontamination is carried out may not actually increase the monetary costs of the combined protective measures substantially, as decontamination may be carried out more efficiently in the absence of people living in the area.

(74) The Commission therefore advises that effective emergency response planning should consider the impact of protective measures taken at one time on decision options available at later times. It may be that one way of ensuring that these interactions are adequately addressed is for the planned response to identify the need for a team to be set up early in an emergency exposure situation, whose responsibility is primarily to consider what might be required later, and how early decisions might impact on this.

(b) Dynamic nature of response

(75) The spatial variation of future exposures inevitably results in some areas potentially having much higher exposures than others. In the case of release of radionuclides to the environment, it is likely that areas close to the source will experience higher levels of contamination than areas further away from the source. For large releases, particularly, it is likely that appropriate reassurance monitoring will enable areas with low contamination to move to a less urgent form of response management, whilst the more highly contaminated areas will remain subject to the protective measures and management approach planned for an urgent response. One consequence of this is that, depending on the plan and the overall emergency response management approach of the country, different authorities may be responsible for management of the different areas. Whilst simultaneous management of the response in different areas may not be problematic in principle, people living and working near the boundaries of such areas, or even living in one such area and working in another, may require particular care and involvement in the decision process. It will thus be important to foresee such situations in planning in order to avoid serious operational and social problems.

(76) In order to develop a protection strategy, it is necessary to evaluate the projected doses for the situation being considered. Only for the very largest emergency scenarios are projected doses received over time scales of fractions of a second up to 1 or 2 days likely to exceed 100mSv (see Annex A). However, there is a wider range of postulated emergency scenarios which may result in projected doses in excess of 100mSv effective dose from intakes over the first year, together with external doses received over that period.

(77) Examples for the relative contribution of different pathways (cloud shine, inhalation, ground shine, ingestion) to the projected dose are given in Fig. 7.1 for an atmospheric release of five radionuclides (⁶⁰Co, ⁹⁰Sr, ¹³¹I, ¹³⁷Cs, and ²³⁹Pu) and for two release scenarios for nuclear power plants (for details, see Annex A).

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• Fig. 7.1. 

  Examples for the relative contribution of different pathways to the total dose.

(78) By contrast, the spread of contamination experienced in London following the poisoning of Mr. Litvenenko in November 2006 resulted in actual or possible acute intakes of an alpha-emitting radionuclide, via inhalation of resuspended particles or ingestion, but no risk from external irradiation nor contamination of foodstuffs (except secondary contamination spread from contamination on hands or contaminated utensils).

(79) The purpose of estimating projected doses and their likely spatial and temporal distributions is three fold: (1) to identify the scale of health consequences that might occur if no protective measures are taken and, therefore, to determine the broad scale of resources it is appropriate to assign to a protection strategy; (2) to identify the broad geographical and temporal distribution of the various likely response phases; and (3) where, in terms of protection, resources are likely to be spent most effectively. Identifying these broad trends helps to highlight the evolving response management issues that need to be addressed, and to provide initial guidance on the sorts of protective measures that might be appropriate. In respect of the third aim, it is likely that protective measures aimed at reducing the dose from the exposure pathway(s) that would otherwise dominate the projected dose will have the potential to avert the greatest dose. It is therefore reasonable to allocate resources to the detailed evaluation of such protective measures. In the context of particulate releases from nuclear reactors, it is likely that ingestion doses will dominate the projected doses over the first year; as a consequence, protective measures on the food chain are likely to have the potential to avert the greatest dose.

(80) The timing and manner of implementation of individual protective measures and how they are combined into a protection strategy will influence the overall net benefit achieved by the protection strategy. It is therefore important to optimise the broad protection strategy. In this context, the Commission’s previous advice on individual protective measures and their optimisation is relevant ICRP, 1991a, ICRP, 1991b, ICRP, 2005.

(81) In principle, the process of applying constrained optimisation to the planning of strategies of protective measures is the same as that for individual protective measures, i.e. all the consequences, harmful and beneficial, expected to result from the imposition of different strategies are evaluated and balanced, and the one with the greatest net benefit, which also results in a residual dose below the reference level, is selected. However, in practice, the problem with this process is that there are so many combinations of strategies that could be considered that the process could quickly become too complex. It is therefore advisable to adopt a more pragmatic approach, in which individual protective measures are optimised separately, and issues associated with their application in combination are identified and explored, as discussed below. A protection strategy composed of individually optimised protective measures will not necessarily be optimised itself, whilst an optimised protection strategy may contain actions implemented in a way that, taken in isolation, would not be optimum.

(82) Some combinations of protective measures can be considered to be largely independent of each other, e.g. commercial food restrictions and the evacuation of populations in close proximity to a radiation source. The actions and resources required to implement these protective measures are very different (buses and evacuation centres for evacuation, food monitoring equipment and facilities for disposing of or processing foods in the case of food restrictions), and the impacts (other than doses averted) resulting from implementing these protective measures are likely to be sustained by different population groups (those evacuated, voluntary groups providing food and bedding, bus drivers for evacuation, farmers, food manufacturers, agencies responsible for monitoring food production and disposing of wastes in the case of food restrictions). These types of protective measures can readily be optimised separately and the relevant levels of averted dose used as a direct guide.

(83) With other combinations, the protective measures are more closely linked, with actions required to implement one being relevant for implementing the other. In this case, there is the potential for significant interaction between the harms (including resources required) and benefits of the options, and so the process of detailed optimisation is less straightforward. In this case, single measure levels of averted dose need to be used more flexibly, taking into account both the enhanced benefits of combining actions and, as above, the need to develop a plan that reflects the characteristics of the surrounding area, such as geographic and demographic areas.

(84) The resources required to implement protective measures are not the only factors that may interact within an overall protection strategy. Other such factors include individual and social disruption, anxiety and reassurance, and indirect economic consequences. It is important to review the proposed overall protection strategy with representatives of all potential stakeholder groups to ensure that the plan is optimised and feasible with respect to these factors, as well as with respect to dose and the resources required. This wider review of the protection strategy may indicate a role for additional actions which, in isolation, do not appear optimum (or even justified). Alternatively, it may indicate that the optimum protection strategy should modify or omit other actions, despite the fact that they appear to be justified and optimised when dose and direct resource requirements alone are considered.

(85) The level of detail of optimisation of the response plan should be commensurate with the needs of the situation. This is a matter for national authorities to decide. In general, events with the potential to result in widespread, high levels of contamination and events that are relatively likely to occur require more detailed planning than very-low-probability events or events that are expected to have limited consequences.

(86) At stages during the detailed optimisation of the protection strategy, the expected residual doses should be compared with the reference level to ensure that the outcome of optimisation remains below this level. Development of the plan is therefore an iterative process, with the degree of iteration depending on the level of detailed optimisation considered appropriate for the significance of the emergency exposure situation and the need to provide for flexibility of response on the day.

(87) Once the protection strategy has been optimised in planning, measurable triggers for initiating its different parts should be developed. Since most protective measures taken early in an emergency exposure situation need to be taken promptly, any delay in decision making would be counterproductive. Therefore, protection strategies should include triggers (IAEA, 2002) that can be used immediately and directly to initiate appropriate protective measures. Once an emergency is occurring, the types of information likely to be available to the decision maker will change with time, e.g. from assessments of plant conditions and limited dose rate measurements, to widespread and increasingly detailed information based on a substantive monitoring programme.

(88) Triggers may be expressed in terms of any observable circumstances or directly measurable quantities, e.g. plant conditions, dose rates, and wind direction. Triggers may be related to dose considerations, but are more likely to be quantities or qualities, such as information that a filter or a pump has failed, which indicate that a situation has occurred for which the plan (or a group of actions within the plan) was developed. Similarly, triggers may be identified which indicate that the event is outside the range of scenarios considered when the plan was developed, thus warning decision makers that the scale of protective measures may need to be escalated from those set out in the plan (in particular, the areas over which urgent protective measures are introduced may need to be enlarged significantly). Once the occurrence of a trigger has been identified, decision makers can advise that the appropriate part of the protection strategy should be implemented immediately, without further delay or discussion.

(89) In order to ensure widespread compliance with protective measures implemented on the basis of triggers, both with respect to those implementing the actions as well as those affected by them, it is important that relevant stakeholders (or their representatives) are involved at the preparedness stage in determining what the appropriate triggers should be. Unless this is achieved, the implementation of prompt actions on the day may be delayed whilst different groups demand further information to assure themselves that this is the best course of action.

(90) In some emergency exposure situations, it may become apparent that protective measures are required that were not envisaged within the plan, or for which the actions implemented were not sufficiently protective. In this case, decision makers should first implement all those urgent actions indicated by the triggers, but may then take additional actions not indicated by the planned triggers. In other words, the triggers should be used to facilitate prompt decision making, but not to prevent necessary flexibility to optimise on the basis of the exact circumstances of the emergency. This is discussed further in Section 8.

(91) Established criteria or indicators may also be helpful for deciding and delineating the extent of later protective measures. For example, once the radionuclide composition of environmental contamination is understood, a dose rate criterion could be applied to delineate where temporary relocation would be advised. Whilst specification of the triggers themselves in the emergency plan may not be appropriate, it may be helpful to include an agreed framework for developing triggers in ‘real time’. The inclusion of such a framework is likely to result in wider acceptance of the ‘real-time’ triggers when they are developed.

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8. Implementing protection strategies 

(92) In the context of the ICRP system of radiological protection, there is at least one fundamental difference between prospectively planning to address the consequences of a radiological emergency exposure situation, and managing consequences that are in the process of occurring or that have already occurred. In the context of planning, optimisation is performed using the appropriate reference level as the upper bound to optimisation, eliminating any protective solutions that result in individual residual doses exceeding the reference level. Protection for all those exposed is optimised, and residual exposures resulting from the application of the protection strategy are below the reference level. In the inherently unpredictable nature of emergency exposure situations, some actual exposures may exceed the preselected reference level. As such, in the context of managing the consequences of an emergency that is in the process of occurring or that has already occurred, the predefined reference level is used as a benchmark against which to judge the results of implementing a planned protection strategy, and for guiding the development and implementation of further protective measures if necessary (see Fig. 6.1).

(93) When reviewing the effectiveness of an ongoing response or making decisions on the implementation or variation of protective measures, it is important to compare the sum of all components of the residual dose with the reference level, i.e. the sum of doses actually received and those expected to be received in 1 year (or during the time frame relevant to the emergency exposure situation) with those expected in the planning stage.

8.1. Tuning protection strategies to actual conditions 

(94) It is likely that if an emergency exposure situation occurs, it will not exactly match the assumptions that were made in planning. Divergence from initial assumptions will most likely increase as an emergency exposure situation progresses in time. However, in most cases, emergency response planning will broadly fit a large range of possible situations, such that the early and urgent implementation of a planned protection strategy should come close to providing the optimum protection, with divergence most likely being on the conservative side. However, there will still be some need to operationally adjust planned protection strategies, justifying any new actions or significant changes to the plans. The need to consider making such modifications will increase as the emergency exposure situation progresses, and the magnitude of changes from the plans will depend on the nature of the emergency exposure situation that occurs (i.e. large and complex, or small and straightforward). It is important, however, that minor modifications to the planned actions are avoided, particularly in the early period as the situation is developing and where uncertainties are greatest, as this is likely to, at best, introduce confusion for very little expected benefit, and at worst, actually result in reduced protection.

(95) Once an emergency exposure situation has occurred, it is likely that many stakeholders will be very interested in providing input to discussions regarding protective measures. Should the emergency exposure situation have an early period requiring urgent protective measures, the ‘reflex’ use of preplanned protection strategies will be necessary with no or very little stakeholder involvement beyond the emergency response authorities and those responsible for the site, facility, or source that is causing the emergency exposure situation. As the emergency exposure situation progresses, however, stakeholders will become increasingly interested and available to participate in discussions leading to protection decisions, such that part of emergency response planning should be the development and implementation of processes and procedures to inform and involve stakeholders.

(96) As an emergency exposure situation progresses, emergency planners may wish to approach optimisation in a stepwise manner, particularly for emergency exposure situations affecting large areas and/or causing long-lasting consequences. Here, periodic re-assessments may indicate that reference levels could be altered, generally in a downward fashion, to best assist the optimisation process as prevailing exposure circumstances evolve.

(97) The early period of an emergency exposure situation can be characterised as following preplanned actions as best as possible to manage any emergency consequences. The focus of protection strategy decisions will be on adapting pre-made plans to best fit the actual situation.

(98) In the initial uncertain period of an emergency exposure situation, the radiological protection objectives of a protection strategy should be to avoid severe deterministic effects and to keep the risk of stochastic effects as low as reasonably achievable. To accomplish this, there may be a need to act very quickly and without much ‘concrete’ knowledge of exposures. Such ‘reflex’ protective measures will, of necessity, follow preplanned scenarios using preplanned procedures and processes. The plan should be developed such that revision of the most urgent protective options would not be required under almost any circumstances. However, re-assessment of the planned response in the light of actual conditions may be necessary after these most urgent measures have been implemented, so that actions best apply to the situation at hand. Re-assessment of the planned urgent response will involve as much specific information concerning the nature of the emergency exposure situation and its possible effects as possible, and any significant deviations from planning assumptions (i.e. extreme weather conditions, unexpected geographical location of the release site, temporary changes in population density due to unexpected circumstances such as large sporting or political events, etc.). In general, any modifications that are made to the planned response will be to extend protective measures in time and space.

(99) As an emergency exposure situation progresses, and understanding of the exact circumstances increases, decisions will increasingly be based on actual circumstances rather than preplanned responses. As understanding increases and the need to act becomes less urgent, there will also be an increased need to plan future protection strategies in greater detail than included in the plan, and thus to involve relevant stakeholders in decision-framing and decision-making processes when judging the justification of protection strategies, and when optimising their application. For this planning of future action, a predetermined reference level will be a useful tool to deal appropriately with the situation at hand. The endpoint of optimisation processes will be at least partially characterised by residual dose, which will have to be agreed by government (e.g. at the local, regional, and national level, and among relevant ministries) and relevant stakeholders (e.g. affected populations, affected businesses, etc.), and can be compared against the predetermined reference level when judging the appropriateness of the protection strategy.

(100) If, in application, protection options do not achieve their planned residual dose objectives, or result in exposures exceeding reference levels fixed at the planning stage, a timely re-assessment of the situation is warranted to understand why plans and results differ so significantly. New protection options could then, if appropriate, be selected, justified, optimised, and applied.

(101) Once protective measures start to be implemented, it is important to review their actual performance against the outcomes expected when the plan was developed. This feedback of actual outcomes and experience should be used to inform the further implementation of protective options and decisions on modifications to the later phases of the emergency plan.

(102) As an emergency exposure situation progresses and the need for urgent decisions dissipates, the decision-making process will inevitably shift away from giving direction towards furnishing an appropriate dialogue process with affected stakeholders so that the optimum protection strategy can be identified and implemented, and such that feedback of experience can help to improve the implementation of such protective measures. To incorporate stakeholder input appropriately into decisional processes, it is essential that structures, processes, and procedures, and perhaps legislation and regulation, are appropriately tuned to allow and encourage such participation.

(103) The active participation of stakeholders will, in general, bring relevant local knowledge, experience, and values to decision-making processes such that the resulting detailed protection strategies are more likely to be well focused, understood, and supported. However, the effective involvement of stakeholders will require appropriate training of the relevant staff from government bodies dealing with the emergency exposure situation in the social and interpersonal aspects of stakeholder involvement, bringing their technical knowledge to the service of the broader decisional process. In the long term, however, as the emergency exposure situation transitions to an existing exposure situation, ongoing stakeholder involvement should become self-standing and independent.

8.2. Termination of protective measures 

(104) The decision to terminate protective measures will need to appropriately reflect the prevailing circumstances of the emergency exposure situation being addressed. Many different aspects must be taken into account when reaching such decisions. Terminating a protective measure may result in the affected population receiving a ‘step change’ increase in dose rate, e.g. if access restriction to a contaminated area was terminated. However, planned protection strategies should consider the impact of termination of protective measures on the residual dose. In general, optimisation of the overall protection strategy during planning and reactive ‘re-optimisation’ of the protection strategy throughout the emergency response will mean that the impact of termination of protective measures on the residual dose will have been factored into decisions. Therefore, in general, it would not be expected that the residual dose will change significantly as a result of the termination of protective measures. However, there may be unforeseen circumstances that require termination of protective measures at a time or in a manner that was not planned for. In this case, the resulting exposures following termination of the measures may be higher than initially planned, and may even exceed the reference level. As with decisions on the initiation of protective measures, whilst the requirement for optimisation of the overall protection strategy remains valid, the focus for decision makers should be on implementing further practicable measures to reduce the exposures of those population groups receiving doses in excess of the reference level. These points are illustrated in Fig. 8.1.

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• Fig. 8.1. 

  Actual dose distribution after applying the planned protection strategy and optimisation (left) followed by the termination of a protective measure (right).

(105) It will be important to assess the potential benefits and harms caused by termination of a protective measure, and how this will affect the overall objectives of the protection strategy. A summary of issues which require consideration and evaluation before such decisions are made is given in Annex C.

(106) It is important to involve, wherever possible, relevant stakeholders in discussions regarding termination of protective measures. While it will be difficult, if not impossible, to discuss decisions with populations sheltered at home, it will be essential to discuss decisions to return to evacuated areas with those who have been evacuated, and the termination of protective measures implemented at a later stage.

(107) The types of information that will be needed for these decisions will, of course, vary between situations. However, in general, it will be important to have sufficient technical data on hand to judge the effects of termination. For example, the decision to allow evacuated populations to return to their homes and offices, i.e. the termination of temporary relocation, should only be taken when the exposures that would result from returning can be assessed appropriately, and this will most likely require an adequate understanding of the contamination conditions. For urgent protective measures that have short-natured effects, it will be essential to consider how their termination will affect the overall protection strategy and the optimisation process.

(108) Decisions regarding the termination of later protective measures will usually be based on the achievement of an optimum level of protection. These decisions will, in general, not be urgent in nature, and will be based on radiological protection input, and social and political judgement. In these cases, the involvement of relevant stakeholders is essential, and processes and procedures should be established to ensure that such involvement can take place efficiently.

(109) One important aspect of the involvement of stakeholders is that, when agreeing on the detailed implementation of any protective measure later in an emergency exposure situation, directly measurable outcomes should also be agreed (e.g. residual contamination levels, dose rates). This will help to ensure that when the action has been completed, it can readily be demonstrated that it has achieved the intended level of protection.

8.3. Permanent relocation 

(110) For some large emergency situations involving the release of high levels of long-lived contamination over large areas, part of the new reality following the situation may be that some areas will be so contaminated as to be incapable of sustaining social, economic, and political inhabitation as previously. In these areas, governments may prohibit human habitation and other land uses. This would mean that any populations evacuated from these areas would not be allowed to return, and that further resettlement or use of these areas would not be allowed.

(111) Clearly, it is not easy for a government and its people to make a decision to permanently (or for the long-foreseeable future) remove people from an area and to forbid its use. As such, the social, economic, political, and radiological aspects of such a choice will need to be discussed in a broad and transparent fashion before a decision is reached (IAEA, 1996, NEA, 2006). Generally, radiological aspects (e.g. contamination level, dose rate, etc.) would be used as part of the criteria to delineate the boundary of such areas, although existing geographic or jurisdictional boundaries may also be considered for social reasons.

(112) In corollary to a decision to define an area of permanent relocation is the fact that beyond such an area, people will be allowed to live. However, lingering contamination may well exist and may require the long-term management of population exposures. Transition from an emergency exposure situation to what is termed an ‘existing exposure situation’ is described in Section 9.

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9. Transition to rehabilitation 

(113) At some point in time, the emergency situation will end. However, for a major accident resulting in the release of radioactive materials at a nuclear site, or a serious malicious contamination incident, some significant residual contamination of the environment may persist for a long period of time and continue to affect the population. The Commission recommends that the management of long-term exposures resulting from emergencies should be treated as an existing exposure situation.

(114) Existing exposure situations resulting from emergencies are characterised by the need for a population to continue living in an area with known or assessable levels of exposure. Typically, such situations have social, political, economic, and environmental aspects that are seen as sustainable by the affected populations and governments, and as being their new reality. Whilst there will not be a sharp transition, the early and intermediate characteristics of an emergency exposure situation will be distinct from those in the subsequent existing exposure situation. This is illustrated schematically in Fig. 9.1.

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• Fig. 9.1. 

  Evolution of an emergency exposure situation with time and the transition to the existing exposure situation.

(115) The change from an emergency exposure situation to an existing exposure situation will be based on a decision by the authority responsible for the overall response. The decision may include considerations of the fact that different geographic areas may undergo this transition at different times. The transition may require a transfer of responsibilities to different authorities. This transfer should be undertaken in a co-ordinated and fully-transparent manner, and be agreed and understood by all parties involved. The Commission recommends that planning for the transition from an emergency exposure situation to an existing exposure situation should be undertaken as part of the overall emergency preparedness, and should involve all relevant stakeholders.

(116) There are no predetermined temporal or geographical boundaries that delineate the transition from an emergency exposure situation to an existing exposure situation. In general, a reference level of the magnitude used in emergency exposure situations will not be acceptable as a long-term benchmark, as these exposure levels are generally unsustainable from social and political standpoints. As such, governments and/or regulatory authorities will, at some point, identify a new reference level for managing the existing exposure situation, typically at the lower end of the range recommended by the Commission of 1–20mSv/year.

(117) If the level of contamination is such that sustainable social, economic, and environmental conditions cannot be achieved through the protection strategies implemented, the authorities may choose not to allow populations to live in some affected areas. The decision to permanently relocate populations will be based on radiological, social, and economic considerations with due recognition of the gravity and irreversibility of such a difficult decision.

(118) The management of existing exposure situations following an emergency will generally rely on the continuation and evolution of protection strategies implemented during the emergency, and the increased reliance on individual/self-help protection actions supported by an adequate infrastructure established by authorities. Generally, further significant reduction of exposures will not be achieved rapidly, but step-by-step optimisation will progressively bring exposures close to or similar to those associated with normal situations.

(119) More detailed guidance for the management of the long-term rehabilitation of contaminated areas following a nuclear accident or a radiation emergency is discussed in the complementary forthcoming ICRP publication.

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9.1. References 

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Annex A. Assessment of the contribution of different exposure pathways to the projected dose 

(A1) In the case of a severe accident with a radioactive source or in a nuclear reactor resulting in an accidental atmospheric release, it is likely that projected doses will be characterised by an initial, relatively high dose rate, inhalation component from inhalation of short-lived beta/gamma emitters during dispersion of the plume. For a reactor accident, this is likely to be followed by a time period lasting days or weeks when I-131 dominates the exposures, through external irradiation from contamination deposited in the environment and from direct contamination on crops and in milk. In the longer term, external radiation from radioactive isotopes of caesium and ruthenium is likely to become dominant, together with longer term contamination of foodstuffs with these radionuclides. Overall, during the first year following the accident, if no protective measures are taken, the largest component of the projected dose is likely to be received from contaminated foods, followed by external irradiation from contamination in the environment, with the smallest components originating from inhalation of radionuclides during dispersion of the plume or of resuspended radionuclides and external irradiation from the plume.

(A2) Assessments of the contributions of different exposure pathways to the projected dose can be based on numerical calculations using state-of-the-art radio-ecological models, which are readily available as part of decision support systems (Ehrhardt, 1997, Ehrhardt and Weiss, 2000). The calculations require definition of a large number of input parameters. The most important are the characteristics of a release (total activity, nuclide vector, release height, and duration), the characteristics of the release site (urban/rural, flat terrain/complex topography), the time of year of a release (summer/winter), the meteorological conditions (wind strength and direction, atmospheric stability), the distance between a release and the area where people need protection, the human dietary and consumption rates, etc.

(A3) The Task Group has performed a variety of calculations of this type using standardised input parameters in order to demonstrate the application of the new system. Unit source terms for some key radionuclides, as well as complex source terms with a multitude of radionuclides which are typically used in risk assessment studies for nuclear power plants, have been used for this purpose.

(A4) Table A.1, Table A.2 (BMBF, 1990) show the results for the radionuclides Co-60, Sr-90, I-131, Cs-137, and Pu-239, as well as for a ‘small release’ (Sm_rel; nuclide vector which is characterised by the following cumulative fractions of the core inventory: Kr-Xe: 0.9, I: 2E-3, Cs: 3E-7, Te: 4E-6, Sr: 2E-7, Ru: 6E-10, La: 6E-8) and a ‘large release’ (Lg_rel; nuclide vector which is characterised by the following cumulative fractions of the core inventory: Kr-Xe: 1, I_org: 7E-3, I₂-Br: 4E-1, Cs-Rb: 2.9E-1, Te-Sb: 1.9E-1, Ba-Sr: 32.E-2, Ru: 1.7E-2, La: 2.6E-3). It is evident from the results of Table A.1, Table A.2 that there are major differences in the contributions of the pathways considered (ingestion, inhalation, cloud shine, ground shine) to the total dose, which for the purpose of this presentation is normalised (100%). The main parameters are the radionuclides, the time of year, and the integration time after a release. For example, for Pu-239, inhalation contributes 100% to the total dose (‘winter’), compared with 1% for a large release (‘summer’). The relative contributions to the normalised yearly dose change with time; e.g. for I-131, ingestion contributes approximately 72% to the total annual dose for the first 10 days after release and another 20% by the end of 3 months. Of course, the absolute values of the annual dose would be markedly different for unit releases of the radionuclides in Table A.1, Table A.2. These differences have to be considered in an appropriate fashion in defining reference levels and in developing protection strategies in the planning state.

Table A.1. Characteristics in ‘summer’ (release 1 July).

Sm_rel, small release; Lg_rel, large release.

Table A.2. Characteristics in ‘winter’ (release 1 December).

Sm_rel, small release; Lg_rel, large release.

(A5) The results presented in Table A.1, Table A.2 represent the conditions in the vicinity of a release. As a result of various processes (dilution due to atmospheric mixing and deposition on ground surfaces), the dose resulting from an airborne release will decrease with increasing distance between the point of release and the area for which protective measures have to be planned. Therefore, it is important to include this in the considerations during planning. Fig. A.1 demonstrates this effect for distances of 10km (top) and 100 km (bottom).

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• Fig. A.1. 

  Time-dependent contributions of projected doses received via various exposure pathways to the total dose in a year.

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Annex B. Characteristics of selected individual urgent protective measures 

B.1. Iodine thyroid blocking 

(B1) Iodine thyroid blocking is based on the administration of a compound of stable iodine (usually potassium iodide) to prevent or reduce the uptake of radioactive isotopes of iodine by the thyroid in the event of an accident involving radioactive iodine. Stable iodine is only of benefit in protecting the thyroid against radioactive iodine (reactor emergencies resulting in the release of radioactive iodine, laboratory emergencies, malicious events involving radioiodine).

(B2) Thyroid blocking prevents dose to the gland in case of exposure by inhalation and ingestion of radioiodines. However, as there is another measure that prevents radioiodine intake directly (restriction of potentially contaminated food consumption), thyroid blocking is considered to be primarily used for reduction of doses that result from inhalation. Iodine thyroid blocking should only be used to reduce the uptake of ingested radioiodine if it is impossible to provide supplies of uncontaminated food, especially for children and particularly in relation to milk; even if this is the case, iodine thyroid blocking is intended for relatively short periods of time, since efforts should be made to provide supplies of uncontaminated food as soon as possible. As iodine thyroid blocking is intended primarily as a protective measure against inhalation, it is therefore primarily a short-term measure (up to a few days) to reduce the risk of thyroid disease.

(B3) To obtain the maximum reduction of the radiation dose to the thyroid, stable iodine should be administered before any intake of radioiodine, or as soon as practicable thereafter. If stable iodine is administered orally within 6 h preceding the intake of radioactive iodine, the protection provided is almost complete; if stable iodine is administered at the time of radioiodine inhalation, the effectiveness of thyroid blocking is approximately 90%. The effectiveness of the measure decreases with delay, but the uptake of radioiodine can be reduced to approximately 50% if blocking is carried out within a few hours of inhalation.

B.2. Sheltering 

(B4) Sheltering is the use of the structure of a building to reduce exposure from an airborne plume and/or deposited materials. Solidly constructed buildings can attenuate radiation from radioactive materials deposited on the ground and reduce exposure to airborne plumes. Buildings constructed of wood or metal are not generally suitable for use as protective shelters against external radiation, and buildings that cannot be made substantially airtight are not effective in protecting against any exposures.

(B5) Sheltering is not recommended for longer than approximately 2 days (IAEA, 1994, IAEA, 1996, IAEA, 2006). Sheltering is easy to implement but, in most cases, cannot be carried out for long periods. In addition, sheltering can be used as a preparation for an evacuation. The people in an area of potential risk can be instructed to ‘go inside’ and listen to their radios for further instruction while preparations for evacuation are being made. However, for very severe reactor accidents, sheltering in a typical home may not be sufficient to prevent deterministic health effects close to the facility. Sheltering is not a long-term protective measure; therefore, monitoring must be performed promptly anywhere sheltering is used in order to locate and evacuate people from areas of high risk.

B.3. Evacuation 

(B6) Evacuation represents the rapid, temporary removal of people from an area to avoid or reduce short-term radiation exposure in an emergency exposure situation. It is most effective in terms of avoiding radiation exposure if it can be taken as a precautionary measure before there is any significant release of radioactive material. Generally, evacuation is not recommended for a period of longer than 1 week (IAEA, 1994, IAEA, 1996, IAEA, 2006).

B.4. Individual decontamination and medical intervention 

(B7) Individual decontamination is the complete or partial removal of contamination from a person by a deliberate physical, chemical, or biological process.

(B8) Urgent individual decontamination may be advised to reduce exposures to external radiation from contamination on skin or inadvertent ingestion of such contamination. This measure may be particularly useful for protecting emergency workers. It is unlikely that individual decontamination will be required outside the area in which evacuation has been advised.

B.5. Preventative agricultural actions 

(B9) Protective measures related to food can reduce or prevent doses from ingestion and include: a ban on the consumption of locally grown food in the affected area; the protection of local food and water supplies by, for example, covering open wells and sheltering animals and animal feed; and the long-term sampling and control of locally grown food and feed. Control of milk is very important because it is a significant part of the diet of children in many countries, as well as concentrating important radionuclides, such as radioiodine.

(B10) If appropriate, emergency plans should provide for considering the need for restriction of food consumption. Where they are needed, the population should be instructed not to drink milk from cows or goats that have been grazing on potentially contaminated pasture. In addition, they should be instructed not to eat fresh vegetables, fruit, or other food that may have been outside during the release and thereby contaminated. Drinking water is not typically a major concern during the initial response as it comes directly from collected rain water. However, water supplies should be monitored regularly during the response in case of a gradual build up of contamination owing to run-off into the water catchment area. If implemented, food and water restrictions should continue until sampling determines that food or milk is not contaminated beyond established levels.

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Annex C. Specific guidance for the termination of protective measures 

(C1) Although some protective measures may remain in effect for long periods, almost all protective measures will eventually need to be terminated. Some protective measures, particularly some of those that are implemented at an early stage, will, because of their nature (e.g. sheltering and use of stable iodine), be implemented for rather short periods (e.g. a one-off thyroid blocking with stable iodine, or sheltering implemented for few hours to a few days). Other measures, such as restrictions on the entry of food into the food chain, may last for longer periods of time. However, there are substantial risks associated with precipitate decisions to terminate protective measures before all the specific circumstances of the situation have been evaluated. For example, if protective measures are terminated too early, the situation may worsen unexpectedly, resulting in further exposures. The need for evaluation of the specific circumstances of the emergency and potential future exposures before making decisions on lifting protective measures means that it is difficult (or even potentially dangerous) to try to plan specific numerical guidance for this in advance. It is recognised that, to date, little guidance has been published on this topic. Therefore, the European Commission has developed a framework to assist the making of such decisions in real time. This annex discusses the Commission’s guidance. In addition, emergency response experts in Europe have been addressing this topic. A recent report on their initial conclusions has been published as part of the European ‘EURANOS’ project (Nisbet et al., 2008).

(C2) The key problem for the decision makers is to balance the need to terminate unnecessary restrictions on people’s lives with the need to ensure that the termination of protective measures does not expose them to unintended risks. This balance may vary between different population groups, and will be associated with considerable uncertainty. It may therefore be appropriate to treat population groups differently. Moreover, protective measures may be terminated at different times in different locations, as the required information on which to base the decision becomes available.

(C3) It may be appropriate to terminate protective measures for some groups of people, whilst continuing to recommend that they be left in place for other groups. This may be required because of local ‘hotspots’ or due to the inhomogeneity of the detailed monitoring. Whilst there may be clear radiological justification for this approach to lift protective measures, the potential for increased anxiety and misunderstanding of the revised advice needs to be recognised and addressed.

(C4) Owing to the passage of time and the possibility of scaling down the response, it is important for the decision makers to consider whether to replace existing protective measures with alternative measures. A prime example of this is sheltering. Sheltering cannot be maintained for a long period of time. From a radiological protection perspective, the protection afforded by sheltering will decrease with time, as radionuclides increasingly penetrate from the outside into the building. People require access to food, medicines, exercise, and contact with other people. Therefore, at some point, it will be necessary to discontinue sheltering, regardless of whether or not the release has stopped. At this point in time, the decision makers have to consider whether to terminate the advice to shelter altogether, or whether to replace it with alternative advice, such as evacuation.

(C5) Whilst every accident will have specific characteristics that influence decisions on how and when protective measures should be withdrawn, it is possible to provide general guidance on issues that require consideration and evaluation before such decisions are made. The following sections provide this guidance for the termination of protective measures implemented at an early stage, and the termination of those implemented at a later stage.

C.1. Guidance on the termination of urgent protective measures 

(C6) The prime protective measures likely to be considered initially are the administration of stable iodine, advice to shelter or evacuate, and advice to avoid foods that may have become contaminated until a measurement programme can provide the information necessary to give more detailed advice regarding protective measures for food. The factors that require consideration for the termination of these protective measures differ between termination at an early stage and termination at a later stage after an accident.

(C7) There will be no requirement to consider the termination of evacuation or initial food advice until after the release has stopped. In the case of stable iodine, the decision is whether to advise a second administration of stable iodine in the event of a release lasting for more than 1day, rather than whether or not to terminate this protective measure. In this situation, the Commission advises that if the population would otherwise require a second administration, every effort should be made to evacuate the population until the cessation of the release. Sheltering, however, is different. It may be necessary to terminate sheltering after a short period of time, either because it is not possible to maintain the measure for an extended period of time, or because it is decided that the population should be evacuated. In these situations, it is particularly important to determine how exposures and public anxiety and confidence will be impacted by the decision. Such decisions should be based on an informed understanding of the needs and concerns of the people affected, ideally through dialogue with potentially affected population groups prior to the occurrence of any accident. Such dialogue will assist in managing the expectations of those affected, so that sheltering followed by evacuation is expected. It will also inform decisions concerning how long sheltering can be maintained by different population groups, and whether specific support measures, such as the provision of emergency supplies and re-uniting of families, are practical alternatives to the early termination of sheltering.

(C8) As the emergency situation is developing, there may be very strong pressure to terminate all protective measures. However, it is important to fully evaluate the options and their likely consequences, and to avoid making precipitate decisions. Decisions to withdraw sheltering, evacuation, and food advice will need to reflect the prevailing circumstances of the emergency situation being addressed. Premature decisions to withdraw protective measures before all of the specific circumstances of the situation have been evaluated may result in further exposures if the situation worsens unexpectedly. In general, protective measures implemented at an early stage will be withdrawn because they have achieved their desired effect, or their continued application will cause more harm than good (e.g. sheltering for an extended period becomes too disruptive). Many different aspects must be taken into account when reaching such decisions, and as with all decisions regarding termination of protective measures, it is important to involve, wherever possible, relevant stakeholders in discussions. While it will be difficult, if not impossible, to discuss decisions with sheltered populations, it will be essential to discuss decisions to return to evacuated areas with those who have been evacuated. Non-radiological (e.g. economic, social, and psychological) consequences may become worse than the radiological consequences if there is a lack of pre-established guidance that is understandable to the public and officials. Table C.1, Table C.2, Table C.3, Table C.4 summarise the key issues that should be considered.

Table C.1. Checklist for terminating the advice to shelter.

Issue	Comments/considerations
Duration	Unlikely to be practicable for more than 1day.
Release status	Partial lifting (e.g. re-uniting of families) or phased evacuation may be considered before formal advice is given that the release has been terminated.
Contamination	Detailed monitoring in the sheltered area is likely to be a priority. Ensure that measurements are ‘published’ for access by media and public.
Information	Withdrawal of advice to shelter will probably be carried out without significant interaction with stakeholders because of the short time scales involved.
Health	Detailed information for all those affected is required for subsequent dose estimation and decisions on health follow-up programmes.
Stakeholders	Those affected should have been given the opportunity to contribute to the development of a protection strategy for withdrawing sheltering. They may need a mechanism to provide an input into decisions on the recovery strategy, should one be required.
Order of priority	Decisions on withdrawing sheltering will normally be accorded the highest priority.

Table C.2. Checklist for terminating the advice to evacuate.

Issue	Comments/considerations
Duration	Prolonged evacuation requires the provision of acceptable living conditions; many evacuation centres cannot provide such conditions. Supervised visits to the evacuated area in order to retrieve personal belongings or deal with animals left behind may reduce pressure for an early lifting of evacuation.
Release status	If a release occurs, the need to delay decisions on lifting of evacuation until a formal statement can be given that the release has definitely been terminated means that emergency plans should assume that evacuation will last from several days up to perhaps 1week.
Contamination	Priority should be given to monitoring those areas in which it is expected that withdrawal of evacuation can take place. Measurement results should be ‘published’ for access by the media and the public.
Information	It is important to establish a mechanism for direct information and dialogue with the evacuees prior to their return to the area.
Health	Detailed information for all those affected is required for subsequent dose estimation and decisions on health follow-up programmes.
Stakeholders	Those affected should have been given the opportunity to contribute to the development of a protection strategy for stable iodine blocking. They may need a mechanism to provide input into decisions on the recovery strategy, should one be required.
Order of priority	Lower priority (relative to decisions on withdrawal of sheltering).

Note: it is important to distinguish between the admission of closely supervised people into an evacuated area in order to monitor, retrieve items, undertake maintenance activities, or provide security, and the provision of advice to an evacuated population to return home. This table provides a checklist for consideration before full withdrawal of evacuation.

Table C.3. Checklist for deciding that further doses of stable iodine should not be administered.

Issue	Comments/considerations
Duration	One dose of stable iodine will provide protection for approximately 24h. Normally, evacuation would be preferred to administration of a second dose. Where the potential for prolonged releases indicates that multiple administrations to a sheltering population may be required, the emergency plan should address how this will be achieved.
Release status	Multiple administrations should not be considered unless a release is actually detected more than 24h after the first administration, and evacuation is not practicable.
Contamination	Ideally, stable iodine prophylaxis should not be used to provide protection against contamination of food. Wherever practicable, restrictions on food should be implemented to provide protection against intake by ingestion.
Information	Stable iodine prophylaxis should be combined with either sheltering or evacuation, and has the same associated needs for information provision.
Health	The thyroids of infants born shortly before or shortly after the accident should be monitored individually if either the child or the mother received stable iodine. Details of all those who received stable iodine should be recorded in case of subsequent health problems.
Stakeholders	Those affected need a mechanism to provide input into decisions on the recovery strategy.
Order of priority	The multiple administration of stable iodine is only relevant to a sheltering population, which would normally be afforded the highest priority.

Table C.4. Checklist for terminating initial advice to avoid foods that may have been contaminated.

(C9) One key difference between protective measures implemented at an early stage and those implemented at a later stage is that the former are likely to have been implemented on the basis of limited information concerning the actual situation and its impact. By the time when no further release is judged likely, additional information will have been gathered. This may demonstrate that the initial actions were an over-response, in which case there will be a strong incentive for those responsible for managing the response to reduce the extent and severity of protective measures as promptly as possible. However, even for these situations, it is important to ensure that the issues in Table C.1, Table C.2, Table C.3, Table C.4 are explored in order to avoid the possibility of unexpected problems subsequently emerging.

C.2. Guidance on the termination of protective measures implemented in later stages 

(C10) There is an important difference between protective measures initiated at an early stage and those implemented at later stages of an emergency exposure situation. The primary aim of urgent protective measures is to protect people from relatively high, short-term exposures. Decisions on their implementation are likely to be taken in a context of significant uncertainty. However, as the situation develops further, it will be much better characterised, whilst the protective measures put in place may well need to continue for weeks or months. These differences mean that for protective measures implemented at a later stage, it is both possible and desirable to establish the criteria for terminating those measures in advance of their initiation. These ‘termination’ criteria should be defined in terms of directly measurable or observable quantities, so that it is clear when they have been met. The criteria should also be discussed and agreed with stakeholders, so that the termination of the relevant protective measures is accepted. For some measures, e.g. permanent relocation, the criteria may be expressed in terms of the residual dose rates in the areas to be returned to; for others, such as decontamination, they are more likely to be expressed as the maximum level of residual contamination that will be accepted on the surface subject to a particular decontamination technique.

(C11) Protective measures implemented at later stages do not need to be initiated as urgently as those implemented at an early stage. This means that more time is available for dialogue with those who will be affected in order to implement the measures in a way that is truly optimal for stakeholders. Whilst it may not be possible to meet the expressed priorities of every individual, the process of involving stakeholders in decisions that are affecting their lives can help to reduce anxieties and frustrations, and contribute towards an efficient transition to management of the situation as an existing exposure situation.