ICRP Publication 109
Application of the Commission's Recommendations for the Protection of People in Emergency Exposure Situations
Recommended citation
ICRP, 2009. Application of the Commission's Recommendations for the Protection of People in Emergency Exposure Situations. ICRP Publication 109. Ann. ICRP 39 (1).
Abstract - This report was prepared to provide advice on the application of the Commission’s 2007 Recommendations. The advice includes the preparedness for, and response to, all radiation emergency exposure situations defined 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’. An emergency exposure situation may evolve, in time, into an existing exposure situation. The Commission’s advice for these types
of situation is published in two complementary documents (that for emergency exposure situations in this report, that for existing exposure situations following emergency exposure situations in a forthcoming report entitled ‘Application of the Commission’s recommendations to the protection of individuals living in long-term contaminated territories after a nuclear accident or a radiation emergency’).
The Commission’s 2007 Recommendations re-state its principles of justification and optimisation, and the requirement to protect against severe deterministic injury, as applying to emergency exposure situations. For the purpose of protection, reference levels for emergency exposure situations should be set in the band of 20–100 mSv effective dose (acute or per year). 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. The Commission considers that a dose rising towards 100 mSv will almost always justify protective measures. Protection against all exposures, above or below the reference level, should be optimised.
More complete protection is offered by simultaneously considering all exposure pathways and all relevant protection options when deciding on the optimum course of action in the context of an overall protection strategy. Such an overall protection strategy must be justified, resulting in more good than harm. In order to optimise an overall 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. If, in application of an overall protection strategy, protection measures do not achieve their planned residual dose objectives, or worse, result in exposures exceeding reference levels defined at the planning stage, a re-assessment of the situation is warranted. In planning and in the event of an emergency, decisions to terminate protective measures should have due regard for the appropriate reference level.
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, and may take place at different geographical locations at different times. The transfer should be undertaken in a co-ordinated and fully transparent manner, and should be understood by all parties involved.
© 2009 ICRP. Published by Elsevier Ltd. All rights reserved. Keywords: Emergency exposure situation; Reference level; Constrained optimisation; Protection strategy.
Key Points: Not included in this publication
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 20 mSv and 100 mSv effective dose (acute or per year, as applicable to the emergency exposure situation under consideration). Reference levels below 20 mSv 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 100 mSv 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,b) 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 coordinated 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 20 mSv/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.
References
ICRP, 1991a. 1990 Recommendations of the International Commission on Radiological Protection. ICRP Publication 60. Ann. ICRP 21(1–3).
ICRP, 1991b. Principles for intervention for protection of the public in a radiological emergency. ICRP Publication 63. Ann ICRP 22(4).
ICRP, 2005. Protecting people against radiation exposure in the event of a radiological attack. ICRP Publication 96. Ann. ICRP 35(1).
ICRP, 2007. The 2007 Recommendations of the International Commission on Radiological Protection. ICRP Publication 103. Ann. ICRP 37(2–4).
ICRP, 2009. Application of the Commission's Recommendations for the Protection of People in Emergency Exposure Situations. ICRP Publication 109. Ann. ICRP 39 (1).
Abstract - This report was prepared to provide advice on the application of the Commission’s 2007 Recommendations. The advice includes the preparedness for, and response to, all radiation emergency exposure situations defined 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’. An emergency exposure situation may evolve, in time, into an existing exposure situation. The Commission’s advice for these types
of situation is published in two complementary documents (that for emergency exposure situations in this report, that for existing exposure situations following emergency exposure situations in a forthcoming report entitled ‘Application of the Commission’s recommendations to the protection of individuals living in long-term contaminated territories after a nuclear accident or a radiation emergency’).
The Commission’s 2007 Recommendations re-state its principles of justification and optimisation, and the requirement to protect against severe deterministic injury, as applying to emergency exposure situations. For the purpose of protection, reference levels for emergency exposure situations should be set in the band of 20–100 mSv effective dose (acute or per year). 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. The Commission considers that a dose rising towards 100 mSv will almost always justify protective measures. Protection against all exposures, above or below the reference level, should be optimised.
More complete protection is offered by simultaneously considering all exposure pathways and all relevant protection options when deciding on the optimum course of action in the context of an overall protection strategy. Such an overall protection strategy must be justified, resulting in more good than harm. In order to optimise an overall 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. If, in application of an overall protection strategy, protection measures do not achieve their planned residual dose objectives, or worse, result in exposures exceeding reference levels defined at the planning stage, a re-assessment of the situation is warranted. In planning and in the event of an emergency, decisions to terminate protective measures should have due regard for the appropriate reference level.
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, and may take place at different geographical locations at different times. The transfer should be undertaken in a co-ordinated and fully transparent manner, and should be understood by all parties involved.
© 2009 ICRP. Published by Elsevier Ltd. All rights reserved. Keywords: Emergency exposure situation; Reference level; Constrained optimisation; Protection strategy.
Key Points: Not included in this publication
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 20 mSv and 100 mSv effective dose (acute or per year, as applicable to the emergency exposure situation under consideration). Reference levels below 20 mSv 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 100 mSv 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,b) 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 coordinated 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 20 mSv/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.
References
ICRP, 1991a. 1990 Recommendations of the International Commission on Radiological Protection. ICRP Publication 60. Ann. ICRP 21(1–3).
ICRP, 1991b. Principles for intervention for protection of the public in a radiological emergency. ICRP Publication 63. Ann ICRP 22(4).
ICRP, 2005. Protecting people against radiation exposure in the event of a radiological attack. ICRP Publication 96. Ann. ICRP 35(1).
ICRP, 2007. The 2007 Recommendations of the International Commission on Radiological Protection. ICRP Publication 103. Ann. ICRP 37(2–4).
