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| REVIEW ARTICLE |
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| Year : 2015 | Volume
: 38
| Issue : 3 | Page : 68-71 |
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Emergency exposure situations: An update
Pushparaja
Ex-Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India
| Date of Web Publication | 10-Nov-2015 |
Correspondence Address:
Pushparaja
D-801, Synchronicity, Nahar Amrit Shakti Road, Chandivali Powai, Mumbai - 400 072, Maharashtra
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0972-0464.169372
International Commission on Radiological Protection (ICRP) publication 103 (2007) provided the basic recommendations on radiological protection to cover all radiation exposure situations. It has provided dose limits, dose constraints, and reference levels for use in such situations. Based on these recommendations, International Atomic Energy Agency (IAEA), in its revised basic safety standards (BSS, 2014), provided generic requirements and guidance levels for use by the operators, radiation protection professionals, and the regulators. However, these are generic in nature, and national regulatory authorities are required to decide on the levels for use in their own emergency preparedness and response plans as appropriate: This article just updates the present scenario for emergency exposure situations. The information/material provided in this paper is extracted from the documents listed in the references. For detailed information required for any medical/legal purposes, the readers are expected to refer to the original documents, ICRP-103 (2007) and IAEA-BSS-2014. Keywords: Emergency exposure situations, International Atomic Energy Agency-basic safety standard (2014), International Commission on Radiological Protection-103 (2007), reference level
How to cite this article:
Pushparaja. Emergency exposure situations: An update. Radiat Prot Environ 2015;38:68-71 |
| Introduction | |  |
A certain level of exposure to radiation is expected to occur due to operation of a source in planned exposure situations. During the course of an assessment of the situations, exposures from events such as deviations from planned operating procedures or accidents, with potential for exposure of large number of people resulting in health risks and other detriments are also considered. [1] Such potential exposures can turn out to be real exposures if a serious accident occurs during operation of a planned situation or any malicious event. Such situations are termed as emergency exposure situations and the situations require urgent action to avoid or reduce the undesirable consequences to humans and the environment.
[TAG:2]ICRP PUBLICATION 103, 2007 [2][/TAG:2]
The ICRP publication 96 (2005) [3] recommends occupational exposure of 1000 mSv effective dose to avoid serious deterministic effects and keep the exposures below 500 mSv to avoid other deterministic effects. The exposures for other urgent rescue operations, the recommended occupational exposure are ≤100 mSv. ICRP publication (ICRP-103, 2007) recommends no dose restrictions if the benefits to others outweigh rescuer's risk.
ICRP 1990 recommendations (ICRP-60, 1991) [4] provided intervention levels for public exposures, viz., foodstuffs, distribution of stable iodine, sheltering, temporary evacuation, and permanent relocation. The ICRP-103 (2007), [2] allows flexibility of selecting doses in the band of 20 to 100 mSv of projected dose depending on the seriousness of the situation. Following this immediate action of selecting a reference level, projected residual dose distribution is assessed using the selected reference level as the benchmark. Protection strategy that would not reduce the residual doses to below the reference level is rejected at the planning stage. However, if the projected dose (the dose which would have been received if no protective actions were taken) is closer to 100 mSv, protective actions are almost always justified. Since in emergency situations, the dose rate can rise to high levels in a short time, appropriate protective actions need to be taken to prevent severe deterministic effects, considering societal, economic, and other consequences.
The 2007 recommendations emphasize the importance of justification and optimization of the protection strategies for application in emergency exposure situations. The selected reference level is used for the optimization of protection. Possible multiple exposure pathways need to be taken into account while considering protection strategy. The protection strategy is likely to be modified, since the emergency situation is unpredictable, the affected persons and the consequences may change with time and place. Particular attention is given to pregnant women and small children.
The ICRP defines the three terms, viz., projected dose, averted dose, and residual dose. Projected dose is the dose which is projected to occur in the absence of taking any protective actions. Averted dose is the dose avoided by the set of protective actions (or countermeasures). It is the difference between the projected dose in the absence of any protective actions and the actual projected dose. Averted dose is used in the optimization process, and it is the individual dose that will be averted due to the protective actions taken. [5]
Residual dose is the chronic dose expected to be incurred after the protective actions are implemented. The reference levels (20 mSv-100 mSv) recommended by the ICRP are the planned maximum residual doses to an individual, acute or on an annual basis, not to exceed as a result of emergency. The reference level selected is used in the process of optimization. However, the ICRP now recommends optimization of overall protective strategy rather than the individual measures.
The emergency response as quoted in the ICRP 103 (Para 282) is, "In the event that an emergency exposure situation occurs, the first issue is to recognize its onset. The initial response should be to follow the emergency plan in a consistent but flexible way. The protection strategy initially implemented will be that described in the emergency plan for the relevant event scenario, based on the generic optimization undertaken as part of the planning stage. Once the measures in the emergency plan have been initiated, emergency response can be characterized by an iterative cycle of review, planning, and execution."
| IAEA-BSS (2014) | | |
As per the latest International Atomic Energy Agency (IAEA) basic safety standards (BSS) (2014) GSR Part 3, the generic requirements governing the emergency exposure situations are:
A. The government shall ensure that an integrated and coordinated emergency management system is established and maintained (Requirement no. 43).
The emergency management system is established to respond to any nuclear or radiological emergency to protect human life, health, and the environment. The system is designed based on the hazard assessment to enable it to respond effectively to reasonable foreseeable events at local, national, and international levels. Some of the essential elements are:
- Clear allocation of responsibilities to individuals and organizations and their roles in the arrangement for emergency preparedness and response
- Provision for monitoring, individuals, and environment and for dose assessment
- Arrangements for the medical response and the public health response in an emergency
- Effective communication system for conveying information to the responders and the public
- Education and training of all persons involved in the management of emergency situation.
B. Preparedness and Response for an emergency (Requirement 44).
The government shall ensure that protection strategies are developed, justified, and optimized at the planning stage, and that emergency response is undertaken by their timely implementation.
The major steps in the development of a protection strategy are:
- Setting of an appropriate reference level expressed in terms of residual effective dose in the dose band of 20 to 100 mSv to cover all exposure pathways. The protection strategy shall be so planned and optimized as to maintain the doses as low as reasonably achievable below the selected reference level
- Optimization of the protection strategy using the reference level and based on the outcome, a set of generic criteria for protective actions and other response actions are developed. The numerical numbers are in terms of projected dose or that of dose that has been received
- Operational criteria, such as operational intervention levels and emergency action levels derived from the generic criteria, are expressed in terms of on-scene observable parameters or conditions. These are primarily for the initial phase of the emergency situation. Depending on the prevailing conditions, as they evolve, the operational criteria may need to be revised.
The emergency situations are dynamic and decisions taken at any given time may change depending on the prevailing conditions and requirements at the site. However, every protective action needs to be justifiable in the context of the protection strategy.
The government authority ensures that:
- Protective or response actions are taken promptly to avoid exposures or to keep exposures below the levels which will cause severe deterministic effects
- Effectiveness of the protective/response actions taken is assessed, and modify the actions if required
- Compare the residual doses or the doses actually received with the reference level and develop a set of general criteria for the protective action taken. Focus on the group which exceeds the reference level
- Based on the generic criteria available, operational criteria such as intervention/action levels are established account being taken of the prevailing/observable field information. Further protective strategies may be implemented as required.
C. Arrangements for controlling the exposure of emergency workers (Requirement 45).
A program needs to be established by the government for managing, controlling, and recording the doses received by the emergency workers and ensure that it is being implemented through the response organizations or employers. The response organizations or employers are required to ensure that no worker receives doses in excess of 50 mSv. Exceptions being:
- For saving life or preventing serious injury
- For preventing development of serious catastrophic conditions that could significantly affect people and the environment
- For actions to avert a large collective dose.
Such exposures are acceptable in situations where the expected benefits clearly outweigh the risks to the emergency workers. The workers are well-aware of the risks of exposure, and the actions by the emergency workers are voluntary. As per the BSS (2014), the doses received in an emergency by emergency workers and the associated health risks need to be communicated to the workers.
The workers who receive doses in an emergency situation are not precluded from incurring further occupational exposures. However, if a worker receives dose exceeding 200 mSv, or if the worker requests for it, qualified medical advice has to be obtained before any further occupational exposure. As per the ICRP-103, the responders undertaking the recovery and restoration operations are considered as occupationally exposed workers and their exposures are governed by the applicable dose limits.
D. Arrangements for transition from an emergency exposure situation to an existing exposure situation (Requirement 46).
Existing exposure situation, in this case, is the exposure scenario after the declaration of ending of a nuclear/radiological emergency, and the exposures are the result of residual radioactive materials. It is the responsibility of the government to ensure that as part of an overall emergency preparedness, arrangements are in place for the transition from emergency exposure situation to an existing exposure situation. The arrangements for coordinated and orderly transition to existing exposure situation include identifying the responsible authority for taking decision, and transfer of the responsibilities in consultation with all the involved parties.
Protection of all the personnel involved in undertaking the above transition work is governed by the requirements for occupational exposure in planned exposure situations.
Generic criteria
IAEA-BSS (2014) [6] provides quantitative generic criteria for exposures received within a short period of time for which protective response actions are undertaken, under any circumstances to avoid or minimize severe deterministic effects. The generic guidance values are given in [Table 1]A and B.
Guidance value of personal dose equivalent, H p (10) of <500 mSv, is also recommended by the BSS for restricting exposure of emergency workers for life-saving actions. The value may be exceeded if the benefits to others outweigh the health risks of the emergency workers, who volunteer to take the action, and the associated health risk is acceptable to them. The same guidance value is also applicable for actions being taken to prevent severe deterministic effects or to prevent the development of catastrophic conditions likely to affect people and the environment. Personal dose equivalent of <100 mSv is also acceptable for actions to avert a large collective dose.
(Note: The guidance values apply only to external exposure to strongly penetrating radiation. It is expected to prevent, by all possible means, exposure from weakly ionizing radiation, skin contamination, and any intakes. If not possible, minimize the health risk to the individuals).
| Conclusions | | |
The IAEA-BSS (2014) gives additional quantitative generic criteria for application in emergency exposure situations in addition to the personal dose equivalent values similar to the ICRP values. [2] These provide generic criteria and guidance for national regulatory authorities to frame their own country-specific appropriate preparedness plan (Atomic Energy Regulatory Board [AERB], 2014). [7]
Reference levels selected (based on the informed judgment) is used in the process of optimization, and as the situation evolves, the expected residual dose values after the protection measures taken are compared with the initial reference level to judge the adequacy of the measures taken. It is expected that the residual doses are below the reference level. Any protection strategy which is unable to bring down the residual doses below the reference level is be reviewed, rejected, or revised.
In the real time, when an emergency situation occurs, the onset of the situation is recognized and the initial emergency response measures taken will be as per the approved emergency plan specific for the event scenario, which may be facility-specific, site-specific, or at national level. The response includes: Collect relevant information from the affected facility and the prevailing meteorological conditions, assess the type and amount of radioactivity release, initiate area and air monitoring, assess dose levels and contamination levels, etc., Any further response will follow the continuous cycle of review of its impact, further planning, and execution.
Once the emergency situation is called off, the management of the persistent low-level contamination, often over large area, will be managed as existing exposure situation.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
| References | | |
| 1. | International Commission on Radiological Protection (ICRP). Protection from Potential Exposures: Application to Selected Radiation Sources, ICRP Publication 76. 1997.  |
| 2. | International Commission on Radiological Protection (ICRP). The 2007 Recommendations of the International Commission on Radiological Protection, ICRP Publication 103. Elsevier; 2007. |
| 3. | International Commission on Radiological Protection (ICRP). Protecting People Against Radiation Exposure in the Event of a Radiological Attack, ICRP Publication 96. 2005. |
| 4. | International Commission on Radiological Protection (ICRP). 1990 Recommendations of the International Commission on Radiological Protection, ICRP Publication 60. 1991. |
| 5. | International Commission on Radiological Protection (ICRP). Principles for Intervention for Protection of the Public in a Radiological Emergency, ICRP Publication 63. 1992. |
| 6. | International Atomic Energy Agency (IAEA). Radiation Protection and Safety of Radiation Sources: International Basic Safety Standards, General Safety Requirements Part 3. Vienna: IAEA; 2014. |
| 7. | Atomic Energy Regulatory Board (AERB). Criteria for Planning, Preparedness and Response for Nuclear or Radiological Emergency, AERB Safety Guide, AERB/NRF/SG/EP-5 (Rev. 1). Mumbai, India: AERB; 2014. |
[Table 1]
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