The massive earthquake and resulting tsunami on 11 March 2011 that struck the northeast coast of Japan disabled the Fukushima Daiichi nuclear plant. The earthquake triggered the shutdown of the three active reactors at the plant and the subsequent tsunami stopped the plant's backup diesel generators, causing a station blackout. The subsequent lack of cooling led to explosions and partial meltdowns at the plant facility, with problems at all six reactor units and the central spent fuel pool. Radiation releases1 caused large evacuations, concern over food and water supplies, and the treatment of nuclear and emergency workers.
Risks for the emergency workers
Workers working in response to the emergency at the site of the Fukushima Daiichi's nuclear plant are exposed to traditional OSH risks including explosion and fire as well as to radiation.
Exposure to ionizing radiation can induce the death of cells on a scale that can be extensive enough to impair the function of the exposed tissue or organ. At whole-body doses approaching 1Gray (Gy) and above, acute health effects such as acute radiation syndrome may develop. The effect is more severe for a higher dose.
Exposure to moderate levels can result in radiation sickness, which produces a range of symptoms. Nausea and vomiting often begin within hours of exposure, followed by diarrhoea, headaches and fever.
After the first round of symptoms, there may be a brief period with no apparent illness, but this may be followed within weeks by new, more serious symptoms.
At higher levels of radiation, all of these symptoms may be immediately apparent, along with widespread - and potentially fatal - damage to internal organs. Exposure to a radiation dose of 4 Gy will typically kill about half of all healthy adults.
Exposure to radiation can also induce the non-lethal transformation of cells, which may still retain their capacity for cell division. The human body’s immune system is very effective in detecting and destroying abnormal cells. However, there is a possibility that the non-lethal transformation of a cell could lead, after a latency period, to cancer in the individual exposed, if it is a somatic cell; or may lead to hereditary effects, if it is a germ cell. Such effects are assumed to be proportional to the dose received and have no threshold. The “detriment-adjusted nominal risk coefficient of dose”, which includes the risks of all cancers and hereditary effects, is 5% per sievert (Sv).
Prevention and protection measures for emergency workers
The International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources (BSS), formally published in 1996, are jointly developed and sponsored by the Food and Agriculture Organization of the United Nations (FAO), the IAEA, the ILO the Nuclear Energy Agency of the Organization for Economic Co-operation and Development (OECD/NEA), the Pan American Health Organization (PAHO) and the World Health Organization (WHO). The BSS provide a worldwide basis for harmonized radiation protection standards that complement the ILO Convention No. 115. As to the protection of workers engaged in nuclear and radiological emergency operation, the BSS stipulate:
V.27. No worker undertaking an intervention2 shall be exposed in excess of the maximum single year dose limit for occupational exposure specified in Schedule II, except:
(a) for the purpose of saving life or preventing serious injury;
(b) if undertaking actions intended to avert a large collective dose; or
(c) if undertaking actions to prevent the development of catastrophic conditions.
When undertaking intervention under these circumstances, all reasonable efforts shall be made to keep doses to workers below twice the maximum single year dose limit, except for life saving actions, in which every effort shall be made to keep doses below ten times the maximum single year dose limit in order to avoid deterministic effects on health. In addition, workers undertaking actions in which their doses may approach or exceed ten times the maximum single year dose limit shall do so only when the benefits to others clearly outweigh their own risk.
V.28. Workers who undertake actions in which the dose may exceed the maximum single year dose limit shall be volunteers3 and shall be clearly and comprehensively informed in advance of the associated health risk, and shall, to the extent feasible, be trained in the actions that may be required.
V.29. The legal person responsible for ensuring compliance with the foregoing requirements shall be specified in emergency plans.
V.30. Once the emergency phase of an intervention has ended, workers undertaking recovery operations, such as repairs to plant and buildings, waste disposal or decontamination of the site and surrounding area, shall be subject to the full system of detailed requirements for occupational exposure prescribed in Appendix I.
V.31. All reasonable steps shall be taken to provide appropriate protection during the emergency intervention and to assess and record the doses received by workers involved in emergency intervention. When the intervention has ended, the doses received and the consequent health risk shall be communicated to the workers involved.
V.32. Workers shall not normally be precluded from incurring further occupational exposure because of doses received in an emergency exposure situation. However, qualified medical advice shall be obtained before any such further exposure if a worker who has undergone an emergency exposure receives a dose exceeding ten times the maximum single year dose limit or at the worker's request.
Annex – Dose limits for workers engaged in nuclear and radiological emergencies in
The Radiation Protection Regulations state the following under the heading “Emergencies”:
15. (1) During the control of an emergency and the consequent immediate and urgent remedial work, the effective dose and the equivalent dose may exceed the applicable dose limits prescribed by sections 13 and 14, but the effective dose shall not exceed 500 mSv and the equivalent dose received by the skin shall not exceed 5 000 mSv.
(2) Subsection (1) does not apply in respect of pregnant nuclear energy workers who have informed the licensee in accordance with subsection 11(1).
(3) The dose limits prescribed by sections 13 and 14 and subsection (1) may be exceeded by a person who acts voluntarily to save or protect human life.
Note that sections 13 and 14 stipulate the “regular” equivalent and effective dose limits for both workers and the public.
The present regulation is the following:
- 100 mSv during the whole intervention (emergency exposure situations)
- 300 mSv when the intervention is for saving lives which can be exceeded in exceptional circumstances for saving human lives. These exceptional cases require special authorization with voluntary rescue operators well informed about the risk they take.
- In no case the total cumulated effective dose must exceed 1 Sv.
The above values are for "specialists" of interventions in emergency situations (people who have received a special training).
For "non-specialists" the reference level is 10 mSv per intervention (these people are only informed about the risk).
The Republic of Korea
The Korean regulations which adopted the 1990 ICRP Recommendations set the dose limits for emergency workers as follows:
- Effective dose: 500 mSv
- Skin (extremity): 5 Sv(Gy)
- No limits in case of life saving actions.
The regulations include no specific criteria for applying these limits.
The Russian Federation
The Russian regulations of Radiation Safety Standards NRB-99/2009
Maximum doses for emergency workers in the emergency exposure situations are:
- Effective dose 200 mSv;
- Equivalent dose to the lens of the eye – 600 mSv;
- Equivalent dose to the skin – 2000 mSv;
- Equivalent dose to the extremity – 2000 mSv.
1 On 11 March 2011, the Japanese government declared a "nuclear power emergency", evacuated residents living within a 20 km (12 mile) zone around the plant and urged that those living between 20 km and 30 km from the site to stay indoors. The latter zone was later subject to voluntary evacuation. About 170,000–200,000 people were evacuated after officials voiced the possibility of core damage. On 18 March, based on the International Nuclear and Radiological Event Scale (INES), the Japanese Ministry of Economy, Trade and Industry assessed the safety significance rating of the accident at the plant as Level 5. On 12 April, this assessment was revised to Level 7 following information obtained from estimations of the amount of radioactive material discharged to the atmosphere.
2 Workers undertaking an intervention may include, in addition to those employed by registrants and licensees, such assisting personnel as police, firemen, medical personnel and drivers and crews of evacuation vehicles.
3 Workers undertaking an intervention may include, in addition to those employed by registrants and licensees, such assisting personnel as police, firemen, medical personnel and drivers and crews of evacuation vehicles.