1The threat categories are discussed in paras 2.19 and 2.20.

2A dangerous source is a source that could, if not under control, give rise to exposure sufficient to cause severe deterministic health effects. This categorization is used for determining the need for emergency response arrangements and is not to be confused with categorizations of sources for other purposes. Dangerous sources are discussed further in Appendix III.

3A serious overexposure is one that can result in severe deterministic health effects.

4‘Severe deterministic effect’ is defined in the Glossary under ‘deterministic effect’.

5In the Chernobyl accident, dose rates off the site were higher than 1 Gy/h from the deposition of radioactive material, which is sufficient to cause severe deterministic health effects within a few hours [15]. Fortunately, these dose rates occurred only in uninhabited areas.

6As of 2000 no excess solid cancers had been observed among the approximately 200 000 people who performed recovery operations within the 30 km zone in 1986–1987 where the highest doses were received following the Chernobyl accident [15]. However, a major increase was detected in the incidence of thyroid cancer among those persons who had received radiation doses as a foetus or child following the Chernobyl accident.This detectable increase in incidence in this population group was due to a very largerelease of radioiodine, resulting in high thyroid doses in hundreds of thousands of children (primarily due to the consumption of contaminated milk and leafy vegetables).This radiation induced rise in cancer incidence was easily detected epidemiologicall because of the very low spontaneous rate of thyroid cancers among the children.

7Studies on adverse consequences relating to the Chernobyl accident have been performed in those areas close to the plant where the doses were highest. “So far, no increase in birth defects, congenital malformations, stillbirths, or premature births could be linked to radiation exposure caused by the [Chernobyl] accident” [15].

8In one emergency, a family member picked up a tiny, shiny cylinder (a lost radiography source) and took it home. This resulted in the deaths of eight family members and relatives in the following three months [21].

9See Table 9 for the D values of different radionuclides.

1010 Appendix III provides a plain language explanation of the possible impacts of emergencies involving dangerous sources.

11Resuspension could be an important pathway of exposure if the deposited material contains significant amounts of alpha emitters (e.g. Pu).

12Criticality accidents cannot produce sufficient amounts of fission products to result in a significant airborne radioactive release; however, the energy produced could result in an airborne release of other hazardous material that may be present at the time of the criticality.

13The term ‘threat assessment’ does not imply that any threat, in the sense of an intention and capability to cause harm, has been made in relation to such facilities, activities or sources.

14For example, to notify promptly those States with territory within the emergency zones in the event of a general emergency.

15Including events with a very low estimated probability of occurrence.

16Annex II of Ref. [2].

17Annex III of Ref. [2].

18Annex I of Ref. [2].

19See Annexes II and III of Ref. [2].

20For facilities it may be possible for the criteria for decisions on protective actions to be established at the time of the emergency, provided that there is a high degree of assurance that they can be established and implemented immediately upon the receipt of field monitoring results.

21For example, in some emergencies first responders have been reluctant to perform life saving actions or to treat victims because of indications that radioactive material was present.

22After the Chernobyl accident, imposition of restrictions on the consumption of contaminated milk was delayed for several days. This delay probably resulted in several thousand avoidable cases of thyroid cancer among children.

23In most cases, a meeting was held to decide what to do and who should do it. In addition, the decision makers were untrained (often they were too busy to attend training courses or exercises). In one case, a regulatory body interfered in the process for making decisions on protective actions even though it had no designated role in this area.

24Such infrastructure includes, for example, buildings and transport networks.

25The full range of possible emergencies includes those of very low probability.

26During the Three Mile Island emergency in the USA in 1979, the President of the USA directed that all official information should come from one place in order to prevent the confusion that resulted from providing information from several places [32].

27The IAEA and WHO have, under the terms of the Assistance Convention [1], arranged for consultations with or treatment at international specialized centres in numerous emergencies.

28See the guidelines reproduced in Annex III of Ref. [2].

29This includes measures relating to livestock, food production, gardens, forest products, fishing and water supplies.

30Inappropriate actions include, for example, discrimination against possibly exposed persons, spontaneous evacuation, the hoarding of food and unwarranted terminations of pregnancy.

31In one case, the response to an intruder included essentially locking all the doors in a nuclear power plant, which interfered with activation of the emergency centres, off-site communications and notifications.

32This occurred in the USA following the attacks on 11 September 2001, earthquakes and the Three Mile Island emergency in 1979 and, in at least one case, by people telephoning for tickets for a rock music concert.

33There may be emergencies, such as transnational emergencies, for which it is not reasonable for the command post to be located near the scene of the emergency.

34Criticalities cannot produce sufficient amounts of fission products to result in an airborne radioactive release that would warrant the implementation of urgent protective actions off the site. Nonetheless, it is likely that the energy produced by a criticality would result in the release of other hazardous materials that may be present.

35A serious overexposure is one that could result in severe deterministic health effects.

36Powders, gases and liquids, and especially volatile, combustible, water soluble and pyrophoric material, should be considered to be at risk of dispersal.

37It is possible, but unlikely, that a smaller amount than this could cause injury.However, sources this large are considered sufficiently dangerous to warrant taking extraordinary measures (searches, public announcements) to secure them if control over them is lost (e.g. by their being stolen or lost) and if they could be in the public domain.

38This does not refer to the possibility of causing cancer, which is very small, as discussed in the following.

39Facilities in threat categories I, II and III.

40This is made difficult by the uncertainties associated with projections of the timing (duration) and size of major releases and plume movements, as was seen following the Chernobyl accident in 1986.

41In the Chernobyl accident, water contaminated with radioiodine soaked through the protective clothing of the fire-fighters, resulting in beta radiation burns that contributed to several fatalities. In many responses, on-site efforts have been hampered by a lack of protective equipment (e.g. field radiation detection instruments with a high range (e.g 10 Gy/h) or air tanks for self-contained breathing apparatus).

42Some emergency plans state that vehicles or facilities that are contaminated cannot be used, but do not define what levels of contamination constitute being contaminated.

43The consumption of milk contaminated with radioiodine was the primary cause of an increase in the incidence of thyroid cancers among children following the Chernobyl accident. Radiation induced thyroid cancers due to the Chernobyl accident occurred among people living at different distances from the plant and the vast majority were observed at more than 50 km from the plant. The most effective protective action to prevent or reduce these thyroid cancers would have been to restrict the consumption of potentially contaminated food and milk.

44This should be accomplished as soon as possible. Over the past 20 years, the USA has demonstrated that this goal can be achieved within 15 minutes of detection of the event. This goal has been further formalized as part of the US emergency preparedness requirements in accordance with Ref. [49].