(Ref: Paragraphs 1.6.3, 3.3.5 g), 3.4.8 b) & 3.4.9)

Protective Action Levels (PALs) are used as guidance for decision-makers in determining the protective and ingestion control measures that should be undertaken to protect public health and safety.

Exposure control measures

Protective measure Lower level Upper level
Effective Dose Thyroid Dose Effective Dose Thyroid Dose
Sheltering 1 mSv
(0.1 rem)		 10 mSv
(1 rem)		 10 mSv
(1 rem)		 100 mSv
(10 rem)
Evacuation 10 mSv
(1 rem)		 100 mSv
(10 rem)		 100 mSv
(10 rem)		 1 Sv$2
(100 rem)
Thyroid Blocking n/a 100 mSv
(10 rem)		 n/a 1 Sv$2
(100 rem)

Ingestion control measures

Banning food/water consumption Radionuclide concentration level
Cs-134, Cs-137,
Ru-103, Ru-106,
Sr-89		 I-131 Sr-89 Am-241, Pu-238,
Pu-239, Pu-240,
Pu-242
Foods for general consumption 1 kBq (27 nCi)
per kg		 1 kBq (27 nCi)
per kg		 100 Bq (2.7 nCi)
per kg		 10 Bq (270 nCi)
per kg
Milk, Infant Foods, Drinking Water 1 kBq (27 nCi)
per kg		 100 Bq (2.7 nCi)
per kg		 100 Bq (2.7 nCi)
per kg		 1 Bq (27 nCi)
per kg

Application

  1. The PALs for exposure control measures are expressed in terms of, and shall be related to, the highest projected dose likely to be received by the most exposed individual in the relevant critical group (see Glossary in Annex E, for definitions of these terms).
  2. PALs are expressed over the duration of significant releases.
  3. The PALs for ingestion control measures should be applied to food prepared for consumption. The PALs are to be applied to the sum of the activity levels for each radionuclide within a group. However, they are applied independently to each group. For example, if in a foodstuff the radiocesium is 50% of the permitted concentration while the quantity of rubidium (which is in the same group as cesium) is 60% of the permitted concentration, the item should be banned. However, an item containing 50% of the permitted concentration of radiocesium and 60% of the permitted concentration of Sr-90 (which is in a different group) would be acceptable.

(Note: I-131 is grouped with radiocesium, etc. in the case of foods for general consumption, but is grouped with Sr-90 for infant food and water).

Notes

  1. The effective dose PALs above were adopted by the Government of Ontario in 1984 upon the recommendation of Provincial Working Group # 3 and are generally consistent with Health Canada Intervention levels as published in Canadian Guidelines for Intervention During a Nuclear Emergency (2003). The latest authoritative international guidance on the subject confirms their continuing validity. (Cf. International Basic Safety Standards for Protection Against Ionizing Radiation and for Safety of Radiation Sources, International Atomic Energy Agency. Safety Series No.115, 2004).
  2. The intervention levels recommended in the International Basic Safety Standards (IBSS) are in terms of avertable dose, whereas the Ontario PALs are in the form of projected dose. This difference is essentially academic since the PALs are used most often in decisions on protective measures taken prior to any radiation exposure, and hence are being compared to avertable dose. In most cases where radiation exposure is already occurring, it would neither be possible nor desirable to base protective action decisions on calculations involving PALs; instead, they would be based on pre-planned responses and conservative estimates. (See Operational Response Strategy, PNERP Master Plan Chapter 6).
  3. It is necessary to express PALs in terms of projected dose in order to conform to the Plan principle that protective measures should avert (or at least reduce) risk resulting from radiation exposure. Thus, expressed as projected doses, PALs in essence represent levels of risk from potential exposure, which justify the initiation of various protective measures. The risk commences when radiation exposure begins, and not when the emergency management organization starts to use PALs to assess the need for protective measures. If this assessment occurs in some circumstances after radiation exposure has commenced, the use of PALs in the prescribed manner will fulfill the above principle adopted in this Plan.
  4. The PALs for exposure control measures are prescribed as a range for each protective measure because the decision on applying a protective measure is based not only on technical factors but also on operational and public policy considerations. To enable these considerations to be applied, it is appropriate to provide decision-makers with technical advice ranging between when a measure should be considered for application (on purely technical grounds) and when it becomes necessary on the same grounds. This span also allows for the fact that there are inherent uncertainties in the results of technical assessments.
  5. The factor of 10 used to obtain the thyroid dose equivalent to the effective dose is based on the assumption that non-fatal or curable cancers of the thyroid carry the same socio-economic impact as fatal thyroid cancers. This assumption is presumed to be valid in the context of public safety and the low dose (or risk) levels used in the PALs.
  6. The PALs for banning food and water consumption are consistent with International Atomic Energy Agency. Safety Series No. GS-R-2 'Preparedness and Response for a Nuclear and Radiological Emergency' (2002), and the Canadian Guidelines for the Restriction of Radioactively Contaminated Food and Water Following a Nuclear Emergency: Guidelines and Rationale, Health Canada (2000).