|PART 2 OF 3
Per Wikman, Philosophy Unit, Royal Institute of Technology, Stockholm, Sweden.
2. DOSE CONSTRAINTS
The draft introduces a new rationale for choosing maximum dose constraints (based on the natural background). Previously dose constraints were bounded by dose limits. In cases where dose limits are applicable it seems reasonable that dose constraints are bounded by the dose limits. This is not clear from the present draft.
Also, it is not clear why there is a need for another rationale if dose constraints already are limited by dose limits. The levels of the proposed maximum constraints are essentially the same as the dose-limits, which only further increases the potential for confusion. Another problem is that the new draft does not provide any much help of deciding particular dose constraints.
It is likely that it can be very pedagogical to use the natural background as a comparison when explaining the risk from practices involving radiation to the public. But using natural background to deduce dose constraints should be avoided. Any multiples of the natural background have to be arbitrary, and the natural background-rationale is subject to accusations of committing the so-called “naturalistic fallacy” – to draw conclusions about how things ought to be based solely on information about how things are in fact.
My suggestion is that a coherent rationale for choosing the maximum levels of constraints is introduced. Preferably this rationale should be based on dose limits. For situations where there at present is no dose limit, a maximum level can be chosen on other grounds (e.g. deterministic effects or similar rationale as for the dose limits). It is also suggested that more guidance should be given on how to choose particular dose constraints.
2.2. WHY INTRODUCE A NEW RATIONALE?
The new Recommendations provide a way of determining the maximum values of dose constraints (based on a comparison with the natural background). That dose constraints should be limited by dose limits is not stated explicitly in the new draft, but it seems that this is the logical implication of having dose limits. For how could a dose constraint be higher than the applicable dose limit? If the maximum level of constraints already is bounded by dose limits, it is not clear what the reason is to introduce yet another rationale for establishing them. Furthermore, the levels of the maximum dose constraints are the essentially the same as the dose-limits. This only further increases the potential for confusion.
In fact, the draft states that the new maximum levels are consistent with the old system: ”The Commission’s recommended constraints are consistent both with the scale [...] of need for action and, as far as possible, the quantified values of the current system which includes limits, specified constraints and action levels. The choice of the Commission’s recommended constraints is thus influenced by the benefit of consistency with previous decisions.” (ICRP 2004, Paragraph 162).
That dose constraints ought to be limited by dose constraints was stated in Publication 60: “Dose limits are needed as part of the control of occupational exposure, both to impose a limit on the choice of dose constraints and to provide a protection against errors of judgement in the application of optimisation.” (ICRP 1991, paragraph S23).
Basing the maximum value of dose constraints on the dose limits is an obvious solution. For situations where there at present is no dose limit, a maximum level can be chosen on other grounds (e.g. deterministic effects or similar rationale as for the dose limits).
2.3. COMPARISON WITH NATURAL BACKGROUND
The new maximum values are based on “need for action” (ICRP 2004, Paragraphs 157, 158, 160, 161, 162, 164 inter alia), and a comparison with the global average annual exposure from the natural background radiation and its variation from place to place.
But it is not clear how this “need for action” is deduced from the comparison with the natural background. According to the new Recommendations the ”need for action” is, in different contexts, 100 times the natural background, 20 times, 1 time and 0.01 times. But what are the reasons for using precisely these factors for determine the ”need for action”? What makes a factor of 100 more appropriate than a factor of 1000 or a factor of 3?
In addition to this, the view that a comparison with natural risks are relevant for deciding the dose constraints has been criticised for being an instance of the so-called naturalistic fallacy – to think that we can deduce moral statements from scientific facts (cf. Shrader-Frechette and Persson 2002). The fallacy is that we cannot directly draw conclusions about how things ought to be based solely on information about how things are in fact. We always have to make a value judgement of the fact. Saying that X is natural – therefore we ought do Y (e.g. choose a “need for action”, a level of constraints etc) often hides other premises or assumptions that are value judgements. Examples of such premises could be that “Natural risks are small (therefore we should not consider them)”, ”We are protected against natural risks (therefore we should not consider them)”, ”Natural risks are be difficult to remove (we should spend our resources elsewhere)”. Any implicit assumptions, premises and value judgements that lies behind references to naturalness ought to be discussed explicitly instead.
It is likely that it can be very pedagogical to use the natural background as a comparison when explaining the risk from practices involving radiation to the public. But arguments of type: “this constraint is set to 20 mSv/year because this level represents 20 times the average annual natural background radiation and therefore the need for action is x (low or high?)” is quite an arbitrary way of justifying a particular constraint.
2.4. SETTING THE LEVELS OF CONSTRAINTS
The Commission states that “the rationale behind the establishment of the corresponding quantified values should be clear enough that the relevant constraint can be easily chosen so as to apply to the situation of exposure considered.” (ICRP 2004, Paragraph 162).
But the new draft does not give any “clear enough” rationale how to set the level of constraints, suffice that they ought to be less than a maximum level. It does not discuss the complexities and the problems involved in setting a “wrong” dose constraint might lead to problems.
One problem could be that excessive costs would be needed in order to reduce the dose to the most exposed individual (e.g. if the dose constraint is set too low). A related problem is that dose constraints could imply situations where substantial increases in collective doses would have to be accepted only because a few individual doses may go over a specific dose constraint. A hypothetical example illustrates this point:
Say that a national regulator suddenly decides to set a dose constraint concerning a specific practice to 10 mSv/yr (e.g. based on that it is 10 times the average global background?). For the example we assume that exposure currently are distributed so that a group consisting of ten people are exposed to 11 mSv/yr, while a group consisting of 10 000 individuals are exposed to 1 mSv/yr. Now, assume that lowering the ten individuals below the constraint (to 9 mSv/yr) also would mean that the previous protection for the group consisting of the other 10 000 individual cannot be upheld. Instead, these are now also exposed to 9 mSv/yr. So, while reducing the individual dose for ten people with 2mSv/yr we also have to accept that the individual dose for the groups of 10 000 individuals are increased with 8 mSv/yr for each individual and the total collective dose increases with approximately 80 000 man mSv/yr.
The example shows that we have to be very careful when choosing a specific dose constraint, as a dose constraint could at the same time imply very small decreases in doses for few individuals, and substantial increases for many individuals.
These problems suggest that a more complex way of determining dose constraints is needed. This more manifold way of thinking seems to be present in the previous Recommendations when discussing occupational dose constraints: “For many types of occupation, it is possible to reach conclusions about the level of individual doses likely to be incurred in well-managed operations. This information can then be used to establish a dose constraint for that type of operation” (ICRP 1991, Paragraph 144), and “The choice of an action level is complex, depending not only on the level of exposure, but also on the likely scale of action, which has economic implications for the community and for individuals” (ICRP 1991, Paragraph 217).
Up till now there have been many different constraints and a numerous number of ways to justify them: “When ICRP 60 is included, there exist nearly 30 different numerical values for ‘constraints’, [...] in the ten reports that define current ICRP recommendations. Further, the numerical values are justified in some six different ways, which include: (a) individual annual fatal risk, (b) upper end of an existing range of naturally occurring values, (c) multiples or fractions of natural background, (d) formal cost–benefit analysis, (e) qualitative, non-quantitative, reasons, and (f) avoidance of deterministic effects.” (ICRP 2003, p.131).
Without going through each and every case of these constraints, it seems likely these constraints have been carefully chosen for a specific application. Does the ICRP now intend that this should be replaced with a comparison with the natural background? This is not clear from the new draft.
A dose constraint for a specific practice probably ought to be decided on a case-by-case basis. Factors that could influence the dose constraint should include; who is exposed and why, best-practice or best-available technology, the inequality of actual (or possible) distributions or by what is a reasonable dose-constraint for a practice compared to risks from other practices (not involving radiation).
My suggestion is that the forthcoming Recommendations should
1) Discard the natural-based rationale, and instead explicitly state that the maximum levels of constraints should be limited by the dose limits. For situations where there is no dose limit, a maximum level can be recommended on other grounds (e.g. deterministic effects or similar rationale as for the dose limits). The main argument for this is that the new draft confuses by introducing a new rationale for choosing maximum dose constraints, while also referring to the dose limits. A coherent approach is preferable than two parallel approaches.
2) Give more guidance on what considerations should be involved in choosing a particular constraint for a specific practice. The task of choosing a “good” dose constraint should be discussed. Examples should be given where a “wrong” constraint could lead to problems such as excessive costs or unreasonable protection options. Choosing a “good” constraint for a particular practice should involve both practical considerations (e.g. cost and best practice etc.) as well as ethical considerations (e.g. inequality, who is exposed and why, voluntary/involuntary etc).