ICRP draft guidance on “Radiological Protection against Radon Exposure” – dated 6 December 2011.
Comments are only provided on the main sections of the report (Glossary and sections 1 – 4) and not the summary or Main Points sections.
The comments are split into the following sections:
· doses arising from indoor radon;
· optimisation of protection;
· revised dosimetry, reference levels and workplace radon;
· radon and smoking;
· document written style and detailed editorial points.
1. Doses arising from indoor radon
1.1 The draft document gives significant attention to important issues of dosimetry of radon and risk estimates from radon exposure. However, it fails to reflect some important aspects of radon exposure.
1.2 Log-normal distribution. Figure 6, showing distribution of radon exposure, and para 26 (range of indoor concentrations spanning 10 – 70,000 Bq m-3) gives some indications about the range and statistical distribution of indoor radon levels. What is not clear from the document is that an approximately log-normal distribution of radon levels is regularly observed. This characteristic supports activities such as radon mapping and implies that, in many countries, there will be significant numbers of buildings with radon levels much greater than the reference level. Since this is a general characteristic of indoor radon concentrations, it provides important information about the range of annual doses from indoor radon and can be an important feature in designing protection strategies.
1.3 Section 2.2.2 contains significant detail about radon risk. However, it does not illustrate the likely range of doses that are received in the absence of an effective radon strategy. By bringing together the range of observed indoor concentrations, the approximate log-normal distribution of these concentrations and the dosimetric information, it is clear that many countries will have a distribution of annual effective doses from indoor radon that will result in average annual doses from indoor radon being of the order of a few millisieverts (making radon the single largest source of public radiation exposure); and highest annual doses from indoor radon exceeding 100 millisieverts (arising from an annual average indoor concentration of a few thousand Bq m-3 or more). Many of these very high exposures will occur in radon prone areas.
1.4 High doses from indoor radon. Since statistical distributions of indoor radon can be estimated and, in many countries, result in significant numbers of high annual exposures, it is worth considering these high annual exposures in the light of ICRP’s advice on the matter. ICRP 103, (para 236) states that “exposures above 100 mSv incurred either acutely or in a year would be justified only under extreme circumstances”.
1.5 This suggests that ICRP guidance on radon should consider these high exposures explicitly. This might include: recognition that very high exposures from radon do occur; their likelihood and number can be estimated from statistical distributions of indoor radon concentrations; very high indoor radon exposures are likely to be most prevalent in radon prone areas. It might also be worth noting that, in the absence of any significant changes to the properties concerned, these exposures are more likely to be ongoing rather than “one off” in the absence of action.
1.6 ICRP guidance should emphasise that national radon programmes should: reflect these points above; provide a means to identify such properties where they are predicted to exist in significant numbers; provide additional encouragement, support or a requirement to reduce very high levels.
1.7 This could be reflected in ICRP guidance as part of a “graded approach” for homes, including some or all of the following elements progressively: advice to householders/landlords on the need to measure radon in homes, potentially focused on radon prone areas; use of a reference level on which to base remediation advice; additional support for those at greatest risk (high radon exposure and/or current smokers).
2. Optimisation of protection
2.1 Section 3.3.3 considers optimisation of protection against radon. This highlights the need to optimise in light of both overall population risk and risks to the most exposed individuals. At present the document does not present a full picture of the different forms of optimisation that are relevant in the context of indoor radon exposure. It might be useful for the document to illustrate these more clearly as part of a graded radon strategy, including: input to national issues such as building codes to prevent exposures in new buildings; establishing a national policy on universality or targeting of radon measurements in radon-prone areas; the design and operation of targeted programmes for existing buildings in radon prone areas; the selection of and guidance on remedial techniques, using evidence of performance and cost. Each of these represents an application of optimisation of protection.
2.2 The document references optimisation using cost-benefit analysis (para 91). This only mentions using “standard cost-benefit analysis” with lung cancers as the principal adverse outcome to be avoided. It would be better to reference the table of attributes in ICRP 101(Table 3.1) since that includes wider issues including high individual exposures and informational benefits gained and not just lung cancers avoided. These are all important elements of a radon protection strategy.
3. Revised radon dosimetry, reference levels and workplace radon
3.1 As noted in the document, there is not a unique relationship between observed long term radon concentration and effective dose. The recent changes in radon dosimetry suggest that a “default” relationship equating 300 Bq m-3 with 10 mSv is not applicable. We note that 300 Bq/m3 in homes is equivalent to 18 mSv according to dosimetric calculations (Harrison and Marsh, Proc. ICRP Symposium). There is a desire, expressed in the document, to establish a reference level that is applicable across most premises, whether homes or workplaces. This suggests that it might be appropriate for ICRP to adopt a reference level in terms of annual average concentration as its primary tool for protection decisions, recognising that, in many settings, it corresponds to doses that are in the region 1 – 20 mSv, the appropriate reference level range set out in Publication 103. The role of the dose related reference level might then be reserved for use in workplace situations (eg where radon levels are persistently high) and the site-specific assessment indicates doses over this level. It might also be helpful to include a short discussion of different values of dose per unit exposure obtained by different approaches to give some perspective on the dose at 300 Bq/m3.
3.2 The document discusses situations in which exposures in workplaces should be considered to be “occupational exposures”. This is expressed in terms where the situation can reasonably be regarded as the “responsibility of the operating management”. This is not new in this document but it is this document that considers, in more detail, its application to radon exposures in workplaces. The current document extends the concept a bit further than para 298 of Publication 103 (“Radon exposure at work at levels above the national reference level should be considered part of occupational exposure whereas exposures at levels below should not”) by only treating as “occupational exposures” those exposures that occur in situations (para 109) where the exposure remains “durably above 10 mSv/y”. It could be perceived that this definition does not align with wider workplace health and safety principles since those principles tend to view many hazards and risks incurred in the workplace as the responsibility of the management even if they are not caused by the work activity or management. Importantly however, the document also states (section 3.3.6) that where exposures occur in workplaces but are not considered to be “occupational” the exposures should still “treated in the same way as members of the public”. This recognises a responsibility of the management to the individuals who occupy the workplace even if their radon exposures are not treated as “occupational”. A single reference level expressed in concentration terms provides a unifying practical criterion here. The document would benefit from placing clearer emphasis on the duty of employers to assess and manage radon exposures in their workplace regardless of whether they are treated as “public” or “occupational”.
3.3 The document advocates a default (“a priori”?) upper value for radon reference level of 300 Bq m-3 for all premises. The significant uncertainties inherent in many aspects of radon concentration, exposure, dose and risk, suggest that a fairly pragmatic approach should be adopted that avoids over-precision, represents real ambition in terms of managing high radon exposures and is achievable in many circumstances. The currently proposed value of 300 Bq m-3 (as an annual average) represents an appropriate balance for homes and other places where members of the public spend significant periods of time.
4. Radon and smoking
The document reflects current understanding that a given radon exposure presents a greater absolute risk to smokers and ex-smokers than to lifelong non-smokers. The guidance suggests that national strategies should be based on the same approach for smokers and non-smokers. This is appropriate for general strategies and workplaces but it may be more appropriate if advice to individual householders were to reflect the higher risk to some groups (smokers and ex-smokers), especially where householders themselves may be making an investment in radon remediation measures. This would be a practical application of the guidance (para 155) that radon and anti-smoking strategies should be linked.
5. Document style and detailed editorial points
5.1 The document would benefit from further editing to ensure consistent and common English phrasing is used.
5.2 Consistent terminology needs to be applied throughout the document for issues that are central to radon management. For example, the document would be improved by consistently using one of either “mitigation” or “remediation” throughout when referring to implementing radon reduction measures in existing buildings rather than a mixture (eg “remediation” line 1482, “mitigation” line 1747) that might lead reader to think there is a difference. Similarly, with “homes” [line 847, 1415] or “dwellings” [line 1524].
5.3 Many sections contain lists of situations, professions or users. It is not always clear whether these are to be considered definitive or indicative, and the lists change slightly when referring to the same situation in different sections of the main text. For example, lines 592 compared with 1517.