Radiological Protection against Radon Exposure

Draft document: Radiological Protection against Radon Exposure
Submitted by Ches Mason, BHP Billiton
Commenting as an individual

General comments

G1. It appears that this draft has been released prior to editing. This is a good thing in that it allows for substantial comment before the text becomes locked in, but the draft requires a thorough review by a professional editor to bring it up to the standard expected of ICRP publications. Much greater attention should be paid to precision of language.

G2. The draft does not deal properly with the effect of smoking. This is a serious deficiency, as the text, like Publication 115, is misleading on the quantitative risks of lung cancer from the contributing carcinogens: tobacco smoke and radon progeny. Some detailed comments on this point are made below.

G3. The section on radon exposure in workplaces (3.3.6) is rather weak, and paragraph 112, especially, is inadequate for planned exposure situations. Similarly, section 4.3 does not adequately address the guidance required for occupational exposure in uranium mines.

G4. Although the draft purports to cover both Rn-222 and Rn-220, it deals primarily with Rn‑222. The text relating to Rn-220 should be reviewed for adequacy, and in order to avoid protection criteria derived for Rn-222 (such as a reference level of 300 Bq m-3) being inappropriately applied to Rn-220.

Specific comments

As noted above, there are numerous editorial and language amendments that could be made: too many to be dealt with here. As an example, the first 17 comments below provide a reasonably detailed, but not exhaustive, commentary on the Executive Summary. The remaining comments pick out some particular points from the rest of the text.

Executive Summary

1. Para (b): ‘Radon 222 is a radioactive decay product of uranium 238…’. Actually, it is strictly a radioactive decay product of radium 226. It is one of a sequence, or chain, of decay products beginning with uranium 238. A similar comment applies to radon 220.

2. Para (b): ‘Because radon is a gas…’. It is not because it is a gas, it is because it is chemically inert that it escapes from the ground and into the air. In any case, the concept of a gas has little meaning when dealing with single radon atoms suspended in an atmosphere of (mostly) oxygen and nitrogen molecules.

3. Para (c): The short-lived radon progeny appear out of the blue here – so far, only radon has been mentioned. It would be good to explain what they are, and in particular to clarify that most of the radon progeny in inhaled air are already present in the ambient air, while a small contribution would be made by radon atoms that decay while in the lung.

4. Para (c): ‘Depending on the diffusion properties of the particles…’. Which particles? Nothing has been said about particles to this point. And diffusion is not the only process at work. One of the physical processes involved is impaction at bifurcations of the bronchial tree arising from mass movement of air through the airways.

5. Para (d): ‘There is now compelling evidence…’. ‘Now’ should be deleted. There has been compelling evidence for over 20 years. Radon (together with its decay products) was formally identified by WHO as a carcinogen in 1986. What seems to be meant here is that recent studies provide statistically significant evidence at radon concentrations down to about 200 Bq m-3.

6. Para (d): ‘…a detriment-adjusted nominal risk coefficient for a population of all ages of 8 x 10-10 per Bq h m-3…’. This is only true if tobacco-smoke risk is included. The words: ‘and for a population-average level of smoking’ should be inserted between ‘ages’ and ‘of’, or a similar clarification made. It should be noted somewhere, and here is a suitable spot, that most of the numerical value of this risk is attributable to tobacco smoke. In the absence of smoking, the risk is about 6 times smaller; that is, in the region of 1 to 2 x 10-10 per Bq h m-3. As long as the text remains silent on this point, it is misleading.

7. Para (e): ‘…from the outset by national authorities.’. This is the first of many instances referring to national authorities. It would be better to say ‘regulatory authorities’, since in several countries, radiation protection is dealt with at the state or provincial level. The text should allow for different jurisdictional arrangements in different countries and not impose a Eurocentric view.

8. Para (k): ‘The Commission considers that radon strategies should address together both smokers and non-smokers.’ What does this mean? Should smokers be treated as non-smokers? Should non-smokers be advised to give up smoking(!)? Presumably it means that the protection policy should take into account both the risk for smokers and the risk for non-smokers. But the two groups cannot be treated in entirely the same way when heavy smokers (more than 15 cigarettes a day) are about 3000% more likely to develop lung cancer than never-smokers. Focussing only on radon (which typically increases lung cancer risk by a few percent) while ignoring the effect of smoking is misleading and unacceptable.

9. Para (l): ‘…for the sake of equity…’. This phrase should be deleted. It’s not a matter of equity, which is a concept applicable to optimization of protection in planned exposure situations.

10. Para (m): ‘Further, the value of 10 mSv…’. The previous sentence says the reference level should be chosen between 1 and 20 mSv, so adopting a value of 10 mSv needs to be explained because it restricts the freedom of regulatory authorities to choose a value in the range recommended in ICRP Publication 103. Is there a rationale for this number, other than the fact that it was suggested in ICRP Publication 65? Incidentally, the logic in Publication 65 was quite different: ‘It seems clear that some remedial measures against radon in dwellings are almost always justified above a continued annual effective dose of 10 mSv.’ (Para.72). In this draft, 10 mSv in a year is a reference level below which action should be taken to optimize protection. Nevertheless, 10 mSv in a year represents a risk of about 1 in 2000 per year, or about 1 in 10 over 50 years for the death of one of a family of 4. It seems likely that many people would regard this as a level of risk of some concern, and would be willing to commit resources to reducing it. Perhaps some discussion along these lines, to put the value of 10 mSv per year in context, could be included in Section 3.3.2?

11. Para (n): ‘300 Bq m-3’. The text offers no connection between the value of 10 mSv per year recommended in the previous paragraph and this radon concentration value. It should say that 300 Bq m-3 (in a dwelling) corresponds to about 10 mSv per year if tobacco-smoke risk (averaged over the population) is included. It should also note that, in the absence of tobacco smoke, 300 Bq m-3 in a dwelling would correspond to about 2 mSv per year.

12. Para (o): The first sentence is almost undecipherable. Presumably it means that the public health policy for protection against radon should include:

(1) the provision of advice to home owners, employers and owners of workplaces to have a radon measurement made and to then discuss with a professional service provider the need and options for remediation;

(2) the possibility of government support – financial or logistical; and

(3) the possible need to develop regulatory instruments where voluntary actions are insufficient or not appropriate.

13. Para (p): ‘Where workers’ exposures to radon are not considered as occupational exposures, i.e. when workers exposures to radon cannot reasonably be regarded as being the responsibility of the operating management…’. If the operating management or employer is not responsible for the air quality in a workplace, who is? This attempt to redefine occupational exposure should be abandoned. The generally accepted definition of occupational exposure is that used by both the ILO and IAEA and given in the International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources (1996): “All exposures of workers incurred in the course of their work, with the exception of exposures excluded from the Standards and exposures from practices or sources exempted by the Standards.”. Occupational exposure is exposure received at work, except for exposure that is excluded from regulatory requirements. Some occupational exposures to radon are regulated as occurring in a planned exposure situation. Some are managed through recommendations or requirements for existing exposure situations. Some exposures to radon at work are excluded from regulatory requirements and are then not considered to be occupational exposures.

14. Para (p): ‘…the first step…’. This is awkward language. It would be better to say that ‘the ideal outcome is to reduce…’. Then the next sentence could say: ‘If difficulties are met in achieving this objective, a dose reference level of 10 mSv per year should be used.’ (Provided that an adequate answer is given for Comment 10, above.)

15. Para (q): ‘The Commission recommends applying the optimisation principle and the relevant requirements for occupational exposure’. This is a tautology, since the requirements for occupational exposure in planned exposure situations include application of the optimization principle.

16. Para (u): This is another sentence that is difficult to understand. Presumably what it means is that prevention is concerned with keeping exposures ALARA for future building construction – through design and building codes, etc; while mitigation is concerned with remedying existing situations where exposures are found to be unacceptably high or where protection is not already optimised. (Incidentally, this illustrates the awkwardness caused by the ICRP’s adoption of the term ‘existing exposure situation’ when it applies to situations that do not yet exist.)

17. Para (w): What does the last sentence mean? It needs re-writing to reflect the intended meaning.

Remainder of the draft

(selected points only)

18. The list of Main Points (pp.10-11) should be deleted. Anything not covered in the Executive Summary should be either included there or omitted. The draft is quite verbose as it is; this is one level of repetition that can be excised.

19. The Glossary (pp.12-15) is problematical. Several of the terms have been previously defined in Publication 103 and are not accurately reproduced here (e.g.: existing exposure situations; occupational exposure; optimisation of protection; planned exposure situations; public exposure; reference level). Either ensure that they are identical with Publication 103 or simply reference Publication 103 instead. If a definition is to be changed, this should trigger a corrigendum to Publication 103, not a divergent definition in a separate publication. One or two terms are used in an ordinary dictionary sense and do not need to appear in a glossary (e.g.: employer; worker).

If Publication 103 terms are to be retained, then a definition of ‘effective dose’ is missing. The definition should include not only the summation formula, but also a description of the intended role of effective dose as a generic measure of radiation detriment.

The term ‘exposure’ (or, possibly, ‘radon exposure’, to avoid confusion) is also missing, together with explanations of units (Bq h m-3; mJ h m-3). Working Level and Working Level Month are given, but these are historical units and should be abandoned in favour of SI units (they could be appended in parentheses where necessary).

The definition of ‘member of the public’ is unhelpful. The definition given applies to everyone, since everyone receives exposures that are neither occupation nor medical.

The definition of risk refers only to relative risk. The system of radiation protection requires absolute risks, such as lifetime excess absolute risk (LEAR).

20. Section 1.2, headed ‘Scope’, really deals with the objective of the document (see opening words of para.8), not its scope (what is covered; what is not covered). The figures giving the uranium series and thorium series decay chains can be found in any undergraduate text dealing with the physics of radioactivity and are not needed. The text doesn’t mention Rn‑219 in any case.

21. Para.9: It is difficult see what benefit is gained by comparing exposure to radon to situations involving ‘contaminated territories’. Fortunately, contaminated territories are rare – while radon is ubiquitous – and they are associated with disastrous events such as the Chernobyl and Fukushima accidents. Such a comparison may lead to fear and panic in the minds of the public, but to what beneficial purpose? The global average level of indoor radon is about 45 Bq m-3, according to UNSCEAR. At this level, the risk of lung cancer for a non-smoker from residential radon is broadly equivalent to the risk of death from a radiation dose of around 0.3 mSv per year – similar to what we get, as a global average, from the food we eat (0.3 mSv/y), and less than the contributions from cosmic rays (0.4 mSv/y) and terrestrial gamma radiation (0.5 mSv/y). In other words, for a non-smoker, as a global average, radon contributes somewhere in the region of 20% of total natural background radiation risk. While reducing radon exposure, especially for homes having high concentrations, is expected to be beneficial, this is not a situation calling for fear and panic.

22. Para.26 contains some repetition.

23. Para. 27: What is an ‘ultrafine’ atom? How does it differ from a regular atom?

24. Para.31: The first sentence describes some factors that influence the (effective) dose received from exposure of the lungs, but no mention is made of the most significant factor by far – in the manner in which the ICRP calculates effective dose – namely, tobacco smoke. That is, the ICRP currently includes the risk (as a population average) from tobacco smoke – a separate carcinogen – when converting radon exposure to effective dose through a dose conversion convention. This inflation of the alleged radiation risk will persist if the ICRP moves to a dosimetrically-derived dose coefficient that assumes smoking is taken into account through the tissue weighting factor for lung. This needs to be properly explained, as the contribution from smoking dominates the contribution from radon several fold. Without such an explanation, the text is misleading.

25. Para.31: The last sentence is puzzling and of doubtful validity. Perhaps some accident of drafting has confused the intended message.

26. Para.32: A discussion of discrepancies between risks estimated from epidemiology and from dosimetric modelling, but still no mention of tobacco smoke, which dominates the magnitude of the risk values derived.

27. Para.33: At last, a mention of smoking in the quotation from Publication 115. The fifth dot point notes the huge difference in risk between non-smokers and smokers, but by the seventh dot point it is forgotten again. To repeat, the risk coefficient adopted by the ICRP in the seventh dot point is mostly attributable to tobacco smoke. In the absence of tobacco smoke, the risk would be around 1 x 10-4 WLM-1, not 5 x 10-4 WLM-1. This text is a quotation from another document so cannot be altered, but an explanation should be appended immediately afterwards pointing out the role of tobacco smoke in the derivation of the numerical value adopted for the risk coefficient.

28. Para.34: A similar comment applies here to the one above. In the absence of tobacco smoke, the risk coefficient would be in the region of 1 to 2 x 10-10 per Bq h m-3, not 8 x 10‑10 per Bq h m-3. This should be made clear.

29. Para.36: As noted above (Comment 21), the comparison with contaminated territories is unhelpful and may be counterproductive. There is in fact little similarity between the two cases, apart from the overarching philosophy regarding optimizing protection below a reference level. It would be better to compare with exposures from NORM and omit references to contaminated territories.

30. Para.37: The statement that exposure from radon ‘is impossible to control directly at the source’ is too strong. Exposure from radium-bearing building materials, for example, is controllable by not using them. The meaning of the last sentence is unclear. If ‘behaviour’ is meant to convey ‘actions taken or not taken in the light of information available’ then say so.

31. Para.39: It is not at all clear what this paragraph means. If it is simply saying that ‘economic and social factors’ (in the broadest sense) need to be taken into account, then this is covered by implementation of the principle of optimization of protection, which is already a major part of radiological protection, which is said to be insufficient in the first part of the first sentence. This inconsistency needs to be tidied up.

32. Para.40: The first sentence is over the top and should be deleted. What is seen by some as ‘denial’ may be seen by others as informed acceptance of a relatively minor risk. At a radon level of 300 Bq m-3 – the recommended reference level, the risk of lung cancer for a non‑smoker is similar to the risk of death from a radiation dose of around 2 mSv/y. Some 90% to 95% of homes have radon concentrations less than 300 Bq m-3. As noted above, the global average is about 45 Bq m-3, implying a risk corresponding to a radiation dose of around 0.3 mSv/y for a non-smoker, or about one cancer death every 60,000 years for a home occupied by a (succession of) single non-smoker(s), which in turn is about 20 times the period of human civilisation on the planet. At 300 Bq m-3, this comes down to around 10,000 years. Scaremongering by comparing the situation with the aftermath of Chernobyl (contaminated area or contaminated territories) would be unacceptable.

33. From this point (Para.43) on, there is considerable overlap between the material in Chapter 2 and Chapter 3, and between Chapter 3 and Chapter 4. Chapter 2 seems to have been intended as a ‘background’ chapter, but Section 2.4 begins to make recommendations, which is the province of Chapter 3. From this point on, weariness is also setting in for making specific comments! There are many, many editorial comments that could be made, but hopefully these will be addressed when a professional editorial pass is made through the document. A handful of points are picked out in what follows.

34. Paragraphs 67 and 68 are almost unintelligible and need rewriting if they have a point to make.

35. Para.72: This says that the principle of justification should be applied by governments and authorities to the decision on whether or not to implement a protection strategy against radon exposure, and then goes on to make the decision for them by saying it is justified! The paragraph continues quite extraordinarily by suggesting that ‘reducing radon concentration contributes (to) mitigating (the) health effects of tobacco’. The risk of lung cancer for continuing heavy smokers (more than 15 cigarettes per day) is about 30 times (that is 3000%) higher than for never-smokers. Reducing radon concentration by as much as 100 Bq m-3, which would be achievable in only a small minority of homes, would reduce the risk of lung cancer by a few per cent. With a relative difference approaching three orders of magnitude, would it be better to focus on reducing heavy smoking (which would actually save money both for the state, in health care costs, and for the individual) or on reducing radon (which costs money)? How is it that, against all logic, the priorities are back to front?

36. Para.73: This is a bit garbled, but the message is, or should be, that the system of radiation protection should be designed to provide protection for both smokers and non-smokers. One way to do this is to set reference levels on the basis of the combined risk from a population average level of smoking and from radon. Protection should then be optimized below the reference level. However, the combined risk should not be converted into radiation dose, as it is a risk arising mostly from tobacco smoke and only partly from radon. Conversion from risk to dose should be done on the basis of a never-smoker reference individual. The risk implied by such a radiation dose is then amplified for any individual by his or her smoking status to create the combined risk.

37. Para.74: The discussion in the last sentence could be omitted. The idea of limiting inequity is really intended for the exposures caused by introducing a radiation practice (that is, in a planned exposure situation). The real reason for keeping below the reference level in an existing exposure situation is to do with staying consistent with judgements about the acceptability of the magnitude of risk of harm.

38. Para.81: It should be pointed out that the 10 mSv referred to here is ‘smoking effective dose’; that is, it includes tobacco smoke risk.

39. Para.84: Similarly to the comment above, it should be pointed out that a radon concentration of 300 Bq m-3 in a home corresponds to an effective dose of 10 mSv per year only if tobacco smoke risk (averaged over the population) is included. In the absence of tobacco smoke, 300 Bq m-3 corresponds to the risk of death from a radiation dose of about 2 mSv per year.

40. Para.88: Figure 5 shows a planned ‘existing exposure situation’ on the left and an existing ‘existing exposure situation’ on the right. As a ‘clarification’, this paragraph fails, and should be rewritten.

41. Para.89: Figure 6 is referenced in the second sentence, but it is not clear why. What are the ‘steps’ referred to in the figure, but not in the text?

42. Para.92: Another paragraph that is unintelligible and needs rewriting…

43. Para.108: …is another one…

44. Paras. 109 to 112: …in fact all of these. This subsection needs to be completely rewritten.

45. Para.116: Figure 7 is unnecessarily complicated and could be greatly simplified. There is no need to separate out into building types until after the ‘ALARA’ box, since everything is the same to that point. The third-row box (Reference level = 10 mSv/y) should be deleted, because it is not a step or decision point. Incidentally, ‘ALARA’ should be replaced by ‘optimize protection’.

46. Para.132: Figure 8 should be deleted. It is out of place in a document of this kind.

47. Sections 4.2 and 4.3: These paragraphs cover radon exposure in planned exposure situations and are not comprehensive enough for the purpose. It may be simplest to delete them, to retitle the document ‘Radiological Protection against Radon in Existing Exposure Situations’, and to leave guidance on radon in planned exposure situations for another day. For example, the IAEA is planning to prepare a Safety Guide covering all occupational exposure in the coming months.