|Entry point for applying radiation protection requirements
Para. 5 of the ICRP Statement recommends 1000 Bq/m3 as an entry point for applying occupational protection requirements in existing exposure situations. This seems to be inconsistent with ICRP 103 which recommends that existing exposure situations be managed through the use of reference levels.
The setting of reference levels is not based solely on considerations of effective dose. Indeed, the distribution of indoor radon levels in the country in question is often the more important consideration. If properly applied, the resulting reference level for radon in workplaces will normally be less than 1000 Bq/m3. Indeed, several European countries already have national reference levels of 400 Bq/m3 for workplaces managed as existing exposure situations. It is unclear as to what approach should be taken at the national level when measured radon concentrations exceed the national reference level but are less than the 1000 Bq/m3 'entry point' advocated by the ICRP.
As you know, the text of the revised BSS (see extract below) refers to radon concentrations above the national reference level as the entry point for applying the relevant occupational protection requirements. From the point of view of practicality and consistency, this seems a more realistic approach than that proposed by ICRP in its Statement on Radon, which is fundameltally different to the advice offered in ICRP 103.
Extract from draft 4.0 of the revised BSS
5.27. The regulatory body or other relevant authority shall establish a radon protection strategy for workplaces, including the establishment of an appropriate reference level, the value of which takes into account the prevailing social and economic circumstances but which does not exceed an annual average radon concentration of 1000 Bq/m3. 
5.28. Employers shall ensure that:
(a) Protection is optimized by making all reasonable efforts to reduce radon concentrations and radon exposures;
(b) To the extent possible, radon concentrations in workplaces are reduced to below the reference level established in accordance with para. 5.27.
5.29. If, despite all reasonable efforts by the employer to reduce radon levels, the radon concentration in the workplace remains above the reference level established in accordance with para. 5.27, exposure to radon shall be subject to the relevant requirements for occupational exposure in planned exposure situations given in section 3, including the requirement for a graded approach to regulation.
Radon exposure incurred at work
Para. 6 of the ICRP Statement uses the expression "exposure to radon incurred as a result of their work". It is not clear what "as a result of" really means and some clarity would be helpful. With the ICRP wording, it could be argued that, in a planned exposure situation involving the use of a radioactive source, the additional exposure received from radon in the same workplace should be regarded as occupational exposure. I do not think this is what is meant, but rather that when exposure to other radionuclides in the uranium decay chain is controlled as a planned exposure situation, the dose received from radon is also occupational exposure. Therefore, for example, if there are high gamma radiation levels in an underground zinc mine and it is controlled as a planned exposure situation, account must also be taken of any exposure to radon, no matter how small. On the other hand, if the gamma radiation levels are low in that same mine and it is controlled as an existing exposure situation (or not at all), then exposure to radon is also controlled as an existing exposure situation, unless it cannot be reduced below the national reference level.
An important point, that you may consider worth commenting on, is that there is potentially a higher level of protection offered in existing exposure situations than in planned exposure situations i.e. the reference level for existing exposure situations is based on a maximum effective dose of 10 mSv while, in planned exposure situations, the dose limit is 20 mSv (or up to 50 mSv in some countries). While in practice the doses actually received depend on how optimization can be and is applied, many regulators wrongly consider that they have less 'control' in managing existing exposure situations, whereas in fact they may have more.
Excess relative risk of 16%
Table 2.2 quotes values of 1.08, 1.10 and 1.13 for relative risk per 100 Bq/m3 for the European, North American and Chinese pooled residential studies respectively, with 95% condidence intervals of 0.99 to 1.36. Para. 21 then states that "the European pooling reported an excess relative risk increase of 16% per 100 Bq/m3 when uncertainties in the radon activity concentrations were considered....and can be considered a reasonable estimate of the risk....". This use of this value of 16% is fundamental to all subsequent analysis and conclusions and to accept it almost without justification or comment is most unusual, in particular when the figues quoted in Table 2.2 would suggest that a value between 9% and 11%, as referred in para. (c) of the Executive Summary, might be more appropriate. Without such justification, all subsequent analysis becomes highly questionable.
Radon and smoking
It is not clear where the ICRP stands on the synergy, observed in the pooled residential studies, between exposure to radon and smoking. This is referred to in para. (f) of the Executive Summary and in para 23. [My understanding of the epidemiology is that the 25-fold increased risk in smokers is from radon alone and is in addition to the risk from smoking, but this is not made clear in the text].
Section 3.3. (paras. 33 and 34) says little more than that there is limited data from the studies of underground miners but that "the relationship between lung cancer mortality and radon exposure persists when account is taken of smoking habits". There is no discussion of synergy between radon exposure and smoking, nor any comparison with the data from the pooled residential studies.
Any synergy between radon exposure and smoking has very significant implications for
radon exposure in workplaces and, ultimately, for international labour law. While the ICRP may not be in a position to resolve the issue, it is important that it is at least discussed in the document and the implications pointed out.
I hope you find this helpful.