1. The draft describes the lung cancer risk from radon strongly depends upon smoking habit. However, the nominal risk that averages non-smokers and smokers is used for estimation of the lung cancer risk due to radon exposure. The nominal risk aims to target the population including different ages and sexes for radiation protection to compare the unified level such as the dose limits. If the smoking habit is considered to define the nominal risk, the effect of smoking habit on radon risk is likely to be neglected. In order to recommend the role of smoking cessation in any radon control program, ICRP should replace the current nominal risk with different values depending upon smoking habit. 2. ICRP concluded that doses from radon and radon progeny should be calculated using ICRP biokinetic and dosimetric models, replacing the dose conversion convention approach which is based on epidemiological data.@In the present draft, however, the rationale for the replacement is not clearly explained. The strengths and weaknesses of the two approaches should be discussed. 3. In CONCLUSIONS, lines 1058-1062 says gDoses from radon and its progeny will be calculated using ICRP biokinetic and dosimetric modelsc. This will apply to thoron (Rn-220) and thoron progeny as well as radon (Rn-222) and radon progeny.h A number of studies (e.g., Yamada et al., J. Toxicol. and Environ. Health, 69, 723-724, 2006) showed that thoron interference resulted in a large uncertainty in the radon measurements. Therefore, to add the following statements should be helpful for future studies. - Thoron interference in radon measurements can be regarded as one of major uncertainties of radon measurements - Comprehensive dose assessment of both radon and thoron should be carried out in future residential studies.