Practical usefulness of radon risk maps and detailed in-situ classification of radon risk

The presentation answers the frequent question about the practical usefulness, advantages and disadvantages of radon risk maps and detailed in-situ classification of radon risk. Czech Radon Programme derives the benefit from radon maps on various scales - 1:500 000, 1:200 000 and 1:50 000, as well as from the uniform method for direct detailed classification of radon risk. The reliability assessment of the practical usefulness is based on the direct comparison between the results obtained from detailed in-situ classification of radon risk of building sites and the corresponding reading from the radon risk map. Altogether almost one thousand of detailed radon risk assessments, i.e. tens of thousands of soil-gas radon concentration measurements, were compared with the expected radon risk categories in five radon risk map sheets on the scale 1:50 000. The new results more specify and correspond to the previous results from comparisons performed in 1992, 1995 and 2002. We can prepare quite consistent maps, which can be successfully used to direct the search of existing houses with higher indoor radon values. On the other hand, the risk of underestimation or overestimation in the case of deriving the radon risk classification of a specific building site from the map seems to be too high to use the maps for direct assessment of specific sites. For new buildings, it is recommended to use detailed in-situ measurements and classification. (authors)