The high values in Sweden (and partly perhaps Finland) was partly(there are also geological reasons) due to a popular popular brand of concrete (called Blue Concrete colloquially) being made with Alum Shale that happened to contain a large amount of Uranium (and thus the radiation/decay will eventually produce Radon gas).
This combined with Sweden being a fairly cold country (with people keeping their windows shut) was a recipe for disaster with the further combined effect of smoking and radon gas leading to quite a few fatalities.
These days multi-family housings are regularly inspected to make sure that Radon gas amounts aren't too high (even if the required limits are fairly high in an international context).
This combined with Sweden being a fairly cold country (with people keeping their windows shut) was a recipe for disaster with the further combined effect of smoking and radon gas leading to quite a few fatalities.
These days multi-family housings are regularly inspected to make sure that Radon gas amounts aren't too high (even if the required limits are fairly high in an international context).