Indoor radon mapping in Finland

For over ten years STUK (The Radiation and Nuclear Safety Authority, Finland) has performedsystematic indoor radon mapping with municipal health authorities. In the most radon-proneprovinces (Uusimaa, Kymi and Hme) there are about 480,000 low-rise dwellings. It is expectedthat in 51,000 homes the action level of 400 Bq/m3 is exceeded, of which about 6,000 have beendetected. In the rest of Finland the numbers are: 820,000 low-rise dwellings, 17,000 expectedcases of exceeding the limit, of which 800 were detected, respectively. In the threeabovementioned provinces 20% of the houses investigated exceed the level of 400 Bq/m3 and 40-50% exceed the level of 200 Bq/m3. In the rest of Finland the figures are 4% and 13%,respectively. The most powerful search for radon should be focused on the provinces of Uusimaa,Kymi and Hme, where almost 80% of the houses exceeding the action level are situated. Thesearch for high concentrations is worthwhile everywhere in Finland in areas where they havealready been found. The search is easiest in esker areas and other sand and gravel deposits becausethey are easy to locate from geological maps.