|Supervision and corrective action|
This map of the French departments shows the average radon concentration in buildings throughout France. As useful as such a map can be, it skims over the variations that can exist between neighbouring villages and even neighbouring houses. For instance, in some departments the concentration can vary from several becquerels per cubic metre to several thousand becquerels per cubic metre. A decree foresees compulsory measurements of the radon concentration in public places every ten years. According to the measured concentration, corrective actions should be taken in these buildings and buildings under construction.