The map below illustrates the current radon action limits in different countries in Europe, which support actions against radon in homes. To clarify the differences, the degree of regulation is presented in a four-color code. The most protection of the residents and the lowest limit level by regulation is colored green. The worst case is white, which means no regulation at all.
Source: Radiological Protection Institute of Ireland (RPII)
 

 White  = No Regulation at all.

 Blue    = An advisory radon content limit of 400 Bq/m³ in indoor air is recommended.

 Cyan    = An advisory radon content limit of 200 Bq/m³ in indoor air is recommended.

 Green = A compulsory radon content limit of 200 Bq/m³ in indoor air is set.