The national territory is divided into three radon potential zones defined on the basis of radon exhalation flows from the ground:
1° Zone 1: areas with low radon potential ;
2° Zone 2: areas with low radon potential but where particular geological factors may facilitate the transfer of radon to buildings;
3° Zone 3: areas with significant radon potential.
The list of municipalities divided into these three zones is set by the order referred to in Article L. 1333-22.