Know the radon potential of my commune

Radon is a radioactive gas produced by the natural decay of uranium present in rocks. A pulmonary carcinogen, it can pose a health risk when it accumulates in buildings. Knowledge of the characteristics of geological formations on the territory makes it possible to identify areas where radon at high concentrations in buildings is most likely. This work, carried out by IRSN at the request of the Nuclear Safety Authority, made it possible to establish a mapping of radon potential covering the entire metropolitan territory. This mapping leads to classify the municipalities into 3 categories: **Category 1** The municipalities with radon potential category 1 are those located on geological formations with the lowest uranium content. These formations correspond in particular to the limestone, sandy and clay formations constituting large sedimentary basins (Paris basin, Aquitaine basin) and basaltic volcanic formations (central mass, French Polynesia, Antilles...). On these formations, a large majority of buildings have low radon concentrations. The results of the national measurement campaign in metropolitan France show that only 20 % of buildings exceed 100 Bq.m-3 and less than 2 % exceed 400 Bq.m-3. **Category 2** The municipalities with radon potential category 2 are those located on geological formations with low uranium content but where specific geological factors can facilitate the transfer of radon to buildings. The municipalities concerned are in particular those intersected by major faults or whose basement houses underground mining works... These particular geological conditions can locally facilitate the transport of radon from rock to the soil surface and thus increase the likelihood of high concentrations in buildings. **Category 3** Class 3 radon potential municipalities are those that, on at least part of their area, have geological formations with an estimated higher uranium content compared to other formations. The formations concerned include those constituting granite massifs (Armoricain Massif, Central Massif, French Guiana...), some volcanic formations (central mass, French Polynesia, Mayotte...) but also some black greases and shale. Of these more uranium-rich formations, the proportion of buildings with high radon concentrations is higher than in the rest of the territory. The results of the [national measurement campaign](http://www.irsn.fr/FR/connaissances/Environnement/expertises-radioactivite-naturelle/radon/Pages/4-Campagne-nationale-mesure-radon.aspx#) in metropolitan France show that more than 40 % of the buildings on this land exceed 100 Bq.m-3 and more than 6 % exceed 400 Bq.m-3. Note: in the case of municipalities with a large area — as is the case in particular for some Overseas — the formations concerned sometimes occupy only a limited proportion of the communal territory. In this case, the mapping per commune does not represent the actual surface of a territory affected by radon potential but, in a way, the likelihood that there will be a source of exposure to high radon even highly localised within the territory of a commune. In order to visualise different areas within the communal territory and to better appreciate the real radon potential in this territory, reference should be made to the [mapping depicted according to the contours of the geological formations](http://www.irsn.fr/FR/connaissances/Environnement/expertises-radioactivite-naturelle/radon/Pages/4-cartographie-potentiel-radon-formations-geologiques.aspx). To find out more: [www.irsn.fr/carte-radon](http://www.irsn.fr/carte-radon)