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Geology for society

Radon Hazards

Published: August 15th 2017 | Last change: July 10th 2020
Long term exposure to radon in indoor air is responsible for between 250 and 300 new cases of lung cancer each year in Norway. Radon awareness maps covering the region around Oslo and Oslo fjord help the public and decision makers identify the areas worst affected by radon.

The Geological Survey of Norway (NGU) and Norwegian Radiation Protection Authority (NRPA) have cooperated to develop radon awareness maps.  These online maps are helpful tools for municipalities to find out the levels of radon in existing dwellings and when planning new building projects.

Uranium in the ground

With the help of planes and helicopters, NGU has conducted comprehensive surveillance of the natural-sourced background radiation. The NRPA contributed measurements of indoor radon in 6326 dwellings within the study area. Comparison of these data sets, and incorporation of information on bedrock and drift geology, resulted in radon awareness maps covering some 10,000 square kilometres from Hadeland and Romerike in the North to Fredrikstad and Skien in the South. Almost two million people reside in this area.

Factors forming the basis of Radon Awareness maps:

The maps contain four important factors used in the evaluation of radon awareness:

  • Existing measurements of radon concentrations in indoor air
  • Airborne Gamma ray spectrometer measurements, which provide overview of uranium concentrations in the ground
  • Distribution of permeable drift deposits. Sand and gravel can permit the transport of radon from large ground volumes into dwellings. The presence of these kinds of deposits in the substrates of dwellings is generally regarded as a high radon hazard factor
  • Bedrock - rock types that contain uranium and increase levels of radon gas.

In addition, the map provides a clear overview of the bedrock geology in the Oslo region. Bedrock can be categorized according to the likelihood of the presence of uranium-rich granite and uranium-rich gneiss. These rock types are commonly associated with elevated levels of radon in indoor air.

This research is vital: Norway has concentrations of radon gas in dwellings that are among the highest in the world.

Over the limit

The extensive radon measurements conducted throughout Norway reveals that as many 9 % of all dwellings (175,000) have radon concentrations in indoor air above the recommended action limit of 100 Bq/m3.


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