Radon is a radioactive gas that originates from uranium. It occurs naturally in the ground, and is the most common cause of radon problems in indoor air. Radon can also be emitted from building materials. In Sweden, blue concrete was commonly used as a building material between 1929-1975 and contains alum shale. The use of blue concrete has been limited in Norway.
The Norwegian Radiation and Nuclear Safety Authority (DSA) estimates, that radon contributes to approximately 370 new cases of lung cancer each year. The risk increases with increased exposure to radon. The government recommends keeping the radon levels as low as possible, and that radon mitigation be performed when the radon levels exceed 100 Bq/m3 in living spaces. Since radon has no smell and is invisible, measurements are required to detect the gas. Such measurements are performed by Eurofins.