Radon

Radon is a non-odourless, tasteless and invisible radioactive gas generated as a result of the fission of uranium. It continues to degrade into solid degradation products. Degradation products are transported from indoor air to the lungs via inhalation and attach on the inside of the lungs. The radon gas is removed with exhalation. The lung radiation dose resulting from this has been found to increase the risk of lung cancer. To a highly varying extent, uranium is present in the bedrock and mineral soils.

According to a study by the Radiation and Nuclear Safety Authority, Espoo falls under category 3, the second lowest-risk, in a four-tier risk classification used in Finland. Thick clay zones are the most safe environments, because clay material is so tight that radon cannot move in it. Houses built on clayey soil often have fewer problems with radon. Any radon in these houses may come from building materials and filling stone materials.

Enrichment of radioactive minerals into the bedrock has been reported in Espoo. Enrichment has taken place here and there randomly and often in a pocket-like fashion, so that reliable location-specific forecast data cannot be provided. Even on the same plot, variation can be detected in the bedrock in terms of radiating pockets. These constitute potential radon sources that increase the radon risk if radon protection is not taken into consideration

Rock fracture affects the radon risk. The more fractured the bedrock is, the more there are channels available for radon. It would be recommended to limit blasting to the necessary minimum and to use as small charges as possible.

In recent decades, the use of ground slabs, breeze blocks and slope solutions has become more common in the foundations of buildings. These construction methods increase the routes available for radon from the ground into the dwelling. The difference between the outdoor and indoor temperatures creates a vacuum that ‘absorbs’ radon-rich air from the ground into warm indoor spaces. In winter, temperature differences are greater, which means that the flow of radon into the dwelling is also higher. The lack of replacement air valves in mechanical venting may increase the vacuum and the radon concentrations of room air. Radon may also carry into dwellings with building materials. However, no high indoor air radon concentrations caused by building materials have been observed in Finland. In addition, radon may be released with the use of domestic water. The radon concentration in borehole water may be so high that when showering and washing clothes or dishes, for example, the radon concentration in room air increases.

The main route for radon to access dwellings is through the foundations and through fractures and cracks carried by air flows. In radon areas, the base floor structure should be such that radon flow routes are cut and the foundation is ventilated.

The Building Information Foundation RTS sr has published an RT file (RT 81-11099)(external link, opens in a new window). The file provides an illustrative description of how to protect from radon.