Since environmental radon on average accounts for about half of all human exposure to radiation from natural sources, increasing attention has been paid to exposure to radon and its associated health risks. This interest has been intensified especially through relevant international recommendations (ICRP 103, 2007; IAEA 126, 2014; Directive 13/59/Euratom) to include radon exposed workplace in the radiation safety control.

Although radon measurements in Bulgaria have started in the last century and there are a lot of regional surveys, the systematic measurement of dwellings started in 2015. Most of the countries in the world have been completed their detail geological radon survey many years ago, while Bulgaria is at the beginning. Although the new Strategy, adopted in 2018, includes buildings with public access, dwellings have been prioritized in order to be created a Bulgarian radon map.

The radon concentration does vary not only with seasonal changes, but also with the age, the construction mode of buildings, the ventilation conditions and with specific sites and geological materials. From other hand the all buildings could not to be measured, however the buildings with public access should be control, especially the kindergartens and schools where the children grown up.