For the public, radon danger is mainly related to uranium mines and lung cancer among the miners (in the Middle Ages called the "miner's disease"). After the discovery of radon, nearly one hundred years ago, radon was recognized as a possible cause of this disease. But in 1952, Bale and independently also Běhounek, a member of the Czech Academy of Science, discovered the main reason for the disease - the inhalation of short-lived radon decay daughters (i.e., Po, Bi, and Pb), their deposition on the surface of air passages and the exposure of bronchial epithelium cells arising from this deposition. This discovery led to the goal-directed effort to reduce the occurrence of lung cancer among uranium miners, classify the professional risks, and find a relationship between the exposure to radon daughters and lung cancer. This was discussed in several epidemiological studies of lung cancer among the selected radon exposed uranium miners (in our country organized by Dr. Ševc).
In 1956, Hultqvist discovered radon occurrence in Swedish houses. It was assumed that this had been a local problem; therefore, this aspect was ignored. In the 1970s, high radon concentrations had been found even in other countries, and the national radon programmes were launched. In our country, the preparation for the radon programme was started in Jáchymov, 1978. It was demonstrated that this had been a world-wide unique matter that was affected by two aspects:
1. A higher radon risk from soil that was partly contaminated from former silver mines with a higher uranium concentration
2. For construction of the houses in Jáchymov, building materials with high radioactive waste from local uranium paint production and radium production were used.
In 1980-81, the radium concentrations that were higher than the values of radium concentrations permitted in the draft of the standard were found in porous concrete that was produced in Poříčí near Trutnov. This was caused by raw material used for porous concrete production, i.e., fly ash from the local power station in Poříčí near Trutnov. This power station burnt bituminous coal from Baltazar mine, Žacléřsko-Svatoňovická coal bed, rich in uranium mineralized ore. The decision was issued to reduce the radium concentration in building materials that were produced in the plant. Nevertheless, only a low percentage of the houses in which the material was used (total number was about 30,000 family houses) exceeded the levels for air radon concentration in houses specified in the draft of the standard. Because of this case, research of remedial measures, organized by the Ministry of Construction Industry, was started, and mainly focused on building materials not on protection against the main source - radon from soil.
The other similar case appeared in Rynholec u Nového Strašecí where building material from a former power plant was used for the production of slag. The radium concentration in slag was found four times higher on average compared to porous concrete in Poříčí; fortunately radon emanation from this building material was lower. The cause was again found - a uranium-rich cave of the former local mine called Anna (later the ČSA mine) in the Rakovník region of the Kladno coal bed. The first signal came in about 1960, which was before the radon era. At that time, no radiation protection standards were available (only the exposure to gamma radiation emitted from clinker concrete peripheral walls was assessed in the centre of a room, and the value was at most twice higher compared to the normal values in houses). The Public Officer decided that the existing houses (for example, Praha - Petřiny housing estate, and the housing estate in Stochov) would not be reconstructed, but the future construction would be reduced or improved by eliminating harmful slag. After 1968, the new management of n.p. Prefa Hýskov in Rynholec decided to start the production of clinker concrete panels for START type prefabricated houses. About 3,000 houses were produced from 1972 to 1983. In addition to higher radon concentrations (i.e., twice higher compared to the standard value), higher gamma dose rates were also measured in these dwellings (i.e., on average from 5 to 10 times higher compared to gamma natural background). This problem was solved before 1989. Under pressure of the Association of START House Owners, the government offered to purchase or to reconstruct the START houses (only some of the owners decided to sell their houses; the others decided for remedial measures). This case has revealed the complexity of radon risk and its exposure.
In the middle of the 1980s, houses with extremely high radon concentrations were found. The high radon concentrations were caused by entering radon from soil. In cooperation with the Czech Geological Institute, the regions with expected low, middle and high radon risk were predicted. The systematic measurements were successively started in the regions of the Czech Republic, and the public and the government focused on the problem of radon entering from soil. In addition to the systematic measurements in the Czech Republic, the experimental verification of the reconstruction methods and their financial support were commenced. More than 2,000 family houses and children's facilities have been reconstructed (i.e., remedial measures). The problems were regulated by Regulation of the Ministry of Health no. 76/1991 Coll. and by Government Resolution on Radon Problems no.150/1990 Coll. and no.709/1993 Coll. The basic problems are now regulated by "Atomic" Law no. 18/1997 Coll, and SUJB Regulation no. 307/2002 Coll.