[en] High radon concentration in work and living places are caused by a high geological radon potential of the soil, by technological processes, the use of building materials with high uranium, thorium and radium content and the building construction. Further the influence of the working and living conditions on the dose estimation is very important. Especially the equilibrium factor and the unattached fraction are influenced by the working and living conditions. Further we report on radon risk mapping, the search for radon affected work and living places and the experiences to propose the remedial action or radon protected building construction resulting from the radon risk of the soil. Further the quality control of this remediation or construction process respectively the efficiency of the radon protection will be presented. But not in all situations are remedial actions possible. Therefore is for exposure reduction a radon personal dosimetry necessary for a limitation and optimization the working or living time under high radon concentration. The personal radon dosimetry on workplaces, for instance water works, mines, show caves and other work places with high radon levels is up to now not sufficient resolved. The possibility to include alert functions, the signalisation of high dose rate and also the time resolute dose determination give new chances for a real online dosimetry in such very dangerous places. (author)