Difficulties in radon measurements at workplaces

Different legislation systems can be found in the world concerning radon levels at workplaces. Following the European Union suggestion, a reference level for radon concentration in the air at workplaces was established in several European countries. In Hungary, the relevant legislation has come into effect on 1 January 2003. The determination of average radon concentration might present a problem, especially in places where the monthly average concentrations vary to a great extent. For example, the monthly averages measured in a hospital cave used for treating respiratory diseases showed a 24-fold difference depending on the chosen month. In such cases, attention should be paid when choosing the months and using the results of measurements for dose assessment. Another uncertainty emerges when estimating the annual dose, based on the data coming from long-term measurements, usually using integrated methods such as track detectors. There is a considerable difference between the averages measured during the working hours and over the total time (including nights and weekends), mostly in the cases of rooms with frequent air change like schools, kindergartens and ventilated workplaces. This can lead to a significant overestimation in dose calculation. Special attention needs to be paid to workplaces such as mines, tunnels and open air uranium tailings sites. This paper discusses the possible inaccuracies caused by the improper selection of time periods and methods in the measurements of the average radon concentration at workplaces.