Determination of the radon potential of a building by a controlled depressurisation technique (RACODE)

Action levels and limits for radon in homes apply to the annual mean radon concentration. Because the indoor radon concentration varies strongly with time short term measurements are often not accurate; on the other hand, long term measurements do not allow rapid assessment of the exposure to radon. This paper presents methodology and results of a new method for the rapid determination of the building radon potential (RACODE (radon potential determination by controlled building depressurisation)). A fan produces a small pressure differential (10 - 50 Pa) between building and outdoors and the measurement of the flow rate and the radon concentration of the fan exhaust air at steady state yields the convective radon entry rate. Furthermore building characteristics like air exchange rate, equivalent leakage areas, and leakage distribution are determined. With appropriate modelling the mean radon concentration is deduced from these data. RACODE was applied to eight buildings where the mean radon concentration was known from long term passive measurements (2 x 3 months). Sometimes the use of a second fan was necessary to produce the pressure differential in the lower part of the building only and to determine the leakage distribution of the building. The radon concentrations obtained by RACODE agree well in most cases with those from the long term measurements. The uncertainty depends strongly on the type of building, i.e. whether it is possible to simulate stack effect conditions well enough with the fan(s) and whether the leakage distribution can be determined accurately. Besides the determination of the mean radon concentration RACODE should be useful for the rapid assessment of the effectiveness of mitigation measures if the same kind of measurements at defined pressure conditions are performed before and after mitigation. (orig.)