1: J Radiol Prot

The (222)Rn concentration in air was measured in a thermal water spa used as a hydrotherapy centre in Tunisia. The associated health risk for employees and patients due to the inhalation of (222)Rn and its progeny was estimated. A protection scheme for the employees of the spas has been designed. Results show that the (222)Rn concentration varies in the range 33-589 Bq m(-3). The (222)Rn concentrations measured in the present study show lower values in comparison to those reported for thermal spas in other countries. The (222)Rn concentration in different rooms of the spa depends mainly on the ventilation rate. A model based on a dosimetric approach was adopted to estimate the radon risk considering the (222)Rn concentration, the time spent in the spa, and the radioactive equilibrium factor F. The annual effective dose was found to vary between 0.2 and 1.7 mSv for workers while the range for patients was from 2.8 x 10(-4) to 1.1 x 10(-4) mSv. These values are within the ICRP recommended values.