Since 1994 the Radiological Protection Institute of Ireland has been conducting a pilot programme ofpersonal monitoring of workers in workplaces with high radon concentrations. Initially theprogramme involved staff employed by the operators of commercial show caves, but in January 1999it was extended to incorporate non-show cave workers when employees in aboveground offices in twosmall Departments in an Irish University were included.Personal monitoring of show cave staff confirmed the fact that employees in two caves receivedannual radiation doses in excess of 4 mSv.
The aim of this study was to compare the measured and the calculated concentrations of indoorradon caused by building materials at 23 workplaces. The measured concentrations of radon wereclearly higher than the calculated radon concentrations from the building materials indicating thatthe main source of indoor radon was the soil under and around the buildings. The highest means ofcontinuously (933 Bq m-3) and integrated (169 Bq m-3) measured and calculated (from 70 to 169Bq m-3) concentrations of radon were found in hillside locations.