Survey and mitigation of occupational exposure of radon in workplaces

The mean radon concentration during working hours was 36% higher in the underground spaces than at ground level. The highest mean radon concentration was found in hillside rooms. The violation of the Finnish occupational exposure limit (OEL is 400 Bq m−3) was 17% in the whole data. To quantify the importance of soil as the main source of indoor radon was problematic in underground spaces because of the large variability of air exchange rates and pressure differences in the sites studied. The weather conditions and the different timing of using the ventilation confused the results especially in reference rooms at ground level. Improving the existing ventilation in underground workplaces appears to be an effective mitigation method. Radon levels during working hours can be estimated with the integrated method in underground and hillside sites (R2>0.9).