Detection and mitigation of occupational radon exposure in underground workplaces.

The aim of this study was to unravel the occupational exposure to radon among underground workers. The possibility for radon mitigation by improving ventilation or by sealing was also investigated. 65 workrooms in 19 workplaces has been investigated in the ground floor, in basements and in underground spaces in southern Finland and in middle Finland. Radon concentration varied from 15 to 1636 Bq/m³du ring working hours resulting in annual dose of 0.09 to 10.3 mSv. The average radon concentration in all places studied was 359 Bq/m³ (2.2 mSv) and the average in working time was 293 Bq/m³ (1.8 mSv). Concentration of radon exceeding 400 Bq/m³ (which is the occupational limit on annual average radon exposure in Finland) was detected in 13 (20 %) workrooms. The mitigation methods utilized were enhanced ventilation, adjustment of exploitation time, and sealing yielding reduction of 45 - 75 % in radon exposure levels.