Radon in Brazilian underground mines

Radon is a chemically inert noble radioactive gas found in several radioactive decay chains. In underground mines, especially those that contain or have contained ores associated with uranium-bearing minerals, workers might be exposed to high levels of radon and its decay products (RDP). This work aims to investigate whether the exposure of workers to radon gas and its progeny has been evaluated in Brazilian non-uranium and non-thorium underground mines. Any such results and control measures undertaken or recommended to maintain concentrations under Brazilian occupational exposure limits (OELs) are documented. The methodology we adopted consists of three main phases. The first was an extensive bibliographical survey of the concentration levels of radon and RDP, as well as the radiation dose estimates, considering measurements made heretofore by various Brazilian researchers and exhibiting original measurement work undertaken by the one of the authors (mine O). In the second phase, the values obtained were compared with OELs. In the third phase, any control measures undertaken in mines with high exposure of workers to radon and its progeny were verified, and the adopted controls were determined. Radon concentration data obtained from 52 campaigns in 40 underground mines were analyzed. The results show that assessment of the exposure of workers to radon and its progeny was undertaken in many mines at least once, and that radon levels in 62.5% of the mines, when visited for the first time, were below the Brazilian OELs. As expected, the main control measure adopted or recommended was improvement of the ventilation system.