REDUCTION OF RADON DAUGHTER CONCENTRATIONS IN MINES BY RAPID MIXING WITHOUT MAKEUP AIR

Measurements of radon daughter concentrations and their relative states of equilibrium were made in closed sections of two uranium mines to investigate the removal of radon daughters from the atmosphere by rapid mixing. Recirculation of the air within the enclosed space once per minute reduced the working level by a factor of 20. This reduction was associated with extreme disequilibrium among the radon daughters. The lowest ratio observed between Ra-A and Ra-B was 0.06. In this sample Ra-C was not measurable. The mechanism involved may be convective or turbulent diffusion to the walls of the mine. Because the atmosphere sampled became extremely clean (< 200 particles/cc measured with a condensation nuclei counter) the diffusion constant was probably that associated with free atoms. The state of equilibria measured indicates that removal of Ra-B and Ra-C was more efficient than that of Ra-A, probably because the Ra-B and Ra-C have longer mean lives. It appears that with adequate stirring it may be possible to remove radon daughters from mine atmospheres without the introduction of burdensomely large amounts of fresh air. These results may not be applicable to atmospheres with higher particle concentrations. These results strongly suggest that further research should go into methods of ventilation in which large amounts of makeup air are not required. © 1969 Health Physics Society.