While the facts on how underground coal heatings occur is reasonably well-known, a technique for locating the heatings - especially in the inaccessible goaf - has proven difficult. Since 2002, the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the Australian Coal Association Research Program (ACARP) have investigated the surface-based radon technique.

The technique was initially developed by Taiyuan University of Technology, China, in 1992. It was then used commercially to locate underground heatings in 1995. Since then, it has been used to locate more than 30 underground heatings in China.

Radon-222 (Rn-222) gas occurs naturally as a decay product of the long-lived uranium-238, a common rare element in rock/coal/soil strata. Limited experimental investigations indicate temperature has a significant influence on Rn-222’s emanation ratio from coal.

ACARP sponsored a project in 2002 where the technique was demonstrated in two areas of suspected heatings at the Dartbrook mine in New South Wales. The areas were located in the goaf at depths of 340m and 200m. Five heating zones in the area were identified with the radon technique. The results were consistent with those based on analyses of gas monitoring data and mining sequences.

The study also identified that in order to apply the radon technique in Australian coal mines with greater confidence, detailed studies on the temperature dependence of the radon emanation ratio from coal and its upright movement in overlying strata should be spotlighted in any future research projects. With this in mind, ACARP this year funded further studies into the technique.

The current project is investigating temperature dependence of radon emanation from coal and the effect of heatings on radon vertical movement in overburden strata. This dependence and effect are the core science upon which the radon technique for locating coal heating is based. Bench-scale testing will be carried out for the study.

A portable prototype of a radon detector and collector suitable for field measurement of radon measurement in mines will be developed. The prototype will be evaluated by re-surveying the surface radon flux over the goaf at Dartbrook mine and one other heating event, if the opportunity arises.

The project started in April 2004, and according to its researchers, is progressing well. A bench-scale test rig is being set up and the portable prototype of a radon collector and detector has been designed and ordered for manufacturing.

The project will be completed by the end of this year.

Article based on a paper presented at the 2005 AUSIMM Coal Conference by CSIRO’s S Xue and Dartbrook’s N Winkelmann.