The Daily Mercury quotes a spokesman from the Queensland Department of Natural Resources and Mines saying the electrician had entered a "noxious atmosphere".

"Mine management reported that an electrician working underground was discovered unconscious at approximately 3pm yesterday [Tuesday]," a DERM spokeman reportedly said.

"Preliminary indications suggest the electrician entered a closed area of the underground mine workings and may have been asphyxiated by a noxious atmosphere."

The effect of the incident on mine production and morale is hard to gauge with all underground personnel having been withdrawn as a precaution.

The Capcoal complex, which is a combined open cut and underground operation that includes Grasstree, was slated to produce 11 million tonnes per annum of hard coking and pulverised coal injection coal from 2014.

At December 2012, estimates for run-of-mine reserves are approximately 193Mt of predominantly hard coking coal and minor export thermal quality, with an additional 186Mt of mineable in-situ resources outside the existing mine layout.