A New South Wales Mine Safety Unit investigation into the wall collapse at Austar that killed two miners is examining its design, the incident site geotechnical conditions, and the suitability of engineering and strata controls.

With longwall top coal caving (LTCC), the longwall has a second armoured faced conveyor (AFC) that runs behind the base of the supports to clear the coal that falls from the roof once the chocks have moved forward.

A flap at the base of the rear of each shield is raised to allow the coal in the roof above the longwall.

The system is considered ideal for thick seams (from 5-12m), whereas standard long wall equipment is only capable of mining in seams of up to 4.5m.

The Greta seam, in the area of the Austar coal mine, is a thick seam and thus by using this mining method, up to 80% of the additional coal can be accessed, which would otherwise be lost.

The system has also proven to provide safety advantages in the areas of face stability and control of the operation as well as the management of spontaneous combustion.

Also the environmental impacts such as subsidence can be more readily tailored to the sensitivity of the area by controlling the extent of coal recovery from the caving process.

Research and evaluation undertaken by CSIRO, the School of Mines, University of NSW and Strata Control Technology Operations Pty Limited, has indicated that LTCC is suited to Australian conditions and has application throughout Australia for longwall mining, particularly in thick coal seams.

The company holds patent rights to the design in China and Australia and the Austar equipment is being manufactured under licence by a German company DBT.