When the statutory limitations on pillar extraction by mechanical means were lifted in NSW, a number of problems became evident due to the time which had elapsed from the development of the original workings.
Many pillars had partially crushed due to the time they had stood unworked or due to insufficient dimensions (for proper support). There were also other problems associated with the original dimension being non-uniform throughout the original workings.
Generally, the system known as The Old Ben System (which was developed at the Old Ben Colliery in Illinois, USA) was based on developing multiple headings, usually three, to the limits of the area to be extracted. These panels, along with newly formed pillars (in the virgin coal) were extracted in retreat.