Preventing roof fall fatalities during pillar recovery: A ground control success story

For decades, pillar recovery accounted for a quarter of all roof fall fatalities in underground coal mines. Studies showed that a miner on a pillar recovery section was at least three times more likely to be killed by a roof fall than other coal miners. Since 2007, however, there has been just one fatal roof fall on a pillar line. This paper describes the process that resulted in this historic achievement. It covers both the key research findings and the ways in which those insights, beginning in the early 2000s, were implemented in mining practice. One key finding was that safe pillar recovery requires both global and local stability. Global stability is addressed primarily through proper pillar design, and became a major focus after the 2007 Crandall Canyon mine disaster. But the most significant improvements resulted from detailed studies that showed that local stability, defined as roof control in the immediate work area, could be achieved with three interventions: (1) leaving an engineered final stump, rather than extracting the entire pillar, (2) enhancing roof bolt support, particularly in intersections, and (3) increasing the use of mobile roof supports (MRS). A final component was an emphasis on better management of pillar recovery operations. This included a focus on worker positioning, as well as on the pillar and lift sequences, MRS operations, and hazard identification. As retreat mines have incorporated these elements into their roof control plans, it has become clear that pillar recovery is not “inherently unsafe.” The paper concludes with a discussion of the challenges that remain, including the problems of rib falls and coal bursts.