For most of the last century, coal has been extracted and produced from two major types of mining operations - underground and surface.
But according to the United States Labor Commission, the methods for recovering coal from the earth have undergone significant changes in the past 25 years, as a consequence of technological advances.
On Monday, Amy Louviere, spokesperson for the U.S. Mine Safety and Health Administration, indicated that UtahAmerican Energy was approved to conduct retreat mining at Crandall Canyon at the time of the collapse on Aug. 6.
Louviere further reported during a telephone interview that UtahAmerican had submitted an amendment to the company's previously approved pillar removal plan in May and the amendment was accepted by MSHA in June.
While retreat mining was approved by MSHA at the Crandall Canyon mine, UtahAmerican owner Robert Murray has repeatedly denied during recent press conferences that the coal extraction method was being performed at the time of the collapse.
According to the U.S. Labor Commission's website, more than two-thirds of the coal produced underground is extracted by continuous mining machines in the room and pillar method. The method along with previous longwall extraction and current retreat pillar mining have all been used at Crandall Canyon, where six men remain trapped underground following the Aug. 6 incident.
During retreat mining, support pillars that have been left behind to provide stability within the underground operation are removed as a final step in getting all useful coal from a production site.
According to safety officials, retreat mining requires exact planning and detailed documentation of the sequence of pillars to be mined. The planning and documentation are required to insure that support within the mine stays within safe parameters.
To help ensure adequate support, the National Institutes of Occupational Safety and Health have been working on developing software for the last 10 years to help prevent "squeezes, collapses and other pillar failures through better pillar design, thereby enhancing safety for underground mine workers." According to the the agency's analysis of retreat mining and pillar stability, the ARMPS program uses computer processing to evaluate the load bearing capacities of coal pillars used in retreat mining.
The analysis further stipulates that, "proper pillar design is essential for safe pillar recovery operations."
Between 1989 and 1996, 25 percent of all roof and rib fatalities in the United States occurred on pillar recovery sections, according to NIOSH data.
Officials in Kentucky are calling for tougher regulations on the way in which pillar mining is conducted.
According to a report released in March 2006 and last modified in March 2007, researchers from Marshall Miller and Associates in Lexington evaluated 34 coal mines actively engaged in retreat mining.
The report estimates that there are more than 100 operations in eastern Kentucky with approved plans to conduct retreat mining.
The report further stipulates that these mines produce one-third to one-half of the 52 million tons of underground coal mined annually in eastern Kentucky.
Recommended changes to roof control plans include:
Minimizing workers near the active pillar line, where pillars are being removed.
Requiring the application of the analysis of retreat mining pillar stability calculations.
The software has the capability to model and predict roof stability and pillar strength.
The final part of the study which is posted on the websites of the U.S. Department of Natural Resources and federal office of mine safety and licensing recommends in closing that "miners should be better trained to geological conditions inside the mine and have a better working knowledge of the roof control plans and retreat mining plans. Improved training materials should also be prepared that specifically address retreat mining."