As poor economic fundamentals continue to force US coal mines to be idled, safety and compliance issues also played a role at some of the largest US mines, according to an SNL Energy analysis of Mine Safety and Health Administration data.

“As the US coal industry continues to endure tough market conditions, coal producers are focused on reigning in production costs, including idling uneconomic coal mines,” according to the report.

“But economics was not the only factor driving the closures. Several of the largest mines idled in the second half of 2013 were closed due to health and safety issues.”

According to the SNL Energy report, 112 coal mines were idled in the second half of 2013. This includes 14 mines idled in the third quarter, 69 in the fourth quarter and 29 mines idled over both quarters. That compares with 151 coal mines idled in the first half of 2013.

Production data from MSHA shows that mines idled in the second half of 2013 produced a combined 8.1 million tons of coal in the 12 months ended the second quarter.

Of the mines idled during the period, 70 were surface mines, 37 were underground operations and five were mine facilities.

Of the 10 largest mines idled during the second half of 2013, 50% were in Central Appalachia. Production in Central Appalachia was down 13% year over year.

Illinois Basin and Powder River Basin coals provided an alternative, as power generators shifted away from more expensive, high-Btu, low-sulfur Central Appalachian coal.

The Illinois Basin saw few mines idled during the second half of 2013, as demand for the region's coal continued to grow. Among the 10 largest mines idled in the second half of the year, two were in the Illinois Basin. However, both were idled due to mine safety and compliance issues