In a photo released by China's Xinhua News Agency, rescuers work at Jinshangou Coal Mine in Chongqing, southwest China, on Monday. An explosion at the mine has killed at least 13 people, and 20 more miners are either dead or trapped alive. Tang Yi/Xinhua via AP hide caption

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Tang Yi/Xinhua via AP

Wreaths and flowers commemorating those killed in the Crandall Canyon Mine collapse are posted at the mine entrance on Dec. 10, 2007, outside Huntington, Utah. A settlement Thursday includes mine owner Murray Energy's acceptance of four violations considered "contributory" to two fatal August 2007 mine collapses at Crandall Canyon. Douglas C. Pizac/AP hide caption

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Douglas C. Pizac/AP