Miners walk outside the Zasyadko coal mine in eastern Ukraine a day after a methane explosion killed 100 workers there. The blast, which occurred November 18 about 3,300 feet underground, was likely caused by a combination of defective electrical equipment and explosive levels of methane gas. Four similar explosions at the same mine killed a total of 137 between 1999 and 2006. Since 1991, more than 4,700 miners in Ukraine been killed on the job as a result of unsafe conditions. On average, three miners are killed for every 1 million tons of coal extracted.

—DOUG NELSON