(LIU CHAN)

A rescuer walks out of a pit at Tonghua Coal Mine in Qijiang County, southwest China's Chongqing Municipality, where a gas explosion killed 30 miners and injured 77 on May 30.

Investigators blamed the accident on excessive use of explosives during the colliery's renovation projects and poor evacuation procedures. When the explosion occurred, 131 miners were working about 1,000 meters underground.

The 50-year-old Tonghua Coal Mine is affiliated with the state-owned Songzao Mining Bureau. Its designed annual production capacity was 300,000 tons, which had been expanded to 600,000 tons.