Superior, Pinal County, Arizona May 10, 1982 No. Killed - 4
On May 4, 1982, blasting was conducted in the Magma Mine, an underground copper mine. Distracted by deteriorating tramway conditions, miners failed to quickly follow-up this blasting with timbering.
As a result of this delay, ground control problems were encountered on May 10. At about 2:40 a.m., as two miners were responding to these problems by barring down some loose ground near timbers, a cave-in suddenly occurred without warning. One of the miners was trapped in the collapse.
After unsuccessfully attempting to free the trapped miner, the other miner summoned three miners who were working in an adjacent area. Their rescue attempts went awry when one of the rescuers removed a steel bar near the trapped miner, triggering a second cave-in. This collapse fatally injured another miner.
Shortly thereafter, a third cave-in occurred. This collapse killed the trapped miner as well as a fourth individual. MSHA investigators attributed the disaster to the failure of temporary ground support. The lag time between blasting and the installation of permanent ground supports also contributed to the disaster.
Source:
Historical Summary of Mine Disasters in the United States - Volume I
