Just a horrific workplace tragedy in Montcoal, West Virginia:

If, as feared, the four missing miners are found to have perished and the death toll at Upper Big Branch rises to 29, it would be the worst U.S. mining disaster since 1970, when 38 were killed by an explosion at Finley Coal Co. in Hyden, Ky.

The cause of Monday’s explosion has not been determined, but a buildup of methane or coal dust was considered the likeliest culprit.

Although Massey Energy boasts on its Web site of achieving its best safety record in 2009 and beating the industry average for the sixth consecutive year, safety officials said the Upper Big Branch Mine, run by Massey subsidiary Performance Coal Co., has a history of violations for not properly ventilating methane gas.

Federal inspectors fined the company more than $382,000 in the past year for repeated serious violations involving its ventilation plan and equipment at Upper Big Branch, the Associated Press reported. The violations also cover failing to follow the plan, allowing combustible coal dust to pile up and having improper firefighting equipment.