Federal studies show the method of mining used at the Utah mine that collapsed has a history of being disproportionately deadly.

The Crandall Canyon mine collapse occurred Monday while miners using a method called "retreat mining."

In retreat mining, pillars of coal are used to hold up an area of the mine's roof. When that area is completely mined, the company pulls the pillar and grabs the useful coal, causing an intentional collapse.

A 2003 study by the National Institutes of Occupational Safety and Health shows that retreat mining is one of the biggest causes of mine roof collapse deaths. The study found that between 1992 and 2001, 27 of the 100 roof fatalitiies were from retreat mining.

Last month, federal regulators cited Brooks Run Mining for safety violations that resulted in the deaths of two workers in a roof fall at a mine in southern West Virginia. MSHA said the company ignored its roof control plan and inadequately trained workers on safe retreat mining practices.