The agency said on Tuesday three rib fall fatalities and two roof falls in 2010 killed three US miners, and two miners had already died this year as a result of rib failures underground.

"While recent trends have shown a decline in roof fall fatalities, the incidence of rib fall deaths has remained nearly constant," assistant secretary of labor for mine safety and health Joseph Main said.

"Furthermore, approximately 100 miners are injured by rib falls every year, due in large part to the rise in mining heights underground."

MSHA said the two greatest risk factors in rib fall hazards were mining height and depth of cover. A detailed study of federal records by the agency found that 22 of the 24 rib fall deaths recorded since 1995 involved these elements.

Today’s mines, in many cases, are located in coal reserves previously avoided due to poor roof conditions, and these operations are frequently deeper and are under or over more abandoned workings. This, unfortunately, creates additional roof and rib stress.

Other risk factors include multiple seam interactions, rock partings in the seam and retreat mining activities. Also, joints or smooth-surfaced slickensides that dismember the rib increase risk.

MSHA said about three quarters of the reported rib fatality victims were either roof bolting or operating continuous mining machines.

"Over the past few decades, improvements in roof control technology such as new bolting systems, automated temporary roof support systems, use of cabs and canopies, and mobile roof supports have led to a significant reduction in roof/rib fall fatalities," Main said.

"Through PROP, we hope to increase mine operators' awareness about the hazards and precautions necessary to prevent such accidents."

MSHA has developed a new brochure, Coal Mine Rib Control for Mine Operators, which highlights key trends observed in recent roof and rib accidents. It also provides mines with safety advice and tips for maintaining proper control.

Federal inspectors are now delivering the publication to underground mines along with other educational materials, and staff plan to distribute an alert to mine operators on the hazards and actions needed to prevent accidents.

MSHA kicked off its 2011 PROP effort last month with a roof control seminar at the National Mine Health and Safety Academy near Beckley, West Virginia.

For more information about the PROP initiative, visit the MSHA website.