This was the finding of the US Department of Labor’s Mine Safety and Health Administration report into the accident that killed Todd Trimble, who had three years and 11 months of mining experience, at the mine in Indiana County, Pennsylvania.
Trimble was between the last full row of permanently installed roof bolts and the automated temporary roof support, installing wire roof screen in the No 2 slope entry of A Mains at the mine.
The large roof rock fell between the last row of permanent supports and the ATRS, pinning him against the drill head canopy, causing fatal crushing injuries.
The roof rock was 0.25-1.3 feet (76.2mm-396mm) thick, 3 feet in width, and 11.5 feet in length.
Trimble was preparing to install permanent supports when he was struck by the rock.
The last fully revised and consolidated roof control plan for the Rosebud mine was approved on September 18 2013. There was a slope addendum approved on September 17 2014, for the procedures and precautions for development of three slopes from the lower Kittanning seam (B Seam) to the Brookville coal seam (A Seam).
The plan permitted a maximum mining width of 20 feet and required the roof to be supported with fully-grouted roof bolts at least 48 inches long in normal mining conditions.
The slope plan required the roof to be supported with fully-grouted roof bolts at least 72 inches long with stipulations that when encountering coal seams, bed separations, defective roof conditions, an obvious or predominant slip, or a visible clay vein fault, supplemental roof support be installed.
During the accident investigation interview process, it was discovered the wire roof screen installation was not being conducted in a consistent manner by all roof bolters.
Four of the seven roof bolters told investigators they walked in front of the drill mast to install support wire and felt that it was acceptable, since they said they were under the ATRS at all times.
However, during re-enactment of the accident it was determined that the distance from the outby edge of the ATRS to the drill mast ranged from 18-22 inches.
At the time of the accident, the right hand canopy was approximately 4.3 feet off the mine floor and the left side canopy was approximately 4.5 feet off the mine floor.
The drill station canopies were lowered to place the wire roof screen on top of the canopies for installation. This practice causes the drill station canopies to not be in a position to protect the roof bolters from potential roof hazards while positioning the wire roof screen.
As a result of the investigation, the mine’s roof control plan was revised to include a safer means of installing wire roof screen.
“The mine operator failed to prevent miners from working in an area that was not adequately supported or otherwise controlled to prevent hazards from falling roof,” the US Department of Labor’s report found as the “root cause”.
“The roof bolting machine operators were allowed to position themselves between the drill mast and the ATRS, with the drill station canopies lowered, while positioning the roof screen.
“This practice exposed roof bolting machine operators to hazards from falling roof.”