Continuous mining machine helpers Michael Carter and Justin Travis were killed April 28 at Alliance Resource Partners’ Dotiki operation in Hopkins County while working in the mine’s No. 6 section.

Travis was operating the miner in the No. 3 entry cleaning up loose rock with the assistance of Carter when the roof fall occurred.

“Travis and Carter were in the process of moving to the next proposed cut in No. 2 Left Crosscut when draw rock, approximately 6 to 12 inches thick, fell in the unbolted face of the No. 3 entry,” US Mine Safety and Health Administration investigators said.

In its review of the Dotiki incident, the agency found hidden slickensides, or slips, in the face of the No. 3 entry of No. 6 section and that unsupported area above the fresh cut, mined in the face of the No. 3 entry, allowed the overlying roof weakened by the slips to break the strata’s layers.

The total fall was estimated to measure 76 feet long, 19ft wide, and a maximum 10ft thick, and covered both the workers and the continuous mining machine.

MSHA said the mine was working with a compliant approved roof control plan at the time of the incident, and all training was current and met federal Part 48(e) requirements for underground training.

“The two fatalities occurred when the mine encountered an anomaly of multiple hidden intersecting slickensides … which were not detected by the mine operator,” investigators concluded.

“The most likely fall propagation mode was roof failure in the unbolted cut that had the momentum to pull down the roof in the bolted portion of the entry where the miners were working.

“The bolted portion of the entry also had non-visible or hidden slickensides in the overlying bolted strata that weakened the overlying rock beds and allowed the bolted roof to be pulled down where the miners were working.”

The group also found that there were no signs of slips in the immediate roof, providing no warning for the need to install supplemental or additional supports.

To address the slickenside issues, Dotiki management proposed the installation of a robust support system near the last row of bolts in areas where overburden exceeds 750ft.

The company said the addition would prevent roof falls that originate in the unbolted cut extending outby and which exceeds the roof support system’s capacity.

The corrective action and others developed to bolster the roof control support system were given federal approval to supplement the operator’s approved RCP.

MSHA issued a 104(a) citation to Dotiki for a violation of 30 CFR Section 75.202(a) for inadequate support.

“Reportedly, no supplemental support had been installed in the roof fall area,” investigators said.

“The roof support was installed according to the approved roof control plan. This citation is being issued as enforcement action based upon the fatal accident investigation.”

Mine owner Alliance Resource Partners responded to the investigators’ findings late last week and mirrored its input on the contents, but took issue with the issued citation.

"The MSHA investigation confirms the factual findings of our own internal investigation – this roof fall was an unpredictable accident involving unforeseeable geological conditions," Webster County Coal operations vice-president Kenny Murray said.

However, regarding the citation, he noted MSHA did not indicate in any point in its probe that the accident was preventable or that the mine or operator was negligent.

“[T]he MSHA report specifically acknowledges '[t]he approved roof control plan was being complied with at the time of the accident' and that '[t]he absence of any sign of 'slips' in the immediate roof gave no warning for the need to install supplemental or additional support',” Murray said.

“Furthermore, in its citation MSHA specifically found that Webster County Coal was not negligent. In light of these facts, we strongly believe the citation issued today by MSHA is not justified."

The 413-worker Dotiki mine produces 26,000 tons daily on average from 10 mechanized mining units.

The operation’s non-fatal days lost incidence rate for the mine in 2009 was 3.68, versus the national average of 4.16.