Mine Safety and Health Administration (MSHA) - Report of ...

model flaws. They did not make further corrections to the model when this analysis result still did
not accurately depict known failures that AAI and GRI observed in the North Barrier section.
The mine designs recommended by AAI and implemented by GRI did not provide adequate
ground stability to maintain the ventilation system. The designs did not consider the effects of
barrier pillar and remnant barrier pillar instability on separation of the working section from the
adjacent sealed areas. Failure of the barrier pillars or remnant barrier pillars resulted in inundation
of the section by lethally oxygen-deficient air. AAI and GRI also did not consider the effects of
ground stability on ventilation controls in the bleeder system. GRI allowed frequent destruction of
ventilation controls by ground movement and by air blasts from caving. GRI mined cuts from the
barrier pillar in the South Barrier section between crosscuts 139 and 142 intended to be left
unmined to protect the bleeder system.
GRI’s mining practices, including bottom mining and additional barrier slabbing between
crosscuts 139 and 142, reduced the strength of the barrier and increased stress levels in the vicinity
of the miners. As pillars were recovered in the South Barrier section, bottom coal (a layer of coal
left in the mine floor after initial mining) was mined from cuts made into the production pillars
and barrier. The effect of this activity was to reduce the strength of the remnant barrier behind the
retreating pillar line. Bottom mining was not addressed in AAI’s model to evaluate the mine
design or in GRI’s approved roof control plan. Similarly, barrier mining was conducted in
violation of the approved roof control plan. A portion of the barrier immediately inby the last
known location of the miners was mined even though it was required by the roof control plan to be
left unmined. Barriers are solid blocks of coal left between two mines or sections of a mine to
provide protection. Although neither of these actions is a fundamental cause of the August 6
collapse, they increased the amount of load transferred to pillars at the working face and reduced
the strength of the barrier adjacent to it.
The mine operator did not report three coal outbursts that occurred prior to August 6 to MSHA or
properly revise its mining plan following these coal bursts. Between late 2006 and February 2007,
the 448-foot wide barrier north of Main West was developed by driving four entries parallel to the
existing Main West entries. Smaller barriers remained on either side of the new section entries (53
feet wide on the south side and 135 feet wide on the north side). The 135-foot wide barrier that
separated the North Barrier section from the adjacent longwall panel gob was insufficient to
isolate the workings from substantial abutment loading. Despite the high stress levels associated
with deep cover (up to 2,240 feet of overburden) and longwall abutment stress, the section
remained stable during development. However, as pillar recovery operations retreated under a
steadily increasing depth of overburden, conditions worsened. On March 7, 2007, a non-injury
coal outburst accident occurred that knocked miners down, damaged a ventilation control, and
caused a delay in mining. These worsening conditions culminated in a March 10, 2007, outburst
accident of sufficient magnitude to cause the mining section to be abandoned.
Between March and July 2007, four entries were developed in the barrier south of Main West.
Once again, the section was developed without incident but conditions worsened during pillar
recovery. On August 3, 2007, another non-injury coal outburst accident occurred as the night shift
crew was mining. Coal was thrown into the entries dislodging timbers and burying the continuous
mining machine cable. The continuous mining machine operator was struck by coal.
GRI did not notify MSHA of these three coal outburst accidents within 15 minutes as required by
30 CFR 50.10. GRI’s failure denied MSHA the opportunity to investigate these accidents and
ensure that corrective actions were taken before mining resumed in the affected area. GRI did not
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