DEPARTMENT OF LABOR
MINE SAFETY AND HEALTH ADMINISTRATION
ACCIDENT INVESTIGATION REPORT
(Underground Coal Mine)
FATAL FALL OF ROOF
Darby Fork No. 1 (ID:15-02263)
Lone Mountain Processing, Inc.
Holmes Mill, Harlan County, Kentucky
October 10, 1998
Dennis J. Cotten
Originating Office - Mine Safety and Health Administration
Coal Mine Safety and Health
H.C. 66, Box 1762, Barbourville, Kentucky 40906
Joseph W. Pavlovich, District Manager
Report Release Date : February 24, 1999
At approximately 12:25 a.m. on Saturday, October 10, 1998 a fatal fall of roof accident occurred at the Lone Mountain Processing, Inc., Darby Fork No. 1 Mine.
Gary Merrill, a 28 year old continuous mining machine operator with 9 1/2 years experience, suffered fatal injuries while operating a 14-10 CM Joy continuous mining machine by remote control on the 002 MMU. The victim, positioned along the right rib, was engaged in taking the second lift from the No. 4 pillar when he was struck by a piece of mine roof measuring 12.5 feet by 13.0 feet by 9 inches in thickness.
Roof bolts in the accident area failed due to horizontal and lateral loading of the roof bolts. Second mining had caused additional weight to be shifted to the area of the accident which resulted in lateral movement in the immediate roof along a previously detected bedding plane. The mine operator was aware that there was a separation in the roof strata seven inches above the roof line, and the increase overburden pressures were creating sloughing rib conditions in the accident area, but failed to install additional roof support or otherwise control the mine roof where miners worked and traveled.
The Darby Fork No. 1 mine, located in Holmes Mill, Harlan County, Kentucky, is operated by Lone Mountain Processing, Inc. The mine employees 118 persons underground and three persons on the surface. The mine is opened by one shaft, two slopes, and four drifts into the Darby seam which averages 48 inches in thickness. The mine is ventilated by an exhausting eight foot diameter Jeffrey fan which is located near the shaft opening. The mine produces coal on two shifts per day, five days per week utilizing the room and pillar method with maintenance and support work being performed on third shift. The approved roof control plan allows entries and crosscuts to be developed to a maximum width of 20 feet, with entry centers a minimum of 50 feet, and crosscut centers a minimum of 80 feet.
Three continuous-mining machine sections produce an average of 4,000 tons of coal daily. Coal is hauled from the face areas to the section loading points by Long-Airdox Un-A-Haulers and Stamler Ram Cars and transported to the surface by belt conveyor. The roof is supported during advance mining by Grade 60, 5/8 inch diameter "re-bar", 48 inch fully grouted roof bolts. The mine property is owned in fee by Ark Land Company which is a landholding company for Arch Minerals.
The principal officers of the operation are as follows:
|Gaither Frazier||Mine Manager|
|Ronnie Biggerstaff||Safety Manager|
The last Mine Safety and Health Administration (MSHA) regular Safety and Health Inspection (AAA) was completed on September 29, 1998.
DESCRIPTION OF THE ACCIDENT
At 11:00 p.m. on October 9, 1998, Jack Roberts, section foreman, and his third shift crew of nine miners entered the mine and traveled to the working section (MMU 002). The third shift crew changed out with the second shift crew and did not leave the 002 section until shortly after the third shift crew arrived. Before work started, Roberts conducted an examination across the pillar line. According to statements obtained during interviews there was a crack observed at 7 inches in a test hole immediately behind the continuous mining machine by Johnathan Smallwood, third shift roof bolter operator, in the No. 4 entry. Shortly thereafter, Roberts questioned Smallwood regarding what he had determined from his examinations of the test holes and was told about the crack at 7 inches in the No. 4 entry. Roberts took no action to have additional roof support installed in the area.
The third shift crew members consisting of Gary Merrill, continuous mining machine operator, Harold Brock, continuous miner helper, Johnathan Smallwood, roof bolt operator, Roy Cook, roof bolt operator (operating a ram car), and Glenn Browning, ram car driver, began mining in the No. 4 entry by taking the first lift of pillar No. 3. After the first cut was completed in the No. 3 pillar, five breaker posts were set in preparation for mining the second lift of the No. 4 pillar. The continuous mining machine had mined approximately 20 feet of the second lift when the roof fell, entrapping Gary Merrill, the continuous mining machine operator.
Immediately, the crew started removing the rock off of Merrill, by using a lifting jack and other tools to raise the rock off the victim. It took approximately 10 to 15 minutes to remove Merrill from under the debris. Merrill was examined for vital signs by Jack Roberts, section foreman, and Glenn Browning, ram car operator, but none were detected. Roberts and Browning, both certified EMT's began CPR. Merrill was then placed onto a stretcher, taken to the section mantrip and transported to the surface.
The victim was examined by emergency personnel with the Keokee Rescue Squad and was transported to the Lee County Community Hospital located in Pennington Gap, Virginia. Dr. Robert D. Hayes, D.O., pronounced the victim dead at 2:45 a.m. The cause of death was "mechanical asphyxiation".
INVESTIGATION OF THE ACCIDENT
At approximately 1:15 a.m. on October 10, 1998, Robert Rhea, Supervisory Coal Mine Safety and Health Inspector of MSHA's Harlan, Kentucky Field Office, was notified by Ronnie Biggerstaff, Safety Manager, that a serious accident had occurred. The MSHA accident investigation team was assembled and arrived at the mine at 3:00 a.m. A 103 (k) Order was issued to ensure the safety of the miners until an investigation could be conducted.
MSHA and the Kentucky Department of Mines and Minerals jointly conducted the investigation with the assistance of mine management and the miners.
PHYSICAL FACTORS INVOLVED
The following physical factors were determined to be relevant to the occurrence of the accident.
- The victim was remotely operating a 14-10 CM Joy Continuous
Mining Machine (Serial No. JM5089-R) on the 002 section when
the accident occurred.
- The section had been developed on 85 foot x 95 foot centers
leaving a coal pillar approximately 65 foot by 75 foot in
size. The roof was supported with Grade 60, 5/8 inch
diameter "re-bar", 48 inch fully grouted roof bolts. Straps
in conjunction with roof bolts had been installed in the
accident area when this area was developed.
- The roof bolting machine operator detected a crack about
seven inches above the roof line in a test hole
approximately 45 minutes prior to the occurrence of the
accident in the area immediately adjacent to the fall. The
crack was located at the same horizon as the roof which
fell. The roof bolting machine operator advised the
foreman of the presence of the crack prior to the fall.
- Additional supports had previously been installed in the
intersection outby the accident scene. These were installed
for the purpose of additional roof support due to
abnormalities observed in the roof and rib conditions in
that area. The additional support consisted of six, nine
foot, "superbolts" ( these roofbolts were Excel Double Lock
7/8" diameter Grade 75 steel, installed with a two foot
polyester resin cartridge and an installed torque between
300 and 350 ft./lbs.).
- The fallen roof material broke into three large sections of
rock upon impact. The largest piece, which struck the
victim, measured 12.5 feet by 13 feet by 9 inches in
thickness. The first of the other two pieces measured 9
feet by 2.5 feet by 8 inches in thickness and the other
piece measured 7.5 feet by 2 feet by 8 inches in thickness.
- There was a failure of the roof support system where the
roof fall occurred. Three of the failed Grade 60, 5/8 inch
diameter "re-bar", fully grouted 48 inch roof bolts were
collected for the purpose of testing. Two of the 48 inch
straps were also broken by the falling material. The
failure of these materials is more thoroughly addressed in
- The overburden in the area of the accident was approximately
1,900 feet above the coal seam and is composed of
sedimentary rock formations of sandstones, siltstones,
shales, and coals.
- There was lateral movement in the immediate top along a bedding plane as could be observed in the test holes in the area. This lateral movement created a shearing type load on the installed roof bolts in the area.
The three broken roof bolts and the three accompanying bearing plates were retrieved from the accident site for the purpose of evaluation and possible testing at the Pittsburgh Safety and Health Technology Center. The three (3) recovered bolt segments were portions of Grade 60, 5/8-inch diameter "re-bar" which were originally 48-inch long bolts, and manufactured by Excel/Ani. The actual lengths of the three bolt segments obtained at the mine were 8-1/2, 6-1/4, and 12-3/8 inches. Due to the physical limitations of the Roof Control Division's (RCD) universal testing machine, only the longest portion could be tested. A check with an independent testing lab revealed the same limitations utilizing their testing equipment.
A tensile strength test was conducted in the RCD lab on October 22, 1998 utilizing a Tinius-Olsen Universal Testing Machine on the longest segment of roof bolt. The ultimate tensile strength of the specimen was determined to be 33,300 pounds, which exceeds the required minimum ultimate tensile strength of 27,900 pounds for a No. 5, Grade 60 "re-bar" as set forth by the standard required by the American Society of Testing and Materials (ASTM).
A visual examination of the "re-bar" and bearing plates lead to the following observations and conclusions:
- Two of the "re-bars" appear to have been fully grouted. One
of the specimens does not appear to have been fully grouted.
- The bearing plates installed on the two portions of "re-bar"
appeared to have been fully grouted and were slightly
deformed. This deformity indicated that the bearing plates
were subjected to loading either prior to, or during, the
- The bearing plate installed on the "re-bar" that appeared to
have been not fully grouted was not deformed, indicating
that the apparent un-grouted portion of "re-bar" along with
the bearing plate was not subjected to any substantial
loading. From this it can be concluded that the lack of
grout was not a factor in the bolt failure.
- The condition of the broken ends of the "re-bar" do not appear to indicate an abnormal failure. The lack of an obvious reduction in "re-bar" cross-section (commonly referred to as "necking-down") is most likely due to a combination of the bolt type and the type of loading to which the bolts were subjected. Due to the stiffness of a grouted "re-bar", a failure in a segment of "re-bar" that is grouted will not generally result in a substantial reduction in cross-section. Regarding the effect of method of loading on the condition of the break, a shearing type load and/or a load that would tend to bend the "re-bar" will not result in substantial necking-down.
According to statements obtained during interviews, a few days prior to the accident, there was a similar fall of roof in the No. 5 entry which caused the bolts to fail, resulting in minor injuries to the continuous mining machine operator on the 002 MMU.
The area in the crosscut outby the accident scene had six, nine foot, "superbolts" installed for additional support due to deteriorating conditions in the area. Before the second lift was taken from the No. 4 pillar, five turn posts were set, which exceed the minimum number of three required in the Approved Pillar Recovery Plan for the 5-entry car haulage section panels. There was no additional roof support installed in the immediate area where the accident occurred.
Due to the fact that roof conditions can deteriorate over time and also since second mining can create adverse and abnormal conditions, the Approved Roof Control Plan states, in part, " a roof evaluation will be made when entering a previously mined area for the purpose of pillar recovery. When inadequate roof support is encountered, the necessary corrective actions will be taken".
The mine roof fell as a result of a failure of the installed roof control system. The installed roof bolts failed as a result of both horizontal and lateral loading on the roof bolts which was caused by second mining in the area. The second mining had caused additional weight to be shifted to the area of the accident which resulted in lateral movement in the immediate roof along the previously detected bedding plane. Despite increasing overburden pressures, adverse, and deteriorating roof and rib conditions being present, the mine operator failed to install additional roof support in order to support or otherwise control the mine roof where miners worked and traveled.
- A 103 (k) Order, No. 7457184, was issued to ensure the
safety of the miners until an investigation could be
- A 104 (d)(1) Order, No. 7452131 was issued for a violation of Title 30, Part 202 (a), for the mine operator's failure to support or otherwise control the roof where persons were required to work and travel.
Dennis J. Cotton
Approved by: John M. Pyles
Assistant District Manager for Enforcement
CMS&H, District 7
Joseph W. Pavlovich
CMS&H, District 7
Coal Mine Safety and Health Inspector
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