DEPARTMENT OF LABOR
MINE SAFETY AND HEALTH ADMINISTRATION
District 9
ACCIDENT INVESTIGATION REPORT
(Underground Coal Mine)
Fatal Coal Mine Burst (Fall of Face)
Aberdeen Mine (ID 42-02028)
Andalex Resources, Inc.
Price, Carbon County, Utah
by
Bob E. Cornett, CMS&H, Supervisor (Roof Control)
Archie L. Bailey, CMS&H, Mine Inspector
Carl Schmuck, Denver S&HTC, Mining Engineer
R. Karl Zipf, Jr., Denver S&HTC, Mining Engineer
Originating Office - Mine Safety and Health Administration
Coal Mine Safety and Health, District 9
P. O. Box 25367, DFC, Denver, CO 80225-0367
John A. Kuzar, District Manager
OVERVIEW
At approximately 6:30 p.m., November 14, 1996, a coal burst occurred on the 3rd West longwall panel of Andalex Resources, Inc.'s, Aberdeen Mine. One miner was killed and one miner was knocked down by coal propelled from the longwall face. One other miner working on the face was not injured. Three crew members working at or near the headgate were not injured either.
Following the start of afternoon shift, the mining crew had made three successful passes along the longwall face. The burst occurred as the shearer started into the "snake" turn near the tailgate to begin the fourth mining pass. Coal was propelled from the face across the conveyor pan and into the shields for approximately 100 feet along the face (shield no. 113 to shield no. 131 at the tailgate). The coal struck a miner working at shield no. 124 and caused fatal injuries.
Examination of the immediate face and tailgate areas showed that the roof behind the shields was hung up about 50 feet along the shield line and back about 50 feet into the gob behind the shields. Floor, roof and rib damage from the burst was evident for approximately 150 feet along the tailgate entry, outby the face. An examination of the tailgate entry from the longwall face to the main entries found that the roof between the yield pillars was intact for approximately 1000 feet along the tailgate. This would allow stress transfer from the adjacent mined-out panel (2nd West) into the active panel (3rd West).
Although no previous bursts were reported in 3rd West longwall panel, coal bounces (consisting of sudden forceful vibrations) had been felt in the panel prior to the burst that caused the fatality. An increase in broken torque shafts on the tailgate shearer was reported to have occurred during the two-week period immediately prior to the burst. The torque shaft breakage occurred while cutting the floor near the tailgate end of the longwall face and was accompanied with floor vibrations.
The depth of cover (overburden) above the longwall face varied from approximately 1700 feet at the headgate to just under 1600 feet at the tailgate. Additional overburden weight was placed on the face because the coal seam pitches 6o to 12o downward from the tailgate to the headgate. A massive sandstone formation, the Kenilworth Sandstone, sets approximately ten feet above the coal seam. Another massive sandstone formation, the Aberdeen Sandstone, lays directly beneath the coal seam.
Stress from overburden weight provided the energy for the burst. With a strong floor (Aberdeen Sandstone) and strong roof (Kenilworth Sandstone), the coal seam was the weak link in the system. Other contributing factors included the change in stress from overlying topography, overriding stress from the uncaved gob behind the shields, and overriding stress from the previously-mined panel.
The Aberdeen Mine (I.D. No. 42-02028) is an underground coal mine owned by Andalex Resources, Inc., of the State of Delaware, a subsidiary of Andalex Resources B.V. The corporate address is 9300 Shelbyville Road, 1201 Hurstbourne Place, Louisville, Kentucky. The mine is located in Deadman Canyon in Carbon County, Utah, approximately 10 miles northeast of Price, Utah, on the airport road.
Andalex Resources, through the Tower Division, bought the coal reserves in 1977 from the AMCA Coal Leasing Corporation. The Tower Division has operated mines in the Lower Sunnyside (Apex Mine), Centennial (Pinnacle Mine), and Gilson (Pinnacle Mine) coal seams which lay above the Aberdeen coal seam. In 1989, surface construction began for the Aberdeen portals. The new portals were driven in a northwesterly direction into the coal seam crossing through old works that were mined in the 1930's. The older mine workings were sealed on the surface and along the new main ventilation entries.
The Aberdeen Mine consists of three development sections with advancing room & pillar mining, continuous miner sections using electric shuttle cars, and one longwall section. Coal is hauled to the surface through a belt conveyor system. The coal is then loaded in haulage trucks and transported to load out facilities in the Price area. The mine is provided with diesel mantrips, diesel utility vehicles, and diesel material haulage vehicles that support the continuous miner sections and the longwall.
At the time of the fatality, the Aberdeen Mine employed 97 underground and 7 surface employees, who worked on two production shifts and one maintenance shift per work day. The mine operates 5 days per week with a two-week rotation for day and swing shift production crews. Total daily production averages 10,155 tons.
The principal management officers at the mine are:
Sam Quigley.........................General Manager/Vice President Western Operations
Kent Pilling...........................General Superintendent
Tom May..............................Safety Manager
Fred Sanchez........................Safety Coordinator
Larry Johnson.......................Mine Engineer
The Mine Safety and Health Administration (MSHA) had completed a safety and health inspection on the day shift of November 14, 1996.EVENTS OF THE ACCIDENT
Bret Robertson, the foreman for the 3rd West Longwall, and his crew started the afternoon shift at 2:30 p.m. on November 14, 1996. They arrived at the longwall at approximately 3:00 p.m. and proceeded to their respective job assignments at the headgate and along the face. Jim Berryhill (Mechanic) went to the central computer, cleared all the errors and up-loaded the face. The normal daily work and production procedures were in progress as Berryhill set shield jacks and pushed the pan line for two shearing passes along the face. He stopped and fixed the leg distributor at shield no. 69 and then fixed the leg set solenoid at shield no. 81. By the time this work was completed, the first half of the third pass had been mined which brought the shearer from the tailgate to the headgate. At this time, Berryhill was told by Robertson to take a break and that he, "Robertson," would complete the third pass and make the return cut to the tailgate with the shearer.
Shane Hackney (Jack Setter) was repairing a emulsion leak at shield no. 16, when the burst occurred at approximately 6:30 p.m. Hackney and Berryhill in the headgate felt it and observed that the lights went out. Jim Cloward (Headgate Operator) who was near Hackney also felt the burst. Cloward and Berryhill went to reset the lights and the conveyor at the stage loader control panel.
At the same time, Robert Cave (Tailgate Shearer Operator) picked himself up from the force of the coal that rolled into him and traveled to the tailgate. He was looking for Robertson but didn't find him in that area. As he came back from the tailgate, the coal dust generated by the burst had cleared enough so that Cave could see the yellow rain jacket that Robertson was wearing near the tailgate shearer drum at shield no. 124. Robertson was almost entirely covered by coal. Phillip Medley (Headgate Shearer Operator) and Cave began giving CPR to Robertson after digging him out. They also notified the headgate by pager phone to get help and first aid supplies.
Medley told Berryhill that Robertson was down and that they needed first aid equipment and an ambulance. Berryhill and Hackney both went to the aid of Robertson, obtaining necessary items from the first aid kit. When Berryhill and Hackney arrived at the accident scene at shield no. 124, they helped administer CPR in hope of reviving Robertson. Robertson was then placed on a stretcher with a backboard and was carried from the longwall face. The beltmen and the EMTs met the stretcher at about mid-face. They all continued down the face, out the headgate, and then placed Robertson into the bed of a pickup truck. Robertson was then transported to the surface.INVESTIGATION OF THE ACCIDENT
The accident investigation began on November 15, 1996, at approximately 6:00 pm. Archie L. Bailey was appointed Team Leader. On-site support of the investigation was provided by Bob E. Cornett (CMS&H Roof Control Supervisor), Karl Zipf and Carl Schmuck (Mining Engineers, Ground Support Division, MSHA Technical Support).
A briefing for the MSHA investigation team was conducted by Jim Kirk, MSHA Field Office Supervisor in Price, UT, prior to visiting the Aberdeen Mine. The investigation team arrived at the mine office at 7:00 pm. After a short conference with mine personnel, the team broke into two groups. One group, Bob Cornett and Karl Zipf, proceeded to the accident site underground with representative of mine management (Sam Quigley, Kent Pilling, Dave Pilling, and Fred Sanchez). The other group, Archie Bailey and Carl Schmuck, conducted interviews of the longwall crew that were present at the accident site when the burst occurred.
The accident investigation continued on November 16, 1996. Two additional interviews were conducted, then the entire team returned to the underground accident site. The MSHA team again divided into two pairs with Karl Zipf and Carl Schmuck observing the entire mine area related to the 3rd West Longwall Panel where the accident occurred. This effort included visual observations of the headgate entries, tailgate entries, bleeder entries, and the longwall face where the accident occurred. The purpose of this examination was to determine the presence of physical signs of stress in the coal and adjacent geologic formations. This included any evidence of stress by abutment pressures from the overlying mining in the Gilson Coal Seam, which is located approximately 250 feet above the Aberdeen Coal Seam. No evidence of abutment stress from overhead mining was observed in the areas traveled that passed beneath the abutment zones. Other observations are discussed in the Contributing Factors section of this report.
During this time, Archie Bailey and Bob Cornett focused their efforts on detailed observations of the accident scene, starting at the headgate and proceeding to the tailgate area of the longwall face. Investigation activities obtained relevant measurements, position determinations, and photos.
After returning to the mine office, a discussion was held with Laine W. Adair (General Manager, Genwal Resources, a subsidiary of Andalex Resources, Inc.) who was directly involved in the design of longwall sections in the Aberdeen Mine. This meeting included discussion of a consulting report by Agapito & Associates that was specifically written for the design of longwall mining in the Aberdeen Mine. The report by Agapito & Associates is discussed in the Contributing Factors section of this report.DISCUSSION
General Mining Information
Mining Methods
The 1st West, 2nd West, and 3rd West longwall gate entries were developed using a 3-entry system. Entries (20 feet wide) were driven on 50-foot centers; crosscuts were 120 feet apart, and yield pillars were 30 feet wide and 100 feet long. The cover of this area ranged from 1200 feet to 1700 feet. The deepest cover (1600 feet plus) was above the 3rd West longwall panel. The 3rd West panel was approximately 6700 feet long and 750 feet across. At the time of the fatality, mining had progressed approximately 800 feet (12% of the panel length) from the startup room. Mining height on the face was approximately seven feet.
During longwall mining, a complete pass of the shearer consists of two trips along the length (750 feet) of the face. At the time of the accident, the standard procedure was to start a pass with an "S" (snake) cut into the coal near the tailgate. The shearer was then directed down the pitch of the coal seam towards the headgate as it cut out the top 3/4th's of the seam. After reaching the headgate, the shearer was directed back up to the tailgate as it cut out the bottom 1/4th of the seam. The final cutting by the shearer removed the face protrusion between the "S" cut and the tailgate. The conveyor pan is pushed up behind the shearer as it makes the second half of the pass and cuts out the bottom of the seam from the headgate to the tailgate. As the pan line is pushed up behind the shearer, the shields are sequently pulled toward the pan line which prepares the conveyor and shields for the next pass.
A Joy Shearer 4LS, ser. no. LWS359R, and a Halbrock Braun Conveyor were used in the 3rd West longwall panel. Five torque shafts had been replaced within the last two weeks when cutting through into the 2nd West tailgate, No. 3 entry, with the tailgate drum at the floor.
Roof Control
Investigators observed the following support in the accident area:
- Tailgate entry support adjacent to the barrier pillar was accomplished with 60-inch fully grouted resin roof bolts on a maximum of 5-foot centers with a minimum of 4 bolts per row, and 5-foot steel mats used on each row. Crosscuts leading into the tailgate entry were supported the same as the entries except for two rows of timbers on 4 foot centers at the intersection of the tailgate entry.
- Cable bolts were used in the tailgate entry support between adjacent longwall panels with a minimum of 10-foot long cable bolts with 5-foot minimum grouting, also on a maximum of 5-foot centers and a minimum of four bolts per row, steel mats (monster mats) were used on each row, in addition to number a) above.
- In addition to a) and b) above, cribbing was installed as per CFR 75.206 in the tailgate entry. Cribbing material was pine blocks 8-inch by 8-inch by 3-foot long, built on offset 5-foot centers, or in line on 5-foot centers, in the no. 3 entry of each panel between adjacent longwalls.
- Hemschiedt Shields: Model MHW G 738 -13, 72/33,53 were in use to support the longwall face.
Electrical
The longwall equipment was energized with a separate 12,470 high voltage source brought into the mine via a separate cable that served the motors for the emulsion pumps, stage loader, shearer, headgate conveyor drive, and tailgate conveyor drive with 2400 vac inby the last open crosscut. The appropriate interlocks, switches, disconnects, and safety procedures were in place as per the 101 (C) petition for modification, in lieu of 30 CFR 75.1002 and 30 USC 811 (C). This petition for modification was granted on June 24, 1994.
Ventilation
The three developed entries of the headgate panel were ventilated with air that was coursed through two intake entries joined just inby the last open crosscut. One entry, the belt line, is a neutral entry that is regulated near the main return at the junction of the main intake entries and the panel entries.
The minimum air required at the last open crosscut was 51,000 cubic feet per minute (CFM). The observed total was 88,965 CFM. The minimums on the face were 400 feet per minute (FPM) at no. 8 shield and 220 FPM at no. 123 shield. Totals observed were 725 FPM and 790 FPM respective. Bleeder air was regulated through two entries interconnected to and surrounding the entire gob area.
Geology
The mine is located in the Aberdeen Coal Seam, which varies from 4 feet to 13 feet in thickness. Widely-spaced, sample drill holes show that the roof normally consists of a siltstone band of varying thickness immediately above the Aberdeen Coal Seam, then a rider seam of coal (3-5 feet thick), with the Kenilworth Sandstone (approximately 200 feet thick) above the rider seam. The floor below the Aberdeen Coal Seam normally consists of the Aberdeen Sandstone.
Limited testing of rock properties by consultants and the U.S. Bureau of Mines show the following uniaxial compressive strengths of geologic formations relevant to the Aberdeen Coal Seam: a) roof rock - 14,000 pounds per square inch (psi), b) coal seam - 3,500 psi, and c) floor rock - 11,000 psi.
Three coal seams, in which previous mining had occurred, exist above the Aberdeen Coal Seam. The Gilson Coal Seam (250 feet above) and the Centennial Coal Seam (365 feet above) were the seams of the Pinnacle Mine. The Lower Sunnyside Coal Seam (450 feet above) was the seam of the Apex Mine. Room & pillar mining with pillar extraction was done in the three upper seams. Some longwall mining was also done in the Pinnacle Mine.
Contributing Factors to the Burst
A report titled, "Technical Review of Longwall Feasibility for Andalex Resources," by J.F.T. Agapito & Assoc. of Grand Junction, CO, dated November 1993, is relevant to the accident. It lists on page 33 the following eleven significant factors directly relevant to bounce/burst occurrences in the Aberdeen Mine: roof rock strength, floor rock strength, coal strength, cover depth, topographic variations, overburden characteristics, sandstone channels, mine pillar dimensions, panel orientations, panel retreat, and panel widths. Many of these factors are included in the premining plans and longwall panel design. However, site specific factors, such as sand channels, have not been recorded and analyzed as mining progressed.
Agapito's report on longwall feasibility for Andalex, discuss factors that contribute to bursts. Bounces of a lower magnitude can help reduce stress levels at a location to a degree that a burst may be avoided. However, the presence of bounces also signals that the conditions that contribute to a burst are present. As the bounce potential increases, bursts are more likely to occur.
Although planning in advance of Aberdeen Mine development and production analyzed many of the factors listed, local geologic features (e.g., sand channels, faults, rolls) that can affect the occurrence of bumps were not recorded, reviewed and plotted for analysis. The Agapito report of 1993 specifically addresses the issue of geologic mapping on page 42: "The geologic conditions in the Centennial and Aberdeen (A) Seams should be mapped as planned during the development of the gate roads and support systems adjusted according to the conditions encountered." This geologic data could be relevant to the potential for bursts in the longwall panel. For example, the high degree of roll in the coal seam from shield 65 to shield 78, on the longwall face where the accident occurred, would be a contributing factor to stress concentration toward the tailgate. More geologic data obtained as the longwall panel was being mined would have made this determination possible.
Factors contributing to the accident on November 14, 1996, include:
- Cover depth: The longwall face had approximately 1700 feet of
cover over the top of the headgate to approximately 1565 feet on
top of the tailgate. The Agapito report notes on pages 60-61:
"stress levels, particularly in the coal ahead of the face, reach
and exceed bounce prone levels ( 4000-4800 psi) to some degree at
cover depths of 1600 feet."
- Roof and Floor Lithology and Strength: The roof above and
floor beneath the longwall face were strong sandstone. Massive
sandstones are well known to be associated with bounce/bump prone
conditions in coal mines. The presence of thick sandstone layers
above and below the Aberdeen coal seam increased the transfer of
stored energy to the face coal.
- Overriding Gob Stresses: The area behind the shields at the tailgate was not caved tight to the shields for a distance of approximately 50 feet along the shields and back into the gob along the tailgate entry. The hanging roof on the tailgate and uncaved roof across the tailgate entries would cause gob stress from behind the shields and adjacent panel, respectively, to override into the coal face near the tailgate.
CONCLUSION
The fatal accident occurred from a burst in the tailgate area of the 3rd West Longwall face. Bouncing to some degree was indicated throughout this panel, which had been in production approximately a month and a half, and was conspicuously noticed in the tailgate area while the shearer was cutting into the tailgate entry. These bounces were attributed to being the cause of torque shaft breakage of the tailgate drum on a number of occasions when cutting near the floor. The longwall coordinator stated a similar incident had occurred on the tailgate approximately 50 feet back, but not of this severity.
Although bursts have not been previously reported during mining in the Aberdeen Coal Seam, bounce potential was increasing as projected in the studies done by Agapito & Associates. The increase in torque shaft breakage on the tailgate shearer could be an indication of this increasing bounce potential. Regardless, recommendations from the consulting report relevant to longwall mining in the Aberdeen Coal Seam were not being followed in the area where the accident occurred. The Agapito & Associates report of November, 1993, specifically discusses geologic mapping of longwall development being relevant to the potential for bursts.
SUMMARY
The burst was a result of the presence of thick sandstone layers above and below the coal seam, causing high stresses and pressures on the longwall coal panel. The hanging roof in the gob on the tailgate side of the longwall face was an additional factor.
A 103(k) Order No. 3585783 was issued on November 14, 1996, to ensure the safety of all persons working in the coal mine.
A 104(a) S&S Citation No. 7633005 was issued on June 26, 1997, for a violation of 30 CFR 75.202(a); failure to control the roof and face where persons work or travel from bumps in an area known to be bounce prone.
Respectfully submitted by:
Archie L. Bailey
CMS&H Inspector, District 9
Bob E. Cornett
Roof Control Supervisor
CMS&H, District 9
Approved by:
Archie D. Vigil
Assistant District Manager for Enforcement
CMS&H, District 9
John A. Kuzar
District Manager
CMS&H, District 9
Related Fatal Alert Bulletin:
FAB96C33