DEPARTMENT OF LABOR
MINE SAFETY AND HEALTH ADMINISTRATION
Accident Investigation Report
(Surface Coal Mine)
Fatal Machinery Accident
Jim Bridger Coal Mine (ID No. 48-00677)
Bridger Coal Company
Rock Springs, Sweetwater County, Wyoming
July 26, 1999
William E. Vetter
Coal Mine Safety and Health Inspector
James M. Beam
Coal Mine Safety and Health Inspector
Originating Office: Mine Safety and Health Administration
Coal Mine Safety and Health, District 9
P.O. Box 25367, Denver, Colorado 80225-0367
John A. Kuzar, District Manager
There are five seams of coal within the Deadman Coal Zone of the Jim Bridger Coal Field. The seams are designated D5 through D1 from top to bottom. Coal seam thicknesses and quality vary throughout the coal field. Thicknesses range from 2 to 15 feet in areas of more than one seam. Where the coal seams form a single seam, it is a maximum thickness of 32 feet. Partings between the seams vary from a few inches to 50 feet thick. The mine has one active pit approximately 18 miles in length. Overburden ranges in depth from 20 to 80 feet and is blasted, then removed with either a Page, Model 757 dragline equipped with a 62-cubic yard capacity bucket or one of two Marion, Model 8200 draglines each equipped with a 79-cubic yard capacity bucket.
Once the overburden has been removed, the coal is drilled and blasted, then loaded with either Caterpillar, Model 994 and 992; Dart, Model 600; or Hitachi, Model 2500 loading machines. Model 777 and 789 Caterpillar end dump trucks are used to transport the coal to one of three nearpit hoppers where it is crushed to one to six inches in size. An overland belt conveyor system transports the coal to the nearby Jim Bridger Power Plant.
Operating two 12-hour shifts, 7 days per week, the mine employs a work force of 375 persons and produces an average of 22,240 tons per day. The last regular Mine Safety and Health Administration (MSHA) inspection was completed on March 25, 1999.
The principal officers at the mine were:
Pat Akers.........................General Manager
Larry Lawton......................Dir. of Prod/Maint.
Patrick L. James..................Safety Manager
DESCRIPTION OF ACCIDENT
Eddie Turner, a Nondestructive Testing (NDT) Specialist, employed by independent contractor E.T.-N.D.T. Inc., was on site. At approximately 8:30 a.m., Turner began conducting nondestructive testing of the mast head area using an ultrasonic process. He was assisted by Jerry Maes and Steve Eleshuk, both employed by Bridger Coal Company as mechanics. A two person boom truck, operated by Eleshuk, was used to elevate Eleshuk and Turner to a position at the end of the mast tip while Maes was positioned on the mast tip reeving block. Early in the shift, Gary Haines, victim, Rex Harrington, injured miner, and other Bridger Coal employees rolled out bridge strands (cables) on the left side of the dragline boom and attached them to the boom point. At approximately 10:00 a.m., the group working on the bridge strands took a scheduled break at the tool trailer located on site.
After a 15-minute break, the men went about other various task assignments. Harrington rigged and connected one bridge strand to the hoisting cable of a Lima crane in preparation for it to be hoisted to the mast connection point once the NDT was completed. Operated by either Harrington or Haines, a JLG man-lift, model 60F, was used to elevate the 2 men to a position under the mast head, approximately 40 feet off the ground. The man-lift was positioned between the mast point and the support structure near the center and immediately below the cross member of the temporary support. The man-lift maintained this position while the NDT was completed.
Upon completing the NDT procedures, Turner and Eleshuk were in the bucket truck above Harrington and Haines at the front left side of the mast point. Maes, tied off with a safety harness and lanyard, was standing on the reeving block at the mast point. Without warning the cross member of the temporary support shifted, allowing the mast to drop several feet before coming to rest on the right half of the cross member. The cross member struck the bucket truck, the man-lift, and the mechanics in the man-lift.
Haines was pinned between the cross member and the railing on the man-lift, and Harringtons right lower arm was pinned under Haines. Freeing his arm, Harrington called to the crane operator to swing the headache ball over to him. After a bridge strand was disconnected from the hoisting cable, the Lima crane operator positioned the headache ball at the front of the mast tip. Harrington was able to mount the ball and secure himself to the hoisting cable with his lanyard to be lowered to the ground. In the mean time, Eleshuk had lowered the bucket truck to the ground to let Turner out and returned to the mast point to retrieve Maes.
Either the mast or the support structure had the man-lift basket lodged preventing it from being lowered to the ground. Initially, a Link Belt crane, located in the immediate area, was to be used to lift the mast from the damaged support structure. However, before the mast could be rigged for hoisting, it was realized the weight of the mast was too near the maximum lifting capacity of the Link Belt crane to be safely raised. A decision was made to use the dragline motors and raise the mast off the man-lift using the reeving cables. Once the mast was clear of the man-lift, the JLG remote controls, mounted on its base unit, were used to lower the man-lift to the ground with Haines in it. Haines was pronounced dead at the scene by the State of Wyoming, Sweetwater County coroner. Harrington was transported by ambulance to Memorial Hospital of Sweetwater County with internal and upper extremity injuries.
INVESTIGATION OF THE ACCIDENT
The Chief Investigator for MSHA was William E. Vetter, a Coal Mine Safety and Health Inspector from the Delta, Colorado Field Office. Assistance from MSHAs Technical Support consisted of a civil engineer from the Pittsburgh Safety and Health Technology Center and a mechanical engineer from the Approval and Certification Center in Triadelphia, West Virginia. Technical Support was utilized to assess the structural integrity of the dragline mast support system and to evaluate the slip critical connections of the mast support.
Interviews were conducted at the mine site on July 28 and 29, 1999. Investigative work at the mine concluded on July 31, 1999.
PHYSICAL FACTORS INVOLVED
- The machinery involved in the accident were a Page, Model 757 Dragline, serial number 367, manufactured in 1986; a JLG man-lift, Model 60FDR, serial number 0308208213; and a temporary steel support frame used to support the mast above the boom without the use of the cables.
- At the time of the accident, the dragline was down for maintenance. The boom was hinge pinned at the draghouse and rested along the ground on wooden cribs. The mast was also hinge pinned at the draghouse, and was held up at 18 degrees off the horizontal by a temporary support frame mounted on top of the boom. The boom length was 315 feet, and the mast was 140 feet. The support frame contacted the mast approximately 125 feet from the hinge point. The weight of the mast was reported to be just over 82,000 pounds. The reeving block and hardware were an additional 20,000 pounds. A portion of the mast-to-boom pendant lines (bridge strand cables), attached to the right side of the mast, was also being carried by the temporary support frame.
- The support frame consisted of two vertical columns(one on each side) connected to the boom at the bottom and bolted to a horizontal crosshead beam on the top. The mast did not lay flush on the horizontal beam, so small pieces of steel plate were welded to the top of the beam to increase the bearing area for the mast. Both vertical columns were braced at approximately mid-height. The diagonal braces were pinned to the vertical columns on one end, and pinned to the top of the boom at the other. The brackets of the pin assemblies were each welded to a flat plate. Each plate, along with another steel plate, were clamped with bolts around the top chord member of the boom.
- The footing plates, along with six bolts (three on each side), created a slip-critical connection around the top chord of the boom. These bolts were machined at Bridger Coal from hot-rolled, round, ASTM-A-36, one inch diameter steel bars. There was no specific procedure for tensioning these bolts into place. Bridger used a pneumatic Ingersoll-Rand, one-half inch drive, impact wrench powered by a Viper 70, Van-air compressor, regulated at 120 psi, to tighten down the bolts. During the investigation, the impact wrench was used to tighten down another bolt. This bolt was tested with a torque wrench and found that 280 foot-pounds of torque was applied by the impact wrench. In more than one location these clamping bolts were bent to the extent that the bend could be seen by the naked eye. In at least two instances the nut/bolt assembly was loose enough to dismantle without the use of a wrench.
- Two bolts, one from the support structures left diagonal bracing connection and one unused bolt were provided by Bridger Coal Company to MSHA investigators for tensile testing. Testing was conducted according to ASTM F432-95 standards with a Universal testing machine (Tinius Olsen) at MSHAs Roof Bolt Laboratory located at the Pittsburgh Safety and Health Technology Center. The bolts were tensioned to failure. Both bolts exhibited yield strengths in excess of the 36,000 pounds per square inch (36 ksi) required.
- The temporary support structure had been used prior to this accident at the San Juan Coal Company in New Mexico, for maintenance on another Page, Model 757 dragline. The mast and the boom of the Bridger Coal dragline were of different dimensions than that of the San Juan dragline.
- At the time of the accident, the victim and a co-worker were in a man-lift positioned under the supported mast, approximately 40 feet above the ground, preparing to attach bridge strand lines to the mast. The temporary support structure failed, allowing the mast to suddenly drop several feet. The support structure struck the two men, pinning the victim between the man-lift structure and the horizontal crosshead beam of the temporary support and temporarily pinning his co-worker by the right arm.
- The temporary support structure failed by two different modes, one on each side. The two left side connections slid in a scissor manner on the top chord of the boom to which they were clamped. First, the diagonal bracing connection slid approximately three feet forward before impacting a diagonal web member within the boom frame. Then, the column connection slid backward approximately one foot. The sliding of these connections allowed the upper portion of the left column to fall forward, which transferred the weight of the mast to the right side. The right side boom connections held in place, and the column twisted and yielded just above the bracing point. The right side column also bent forward and rotated toward the center of the boom, allowing the mast to fall several feet. The right side vertical column and diagonal bracing, although yielding, did not fail and managed to support the entire weight of the mast.
- It was reported that an explosives shot fired in the Ramp 55� area (approximately a half-mile away) would shake the ground in the Ramp 58 area. Some blasting had occurred in the Ramp 55� area in the week leading up to the accident. No shots were detonated in the Ramp 55� area within the 24 hours prior to the accident.
- At the time of the accident the temperature was approximately 73oF, up from a night low of 53.4oF (5:00 a.m.). Wind readings indicated that the wind was blowing between 4 and 5 miles per hour at the time of the accident. Meteorologic information was taken from data collected at the Bridger Coal Companys Meteorologic Station located at Ramp 5.
CONCLUSIONThe evidence indicated that the normal force applied by tensioning the bolts on the left side diagonal bracing was marginal, upon installation, to resist the horizontal forces applied on the slip critical connection. Once the frictional force was overcome on this connection, failure occurred as described in Physical Factor No. 8. Although no single factor was determined to be responsible for initiating the failure, possible contributing factors could have been thermal expansion of the steel, wind loading of the supported structure, or other external forces acting on or around the structure.
- A 103(k) order, No. 3557567, was issued to the operator on July 26, 1999. The order stated, The mine has experienced a fatal machinery accident in the 58 Ramp area; this order is issued to assure the safety of any person at the coal mine until an examination or investigation is made to determine that Ramp 58 is safe. Only those persons selected from company officials, state officials, the miners representative and other persons who are deemed by MSHA to have information relevant to the investigation may enter or remain in the affected area.
- A 104(a) citation, No. 7625303, was issued to the operator for a violation of 30 CFR 77.405(b) on August 18, 1999. The citation stated, The operator failed to assure the Page, model 757 dragline mast was securely blocked in a raised position while work was being performed under it. During a major repair project at Ramp No. 58, a temporary support structure had been placed near the mast tip to support the mast in an inclined position. On July 26, 1999, after several components of the mast had been replaced during previous shifts and the repair work was nearing completion, the supporting structure failed to maintain its position. The horizontal cross member of the support structure suddenly shifted toward the boom tip and in a downward direction, striking two maintenance personnel and the man-lift basket they were in, resulting in fatal injuries to one person and serious injuries to the other.
William E. Vetter
Coal Mine Safety and Health Inspector
James M. Beam
Coal Mine Safety and Health Inspector
Irvin T. Hooker
Assistant District Manager of Inspection Program
John A. Kuzar
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