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DEPARTMENT OF LABOR MINE SAFETY AND HEALTH ADMINISTRATION SOUTH CENTRAL DISTRICT METAL AND NONMETAL MINE SAFETY AND HEALTH ACCIDENT INVESTIGATION REPORT Surface Nonmetal Mine FATAL ELECTRICAL ACCIDENT Rocky Point Material I.D. Number 03-01399 Tommy Gipson Construction Company Southside, Independence County, Arkansas April 26, 1996 By James R. Bussell Mine Safety & Health Inspector (Electrical) Joseph O. Olivier Mine Safety and Health Inspector Originating Office Mine Safety & Health Administration 1100 Commerce Street, Room 4C50 Dallas, Texas 75242-0499 Doyle D. Fink District Manager GENERAL INFORMATION Timothy Martin, crusher operator, age 34, was fatally injured at about 9:45 a.m. on April 26, l996, when he contacted the sheet metal siding on a crusher control booth that had become electrically energized. Martin had a total of eight weeks mining experience, all at this mine as a crusher operator. MSHA was notified by a telephone call from Tommy Gipson, owner, at 10:15 a.m. on the day of the accident. An investigation was started the following day. The Rocky Point Material mine, an open pit crushed limestone operation, owned and operated by Tommy Gipson Construction Company, was eight miles south of Batesville, Independence County, Arkansas. Principal operating officials were Tommy Gipson, owner, and Larry Williams, foreman. The mine was normally operated one, 9-hour shift a day, five days a week. A total of 5 persons was employed. Limestone was extracted by drilling and blasting multiple benches in the pit. Broken material was hauled to a crusher by front-end loader and conveyed by belt to an adjacent plant for further processing. Crushed base material was the principal product, but they also produced multiple sizes of graded rock. Martin had not received training in accordance with 30 CFR, Part 48. The last regular inspection of this operation was completed on May 11, 1995. Another inspection was conducted in conjunction with this investigation. PHYSICAL FACTORS The crusher control booth was a 5-x 10-foot wood frame structure with 20-gauge galvanized sheet metal outer covering. The booth with stairway access was mounted eight feet above ground level on wood posts and was positioned at approximately a 45-degree angle to the jaw crusher opening. A section of the hand railing had been removed from the crusher expanded metal work platform to allow for one end of the control booth to extend over the platform. The remaining handrail between the booth and the crusher opening created a triangular shaped space where Martin was electrocuted. The metal siding was five inches from the handrails and was insulated from the metal frame of the adjacent jaw crusher by the wood frame construction of the booth. The corrugated metal sheets were positioned horizontally and did not extend below the booth. Flashing was installed on the corners of the booth and the bottom of the corner flashing involved in the accident was bent about 1�-inch at approximately 90 degrees where the power cable passed over it. Electrical power for the crushing plant was provided by a Kohler 260 KW, three-phase, 480-volt generator connected in a solid grounded wye configuration producing a potential of 277 volts to ground. The wiring in the plant was four-conductor SOW-A cable, which was routed overhead to most of the plant equipment. The ground bed was next to the generator and consisted of a single 5/8-inch diameter copper rod driven 16 feet deep. All of the plant electrical components were connected back to the rod and the neutral point of the generator windings through a fourth wire. The jaw crusher frame structure was bonded back to the generator neutral by the crusher feeder motor which was mounted on the crusher frame structure. The branch motor circuit for the Long SB-2 conveyor consisted of a 30-ampere Gould circuit breaker with variable short-circuit settings of 70 to 220 amps that was set at mid-scale, or about 145 amps. The magnetic starter was an Allen Bradley size 0 with N29 or 7.85 ampere heaters. The panel wiring consisted of #12 THW wire. These components were installed in an Allen Bradley enclosure that was mounted on a panel board beneath the control booth. The power cable involved in the accident was a rubber-jacketed type SOW-A, 14-4, 90C-rated cable, manufactured by AIW Corporation. It was approximately 70 feet in length, and furnished power to the Long SB-2 stacking conveyor, which was driven by a 5-horsepower motor. The cable exited the starter enclosure below the control booth and was routed up through the wood structure to the bottom corner of the booth. At the corner, the cable looped 12 inches up the side of the booth over the sharp edge of the corner flashing and through a sling made from a section of 1/2-inch wide v-belt nailed to the side of the booth. It then looped 10 additional feet to a wood support pole and terminated at the conveyor motor. Without adequate mechanical protection for the power cable, the sharp edge of the corner flashing progressively cut through the outer jacket and phase conductor insulation. The resulting fault energized the sheet metal on the control booth to a potential of 277 volts. A total of four, 10-4, SOW-A cables were mounted in the same area. However, the SB-2 power cable was the only one positioned so that it could be cut by the corner flashing. The Batesville area had experienced high winds two days before the accident, which could have placed additional strain on the cable, accelerating the damage caused by the metal flashing cutting into the cable. DESCRIPTION OF THE ACCIDENT On the day of the accident, Timothy Martin (victim) reported for work at 7:00 a.m., his regular starting time. He performed his routine duties as crusher operator until about 9:15 a.m., when James Williams, loader operator, who was feeding the crusher, noticed a large rock in his loader bucket. After dumping the rock a short distance from the control booth, Williams began breaking it with a sledge hammer. The hammer handle came off, and while Williams was repairing it, Martin shut off the feeder and the crusher. A short time later, the hammer repair and rock-breaking tasks were completed and Williams signaled for Martin to restart the crusher. He noticed that Martin was slumped between the crusher platform handrail and the control booth. Williams called to him, but received no response. Williams immediately went up the stairway to the crusher platform and again spoke to him with no response. Martin did not appear to be breathing and Williams could not detect a pulse. James Williams then drove to the pit and notified Larry Williams, foreman. The two men returned to the crusher and again checked the victim, but could detect no signs of life. James Williams went to the office to call 911. After returning, he noticed burn marks on Martin's hands, so he shut off the generator. At about this time, Tommy Gipson, owner, arrived on the scene and the three of them removed the victim from behind the handrail. CPR was administered for about 10 minutes until the first response team from the local fire department arrived. CPR efforts were continued for an additional 15 minutes until the ambulance service arrived. Martin was transported to a local hospital where he was pronounced dead on arrival. CONCLUSION The accident occurred because the power cable was not protected against mechanical damage. The movement and tension of the cable against the sharp edge of the control booth flashing progressively cut through the protective jacket and conductors' insulation, energizing the metal siding on the control booth. The victim was electrocuted when he contacted the siding on the control booth and the hand railing. VIOLATIONS Citation No. 4445943 Issued on 5/16/96 under the provisions of section 104 (a) for violation of standard 56.12004: |
[FAB96M15]