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UNITED STATES
DEPARTMENT OF LABOR
MINE SAFETY AND HEALTH ADMINISTRATION
Metal and Nonmetal Mine Safety and Health

REPORT OF INVESTIGATION

Surface Nonmetal Mine
(Cement)

Fatal Machinery Accident

June 3, 2002

Lone Star Quarry & Mill
Lone Star Industries, Inc.
Cape Girardeau, Cape Girardeau County, Missouri
Mine I.D. No. 23-00134

Accident Investigators

Rick J. Horn
Mine Safety and Health Compliance Specialist

David L. Weaver
Mine Safety and Health Specialist

Phillip L. McCabe
Mechanical Engineer

Thomas D. Barkand
Electrical Engineer

Originating Office
Mine Safety and Health Administration
South Central District
1100 Commerce Street, Room 462
Dallas, Texas 75242-0499

Edward E. Lopez, District Manager

OVERVIEW

On June 3, 2002, Robert L. St. Cin, maintenance mechanic, age 41, was fatally injured when he was struck by metal fragments.

The accident occurred because of a catastrophic failure of one of the components, which caused a bucket conveyor to over speed in the reverse direction sending material fragments of the component flying outward where the victim was working.

St. Cin had 11 years and 9 months total mining experience, all at this location, including 2 years and 10 months as a maintenance mechanic. He had received annual refresher training in accordance with 30 CFR, Part 46.

GENERAL INFORMATION

Lone Star Quarry and Mill, a surface limestone mine and cement plant, owned and operated by Lone Star Industries, Inc., was located in Cape Girardeau, Cape Girardeau County, Missouri. The principal operating official was William S. Leus, Jr., plant manager. The plant and mine operated three, 8 hour shifts per day, 7 days a week. Total employment was 97 persons.

Limestone was mined from multiple benches. The limestone was drilled, blasted and hauled to the crusher by truck. The crushed limestone was then conveyed to the mill where other ingredients were added through various processes to produce cement. The finished product was sold for construction use.

A regular inspection was in progress on the day of the accident.

DESCRIPTION OF ACCIDENT

On June 3, 2002, Robert L. St. Cin, (victim) reported for work at 6 a.m., his normal starting time. St. Cin and Robert L. Hahs, maintenance mechanic, were assigned the task of replacing bolts on the vibrator above the number 8 clinker belt. At about 8:30 a.m., they completed the job and returned to the shop. At about 9:15 a.m., Walter Jones, shift supervisor, called Charles Miller, maintenance foreman, on the radio and advised him that the air slide feeding the main kiln was jammed. Miller, St. Cin, and Hahs went to the ninth floor of the pre heater building to assess the problem. When they arrived, they found Jones, Mark Kluesner, production manager, Dennis Lockhart, control room attendant, Larry Bartles, tower attendant, and Michael Counts, shift laborer, preparing to clean the air slide.

Jones, Miller and St. Cin began cleaning the jammed material from the airslide while Lockhart and Bartles went down to the third stage area to work on another stoppage. After the air slide was cleaned out, Jones, Hahs and St. Cin went to the top level of the vertical bucket conveyor to make sure it was clear. Kluesner, Miller and Counts began putting the covers back on the air slide and checked the blower fans.

At about 9:40 a.m., Jones called the control room attendant and advised him he was going to jog the bucket conveyor to clean out the bottom of the conveyor and check the air slide to make sure it was operating properly. He then called Kluesner and Counts to make sure they were in the clear prior to jogging the bucket conveyor.

Jones went to the jog switch that was located about two feet away from the drive motor. Hahs stood to his left, with St. Cin on Jones' right side and about a half step behind.

Jones manually held the jog switch in for about two minutes until Hahs signaled him that the system was clear. Jones released the jog switch and it returned to the off position. When he stepped back to call the control room attendant he heard a loud whirling sound, followed by a bang. The coupler connecting the drive motor to the bucket conveyor speed reducer had disintegrated and the backstop housing had broken apart. St. Cin was struck in the chest by pieces of metal fragments thrown from the drive train. Emergency medical personnel and the coroner were summoned to the accident site. The victim was pronounced dead at the scene. Death was attributed to massive trauma to the chest.

INVESTIGATION OF THE ACCIDENT

MSHA was notified at 11:27 a.m., on the day of the accident by a telephone call from Robert L. Cox, safety and health manager, to Robert Seelke, mine safety and health compliance specialist. An investigation was started the same day. An order was issued under the provisions of Section 103(k) of the Mine Act to ensure the safety of miners. MSHA's accident investigation team traveled to the mine, conducted a physical inspection of the accident site and equipment involved in the accident, interviewed a number of employees, and reviewed training records, conditions and work procedures relevant to the accident. MSHA conducted the investigation with the assistance of mine management, the miners' representative, and miners.

DISCUSSION

  • The accident occurred on the top level of the pre-heater tower, where the vertical bucket conveyor fed the main kiln. Raw material was fed directly into the bottom of the bucket conveyor from a horizontal belt and lifted to the top of the tower where the material was transferred into a 50-ton hopper tank through an air slide. The bucket conveyor was a Beumer Model 630 X 91.5 X 900. It was 292 feet high from head pulley to tail pulley, and was originally assembled with 349 steel buckets, or scoops, each bucket having a capacity of approximately 1 cubic foot. The vertical conveyor was modified in 1997 to carry 502 buckets, with no change to the bucket carrying capacity. Primary maintenance on the bucket conveyor was performed by outside contractors with only light maintenance and lubrication performed by Lone Star employees.


  • The bucket conveyor was comprised of several mechanical drive components. These components were in a series arrangement with an electrical motor, fluid coupling, anti-rotation backstop, right-angle gearbox, flexible coupling, and finally, the drive drum on the bucket conveyor.


  • The motor powering the bucket conveyor was a General Electric, 460-volt AC, 3-phase, 150-horsepower, 1800 rpm, 180 ampere, Frame 445T. The motor had been reconditioned on November 21, 2000, by Kagmo Electric of Cape Girardeau, Missouri.


  • The bucket conveyor control was equipped with a manually operated jog switch. The switch was located by the drive motor and was accessible from a platform installed at the top of the bucket conveyor. The switch had three positions: "Automatic", "Off", and "Jog". In the "Jog" position, the spring-loaded switch had to be manually held in place. It returned to the "Off" position when released. The switch was found in the "Off" position following the accident. When tested, the bucket conveyor could be started remotely from the control room only if the platform switch was in the "Automatic" position.


  • The electric motor output shaft was connected to the input shaft of the gearbox by a fluid coupling. The fluid coupling was a Voith Turbo-coupling, Model #422 TVC. It provided a means to gradually increase the transmitted torque while decreasing the sudden shock load induced when the motor was first turned on. The coupling picked up speed through the movement of the fluid inside the coupling. There were three essential parts to the fluid coupling: the driving (input) section known as the impeller, the driven (output) section known as the runner, and the oil-tight casing that was bolted to the impeller and housed the runner. The torque-transmitting characteristics of the coupling could be altered by the use of different types of hydraulic fluids and fluid levels. Reportedly, this coupling was filled with Dextron automatic transmission fluid to the maximum recommended fill capacity of 80%. Two heat fusible melt plugs were installed in the outer periphery of the coupling casing that would melt at 160 degrees Centigrade should the coupling stall under load. The coupling impeller was mounted on the end of the gearbox input shaft using a keyway and a bolt. Two fluid lubricated bearings were mounted on the impeller to permit the outer casing to rotate freely about the impeller.


  • The backstop was a Falk Size #60, M.O. 96-068607-01, manufactured in 1996. The anti-rotation backstop was installed on the input shaft of the gearbox between the fluid coupling and the gearbox. The bucket conveyor was not equipped with a braking system. The purpose of the backstop was to prevent the bucket conveyor from turning in the reverse direction and hold the conveyor stationary in the event of a conveyor shutdown. When the AC drive motor was deenergized, the bucket conveyor would coast until gravity or friction would bring it to a stop. When the motor switch opened, the weight of the buckets on the supply side would equalize or balance the load, bringing it to a stop.


  • The backstop was designed to prevent reversal of the conveyor by the use of four spring-loaded metal tooth-like pawls that were activated by centrifugal force as the gearbox input shaft rotated at rated speed. The L-shaped pawls were attached to a center hub by four pivot pins, and the pawls and center hub assembly was mounted to the gearbox input shaft by a slipfit and keyway. The keyway transmitted all of the torque to the backstop hub and pawls. Once the hub and pawls reached operating speed, the pawls were blocked in the freewheeling position by small protrusions on the center hub. When the motor stopped and the center hub and pawls stopped rotating, the springs on the pawls overcame the centrifugal force, and the teeth on the pawls dug into the smooth interior surface of the stationary backstop housing B similar to a pipe wrench. The greater the force on the hub to turn backward, the harder the teeth would dig into the stationary housing. The stationary housing had a bearing housing bolted to each end, which permitted the entire assembly to float on the input shaft. In addition, a lever was connected between the exterior stationary housing and a mount that was bolted to the gearbox housing, which transmitted the resisting and holding torque of the backstop unit to prevent reversing of the conveyor. This backstop operated at 1800 revolutions per minute and was considered to be a high-speed application.


  • The right-angle gearbox rotated the upper drive drum of the bucket conveyor. The gearbox was a Falk, Model 2130YB3-S, MO #7-866438-01. The gearbox was a single-speed unit with a 46.73 to 1 gear ratio, which means the output shaft turned 46.73 times slower than the input shaft. This allowed the drive motor to rotate at a high speed and the bucket conveyor to turn at a very low speed while transmitting a large amount of torque. The gearbox design consisted of an input shaft with a ring-and-pinion spiral bevel gearset, which formed the right-angle drive. The gears were mounted in a large metal box-shaped housing and were lubricated with an oil-splash system. The ring gear transmitted the torque through additional helical spur gears mounted on parallel shafts to the final output shaft of the gearbox. A large grid-type coupling was used to connect the gearbox output shaft to the upper drive drum shaft of the bucket conveyor.


  • Following the accident, small metallic fragments were found strewn across a large area of ground, as was the 16 gauge steel guard, which had surrounded the fluid coupling. The guard was heavily damaged but intact. Similar metallic fragments were found surrounding the motor and gearbox on the upper deck near the bucket conveyor. The fluid coupling was almost completely destroyed. Part of the fluid coupling was still attached to the gearbox input shaft. The backstop stationary housing was intact with minimal damage, however, both of the bearing housings for the backstop were broken with fragments missing. The gearbox input shaft with backstop and coupling remnants were drooped downward. The input shaft appeared to be bent or broken.


  • Inspection of the bucket conveyor after the accident determined there were 107 loaded buckets and 141 empty buckets on the supply side. This indicated the bucket conveyor had reversed direction and traveled backwards a considerable distance.


  • The bucket conveyor had failed to hold stationary after the jog switch was released. The jog switch was held in the on position for a short period of time to operate the bucket conveyor to check if the material would flow through the airside.


    • CONCLUSION

    The cause of the accident could not be determined. The accident occurred because of a catastrophic failure of one of the components, which caused the bucket conveyor to overspeed in the reverse direction sending metal fragments of the component flying outward where employees were working.

    ENFORCEMENT ACTIONS

    Order No. 6210670 was issued on June 3, 2002, under the provisions of Section 103(k) of the Mine Act:
    A fatal accident occurred at this operation on June 3, 2002 when a maintenance mechanic was struck by shrapnel from a shattered coupling from the KB 1600 kiln feed vertical bucket conveyor at the top of the RSP tower. This order is issued to assure the safety of persons at this operation and prohibits any work in the affected area until MSHA determines that it is safe to resume normal operations as determined by an Authorized Representative of the Secretary of Labor. The mine operator shall obtain approval from an authorized representative for all actions to recover and/or restore operations in the affected area.
    This order was terminated on June 14, 2002. Conditions that contributed to the accident have been corrected and normal operations could resume.

    Related Fatal Alert Bulletin:
    Fatal Alert Bulletin Icon FAB02M17



    APPENDIX A

    Persons Participating in the Investigation


    Lone Star Industries, Inc.
    Lawrence L. Hofis .......... senior vice president, operations
    Gregory A. Cunningham .......... corporate safety and health manager
    William S. Leus, Jr. .......... plant manager
    Dennis C. Tew .......... engineering & maintenance manager
    Robert L. Cox .......... safety and health manager
    William K. Doran .......... attorney, Heenan, Althen & Roles
    Debbie Hayes .......... safety and health representative, PACE International Union
    Herman R. Potter .......... safety and health representative, PACE International Union
    Jimmy W. Pruitt .......... president, PACE Local No. 5-0164
    Tim Schleinger .......... safety and health representative, PACE Local No. 5-0164
    Mine Safety and Health Administration
    Rick J. Horn .......... mine safety and health compliance specialist
    David L. Weaver .......... mine safety and health specialist
    Phillip L. McCabe .......... mechanical engineer
    Thomas D. Barkand .......... electrical engineer

    APPENDIX B

    Persons Interviewed

    Lone Star Industries, Inc.
    William S. Leus, Jr. .......... plant manager
    Dennis C. Tew .......... engineering and maintenance manager
    Walter R. Jones .......... shift supervisor
    Mark G. Kluesner .......... production manager
    Charlie L. Miller, Jr. .......... maintenance foreman
    Randy L. Hahs .......... maintenance mechanic
    Allen E. Crenshaw .......... control room operator
    Michael L.Counts .......... shift labor
    Global Gear and Machine Company, INC.
    Russell P. Bottoms