UNITED STATES
DEPARTMENT OF LABOR
MINE SAFETY AND HEALTH ADMINISTRATION


North Central District
Metal and Nonmetal Mine Safety and Health


Accident Investigation Report
Surface Nonmetal Mine
(Limestone)

Fatal Powered Haulage Accident

Colchester Plant #51
Central Stone Company
Colchester, McDonough County, Illinois
(I.D. No. 11-00033)

July 8, 1996


By


William T. Owen
Mine Safety and Health Inspector


Originating Office
Mine Safety and Health Administration
Federal Building, U.S. Courthouse
515 West First Street, #228
Duluth, MN. 55802-1302


James M. Salois
District Manager

GENERAL INFORMATION

Harold L. Thomas, mechanic, age 52, was fatally injured at about 9:15 a.m. on July 8, 1996, when he was on the front access ladder of a truck that traveled through a maintenance shop door. Thomas had five years mining experience as a mechanic, all at this operation. He had received annual refresher training in accordance with 30 CFR Part 48 on May 31, 1996.

MSHA was notified by a telephone call from Nedwra Everett, mine scale operator, at 10:15 a.m. on the day of the accident. An investigation was started the same day.

Colchester Plant #51, a multiple bench, open pit limestone quarry, owned and operated by Central Stone Company, was located near Colchester, McDonough County, Illinois. The principal operating official was James O. Ellis, president. The quarry and plant were normally operated one shift per day, five days a week. A total of 11 persons was employed.

Limestone was drilled, blasted, crushed, sized, and stockpiled for sale as construction aggregate. The quarry had been in operation since the early 1950's and under present ownership since 1987. The employees at this mine were represented by Operating Engineers Local 649 and Teamsters Local 455.

The last regular inspection at this mine was completed April 30, 1996. Another regular inspection was conducted after completion of the investigation.

PHYSICAL FACTORS INVOLVED

The truck involved in the accident was a Wabco 35C, serial No. PGF9933CFA19-Z, company No. 4727702. It had an air-over-hydraulic brake system and was powered by a Detroit diesel V-12 engine. The truck was also equipped with an Allison CLBT 5860 automatic split transmission, serial No. 30649, part No. 6674862.

The transmission had six forward speed ranges, an integral hydraulic retarder, a manual electric shift with lever selector, and a lock-in range feature. It also had a safety switch that would prevent starting of the truck unless the shift lever was in neutral, however, the switch had been bypassed during the recent shift tower replacement. A tear down of the complete transmission identified significant damage which contaminated the transmission fluid, resulting in unpredictable control of the transmission. The erratic behavior included the transmission remaining in gear even though the shift lever was in neutral.

Testing after the accident indicated the transmission was in a mid-range forward gear and the shift lever was in neutral. The truck also drove through the parking brake in five of the six gear selector positions when the engine accelerated high enough to override the park brake. The park brake was found to be functional but was not designed to hold against the vehicle's power train.

The truck had been removed from service several days prior to the accident to repair a brake air leak and to change the engine's fuel injectors. It had also been out of service about a week earlier to correct a hesitation in transmission engagement when shifting from forward to reverse. The hesitation required the truck driver to pause at each shift point, causing the lever selector shift tower to be replaced. Shift tower replacement did not correct the transmission problem.

The accident occurred at the maintenance shop. The unblocked truck had been parked outside the shop for maintenance by Thomas because the overhead clearance was not adequate to drive it inside. The shop was of pole barn construction with 14 feet 6 inch sliding doors on the north and south ends. The truck, which was 14 feet 8 inches high, was parked about 9 feet from the south side door for several days while repairs were in progress. The ground outside the shop sloped away at 1-1/2% grade for drainage.

Initial MSHA inspection of the truck found that one end of the return spring on the throttle linkage was not attached on the linkage end. The hook had broken off previously and had been bent to create a new hook. Tests performed with the throttle return spring disconnected showed the truck engine would maintain low idle for a period of 20 to 28 seconds, then it would accelerate to full throttle within two seconds.

DESCRIPTION OF THE ACCIDENT

On the day of the accident, Harold L. Thomas (victim) arrived for work at about 6:45 a.m., his normal starting time. Larry Wolfmeyer, superintendent, asked him to clean up oil spillage on the maintenance truck before working on the Wabco haul truck. Thomas cleaned up the oil then continued reassembly work he began the previous day on the Wabco truck fuel injectors.

After installing the fuel injectors, Thomas attempted to start the truck but the batteries were low. Wolfmeyer instructed him to hook up the battery charger then left to check on workers in the pit. Thomas attached the charger to the battery cables at the starter behind the left front wheel and, it is surmised, he climbed into the truck cab and started the engine.

Bobby Fawcett, crushing plant operator, was working on the plant and heard the truck start, then rev up and down a few times, before returning to idle. A short time later he heard the truck engine accelerate wide open. Looking up, he saw the truck crash through the shop door. He ran to the plant switch house and shut off electric power before running to the shop. Fawcett and Wolfmeyer, who had just returned from the pit, arrived at the shop simultaneously.

The truck had stopped against the west wall with a large amount of debris between it and the wall. Wolfmeyer entered the truck cab through the right cab door and attempted to shut the truck off but was unsuccessful due to his unfamiliarity with the truck's shut down procedure and a faulty emergency air shut off cable. He then crawled under the truck to the fuel shut off valve behind the left front wheel and shut off the valve. At the same time, Bobby Fawcett manually tripped the engine air shut off, which stopped the engine.

After the truck was shut down, Wolfmeyer observed Thomas's feet on the truck access ladder. The truck was pulled back about 4 feet from the wall to remove Thomas. The local rescue squad and county sheriff's deputy responded to the accident call and recovery efforts went on for about a half hour before the county coroner pronounced Thomas dead at 10:04 a.m.

Based on information obtained at the accident scene, testing of the truck, and interviews of persons at the mine, it was determined the following occurred: Thomas was positioned on the forward mounted, access ladder when the engine revved and the truck pulled through the park brake and smashed through the shop. The throttle return spring had either been left unattached or unattached itself. In either event, from the time the spring was disconnected, the engine would have gone from low idle to wide open in 22 to 30 seconds.

CONCLUSION

The failure to block the Wabco truck against hazardous motion prior to performing maintenance was the direct cause of the accident. The truck transmission and throttle linkage defects, and the truck being able to drive through the functional park brake system when it revved up, also contributed to the accident.

VIOLATIONS

Order No. 4421223

Issued on July 9, 1996 under the provisions of Section 103(k) to prohibit any use of the truck involved in this accident pending inspection and testing to determine its serviceability and condition.

This order was terminated on July 12, 1996 when the company removed this truck from service.

Citation No. 4421235

Issued on July 31, 1996 under the provisions of Section 104(a) for violation of 30 CFR 56.14100(b):

A mechanic was fatally injured at this operation on July 8, 1996, when he was crushed between a Wabco 35C haul truck, unit #4727702, and the maintenance shop building. Tests after the accident revealed that the transmission would remain in gear, even though the gear selector had been returned to the neutral position. Also, the throttle linkage return spring was not attached on the linkage end of the spring. The original hook on the linkage end of the spring had broken off and the spring had been bent to reattach it to the linkage. Post accident testing revealed the modified spring could detach unexpectedly, causing the engine to accelerate from 700 RPM (idle) to 2500 RPM (governor limit).
This citation was terminated August 1, 1996 as the truck had been removed from mine property for correction of all hazards prior to its return to service.

Citation No. 4421236

Issued on July 31, 1996 under the provisions of section 104 (a) for a violation of 30 CFR 56.14105:

A mechanic was fatally injured at this operation on July 8, 1996 when he was crushed between a Wabco 35C haul truck, unit #4727702, and the maintenance shop building. The victim had started the engine and was on the front access ladder when the truck lurched forward, smashing through the shop door. Blocking had not been used to prevent the motion of the truck prior to starting the engine.

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