DEPARTMENT OF LABOR
MINE SAFETY AND HEALTH ADMINISTRATION
Metal and Nonmetal Mine Safety and Health
REPORT OF INVESTIGATION
Surface Metal Mine
Fatal Machinery Accident
June 12, 2002
Sherwin Alumina Company
Sherwin Alumina Company
Ingleside, San Patricio County, Texas
Mine I. D. No. 41-00906
Mine Safety and Health Compliance Specialist
Terry L. Worley
Mine Safety and Health Compliance Specialist
F. Terry Marshall
Laman J. Lankford
Mine Safety and Health Specialist
Mine Safety and Health Administration
South Central District
1100 Commerce Street, Room 462
Dallas, TX 75242-0499
Edward Lopez, District Manager
On June 12, 2002, Robert Perez, Jr., equipment cleaner helper, age 35, was fatally injured when he was struck by a drill motor. Perez was drilling the heat exchanger core when the drill motor detached from the drill housing and fell about 30 feet.
The accident occurred because the bolts used to secure the motor to the gear housing were not properly sized for this application. A contributing cause was the failure to identify the cause of the recurring problem of the drill motor bolts loosening and initiating corrective preventative maintenance procedures.
Perez had 7 years and 2 months total mining experience, all at this location, including 6 years and 11 months as an equipment cleaner helper. He had received training in accordance with 30 CFR, Part 48.
Sherwin Alumina Company, a surface alumina mill, owned and operated by Sherwin Alumina Company, a Division of BPU, Reynolds, Inc. Delaware, was located in Ingleside, San Patricio County, Texas. The principal operating official was Peter Bailey, CEO. The mine operated two, 12-hour shifts per day, 7 days per week. Total employment was 830 persons.
Bauxite ore was shipped to the mine from sources in various foreign countries. The ore was conveyed to the mill, where it was upgraded through the Bayer process into calcined aluminum oxide (alumina). The finished product was then used to produce aluminum metal for a variety of industrial uses.
The last regular inspection at this operation was conducted on April 18, 2002. A regular inspection was conducted following the investigation.
On June 11, 2002, Robert Perez, Jr. (victim) reported for work at 7:00 p.m., his normal starting time. He was working a voluntary overtime shift as part of scheduled maintenance on the NO. 3-17 heat exchanger. Perez was assigned to clean scale material that had built up inside of the heat exchanger using an air-powered, mast-mounted drill. Perez and David Flores, equipment cleaner helper, were assigned to drill on the same heat exchanger on an alternating basis. Flores drilled first while Perez waited his turn in the area break room.
At 10:00 p.m., Perez relieved Flores. At about 10:40 p.m., Perez was having problems drilling and left the heat exchanger to speak to Flores. Perez told Flores it was taking him about 20 minutes per hole and asked Flores if he had experienced any problems. Flores told him no, that it had been taking him only three minutes. Perez then returned to the heat exchanger.
At about midnight, Flores returned to the drill and found Perez laying unconscious on the work platform. The drill motor was dangling by the air hose against the side of the heat exchanger. Flores immediately went to the NO. 4 digester unit for help where he found George Reyes, equipment cleaner helper.
Reyes went to the accident scene while Flores found an area telephone and called the emergency control team. Members of the team arrived at about 12:02 a.m., and finding no pulse, immediately began CPR. At 12:30 a.m., Perez was transported by company ambulance to Portland, Texas, where he was transferred to a Tri-County EMS ambulance. Perez was taken to a hospital in Corpus Christi, Texas, where he was pronounced dead at 1:00 a.m. Death was attributed to fracture dislocation of the cervical spine.
MSHA was notified of the accident at 1:45 a.m., on June 12, 2002, by a telephone call from Arlon Boatman, manager of health, safety and security, to Ralph Rodriguez, supervisory mine safety and health compliance specialist. An investigation was started the same day. 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 persons, reviewed training records, and reviewed conditions and work procedures relative to the accident. An order was issued under the provisions of Section 103(k) of the Mine Act to ensure the safety of miners. MSHA conducted the investigation with the assistance of mine management, the miners= representative, and miners.
The accident occurred at the NO. 3-17 vertical heat exchanger. There were 18 heat exchangers located on the second floor of the processing plant. Wet slurry entered the heat exchanger at about 208 degrees Fahrenheit and was heated to 401 degrees Fahrenheit prior to transfer into a storage tank. The heat exchangers were 32 feet high and extended 4 feet and 6 inches above the second floor work platform. They were 3 feet and 4 inches in diameter, with about 472 tubes comprising the core. The tubes had an inside diameter of 1 and 1/4 inches.
Drilling was required to remove scale buildup on the inside of the tubes that occurred during the process. The heat exchangers had to be cleaned about every 35 days. A vertical drill was stationed in each of the 4 heat exchanger areas for this purpose. The drills were moved by crane over the exchanger to be cleaned.
The drill mast and drill assembly had been fabricated in-house. The drill mast was vertical and stood about 29 feet,10 inches above the exchangers. This height accommodated the 30-foot drill steel required to drill the full length into the exchanger core. The bottom of the mast was about 5 feet above the work platform floor. An air-operated Ingersoll-Rand, Model 4840M, reversible motor provided power for the drill to travel up and down the mast. The drills utilized a 1-inch x 30-foot drill steel and a wet bit to clean the heat exchanger tubes.
The tube cleaning process required the drill operator to manually orient the drill, one hole at a time, while being positioned near the mast. He would collar the bit into the heat exchanger tube using the hand valve control. After collaring the bit, the operator moved to the remote operator=s station, located about 20 feet from the outboard heat exchanger and monitor completion of the task.
A spring-centered hand valve control mounted at the bottom of the drill mast was used to raise or lower the drill head. To use this control, the operator had to stand beside the mast. Air pressure supplied to this hand control was in the range of 80-90 psig. The drill head could also be left to gravity feed itself in the down direction.
The motor that fell and struck the victim provided drill steel rotation. It was an air operated, Ingersoll-Rand, model 4800M. Drive motor speed was approximately 560 rpm with 52 foot-pounds of torque. The motor was approximately 11 inches long with adapter and had a diameter of approximately 4 and 1/2 inches, weighing 24 and 3/4 pounds with 4 feet of air hose attached. After the accident, the drill head assembly was found near its uppermost position with the drill bit extended into the top of a heat exchanger tube. This indicated that the drill operator was starting to drill a new hole when the accident occurred.
The gear reducer for the drill head drive motor was a Dodge Model HT12, with a modified input shaft coupling and a reduction ratio of 5.62 to 1. The cast reducer housing was made of Class 30 gray iron. The reducer specifications indicated that the drill steel speed was approximately 100 rpm with 292 foot-pounds of torque.
The reducer housing was designed to mount to an input motor using six fasteners in an equally spaced, 60 degree radial pattern, with a bolt center pattern of 3 and 11/16 inches in diameter. The fastener threads were 5/16 inch, 18-NC threads tapped 1/2 inch deep in 3/4 inch deep holes. Correct attachment required the full depth of all 6 of the fastener thread holes in the housing to be utilized for securing the motor.
A circular adapter mounted the drill motor to the reducer housing. This adapter had separated from the reducer, allowing the drill motor to fall. The flange on the adapter fastened to the drive motor was 3/8 inch thick, 4 inches in diameter, and had six equally spaced holes 11/32 inch in diameter on a bolt center three inches in diameter. The flange on the adapter that fastened to the reducer housing was 3/8 inch thick, 4 and 3/8 inches in diameter, and had six equally spaced holes, 11/32 inch in diameter, on a bolt center of 3 and 11/16 inches in diameter. The overall installed length from outside of the reducer flange to outside of the motor flange was 2 and 5/16 inches and the length between the inside edges of the flanges was 1 and 9/16 inches. The space limitations between the flanges indicated that the longest bolt possible to fasten the adapter to the reducer or motor would have a total length of 1 and 2 inches.
The 20 foot air hose supplying the drill head drive motor was mounted approximately 15 feet below the drill motor. When the motor fell, it came to rest about 1 inch off the work platform floor, hanging from the hose.
Four bolts and four lock washers were recovered in the accident area. They were identified as those used to mount the drill head drive motor adapter to the reducer housing. The hex-head threaded bolts were identified as ASTM 307A, SAE Grade 1 equivalent, 5/16 inch, 18-NC, with a thread length of 3/4 inch and a total length of approximately 1 inch. The lock washers were a helical-spring type for a 5/16 inch diameter bolt, with a flattened thickness of approximately 1/12 inch. The resulting thread engagement would have been less than 5/16 inch depth in the gear reduction housing with the lock washer fully collapsed. The housing and adapter had 6 mounting holes. Grit and grease in two of the holes indicated that only four bolts were in at the time of the accident.
The threads on the recovered bolts had various degrees of wear damage to the threads. The center sections of the bolts showed the most significant wear. Damage to the threads was consistent with the threads wearing against the flange of the drive motor adapter. Significant damage was not observed to the reducer casing fastener holes or threads, nor were metal shavings imbedded within the threads to indicate the bolts had been stripped out of the holes.
The bolts used to mount the drill head drive motor adapter to the reducer did not fully utilize the 1/2 inch thread depth of the reducer housing fastener holes. The resulting thread engagement was less than 1.5 times the bolt diameter, which is the recommended and typical engineering practice for this type of application. Using typical engineering practice, a bolt thread length of 1 inch would have been required, with an overall bolt length of at least 1 and 1/4 inches. The length of the bolts used to mount the drive motor adapter to the reducer housing did not allow a sufficient number of threads to be inserted into the bolt holes to prevent loosening when subjected to vibration.
The investigation concluded that the ASTM 307A bolt, SAE Grade 1 equivalent, 5/16 inch, 18-NC, with a thread length of 3/4 inch had been commonly used to mount the drill motors. Statements revealed that it was a common occurrence for the motor mounting bolts to come loose.
The root cause of the accident was the failure to establish effective preventative maintenance procedures. Previous occurrences were strong indicators the problem of loose bolts had not been resolved. The accident was caused by the failure to use the appropriate size bolts to attach the motor.
Order No. 6223204 was issued on June 13, 2002, under the provisions of Section 103(k)of the Mine Act:
An accident occurred at this operation on 6/12/2002, which resulted in a fatality. The employee was attempting to clean the NO. 317 heater. This order is issued to assure the safety of persons at this operation. It prohibits all activity at the NO. 317 heater and affected area until MSHA has determined that it is safe to resume normal operations in the area. The mine operator must obtain prior approval from an authorized representative for all actions to recover and/or restore operations to affected area.This order was terminated on June 14, 2002. Conditions that contributed to the accident have been corrected and normal operations can resume.
Citation No. 6223229 was issued on August 16, 2002, under the provisions of Section 104(d) of the Mine Act for violation of 30 CFR 56.7002:
A fatal accident occurred at this operation on June 12, 2002, when an air motor fell from the top of a drill mast, striking the drill operator. The bolts used to secure the motor to the speed reducer were not the correct size for this application and would not fully engage to the required 2 inch thread depth. The mine operator was aware of a reoccurring problem with the bolts falling out during drill operation. Failure to ensure that the correct bolts were used to fasten the drill motor constituted more than ordinary negligence and is an unwarrantable failure to comply with a mandatory standard.This citation was terminated on August 19, 2002. The mine operator obtained bolts that were suitable for fastening the drill motors. Employees were instructed in proper reporting and repair procedures regarding equipment defects.
Related Fatal Alert Bulletin:
Sherwin Alumina Company
A.C. Rodriguez ......... plant safety coordinatorMine Safety and Health Administration
Lloyd B. Ferran ......... mine safety and health compliance specialistUnited Steel Workers of America
Terry L. Worley ......... mine safety and health compliance specialist
F. Terry Marshall ......... mechanical engineer
Laman J. Lankford ......... mine safety and health specialist
Douglas Edwards ......... miners' representative
Sherwin Alumina Company
David J. Flores ......... equipment cleaner helper
George Ruiz ......... equipment cleaner helper
Joe L. Lopez ......... equipment cleaner helper
Tim Lowderdale ......... equipment cleaner helper
Modesto G. Delesantos ......... supervisor
Joe Gaytan ......... emergency control team
Gary L. Calloway ......... emergency control team
Trino L. Lopez ......... emergency control team
John M. Edwards ......... maintenance general foreman
Marty J. Diegel ......... area 4 superintendent