MINE SAFETY AND HEALTH ADMINISTRATION
Metal and Nonmetal Mine Safety and Health
Surface Nonmetal Mine
(Sand and Gravel)
Fatal Explosion of Combustible Mixture
R & S Sand and Gravel, Mine I.D. 22-00381
Martin Marietta Aggregates
Tremont, Itawamba County, Mississippi
May 26, 1999
William L. Wilkie
Supervisory Mine Safety and Health Inspector
Donald H. Daniels
Mine Safety and Health Inspector
Derrick M. Tjernlund, PE
Fire Protection Engineer
U.S. Department of Labor
Mine Safety and Health Administration
135 Gemini Circle, Suite 212;
Birmingham, AL 35209
On May 26, 1999, Thomas E. Allen, control person, age 42, was fatally injured while he and a co-worker were replacing an impeller on a slurry pump. After several failed attempts to remove the impeller from the threaded shaft, heat from a torch was applied to the impeller cone. The cone exploded and metal fragments struck the victim.
The accident occurred because heat from a torch was applied to the enclosed impeller cone which contained combustible materials.
Allen had a total of 2 years mining experience, all at this mine as a control person. He had received training in accordance with 30 CFR, Part 48.
The R & S Sand and Gravel Mine, a sand and gravel operation owned and operated by Martin Marietta Aggregates was located at 2050 Cotton Gin Road, Tremont, Itawamba County, Mississippi. The principal operating official was Tim Rakestraw, general manager. The mine was normally operated one 9-hour shift a day, 5 days a week. Total employment was twenty persons.
Sand and gravel was excavated from a single bench. The material was hauled by truck to the plant where it was crushed, screened, washed, and then conveyed to stockpiles. The finished product was sold for use in construction.
The last regular inspection of this operation was completed March 18, 1999. Another inspection was conducted at the conclusion of this investigation.
DESCRIPTION OF ACCIDENT
On the day of the accident, Thomas Allen (victim), reported for work at 7:00 a.m., his normal starting time. He was instructed by Tim Rakestraw, plant manager, to work with Richard Pennycuff, truck driver, to replace the impeller in the slurry pump at the number 3 crusher.
Allen and Pennycuff removed the pipes and plate covers on the pump without incident. Pennycuff went behind the pump and used a pipe wrench to hold the shaft while Allen used a pipe wrench in front of the pump to try to loosen the hub. When they could not get it to turn Allen used a steel bar to obtain leverage with the pipe wrench but they still were unable to get the hub loose. They then broke the fins off the impeller with a hammer, leaving the cupped front section of the impeller and the hub. Attempts to loosen the hub by prying and hammering were unsuccessful and Allen was instructed by Rakestraw to get the boom truck and use the oxygen/acetylene torch to apply heat to the hub. The truck was brought to the pump and Rakestraw showed Allen where to apply the heat then left the area. Allen knelt in front of the impeller and applied heat for approximately three minutes. As he was laying the torch down, Pennycuff told him to wait so he could go behind the pump to hold a pipe wrench that was attached to the shaft before Allen tried to loosen the hub. As Pennycuff was walking behind the pump, the cone of the impeller exploded and a piece of metal struck Allen in the left side of his chest, causing him to fall to the ground, face down. Pennycuff went to Allen and asked if he was hurt. Allen replied that he was and Pennycuff applied pressure to the wound and turned him over.
Bobby Conn, lab technician, heard the explosion and ran to the area. Pennycuff instructed Conn to call for help. Pennycuff continued first aid and when he could not find Allen's pulse he started administering CPR. Local emergency personnel arrived a short time later and Allen was air-lifted to the hospital where he was pronounced dead from Left Hemothorax, due to trauma to the left chest.
INVESTIGATION OF THE ACCIDENT
At 11:55 a.m., on May 26, 1999, Harry L. Verdier, Assistant District Manager of MSHA's Southeastern District Office, Birmingham, Alabama, was notified of the accident by a telephone call from Charles Fisher, Safety Director for Martin Marietta Aggregates. Upon arrival at the mine, MSHA's accident investigative team issued an order under the provisions of Section 103(k) of the Mine Act to ensure the safety of miners until the affected area of the mine could be returned to normal operations. MSHA conducted an investigation with the assistance of mine management and the miners. There was no designated miners' representative at this mine.
1. The slurry pump involved in the accident was a single suction, centrifugal unit that was belt driven. It was powered by a 30 horsepower, 460 volt electric motor which produced 1760 revolutions per minute. The pump, model number 3X4LCC-12 was manufactured in 1992 by Georgia Iron Works.
2. The impeller was made of a hardened, cast white iron alloy and threaded onto the end of the pump drive shaft. The central part of the inner impeller plate was cone shaped and completely covered the end of the shaft when installed. Once the impeller was threaded into position on the shaft, the cone created a sealed cavity between the back side of the cone section and the end of the shaft.
3. Based upon the dimensions of a replacement impeller, the cavity created between the shaft end and the impeller cone was measured to be approximately 1 liquid ounce (30 milliliters). The replacement impeller weighed approximately 42.4 pounds. The hub and cone section of the damaged impeller that remained on the shaft weighed approximately 5.4 pounds. The major diameter of the threaded shaft was 1.75 inches with 5 threads per inch.
4. The pump manufacturer's service literature recommended the application of a heavy amount of anti-seize compound on the shaft threads prior to installing an impeller onto the shaft. The service literature also provided a warning against the application of heat to the impeller because there was an explosion hazard.
5. Two warning labels were located on the front legs of the pump but were covered with dirt and dust and not clearly visible. The warning labels stated that heat should not be applied to the impeller hub.
6. The replacement impeller, the damaged impeller, and the shaft were provided with right-hand threads.
7. Removal of the impeller hub from the shaft at the Approval & Certification Center required the use of approximately ten feet of torque leverage and application of more than 100 pounds of force. Once the hub was turned approximately the first 1/8 of a turn, it became free and could be removed by hand.
8. The threads of the impeller shaft and the damaged impeller hub had a lighter, gray-like substance resembling a typical anti-seize compound. The replacement impeller threads and inner cone surface had a noticeable amount of a grease-like substance that resembled wheel bearing grease. A sample of both materials was subjected to a burn test using a natural gas pilot flame approximately 1/4-inch in diameter. Each sample of both materials demonstrated continued flaming once removed from the gas pilot flame.
9. The eyewitness reported that the victim applied direct flame from an oxygen/acetylene torch to the perimeter of the hub remnant while it was on the shaft. The witness stated the flame was applied for no longer than three minutes.
10. The torch used was a Victor, model number 315C/S-928773 and equipped with a Rosebud tip, model number 8MFA. The torch was tested at the site and found to be in working order. The settings on the tank regulators were found to be 42 psig for the oxygen, and 13 psig for the acetylene.
The direct cause of the accident was the application of heat to the enclosed cone of the impeller which contained combustible materials. Failure to refer to the service manual for this pump and failure to determine the proper procedures to utilize when performing this repair were root causes of the accident.
Order number 7761521 was issued on May 27, 1999, under the provisions of Section 103(k) of the Mine Act:
A fatal accident occurred at this operation on May 26, 1999, when an impeller hub on a water pump exploded after heat was applied with a cutting torch. Pieces of the impeller hub struck the victim causing fatal injuries. This order is issued to assure the safety of persons at this operation until the mine or affected areas can be returned to normal operations as determined by an authorized representative of the Secretary. The mine operator shall obtain approval from an authorized representative for all actions to recover equipment and/or return affected areas of the mine to normal.This order was terminated on June 7, 1999, when conditions that contributed to the accident were corrected.
Citation number 7761543 was issued on June 12, 1999, under the provisions of Section 104(d)(1) of the Mine Act for violation of 30 CFR standard 56.14205:
A fatal accident occurred at this operation on May 26, 1999, when a control operator was struck in the chest by metal fragments of an impeller hub. The victim and a co-worker were replacing an impeller on a larger slurry pump. The impeller was seized onto the threaded shaft and when heat from a torch was applied to the impeller hub it exploded. The equipment manufacturer's operation and maintenance manual warns of the explosive hazards generated by heating the impeller hub or the impeller nose. The supervisor engaged in aggravated conduct constituting more than ordinary negligence, in that he instructed the victim to apply heat to the impeller hub with an oxygen/acetylene torch. Failure to assure safe work procedures is a serious lack of reasonable care and is an unwarrantable failure to comply with a mandatory safety standard.This citation was terminated on June 16, 1999. The mine operator trained employees in the proper procedure and tools used to remove an impeller from a slurry pump. Also, employees were instructed to follow manufacturer recommendations and never apply any heat source to impeller.
Related Fatal Alert Bulletin:
Persons participating in the investigation:
Martin Marietta Aggregates
Charles Fisher .................... safety directorPatton Boggs LLP Attorneys at Law
Richard Pennycuff .................... truck driver
Henry Chajet .................... attorneyMine Safety and Health Administration
William L. Wilkie .................... supervisory mine inspector
Donald H. Daniels .................... mine safety and health inspector
Derrick M. Tjernlund, P.E. .................... fire protection engineer
Martin Marietta Aggregates
Richard Pennycuff .................... truck driver