DEPARTMENT OF LABOR
MINE SAFETY AND HEALTH ADMINISTRATION
Metal and Nonmetal Mine Safety and Health
Report of Investigation
April 8, 1999
Surface Nonmetal Mine
Fatal Explosion of Combustible Mixture
United States Gypsum Company
Sigurd, Sevier County, Utah
I.D. No. 42-00160
Richard R. Laufenberg
Supervisory Mine Safety and Health Inspector
Richard L. Arquette
Mine Safety and Health Inspector
F. Terry Marshall
Donald P. Peiffer
Originating Office-Mine Safety and Health Administration
Rocky Mountain District
P.O. Box 25367, DFC, Denver, CO 80225-0367
Robert M. Friend, District Manager
On April 8, 1999, Gerald E. Tocher, quarry maintenance supervisor, age 63, was fatally injured while he and a coworker were replacing the seals on the rear suspension cylinder of a haulage truck. While dismantling the suspension cylinder, a small threaded valve broke off. After unsuccessful attempts to remove the threaded portion of the broken valve, penetrating oil was sprayed into the valve port and heat was applied with a torch. An explosion occurred in the cylinder and the rod was forcefully ejected, striking the victim.
The accident occurred as a result of using a combustible liquid and then applying heat with the torch.
Tocher had a total of 6 years, 10 months mining experience, all at this mine, 3 years as a quarry maintenance supervisor. He had not received training in accordance with 30 CFR, Part 48.
The Jumbo-Jensen mine, a surface gypsum operation, owned and operated by United States Gypsum Company, was located at Sigurd, Sevier County, Utah. The principal operating official was Lee W. Taylor, plant manager. The mine was normally operated one, 10-hour shift, six days a week. Total employment was nine persons.
Gypsum ore was drilled, blasted, loaded on haul trucks and transported to the plant where it was crushed and milled. The finished product was used in the manufacture of gypsum board.
The last regular inspection of this operation was completed on March 4, 1999.
DESCRIPTION OF THE ACCIDENT
On the day of the accident, Gerald Tocher (victim) reported for work at 6:00 a.m., his normal starting time. At about 9:30 a.m., he and Cortney Hunt, mechanic, began replacing the seals in the left rear suspension cylinder on a haulage truck. Tocher and Hunt were removing the nitrogen charging valve from the top of the cylinder rod, when the threaded portion of the valve broke off inside the rod. They first attempted to remove the broken section by spraying penetrating oil into the valve port and using an easy-out extracting tool. When this failed, heat was applied to the valve port area with a torch. The broken valve could not be removed.
Tocher and Hunt completed other tasks then stopped for lunch. They returned to the shop at about 1:10 p.m., and resumed working to remove the broken valve. Tocher sat on a block of wood directly in front of the rod applying heat to the broken valve area with the torch. Hunt walked a short distance to a work bench in front of the truck. Hunt heard a sucking noise, followed by a pop, and the shop door rattled. He ran to the rear of the truck and found Tocher lying on the floor with the rod across his upper leg area. Hunt briefly checked the extent of Tocher's injuries, then summoned help.
Local authorities and emergency medical personnel arrived at the mine a short time later. Tocher was transported to a local hospital where he was pronounced dead. Death was attributed to blunt force injuries to the abdomen.
INVESTIGATION OF THE ACCIDENT
MSHA was notified at 4:15 p.m., on the day of the accident by a telephone call from the office manager for the mining company. Upon arrival at the mine, MSHA's accident investigation 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. The miners did not request nor have representation during the investigation.
1. The accident occurred in the maintenance shop at the plant. The suspension cylinder assembly involved in the accident was mounted on the left side of the rear (drive) axle of a 35-ton, Model 769C Caterpillar haulage truck.
2. The victim and a coworker were replacing the seals on the suspension cylinder. The victim sat on a wood block directly in front of the assembly while doing the repairs.
3. Examination of the suspension cylinder assembly provided the following information:
4. Nitrogen contained in the suspension cylinder had been bled out through the nitrogen charge valve before beginning the repairs. The upper connector pin had been removed and the assembly rotated to a position approximately parallel to the shop floor. Work was done with the rod inside the 14-inch long cylinder bore. Hydraulic oil was drained from the assembly. Nitrogen and hydraulic oil charging valves were removed from the rod to allow for the removal of the assembly cap. As the nitrogen charging valve was removed, the lower threaded section broke off in the rod.
assembly length (not pressurized)- 30.1 inches rod length - 25.2 inches rod diameter - 7 inches rod weight - 114 lbs
5. The port within the broken portion of the valve tip was drilled out to a larger diameter to facilitate the use of an easy-out. CRC Power Lube was applied to loosen the valve threads. Compressed air was used to dislodge and flush any blockage in the nitrogen charging valve port. Air supply to the nozzle had a tank pressure of 140 psi. An oxygen-acetylene torch with a welding/brazing tip was used to heat the valve tip.
6. Flammability tests conducted on samples of the hydraulic oil collected from the rod determined the flash point was 374 degrees F. Flammability tests conducted on a sample of the CRC Power Lube penetration oil determined the flash point was 175 degrees F. The resultant flash points and auto-ignition temperature values indicated that these fluids are combustible and can be ignited by a flame or hot surface.
7. Tests were also conducted to determine if the use of compressed air would create enough internal pressure within the suspension cylinder to discharge the rod. No significant internal pressure was detected when 140 psi of air was supplied through the nitrogen charging valve. The compressed air escaped from several cylinder assembly ports preventing any measurable increase of air pressure above atmospheric.
8. Explosion tests were conducted on the suspension cylinder assembly with spray applications of CRC Power Lube injected through the nitrogen valve, followed by the injection of compressed air, and application of an oxygen-acetylene torch in a manner similar to what was done by the victim. During the test an explosion resulted in the suspension cylinder, causing the rod to be forcefully ejected.
9. The mine operator was issued a citation for failure to provide annual refresher training, in that, two required courses of instruction were not given to the victim. However, the victim's lack of training in the subjects of ground control and self-rescue and respiratory devices, were not considered factors contributing to this accident.
The accident was caused by the application of heat to the suspension cylinder rod after a combustible penetrating oil had been sprayed into the valve port. This caused a buildup and subsequent explosion of a combustible mixture inside the suspension cylinder assembly.
Order No. 7907223 was issued on April 9, 1999, under the provisions of Section 103 (k) of the Mine Act:
A fatal accident occurred at this operation on April 8, 1999, when a maintenance supervisor was struck by a suspension rod. This order is issued to assure the safety of persons at this operation until the affected areas can be returned to normal operations. 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 April 11, 1999. Conditions that contributed to the accident have been corrected and normal mining operations can resume.
Citation No. 7923657 was issued on June 8, 1999, under the provisions of Section 104 (d) (1) of the Mine Act for violation of 30 CFR 56.4100:
A fatal accident occurred at this mine on April 8, 1999, when a maintenance supervisor was struck by a suspension cylinder rod while attempting to remove a broken valve from the rod. After attempting to remove the valve, a combustible liquid was applied and the valve was heated with a torch. The liquid formed a combustible mixture which exploded inside the suspension cylinder assembly. Use of an open flame where combustible liquids are used is a serious lack of reasonable care which constitutes more than ordinary negligence and is an unwarrantable failure to comply with a mandatory safety standard.This citation was terminated on June 9, 1999, after all employees had received additional training on the hazards associated with the use of open flames where flammable or combustible liquids are used or transported in a manner that could create a hazard. The mine operator committed to strict enforcement of prohibiting this practice and to provide appropriate training to employees at all their operations nationwide.
Related Fatal Alert Bulletin:
Persons participating in the investigation:
United States Gypsum Co.
Lee W. Taylor, plant manager Bryan M. Tilley, quarry and mill manager Donald L. Schaefer, director occupational safety Joy B. Sullivan, safety and training managerMine Safety and Health Administration
Richard R. Laufenberg, supervisory mine safety and health inspector
Richard L. Arquette, mine safety and health inspector
F. Terry Marshall, mechanical engineer
Donald P. Peiffer, physical scientist
United States Gypsum Co.
Bryan M. Tilley, quarry and mill manager Cortney Hunt, mechanic
A laboratory investigation was conducted at the Approval and Certification Center as part of the technical assistance to the MSHA, Metal/Nonmetal Mine Safety and Health, Rocky Mountain District, on the suspension cylinder explosion accident that occurred at the U.S. Gypsum Jumbo-Jensen Mine, a surface gypsum mine located in Sigurd, Utah. The laboratory investigation included literature review, visual and microscopic examination, chemical tests, flammability, air pressure, and explosion tests.
Flammability tests were made on evidence samples of hydraulic fluid collected from the suspension cylinder involved in the accident and on a sample of CRC Power Lube penetrating oil that was used by the victim during his work on the suspension cylinder. The resultant flash point and auto-ignition temperature values indicated that these fluids are combustible and can be ignited by a flame or hot surface.
Tests were also conducted to determine if the use of compressed air would create enough internal pressure within the suspension cylinder to discharge the rod assembly. No significant internal pressure was detected when the suspension cylinder was supplied with 140 psi of air through the nitrogen charging valve. The compressed air escaped from several rod assembly ports that were open to the atmosphere, preventing any measurable increase of the air pressure above atmospheric.
Explosion tests were conducted on the suspension cylinder with spray applications of CRC Power Lube injected through the nitrogen valve, followed by the injection of compressed air, and application of an oxygen-acetylene torch in a manner similar to what was believed done by the victim. During a test, an explosion resulted in the suspension cylinder, causing the rod assembly to be forcefully ejected through the air.