Metal and Nonmetal Mine Safety and Health

Accident Investigation Report
Surface Nonmetal Mine
(Sand & Gravel)

Fatal Exploding Vessel Under Pressure Accident

RDO Equipment Company
I.D. No. ZEL


Trinity Materials Incorporated
Waco Pit
Waco, McLennan County, Texas
I.D. No. 41-03492

February 17, 1999


Michael C. Sanders
Mine Safety and Health Inspector

Donald Peiffer
Physical Scientist

Richard Dunst
Chemical Engineer

Originating Office
Mine Safety and Health Administration
South Central District
1100 Commerce Street, Room 4C50
Dallas Texas 75242-0119

Doyle D. Fink
District Manager


Brad Johnson, service technician, age 35, was critically injured at about 1:30 p.m., on February 17, 1999, when a tire exploded after heat had been applied to the rim. He died on March 1, 1999. Johnson had 10 years experience as a service technician, 5 years with this employer. He had not received training in accordance with 30 CFR part 48.

MSHA was notified at 2:00 p.m. on the day of the accident by a telephone call from the safety director for the mining company. An investigation was started the same day.

The Waco Pit, a surface sand and gravel operation, owned and operated by Trinity Industries, Inc., was located near Waco, McLennan County, Texas. The principal official was Walter Poston, manager. The plant and pit were normally operated one, 10?hour and one, 12?hour shift a day, five days a week. A total of 23 persons was employed.

Sand and gravel was extracted by dragline and hauled to the plant where it was washed, sized and stockpiled. The finished products were sold for use in the construction industry.

The victim was employed by RDO Equipment Company, an independent contractor in Hewitt, McLennan County, Texas. The contractor was enlisted by the mine operator to repair the brakes on a haulage unit. The principal operating official was Bradley Campbell, general manager.

The last regular inspection at this operation was completed on September 9, 1998. Another inspection was conducted at the conclusion of this investigation.


Physical Factors Involved

The accident occurred in the main shop building at the plant. The equipment involved was a 1975 Euclid B-30 tractor and bottom dump trailer rated at 60,000 pounds capacity. The trailer had been removed from service to repair the left rear brakes.

The tire was a Firestone tubeless type Super Rock Grip WB size 29.5 X 25 with 28-ply rating. It weighed approximately 1500 pounds. The diameter was 67 inches and tread width was 26 inches. The tire was mounted on a 25-inch diameter rim secured with a five-piece lock-ring assembly. The tire and rim assembly was secured to the wheel with 20 wheel clamps, tensioning washers and nuts. Normal cold operating pressure was 60 PSI.

The oxygen/acetylene cutting torch used to heat the rim was mounted on a two-wheel cart. The compressed gas cylinders had been secured to the cart with a chain and provided with protective valve covers. The heating tip was a multiple flame heating nozzle (rosebud).

Laboratory tests indicated that the application of heat caused the tire material to produce combustible gases inside the tire. The heated rim and tire provided an ignition source for the combustible gases, which resulted in the explosion.

The victim was using a fork lift truck to remove the tire. The fork lift was a Hyster model H80C, rated at 8,000 pounds load capacity.


Description of the Accident

On the day of the accident, Brad Johnson (victim) reported to the mine shop at 9:00 a.m. and received his work assignment from Robert Farmer, purchasing agent for Trinity Materials. Johnson was assigned to repair the brakes on the Euclid B-30 trailer. Johnson and Terry Heard, mechanic for Trinity Materials, backed the trailer into the maintenance shop. Johnson then drove Heard to the pit to pick up the fork lift. Heard drove the fork lift back and parked it in the shop near the trailer.

Heard went about other duties in the shop while Johnson jacked up the trailer and supported the left rear with a jack stand. He removed the wheel clamps, tensioning washers and nuts then positioned the fork lift with the forks under the tire. He wrapped a chain around the back of the tire/rim assembly and attached it to the load carrier guard on the fork lift.

Johnson attempted several times to loosen the tire/rim assembly from the wheel by hammering on the back of the rim and tugging on it with the fork lift. He also used compressed air to remove any sand and gravel lodged between the rim and wheel that might be binding the assembly.

At about 12:30 p.m. Johnson, Heard and Farmer stopped for lunch. Johnson and Heard discussed the problem of the rim being stuck to the wheel. After lunch, Heard suggested that they let the air out of the tire. Johnson removed the valve cap and depressed the valve core for 10 to 15 minutes. Johnson attempted several more times without success to remove the tire and rim assembly by tugging on it with the fork lift.

The jack stand had begun to slip out of place so Johnson repositioned it and then asked Heard about using heat. Heard replied that it was up to Johnson. Johnson positioned the oxygen/acetylene cart behind the left rear of the trailer and began to heat the rim. After 45 minutes to an hour, Johnson called out for Heard to come to the trailer. As Heard approached the right side rear of the trailer the tire exploded throwing him backward. Heard recovered momentarily and found Johnson lying unconscious against the inside of the right side rear tire.

Johnson's pants leg was on fire and while Heard was extinguishing the flame, Robert Villa, plant manager, arrived. They pulled Johnson from under the trailer. He did not have a pulse and was not breathing. Heard administered five or six chest compressions and Johnson's pulse was restored and he began breathing on his own. Villa administered first aid to control bleeding and Farmer called the local 911 emergency assistance number. The sheriff's deputies and an ambulance arrived a short time later. Johnson was transported to a local hospital, where he died on March 1, 1999.



The accident was caused by the application of heat to the tire rim, which caused a buildup and subsequent ignition of combustible gases inside the tire.



RDO Equipment Company

Citation No. 7874001 was issued on February 17, 1999, under the provisions of section 104(a) of the Mine Act for violation of 30 CFR 56.4500:

This citation was terminated on February 26, 1999 after the contractor issued a hazard alert to all employees and provided training nationwide in safe work practices for removing wheels from mobile equipment and prohibited the use of heat from any source.

Trinity Materials, Inc.

Citation No. 7874002 was issued on April 5, 1999, under the provisions of section 104(a) of the Mine Act for violation of 30 CFR 56.4500:

This citation was terminated on April 8, 1999, after the mine operator provided training at all company operations in safe work practices for removing wheels from mobile equipment and prohibited the use of heat from any source.

Related Fatal Alert Bulletin:  FAB99M10



List of Participants in the Investigation

RDO Equipment Company

Trinity Materials, Inc.

Mine Safety and Health Administration


Executive Summary of Laboratory Analysis
Trinity Materials, Inc.
Mine ID #41-03492, MSRS 049921

A laboratory investigation was conducted at the Approval & Certification Center (A&CC) as part of the accident investigation for MSHA, Metal and Nonmetal Mine Safety & Health, South Central District on the tire explosion accident that occurred at Trinity Materials, a surface sand and gravel aggregate facility. The laboratory investigation included literature review, visual and microscopic examination, and ignition and heating tests on the damaged and undamaged liner materials.

After completion of the laboratory testing and analysis, it was concluded that the most likely event that caused the accident was the heating of the rim and brake drum assemblies with an acetylene cutting torch. The heat from the acetylene torch was conducted through the rim and into the tire material. The tire material decomposed and produced hot embers and a combustible gas mixture within the tire. The heated tire material provided an ignition source for the combustible gases which subsequently ignited, causing the tire to explode.

Given that the tire before the explosion was at least at an initial pressure of about 36 psig, a maximum explosion pressure of approximately 325 psig could have developed. This explosion pressure would be over 3 times greater than would develop from a combustion explosion at normal atmospheric pressure and over 3 times greater than the pressure at which the tire would be expected to fail if over pressurized with air. The rate of explosion pressure rise could have been about 7500 psi/sec and would be several times greater than would have developed from a combustion explosion at normal atmospheric pressure. This magnitude of maximum pressure and rate of pressure rise from an explosion in the tire is consistent with the degree of physical damage observed at the accident site.

Comprehensive test results can be obtained from the Chief of the A&CC, RR 1, Box 251, Industrial Park Road, Triadelphia, West Virginia 26059.