DEPARTMENT OF LABOR
MINE SAFETY AND HEALTH ADMINISTRATION
Metal and Nonmetal Mine Safety and Health
REPORT OF ACCIDENT
Surface Nonmetal Mine
Exploding Vessels Under Pressure Accident
October 24, 2002
Foreman Quarry and Plant
Ash Grove Cement Company
Foreman, Little River County, Arkansas
Mine I.D. No. 03-00256
Wyatt S. Andrews
Supervisory Mine Safety and Health Inspector
Jerry Y. Anguiano
Mine Safety and Health Inspector
Bruce B. Palmer
Richard A. Skrabak
Mine Safety and Health Administration
South Central District
1100 Commerce Street, Room 462
Dallas, Texas 75242
Edward E. Lopez, District Manager
On October 24, 2002, Jerimy A. Pearson, fuel handler, age 27, was fatally injured when the Moyno grinder exploded, covering him with flammable waste fuel. The fuel ignited, causing second and third degree burns over 90 percent of his body. Pearson had started the pump for the south waste fuel system and was attempting to bleed air from the system when the accident occurred.
The accident occurred because the safety monitoring system designed to shut off the waste fuel system pump had not been maintained in a functional condition.
Pearson had 2 years and 7 months of mining experience, all at this location. He had been a fuel handler for 8 months.
The Foreman Quarry and Plant, a surface quarry and cement plant, owned and operated by Ash Grove Cement Company, was located in Foreman, Little River County, Arkansas. The principal operating official was Terry Kerby, plant manager. The plant operated three 8 hour shifts, 7 days a week. The quarry operated one 8 hour shift, 5 days a week. Total employment was 167 persons.
Limestone was mined from a single bench quarry using bulldozers equipped with rear mounted rippers. The material was transported by pan scrapers to the stockpile, conveyed to a primary crusher, crushed, and conveyed to the plant for processing into portland cement. The finished product was sold for use in the construction industry.
Heat to the kilns was supplied primarily by burning coal and natural gas, supplemented by liquid waste fuel. The waste fuel was a mixture of various organic solvents, oils, and other petroleum byproducts. The company began utilizing liquid waste fuel in 1995 because of its high energy output and relatively low cost. This fuel was delivered to the plant in bulk via tanker trucks or railcars, and pumped into large storage tanks in the area of the plant near where the accident occurred.
The last regular inspection of this operation was completed on September 16, 2002.
Description of the Accident
On October 24, 2002, Jerimy A. Pearson (victim) reported for work at 7 a.m., his normal starting time. After a short meeting with Terry Smith, supervisor, Pearson was assigned to operate a front end loader.
At about 12:45 p.m., Smith informed Pearson a decision had been made to shut down the north waste fuel system due to elevated temperatures at the north pump seal. He directed Pearson to switch the pumps delivering waste fuel to the kiln from the north system to the south system, which had been idle since 3 days earlier when the south pump grinder motor had been replaced due to a bad seal. At about 12:46 p.m., Pearson went to the containment area where the pumps were located and began checking the valves to see if they were positioned correctly to make the switch. Pearson shut down the north system pumps and started the south system pumps at about 12:48 p.m.
Ola Mae Williams, kiln control operator, was located in the control room of the plant, monitoring the fuel system through fuel line sensors. She radioed Smith, who was in the containment area with Pearson, and advised fuel was not getting to the kilns. Believing the cause of the problem was air in the system, Smith began bleeding air from the �-inch ball valves installed in the waste fuel piping system while Pearson bled air at the pumps. Pearson then radioed Williams to determine if fuel had begun flowing to the kilns and was told it had not. Smith left the area for a few moments to get a rubber drain hose. When Smith returned, he began bleeding the valve at the south 330 pump while Pearson was checking the other valves to see if they were in the open position.
At about 12:58 p.m., Smith observed the pipe entering the south grinder begin to shake and vibrate. Suddenly, the grinder exploded and was propelled off its base. Fuel sprayed from the grinder base covering Pearson and Smith. The fuel ignited and fire spread over the entire area. Smith's clothes caught fire and he ran through the containment area to the outside where he extinguished himself. When Pearson exited the containment area, Smith used a fire extinguisher to extinguish Pearson's burning clothing.
Williams saw the fire from the control room and radioed for help. David Davis, control room supervisor, activated the manual emergency shut down on the pumps, and called 911 for assistance.
Emergency medical personnel arrived and transported Pearson to a nearby hospital. He was later flown to the Little Rock, Arkansas, burn center where he died from his injuries at 11 p.m.
Investigation of the Accident
MSHA was notified of the accident at 2 p.m. on October 24, 2002, by a phone call from Floyd F. Arnold, day shift supervisor, to Wyatt S. Andrews, supervisory mine safety and health inspector. An investigation was started the same day. MSHA's accident investigation team traveled to the mine, conducted a physical inspection of the accident scene and equipment involved in the accident, interviewed employees, reviewed training records, conditions, and work practices 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, miners and representatives of the Cement, Lime, Gypsum and Allied Workers - Division of Boilermakers, International Local No.0397.
Location of the Accident
The accident occurred at the grinder for the south liquid waste fuel delivery system.
Waste Fuel System
The liquid waste fuel was known by the trade name of "Chem-Fuel K Blend," (Chem-Fuel). It was a mixture of various organic solvents, oils, and other petroleum byproducts and wastes. The primary ingredients were ketones and acetates. Chem-Fuel was classified as a hazardous waste because it was highly flammable as well as hazardous to the environment if improperly handled.
There were two separate liquid waste fuel delivery systems: one designated as the north waste fuel delivery system and the other as the south waste fuel delivery system. Both were located in the basement of the waste fuel containment area. Each of the waste fuel delivery systems consisted of a 100,000-gallon storage tank, two centrifugal pumps, a series of valves, piping, and a grinder. During normal operation, fuel flowed from the tank through the north or south system to the three plant kilns. The two systems worked independently of each other, and manual shutoff valves were used to prevent the north system from operating at the same time as the south system.
The equipment involved in the accident was the grinder for the south waste fuel delivery system. Its purpose was to provide a more homogeneous liquid fuel by effectively reducing the particle size of solids suspended in the fuel. The grinder was a Moyno, Pipeliner Model 401, industrial-duty solids reduction unit. It weighed approximately 1,300 pounds and was rated for a maximum pressure of 150 pounds per square inch gauge (PSIG).
The grinder impact chamber consisted of a single shaft rotating in a headstock, containing tungsten carbide-tipped cutting edges running against a hardened tool steel shear plate. The shear plate was provided with holes between 6 mm to 8 mm in diameter to allow the fluid to pass through. A seal on the grinder motor for the south system failed earlier in the week and the entire motor was replaced 3 days prior to the accident. As a result, the south system had been idle until just 10 minutes before the accident. Examination of the grinder components, mount, and bolts indicated no structural weakness or predisposition to disintegrate under normal pressurization.
There were two types of centrifugal pumps in each system, a Gould CV3196 2X3X13 and a Summit CV2196 2X3x13. These pumps were essentially identical. A 125 horsepower motor powered each pump. Each pump was capable of producing a maximum pressure increase of approximately 334 PSIG. Since they are in series (two in the north system and two in the south system), together they could theoretically produce a maximum pressure of approximately 668 PSIG. According to their operating manuals, the pumps should not be run dry or started unless they have been sufficiently "primed" (fuel in the system). The motors running the pumps operated on an automatic step increase program based on the fuel pressure in the line. The pump speed was ramped up over time until a pressure of 70 PSI was achieved in the line in the vicinity of the kiln floor. Based on feedback from the kiln area pressure sensor, the pump speeds were regulated to maintain and not exceed that pressure.
The switchover from the north to the south fuel system required air to be bled from the system on startup. Air in the system was apparently the cause of low pressure in the fuel line in the kiln area. It was customary to bleed the air before starting the pumps. On one previous occasion, the fuel handlers bled air from the lines while the pumps were operating, as the victim and his supervisor did just prior to the accident. The pump manufacturer recommended strongly against bleeding air while the pumps operated because it could place undue strain on the components of the system. This procedure caused the fuel pipe, between the grinder and the pumps, to vibrate violently just prior to the explosion.
The lack of flow in the fuel line following startup was due to some type of blockage, either a clog or a closed valve. Just prior to the accident, the blockage was abruptly removed, and the pumps immediately elevated the pressure in the system. As the pumps reached their maximum speed, a "water hammer effect" caused an instantaneous over-pressurization to occur in the south pump system, converging at the grinder. Under this extreme pressure, the grinder was torn loose from its base and propelled upwards 15 to 20 feet into the air. The 480-volt power cable was pulled loose from the grinder motor. The ignition source of the fuel fire and explosion was created by the exposed electrical conductors sparking into the surrounding airborne fuel.
The control room monitored the two systems by means of sensors that activated alarms and displayed warnings on monitor screens when specific set points for temperature or pressure were exceeded. Three pressure sensors were installed on the fuel line: one in the kiln area of the plant, and one each on the north system and south system just prior to the point where the two system lines merged into a single line leading to the plant. No alarms were installed in the waste fuel containment area where valve adjustments on the systems were done manually when necessary. If an alarm sounded or a warning was displayed, the control room operator used two-way radios to communicate with personnel at other areas.
Two independent but interconnected electronic systems monitored and controlled both the north and south fuel delivery systems. The Foxboro I/A DCS, (Intelligent Automation, Distribution Control System), manufactured by Invensys systems, Inc., Foxboro, Massachusetts, was used to monitor and record normal operating parameters (temperatures, pressures, etc.) as well as audible and visual alarms. These could be viewed on displays at the plant control room. A PLC (Programmable Logic Controller) network performed the basic startup/shutdown of the system and responded to electronic commands from the Foxboro. The Foxboro recorded information it sensed, but it did not record the PLC's actions.
One of the commands that the Foxboro was programmed to send to the PLC was to de-energize all pumps in the fuel delivery system if a pressure of approximately 60 PSI was not sensed at the line in the kiln floor area within 3 minutes of system startup. The 3-minute set point was based on a normal delay of 3 minutes for pressure to reach approximately 60 PSI at the kiln area from the time the pumps were started. The accident occurred 10 minutes after the pumps started. When no pressure was detected in the line at the kiln area, the Foxboro functioned properly in signaling the PLC to shut down the pumps 7 minutes before the accident, but the PLC did not respond. Three months prior to the accident, an older PLC system was replaced by a new PLC, and the Foxboro connections to the older PLC system were never changed over to the new PLC. A test of the fuel pump automatic shutoff functions was scheduled 3 days prior to the accident, but was aborted when the south pump grinder motor failed, and the test was never rescheduled.
The victim had not received specific training regarding safe work procedures and the specific hazards associated with the task that he was assigned to perform.
The victim and his supervisor had not been trained regarding the manufacturer's warning to not bleed the lines of air while the pumps were operating. Both had attended a training class on waste fuel system operation taught by Ash Grove Cement, but this procedure was not included in the training subject materials. Likewise, neither the supervisor nor any of the fuel handlers had been trained to recognize that the pumps should shut down automatically (as a result of the electronic sensor system) 3 minutes after they were started if insufficient pressure was detected in the line.
ROOT CAUSE ANALYSIS
A root cause analysis was conducted. The following causal factors were identified:
Causal Factor: The victim was not adequately trained relative to safe work procedures and hazards associated with his job.
Written guidance from the Moyno Pipeliner grinder and Gould pump manufacturers stated that the units should not be operated without flow. The victim had not been trained on this guidance.
Corrective Action: Implement procedures requiring all equipment operators and their supervisors to review manufacturers' instructions and recommendations to ensure machinery and equipment is operated according to manufacturer's guidelines.
Causal Factor: There was no alarm to warn of excessive fuel system temperature or pressure in the waste fuel containment area.
Audible and visual alarms were installed in the control room, but not in the fuel pump area. An alarm sounded in the control room alerting of excessive pressure in the south pumps shortly before the accident. If there had been an alarm in the fuel pump area, the victim may have been able to evacuate the area before the grinder exploded.
Corrective Action: Install audible and/or visual alarm systems in the waste fuel containment area.
Causal Factor: There were insufficient administrative procedures relating to the installation and maintenance of equipment.
The electronic system (Foxboro) that monitored the pressure in the waste fuel lines was incorrectly connected to the PLC system designed to de-energize the pumps when excessive pressure occurred. The two systems did not perform as designed because, when a new PLC was installed 3 months before the accident, the Foxboro had not been disconnected from the old PLC and reconnected to the new one. Follow up maintenance checks were not performed after the new PLC system was installed.
Corrective Action: Ensure equipment is installed according to the manufacturer's requirements. Develop procedures and schedules and monitor them to ensure that the required maintenance is performed.
Causal Factor: The fire suppression system in the waste fuel containment area did not activate until several minutes after the fire broke out.
The sensors for the fire suppression system were mounted 40 feet above the containment floor and the fireball occurred approximately 20 feet above the ground.
Corrective Action: Add additional fire sensors in the waste fuel containment area to detect heat from fire and activate the fire suppression system more rapidly.
The cause of the accident was the failure to maintain the monitoring system for the Programmable Logic Controller (PLC) that would have automatically deactivated the pumps when they failed to pressurize within 3 minutes of startup. The failure to establish maintenance procedures and to thoroughly train employees in all aspects of operating this system were found to be root causes.
Order No. 6219645 was issued on October 24, 2002, under the provisions of Section 103(k) of the Mine Act:
A fatal accident occurred at this operation on October 24, 2002, when a miner was attempting to start the liquid waste fuel system at the tank farm area. This order is issued to assure the safety of all persons at this operation. It prohibits all activity in the containment area until MSHA has determined that it is safe to resume normal operations in the area. The mine operator shall obtain prior approval from an authorized representative for all actions to restore operations in the affected area.This order was terminated on January 16, 2003. Conditions that contributed to the accident had been corrected and normal operations can resume.
Citation No 6227602 was issued on January 14, 2003, under the provisions of Section 104(a) of the Mine Act for violation of 30 CFR 46.7(a):
A fatal accident occurred at this mine on October 24, 2002, when a grinder exploded causing flammable liquid to be sprayed in the Liquid Waste Fuel containment area. The fuel ignited and burned the victim who was attempting to bleed excess air from the flammable fuel delivery system. The employee had not received training relative to the specific safe work procedures and hazards associated with the task he was assigned to perform.This citation was terminated on January 17, 2003, after all persons who may be exposed to hazards of the liquid waste fuel delivery system were trained in the specific safe work procedures and hazards associated with the task.
Citation No. 6227603 was issued on December 27, 2002, under the provisions of Section 104(a) of the Mine Act for violation of 30CFR 56.14100(b).
A fatal accident occurred at this mine on October 24, 2002, when a grinder exploded causing flammable liquid to be sprayed in the Liquid Waste Fuel containment area. The fuel ignited and burned the victim who was attempting to bleed excess air from the flammable fuel delivery system. During the investigation it was determined that the safety monitoring system designed to de-energize the liquid waste fuel pump in the event that flow was not maintained, was inoperative. Excessive pressure built up and caused the grinder to explode.This citation was terminated on April 1, 2003, when it was determined that the safety monitoring system was fully functional and would de-energize the liquid waste fuel pump in the event that flow was not maintained. Additionally, all start/stop switches in the kiln delivery system containment area were removed and such controls have been programmed into the liquid waste/derived fuel computer system. A siren and red strobe light will be activated for 20 seconds prior to pump startup to alert all personnel to leave the containment area prior to the pump starting. The light will continue to operate for 5 minutes, alerting personnel not to enter the containment areas until the fuel has been pumped through the kiln delivery loop to ensure proper system operation.
Related Fatal Alert Bulletin:
Persons Participating in the Investigation
Ash Grove Cement Company
Fran L. Streitman ............... vice president, environmental affairsBoilermakers Union
Clint Nelson ............... safety and human resources manager
Terry Kerby ............... plant manager
Ed Pierce ............... vice president, manufacturing, midwest region
William K. Doran ............... attorney
Freddie W. Jez ............... president, Local 397DMine Safety and Health Administration
Mike J. Mason ............... safety representative, Local 397D
Wyatt S. Andrews ............... supervisory mine safety and health inspector
Jerry Y. Anguiano ............... mine safety and health inspector
Bruce B. Palmer ............... industrial hygienist
Richard A. Skrabak ............... mechanical engineer
Derek Tjurnland ............... mechanical engineer
Persons Interviewed During The Investigation
Ash Grove Cement Company
Floyd F. Arnold ............... production foreman
James L. Baker ............... fuel handler
Jason Brinkley ............... fuel handler
Collette Brown ............... fuel handler
David Davis ............... control room supervisor
Calvin Gauldin ............... fuel handler
Freddie W. Jez ............... maintenance
Heath E. Murry ............... electrical supervisor
Ricardo Nelson ............... fuel handler
Charles M. Newton ............... instrument technician
Perry O'Neal ............... maintenance
Allen Oglesby ............... fuel handler
Jimmy D. Purtell ............... fuel handler
Robbie Smith ............... fuel handler
Terry Smith ............... waste fuel supervisor
Toddrick Smith ............... fuel handler
Chris R. Whisenhunt ............... automation engineer
Ola M. Williams ............... control room operator