DEPARTMENT OF LABOR
MINE SAFETY AND HEALTH ADMINISTRATION
District 2
ACCIDENT INVESTIGATION REPORT
SURFACE COAL MINE
FATAL MACHINERY
River Hill Coal Co. (I.D. No. 36 00884)
River Hill Coal Co., Inc.
Karthaus, Clearfield County, Pennsylvania
October 18, 1995
By
William D. Sparvieri, Jr.
Coal Mine Safety and Health Inspector
and
Michael M. Zenone
Coal Mine Safety and Health Inspector
Ronald Medina
Mechanical Engineer
Technical Support Approval and Certification Center
Originating Office - Mine Safety and Health Administration
New Stanton District Office
R.R. 1, Box 736, Hunker, Pennsylvania
Joseph J. Garcia, District Manager
GENERAL INFORMATION
The River Hill Coal Co. mine, operated by River Hill Coal Co., Inc., is located 1.7 miles off State Route 879 in Karthaus, Clearfield County, Pennsylvania. The mine consists of seven active strip pits and a preparation plant. Employment is provided for 99 persons. Coal is mined from the Upper and Lower Kittanning and Moshannon coal seams, which has a combined thickness of up to 75 inches. The mine operates two 9-hour shifts a day, five days a week; and one 8-hour shift on Saturday.
Average production is 3,000 raw tons of coal a day.
Overburden is drilled with highwall drills, shot, and removed with a dragline, hydraulic excavators, bulldozers, and rock trucks. Coal is loaded into trucks with front-end loaders and transported to the preparation plant for processing.
The principal officers at the mine are:
Harry J. Hanchar . . . . . . . . . . . . . . . . . President
Samuel D. Confer . . . . . . . . . . . . . . . . .Safety Director
The last regular Safety and Health inspection was completed on September 25, 1995.
DESCRIPTION OF ACCIDENT
On Wednesday, October 18, 1995, the 004-0 pit crew, under the supervision of Joseph Potter, foreman, started their shift at 6:00 a.m. The crew's assignment was to load overburden which had been previously drilled and blasted. Upon arrival at the 004-0 pit, they met the maintenance crew, who had just completed an oil change on the Hitachi EX3500 hydraulic excavator. The 004-0 pit crew conducted a pre-operational inspection of the Caterpillar 785B rock trucks and the Hitachi EX3500 hydraulic excavator.
At approximately 6:15 a.m., Mark Hurd, Hitachi EX3500 operator, began loading overburden in the 004-0 pit. Loading operations continued without incident until 9:00 a.m., at which time the crew suspended normal operations for their scheduled 15 minute break. At the conclusion of the 15 minute break, and in preparation for resuming normal operations, Hurd started the left engine of the Hitachi EX3500 excavator. When an attempt was made to start the right engine, one of the batteries, supplying electrical current to the starter, exploded. Hurd immediately turned off the left engine and using the two-way radio, notified Arnold Hoffman, maintenance foreman.
At approximately 9:25 a.m., Hoffman arrived at the 004-0 pit and instructed Hurd and Richard Michaels, rock-truck driver, to go to the Karthaus shop and pick up a new battery. Hoffman removed the damaged battery and made repairs to the battery cables. En route to the Karthaus shop, Hurd and Michaels met Potter traveling to the 004-0 pit. Potter instructed Michaels to use the 400 Hough front-end loader to clean the haulroad, while he and Hurd traveled to the Karthaus shop to pick up a new battery. At approximately 11:00 a.m., Potter and Hurd arrived at the 004-0 pit with a new battery. Hoffman installed the new battery while the excavator was refueled and he left the area.
At approximately 11:15 a.m., Hurd started both engines of the Hitachi EX3500 excavator. Hurd allowed the engines to warm up for several minutes before loading the rock truck operated by Burton Fry. Hurd, using his two-way radio, asked "what time is it?". Potter responded, "It's 11:28". Fry stated that shortly after this he heard the engines of the Hitachi EX3500 excavator change pitch and immediately looked out the driver's side window of the rock truck. Fry could see oil going through the cab of the Hitachi EX3500 excavator and immediately tried to contact Hurd over the two-way radio but received no response. Fry saw that Hurd was slumped to the left side of the operator's cab. Fry exited his rock truck and boarded the excavator. Hearing Fry's attempt to contact Hurd, Michaels looked in the direction of the excavator, and saw the damage to the operator's cab and the oil going through the cab. Michaels contacted Potter on the two-way radio and told him to call an ambulance and to hurry to the pit. Hoffman, overheard the conversation and also started toward the pit. By this time, Fry had reached the operator's cab of the excavator. Looking in the rear window, he could see Hurd slumped to the left of the cab and 4 to 6 inches of hydraulic oil on the cab floor. Fry entered the operator's cab and checked the victim for a pulse but found none.
Michaels arrived at the excavator, boarded, and entered the operator's cab. He also checked the victim but could not detect any pulse. Michaels saw that a hydraulic line had entered the right side cab window. He looked towards the excavator boom, and saw that the end cap and pilot line had separated from the switch valve. Michaels exited the excavator and joined Fry as Hoffman arrived at the pit. Michaels informed Hoffman that Hurd's injuries appeared to be fatal. Hoffman boarded the excavator, entered the operator's cab and turned both ignition keys off.
Potter arrived at the pit and observed the accident scene. Knowing there were two Hitachi model EX1800 excavators in service at the mine, equipped with identical switch valves, Potter immediately removed both model EX1800 excavators from service.
At 12:01 p.m., an ambulance and Emergency Medical Technicians from the Karthaus, Pennsylvania Fire Department, arrived at scene. During their initial evaluation of the victim, the EMTs determined the injuries were fatal and the Clearfield County Coroner was notified. R. Joel Heath, Clearfield County Coroner, arrived at 1:32 p.m. and the victim was pronounced dead at 1:40 p.m. The cause of death was listed as massive head trauma. MSHA was notified of the accident and the investigation into the cause started immediately.
PHYSICAL FACTORS INVOLVED
The investigation revealed the following factors relevant to the
occurrence of the accident:
- The equipment involved was a Hitachi EX3500 hydraulic
excavator, Serial No. 185-00120.
- The hydraulic excavator is powered by two 12 cylinder
Cummins diesel engines and is equipped with a 23.5 cubic
yard bucket.
- The hydraulic excavator was purchased new and put into
service at the mine in September 1990. At the time of the
accident, the hour meter, located in the operator's cab,
indicated the excavator had been in service for 25,014
hours.
- The hydraulic excavator is equipped with a pilot operated
hydraulic system. Pilot pressure is used to control the
main valves. The pilot relief pressure is 45 KgF/CM2 (640
PSI). The working pressure, which controls the movement of
the hydraulic cylinder, is 300 KgF/CM2 (4266 PSI) and the
main overload relief pressure is 320 KgF/CM2 (4550 PSI).
- The arm level luffing switch valve (switch valve) is
installed on the boom adjacent to the operator's
compartment. The switch valve directs the oil flow from the
level cylinder to the boom cylinders to move the bucket
horizontally in a level plane during loading operations.
Level luffing is the function that eliminates the arc
movement that would result if the arm was extended without
any corresponding movement of the boom.
- The switch valve is a two-position hydraulic valve that can
be turned on or off using the electric switch located in the
operator's compartment. During loading operations, when the
arm is extended, the boom is automatically lowered to
control the bucket's forward movement horizontally in a
level plane. When the arm is extended, level luffing occurs
regardless of whether the electric switch is "on" or "off".
When the arm is retracted, the bucket movement is dependent on the position of the electric switch. When the electric switch is turned on, level luffing occurs and the boom is automatically raised when the arm is retracted. This results in a level horizontal movement of the bucket. When the electric switch is turned off, the level cylinder and the boom cylinders are not hydraulically connected. The boom cylinders do not compensate for any arm movement; therefore, the bucket returns in arc.
- During the investigation, this electric switch was found in
the off position. Statements made to the investigators by
employees of River Hill Coal Co., Inc. indicated that the
victim and all other operators of the excavator operated
with the electric switch in the "on" position. During the
investigation, the bucket was found partially loaded
indicating the victim was loading (arm being extended) when
the accident occurred. It was the consensus of the
investigation team that the electric switch was
inadvertently moved to the off position during the accident
or recovery of the victim.
- The switch valve is controlled by pilot pressure that enters
the switch valve through pilot pressure lines. The two
pilot pressure lines, 17mm outside diameter, steel pipe, are
threaded into the end caps. The two end caps, one on each
side of the switch valve, are secured to the valve with 12mm
x 45mm (.47 inch x 1.77 inch) socket head cap screws. Each
end cap is secured with two of these cap screws (see
Appendix No. 2).
- Initial inspection of the EX3500 excavator revealed that the
two socket head cap screws holding the pilot line end cap
failed. This allowed the valve spool to be forcefully
ejected from the valve body. The spool entered the right
side cab window, struck the victim, and exited the left side
window. The valve spool was found on the ground between the
excavator and the rock truck being loaded. Evidence was
found to indicate the valve spool struck the left rear wheel
of the rock truck.
- The two socket head cap screws that failed were found as
follows:
- The lower portion (threaded) of each cap screw was
found in the valve body. The top left cap screw was
found broken flush with the machined surface of the
switch valve. The bottom right cap screw was found
broken with two threads exposed.
- The upper portion of the top left cap screw was found
in the end cap.
- The upper portion of the bottom right cap screw could not be found during the investigation.
- The lower portion (threaded) of each cap screw was
found in the valve body. The top left cap screw was
found broken flush with the machined surface of the
switch valve. The bottom right cap screw was found
broken with two threads exposed.
- The socket head cap screws were collected for evaluation and
sent to Touchstone Research Laboratory LTD., Triadelphia,
West Virginia. In the presence of representatives of MSHA
Approval and Certification Center, Mechanical Safety
Division, the socket head cap screws were evaluated. The
examination revealed the following:
- The top left cap screw failed primarily in fatigue.
The fatigue marks extended over approximately 90% of
the fracture surface, the only exception being a small
area of final catastrophic failure.
- The bottom right cap screw failed primarily due to a
single event.
- The metallurgical examination of both specimens did not detect any condition that would indicate a material defect that led to the failure of either cap screw.
- The top left cap screw failed primarily in fatigue.
The fatigue marks extended over approximately 90% of
the fracture surface, the only exception being a small
area of final catastrophic failure.
- The switch valve body and spool were collected and sent to
MSHA Approval and Certification Center, Mechanical Safety
Division, Triadelphia, West Virginia, for evaluation. The
evaluation did not reveal any defects that would have
contributed to the cause of the accident.
- The hydraulic excavator was maintained by personnel from
River Hill Coal Co., Inc. and an authorized Hitachi dealer,
Rudd Equipment Company, Clearfield, Pennsylvania. A
complete review of all service records of both River Hill
Coal Co., Inc. and Rudd Equipment Company did not produce
any evidence of maintenance or repair work to the switch
valve. An inspection of the cap screws showed the original
paint, in the socket heads of the cap screws intact.
- The excavator is equipped with a 24V/DC electrical system.
Prior to the accident, one of the six 12V batteries
exploded. During the investigation, there was no evidence
to indicate that the battery explosion or the electrical
system caused or contributed to the accident.
- The Hitachi EX3500 excavator is equipped with an onboard
micro-computer. The computer monitors and regulates engine
and pump functions. The computer does not control hydraulic
pressure.
- After repairs and the installation of a new switch valve, pressure tests were conducted. The pilot pressures to the switch valve were monitored during the normal loading cycle, with the electric switch in both the "on" and "off" positions. No excessive pilot pressures were observed which would have contributed to the failure of the socket head cap screws.
CONCLUSION
The accident was caused by the failure of two 12mm x 45mm socket head cap screws that secured the pilot line end cap to the arm lever luffing switch valve. The top left cap screw failed due to fatigue resulting in an overload on the remaining cap screw. When the two cap screws failed, the valve spool shifted, allowing high pressure to forcefully eject the valve spool from the valve body and propelled it through the right side cab window, striking the victim.
VIOLATIONS
A 103(k) Order was issued to ensure the safety of the miners until an investigation could be conducted.
Respectfully submitted by:
William D. Sparvieri, Jr.
Coal Mine Safety and Health Inspector
and
Michael M. Zenone
Coal Mine Safety and Health Inspector
Ronald Medina
Mechanical Engineer
Technical Support Approval and Certification Center
Approved by:
Joseph J. Garcia
District Manager--Coal Mine Safety and Health District 2
Related Fatal Alert Bulletin:
[FAB95C35]