Skip to content

District 2


River Hill Coal Co. (I.D. No. 36 00884)
River Hill Coal Co., Inc.
Karthaus, Clearfield County, Pennsylvania

October 18, 1995


William D. Sparvieri, Jr.
Coal Mine Safety and Health Inspector


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


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.


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.


The investigation revealed the following factors relevant to the occurrence of the accident:

  1. The equipment involved was a Hitachi EX3500 hydraulic excavator, Serial No. 185-00120.

  2. The hydraulic excavator is powered by two 12 cylinder Cummins diesel engines and is equipped with a 23.5 cubic yard bucket.

  3. 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.

  4. 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).

  5. 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.

  6. 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.

  7. 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.

  8. 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).

  9. 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.

  10. The two socket head cap screws that failed were found as follows:

    1. 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.

    2. The upper portion of the top left cap screw was found in the end cap.

    3. The upper portion of the bottom right cap screw could not be found during the investigation.

  11. 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:

    1. 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.

    2. The bottom right cap screw failed primarily due to a single event.

    3. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.


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.


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


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:
Fatal Alert Bulletin Icon [FAB95C35]