DEPARTMENT OF LABOR
MINE SAFETY AND HEALTH ADMINISTRATION
Rocky Mountain District
Metal & Nonmetal Mine Safety and Health
ACCIDENT INVESTIGATION REPORT
SURFACE METAL MINE
FATAL ELECTRICAL ACCIDENT
Phelps Dodge Morenci, Incorporated (mine)
Mine I.D. No. 02-00024
Phelps Dodge Morenci, Incorporated
Morenci, Greenlee County, Arizona
October 31, 1995
Lee D. Ratliff
Supervisory Mine Safety and Health Inspector
Danny A. Frey
Mine Safety and Health Inspector
P.O. Box 25367 DFC
Denver, CO 80225-0367
Robert M. Friend
Lance Dru Nohl, instrumentation electrician, age 30, was severely burned and shocked on October 31, 1995, at approximately 12:01 p.m., when he was working inside a confined high voltage fuse compartment within close proximity to energized 13,800 volts (13.8kv) terminals. He died on November 1, 1995. Nohl had a total of 6 years and 3 months mining experience, 2 years and 2 months at this mine as an instrumentation electrician.
The Rocky Mountain District MSHA office, Denver, Colorado was notified of the accident on October 31, 1996, at 3:00 p.m., by a phone call from Harold L. Boling, safety and hygiene supervisor, Phelps Dodge Morenci, Inc. An investigation was started on November 1, 1995.
The mine, owned and operated by Phelps Dodge Morenci, Inc., was located at 4521 U.S. Highway 191, Morenci, Greenlee County, Arizona. Copper ore was drilled, blasted and loaded on trucks by electric-powered shovels. Ore then was transported to various locations throughout the mine for crushing/milling. Total mine employment was 2,475 persons. The work schedule was 3, 8-hour shifts a day, 7 days a week.
Principal operating officials for Phelps Dodge Morenci, Inc. were:
Timothy R. Snider, president
Donald J. Quinn, mine manager
Harold L. Boling, safety and hygiene supervisor
The training plan required by 30 CFR, Part 48, Subpart A was approved on May 11, 1979, and revised October 19, 1993.
The last regular inspection at this operation was completed on
September 26, 1995.
PHYSICAL FACTORS INVOLVED
The accident occurred inside the 001 high voltage fuse compartment located in the switchgear room at the southside electrical substation (Appendix 3). A draw-out carriage inside the compartment contained fuse protection for a single phase control power transformer (CPT), which was located behind the 001 fuse compartment. Short circuit and ground fault protection for the CPT were 15E ampere fuses, type EJ-O-ID.
Primary input voltage to the 50 kilovolt amperes CPT was 13.8 kv. Secondary voltage was single phase 120/240 volts, alternating current (ac). With the fuse carriage rolled in place and engaged, a 13.8 kv fused circuit was provided to the primary of the CPT.
Inside dimensions of the compartment with the fuse carriage removed were 24 inches high by 40 inches deep by 36 inches wide. Located inside the 001 fuse compartment was an insulated moveable shutter board guarding four high voltage bushings. Stab connectors were bolted to the top of each bushing for mating to the fuse carriage pressure terminals. Center phase bushings were not used as single phase service was required for the CPT (Appendix 4).
The top two bushings were for the incoming 13.8 kv "line" side and were mounted 18-1/8 inches apart, horizontally. The bottom two bushings were connections for the "load" side of the fuse carriage and the primary H1 and H2 leads for the CPT. Distance between the top and bottom bushings was 8-1/8 inches, vertically. However,oversized lugs had been installed on each bushing stab terminal which reduced the flashover distance between the top and bottom 13.8 kv terminals from 8-1/8 inches to 3-1/2 inches.
Primary power to the southside substation was 46,000 volts ac which was transformed (stepped down) to 13.8 kv. The 13.8 kv was fed to the switchgear room for additional circuit distribution and further transformation for control power, lighting, and battery charging systems. The southside substation and switchgear room also provided high voltage power for the southside solvent extraction-electrowinning (SX-EW) facilities.
Control power for the 13.8 kv substation switchgear room was supplied by two 50 kva single phase CPT's that were located in identical compartments directly behind the fuse carriages in compartment numbers 001 and 002.
Transformer secondary power was fed to a single phase 120/240 vac distribution panel at the switchgear room. One branch circuit provided 120 vac to a direct current (dc) rectifier charging unit which provided continuous charging for a bank of batteries located in the switchgear room. The batteries supplied 125 volt dc power to operate the 13.8 kv switchgear controls and associated devices for the substation when a loss of power occurred.
On the day of the accident electricians had been troubleshooting loss of control power in the southside substation switchgear room. They discovered primary control fuses on the H2 leads for 001 and 002 transformers had blown. Insulation had burned off the 15 kv primary H2 leads to both transformers which allowed contact with grounded metal compartment frames.
Blown fuses caused an interruption of power to the battery charging units. After a period of time, the batteries discharged and could not provide dc control power to operate the switchgear.
When the accident occurred protective devices at the 13.8 kv switchgear room were not operable and the electrical fault was opened at the powerhouse by a time delay, phase overcurrent relay which monitored the 46,000 volt powerline. Employees stated that all lights dimmed and estimated the fault lasted approximately 2 to 2� seconds. (Note: Normally, a fault of this magnitude should be cleared in approximately 1/10 of a second.)
A violent electrical arc and explosion occurred inside compartment 001 that charred most of the interior compartment walls, components, and insulating shutter boards at the back of the cubicle. The shutter mechanism was designed to slide up to expose the stabs. Bolt heads used to secure the stabs and terminal lugs onto the high voltage insulated bushings could be accessed by removing the shutters or by raising the outer shutter to align access windows with the stabs (Appendix 6). Following the accident the moveable shutter was observed in the down (closed) position.
The high voltage switchgear was installed in June 1995, and
placed in service approximately 3 months prior to the accident.
DESCRIPTION OF THE ACCIDENT
Lance Dru Nohl, victim, and Tom Crawford, electrician, reported for work on day shift at 7:00 a.m., October 31, 1995. After receiving work instructions from Wayne Spivey, instrumentation electrical supervisor, Nohl began checking "current metering" on rectifiers at the southside SX-EW facilities.
Crawford began scheduled substation maintenance checks as assigned by Jim Denton, electric shop supervisor. At approximately 9:30 a.m., Crawford arrived at the southside substation and discovered that batteries for the 125 volt dc control power for the high voltage switchgear were discharged.
He also observed that the 120/240 volt dc control power and lighting systems were not functioning. Crawford reported the condition to Denton.
Meanwhile, Nohl reported to Spivey that all indicating lights for the feeder breakers at the southside SX-EW were out due to a loss of dc control power.
Nohl proceeded to the southside substation switchgear room to investigate the power problem and found Crawford investigating the same condition. Both workers began troubleshooting.
The electricians located compartments 001 and 002 which housed the 120/240 volt breakers for the control power circuitry and the 13.8 kv fused draw-out carriages. They locked out the single phase 120/240 breakers and unlocked the fuse carriages. Crawford rolled out the carriages from compartments 001 and 002.
Testing of the fuses revealed that the H2 lead was open (blown) for each transformer. At approximately 10:00 a.m., Nohl reported to Spivey that they needed fuses and to ask him where the transformers were located. Spivey informed Nohl the transformers were located in the compartments directly behind 001 and 002 carriage compartments.
Spivey arrived at the switchgear room and found that the electricians had removed the cover plates from both transformer compartments. Nohl, Crawford, Spivey and David Ogonowski, electrical engineer, gathered around the transformers to observe and discuss the problem.
Observations revealed the following conditions:
- The 15 kv primary H2 leads between the wall isolation bushing to both transformers had most of the insulation burned/melted off.
- Exposed bare copper conductor had contacted the grounded metal compartment frame which had caused the fuses in the H2 leads to blow in both transformer primaries.
- Non-shielded conductors used for the 15 kv H2 primary leads laying on metal surfaces in the compartments created a "corona effect" that caused excessive heating which burned off the insulation.
Spivey instructed Nohl and Crawford to test the 002 transformerto ensure it was in operating condition. He also told them toevaluate what would be necessary to replace the burned H2 lead onthe 002 transformer with the undamaged H1 lead from the 001transformer. Spivey and Ogonowski left the area.
Nohl and Crawford tested the 002 transformer and determined theprimary windings were defective. They tested the 001 transformerand thought it was also defective because the secondary windingshowed "grounded". Further observation revealed that the neutralgrounding connection was still connected to the transformerterminals, resulting in a "grounded" reading. Afterdisconnecting the secondary leads, a followup test indicated thetransformer was not defective.
At approximately 12:00 p.m., Crawford was reconnecting thesecondary leads to the 001 transformer when he heard a sizzlingsound followed by a flash and violent explosion that occurredbehind the wall directly in front of him, where Nohl had beenworking in the 001 fuse compartment. Crawford reported that theexplosion knocked him down and dazed him briefly. He ran aroundto the front of the switchgear compartments to check on Nohl.
John Eddy, Brown and Root electrical contractor superintendent,was standing outside the substation switchgear room when he heardthe explosion. He ran inside and observed Nohl through thesmoke. Eddy, unsure of what happened and not knowing if Nohl wasclear of the voltage source, asked Nohl to come out of thecompartment area. Eddy assisted Nohl outside.
A medic arrived on the scene and administered first aid. Nohlwas taken to a local hospital and later air-lifted to a burncenter in Phoenix, Arizona. He died the following day as aresult of burns received over 63 percent of his body.
Crawford experienced head and muscle pain and was transported toa health care facility for observation. He was released laterthat same day.
The direct cause of the accident was failure to deenergize the13.8 kv feeder bus prior to working in the high voltagecompartment.
The following order was issued during the investigation:
Order No. 4650214, 103 (k)
Issued 10/31/96, at 1520 hours.
The company experienced an electrical accident that involved an employee (instrument electrician) receiving serious burns and possible electrical shock. The victim and another employee (electrician) were performing repairs on the switch gear located in the southside electrical substation switch gear room. This substation is the source of power to the southside tank house.
This order was issued to protect employees and to prevent unauthorized entry.
Terminated 11/1/95, at 1200 hours.
The following citation was issued as a result of theinvestigation:
Citation No. 4665702, 104 (a)
Issued 3/6/96, at 0915 hours for a violation of 30 CFR Part 56.12017.
On October 31, 1995, an instrumentation electrician was seriously injured in an accident at the south side substation switchgear room in high voltage compartment 001. The victim died on November 1, 1995, as a result of burns he received over 63 percent of his body. MSHA investigation has determined the 13.8 kv feeder bus was not deenergized before the victim entered the 001 fuse carriage compartment, nor were other preventative measures taken to safely isolate the energized terminals. The victim was working within close proximity of exposed energized 13.8 kv high voltage terminals inside the fuse compartment. High voltage hot-line equipment was not utilized.
Respectfully submitted by:
/s/ Lee Ratliff
Supervisory Mine Safety and Health Inspector
/s/ Danny A. Frey
Mine Safety and Health Inspector
Robert M. Friend
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