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Mine Safety and Health Administration (MSHA) - Report of Investigation Surface Metal Mine Taconite) Fatal Electrical Accident Occuring October 12, 2006 - #23 MAI-2006-23

UNITED STATES
DEPARTMENT OF LABOR
MINE SAFETY AND HEALTH ADMINISTRATION
Metal and Nonmetal Mine Safety and Health

REPORT OF INVESTIGATION

Surface Metal Mine
(Mill)

Fatal Electrical Accident
October 12 2006

United Taconite, LLC
United Plant
Eveleth, St. Louis County, MN
Mine I.D. No. 21-03404



Investigators


George F. Schorr
Supervisory Special Investigator

Alan J. Brandt
Mine Safety and Health Inspector

Amy Lindgren
Mine Safety and Health Specialist

Nicholas W. Damiano
Electrical Engineer




Originating Office
Mine Safety and Health Administration
North Central District
515 West First Street, Room 333
Duluth, MN 55802-1302
Steven M. Richetta, District Manager




OVERVIEW

Andrew D. Reed, maintenance coordinator, age 24, was fatally injured on October 12,
2006, when an electrical short occurred in a ball mill starter circuit. Reed was
troubleshooting an electrical problem in the motor ladder start-up sequence for the No.
4 ball mill electrical motors. An air-magnetic circuit breaker that provided over current
protection to the circuit failed, resulting in a sustained arc-flash.

The accident occurred because management failed to ensure that the air-magnetic
circuit breaker provided over current protection for the electrical circuit. The failure to
also provide circuit overload protection for the plants incoming power feed circuit also
contributed to the accident.

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GENERAL INFORMATION

United Plant, an iron ore (taconite) milling operation, owned and operated by United
Taconite LLC, was located in Eveleth, St. Louis County, Minnesota. The principal
operating official was Todd D. Roth, vice president and general manager. The plant
normally operated various shifts, 24-hours a day, 7 days a week. Total employment at
the plant was 295 persons.

Raw iron ore was shipped to the plant by train from another location. The material was
crushed and milled in a multiple step process. Iron was separated from the processed
taconite ore by magnetic separation and the iron rich concentrate was processed for
shipping by adding a binder, and rolled to form green pellets. The finished heat-
hardened pellets were shipped by train to port loading facilities and sold for use in steel
manufacturing.

The last regular inspection of this operation was completed on September 8, 2006.

DESCRIPTION OF ACCIDENT

The week prior to the accident, ball mill No. 4 was experiencing random nuisance trips.
On October 11, 2006, the day before the accident, the concentrator ball mill production
lines were taken offline while repairs were being made to the plants taconite tailings
disposal system. After repairs had been completed, the ball mills were started. The No.
4 ball mill was started on the night shift, ran for approximately 20 minutes, and then shut
down automatically. Attempts to restart the No. 4 ball mill were unsuccessful. Bryan D.
Sandnas, electronic technician, was called to troubleshoot the motor start-up sequence
ladder for the motors used to drive the ball mills. The next day Sandnas arrived at the
plant about 4:35 a.m. He tried to diagnose the problem by examining the motor start-up
sequence ladder.

About 6:00 a.m., Andrew D. Reed, maintenance coordinator, started his normal work
shift. He helped Sandnas diagnose the electrical problem. At approximately 7:00 a.m.,
Erik N. Maki, electronic technician, arrived to assist Reed and Sandnas.

Before breaking for lunch, Reed and Sandnas thought they had isolated the problem to
the circuit that controlled the motor starter conductors. They discussed attempting to
start up No. 4 ball mill in test power.

About 12:20 p.m., the crew returned to the motor control room (MCC) and prepared to
start up the No. 4 ball mill. Sandnas closed and bolted the No. 4 south and north motor
control cabinets and then racked in the motor starter. He called the control room to
request that the No. 4 ball mill be started. The control room operator initiated the start-
up sequence. Sandnas and Maki were standing apart, but along the east side of the
motor control center room, so they could both watch the relays associated with the start-
up of No. 4 ball mill. Sandnas was standing by the DHX relay cabinet, adjacent to a
door, while Maki stood in front of the No. 4 DC drive cabinet. Russell A. Korpi, lube
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technician, passing the motor control room, saw Reed standing near the west wall by
the ball mill motor control starter relay cabinets.

When the pre-mill start-up procedures were completed, the start-up of the No. 4 mill
was initiated by the control room. As the mill tried to start, Sandnas and Maki initially
heard a loud noise and then saw a large ball of fire coming from the opposite side of the
MCC room near Reed. Maki attempted to move toward Reed but retreated due to fire
and smoke. Maki and Sandnas evacuated the MCC Room and Sandnas then called on
his radio, requesting that No. 4 ball mill be shut down.

Plant emergency response personnel and the local fire and emergency medical
services were called to the scene. Emergency responders searched for Reed and
found him in the MCC room. The victim was pronounced dead at the scene by a St.
Louis County medical examiners deputy coroner. Death was attributed to smoke
inhalation.

INVESTIGATION OF THE ACCIDENT

MSHA was notified of the accident on October 12, 2006, at 1:30 p.m., by a telephone
call from Kelly R. Campbell., section manager for safety and loss control, to George F.
Schorr, supervisory special investigator. An investigation began the same day. An
order was issued pursuant to Section 103(k) of the Mine Act to ensure the safety of the
miners.

MSHAs accident investigation team conducted a physical inspection of the accident
site, interviewed employees, and reviewed conditions and work procedures relevant to
the accident. MSHA conducted the investigation with the assistance of mine
management, employees, and the miners representatives.

DISCUSSION

Location of the Accident

The accident occurred in the new side motor control center located on the balling mill
floor in the concentrator building. The air-magnetic circuit breaker over-current
protective device that failed to clear the fault was located in the new side substation
distribution building, part of the plants electrical power feed substation.

Electrical Equipment

Electrical power entered the mine site at the main substation by means of two 115kV
feeds and immediately entered two Allis-Chalmers oil circuit breakers (OCB). Electrical
power was then distributed through a 115kV bus that fed five 115kV/4160V
transformers. Transformer No. 5, which was involved in the accident, fed the new side
substation distribution room (SDR) 4160V bus 50. Electrical power was further
distributed to the plant through Allis-Chalmers air-magnetic circuit breakers (ACB).
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Electrical power was provided to the concentrator building new side ball mill motor
control center (MCC) room by approximately 1000 feet of 750 MCM cables (Appendix
B).

As a result of the accident, the MCC room (where the victim was found) and the new
side SDR were badly damaged. The 4160 electrical conductors that ran from the SDR
to the MCC room also sustained significant damage during the accident.

The MCC room sustained damage to the entire west wall (incoming bus) where the
arcing originated. Due to the extent of damage, the origin of the initial fault could not be
determined; however, after the inception of initial fault, the fault enveloped all three-
phases of the electrical power on the line-side of the ball mill motor starter vacuum
contactor in the MCC room.

Damage to the line side of the No. 4 south ball mill motors starter was the most
extensive. The power cables feeding this motor appeared to be burned from the inside
out. Damage to these power cables was evident throughout the entire 1000 feet of
cable between the SDR and the MCC room. The damage to the wires was indicative to
a vast fault current over a period of time. Internal heating of the cables that supplied
power to ball mills No. 3 and No. 5 was evident but not excessive, thus supporting No. 4
ball mill line side feed as the origin of the initial fault.

The electrical circuits that supplied power to ball mills Nos. 3, 4, and 5 were protected
by an Allis-Chalmers ACB. This breaker was located in the SDR and was found in the
closed (on) position after the accident. Electrical power continued to be supplied to the
MCC room through the ACB and was only interrupted when the cables feeding Nos. 3,
4, and 5 ball mills melted, causing a physical break in electrical connection.

Approximately 3.5 minutes after the initial fault occurred, the OCB tripped, interrupting
electrical power to the entire plant. The OCB was equipped with an under-voltage relay
device. The device was designed to open when incoming voltage dropped below a
certain percentage of the original line voltage (usually 5 to 10