Hoeganaes Corporation: Gallatin, TN
Metal Dust Flash Fires and Hydrogen
Explosion
5 Killed, 3 Injured
KEY ISSUES
INTRODUCTION
This case study examines multiple iron dust flash fires and a hydrogen explosion at the
Hoeganaes facility in Gallatin, TN. The first iron dust flash fire incident killed two workers
and the second injured an employee. The third incident, a hydrogen explosion and resulting
iron dust flash fires, claimed three lives and injured two other workers.
HOEGANAES CORPORATION
Hoeganaes Corp. is a worldwide producer of atomized steel and iron powders. Headquartered
in Cinnaminson, NJ, Hoeganaes has facilities in the U.S., Germany, China, and Romania.
The Hoeganaes Corp. is a subsidiary of GKN, a multinational engineering company headquar-
tered in the United Kingdom. GKN has businesses in addition to powder metallurgy, including
aerospace and automotive driveline industries. GKN acquired the Hoeganaes Corp. in 1999.
The largest consumer for the powdered metal product is the automotive industry, which
presses and sinters the powder into small metal parts.
FACILITY DESCRIPTION
The Hoeganaes Gallatin facility, located 30 miles northeast of Nashville, Tennessee, employs
just under 200 employees. Since becoming operational in the 1980s, they have increased their
manufacturing capability over 550 percent from 45,000 to over 300,000 tons.
PROCESS DISCUSSION
Hoeganaes receives and melts scrap steel. Various elements are added to the molten metal
to meet customer specifications, but the “workhorse” product, Ancorsteel 1000™, is over
99 percent iron. The molten iron is cooled and milled into a coarse powder that is processed
in long annealing furnaces to make the iron more ductile. The furnaces are called “band
furnaces,” for the 100 foot conveyor belt, or band, that runs through them. A hydrogen
atmosphere is provided in the band furnace to reduce the iron by removing oxides and
preventing oxidation. The hydrogen is supplied to the facility by a contract provider, onsite.
Hydrogen is conveyed to the furnaces via pipes located in a trench under the floor and
covered by metal plates.
In the process of going through the furnace, the coarse powder becomes a thick sheet called
“cake.” The cake is sent to a cake breaker and ultimately crushed into the fine PM product.
The majority of the finished PM product has a particle diameter between 45-150 microns,
or roughly the width of a human hair.
THE INCIDENTS
JANUARY 31, 2011 (TWO FATALITIES)
PM product is transferred through the plant by various mechanisms including screw
conveyors and bucket elevators. Bucket elevators have a tendency to go “off-track” when the
belt pulling the buckets becomes misaligned. Once sufficiently off-track the strain on the
motor increases until the torque is too great and the motor shuts down. On January 31, 2011,
at about 5:00 am Hoeganaes plant operators suspected bucket elevator #12 of being off-track
and a maintenance mechanic and an electrician were called to inspect the equipment.
Elevator Enclosure
Based on their observations, they did not believe that the belt was off-track and re-
quested, via radio, that the operator in the control room restart the motor. When the
elevator was restarted, vibrations from the equipment dispersed fine iron dust into the
air. During a CSB interview, one of the workers recalled being engulfed in flames,
almost immediately after the motor was restarted.
City of Gallatin emergency responders arrived with ambulances and transported the
mechanic and electrician to the Vanderbilt Burn Center in Nashville, TN. Both employees
were severely burned over a large percentage of their bodies. The first employee died from
his injuries two days later. The second employee survived for nearly four months before
succumbing to his injuries in late May 2011.
MARCH 29, 2011 (ONE INJURED)
As part of an ongoing furnace improvement project, a Hoeganaes engineer and an outside
contractor were replacing igniters on a band furnace. The pair experienced difficulty in re-
connecting a particular natural gas line after replacing an igniter. While using a hammer to
force the gas port to reconnect, the Hoeganaes engineer inadvertently lofted large amounts
of combustible iron dust from flat surfaces on the side of the band furnace, spanning 20
feet above him. As soon as the dust dispersed, the engineer recalled being engulfed in
flames. He jumped and fell from a rolling stepladder in his attempt to escape the fireball.
He received first- and second-degree burns to both thighs, superficial burns to his face, and
scrapes from his fall. After seeing the initial flash of the dust igniting, the contractor took
evasive action and escaped without injury.
The engineer was wearing the Hoeganaes-designated personal protective equipment, which
included pants and a shirt that were rated as flame resistant clothing (FRC). He was also
wearing an FRC rated jacket that provided extra shielding to his upper torso from the flash
fire.
MAY 27, 2011 (THREE FATALITIES, TWO INJURIES)
Around 6 am on May 27, 2011, operators near band furnace #1 heard a hissing noise that
they identified as a gas leak. The operators determined that the leak was in a trench, an area
below the band furnaces that contains hydrogen, nitrogen, and cooling water runoff pipes,
in addition to a vent pipe for the furnaces. The operators informed the maintenance
department about the hissing, and six mechanics were dispatched to find and repair the
leak. One annealing area operator stood by as the mechanics sought out the source of the
leak.
Although maintenance personnel knew that hydrogen piping was in the same trench, they
presumed that the leak was nonflammable nitrogen because of a recent leak in a nitrogen
pipe elsewhere in the plant and began to try to remove trench covers. However, the trench
covers were too difficult to lift without machinery. Using an overhead crane, they were
able to remove some of the trench covers. They determined that the leak was near the
southern- most trench covers, which the crane could not reach. Shortly after 6:30 am,
maintenance personnel acquired a forklift equipped with a chain on its forks, and were able
to reach and begin removing the southernmost trench covers.
Feb 07 May 28
2011 2011
Interviews with eyewitnesses indicate that just as the first trench cover was wrenched from
its position by the forklift, friction created sparks, followed by a powerful explosion.
Several days after the explosion, CSB investigators observed a large hole (approximately
3 x 7 inches) in a corroded section of piping that carried hydrogen and ran through the
trench. As the leaking hydrogen gas exploded, the resulting overpressure dispersed large
quantities of iron dust from rafters and other surfaces in the upper reaches of the building.
Portions of this dust subsequently ignited. Multiple eyewitnesses reported embers raining
down and igniting multiple dust flash fires in the area. They also reported visibility so limited
in some instances that flashlights were required; one eyewitness said that even with a
flashlight, he could see only 3 to 4 feet ahead due to extensive dust and smoke.
The hydrogen explosion and ensuing iron dust flash fires injured four of the responding
mechanics and the annealing operator. The two mechanics near the forklift were transported
to a local hospital where they were treated for smoke inhalation and released shortly
thereafter.
Two other mechanics and the operator who stood by during the operation were rushed to
Vanderbilt Burn Center. Less than a week after the incident, two employees succumbed to
their injuries. The third seriously injured employee died from his injuries almost seven
weeks after the incident.
Due to the extensive nature of the injuries, and the abundance of both hydrogen and
combustible dust present at the time of the incident, it is difficult to specifically determine
which fuel, if not both, caused the fatal injuries to the victims.
PROCESS SAFETY BARRIERS FAILURE
IGNITION SOURCES
Witnesses indicated that the May 27, 2011, hydrogen explosion was ignited by sparks generated
during the lifting of the trench cover. This is reasonable considering that the MIE of hydrogen
is 0.02 mJ, and the energy of mechanical sparks from metal to metal contact can be several mJ.
The testing contracted by Hoeganaes in 2010 determined that the minimum ignition energy
for representative iron dust samples was greater than 500 mJ, and that a continuous arc
would ignite the samples. One witness at ground level reported hearing an “electric sound”
at the time of the incident. The motor operating bucket elevator #12 was a likely source of
ignition since it had exposed wiring, was not properly grounded, and was within a few feet
of the dust cloud source. The wiring was exposed because the electrical conduit supplying
power to this motor was not securely connected to the motor’s junction box.
Prior to the CSB notifying Hoeganaes that evidence from the incident area needed to be
preserved, the company removed and modified evidence from the scene, including the
elevator motor, wiring, and conduit. However, on examination, there were spots that
appeared to be arc marks both inside the junction box, and on the outside of the motor
housing.
HAZARD RECOGNITION
In general industry the combustibility of metal dust is a well-established hazard, but metal dust
fires and explosions continue to claim lives and destroy property. The CSB reviewed three
publications dating back to the 1940s and 1950s that addressed metal dust (including iron dust)
hazards and explosion protection methods. The National Fire Protection Association (NFPA)
code for the Prevention of Dust Explosions, published in 1946, lists general precautions for all
types of dusts, including metal powder, and specific provisions for certain types of dusts.
The Building Construction section of the code states, “Avoid beams, ledges or other places
where dust may settle, particularly overhead.” The Gallatin facility, built in the 1980s, was not
designed to avoid significant overhead accumulations of dust. The code calls for designing and
maintaining dust-tight equipment to avoid leaks and, where this is not possible, to enforce good
housekeeping procedures.
The code also cautions against sources of ignition in areas containing dust and recommends
locating dust collectors outdoors or in separate rooms equipped with explosion venting.
Representatives from Hoeganaes told the CSB that the dust analysis results did trigger an
operator training program for the recognition of combustible dust hazards. However,
Hoeganaes did not mitigate the dust hazard. Since Hoeganaes did not control the combustible
dust hazard, operators were forced to tolerate the conditions at the facility. Over time, these
flash fires became normalized, since they did not result in any serious injuries prior to the
fatal incident on January 31, 2011.
Operators and mechanics reported being involved in multiple flash fires during their employ-
ment at the Gallatin facility. At the time of the incidents, many were aware that the iron dust
could burn or smolder. However, they were not trained to understand the potentially severe
hazard when accumulated dust is dispersed in air. Rarely would operators report the minor
flash fires and near-misses that periodically occurred.
EMERGENCY RESPONSE
The Gallatin Fire Department (GFD) has responded to 30 incidents of various types over
the past 12 years at the Hoeganaes Corp., including the January 31, March 29, and May 27
incidents. In June 1999, the GFD responded to a fire caused by iron dust that ignited in a
baghouse. One person suffered smoke inhalation injuries as a result of the incident.
Before the GFD arrived at each of the 2011 incidents, Hoeganaes volunteer first respond-
ers cared for the injured. Hoeganaes volunteers participate in annual training that covers
first response, CPR, and first aid. They are instructed to provide care until GFD and EMS
responders arrive.
Immediately following each incident, the volunteers provided first aid and comfort to the
injured by applying water to cool the burns and covering the victims with a burn blanket
to keep them comfortable. EMS arrived within minutes of the initial 9-1-1 call and trans-
ported the injured personnel to hospitals.
ENGINEERING CONTROLS
Thorough hazard recognition is key to effectively managing the risk from combustible dust.
Once the hazard is recognized, applying the “hierarchy of controls” for fire and explosion
prevention helps address the fugitive dust issue at the source: the material itself, the
processing equipment, and the work procedures. The hierarchy of controls is a safety
concept in which a hierarchal ordering of control mechanisms is applied to reduce risk. It
covers the spectrum from elimination at the source, at the top of the hierarchy, through
engineering and administrative (procedural) controls to personal protective equipment
(PPE), at the bottom of the hierarchy.
Installing and maintaining engineering controls to eliminate fugitive dust accumulation is
the most effective method to prevent dust fires and explosions. Conveyance systems and
appropriately sized dust collection equipment are examples of engineering controls that
eliminate or mitigate fugitive dust generation at the source. Engineering controls are
preferred over housekeeping, but a robust housekeeping program is important to man- age
fugitive dust accumulations in areas where engineering controls need maintenance or
improvement. Additionally, administrative controls, such as worker training and operating
procedures, complement robust engineering controls.
Significant quantities of iron dust escaped from equipment throughout the Hoeganaes facility.
Enclosures on the conveyance equipment leaked fugitive emissions of iron dust. In addition,
the dust collection systems were historically unreliable and did not prevent large amounts of
combustible iron dust from becoming airborne and accumulating on elevated surfaces
throughout the processing areas.
ADMINISTRATIVE CONTROLS
Observations by CSB investigators at the Gallatin facility shortly after the first incident
indicated that combustible dust was leaking from equipment and that housekeeping was
ineffective. Combustible iron dust coated almost every surface up to 4 inches deep and was
visible in the air. Mitigation of the combustible dust hazard by Hoeganaes was limited to a
less-than-adequate vacuuming service, sparsely enclosed conveyance equipment, and an
inadequate baghouse filtration system.
Although bucket elevators and some conveyance equipment were enclosed, fugitive dust
emissions were evident throughout the facility. Moreover, the CSB investigators observed
leaks of fugitive dust to the atmosphere when the bags used in the baghouse filtration sys-
tem were pulsed, which allowed dust to escape into the work areas many times each hour.
The baghouse filters are designed to collect the smallest, and consequently most dangerous,
dust particles. Yet, the CSB found that the baghouses were often out of service. Employees
reported that the baghouse associated with bucket elevator #12 was out of service
sporadically for the 7 days leading up to the fatal incident on January 31, 2011, allowing
fine combustible iron dust to remain in the area, from which it was dispersed when the
elevator was restarted during maintenance.
PERSONAL PROTECTIVE EQUIPMENT
Workers in production-related operations wear flame resistant clothing (FRC) to reduce risk of
thermal injury from flash fire incidents. As part of the Personal Protective Equipment (PPE)
Standard (29 CFR 1910.132), OSHA requires employers to provide workers with FRC in
workplaces when flash fire or explosion hazards are present.
FRC can reduce the severity of burn injuries sustained during a flash fire when engineering
and administrative controls fail. FRC, usually worn as coveralls, is made of treated natural or
synthetic fibers that resist burning and withstand heat.
There are two NFPA standards that provide guidance on the design and use of FRC. NFPA
2112, Standard on Flame-Resistant Garments for Protection of Industrial Personnel Against
Flash Fire, provides the minimum requirements for the design, testing, and certification of
FRC. NFPA 2113, Standard on Selection, Care, Use, and Maintenance of Flame-Resistant
Garments for the Protection of Industrial Personnel Against Flash Fire, provides guidance
for the selection, use, and maintenance of FRC. The 2009 edition of NFPA 484 included a
requirement for workers to wear FRC if working in metal dust-handling operations, but it
did not specifically reference NFPA 2112 or 2113 in the standard. The 2012 edition of NFPA
484 requires that new and existing facilities covered by the standard adhere to the
requirements of NFPA 2113 for FRC.
Hoeganaes employees were required to wear RC, and the injured and fatally injured
employees were wearing the Hoeganaes-designated FRC at the time of the 2011 flash fire
incidents. Though FRC is intended to reduce the severity of thermal injuries, five severely
burned employees died following the January and May incidents. The specific FRC worn did
not provide any significant protection against the combustible iron dust flash fires and the
hydrogen explosion at Hoeganaes.
REFERENCES
https://www.csb.gov/hoeganaes-corporation-fatal-flash-fires/
https://www.csb.gov/file.aspx?DocumentId=5669
ADAMSON UNIVERSITY
College of Engineering
Chemical Engineering Department
M a n i l a
SAFETY ENGINEERING
CASE STUDY
(Hoeganas Corporation Disaster)
Submitted by:
Megio, Jona E. 201411508
Ty, John Albert S. 201412992
Submitted to:
Engr. Jeremiah Emier C. Villanueva
May 13, 2019
