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Hoeganaes Corporation Fatal Flash Fires

Overview

Three combustible dust incidents occurred over a six-month period at the Hoeganaes facility in Gallatin, Tennessee. The incidents resulted in five fatalities and three injuries. The events involved metal dust flash fires and a hydrogen explosion with resulting iron dust flash fires at a facility producing powdered iron.

Incident Snapshot

Field Value
Facility / Company Hoeganaes Corporation
Location Gallatin, TN
Incident Date January 31, 2011; March 29, 2011; May 27, 2011
Investigation Status The CSB's investigation was approved by the board on December 16, 2011. The case study was released at a news conference in Nashville, TN, on January 5, 2012.
Accident Type Combustible Dust Explosion and Fire Investigation
Final Report Release Date 01/05/2012

What Happened

On January 31, 2011, bucket elevator #12 was suspected of being off-track. A maintenance mechanic and electrician inspected the equipment. The motor was restarted. Vibrations dispersed fine iron dust into the air. A flash fire occurred.

On March 29, 2011, a Hoeganaes engineer and an outside contractor were replacing igniters on a band furnace. While using a hammer to force the gas port to reconnect, combustible iron dust was lofted and ignited in a flash fire.

On May 27, 2011, operators heard a hissing noise identified as a gas leak in a trench below the band furnaces. Maintenance personnel removed trench covers. Friction created sparks, followed by a powerful explosion. Hydrogen exploded, and resulting iron dust flash fires occurred.

Facility and Process Context

  • Hoeganaes Corp. is a worldwide producer of atomized steel and iron powders.
  • The Hoeganaes Gallatin facility is located about 30 miles northeast of Nashville, Tennessee.
  • The Hoeganaes Gallatin facility employs just under 200 employees.
  • Hoeganaes receives and melts scrap steel.
  • The molten iron is cooled and milled into a coarse powder that is processed in long annealing furnaces to make the iron more ductile.
  • A hydrogen atmosphere is provided in the band furnace to reduce the iron by removing oxides and preventing oxidation.
  • 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.
  • The plant collects scrap iron, which is then melted, sprayed into powder form, and then annealed using hydrogen gas and a large continuous furnace.
  • The powder is then further milled, packaged, and eventually sold as a final product.

Consequences

  • Fatalities: 5
  • Injuries: 3
  • Environmental Release: Not reported
  • Facility Damage: Several days after the May 27 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.
  • Operational Impact: The report states that the Gallatin facility had not been fully operational for about three months when a sample was taken in August 2011.

Key Findings

Immediate Causes

  • When the elevator was restarted, vibrations from the equipment dispersed fine iron dust into the air.
  • As soon as the dust dispersed, the engineer recalled being engulfed in flames.
  • 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.
  • 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.
  • The initial explosion involved hydrogen gas that had been leaking into the trench from a large hole in the vent pipe.
  • Combustible iron dust was also involved in the aftermath of the explosion.

Contributing Factors

  • Significant accumulations of combustible iron powder at the Hoeganaes facility.
  • Hoeganaes facility management were aware of the iron powder combustibility hazard two years prior to the fatal flash fire incidents but did not take necessary action to mitigate the hazard through engineering controls and housekeeping.
  • Hoeganaes did not institute procedures such as combustible gas monitoring or training for employees to avoid flammable gas fires and explosions.
  • 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.
  • Hoeganaes did not regularly inspect the pipes in the trench.
  • Hoeganaes had no written procedure or protocol to mitigate gas leaks, and maintenance crews were allowed to begin investigating a suspected leak without testing the atmosphere for concentrations of explosive gas.
  • 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.
  • Combustible dust had accumulated on surfaces, especially elevated surfaces.
  • 2 to 3-inch layers of dust were observed on flat surfaces, rafters, and railings throughout the facility.
  • The dust collection system at the Hoeganaes plant is severely deficient, is improperly designed, and has leaks.
  • The electrical equipment throughout most of the plant is only suitable for general industrial use, not for a flammable environment.
  • The plant has many uncontrolled potential ignition sources.
  • The trench that held the pipe showed signs of dust intrusion.
  • Pipes inside the trench showed signs of corrosion.
  • The inadequate maintenance of hydrogen piping is yet another serious concern.

Organizational and Systemic Factors

  • Hoeganaes did not mitigate the dust hazard.
  • Operators and mechanics reported being involved in multiple flash fires during their employment at the Gallatin facility.
  • At the time of the incidents, many were aware that the iron dust could burn or smolder.
  • 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.
  • Although the majority of the Hoeganaes Combustible Dust Program action items had planned completion dates prior to the 2011 flash fire incidents, the program did not effectively mitigate the combustible dust hazards at the facility.
  • GKN and Hoeganaes did not provide corporate oversight to ensure the Hoeganaes Gallatin facility was adequately managing combustible dusts prior to and throughout the succession of serious incidents at the Gallatin facility.
  • The company removed and modified evidence from the scene, including the elevator motor, wiring, and conduit, prior to the CSB notifying Hoeganaes that evidence from the incident area needed to be preserved.
  • The Gallatin Fire Department conducted three inspections in the previous 12 years, in 1999, 2002, and 2011.
  • The 2011 inspection was performed just two weeks prior to the May 27, 2011, incident.
  • The report for this inspection documented observations at the facility related to fire suppression and emergency egress, but did not mention combustible dust hazards even after the January and March 2011 incidents.
  • The CSB found no evidence that the GFD inspected Hoeganaes against the provisions of the 2006 IFC for the hazards associated with combustible metal dust, electrical installation, and operations that use flammable gases.
  • OSHA did not include iron and steel mills (NAICS code 331111), the industry classification code for Hoeganaes, in its Combustible Dust National Emphasis Program when it was first issued in 2007 or when it was re-issued in 2008.
  • The language in the IFC did not make clear whether compliance with and enforcement of the referenced NFPA standards is a mandatory or voluntary requirement of the IFC.
  • The State of Tennessee and the City of Gallatin had adopted the 2006 edition of International Fire Code (IFC) into law.

Failed Safeguards or Barrier Breakdowns

  • engineering controls
  • housekeeping
  • combustible gas monitoring
  • training for employees to avoid flammable gas fires and explosions
  • preventive maintenance program
  • leak detection and leak mitigation procedures
  • near-miss reporting and investigation policy
  • periodic independent audits
  • flame-resistant clothing (FRC)
  • regular inspection for physical damage and leak tightness
  • testing the atmosphere for concentrations of explosive gas
  • dust collection systems
  • enclosures on the conveyance equipment
  • baghouse filtration system
  • Conveyors and other equipment are not adequately sealed to prevent the release of dust.
  • Combustible dust has been allowed to accumulate on horizontal surfaces, and housekeeping remains inadequate, particularly for elevated surfaces.
  • The dust collection system at the Hoeganaes plant is severely deficient, is improperly designed, and has leaks.
  • The electrical equipment throughout most of the plant is only suitable for general industrial use, not for a flammable environment.
  • The plant has many uncontrolled potential ignition sources, including large open flames and hot surfaces from furnaces, exposed light fixtures, exposed bearings which could overheat from dust, internal combustion engines, and welding equipment.

Recommendations

  1. 2011-4-I-TN-R1 — Recipient: OSHA — Status: Not specified — Summary: Ensure that the forthcoming OSHA Combustible Dust Standard includes coverage for combustible metal dusts including iron and steel powders.
  2. 2011-4-I-TN-R2 — Recipient: OSHA — Status: Not specified — Summary: Develop and publish a proposed combustible dust standard for general industry within one year of the approval of this case study.
  3. 2011-4-I-TN-R3 — Recipient: OSHA — Status: Closed – Acceptable Alternate Action — Summary: Revise the Combustible Dust National Emphasis Program (NEP) to add industry codes for facilities that generate metal dusts (e.g., North American Industrial Classification System, NAICS, code 331111 Iron and Steel Mills, and other applicable codes not currently listed). Send notification letters to all facilities nationwide under these codes to inform them of the hazards of combustible metal dusts and NEP coverage.
  4. 2011-4-I-TN-R4 — Recipient: INTERNATIONAL CODE COUNCIL — Status: Closed – Acceptable Action — Summary: Revise IFC Chapter 2237 Combustible Dust Producing Operations; Section 2204.1 Standards, to require mandatory compliance and enforcement with the detailed requirements of the NFPA standards cited in the chapter, including NFPA 484.
  5. 2011-4-I-TN-R5 — Recipient: TOSHA — Status: Not specified — Summary: Revise the state-adopted Dust National Emphasis Program (NEP) to add industry codes for facilities that generate metal dusts (e.g., North American Industrial Classification System, NAICS, code 331111 Iron and Steel Mills, and other applicable codes not currently listed). Send notification letters to all facilities statewide under these codes to inform them of the hazards of combustible metal dusts and NEP coverage.
  6. 2011-4-I-TN-R6 — Recipient: Hoeganaes Corporation — Status: Closed – Unacceptable Action/No Response Received — Summary: Conduct periodic independent audits of the Hoeganaes Gallatin facility for compliance with the following NFPA standards, using knowledgeable experts, and implement all recommended corrective actions: NFPA 484, Standard for Combustible Metals, Metal Powders, and Metal Dusts; NFPA 499, Recommended Practice for the Classification of Combustible Dusts and of Hazardous Locations for Electrical Installations in Chemical Process Areas; NFPA 497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas; NFPA 2, Hydrogen Technologies Code; NFPA 2113, Standard on Selection, Care, Use, and Maintenance of Flame-Resistant Garments for Protection of Industrial Personnel Against Flash Fire.
  7. 2011-4-I-TN-R7 — Recipient: Hoeganaes Corporation — Status: Closed – Unacceptable Action/No Response Received — Summary: Develop training materials that address combustible dust and plant-specific metal dust hazards and train all employees and contractors. Require periodic (e.g., annual) refresher training for all employees and contractors.
  8. 2011-4-I-TN-R8 — Recipient: Hoeganaes Corporation — Status: Closed – Unacceptable Action/No Response Received — Summary: Implement a preventive maintenance program and leak detection and leak mitigation procedures for all flammable gas piping and gas processing equipment.
  9. 2011-4-I-TN-R9 — Recipient: Hoeganaes Corporation — Status: Closed – Unacceptable Action/No Response Received — Summary: Develop and implement a near-miss reporting and investigation policy that includes facility-wide worker participation in reporting all near-miss events and operational disruptions, prompt investigation and circulation of results, established roles and responsibilities, and operation at all times.
  10. 2011-4-I-TN-R10 — Recipient: METAL POWDER PRODUCERS ASSOCIATION (MPPA) — Status: Not specified — Summary: Communicate the findings of this report to all your members, e.g. through a safety article in an upcoming monthly newsletter.
  11. 2011-4-I-TN-R11 — Recipient: City of Gallatin, TN — Status: Closed – Unacceptable Action — Summary: Require all facilities covered by IFC Chapter 13 (2006 edition) to conform to NFPA standards for combustible dusts including NFPA 484.
  12. 2011-4-I-TN-R12 — Recipient: GALLATIN FIRE DEPARTMENT — Status: Not specified — Summary: Ensure that all industrial facilities in the City of Gallatin are inspected periodically against the International Fire Code. All facility inspections shall be documented.
  13. 2011-4-I-TN-R13 — Recipient: GALLATIN FIRE DEPARTMENT — Status: Not specified — Summary: Implement a program to ensure that fire inspectors and response personnel are trained to recognize and address combustible dust hazards.

Key Engineering Lessons

  • Accumulated combustible iron dust can be dispersed by equipment vibration or mechanical disturbance and ignite when an ignition source is present.
  • Hydrogen piping in trenches requires inspection, maintenance, and leak detection; a corroded vent pipe and leaking hydrogen created the conditions for the May 27 explosion.
  • Dust collection systems that are unreliable, improperly designed, or leaking do not prevent hazardous dust accumulation on elevated surfaces.
  • Housekeeping and engineering controls are necessary; reliance on flame-resistant clothing alone did not provide significant protection against the flash fires and hydrogen explosion.
  • Atmospheres should be tested for explosive gas before maintenance crews begin investigating suspected leaks.
  • Electrical equipment and ignition sources in areas with combustible dust and flammable gas hazards must be appropriately controlled.

Source Notes

  • Priority 1 final report used as primary authority for incident sequence, causes, and recommendations.
  • Priority 3 recommendation status summaries were used to resolve recommendation statuses and later enforcement/inspection context.
  • Priority 4 supporting documents were used only to supplement factual context where consistent with the final report.
  • Where source documents differed in wording or detail, the higher-priority final report terminology was preserved.

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