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Carbide Industries Fire and Explosion

Overview

On March 21, 2011, during calcium carbide production at the Carbide Industries plant in Louisville, KY, an electric arc furnace exploded and overpressured. Solid and powdered debris, flammable gases, and molten calcium carbide were ejected. Hot gases and debris broke through the control room window. Two workers were killed and two others were injured.

Incident Snapshot

Field Value
Facility / Company Carbide Industries, LLC
Location Louisville, KY
Incident Date 03/21/2011
Investigation Status The CSB's final report was approved 3-0 at a public meeting in Louisville, KY
Accident Type Chemical Manufacturing - Fire and Explosion
Final Report Release Date 02/07/2013

What Happened

  • At about 5:40 pm on Monday, March 21, 2011, the EAF at the Carbide Rubbertown facility violently overpressured, ejecting solid and powdered debris, hot gases, and molten calcium carbide at temperatures near 3800°F (2100°C).
  • Witnesses reported an initial overpressure event from the furnace, a large explosion, and two to three more overpressure events.
  • The hot gases and debris blown from the furnace broke through the double-pane reinforced glass window of the control room, severely burning the two workers inside. They died within 24 hours from their injuries.
  • Hot material also was ejected from the active tap hole on the mezzanine level.
  • One worker was in an operating shack about 30 feet from the tap hole.
  • The door to the shack was ajar, and he crouched to the floor, seeking shelter from the hot gases and dust that engulfed him.
  • He received a minor burn to the back of his neck, but did not seek medical treatment.
  • Another worker was walking away from the furnace when the explosion knocked him to the ground and the hot gases and debris engulfed him.
  • He was taken to a maintenance area, where he was given oxygen and his vital signs monitored.
  • He was later taken to the hospital for observation and subsequently released.
  • Incident command was established about two minutes after the event occurred.
  • An Assistant Fire Chief of the Lake Dreamland Fire Department was driving by at the time of the incident and immediately responded by assuming the role of Incident Commander (IC) and activating response based on National Incident Management System (NIMS) protocols.
  • Because of concerns of possible product contamination and the unknown conditions of the immediate location of the incident, the incident commander established a staging area about one-half mile upwind from the facility and a command post at the front gate and called ambulances to the staging area.
  • The first ambulance was dispatched at 5:40 pm with two more dispatched shortly thereafter and arrived on scene within 15 minutes.
  • Carbide personnel and Lake Dreamland Firefighters transported the injured employees to the main gate where they met emergency medical technicians (EMTs).
  • The fire department decontaminated the injured employees with water while the Carbide emergency response team and a fire department paramedic provided oxygen and monitored vital signs.
  • One victim went into cardiac arrest, and the paramedic began performing CPR on him.
  • About 40 minutes after the initial incident, off-site EMS began transporting victims to the hospital.
  • These victims arrived at the hospital about 12 minutes later, and succumbed to their injuries in less than 24 hours.
  • A third ambulance transported the injured worker who had been knocked to the ground and injured by the blast.

Facility and Process Context

  • Carbide Industries, LLC is the larger of two North American producers of calcium carbide and supplies calcium carbide primarily to the iron and steel industry and to acetylene producers.
  • The main Carbide Industries facility is adjacent to the Ohio River in the “Rubbertown” section of western Louisville, KY.
  • The company employs about 160 workers in operations, maintenance, and administration.
  • The Louisville site operated one 50-megawatt (MW) EAF with the capacity to produce 120,000 tons of molten calcium carbide per year.
  • After draining the calcium carbide from the EAF and cooling it to a solid, the site grinds and packages the solid into multiple grades of calcium carbide for sale.
  • Although the facility maintains an acetylene storage tank to collect fugitive acetylene gas from the calcium carbide plant, the operation does not produce acetylene gas to sell.
  • The EAF at Carbide Industries was located on the ground floor of the five-story furnace building.
  • Due to the height of the furnace itself, the cover of the furnace was at the second floor level; the same level as the control room where the furnace operator controlled the chemical and electrical feeds to the furnace.
  • The control room had a window made of dual-paned, one-half-inch thick, wire-reinforced glass.
  • The control room window was about 12 feet from the furnace cover.
  • The furnace was a refractory-lined metal tank with three holes in the sidewall to drain the molten calcium carbide product.
  • These three-hole positions were at the elevation of the mezzanine level, between the second and ground floor.
  • The furnace cover was about four feet tall and made of refractory-lined metal that was water cooled.
  • The furnace cover was fabricated in several sections and bolted together.
  • Cooling water flowed through each hollow section as additional protection against overheating.
  • Three electrodes protruded through the furnace cover.
  • The electrodes extended from the fifth floor down to just below the second floor.
  • Three transformers on the third floor supplied AC power to the electrodes.
  • Tanks on the fourth level held pre-mixed feed until a conveyor system dispensed the material into chutes that distributed the feed around the furnace electrodes.
  • The feed material flowed down into the furnace through the gaps between the electrode sheaths and the holes that the electrodes passed through in the furnace cover.
  • The plant receives truck and rail deliveries of coke and lime respectively.
  • An oven dries the coke and a weighing system mixes the coke with the lime in the desired weight ratio to feed the furnace.
  • A system of tanks and chutes distributes the solid feed mixture (coke and lime) through the EAF cover and around the three electrodes.
  • The furnace contains hot feed material, liquid calcium carbide, and flammable and toxic gases that are byproducts of the EAF, including hydrogen and carbon monoxide.
  • The furnace runs under slight pressure to prevent air from being drawn into the furnace and igniting the flammable gases.
  • The gases produced in the furnace exit primarily through a vent system to a wet scrubber.
  • Some of the gas exits into the second floor of the furnace building through the gaps between the electrode sheaths and the holes that the electrodes pass through in the furnace cover.
  • Workers look through the control room window to judge the process performance by the appearance (volume, color, and motion) of the flames that the process gases create when they exit the furnace and auto-ignite on contact with the room air.
  • Cooling water exits the hollow furnace cover sections and returns to a trough before being recirculated.
  • Molten calcium carbide exits the EAF at about 3800°F through the drain holes in the sidewall of the furnace.
  • The operator uses a motorized train system to move a deep tray on wheels, called a chill mold, to a hole position and an electric arc device to tap a drain hole through the solidified calcium carbide and other materials that plug the hole in the side of the furnace.
  • The molten calcium carbide inside the furnace then drains from the tap hole into the chill mold.
  • After filling multiple chill molds, the calcium carbide in that section of the furnace is drained, and the flow from the tap hole slows significantly.
  • Operators then plug the hole with a mixture similar to mud and clay and move to tap the next location.
  • Downstream units on-site dump the chill molds, grind and screen the calcium carbide, and package the product.
  • The calcium carbide remains in the molds until it cools to about 500°F.
  • The Rubbertown community includes homes and industrial facilities in close proximity.
  • In 2002, the Rubbertown Community Awareness Line (RCALL) notification system was established to alert residents of all natural and manmade disasters.
  • For incidents at the surrounding industrial facilities, a company representative was responsible for calling into the RCALL system to leave a message for the public.
  • In addition, emergency responders sounded a siren that prompted residents to call the RCALL system to hear the message from the company representative.
  • Carbide Industries trained some of its workers to act as on-site emergency responders and to provide general awareness training for contractors.
  • The company also trained the Lake Dreamland Fire Department for occasions where they might be needed to respond to incidents at the facility.
  • The training materials included a slide presentation and a video that focus on furnace area hazards.

Consequences

  • Fatalities: 2 workers died.
  • Injuries: 2 workers were injured.
  • Environmental release: ejecting solid and powdered debris, flammable gases, and molten calcium carbide; hot gases and debris blown from the furnace; hot material also was ejected from the active tap hole on the mezzanine level.
  • Facility damage: the double-pane reinforced glass window of the control room broke; the cloud of debris and smoke obscured the five-story furnace building; much of the refractory lining was worn and holes where cooling water had leaked into the furnace were identified.
  • Operational impact: the furnace violently overpressured; the company had a new furnace cover built, which was waiting for refractory lining at the time of the incident; the community had no updates on the incident for 90 minutes following the explosion.

Key Findings

Immediate Causes

  • The CSB was unable to determine the exact cause of the March 21 incident.
  • The EAF at the Carbide Rubbertown facility violently overpressured.

Contributing Factors

  • Examination of the underside of the furnace cover revealed that much of the refractory lining was worn and identified holes where cooling water had leaked into the furnace.
  • Leaks begin due to thinning of the refractory lining, fouling, and the accumulation of solids inside the hollow chamber where water flows.
  • Because the fouling insulates the metal on the underside of the furnace cover from the cooling water, the high temperature of the furnace softens the metal and the metal sags under its own weight.
  • With continued exposure to the furnace temperatures, the sagging bulge cracks open, which led to the formation of a leak.
  • Another possible cause of leaks is the sudden eruption of hot liquid from the furnace, which the operators call a boil-up.
  • Repeated boil-ups of hot material from the furnace can cause a water leak by contacting the underside of the furnace cover, eroding its ceramic lining, and eventually melting a hole in the metal furnace cover causing a water leak.
  • The presence of electric current requires that the furnace be shut down for workers to climb onto the furnace cover and repair water leaks.
  • Carbide personnel described how they repair small holes by adding a mixture of oats and boiler solder to the cooling water.
  • Carbide repairs larger leaks by welding metal plates on the inside of the hollow cavity through which the water flows to patch the hole.
  • While this method prevents water from leaking into the furnace, it leaves a lower layer of uncooled metal hanging beneath the now patched furnace cover.
  • Maintenance records obtained by the CSB indicated 26 work orders to repair furnace cover water leaks in the four months prior to the March 2011 incident.
  • The CSB interviews with operators indicated that smaller overpressure incidents (“blows”) occurred in the furnace for the last 20 years.
  • In 1991 a large overpressure incident blew in the window to the control room.
  • Carbide replaced the window glass with reinforced glass, which was damaged by a similar incident in 2004.
  • After the 2004 incident, Carbide replaced the single pane reinforced glass with double pane reinforced glass, which was blown in by the March 2011 incident and which directly contributed to the fatal thermal injuries.
  • Despite these previous incidents, Carbide’s response to the previous incidents did not sufficiently address the hazard nor prevent the events from escalating.
  • Because Carbide did not thoroughly determine the root causes of the blows and eliminate them, the occurrence became normalized in the day-to-day operations of the facility, including a blow which occurred earlier during a shift on the day of the incident.
  • The behavior was a tolerance to what should have been abnormal events (the blows).
  • The result was a new normal, in which a boom occurring in the furnace was routine.
  • The furnace involved in the March 21 incident is considered by definition a Class A furnace because it collects and vents flammable gases in a low oxygen environment that are a by-product of the chemical reactions that produce calcium carbide.
  • NFPA 86 is silent on coverage for EAFs operating as Class A furnaces.
  • There are no operational requirements specifically directed to Class A EAFs for provisions such as safety devices, interlocks, and safe distances to occupied work areas.
  • In 1968, Carbide Industries installed the furnace 12 feet from the control room that served as a workstation for one employee continuously for each shift.
  • Their injuries are attributed to their proximity to the furnace, and by the blast and thermal heat transfer when the incident occurred.
  • NFPA 86 does not provide specific requirements on determining the distances between occupied areas and processes capable of producing a fire, explosion or an overpressure event within the same building or enclosure.
  • The EAF process at Carbide Industries did not contain chemicals in large enough quantity to be regulated by OSHA PSM.
  • Carbide failed to implement a mechanical integrity program as would have been required under the PSM standard if it had applied.
  • The company lacked a program to ensure the timely replacement of the furnace cover prior to failure.
  • The Kentucky Labor Cabinet proposed penalties of $72,800.00 as a result of this incident.
  • The facility received two citations—one willful, and one serious.
  • The citations alleged that employees worked in close proximity to electric arc furnaces that were not operated with a robust inspection and preventive maintenance program exposing them to serious or fatal injuries.
  • The citations alleged that Carbide had knowledge of the hazards of furnace explosions and fires as documented in the plant’s 1998 Emergency Response Plan.
  • The facility was also cited because emergency response team members allegedly had not received training with respect to response procedures for furnace explosions.

Organizational and Systemic Factors

  • The facility has operated for over 30 years, and had a history of low consequence incidents in the furnace.
  • The company did not adequately address past explosive incidents, which normalized blows as routine events.
  • The CSB could not find, nor did Carbide provide in response to requests, any documentation to indicate that these incidents or “blows” were investigated to determine their root cause.
  • However, accident/incident investigations were completed when injuries not specifically related to the furnace “blows” occurred.
  • Without a proper investigation of the incident, Carbide could not address the root causes to prevent future incidents, nor could the company perform a detailed hazard analysis that could have identified other potential incident scenarios.
  • By failing to analyze these incidents further, Carbide did not identify and address the potential for even higher consequence incidents.
  • Such an analysis would have likely identified the need to relocate the control room and install video cameras to monitor furnace operations.
  • Carbide Industries had scheduled to replace the furnace cover in May 2011, but the new cover was incomplete at the time of the explosion—it had been fabricated and was waiting for refractory lining.
  • Carbide failed to implement a mechanical integrity program as would have been required under the PSM standard if it had applied.
  • The company lacked a program to ensure the timely replacement of the furnace cover prior to failure.
  • The community notification system in effect on the day of the incident was the Rubbertown Community Action Line (RCALL) system.
  • Carbide personnel were focused on the victim rescue efforts and no one left information on the RCALL line for residents in the surrounding community.
  • Because RCALL was the information conduit, the community had no updates on the incident for 90 minutes following the explosion.

Failed Safeguards or Barrier Breakdowns

  • The control room window was broken by the explosion.
  • Previous furnace overpressure events had broken the control room window but had not caused fatalities.
  • Despite past incidents, neither the previous owners nor Carbide Industries identified that the control room should be relocated and cameras installed to better protect workers while they remotely monitored the furnace.
  • Carbide Industries issued 26 work orders for leak repair for water leaks on the furnace cover in the five months prior to the March 2011 incident, but continued operating the furnace despite the hazard from ongoing water leaks.
  • The company did not adequately address past explosive incidents, which normalized blows as routine events.
  • The company did not have a process safety management program in place that required the elimination of overpressure incidents in the furnace.
  • NFPA 86 does not specify safety requirements for electric arc furnaces operating as Class A furnaces such as the one at Carbide Industries.
  • The training materials did not provide detailed information on the hazards of contacting chemicals such as calcium carbide or calcium hydroxide on site.
  • Carbide personnel were focused on the victim rescue efforts and no one left information on the RCALL line for residents in the surrounding community.

Recommendations

  1. 2011-5-I-KY-R1 — Recipient: NATIONAL FIRE PROTECTION ASSOCIATION — Status: Not provided — Summary: Establish a committee to evaluate and develop a standard that defines the safety requirements for electric arc furnaces operated with flammable materials and low oxygen atmospheres. At a minimum, establish requirements that electric arc furnaces containing flammables have: Adequate safety instrumentation and controls to prevent explosions and overpressure events; Mechanical integrity and inspection programs; A documented siting analysis to ensure that control rooms and other occupied areas are adequately protected.
  2. 2011-5-I-KY-R2 — Recipient: CARBIDE INDUSTRIES — Status: Not provided — Summary: Modify the design and procedures for the electric arc furnace and related structures including the control room to comply with the NFPA standard developed per R1 of this case study.
  3. 2011-5-I-KY-R3 — Recipient: CARBIDE INDUSTRIES — Status: Not provided — Summary: Implement a mechanical integrity program for the electric arc furnace and cover, including preventive maintenance based on periodic inspections, and timely replacement of the furnace cover. At a minimum, the program should include factors such as leak detection and repair and refractory lining wear.

Key Engineering Lessons

  • Electric arc furnaces operating with flammable materials and low oxygen atmospheres require safety requirements that address explosions and overpressure events, mechanical integrity, and siting of occupied areas.
  • Repeated furnace cover water leaks and refractory lining wear can contribute to overpressure events and must be managed through inspection, leak detection and repair, and timely replacement of the furnace cover.
  • Control rooms and other occupied areas should not remain in close proximity to a furnace after prior overpressure events have demonstrated the hazard.
  • Past overpressure events that damage windows or other barriers should trigger root-cause investigation and hazard analysis rather than acceptance of the events as routine.
  • A mechanical integrity program for the furnace and cover is needed to support preventive maintenance and prevent continued operation with known leak hazards.

Source Notes

  • Priority 1 final report used as the authoritative source for incident facts and causal findings.
  • Priority 4 supporting documents were used only to supplement or confirm details where consistent with the final report.
  • Where the final report stated the exact cause could not be determined, that uncertainty was preserved.
  • Recommendation status changes from later documents were included for recommendation status fields only.

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