CSB Cites Risk Tolerance, 'Running Equipment to Failure' in Carbide Industries Blast

The Chemical Safety Board's chair, Rafael Moure-Eraso, said the March 21, 2011, explosion that killed two of the Louisville company's employees is a textbook case. Repeated overpressure events and water leaks were not addressed, he said.

The U.S. Chemical Safety Board has released and posted its investigative report about the March 21, 2011, explosion at Carbide Industries in Louisville, Ky., in which two workers died and two more were hurt. Speaking at a Feb. 7 news conference in the city, Chemical Safety Board Chair Rafael Moure-Eraso and lead investigator Johnnie Banks said the company was not required to comply with the OSHA Process Safety Management standard but could have prevented the incident by doing so voluntarily, and it continued operating the electric arc furnace that blew up despite numerous overpressure events and water leaks.

The men who died were inside a control room with a window located 12 feet from the cover of the furnace; the blast occurred when cooling water leaked into the furnace, and the ejected molten calcium carbide, powdered debris, and hot gases broke the dual-paned, half-inch-thick, wire-reinforced glass window. The men in the control room died of burn injuries within 24 hours.

Banks and Moure-Eraso said there were 26 maintenance orders to fix water leaks on the furnace cover during the months immediately preceding the explosion. "This accident is literally a case study into the tragic, predictable consequences of running equipment to failure even when repeated safety incidents over many years warn of impending failure. When control room windows blew out during previous furnace incidents, the company merely reinforced them, rather than taking the safe course and moving the control room farther from the furnace and investigating why the smaller furnace overpressure events were happening in the first place. It is what we call a 'normalization of deviance,' in which abnormal events become acceptable in everyday operations," Moure-Eraso said.

"One of our key findings was that Carbide Industries issued 26 work orders to repair water leaks on the furnace cover in the five months prior to the March 2011 incident. It was distressing to find that the company nonetheless continued operating the furnace despite the hazard from ongoing water leaks," Banks said. "We also found that the company could have prevented this incident had it voluntarily applied elements of a process safety management program, such as hazard analysis, incident investigation, and mechanical integrity."

Carbide Industries continued operating the furnace even though it planned to replace the furnace cover in May 2011, according to the report.

"We cannot continue to accept this," Moure-Eraso said. "The message that I have is that the deaths of workers simply cannot be a cost of doing business. We have to do something different."

The report lists two possible scenarios by which the explosion may have occurred. Either an accumulation of solid material inside the hollow chamber in the furnace cover caused localized overheating, and then sections of the cover sagged and cracked, or hot liquid from the furnace contacted the underside of the cover and eroded its ceramic lining, melting holes through which water leaked.

The report contains two recommendations for Carbide Industries and one for NFPA. The board asks NFPA to create a committee to develop a standard defining the safety requirements for electric arc furnaces operated with flammable materials and low oxygen atmospheres, and it recommends that Carbide Industries modify its design and procedures to comply with that standard and implement a mechanical integrity program for the furnace and cover.

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